Some Mechanical Characteristics of Nitrogen Structural Steels

Abstract

In this paper, test conditions and microstructural factors have been investigated for newly developed nitrogen steels at load rates and test temperatures suitable for future operating conditions. Static tests have been carried out at i -s -I and dynamic tests at C -lo2 s -I . Different test temperatures enable fracture mechanisms and fracture toughness variations to be studied. Anisotropy of some characteristics in the initial (non-heat-treated) state, together with heat treatment effects and structural changes under two load rates have been analysed. Fracture appearance transition temperature (FAl'T) values have been obtained from absorbed energy and fracture surface crystallinity values. Using yield strength and fracture toughness data, an estimate has been made of critical crack lengths for unstable fracture. NOMENCLATUREa/a, = effective and critical crack lengths B = specimen thickness C = strain rate J/JIQ = the J-integral/provisional K / K = applied stress intensity factor/loading rate KIQ, = Kra from J test KQ/K,, /KIP = fracture toughness: provisional/static/dynamic P / P Q / P y = load/provisional/bending yield uy/uyd/uF = static/dynamic yield stress/at 20°C R = regression correlation coefficient uu = ultimate tensile stress t,/ti = temperature in Charpy test for fully plastic/fdly crystalline fracture surface t,, = temperature at 35 J in CVN test W = specimen width CVN = Charpy inpact energy FA = fracture appearance FATT = fracture apearance transition temperature