Crack Initiating Temperature and Time of Reheat Cracking in Cr-Mo Steels

The Study of Reheat Cracking of Cr-Mo Steels, Report 5

Abstract

The crack initiating temperature and time of rehaet cracking were investigated on three types of commercial heat resistnig steels. Two modified implant test machines were employed, one of which was constant strain type (stress relaxation type) and the other was constant load type. The crack initiating curves for those steels were drawn on the stress-temperature (time) diagrams. The results were summerized as follows. (1) The crack initiating temperatures obtained by the constant strain test were 550, 510 and 540°C for 1/2Mo, 1Cr-1/2Mo and 2 1/4Cr-1Mo steels, respectively, when the stress was high enough (σ_PW>30kg/mm²). The crack initiating temperature elevated with the decrease of the stress. (2) The crack initiating temperatures obtained by constant load test agreed with those by constant strain test, only when the stress was high. The crack initiating curves of the former situated generally in higher stress-and longer duration side than that of the latter. This difference will come from the difference of the stress during the preparation stage prior to crack initiation. (3) The crack initiating temperature was not so much varied by the variation of Cr and Mo contents of a very wide range.