The accurate measurement, calculation, and control of steel hardenability

Abstract

To control hardenability accurately it must be measured accurately. The Jominy test has been refined to do this. Extension of the test has also allowed accurate measurement down to 0.2 in. diam specimens. Illustrations of accuracy and reproducibility are given. Commercial steels show very wide hardenability bands and the influence of residual elements is profound. Correlation of accurately determined hardenability and composition has been examined using computer regression analyses. It is shown that the position of the Jominy curve can be calculated to within ±0.017 in. with 90 pct probability. The accuracy of the method is compared with previous systems. It is shown that other systems (e.g., Grossmann) are generally less accurate even over their best ranges of application. The use of hardenability control in induction hardening is discussed and the width of useful bands derived. Carbon content control is particularly important and it is shown how traditional methods result in inaccurate information. Hardenability control can produce economies to both steel producer and user. The use of control diagrams is discussed.