Brinell Hardness Test: Introduction, Procedure, Formula, Standards (PDF)

The hardness of a material is its ability to resist localized permanent deformation, penetration, scratching, or indentation. So, it is an important parameter in engineering. Hardness Testing provides a means to quantify the hardness of a material and it is a key element in many quality control procedures and R&D work. Several methods are available for hardness testing. However, Brinell, Rockwell, Vickers, Knoop, Mohs, Scleroscope, and the files test are the most widely used hardness tests. In this article, we will learn about Brinell Hardness Test, its procedure, related formula, and standards.

What is the Brinell Hardness Test?

The Brinell Hardness Test method is the most commonly used hardness measurement technique in the industry. In the Brinell Hardness Testing, the hardness of a metal is determined by measuring the permanent indentation size produced by an indenter. Harder materials will generate shallow indentations while the softer materials will produce deeper indentations. This test method was first proposed by Swedish engineer Johan August Brinell in 1900 and according to his name, the test is popular as Brinell Hardness Test.

Brinell Hardness Test Procedure

The Brinell Hardness test is performed in a Brinell hardness test unit. In this test method, a predetermined force (F) is applied to a tungsten carbide ball of fixed diameter (D) and held for a predetermined time period, and then removed. The spherical indenter creates an impression (permanent deformation) on the test metal piece. This indentation is measured across two or more diameters and then averaged to get the indentation diameter (d). Using this indentation size (d) Brinell Hardness Number (BHN) is found using a chart or calculated using the Brinell hardness test formula. The equipment used for Brinell Hardness Testing are:

• Brinell Hardness Testing Machine
• Indenter Sphere, and
• Brinell microscope to measure the generated impression.

Brinell Hardness Testing Machine:

The Brinell Hardness Testing Machine (Fig. 1) consists of a loading system that includes leavers, weights, hydraulic dashpot, and plunger enclosed in the body of the machine. The test material is kept on the adjustable anvil. Using the lever, the spherical ball indenter descends on the material with a pre-decided force that can be read on the screen.

For softer metals the force used is less than harder metals. The force value varies from 1 kgf to 3000 kgf. Common test forces range from 500 kgf often used for non-ferrous materials to 3000 kgf for steels and cast irons.

There are four sizes of the indenter used for the Brinell hardness test. They are 1 mm, 2.5 mm, 5 mm, and 10 mm in size.

To obtain the same BHN with different ball diameters, geometrically similar indentations must be produced. It is possible if F/D² is maintained constant.

Brinell Hardness Test Formula

Once the average indentation diameter is measured the Brinell Hardness Number (BHN or HBW) can be calculated using the following Brinell hardness test formula:

Note that, the term HBW stands for Hardness Brinell Wolfram carbide.
Wolfram carbide (= tungsten carbide) underlines the use of tungsten carbide balls, as opposed to the (softer) steel balls previously used (HBS).

The minimum Test Specimen thickness is at least 10 times the indentation depth as per ASTM standard and the same is at least 8 times the indentation depth as per ISO standard.

Specifying Brinell Hardness Number

While specifying a Brinell hardness number (BHN or HB), the test conditions used to obtain the number must be specified. The standard format for specifying is “HBW 10/3000”. “HBW” refers to a tungsten carbide ball used as an indenter, as opposed to “HBS”, which means a hardened steel ball. The “10” is the ball diameter in millimeters. The “3000” is the force in kilograms force.

Sometimes, the Brinell hardness is also specified as “XXX HB YYD2” where

• XXX is the force to apply (in kgf)
• YY specifies the material type (5 for aluminum alloys, 10 for copper alloys, 30 for steels).

Thus the Brinell hardness of a typical steel could be written: 250 HB 30D2. The following image from wikipedia provides some typical Brinell Hardness Values of common materials.

Requirements for Brinell Hardness Testing

• Before the test, the sample must be cleaned thoroughly. Preferable if the test surface is machined, ground, and polished to get better indentation measurement.
• Proper indenter (Steel ball or carbide Ball) as per requirement need to be selected.
• The applicable force needs to determined beforehand.
• The load on the specimen to be maintained for the exact period of time.
• The indents must be positioned to keep sufficient clearance from the specimen edge and between the individual indents.

Standards for Brinell Hardness Test

The widely used standards for Brinell Hardness Test in industries are:

• ASTM E10
• ISO 6506
• JIS Z 2243

Advantages of Brinell Hardness Test

Brinell Test method has many advantages:

• The hardness of rough samples can be measured which is difficult in other methods.
• Application of high test load (up to 3,000 Kg) is possible.
• Wide measuring range due to availability of a range of indenter sizes and loads
• A Brinell hardness tester can determine the hardness of all types of metals.
• Provides reliable results.

However, Brinell test method has some disadvantages as well:

• There could be measuring errors due to using of optical instruments.
• Surface imperfections can interfere with the test result if the surface not prepared thoroughly.
• The requirement of a flat surface makes this test redundant for cylindrical surfaces.

Brinell vs Rockwell hardness Test

The main difference between Brinell and Rockwell Hardness Test is provided in the table below:

Brinell Hardness Test	Rockwell Hardness Test
In Brinell Hardness Test the indenter is a spherical Tungsten Carbide Ball	For Rockwell Hardness Test the Indenter is a Small Steel Ball (HRB) or a diamond cone (HRC)
Hardness greater than 650 HB can not be measured with this set up.	No such limitation.
It measures the diameter of the indentation to calculate hardness value.	Depth of indentation is measured for calculating Rockwell hardness.
A comparatively slow method.	Quicker process.
Surface preparation required.	No surface preparation.
Comparatively costly	Cheaper option

Brinell, Rockwell, and Vickers Hardness Conversion Table

The approximate conversion of Brinell, Rockwell B & C, and Vickers hardness is provided below for sample only. One more column indicating approximate equivalent tensile strength is also added.

Brinell Hardness (HB)-3000Kg-10 mm Ball	Rockwell Hardness (HRC)-150Kg Brale	Rockwell (HRB)- 100Kg 1/16″ Ball	Vickers Hardness (HV)- Diamond Pyramid 120 Kg	Approx. Tensile strength (N/mm²)
800	72
780	71
760	70
752	69
745	68
746	67
735	66
711	65
695	64
681	63
658	62
642	61
627	60
613	59
601	58		746
592	57		727
572	56		694
552	55		649
534	54	120	589
513	53	119	567
504	52	118	549
486	51	118	531
469	50	117	505
468	49	117	497
456	48	116	490	1569
445	47	115	474	1520
430	46	115	458	1471
419	45	114	448	1447
415	44	114	438	1422
402	43	114	424	1390
388	42	113	406	1363
375	41	112	393	1314
373	40	111	388	1265
360	39	111	376	1236
348	38	110	361	1187
341	37	109	351	1157
331	36	109	342	1118
322	35	108	332	1089
314	34	108	320	1049
308	33	107	311	1035
300	32	107	303	1020
290	31	106	292	990
277	30	105	285	971
271	29	104	277	941
264	28	103	271	892
262	27	103	262	880
255	26	102	258	870
250	25	101	255	853
245	24	100	252	838
240	23	100	247	824
233	22	99	241	794
229	21	98	235	775
223	20	97	227	755
216	19	96	222	716
212	18	95	218	706
208	17	95	210	696
203	16	94	201	680
199	15	93	199	667
191	14	92	197	657
190	13	92	186	648
186	12	91	184	637
183	11	90	183	617
180	10	89	180	608
175	9	88	178	685
170	7	87	175	559
167	6	86	172	555
166	5	86	168	549
163	4	85	162	539
160	3	84	160	535
156	2	83	158	530
154	1	82	152	515
149		81	149	500
147		80	147	490
143		79	146	482
141		78	144	481
139		77	142	480
137		76	140	475
135		75	137	467
131		74	134	461
127		72	129	451
121		70	127	431
116		68	124	422
114		67	121	412
111		66	118	402
107		64	115	382
105		62	112	378
103		61	108	373
95		56	104
90		52	95
81		41	85
76		37	80