Effects of LB/M Duplex Phase Heat Treatment on Microstructure and Mechanical Properties of Cold Working Die Steel DC53

Abstract

The effects of Quenching-Tempering-Austempering （QTA） duplex phase heat treatment process （Q 1 030 ℃， 30 min； T 520 ℃， 2 h； A 250 ℃， 3 h） at different prequenching temperatures on the microstructure， mechanical properties and the friction and wear properties of cold working die steel DC53 were investigated and the results were compared with those of the conventional Quenching-Tempering （QT） heat treatment process （Q 1 030 ℃， 30 min； T 520 ℃， 2 h）. The results show that the microstructure obtained by QT process is mainly tempered martensite and the microstructure mainly composing Lower Bainite/Martensite （LB/M） duplex phase can be resulted from the QTA process. The strength reduction due to the LB and the retained austenite （AR） can be partly offset by the grain refinement strengthening from the refinement of original austenite grain by duplex phases， and the impact toughness of DC53 can be greatly improved by this complex microstructure. Compared with the mechanical properties of the QT process， the hardness of the QTA at prequenching temperature 100 ℃ is only 1.4 HRC lower but the impact absorption energy is 2.44 times higher. Therefore， superior combination of strength and toughness can be obtained by the QTA process.

Keywords

• cold working die steel； dc53； heat treatment； microstructure； mechanical property