Sub-temperature quenching, that is, incomplete quenching of
thick-walled spiral steel pipe, or quenching in critical zone, heating quenching in two-phase zone, means that the steel piece is heated between its critical point Ac1 ~ Ac3 (Accm) temperature and is in a state of rapid combustion. A heat treatment process for obtaining a martensite and ferrite dual phase structure is cooled. The researchers conducted a test analysis of thick-walled spiral steel pipes and concluded that:
1) Thick-walled spiral steel pipe increases with the quenching heating temperature in the critical zone, the percentage of martensite increases, the hardness of the steel increases, the plasticity increases, and the impact toughness changes greatly;
2) When the acicular ferrite is obtained after the secondary quenching, the impact toughness of the thick-walled spiral steel pipe is the best;
3) The former heat treatment process of sub-temperature quenching is preferably completely quenched to obtain a non-equilibrium structure, so as to ensure that the dispersed acicular ferrite is obtained after sub-temperature quenching, if normalized or annealed instead of complete When quenching, the ferrite is thick and can not achieve the effect of strengthening and toughening.
