Effect of austenitising heat treatment on microstructure and properties of a nitrogen bearing martensitic stainless steel

Abstract

The effect of austenitising heat treatment on the microstructure, hardness and metal release of the nitrogen bearing, martensitic stainless steel 420U6 was investigated. The heat treatment was carried out at temperatures between 950 to 1,150 °C with a holding time between 30 to 120min, followed by air cooling. The quenched microstructures observed by a scanning electron microscope indicated that by increasing the austenitising temperature and holding time, the number of carbides decreases while the grain size and the amount of retained austenite increases. For a given holding time, the hardness increases to a peak and then decreases continuously with the increase of temperature. The metal release test, according to the GB 4806.9-2016 standard, reveals that the metal release concentration is highly affected by the austenitising temperature. The parameters of the austenitising heat treatment, which can achieve the optimum combination of hardness and metal release, were obtained.