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Types of Steel | Grades of Steel

Written by Anup Kumar Dey in Civil,Engineering Materials,Mechanical,Piping Interface

Steel is an alloy containing Iron and Carbon as the primary elements. Various other alloying elements are added to it to achieve some desired properties in Steel. It is a prime commodity and finds extensive uses worldwide in buildings, tools, cars, weapons, infrastructure, ships, trains, machines, electrical appliances, etc. Steel can be classified depending on various factors or characteristics. In the following paragraphs, we will explore different types of steel in detail.

Grades of Steel

The widely used engineering material Steel, comes with several distinct grades with different chemical compositions. There are a number of ways by which steel can be classified. However, the most widely popular classification is based on their chemical composition as provided by the American Iron & Steel Institute (AISI).

Types of Steel based on Chemical Composition | Four Types of Steel

Depending on the chemical composition, according to the AISI, the following four basic types of steel are distinctly grouped. They are:

  1. Carbon Steel
  2. Alloy Steel
  3. Stainless Steel
  4. Tool Steel

1. Carbon Steel:

This type of steel accounts for around 90% of total steel production. Most of the steel we find all around is made from this grade of steel because of its strong and durable nature. Carbon Steel contains less than 2% carbon without any purposeful alloying additions. Depending on the amount of carbon present, Carbon Steel is categorized into three main classes. They are

  • Low Carbon Steel or Mild Steel: This grade of steel is the least expensive type and is quite common in use. Low Carbon Steel or Mild Steel contains up to 0.3% carbon. It possesses very good formability and finds wide structural application.
  • Medium Carbon Steel: This type of carbon steel contains 0.31% to 0.6% carbon and 0.31% to 1.60% magnesium. Medium carbon steels are stronger than mild steel, but with an increase in carbon content, the formability reduces. They can be found in applications like gears, railroad tracks, cranks, machinery parts, pressure structures, etc. The properties of medium carbon steel lie in between mild steel and high carbon steel.
  • High Carbon Steel: High carbon steel grades contain more than 0.6% carbon and 0.31 % to 0.9% magnesium. This type of steel has the maximum strength and hardness with the lowest ductility and formability. High carbon steels find their application in bars, plates, spring steel, knives, taps, wire drawing dies, cutters, etc.

2. Alloy Steel:

Alloy steels contain one or more alloying elements (nickel, manganese, titanium, copper, silicon, chromium, molybdenum, cobalt, tungsten, vanadium, and aluminum) in varying proportions. Purposeful addition of these alloying elements is done to manipulate the steel’s properties as required for different applications. Specific properties like hardenability, corrosion resistance, strength, formability, weldability, or ductility can be improved on alloy steels based on applications. Alloy steels are widely available, costlier than common carbon steels, and find their applications in pipelines, transformers, power generators, auto parts, and electric motors. Depending upon the combination of alloying additions, different grades of alloy steels are available. The most widely used alloy steel types are provided below:

  • Tungsten Steel for high heat resistance
  • Nickel Steel for toughness.
  • Manganese Steel for excellent wear resistance and work hardening
  • Vanadium Steel for high shock and vibration resistance.
  • Chromium Steel for corrosion and wear resistance.
  • Chromium-Vanadium Steel for high tensile strength along with ductility.
  • Silicon Steel for producing permanent magnets.
  • Molybdenum Steel for good corrosion resistance, weldability, and toughness.
  • Cobalt Steel for tremendous corrosion resistance, wear resistance, high-temperature strength, and magnetic properties.
  • Aluminum Steel for low weight along with high strength.

3. Stainless Steel:

Stainless steels are made of 10 to 20% chromium as the main alloying element. This grade of steel is highly popular due to its appearance and high corrosion resistance. Stainless steel with more than 11% chromium is approximately 200 times more resistant to corrosion as compared to carbon steel. They are expensive and widely used in the form of plates, sheets, bars, tubes, and wires. Depending on the crystalline structure and composition of stainless steel, this type of steel is sub-divided into five categories as provided below:

Austenitic Stainless Steel:

Austenitic stainless steels are non-magnetic and non-heat-treatable and generally contain 18% chromium, 8% nickel, and less than 0.8% carbon. They form the largest portion of the global stainless steel market and are widely used in food processing equipment, kitchen utensils, and piping.

Ferritic Stainless Steel:

Ferritic steels contain trace amounts of nickel, 12-17% of chromium, less than 0.1% carbon, and molybdenum, aluminum, or titanium in small quantities. They are tough, strong, and magnetic and can be further strengthened by cold working.

Martensitic Stainless Steel:

Martensitic stainless steels contain 11-17% chromium, less than 0.4% nickel, and up to 1.2% carbon. These magnetic and heat-treatable steels are used in knives and cutting tools, as well as dental and surgical equipment.

Duplex Stainless Steels:

This type of stainless contains a combination of ferritic and austenitic structures in their crystal structure. DSS materials are weldable, corrosion-resistant, and possess high strength. I have already published more details about duplex stainless steel. Kindly click here to access that article.

Precipitation Hardening Stainless Steel:

This type of stainless steel is comprised of 17% chromium and 4% nickel. Additionally, small amounts of aluminum, copper, and niobium are also added. As the name suggests, this group of stainless steels is a variety of hardened stainless steels and finds application in engine components and nuclear waste casks.

4. Tool Steel:

Tool Steels are a variety of abrasion-resistant, high-hardness steel types that make them suitable for use as manufacturing tools. Tool steels are available in the form of round, square, or flat bars and are used to make hammers, dies, molds, cutting tools, etc. Common alloying elements of tool steels are molybdenum, vanadium, tungsten, and cobalt, which makes them heat-resistant, durable, and strong. Six grades of tool steels are widely used in industries. They are

  • Air-hardening tool steels
  • Water-hardening
  • High Speed
  • Hot-working
  • Shock-resisting types
  • Oil-hardening

The following image in Fig. 1 provides some properties on the Grades of Steel Chart.

Grades of Steel Chart
Fig. 1: Grades of Steel Chart

Steel Numbering Systems

Two major numbering systems are widely followed in the steel industries. They are:

  • Steel numbering system by AISI and
  • Steel numbering system by SAE (Society of Automotive Engineers)

Both AISI and SAE steel numbering systems consist of a four-digit designation system. However, note that there are certain types of alloy steels designated by five digits. The first digit explains the type of steel. If it is “1” then it indicates Carbon steel. So all carbon steel in this numbering system starts with 1. Similarly, the meaning of the first digit is provided below:

  • “2” denotes Nickel steels.
  • “3” denotes Nickel-chromium steels.
  • “4” denotes Molybdenum steels.
  • “5” denotes Chromium steels.
  • “6” denotes Chromium-vanadium steels.
  • “7” denotes Tungsten-chromium steels.
  • “8” denotes Nickel-chromium-molybdenum steels, and
  • “9” denotes Silicon-manganese steels and various other grades

The second digit usually indicates the concentration of the major alloying element. The last two digits in the steel numbering system refer to the amount of carbon present in that steel grade. For example, SAE 1010 refers to mild steel containing 0.1% Carbon. Similarly, SAE 5130 refers to chromium steel with 1% chromium and 0.3% carbon.

The image in Fig. 2 clearly explains the AISI/SAE Steel numbering system philosophy in detail.

AISI/SAE Steel Number System
Fig. 2: AISI/SAE Steel Number System

Types of Steels based on Steel Smelting (De-oxidation) Process

Depending on the degree of oxidation three types of steel are available. They are:

  • Rimmed Steel: Low-cost, uneven-quality steels that are incompletely deoxidized.
  • Killed Steel: Completely deoxidized steel with high quality and cost.
  • Semi-Killed Steel: Partly deoxidized steel having quality and cost in between rimmed and killed steel.

Steel Types by Manufacturing Method

Depending on the process used to manufacture steel products, they are grouped as follows:

  • Steel parts made by cold rolling are known as Cold Rolled Steel.
  • Steel components produced by hot-rolling are known as Hot-Rolled Steel.
  • Cold Drawn Steel: products made by a cold drawing operation.
  • Cast Steel: Complex shapes made by the casting process
  • Forged Steel: products made by various forging methods.

Types of Steel Depending on Application

Based on the intended application Steel can be classified into various groups as listed below:

  • Structural Steel used in structural applications.
  • Tool Steels used for making tools.
  • Marine Steel used in seawater applications.
  • Boiler Steel to make parts of steam services.
  • Bridge Steel
  • Spring Steel
  • Pressure Vessel Steel, etc

Other Steel Types

Various other types of steel classification can be made as listed below:

  • Based on the steel production method: continuous cast steel, electric furnace steel, etc.
  • Based on microstructure: ferritic steel, pearlitic steel, martensitic steel, etc.
  • Based on heat treatment: annealed steel, quenched steel, tempered steel, etc.
  • Depending on the quality nomenclature: commercial quality steel, drawing quality steel, pressure vessel quality steel, etc.

What is Fracking? | Working of Fracking or Hydraulic Fracturing

Written by Anup Kumar Dey in Piping Interface,Process

Fracking or Hydraulic fracturing is a well-stimulation drilling technique that uses a highly pressurized liquid, usually a water mixture to fracture or create cracks in the deep-rock formations for the purpose of oil or natural gas extraction. This proven fracking methodology of oil extraction has been used commercially for more than 70 years. In this article, we will learn a broad overview of fracking; its meaning, working, pros and cons, and finally why is fracking bad.

Fracking Definition/Fracking Meaning

Fracking is defined as an unconventional method for fossil fuel extraction. Water, sand, and chemical mixtures are injected at very high pressure into the rock forcing the crude oil and gas to flow out to the wellhead. Fracking is also popular as Hydraulic fracturing, hydrofracking, and hydrofracturing. In the year 1947, the first fracking experiment started and the same process is commercialized in 1950. From then onwards, the fracking method with new developments is used extensively in the oil and gas industry to extract petroleum and natural gases.

Working of Fracking or Hydraulic Fracturing

For the fracking process, a fracturing liquid is specially prepared by mixing roughly 90% water, 9.5% sand, and 0.5% chemical additives. This liquid is then pumped down through a petroleum well lined with a steel casing. The pumping pressure is very high depending on the property of the rock. The pressure can be as high as 690 bar. The steel casing through which the fracturing liquid is injected has been perforated at predefined depths through which the liquid reaches the targeted rock formation. The very high pressure of the fracking method easily creates a network of small fractures in the rock.

The proppants (sand) suspended in the fluid remain in the fractures to keep them open when the pumping has stopped. This provides a pathway for the fossil fuel to flow into the well and be recovered. These fracture pathways generated by fracking can be three to six millimeters wide and can extend horizontally up to 400 meters and vertically up to 100 meters within the gas-bearing rock formation.

The basic workflow of fracking can be summed up as follows:

  • Drilling a wellbore lined with a steel casing, deep enough to reach the underground rock, filled with fossil fuels.
  • Loading a perforating gun with explosives and lowering it into the bottom of the well to create small holes usually in the horizontal section of the casing.
  • Injecting the fracking fluid at very high pressure to crack open the rock.

The hydraulic fracturing or fracking process usually completes between 1 to 10 days.

The chemical additives (Hydrochloric acid, acetic acid, Sodium chloride (salt), Polyacrylamide, Ethylene glycol, Borate salts, Sodium and potassium carbonates, Anaerobic, Biocide, BIO—Glutaraldehyde, Guar gum, and other water-soluble gelling agents, Citric acid, Isopropanol) that are mixed in the water mixture serve the following purposes:

  • It makes the fluid thicker so that the sand can suspend the fluid.
  • It increases the flowability of the fracking fluid into the fractures.
  • It helps the natural gas and oil to seep out of the generated cracks.
  • It prevents corrosion and in turn damage to the well;
  • It prevents bacteria build-up; and
  • It helps the sand proppant to fill in the newly-created fractures to keep the cracks open.

Pros and Cons of Fracking

Fracking of hydraulic fracturing provides the following advantages:

  • Easy access to the fossil fuel underneath the Earth’s surface.
  • Dependency on coal reduces due to the extraction of natural gases using fracking techniques.
  • As fracking has created a huge abundance in the oil and gas market, the cost has been reduced.
  • Natural gas extraction by fracking creates 100% clean energy.
  • Huge job creation.

However, there are many drawbacks to the fracking process as well. Those are:

  • Huge waste of fresh water for the fracking process.
  • Studies have shown that fracking is responsible for creating earthquakes.
  • Increase in air pollution due to emission of greenhouse gases.
  • Noise pollution due to the high-level noise of the fracking process.
  • The return water after the fracking operation is contaminated with heavy metals and radioactive components that increase water pollution.

Why is Fracking Bad?

Fracking is bad for the environment and people. There are various reasons behind considering fracking is dangerous. The major reasons that strengthen the idea that fracking is bad are:

  • The fracking method can leak and contaminate groundwater if not built sturdily.
  • The flow-back water that is recovered after the fracking operation can contaminate water supply streams. Sometimes, toxic materials are found in fracking fluids.
  • The fracking method greatly impacts air emissions which directly impacts climate change. Also, various toxic gases are released which negatively impact human health. The noise created during fracking operations creates stress and high blood pressure.
  • Heavy use of water in the fracking process is impacting fish and wildlife.

Online Fracking Course

To learn more on the subject we recommend the following online fracking course which will help you to have an edge over others on the subject:

What is Sheet Metal Fabrication? Sheet Metal Fabrication Process

Written by Anup Kumar Dey in Construction,Maintenance

Sheet Metal fabrication is the creation of useful metallic parts and structures by the application of multiple fabrication processes. Sheet metal fabrication is basically a broad term that involves various complex processes like cutting, forming, bending, welding, machining, and assembling. Fabrication shops or Fab shops are the places where the processes related to sheet metal fabrication are performed. Sheet metal fabrication is a vital process in various industries, from automotive to aerospace, construction, and electronics. In this article, we will explore the materials, processes, and tools required for sheet metal fabrication.

What is Sheet Metal Fabrication?

Sheet metal fabrication is defined as the process of turning flat metal sheets into useful products. Various special tools are used in this process to convert sheet metals into useful components with minimal effort. It is a value-added process to create machines, structures, or component parts following engineering drawings,, which usually serve as the instruction sheet to produce a finished product from the base metal. Sheet metal fabrication refers to the process of transforming flat sheets of metal into desired shapes and structures through various methods, such as cutting, bending, and assembling. The metals commonly used in this process include aluminum, steel, copper, and brass, chosen for their strength, durability, and suitability for specific applications.

Types of Sheet Metal Fabrication Materials

There are many different types of sheet metals available that are suitable for various fabrication processes. The choice of metal depends on the final use of the fabricated parts. Common metals and alloys that are widely used for the sheet metal fabrication process are:

  • Carbon Steel
  • Stainless Steel
  • Aluminum
  • Magnesium
  • Bronze
  • Copper
  • Brass
  • Aluminized steel,
  • Galvanized steel,
  • Titanium

Steps Involved in Sheet Metal Fabrication Process

The steps that usually are followed in sheet metal fabrication jobs are:

  1. Working with blueprints– The first step in the metal fabrication process is to create the blueprints to determine the sheet metal product specifications for making rough drawings.
  2. Creating a final shop drawing– Final engineering drawings are then prepared after rounds of checking of the rough drawings and calculations. It is ensured that the final product meets all necessary specifications and requirements. The final drawings include in-depth calculations of sheet metal stress levels and load limitations to determine the steps of the fabrication process.
  3. The metal fabrication process– The sheet metal fabrication process involves cutting, bending, welding, forming, joining, and finishing.
  4. Product finishing– After fabrication of the component is complete, a product has to undergo the product finishing steps like sandblasting, brushing, polishing, powder coating, plating, etc. After this step, the product will be ready for commercial use.

Types of Metal Fabrication Processes

The journey to the final product from raw sheet metals proceeds through various sheet metal fabrication processes. All the sheet metal fabrication processes can be grouped into the following three categories:

  • Cutting
  • Deformation
  • Assembly

Sheet metal fabrication: Cutting

The most widely and frequently used sheet metal fabrication process is cutting. A variety of different types of machinery are used to cut sheet metal to manipulate it for making a component. They are:

Laser Cutting: Laser cutting is a very quick, energy-efficient, and precise sheet metal cutting process that uses a powerful laser to cut thin or medium gauges of sheet metals.

Water Jet Cutting: In water jet cutting, a high-pressure jet of water with abrasive substances is used to cut the sheet metals. As water jet cutting does not generate heat in the process, this sheet metal fabrication process is particularly useful for metals having low melting points to avoid deformation due to heat generation.

Plasma Cutting: Plasma cutting is used for thicker sheet metals. In this metal fabrication process, a jet of hot plasma is used to penetrate the metal sheets. This method is highly powerful having low setup costs, however, less accurate than laser cutting or water jet cutting.

The comparison between Laser cutting, Water jet cutting, and Plasma cutting is provided in Table 1 below:

Sheet Metal Cutting ProcessLaser CuttingWater Jet CuttingPlasma Cutting
AdvantagesA wider range of materials.
Depth control functionality can engrave and part mark.
Negligible residual burrs.
Low surface roughness.
Small deformation.		No burr.
Precision Cutting.
No Heat Generation.
Wide range of materials.		Cost-effective option.
Suitable for thicker sheet metals.
DisadvantagesHeat distortion may occur.
Costly.
Possibilities of HAZ formation.
Not suitable for thicker gauge sheet metals.		Less precise than laser cutting.
Not suitable for part marking or engraving.
High cost		Produces rough cut with large burr.
Leaves HAZ.
Limited to electrically conductive materials only.
Table 1: Laser Cutting vs Water Jet Cutting vs Plasma Cutting

Punching or Piercing: In this method, a punch and die cut precise holes in sheet metals. The sheet metal is placed between those two components and the metal punch perforates the sheet to remove circular pieces, which can be used as new workpieces known as blanking. For large-scale production, punching is an effective process but not cost-effective for smaller jobs.

Sawing: Different types of sawing operations can be performed to cut softer sheet metals.

Machining: In this process, sheet metals are cut using tools like a drill bit or lathe blade.

Sheet metal fabrication: Forming or Deformation

Deformation is the next major method for sheet metal fabrication processes. In this process, the sheet metal is manipulated or shaped without cutting it. Widely used sheet metal deformation processes are:

Bending: Sheet metal bending is one of the most popular deformation processes. A machine known as a Press brake is used to bend sheet metals into V, U, or other complex shapes. With an increase in gauge thicknesses of sheet metals the force required to bend increases. The process of removing the bends from sheet metal is known as decambering.

Stamping: In the stamping process, a hydraulic or mechanical stamping press equipped with a tool and die is used to perform specific tasks like curling, drawing, embossing, flanging, etc.

Hemming: Hemming is a process by which the edges of sheet metal are folded over itself or another piece of sheet metal to create a rounded edge. In the sheet metal fabrication process, two types of hemming processes are widely involved. They are roll hemming and conventional die hemming. Conventional hemming is used for mass production. A hemming roller is used for roll hemming.

Spinning: Spinning is a metal fabrication process where a lathe machine is used to rotate the sheet metal against a tool to produce conical or cylindrical shapes.

Other sheet metal deformation processes include rolling and wheeling. Rolling involves the use of a pair of rollers to reduce its thickness whereas wheeling produces compound curves in sheet metals.

Sheet metal fabrication: Assembly

Assembly is basically joining sheet metal components produced using above mentioned cutting or bending processes. The common sheet metal assembly process consists of joining by Welding and joining using fasteners.

Welding: In the welding process, sheet metal components are joined together by melting sections with the application of heat to form a solid connection. There are various processes available that are used to weld sheet metals.

Joining using Fasteners: Similar or dissimilar sheet metal parts can easily be joined using fasteners like bolts, screws, rivets, etc.

Brazing: Brazing is a process similar to welding that operates by melting a filler without melting the sheet metals.

Adhesives: Adhesives can be used to hold metal sheets together in conjunction with other joining methods.

Applications of Sheet Metal Fabrication Process

Sheet metal is considered one of the most versatile materials and processes in the world today. Numerous large and small components are developed by designers and engineers. Sheet metal fabrication processes are used in every industry, including:

  • Refrigerators, freezers, and other home appliances
  • Airplane components
  • Automobile parts and Chassis
  • Brackets
  • Metal sinks
  • Consumer goods industry
  • Electrical enclosures
  • lockers, furniture, and Cabinets
  • Busbars
  • HVAC industry
  • Steel shades and garages
  • Electronics and robotics industry
  • Stainless steel kitchen accessories, surgical instruments, tanks, valves, and piping
  • Mounts
  • Construction industry
  • Energy Sector
  • Aluminum sheet metals in phones, laptops, and light casings

Advantages and Disadvantages of Sheet Metal Fabrication

As sheet metal fabrication covers a wide area of techniques and methods, the advantages and limitations will vary depending on the process used during fabrication. The general benefits are:

  • Sheet metal fabrication is fast and can produce high-quality components.
  • A large number of processes are available with a wide range of materials.
  • High strength-to-weight ratio for sheet metal fabricated parts.

The main disadvantages of the sheet metal fabrication process are

  • Each fabrication process has its own limitations.
  • The high initial cost for set up of equipment and tools.
  • Requirement of skilled laborers for each process

How do you fabricate sheet metal?

There are various available techniques or processes which are applied to fabricate sheet metals. The most popular sheet metal fabrication processes are cutting, welding, bending, stretching, forming, shrinking, finishing, etc. Using these methods, any kind of useful sheet metal product can be produced to suit the requirements.

What are the metal sheets used for fabrication?

The metal used for the sheet metal fabrication process depends on the end-use of the product. In general, the metals that are conventionally used for sheet metal fabrication purposes are Steel, Stainless Steel, Aluminum, Brass, Copper, Bronze, Magnesium, etc.

What is a sheet in manufacturing?

The term sheet in manufacturing any final product refers to the raw sheets of metals that are processed and assembled to produce the final product using various metal fabrication techniques.

What are the 3 main fabrication techniques?

The main three types of fabrication techniques are cutting, deforming, and assembling.

What is sheet metal fabrication used for?

Sheet metal fabrication is the process by which industrial products are produced and thus widely used for industrial and consumer parts and in various industries like automotive, robotics, aerospace, energy, etc.

What does a sheet metal fabricator do?

Sheet metal fabricators are the professionals responsible for the fabrication or installation of products made from thin metallic sheets. They prepare the final product following the design drawings and using several fabrication techniques.

What thickness is sheet metal?

The thickness of sheet metal varies from 0.5 mm to 6 mm. When the thickness exceeds 6 mm, it is termed a metallic plate. The thickness of sheet metals being lower are easier to form.

What are the sheet metal fabrication tools?

There is a range of tools that are used by metal fabricators for sheet metal fabrication. Some of the most widely used metal fabrication tools are:

  • Guillotine
  • Oxy-Fuel Cutting Torch
  • Beam Drill Line
  • Overhead Crane
  • Multi-Press
  • Punch and Flange Tools
  • Hole Drilling/Cutting Tools
  • Planishing Hammers
  • English Wheels
  • Dimple Dies
  • Corner Notchers
  • Cutting Saw
  • Hydraulic Bender
  • Mini metal Lathe and Mill
  • Bead Roller
  • Shrinker/Stretcher
  • Shearing tool
  • Sheet metal brake
  • Metal forming kit
  • Grinder
  • Jig Saw Blade

There is much more to learn and the following three online courses will surely help to improve your knowledge of sheet metal fabrication, design, and working:

What is Case Hardening | Case Hardening of Steel

Written by Anup Kumar Dey in Construction,Engineering Materials,Maintenance,Piping Design Basics,Piping Interface

The outermost surface of any metal is the most important area as it suffers from direct impact and abrasion while in operation. So, it is always desirable to make the metal surface abrasion-resistant. This is achieved by altering the surface hardness of the metal using a method called case hardening. This is also popular as the surface hardening process. In the following paragraphs, we will learn more details about the case hardening process, its purpose, types of case hardening methods, and applications.

What is Case Hardening? / Case hardening definition

Case hardening is a material processing technique by which the hardness of the outer surface of a metal is increased while keeping a soft ductile core. This surface hardening method creates a thin layer of a wear-resistant, hard case which in turn increases the impact strength of the component as a whole. The case hardening process involves altering the crystal structure of the metal or chemical composition by adding new elements to the metal surface at elevated temperatures. As with an increase in hardness the machinability usually reduces, the case hardening is performed at the final step after all other fabrication processes.

Purpose of Case Hardening

The main purposes for case hardening processes are:

  • Due to the development of compressive stresses in the outer surface layer, case hardening increases the fatigue strength of the metal and alloy.
  • The combination of hard surface and ductile core imparts optimum wear resistance and toughness properties.
  • Case hardening increases durability and usage economy of parts.
  • Case hardening improves the weldability in certain materials.

Reason for Case Hardening

By case hardening the outer surface only, in place of the entire metal object, the efficiency of the process is improved. The requirement of energy and time both reduces as heating the outer surface requires less heat as compared to the entire metal section. So, these cause huge savings in costs for large manufacturing units. Also, the performance of the material increases.

Metals Suitable for Case Hardening

Ferrous metals are the most common metals which are subjected to case hardening treatment. Special cases of nitriding in some aluminum and titanium alloy can be applied but not frequently. The widely used ferrous materials that are subjected to the case hardening process are:

  • Low carbon steels
  • Stainless steels
  • Cast Irons
  • High Carbon Steels
  • Tool Steels
  • High Strength Low Alloy Steels

Case Hardening of Steel

There are various means by which the case hardening of steel can be achieved. Depending on the desired properties in the finished product and the metals used in manufacturing, the specific type of case hardening process for steel is selected. For case hardening of steel i.e to make the hard case but softcore, two general processes are used:

  • In the first case hardening method, the chemical composition of the outer surface is altered using diffusion processes like carburizing, nitriding, cyaniding, carbonitriding, boriding, titanium-carbon diffusion, etc. and
  • Only the surface layer is hardened by heating and quenching processes. Examples of such case hardening methods are flame hardening, induction hardening, laser hardening, ion implantation, electron beam hardening, etc.

The first method mentioned above is known as the diffusion process. In this case hardening method of steel, the chemical composition of the outer surface of the steel is changed with hardening species such as carbon, nitrogen, cyanide, or boron. Diffusion methods of case hardening are ideally suitable when a large number of parts are to be surface-hardened. Depending on the types of steel the selection of case hardening methods varies as listed below:

  • Low Carbon Steels: Carburizing, Cyaniding, Carbonitriding, Ferritic nitrocarburizing.
  • Alloy Steels: Nitriding, Ion Nitriding
  • Tool Steels: Titanium carbide, Boriding, Salt nitriding, Ion nitriding, Gas nitriding.
  • Stainless Steels: Gas nitriding, Ferritic nitrocarburizing, Titanium carbide, Ion nitriding

Whereas the second method, known as the selective surface hardening method allows localized hardening by heating and quenching. Flame and induction hardening for case hardening of steel materials are generally limited to certain families of steels, such as medium-carbon steels, medium-carbon alloy steels, some cast irons, and the lower-alloy tool steels. The relative benefits of the five most common and widely used case hardening methods are provided in the image below:

Relative benefits of common case-hardening processes
Fig. 1: Relative benefits of common case-hardening processes

Applications of Case Hardening Process

Components subjected to high pressures, constant wear or abrasion, and sharp impacts are usually case-hardened. Examples of such parts include firing pins, rifle bolt faces, or engine camshafts. In all of these components, the bulk of the part is kept in the original ductile state and the surfaces are case hardened to act properly.

Another widely used application of case-hardening is self-drilling screws. To have the properties of drilling, cutting, and tapping into other materials, the drill point and the forming threads are case-hardened keeping the core as soft to retain the ductile behavior. Other examples of case hardening include

  • Gears
  • forging presses
  • Fasteners
  • metal rolling equipment
  • Camshafts
  • machine tools
  • Rods
  • drivelines of mining equipment and heavy-duty transmissions
  • Pins
  • Theft prevention lock shackles and chains
  • earthmoving equipment and heavy-duty construction cranes

What is the difference between surface hardening and case hardening?

The major differences between case hardening and surface hardening and provided in a tabular format below:

Case HardeningSurface Hardening
In the case hardening process, the metal surface is hardened by infusing other elements.In the surface hardening process, no infusion of other elements is done to increase hardness.
The thickness of the hardened outer layer known as the case is comparatively smaller than surface hardening methods.The thickness of the hardened surface is more.
Case hardening process involves red heating of the steel and then infusing carbon or nitrogen into the surface and then quick quenching.Surface hardening involves heating the steel to austenitizing temperature and then quenching the surface immediately.
Table 1: Case Hardening vs Surface Hardening

Advantages of Case Hardening Process

Case hardening of steel provides various advantages as mentioned below:

  • Increases durability and usage economy
  • Increases the machinability of steel making them suitable for heavy-duty applications.
  • Enhances the performance of case hardened steel products.
  • Reduces noise and increases energy saving in some situations
  • Case hardening of steel minimizes the deformation of parts.
  • Improves fracture resistance
  • Improves corrosion and abrasion resistance
  • Increases weldability of steel
  • Reduces distortion
  • Case hardening of steel increases fatigue resistance.

Reference and Further Studies

To know more about case hardening and the various processes click here.

What is Normalizing? Definition, Process, Advantages, and Applications of Normalizing

Written by Anup Kumar Dey in Construction,Engineering Materials,Maintenance,Mechanical,Pipeline,Piping Design Basics,Piping Interface

Normalizing is a widely popular heat treatment process for metals to increase ductility and toughness. This heat treatment is also known as normalizing annealing as the normalizing heat treatment process is very similar to annealing treatment. In this article we will learn more about normalizing; its definition, purposes, process steps, applicability, normalizing vs annealing, etc.

Normalizing Definition/ What is normalizing?

Normalizing is defined as a heat treatment process where a material is heated to a predecided elevated temperature, hold at that temperature for a certain period of time (usually 10-20 minutes), and then allowed to cool freely in the air to reach room temperature. The normalizing process is usually applied to metals that have been subjected to thermal or mechanical hardening processes and require their microstructure to be normalized. After normalizing, the metal gets back its ductility and the hardness is reduced.

Metals Suitable to be Normalized

For the normalizing treatment of a metal, it must be receptive to normalizing. Various metals and alloys are suitable to be normalized like

  • Iron-based alloys like Carbon steel, stainless steel, alloy steel, cast iron, etc.
  • Nickel alloys
  • Copper
  • Aluminum
  • Brass

Purpose of Normalizing

The main purposes of the normalizing heat treatment on metals are:

  • To remove structural irregularities or impurities and defects from the metal.
  • To improve ductility that has been lost in some metal processing.
  • To reduce the hardness that has been increased by mechanical or thermal hardening processes.
  • To increase the toughness of the metal.
  • To relieve internal stresses.
  • To get an improvement in machinability.

The Normalizing Process

Similar to annealing the normalizing process also follows three main stages; the Recovery stage, the Recrystallization stage, and the grain-growth stage. In the recovery stages of normalizing, the internal stresses are relieved by heating the material. Then the metal is heated to elevated temperatures above the recrystallization temperature of the metal where new grains are formed. Finally, in the grain growth stage of normalization, the grains develop fully when the material is cooled by air.

Applications for Normalizing

Normalizing treatment finds broad practical applications across several industries like Aerospace, Automotive, Heavy Equipment, Energy, Agriculture, Oil & Gas, etc. Usually, whenever metal is expected to get high residual stresses due to some kind of manufacturing steps, it is always suggested to normalize the metal using the normalizing heat-treatment process. A few examples include:

  • Carbon steel is normalized when it is cold-rolled to reduce brittleness and increase ductility.
  • After work hardening of ferritic stainless steel stampings in the automotive industry, they are normalized to regain their mechanical properties.
  • After the thermal microstructure alteration during welding in nickel-based alloys in the nuclear industry, normalizing is performed.

Normalizing Steel

Steel normalizing is a heat treatment process performed after rolling, welding, or forging processes to refine the distorted grains in the microstructure. The normalizing process of steel involves the following steps:

  • Steel is heated to about 40-500C (Refer to Fig. 1) above the upper critical temperature (A3 or Acm).
  • The alloy is then held at that temperature for around 10-20 minutes.
  • Cooling it in still or slightly agitated air to bring back to room temperature.
Normalizing temperature of Steel
Fig. 1: Normalizing temperature of Steel

After normalizing, the resultant microstructure is usually perlite. The grain size in normalizing steel is governed by the section thickness. A variation in grain size is observed as the cooling rate varies from the case to the core. The normalizing temperature of steel varies with the carbon content as is clear from Fig. 1. The following table (Table 1) provides recommended normalizing temperatures for steel.

Carbon %0.10.20.30.40.60.81.01.11.2
Temperature, 0C920900880860840820830900925
Table 1: Recommended temperatures for normalizing steel

Difference between Normalizing and Annealing

Even though the process steps for normalizing and annealing are almost similar there are specific differences between normalizing and annealing. The differences between annealing and normalizing are provided below in a tabular (Table 2) format.

NormalizingAnnealing
The cooling rate in normalizing is faster than annealing.Slower cooling rate as compared to normalizing.
Slow cooling in room temperature.Controlled slow cooling in a furnace.
Mechanical Strength and hardness of normalized components are more.Strength and hardness are lower as compared to the normalized parts.
Machinability is more improved in normalizing.Annealed product is soft and thus can stick to the machine during machining.
Slightly less ductility.More ductility.
Less expensiveComparatively costly
Table 2: Normalizing vs Annealing

The image in Fig. 2 shows the typical differences in nominal strength between Normalized and Annealed steel.

Normalized vs Annealed Steel
Fig. 2: Normalized vs Annealed Steel

What Is Annealing Steel | Annealing Process of Steel

Written by Anup Kumar Dey in Construction,Engineering Materials,Mechanical,Piping Design Basics,Piping Interface

Annealing is one of the most popular heat treatment methods to alter the mechanical properties of metals and alloys. Annealing is mostly used to increase the ductility of a material and to reduce the hardness. After annealing treatment, the metals or alloys become more workable. In this article, we will discuss the annealing process in detail.

What Is Annealing?

Annealing is a heat treatment process in which a metal is heated above its recrystallization temperature, kept at that temperature for some time for homogenization, and then cooled slowly to develop an equilibrium structure. In the crystal structure of the metal or alloy being annealed, the number of dislocations is reduced which causes an increase in ductility and relief of residual stresses. Usually for materials that have undergone some cold work or hardening treatment annealing is performed. So the main purposes of an annealing heat treatment are:

  • To eliminate internal residual stresses that occurred during earlier processing steps.
  • To improve the machinability of the metal.
  • To increase ductility which in turn improves formability.
  • To prevent deformation and cracking.
  • To reduce hardness and increase toughness.
  • To improve magnetic properties and decrease electrical resistance.
  • To refine the grain size.
  • To reduce the gaseous contents of the metal or alloy.

Stages of the Annealing Process

Every annealing heat treatment process consists of three stages; the Recovery stage, the Recrystallization stage, and the Grain growth stage. These stages work as follows:

Recovery Stage: In the recovery stage of the annealing process, the metal is heated in a furnace and its temperature is raised to such a point where the internal stresses are relieved.

Recrystallization Stage: In this stage, the metal is heated above the recrystallization temperature where new grains form without any residual stresses. Recrystallization is defined as a process where the deformed grains in a metallic structure are replaced by a new set of defect-free grains at a certain specific temperature range known as the recrystallization temperature.

Grain Growth Stage: In this stage of the annealing process, the material is cooled at a pre-decided rate for new grains to fully develop.

Metals for Annealing Treatment

The annealing process is applicable for most of the common materials like Steel, Cast Iron, Aluminum, brass, copper, etc. However, the material selected should be such that its properties can be altered by heat treatment. The majority of the annealing process is done over the steel alloy. All work-hardened steel materials like sheet metals, wires, and welding processes creating high residual stresses must undergo the annealing of steel processes to recover their properties.

What is Annealing Steel and its Types

Annealing steel means heating it to a predetermined temperature, holding it at that temperature for a certain period of time, and finally cooling at a very slow rate. The temperature to which the steel should be heated and the holding time are determined considering various factors like

  • Chemical composition of the steel (%Carbon content)
  • Shape and size of steel component( thickness)
  • Final properties desired.

Depending on the temperature of annealing treatment, phase transformation, and purpose, the annealing of steel is classified into various groups.

Steel Annealing types based on annealing temperature

Considering the steel annealing temperature, the annealing process is sub-divided into three classes. They are

  • Full Annealing
  • Partial annealing, and
  • Sub-critical annealing

Refer to Fig. 1 below that shows the temperatures at which Steel alloy should be heated for the above-mentioned annealing processes.

Types of Annealing based on Annealing temperature
Fig. 1: Types of Annealing based on Annealing temperature

As understood from the above figure, in the full annealing process, steel is heated above the upper critical temperature (A3) and then cooled very slowly. In the case of partial annealing, steel is heated to a temperature that lies between lower (A1) and upper (A3 or Acm) critical temperature and then cooled slowly. Partial annealing is also known as inter-critical annealing or incomplete annealing. For the subcritical annealing process, the steel is heated below the lower critical temperature (A1). No phase change takes place in subcritical annealing and thus only recrystallization, softening, recovery, and grain growth occur.

Annealing Steel types based on specific purposes

Based on the specific purposes of annealing steel, the process is grouped into various types. They are:

  • Diffusion Annealing
  • Full Annealing
  • Spheroidizing Annealing
  • Recrystallization Annealing
  • Isothermal Annealing
  • Process Annealing

Full Annealing of Steel

Full annealing of steel is also known as phase recrystallization annealing. This process ensures the refinement of grains and the elimination of structural inhomogeneity. The process of full annealing of steel consists of heating the steel alloy to 30 to 500C above (A3 for hypo-eutectoid steels, A1 for eutectoid steel) followed by slow cooling. Almost all castings, forgings, and rolled stocks are provided with this treatment to get enhanced mechanical properties.

Diffusion Annealing of Steel

The purpose of diffusion annealing is to eliminate inhomogeneities of the chemical composition, dendrites, and columnar grains which appear during the crystallization of alloys. Diffusion annealing is usually carried out at a temperature of 1100–13000C (2012–23720F) and then the steel is held at this temperature for 10-20 hours, followed by slow cooling. Diffusion annealing is used to smooth out a difference in the content of alloying elements due to the inter-crystal liquation and chemically homogeneous steel is obtained. To improve the properties of medium-purity steels, this type of annealing is used.

Isothermal Annealing of Steel

In isothermal annealing, after heating the steel to above critical temperatures is held at this temperature for quite some time. It is then rapidly cool to 600-7000C by rapidly transferring the steel to another furnace maintained at the desired temperature. This temperature is maintained for some time and then cooled in the air. This process improves machinability and a better surface finish during machining. The heat treatment cycle is shown in Fig. 2

Heat treatment cycle in Isothermal Annealing
Fig. 2: Heat treatment cycle in Isothermal Annealing: a) hypo-eutectoid steel and b) eutectoid steel

Recrystallization Annealing of Steel

To increase the ductility of cold-worked steels, recrystallization annealing is used. The temperature at which the steel is to be heated depends on the amount of prior deformation, chemical composition, holding time, and initial grain size. Usually, alloy steels and high carbon steels require a higher temperature.

Process Annealing of Steel

Process annealing of steel consists of heating it below A1 temperature and holding it at this temperature for sufficient time and then cooling it. It is usually an intermediate operation for processing the steel further. Process annealing treatment is widely given for steel fabricated by extrusion, stamping, upsetting, and drawing. The temperatures at which steel should be heated for various annealing treatments are provided in Fig. 3 below:

Heating temperatures for various annealing processes
Fig. 3: Heating temperatures for various annealing processes

Spheroidizing Annealing of Steel

Spheroidizing annealing results in carbide spheroids in a ferrite matrix. The degree of spheroidization varies according to heat-treatment temperature and holding time. Various processes are available to get spheroid structures in steel. To improve machinability and ductility, Spheroidizing Annealing is often performed for alloy steels and high carbon steels.

Does annealing increase strength?

Yes, the annealing treatment of metals increases the strength by reducing dislocation sources. The annealing process improves the ductility of material by strengthening grain boundaries’ resistance to intergranular cracks.

Do you quench after annealing?

For annealing of steel, the cooling method applied is slow cooling, not immediate. So, in general, steel is not quenched after annealing.

What are the types of annealing?

The annealing process can be categorized into several types:

  • Complete Annealing.
  • Partial Annealing
  • Isothermal Annealing.
  • Spherical Annealing.
  • Recrystallization Annealing.
  • Diffusion Annealing.
  • Stress Relief Annealing.

What industries use annealing?

Manufacturing industries dealing with Steel, Cast Iron, Aluminum, Copper, Brass, etc use the annealing process widely. Usually, materials are annealed before extreme forming or drawing operations.