1981 Volume 67 Issue 9 Pages 1533-1541
Spheroidization behavior of manganese sulfide inclusions and associate decrease in hydrogen induced cracking were investigated in a hot rolled commercial API-X60 grade steel coil during various heat treatment.
MnS inclusions which were elongated like ribbons in the hot rolled state began to spheroidize at such a low heating temperature as 600°C, and the extent of spheroidization was remarkable above 900°C. At an early stage of spheroidization, thin edges of elongated MnS became blunt to have a dog-bone shape, and subsequently the part was broken into very small particles. At high temperatures at or above 900°C, even the central part was broken into several spheres in the later heating stages.
The hydrogen induced cracking was not much reduced by heating below 900°C, but it was decreased remarkably as the temperature exceeded 1000°C. The cracking initiated preferentially at large inclusions, and the width rather than the length of the inclusions was correlated more closely with the cracking susceptibility ; occurrence of cracking increased with the increase in the width.