Effect of Working Prestrain on Fracture Toughness of S35C Steel and Evaluation of Brittle Fracture Strength of Table Rollers

Abstract

The effect of working prestrain on the hardness, microstructure, strength, and fracture toughness of JIS S35C normalized steel has been investigated. The brittle fracture strength of mill working table rollers has also been discussed. The main results are summarized as follows:
1) The hardness of steel S35C increases with increasing working temperature and reduction in thickness because of work hardening and strain aging, and becomes maximum at a working temperature of about 300°C. The hardness of the surface layer of the table roller, therefore, remarkably increases after a long service.
2) Increasing the hardness results in an increase in strength, decrease in ductility, and shift of Vcharpy impact transition temperature. Besides, it is found that it deteriorates fracture toughness. The fracture thoughness decreases with increasing reduction in thickness by working. The specimens worked at 300°C show the lowest value.
3) The critical crack size for brittle fracture of table rollers whose fracture thoughness in the surface is low is calculated using fracture mechanics. The method for preventing the brittle fracture of table rollers is established from these results.