2007 Volume 47 Issue 9 Pages 1363-1367
Contradicted results have been reported on sensitivities of Cr–Mo low alloy steels to fracture toughness, so it seems further investigations is required in order to establish the reasons for this contradictions. This study tried to rationalize the causes of contradiction and establishes the reasons for variations in the observed changes in fracture toughness of two types of low alloy steels namely 3Cr–1Mo and 2.25Cr–1Mo steels.
For investigating the embrittlement sensitivity in this research, a factor called J used since there are some clams that Cr–Mo low alloy steels with higher J-Factor are more sensitive to temper embrittlement.
For inducing temper embrittlement on these alloys, a step-cooling operation from high temperature to room temperature for a period of 234 h was employed. Then some of the mechanical properties of the embrittled sample and unembrittled alloys were determined and compared. The results showed that step cooling operation had no noticeable effect on tensile and hardness properties of the steels but strongly affected their resistance to impact. In the alloy having a low J-Factor of equivalent to 107, changes in both FATT and TT54J were about 11°C, this was relatively low, while in the alloy having a high J-Factor equivalent to 224, these changes were 70°C and 78°C respectively which indicated this alloy was highly sensitive to temper embrittlement. Changes in temper embrittlement of the two alloys used in this research were found and we tried to justify these changes in this article.
