Effect of P on Properties of 18Cr-12Ni-2Mo type Heat-Resisting Steel (Part I)

Effect of P on properties of heat-resisting (steel-I)

Abstract

Studies were made on the effect of phosphorus on properties of several heat-resisting steels containing 18% chromium, 12% nickel, 2% molybdenum, 0.8% columbium, 0.7% vanadium and 0.2% nitrogen.
The results obtained were as follows:
(1) The phosphorus addition increased the maximum hardness obtained by aging after solution treatment, and decreased the aging time necessary to attain to maximum hardness and accelerated overaging at a temperature higher than 750°C
As a results of metallographic, electric resistivity and magnetic permeability studies, itwas considered that the phosphorus increased the strain energy of the austenite lattice which accelerated the precipitation of chromium carbide particles within austenite grains. and hence produced hardening.
(2) The phosphorus greatly improved the rupture strength, but the rupture elongationand the impact value decreased with increasing phosphorus content.
Small addition of boron improved the rupture life and ductility of the 18Cr-12Ni-2.5Mo steel containing 0.148% P. The stress-rupture values of this B-added steel at 650°C were equivalent to hot-cold-worked 19-9DL and Timken 16-25-6 alloys and those at 700°C were higher than hot-cold-worked 19-9DL alloy.