Abstract
For evaluation of crack susceptibility of medium, high carbon low alloy steels to quenching crack type cold cracking in HAZ during welding, the effects of hardness and chemical compositions on fracture stress during cooling have been studied by the simulated cold cracking test using commercial and laboratorial nineteen kinds of steels.
The fracture stress showed a good correlation with the fraction of intergranular fracture surface. Therefore, it was understood that the fracture stress is useful to evaluate crack susceptibility of quenching crack type cold cracking. The fracture stress had a tendency to decrease with an increase in hardness. With respect to intergranular fracture, it is considered that the steels showing the hardness higher than about Hv600 are susceptible to quenching crack type cold cracking. Moreover, phosphorus is very harmful because it lowers the fracture stress due to increasing intergranular fracture surface considerably. Furthermore, the regression analyses on the fracture stress in relation to hardness and such impurity contents as P, N, Sn and O showed; (i) the fracture stress mainly depends on hardness and P content, (ii) N is harmful, too, but the effect is much less than P, (iii) Sn and O has little effect.
