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.

Constitutive Equation and Hot Processing Map of a Nitrogen-Bearing Martensitic Stainless Steel

“…where N is the number of the data used in the calculation; σ i e is the true stress obtained from the experiment; σ i p is the true stress predicted by the improved constitutive equation; σ e and σ p are the mean values of σ i e and σ i p , respectively. As shown in Figure 8b, the values of R and AARE calculated by Equations (15) and (16) are 0.994 and 4.76%, respectively, which demonstrated a good agreement between the experimental and predicted values. Additionally, the developed constitutive equation was used to predict the true stress for the experimental conditions which had not been used to determine the material constants.…”

“…These parameters are expressed by the following equations: The sixth order polynomials were employed to fit the relationships of these material constants and true strain and the fitting results are shown in Equations (10)-(13), the parameters in these equations are listed in Table 1. According to Equations (3) and (4), the true stress can be expressed by a function of the Zener−Hollomon parameter at a given true strain (ε), this function is shown in Equation (14). Then the material constants at a certain true strain determined by Equations (10)-(13) can be substituted into Equation (14) and the true stress under a given true strain can be determined.…”

“…In the past few years, research into this nitrogen-bearing martensitic stainless steel were mainly focused on its cold rolling and heat treatment processes [14,15]. However, little work has been done on the investigation of the hot working process of this steel.…”

Real-Time Quality Monitoring of Laser Cladding Process on Rail Steel by an Infrared Camera

“…In this work, the faster laser scanning speed led to lower cladding temperatures and a faster cooling rate. The lower cladding temperature resulted in a lower austenization temperature, which could reduce the prior austenite grain size [23]. The martensitic transformation start (Ms) temperature is decreased with decreasing the austenite's grain size [24].…”