Heat treatment for microstructure and mechanical properties improvement of powder plasma arc melted 17Cr-2Ni steel containing boron

Abstract

Plasma arc melted 17Cr-2Ni steel containing boron was studied under conditions of as-deposited and heat-treated state in this paper. The deposits showed high hardness and strength. However, it contained carbides network and martensite lath which are known as a deleterious phase to both mechanical and corrosion properties of steels. Various double austenitizing treatments were performed to improve the mechanical properties of deposits. At first, to reduce the degradation caused by carbides network, the deposits were subjected to different austenitizing temperatures of 1000, 1050 and 1140 °C during the homogenizing treatment. Homogenizing at 1140 °C was selected due to significant dissolution of carbides network and intragranular large size carbides (>2 μm). Second, to reduce the influence of martensite lath on the mechanical properties, the samples were subjected to isothermal quenching (IQ) and tempering at 420 °C for 60 min following the double austenitizing treatment, which were referred to as IQ1140 and T1140, respectively. Different from the microstructure of tempered martensite lath structure of the T1140, the microstructure of pearlite with carbide particles size less than 500 nm was found in IQ1140, which was verified to improve the tensile strength and ductility of steels from 1486 MPa and 0.5% to 1708 MPa and 3.8%, respectively. In addition, MX-type nanoprecipitate were found in the ferrite matrix of heat-treated steels. The deposits heat-treated by IQ1140 process was proved to have comprehensive high hardness, high strength and a certain ductility, with an improvement of 11%, 15% and 660% to the ones of deposits, respectively. • Heat treatment of plasma arc melted 17Cr-2Ni steel containing boron was evaluated. • Carbides were dissolved mainly in the homogenization treatment stage. • MX-type nanoprecipitate existed in intragranular ferrite matrix after heat treatment. • Two sizes of intragranular carbides existed in the isothermal quenched samples. • Modification of martensite is main manner to improve its mechanical properties.