Abstract
The influence of vanadium on the reheat cracking sensitivity was examined on various Cr-Mo steels and the experimental results were discussed from the view point of the combined influence of chromium, molybdenum and vanadium. Steel specimens were prepared in the laboratory ; the chemical composition ranges of them were 0 to 2.0%Cr, 0.28 to 0.8%Mo and 0 to 0.4%V. The cracking test was performed by using an implant test machine of the constant-strain type. The cracking sensitivity of each steel was compared by the term of critical restraint stress to produce reheat cracking. The contour lines of the critical restraint stress were drawn in the Cr-Mo contents diagram and the shift of these lines brought by the addition of vanadium was indicated. The influence of vanadium differs largely depending on each set of Cr-Mo contents. The groups of 0%Cr-Mo steels and Cr-0.28%Mo steels are originally insensitive to cracking. They become very sensitive by vanadium of a small quantity as 0.1%. On the contrary, the groups of Cr-0.5%Mo and Cr-0.8%Mo steels, which are originally sensitive to cracking, are affected a little by vanadium. The critical restraint stress is the function of two factors, the stress-relaxation characteristic and the fracture strength. The decrease of critical restraint stress (the increase of cracking sensitivity) is mainly brought by the decrease of stress relaxation. Vanadium affects little the original value of fracture strength of Cr-Mo steels.
