STL - Hardness Conversion Chart

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Hardness Conversion Chart

Tensile Strength (N/mm2)	Hardness Vickers	Hardness Brinell*	HRB	HRF	HRC	HRA
770	240	228	98.1	114.3	20.3	60.7
785	245	233			21.3	61.2
800	250	238	99.5	115.1	22.2	61.6
820	255	242			23.1	62.0
835	260	247	(101)		24.0	62.4
850	265	252			25.8	62.7
865	270	257	(102)		25.8	63.1
880	275	261			26.4	63.5
900	208	266	(104)		27.1	63.8
915	285	271			27.8	64.2
930	290	276	(105)		28.5	64.5
950	295	280			29.2	64.8
965	300	285			29.8	65.2
995	310	295			31.0	65.8
1030	320	304			32.2	66.4
1060	330	314			33.3	67.0
1095	340	323			34.4	67.6
1125	350	333			35.5	68.1
1155	360	342			36.6	68.7
1190	370	352			37.7	69.2
1220	380	361			38.8	69.8
1255	390	371			39.8	70.3
1290	400	380			40.8	70.8
1320	410	390			41.8	71.4
1350	420	399			42.7	71.8
1385	430	409			43.6	72.3
1420	440	418			44.5	72.8
1455	450	428			45.3	73.3
1485	460	437			46.1	73.6
1520	470	447			46.9	74.1
1555	480	(456)			47.7	74.5
1595	490	(466)			48.4	74.8
1630	500	(475)			49.1	75.3
1665	510	(485)			49.8	75.7
1700	520	(494)			50.5	76.1
1740	530	(504)			51.1	76.4
1775	540	(513)			51.7	76.7
1810	550	(523)			52.3	77.0
1845	560	(532)			53.0	77.4
1880	570	(542)			53.6	77.8
1920	580	(551)			54.1	78.0
1955	590	(561)			54.7	78.4
1995	600	(570)			55.2	78.6
2030	610	(580)			55.7	78.9
2070	620	(589)			56.3	79.2
2105	630	(599)			56.5	79.5
2145	640	(608)			57.3	79.8
2180	650	(618)			58.7	80.0
	660				58.3	80.3
	670				58.8	80.6
	680				59.2	80.8
	690				59.7	81.1
	700				60.1	81.3
	720				61.0	81.8
	740				61.8	82.2
	760				62.5	82.6
	780				63.3	83.0
	800				64.0	83.4
	820				64.7	83.8
	840				65.3	84.1
	860				65.9	84.4
	880				66.4	84.7
	900				67.0	85.0
	920				67.5	85.3
	940				68.8	85.6

* calculate from HB = 0.95 x HV

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Ball Hardness Corrections for Curvatures

Ball Dia	Rockwell 'C' Readings
(mm)	55	56	57	58	59	60	61	62	63	64	65
3.175	6.1	5.7	5.4	5.1	4.8	4.5	4.2	4.0	3.8	3.6	3.4
3.968	5.6	5.3	5.0	4.7	4.4	4.1	3.8	3.6	3.4	3.2	3.0
4.762	5.1	4.7	4.3	4.0	3.8	3.6	3.4	3.2	3.0	2.8	2.5
5.562	4.6	4.3	4.0	3.7	3.5	3.3	3.1	2.9	2.7	2.5	2.3
6.350	4.1	3.8	3.6	3.3	3.1	2.9	2.7	2.5	2.3	2.1	1.8
7.000	3.7	3.4	3.2	3.0	2.8	2.6	2.4	2.2	2.0	1.8	1.6
7.938	3.1	2.9	2.7	2.6	2.4	2.2	2.0	1.9	1.7	1.5	1.3
8.000	3.1	2.9	2.7	2.6	2.4	2.2	2.0	1.9	1.7	1.5	1.3
9.000	2.7	2.5	2.4	2.2	2.0	1.9	1.7	1.5	1.4	1.2	1.1
9.525	2.5	2.3	2.2	2.0	1.9	1.8	1.6	1.4	1.2	1.1	1.0
10.000	2.4	2.2	2.0	1.9	1.8	1.7	1.5	1.3	1.1	1.0	0.9
11.000	2.1	2.0	1.8	1.7	1.6	1.5	1.3	1.1	0.9	0.8	0.7
12.000	1.9	1.7	1.6	1.5	1.4	1.3	1.1	1.0	0.8	0.7	0.6
12.700	1.8	1.7	1.6	1.5	1.4	1.2	1.0	0.9	0.7	0.6	0.5
13.000	1.8	1.7	1.6	1.5	1.4	1.2	1.0	0.9	0.7	0.6	0.5
14.000	1.6	1.5	1.4	1.3	1.2	1.0	0.9	0.8	0.6	0.5	0.4
15.000	1.5	1.4	1.3	1.2	1.1	0.9	0.8	0.7	0.5	0.4	0.3
15.875	1.4	1.3	1.2	1.1	1.0	0.9	0.8	0.7	0.5	0.4	0.3

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This table is useful for converting Rockwell 'C' readings taken on ball surfaces to equivalent value applicable to flat surfaces. Hardness readings of balls are affected by the curvature and hardness level of the ball. Because of these factors, corrections are necessarily added to the as-read hardness. For ball sizes and hardness values other than shown, values shall be interpolated.

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