Novel Gradient Alloy Steel with Quasi‐Continuous Ratios Fabricated by Selective Laser Melting: Microstructure and Corrosion Behavior

Abstract

In this article, a quasi‐continuous ratio gradient alloy steel (GAS) with a 24CrNiMo high‐strength low‐alloy steel matrix for high‐speed railway brake discs is fabricated by selective laser melting (SLM). The composition of GAS is X% 24CrNiMo + (1–X)% wear‐resistant stainless steel (WSS), in which X is 100, 65, 35, and 0. The relationship between the microstructure and the corrosion resistance is intensively studied by electron backscatter diffraction (EBSD) and potentiodynamic electrochemical equipment. With the increase in the content of WSS, the low angle grain boundaries of the GAS increases, and the microstructure refines and the texture intensity decreases. The passivation film of the external WSS strengthening layer is dense; the corresponding corrosion potential and corrosion current density are −0.109 V and 2.08 × 10−8 A cm−2, respectively. The corrosion current density is about 1% of the substrate 24CrNiMo, and the corrosion resistance of the material is significantly improved.

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

“…As can be seen obviously, the reactions (2) and (3) are spontaneous owing to the negative Gibbs free energy in the range of temperature. In addition, the Δ G of reaction (3) is much lower than that of reactions (2) and (4), indicating that the Cr 23 C 6 phase is the thermodynamically favoured products and it is a higher possibility of preferential formation and precipitation [17]. The G5 exhibits similar phase constituents including bcc α-Fe and Cr 23 C 6 phase before and after heat treatments owing to the addition of high Cr content stainless steel to synthesise enough Cr 23 C 6 during LMD process.…”

“…For example, Wang et al [16,17] successfully prepared a quasi-continuous ratio gradient alloy steel from 100% 24CrNiMo substrate to 100% a stainless steel by selective laser melting (SLM) for high-speed railway brake discs. The results showed that corrosion current of gradient alloy steel is 1% of 24CrNiMo substrate and wear rate is 34.8% of 24CrNiMo substrate.…”

Microstructure Characteristics and Corrosion Behavior of Low‐Alloy High‐Strength Steel used for Armor Layer under Exposure to H2S‐Saturated Solution

“…The structural characteristics of the corrosion products, especially the surface morphology, therefore play a vital role in the corrosion behavior. [ 46–48 ] Figure 3 shows the macroscopic surface morphology of the corrosion products formed after different durations of immersion. Figure 3a,b show that two types of surface morphology appeared on the specimen surface after immersion for 24 and 72 h. The partial area of the specimen surface obtained after 24 h of immersion was covered with corrosion products.…”

Phase evolution, microstructure, microhardness and corrosion performance of CoCrFeNiNbx high entropy alloy coatings on 316 stainless steel fabricated by laser cladding

“…The corrosion mainly occurs in dendrites, indicating that the corrosion type is typical intergranular corrosion. According to the reference [45], the corrosion products in the alloy are mainly produced in the following ways in 3.5 wt-% NaCl solution: However, is unstable and further decomposed according to the following equation:

Figure 11 High-magnification corrosion morphology after dynamic potential polarisation test in 3.5 wt-% NaCl solution and element distribution of Nb0.3 HEAC.

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“…The corrosion mainly occurs in dendrites, indicating that the corrosion type is typical intergranular corrosion. According to the reference [45], the corrosion products in the alloy are mainly produced in the following ways in 3.5 wt-% NaCl solution:…”