Effect of various quenching treatments on microstructure and mechanical behavior of a laser additively manufactured 12CrNi2 alloy steel

摘要

A ferrite-austenite 12CrNi2 alloy steel additively manufactured by laser melting deposition (LMD) has been treated by various quenching methods, including direct quenching (DQ), inter-critical quenching (IQ) and step quenching (SQ), respectively, to form the martensite-ferrite dual-phase steel with a similar major volume fraction (62 vol.%) but different grain sizes and lath substructures of martensite. The results demonstrate that SQ, DQ and IQ help to refine the grains of martensite in order, correspondingly decreasing the yield strength, ultimate tensile strength but increasing in the uniform logarithmic strain of the alloy steel. The effect of not only the interface structures and substructures of martensite but also the quenching-route-dependent structures of ferrite on mechanical properties was interpreted in detail. Curiously, the directly quenched steel displays a higher post-uniform logarithmic strain as compared to the inter-critically quenched steel. The abnormal result occurs due to that DQ cannot completely homogenize the microstructural difference between the laser-scanned layers and the interlayer heat-affected zones of the as-deposited alloy steel.