The Effect of Controlled Rolling and Cooling on the Microstructure Evolution of Boron Microalloyed Medium-Carbon Steel

Abstract

The processes of controlled rolling and cooling were simulated using hot compression tests on a Gleeble 1500 simulator with boron microalloyed medium-carbon steel. Effects of finish rolling temperature ranging from 760oC to 840oC and loop-laying temperature ranging from 660oC to 700oC on the microstructure evolution were studied. Experimental observations show that the average grain size of ferrite decreases while the volume fractions of ferrite and spheroidized pearlite increase when lowering rolling temperature. The maximum volume fraction of ferrite (62%) reached in our tests was obtained in the specimen whose rolling temperature and loop-laying temperature was 760oC and 700oC respectively. Excessive precipitation of the ferrite resulted in the carbon enrichment on some grain boundaries. Boron addition is effective to improve hot plastic deformation ability by removing nitrogen from AlN to form coarse BN particles on the grain boundaries.