On the Manufacture of High-Chromium Steels in High-Pressure Nitrogen Atmosphere and the Heat-Resisting Properties of Type 316 L Steels

Abstract

An experimental study was made on the fundamental phenomena occuring in melting and casting of various high-chromium steels in high-pressure nitrogen atmosphere and on the influence of nitrogen content on heat-resisting properties of type 316L steels. It was confirmed that the solubility of nitrogen in the type 316L steel melted at about 1550°C in nitrogen atmosphere up to 10 atm obeys the Sieverts' law, and was represented by the following equation:
%N=0.183 (P_N2) ^1/2
The high-pressure melting was also c1arried out for such steels as 10-25%Cr-20%Ni-Fe alloys, 17-4PH type stainless steels containing 0.5% or 3% of Si, 18%Cr-4%Ni stainless steels, 18%Cr-8%Mn stainless steels, 22%Cr stainless steels containing O or 2% of Ni and LCN-155 alloys, and the effects on ingot soundness of nitrogen contents, melting conditions, casting conditions and of the sort of the phase formed in process of solidification, were discussed in detail. Further, it was confirmed that the nitrogen contained in these ingots did not diffuse out from the steel unless it was heated to high temperatures in high vacuum.
It was observed also that the nitrogen raised the strength of type 316L steels at both room and high-temperatures, the ductility at high temperatures dropped considerably and high temperature creep-rupture strength of the steels showed the maximum at a nitrogen content of about 0.33%.