Steel Hardness Conversions

Steel Hardness Conversion Table

BSS Steelstrip for Cold Rolled Steel Strip in the UK

Note that hardness conversions are approximate only as the different scales use different methods of testing
Brinell	Brinell	Vickers	Rockwell	Rockwell
Impression	Hardness	hardness	Hardness	Hardness	Equiv Rm	Equiv Rm	Equiv Rm
Dia. mm	HB	HV	B	C	tonf/in²	kgf/mm²	N/mm²
2.50	601	640	-	57.0	-	-	-
2.55	578	615	-	56.0	-	-	-
2.60	555	591	120	54.5	-	-	-
2.65	534	569	119	53.5	-	-	-
2.70	514	547	119	52.0	-	-	-
2.75	495	528	117	51.0	-	-	-
2.80	477	508	117	49.5	-	-	-
2.85	461	491	116	48.5	101	160	1569
2.90	444	474	115	47.0	98	155	1520
2.95	429	455	115	45.5	95	150	1471
3.00	415	440	114	44.5	92	145	1422
3.05	401	425	113	43.0	88	139	1363
3.10	388	410	112	42.0	85	134	1314
3.15	375	396	112	40.5	82	129	1265
3.20	363	383	110	39.0	80	126	1236
3.25	352	372	110	38.0	77	121	1187
3.30	341	360	109	36.5	75	118	1157
3.35	331	350	109	35.5	73	114	1118
3.40	321	339	108	34.5	71	111	1089
3.45	311	328	108	33.0	68	107	1049
3.50	302	319	107	32.0	66	104	1020
3.55	293	309	106	31.0	64	101	990
3.60	285	301	105	30.0	63	99	971
3.65	277	292	104	29.0	61	96	941
3.70	269	284	104	27.5	59	93	912
3.75	262	276	103	26.5	58	91	892
3.80	255	269	102	25.5	56	89	873
3.85	248	261	102	24.0	55	87	853
3.90	241	253	100	23.0	53	84	824
3.95	235	247	99	22.0	51	81	794
4.00	229	241	98	20.5	50	79	775
4.05	223	235	97	-	49	77	755
4.10	217	228	96	-	48	76	745
4.15	212	223	96	-	46	73	716
4.20	207	218	95	-	45	71	696
4.30	197	208	93	-	43	68	667
4.40	187	197	91	-	41	65	637
4.50	179	189	89	-	39	62	608
4.60	170	179	87	-	36	57	559
4.70	163	172	85	-	35	55	539
4.80	156	165	83	-	34	54	530
4.90	149	157	81	-	32	51	500
5.00	143	150	79	-	31	49	481
5.10	137	144	77	-	31	49	481
5.20	131	138	74	-	30	47	461
5.30	126	133	72	-	29	46	451
5.40	121	127	70	-	28	44	431
5.50	116	122	68	-	27	43	422
5.60	111	117	66	-	26	41	402
5.70	107	113	64	-	25	39	382
5.80	103	108	61	-	24	38	373

Hardness Testing

Hardness testing for steel is based upon applying pressure to the steel surface and measuring the depth of the indentation. The three major measurement systems are :-

Brinell Hardness

The Brinell hardness test consists in indenting the metal surface with a 10-mm-diameter steel ball at a load of 3,000 kg mass (∼29400 N). For soft metals the load is reduced to 500 kg to avoid too deep an impression, and for very hard metals a tungsten carbide ball is used to minimize distortion of the indenter. The load is applied for a standard time, usually 30 s, and the diameter of the indentation is measured with a low-power microscope after removal of the load. The average of two readings of the diameter of the impression at right angles should be made.

Vickers Hardness

The Vickers hardness test uses a square-base diamond pyramid as the indenter. The included angle between opposite faces of the pyramid is 136°. This angle was chosen because it approximates the most desirable ratio of indentation diameter to ball diameter in the Brinell hardness test.

Because of the shape of the indenter, this is frequently called the diamond-pyramid hardness test. The diamond-pyramid hardness number (DPH), or Vickers hardness number (VHN, or VPH), is defined as the load divided by the surface area of the indentation. In practice, this area is calculated from microscopic measurements of the lengths of the diagonals of the impression

Rockwell Hardness Test

The most widely used hardness test is the Rockwell hardness test. Its general acceptance is due to its speed, freedom from personal error, ability to distinguish small hardness differences in hardened steel, and the small size of the indentation, so that finished heat-treated parts can be tested without damage.

This test utilizes the depth of indentation, under constant load, as a measure of hardness. A minor load of 10 kg is first applied to seat the specimen. This minimizes the amount of surface preparation needed and reduces the tendency for ridging or sinking in by the indenter. The major load is then applied, and the depth of indentation is automatically recorded on a dial gage in terms of arbitrary hardness numbers.