APPROXIMATE HARDNESS CONVERSION NUMBERS FOR STEEL*
Brinell
Indentation Diameter mm |
Brinell Hardness
Number |
Rockwell Hardness
Number |
Tensile
Strength (approxi- mate) 1000 psi |
||
Standard
Ball |
Tungsten-
Carbide Ball |
B Scale
|
C Scale
|
||
2.45
|
—
|
627
|
—
|
58.7
|
347
|
2.50
|
—
|
601
|
—
|
57.3
|
328
|
2.55
|
—
|
578
|
—
|
56.0
|
313
|
2.60
|
—
|
555
|
—
|
54.7
|
298
|
2.65
|
—
|
534
|
—
|
53.5
|
288
|
2.70
|
—
|
514
|
—
|
52.1
|
274
|
2.75
|
—
|
495
|
—
|
51.0
|
264
|
2.80
|
—
|
477
|
—
|
49.6
|
252
|
2.85
|
—
|
461
|
—
|
48.5
|
242
|
2.90
|
—
|
444
|
—
|
47.1
|
230
|
2.95
|
429
|
429
|
—
|
45.7
|
219
|
3.00
|
415
|
415
|
—
|
44.5
|
212
|
3.05
|
401
|
401
|
—
|
43.1
|
202
|
3.10
|
388
|
388
|
—
|
41.8
|
193
|
3.15
|
375
|
375
|
—
|
40.4
|
184
|
3.20
|
363
|
363
|
—
|
39.1
|
177
|
3.25
|
352
|
352
|
—
|
37.9
|
171
|
3.30
|
341
|
341
|
—
|
36.6
|
164
|
3.35
|
331
|
331
|
—
|
35.5
|
159
|
3.40
|
321
|
321
|
—
|
34.3
|
153
|
3.45
|
311
|
311
|
—
|
33.1
|
149
|
3.50
|
302
|
302
|
—
|
32.1
|
146
|
3.55
|
293
|
293
|
—
|
30.9
|
141
|
3.60
|
285
|
285
|
—
|
29.9
|
138
|
3.65
|
277
|
277
|
—
|
28.8
|
134
|
3.70
|
269
|
269
|
—
|
27.6
|
130
|
3.75
|
262
|
262
|
—
|
26.6
|
127
|
3.80
|
255
|
255
|
—
|
25.4
|
124
|
3.85
|
248
|
248
|
—
|
24.2
|
120
|
3.90
|
241
|
241
|
100.0
|
22.8
|
116
|
3.95
|
235
|
235
|
99.0
|
21.7
|
114
|
4.00
|
229
|
229
|
98.2
|
20.5
|
111
|
4.05
|
223
|
223
|
97.3
|
—
|
104
|
4.10
|
217
|
217
|
96.4
|
—
|
103
|
4.15
|
212
|
212
|
95.5
|
—
|
100
|
4.20
|
207
|
207
|
94.6
|
—
|
99
|
4.25
|
201
|
201
|
93.8
|
—
|
97
|
4.30
|
197
|
197
|
92.8
|
—
|
94
|
4.35
|
192
|
192
|
91.9
|
—
|
92
|
4.40
|
187
|
187
|
90.7
|
—
|
90
|
4.45
|
183
|
183
|
90.0
|
—
|
89
|
4.50
|
179
|
179
|
89.0
|
—
|
88
|
4.55
|
174
|
174
|
87.8
|
—
|
86
|
4.60
|
170
|
170
|
86.8
|
—
|
84
|
4.65
|
167
|
167
|
86.0
|
—
|
83
|
4.70
|
163
|
163
|
85.0
|
—
|
82
|
4.80
|
156
|
156
|
82.9
|
—
|
80
|
4.90
|
149
|
149
|
80.8
|
—
|
73
|
5.00
|
143
|
143
|
78.7
|
—
|
71
|
5.10
|
137
|
137
|
76.4
|
—
|
67
|
5.20
|
131
|
131
|
74.0
|
—
|
65
|
5.30
|
126
|
126
|
72.0
|
—
|
63
|
5.40
|
121
|
121
|
69.0
|
—
|
60
|
5.50
|
116
|
116
|
67.6
|
—
|
58
|
5.60
|
111
|
111
|
65.7
|
—
|
56
|
This table, which is based on ASTM A370-68, Table III, lists the approximate relationship of hardness values to corresponding approximate tensile strength values of steels. Some compositions and processing histories may deviate from these relationships. The data in this table do not represent hardness-to-tensile strength conversions for austenitic, ferritic, and martensitic stainless steel. If more precise conversions are required, they should be developed for each specific composition and heat treatment. Related Rockwell superficial hardness numbers, if of interest, may be found in ASTM A370-68.