Effect of high temperature internal oxidation behavior on surface quality of high manganese steel

Abstract

Recently, as the demand for high strength steel increases, there is increasing interest in high manganese steel that can achieve high strength and high elongation. However, due to the high alloying properties of high manganese steel, Mn, Al, etc., which are oxidizing elements, are contained in large amounts and grains are coarse, so that internal oxidation behavior deepen. Due to this feature, high manganese steel is considered in the occurrence of surface defects during the hot rolling process. Such surface defects reduce product quality and yield, resulting in significant economic losses and need effective control to prevent them. In this study, first, internal oxidation behavior of high manganese steel is compared with that of medium carbon steel and high alloy steel. In order to observe the internal oxidation layer on cross-section of the specimen, block specimen was heat-treated at temperature 1000 °C to 1200 °C. And the cross-section was observed by SEM, EPMA, and EDS. Second, relationship between the internal oxidation behavior and the surface cracking behavior of high manganese steel was investigated. The observed internal oxidation behavior and surface cracking behavior obtained from tensile test for specimens after heat treatment were statistically compared. Based on the results, crack sensitivity index which can predict the surface cracking sensitivity by internal oxidation behavior was derived. Third, methods for reducing the internal oxidation behavior of high manganese steels was considered in terms of alloy design. Various elements were added to the basic high manganese steel, and heat treatment was conducted for 30 minutes at the temperature of 1000°C -1300 °C. The cross-section was observed by SEM, EPMA, TEM, EDS. As a result, influence of each element on internal oxidation behavior was confirmed, and alloy design direction which can reduce internal oxidation was derived.