Enhancement of Strength–Ductility Balance of the Laser Melting Deposited 12CrNi2 Alloy Steel Via Multi-step Quenching Treatment

Abstract

A ferrite-austenite 12CrNi2 alloy steel additively manufactured by laser melting deposition (LMD) was heat treated by direct quenching (DQ) and tempering inter-critical quenching (TIQ) at 800 °C for enhancing its strength-ductility balance. Both heat-treated alloy steels have the martensite-ferrite dual-phase (DP) microstructures. The volume fractions of martensite in the two treated alloy steels are nearly similar (~ 85 vol%), while the sizes of the prior austenitic grain for martensite are different. The martensite-dominated DP microstructure resulted in an obvious improvement in strength-ductility balance of the alloy steel. Compared with the DQ treatment, the multi-step TIQ treatment caused the strength-ductility balance of the alloy steel to be enhanced due to its higher total elongation. The better ductility of the TIQ-treated alloy steel can be attributed to the optimization of the microstructure. The preferred orientation of ferritic grain in the as-deposited alloy steel which was adverse to plastic deformation through dislocation slip was eliminated via the multi-step TIQ treatment. Moreover, the TIQ treatment promoted the formation of finer-grained martensite with larger areas of grain boundaries and twinning boundaries which resulted in the enhancement of the coordinated deformability of the martensite with the ferrite.

Characterisation of heat-treated gradient alloy steel fabricated by laser melting deposition

“…During heating and isothermal holding at 800°C, austenite is formed by the decomposition of martensite. The austenitic grains easily grow in the process and transform into the polygonal-like lath martensite (Figure 5(d)) after the IQ treatment [30]. As for the G3 and G5, there is no obvious change in the microstructure after heat treatment compared to G1, and it is characterised by finer microstructures and more spherical particles after Q-IQ and Q-IQ-T heat treatment.…”

“…This study revealed that the elongation and the tensile strength of 12CrNi2 were simultaneously increased after the sample was subjected to tempering process. Zhang et al [30] have adopted direct quenching and tempering intercritical quenching at 800°C to LMD 12CrNi2 alloy steel, and revealed that the alloy steel treated by multi-step possessed higher elongation and better ductility. However, the studies on the camshaft materials prepared by LMD after Q-IQ and Q-IQ-T heat treatment are scarcely reported, especially for analysing the relation of microstructure evolution and the performances such as wear and corrosion on a surface with quasi-continuous ratios gradient material.…”

Study on SLM Forming Process, Residual Stress and Thermal Fatigue of 24CrNiMo Alloy Steel

“…Other scholars have studied the effects of process parameters and cooling rate on residual stress [ 17 ], indicating that cooling rate and temperature gradient are related to the trend of residual stress. Some researchers have verified that the ferrite-austenitic 12CrNi2 alloy steel manufactured by laser melting deposition (LMD) can enhance its strength–ductility balance after heat treatment [ 18 ]. A study has been well verified that SR could effectively enhance the mechanical properties of the alloy [ 19 ].…”