difference between carbon steel and stainless steel

Steel as an engineering material finds diverse applications. The basic components of all steel materials are iron and carbon. Even though Steel signifies a broad range of ferrous metal alloys, most people divide it into two broad categories; Carbon Steel and Stainless Steel. In this article, we will find the main differences between these two broad categories, i.e, Carbon Steel vs Stainless Steel. What is Carbon Steel? Consisting mainly of iron and up to 2.1 percent carbon, Carbon Steel also contain various other alloying elements like manganese (1.65% max), silicon (0.6% max), copper ().6% max), chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium, zirconium, etc. Carbon steel in broader sense sometimes include alloy steel where some specific alloying elements (usually up to 10.5 percent alloy content) are added to have certain required properties. Carbon steel is categorized into two groups; Low Carbon Steel and High Carbon Steel. High carbon steels (Carbon: 0.3 to 2.1%) are very hard, capable of resisting abrasion and retaining shape. But, they are brittle. Whereas, Low carbon steels (Carbon: 0.05 to 3%) are ductile. Depending on type of loading the metal will experience, both high and low carbon steel finds wide applications in engineered products. What is Stainless Steel? Stainless steel is a group of corrosion-resistant ferrous alloy containing more than10.5% chromium and less than 1.2 % carbon. The chromium added to it increases the ability to resist corrosion. Depending on microstructure, broadly three major categories of stainless steel is available. They are austenitic stainless steel, ferritic stainless steel, martensitic stainless steel. Carbon Steel vs Stainless Steel, the Differences Stainless Steel vs Carbon Steel: Rusting (Corrosion Resistance) The main difference between stainless steel and carbon steel is obviously the corrosion resistance. Stainless Steel is manufactured to resist rusting or corrosion. Among the two metals, Stainless Steel is more corrosion resistant than Carbon Steel. A high amount of Chromium is added in stainless steel that creates a chromium oxide layer to prevent corrosion. On the other hand, Carbon steel does not have enough chromium to create such a layer and thereby prone to corrosion and rusting. Carbon Steel vs Stainless Steel: Physical Properties The physical properties of Carbon Steel and Stainless Steel varies. The parameters are provided in table 1 below. Physical parameterCarbon SteelStainless SteelAvearge DensityAverage Density of Carbon Steel is 7850 Kg/m3Average Density of Stainless Steel is 8000 Kg/m3. So Stainless Steel is slightly heavier than Carbon SteelCo-efficient of Linear Thermal ExpansionThe thermal expansion coefficient for Carbon Steel is usually less than that of stainless steel and varies in the range of (10.8 - 12.5) X 10-6 m/(m °C)The expansion coefficient of Stainless Steel is comparatively more than that of Carbon Steel. Depending on grade, the coefficient varies in the range of (10-17.3) X10-6 m/(m °C). So, the thermal growth of Stainless Steel is more than Carbon Steel material.Melting PointThe melting point of Carbon Steel is more than Stainless Steel. Typically Low Carbon Steel have melting point of 1410 Deg C. The melting point of high Carbon steel ranged in between 1425-1540 Deg C.The melting point of stainless steel varies in between 1375 to 1530 Deg C.Table 1: Carbon Steel vs Stainless Steel-Physical Properties Stainless Steel vs Carbon Steel: Mechanical Properties Ductility: Austenitic Stainless Steel grades are more ductile than Carbon Steel. However, Martensitic stainless steel grades are brittle grades of stainless steel which may be more brittle than carbon steel. Mechanical strength: In general, Stainless steel is softer and weaker in strength due to lower amount of carbon present in it. The mechanical properties of carbon steel vs stainless steel is provided in table 2 below: Mechanical propertiesCarbon SteelStainless SteelYield StrengthLow Carbon Steel: 180 to 260 MPa; High carbon Steel: 325 to 440 Mpa.Ferritic Steel: 280 Mpa; Austenitic Steel: 230 MPA; Martensitic Steel: 480 MPATensile StrengthLow Carbon Steel: 325 to 485 MPa; High carbon Steel: 460 to 924 Mpa.Ferritic Steel: 450 Mpa; Austenitic Steel: 540 MPA; Martensitic Steel: 660 MPAElastic Modulus2100000 Mpa1900000 MPaShear Modulus81000 Mpa740000 MPaPoisson's Ratio0.30.27Table 2: Mechanical properties of Carbon Steel and Stainless Steel Carbon Steel vs Stainless Steel: Temperature Capabilities Stainless steel can easily contain fluids having a temperature above 426 degrees C. But for carbon steel, after 4260 C graphitization starts, and thus the application of carbon steel is limited up to temperatures of 426 Degree C. Stainless steel is well noted for high heat resistance capabilities. Normal Carbon steel is normally not suitable for temperatures below -460 C. Special LTCS material is used below -460 C of temperature. However, Stainless steel can be used for much lower temperatures. Stainless Steel vs Carbon Steel: Appearance For Aesthetic looks Stainless Steel is much better as compared to carbon steel. Stainless steel looks great as it is, But carbon steel needs painting of surfaces to avoid rusting. Stainless Steel vs Carbon Steel: Cost Economic consideration is one of the most consideration for Carbon steel and stainless steel materials. In general, Stainless Steel is costlier than Carbon steel. However, cost varies depending on the grades of the material. Because of the special alloy additions like chromium, nickel, etc and manufacturing associated with it, the cost of stainless steel increases. Carbon Steel vs Stainless Steel: Machinability and Weldability Carbon steel can be machined easily and it has good welding capabilities. On the contrary, Stainless steel requires specialized techniques for welding and machining. For machine tools, stainless steel is hard compared to carbon steel. Carbon Steel vs Stainless Steel: Other differences Stainless SteelCarbon SteelThermal conductivity is comparatively lowerHigher thermal conductivity.Excellent wear resistancePoor wear resistance.Heat treatment of Stainless steel is difficultCarbon Steel can easily undergo heat treatment.Stainless Steel is easily cleanableThe cleanability of carbon steel is less than stainless steel.Table 3: Stainless Steel vs Carbon Steel When to Use Carbon Steel vs Stainless Steel Both carbon steel and stainless steel have their own pros and cons with respect to application, properties, and budget. So, selection between stainless steel and carbon steel must always be based on application. If budget is not a concern, and the application requires high temperature (or cryogenic temperature) along with corrosion resistance property, it is always better to go for Stainless Steel. However, for normal, non-corroding environments, carbon steel is good enough.