Combined Influence of Phosphorus, Chromium and Molybdenum on Reheat Cracking of Steels (Study of Reheat Cracking of Cr-Mo Steels, Report 5)

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The combined influence of phosphorus, chromiun and molybdenum on the reheat cracking was investigated using synthetic Cr-Mo steals prepared in the laboratory. The cracking sensitivity was evaluated by the critical restraint stress obtained by the modified implant method. The results are as followed: (1) In the case of constant phosphorus content of 0.01w%, the combined influence of chromium and molybdenum was shown by means of the contour lines of the critical restraint stress m the Cr-Ala contents diagram (Fig. 3). (2) In the case office sets of Cr-Mo contents, the influence of phosphorus in a content range of 0.004 to 0.1wt% was examined. There exists a critical phosphorus content P_<crit>, above which the cracking sensitivity increases abruptly with an increase of phosphorus content (Fig. 4). P_<crit> values are; about 0.05, 0.01, 0.008, 0.014 and about 0.005wt% for 0%Cr-0.5%Mo, 0.5%Cr-0.5%Mo, 1%Cr-0.5%Mo, 1.3%Cr-0.5%Mo and 2%Cr-1%Mo steels, respectively. (3) Phosphorus is initially segregated to a certain extent at austenite grain boundary by the welding thermal cycle. The phosphorus segregation is most intensive for 1%Cr-0.5%Mo steel which is most sensitive to the reheat cracking. (4) The phosphorus segregation in as-welded condition is intensified by reheating at 773 K (500℃) which corresponds to the temperature for initiating the reheat cracking.
社団法人溶接学会の論文
1985-10-01