Abstract
In spring factory, large size springs are manufactured in hot forming process. In many cases, the hardness of hot formed springs is inspected by Brinell hardness test. The quality agreement between customer and manufacturer on hardness is often established by other hardness like Vickers and Rockwell hardness, though the spring hardness quality control in shop floor is done by Brinell hardness. Therefore, hardness conversion is often carried out. SAE-J417 has been used for the hardness conversion in the spring industry for this purpose. However, it is often said that the hardness conversion value is not adequate in the area where the hardness is higher than conventional area. This committee started on investigating the difference between SAE-J417 conversion data and various spring hardness test data on June 2007. The purpose of this committee is to offer the new conversion data between various hardness tests for the spring steel and to establish JSMA standard. As a result of three years activity, following findings were obtained.
(1) It has been understood that the correlation in Brinell hardness, Rockwell hardness and Vickers hardness is not necessarily correct in SAE-J417 data as the result of various hardness tests on SUP9 spring steel.
(2) The dispersion was ±1.5% in maximum when measuring the hardness by Brinell hardness tester, Rockwell hardness tester and Vickers hardness tester.
(3) The dispersion was about one percent as a result of investigating the influence of testing load in Vickers hardness measuring.
(4) The correlation between various hardness tests using several grades of spring steel did not show clear difference by steel grades. (So, the committee made a new conversion table for spring steel by treating all the data from different steel grades as data from one grade.)
