Effect of Heat Treatment on Microstructure and Hardness of a High-Chromium Cast Iron Roll

The effect of tempering and of quenching + tempering including step tempering on the microstructure and properties of centrifugally cast rolls made of high-chromium cast iron HCCI is studied. It is shown that the cast iron microstructure is a matrix consisting of retained austenite and martensite and surrounded by a eutectic. Tempering of cast iron without quenching reduces the amount of retained austenite in the structure but has a little effect on the hardness. Quenching improves significantly the uniformity of the microstructure and increases the hardness, which grows still more after tempering. The quenching temperature affects significantly the martensitic transformation temperature Ms , which decreases with increase of quenching temperature; the step quenching has a stronger effect. The hardness of the roll after quenching from 1100 degrees C with a step at 560 degrees C and tempering at 500 degrees C is 64.4 HRC, which is much higher than the hardness of 58.3 HRC after tempering at 500 degrees C without quenching.