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Rockwell Round Correction Charts

- Reference Information and Standards -

"Round correction" is another overlooked factor in hardness testing. Inexperienced untrained operators are using a sophisticated piece of equipment that is calibrated and they expect it to give good results no matter what the condistions. But users actually need to know what they are doing. Round correction is just like testing close to the edge of a sample -- the material flows more easily to the edge and, in effect, creates a lower hardness value. There is no correction factor for testing close to an edge but there is for rounds; Use the values below to add to your test results depending on the diameter and result. And just like with testing close to an edge, check your vee anvil alignment with the indenter. If it is off by a fraction it could affect your results by a large amount or break a diamond indenter.

ROCKWELL C, A, D SCALES
Diameter .25" .375" 0.5" .625" .75" .875" 1" 1.25" 1.5"
Result 6.4 mm 10 mm 13 mm 16 mm 19 mm 22 mm 25 mm 32 mm 38 mm
20 6.0 4.5 3.5 2.5 2.0 1.5 1.5 1.0 1.0
25 5.5 4.0 3.0 2.5 2.0 1.5 1.0 1.0 1.0
30 5.0 3.5 2.5 2.0 1.5 1.5 1.0 1.0 0.5
35 4.0 3.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5
40 3.5 2.5 2.0 1.5 1.0 1.0 1.0 0.5 0.5
45 3.0 2.0 1.5 1.0 1.0 1.0 0.5 0.5 0.5
50 2.5 2.0 1.5 1.0 1.0 0.5 0.5 0.5 0.5
55 2.0 1.5 1.0 1.0 0.5 0.5 0.5 0.5 --
60 1.5 1.0 1.0 0.5 0.5 0.5 0.5 -- --
65 1.5 1.0 1.0 0.5 0.5 0.5 0.5 -- --
70 1.0 1.0 0.5 0.5 0.5 0.5 0.5 -- --
75 1.0 0.5 0.5 0.5 0.5 0.5 -- -- --
80 0.5 0.5 0.5 0.5 0.5 -- -- -- --
85 0.5 0.5 0.5 -- -- -- -- -- --
90 0.5 -- -- -- -- -- -- -- --

ROCKWELL B, F, G SCALES
Diameter .25" .375" 0.5" .625" .75" .875" 1"
Result 6.4 mm 10 mm 13 mm 16 mm 19 mm 22 mm 25 mm
0 12.5 8.5 6.5 5.5 4.5 3.5 3.0
10 12.0 8.0 6.0 5.0 4.0 3.5 3.0
20 11.0 7.5 5.5 4.5 4.0 3.5 3.0
30 10.0 6.5 5.0 4.5 3.5 3.0 2.5
40 9.0 6.0 4.5 4.0 3.0 2.5 2.5
50 8.0 5.5 4.0 3.5 3.0 2.5 2.0
60 7.0 5.0 3.5 3.0 2.5 2.0 2.0
70 6.0 4.0 3.0 2.5 2.0 2.0 1.5
80 5.0 3.5 2.5 2.0 1.5 1.5 1.5
90 4.0 3.0 2.0 1.5 1.5 1.5 1.0
100 3.5 2.5 1.5 1.5 1.0 1.0 0.5

ROCKWELL 15N, 30N, 45N SCALES
Diameter .125" .25" .375" .5" .75" 1"
Value 3.2 mm 6.4 mm 10 mm 13 mm 19 mm 25 mm
20 6.0 3.0 2.0 1.5 1.5 1.5
25 5.5 3.0 2.0 1.5 1.5 1.0
30 5.5 3.0 2.0 1.5 1.0 1.0
35 5.0 2.5 2.0 1.5 1.0 1.0
40 4.5 2.5 1.5 1.5 1.0 1.0
45 4.0 2.0 1.5 1.0 1.0 1.0
50 3.5 2.0 1.5 1.0 1.0 0.5
55 3.5 2.0 1.5 1.0 0.5 0.5
60 3.0 1.5 1.0 1.0 0.5 0.5
65 2.5 1.5 1.0 0.5 0.5 0.5
70 2.0 1.0 1.0 0.5 0.5 0.5
75 1.5 1.0 0.5 0.5 0.5 0
80 1.0 0.5 0.5 0.5 0 0
85 0.5 0.5 0.5 0.5 0 0
90 0 0 0 0 0 0

ROCKWELL 15T, 30T, 45T SCALES
Diameter .125" .25" .375" .5" .625" .75" 1"
Value 3.2 mm 6.4 mm 10 mm 13 mm 16 mm 19 mm 25 mm
20 13.0 9.0 6.0 4.5 4.5 3.0 2.0
30 11.5 7.5 5.0 3.5 3.5 2.5 2.0
40 10.0 6.5 4.5 3.5 3.0 2.5 2.0
50 8.5 5.5 4.0 3.0 2.5 2.0 1.5
60 6.5 4.5 3.0 2.5 2.0 1.5 1.5
70 5.0 3.5 2.5 2.0 1.5 1.0 1.0
80 3.0 2.0 1.5 1.5 1.0 1 0.5
90 1.5 1 1 0.5 0.5 0.5 0.5


Rockwell Hardness Chart (plus a PDF)
(aka Hardness Scale Conversion Chart)

Round Correction Factor
Hardness Minimum Thickness

ASTM Hardness Test Methods
Rockwell Hardness Scales

Brinell Hardness Chart (plus a PDF)

Rockwell Hardness Testing
Brinell Hardness Testing
Microhardness Testing


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