Accuracy of Standard Blocks for Hardness and Uncertainty of Hardness

− The authors numerically discuss the accuracy of the hardness values of standard hardness blocks by evaluating the uniformity of hardness blocks and the resolution of hardness values according to test method. As a result of reviewing the results of this evaluation and the reasonability of the currently proposed method for evaluating the uncertainty of hardness values, it is revealed that the variance of hardness values of popular standard blocks for hardness—Rockwell and Vickers—is extremely small (σ≦0.05 HRC, including the variance attributable to the tester). It is also found that the depth-measuring Rockwell test method shows higher resolution of hardness values than the Vickers test method using microscopic measurements. Regarding the uncertainty of hardness, it is technically impossible to have discussions on the accuracy of uncertainty. Prior to discussing the uncertainty of hardness testing, we believe more efforts should be directed to studying ways to improve the accuracy and reliability of the testing method itself.