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

Abstract

A gradient alloy steel prepared by laser melting deposition (LMD) was subjected to two heat treatments (quenching-intercritical quenching denoted as Q-IQ and quenching-intercritical quenching-tempering denoted as Q-IQ-T). Results showed that martensite microstructure was changed to a duplex microstructure of martensite and ferrite after heat treatment, with a small number of Cr23C6 phases appearing. The samples before and after heat treatment exhibited random crystallographic orientation, while the grain was refined and the fraction of Cr23C6 increased after heat treatment. The samples after heat treatment possessed more slip systems and exhibited a decrease in hardness and wear resistance in comparison with LMDed sample. The corrosion resistance decreased in the order of Q-IQ > Q-IQ-T > LMDed samples in 3.5 wt-% NaCl solution.

Iso-material manufacturing of 304 stainless steel: Microstructure, corrosion-cavitation erosion synergistic behaviour

“…The mass loss of the untreated and LSMed samples in deionised water is 35 ± 1 and 14 ± 0.3 mg, whereas the mass loss in 3.5 wt% NaCl solution is 40 ± 0.6 and 20 ± 0.3 mg after 8-h CE, respectively. The mean depth of erosion ( MDE ) and the mean depth of erosion rate ( MDER ) can be used to evaluate CE resistance and calculated as follows: 3–57 where Δw is the mass loss (mg), ρ is the density of the materials (g/cm 3 ), s is the eroded area (1 cm 2 in this study), Δ T is the interval time (h), MDE in μm and MDER in μm/h. The CE resistance R e (h μm −1 ) is the reciprocal of MDER.…”

“…Apparently, the materials used in marine parts are supposed to obtain a combination of desirable properties such as high strength and ductility, high resistance to wear, corrosion and CE, while this combination is difficult to co-exist in a single bulk material, and even it does, manufacturing costs might be high. Fortunately, surface modification techniques [14][15][16][17] provide an effective way to solve the above problems through tailoring the surface properties while retaining the bulk properties. During the past decades, the development of surface modification against the wear, high-temperature oxidation and CE primarily relied on the protective coating with extensively expensive elements.…”