Effect of Nitrogen Content on Cold Working Properties of High-strength Mn–Cr–N Steels Made Using Pressurized ESR

Abstract

High-strength Mn-Cr-N steels with high nitrogen content were manufactured using a lab-scale pressurized electro-slag remelting furnace to study the deformability of the steels. Melting experiments were performed under 1.0 MPa pressure N 2 gas in order to have various N contents. Gas porosity and severe macrosegregation were not observed in the remelted ingots. Microstructure observation revealed that nitrides and non-metallic inclusions were small enough not to affect the mechanical properties. After the ESR ingots were heat-treated and forged, the mechanical properties of the steels at a room temperature were measured. The grain sizes were measured in the range from 50 to 300 μm. The results of 0.2% proof stress showed that the steel became stronger with increasing N content according to solid solution hardening mechanism. In addition, with various strain rates, the tensile strain-hardening exponents were determined to be almost the constant values between 0.20 and 0.25. These results suggest that the methods of cold working for conventional 18Mn-18Cr-0.7N steel are applicable to the Mn-Cr-N steels containing over 1.0 mass% nitrogen.

Effects of Nitrogen Gas Pressure on the Solidification Parameters and As-cast Microstructure Revolution during Pressurized Electroslag Remelting AISI 304 Stainless Steel

“…6) A. Patel et al 1) investigated the effect of pressure and types of nitrides on nitrogen distribution in the stainless steel. F. Takahashi et al 7) studied the effect of nitrogen content on deformability of Mn-Cr-N steels manufactured using a lab-scale PESR. Pressure, as an important thermodynamic parameter, shows significant effects on chemical reaction involving gas phase reactant or product, such as increasing reaction rate and solubility of gas or volatile element.…”