ELECTRON-MICROSTRUCTURE OF THE WORK ROLL FOR COLD ROLLING (I)

Abstract

The work rolls for cold rolling mills are usually forged from high-carbon-chromium steel, spheroidized, machined and finally heat treated to secure favorable rolling properties.
The electron microscopic structure at the surface layer of heat-treated roll consists of spheroidized carbides, martensite matrix and some amount of retained austenite. If considerable amount of austenite are retained and spherical carbides are few, the working character of the roll is insufficient.
To obtain properly spheroidized structure after forging, several experiments by small specimens were pursued. The results show that the most effective annealing methods are likely to be the types in which phase transformation are applied.
The cooling rate after holding at 780°C is quite important. The slower cooling rate produces the better carbide distributions. By repeated heatings and coolings between 700°C and 780°C, the carbides grow larger and pearlite lamellae develops remarkably.