1989 Volume 7 Issue 4 Pages 490-495
It was cleared in the previous report that phosphorus is one of the main influence factors to enhance the crack susceptibility of quenching crack type cold cracking because of the grain boundary segregation. In this report, the variation of phosphorus segregation to grain boundaries during weld thermal cycle has been studied by calculation method for JIS SNCM 447 (0.47 wt.%C-Ni-Cr-Mo steel) containing 0.015 and 0.030 wt.%P.
Grain boundary concentration enriched by the grain boundary liquation is further increased with solidification of the liquated part. The concentration decreased rapidly due to homogenization with subsquent cooling, reaching a constant value at about 1273 K. The concentration is increased by equilibrium segregation, reaching a constant value at about 800 K. However, the tendency of the final concentrations under the various cooling conditions did not agree with the result of AES having a tendency to decrease with increasing in cooling time discussed in the previous paper.
In Fe-C-P ternary alloy, the phosphorus concentration was decreased to be caused by the rapid carbon segregation at the temperature range below Ms. Moreover, the degree of decrease was observed to be large in case of the lower cooling rate. This suggested that competition segregation of carbon at grain boundaries should be considered for decreasing of the phosphorus concentration with increasing cooling time
