Deformation-Induced Martensitic Transformation in Laser Cladded 304 Stainless Steel Coatings

Abstract

There are only a few cost-effective solutions for coating applications in combined mechanical loading and corrosive environments. Stainless steel AISI 304 has the potential to fill this niche, showing excellent corrosion resistance while utilizing the deformation-induced phase transformation from γ-austenite to α’-martensite, which results in an increase in strength. However, it is not known whether this can occur in laser cladded material. Therefore, laser cladded AISI 304 coatings in as-cladded condition and after heat treatment at 1100 °C for 60 min were investigated before and after bending deformation, by means of light microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was shown that due to the dendritic microstructure accompanied by an inhomogeneous distribution of the main alloying elements (Cr and Ni), no deformation-induced phase transformation occurred in the as-cladded coating. The applied approach with subsequent solution heat treatment at 1100 °C for 60 min resulted in a homogeneous γ-austenite microstructure, so that a deformation-induced martensitic transformation (DIMT) could occur in the coatings. However, the volume fraction of martensite that had been formed locally at individual shear bands was rather low, which can be possibly attributed to the high Ni content of the feedstock, stabilizing the γ-austenite microstructure. This study shows the possibility of exploiting the DIMT mechanism in heat-treated laser-cladded AISI 304 coatings.

Investigation on Creep Deformation and Age Strengthening Behavior of 304 Stainless Steel under High Stress Levels

“…The creep strain and the initial creep strain rate increase with the increase in stress level. (2) The stress exponent shows that the main mechanism of creep deformation is dislocation slip within the stress range studied, and creep aging is accompanied by defect generation and phase transformation, thus strengthening the material. Moreover, the increase in the austenite content and deformation twins' formation during creep aging collectively improve the plasticity of the material.…”

“…This is because creep aging can provide a phase change driving force for the transformation of martensite, and during the loading process, the material undergoes plastic deformation, and the deformation increases crystal defects such as dislocations, stacking faults and twins. These defects provide favorable nucleation sites for the transformation of the martensite phase and also promote the nucleation and growth of the martensite phase from the austenite phase, and thus the austenite phase content is reduced slightly with the stress level [2,10,51]. In summary, the austenite content and martensite content of the material increase after creep aging, which can also provide a basis for the simultaneous increase in plasticity and strength of the material after creep aging.…”

“…With the continuous development of new technologies, the composition of steel has gradually evolved from the initial two elements of C and Fe to a composite iron-based alloy with Fe as the main element and a large number of other alloying micro-elements added [1]. 304 stainless steel (304 SS) is widely used in aerospace, transport medical and other civil and military fields due to its good low-temperature performance, forming properties, welding performance and low cost [2][3][4][5]. For example, SpaceX's rocket fuel tanks are made of 304 SS, which significantly improves productivity and reduces costs.…”

Prediction Method for High-Speed Laser Cladding Coating Quality Based on Random Forest and AdaBoost Regression Analysis

“…The coating prepared via laser cladding technology can not only ensure the bonding strength but also meet the requirements of protective properties [ 1 , 2 ]. Thus, in recent years, as a representative of green manufacturing, laser cladding has been increasingly used in the preparation of protective coatings.…”