Spheroidisation annealing steel to improve cold formability - preceded by quenching from rolling temp. to reduce annealing time

摘要

A steel prod. is treated, prior to spheroidisation annealing at about 700 deg.C, by quenching from the rolling temp. and interrupting the quench so that the whole section of the product transforms at 575-625 deg.C. Steels of low hardenability are pref. slowly cooled for partial transformation of the austenite into proeutectoid ferrite (at about 50 deg.C below the A1 temp.) or subjected to a staggered quenching permitting partial pseudoisothermal transformation of austenite into proeutectoid ferrite at about 50 deg.C below the A1 temp. prior to the interrupted quench. The quench produces a structure of proeutectoid ferrite plus very fine degenerate pearlite and possibly some bairite which is an ideal structure for rapid spheroidisation annealing and prodn. of a good combination of strength and ductility (for cold forming) in the annealed prod.