Research on Microstructure Evolution of Deposited Metal of Low Nickel High Nitrogen Austenitic Stainless Steel

Yiming Ma,Xiaochun Lv,Yicheng Yang,Yan Zhang,Yinan Xu,Hongliang An,Xingxing Wang,Naiwen Fang,Kai Xu,Kenji Kaneko

doi:10.1155/2021/7655423

Abstract

In this paper, in situ observation of the cooling process of the deposited metal of low nickel high nitrogen austenitic stainless steel obtained by laser-arc hybrid surfacing welding with shielding gas containing only Ar and only N2, respectively, is carried out using the ultra-high-temperature confocal laser scanning microscope (CLSM). An in-depth analysis of the microstructural changes is conducted with SEM, EDS, and EBSD. The results showed that the surface substructure is refined during crystallization with shielding gas Ar. However, grains are seriously coarsened in the δ phase area. Widmanstatten γ and intragranular γ are formed as a result of δ ⟶ γ phase transition through the shear-diffusion mechanism. In the cooling process with shielding gas N2, the temperature range of each phase area narrowed obviously. Blocky γ began to appear because of the δ ⟶ γ phase transition through the diffusion mechanism. Generally, Ar and N2 have a strong effect only on the very shallow range from the surface. The area with a larger local misorientation with shielding gas Ar is at lath γ on the surface. With shielding gas N2, the large local misorientation area is the last contact position of γ during the δ ⟶ γ phase transition on the surface and cross section.

Highlights

Cr-Ni stainless steel has been widely used in many critical fields in China because of its good plasticity, corrosion resistance, and weldability
Domestic and foreign scholars have researched the weldability of low nickel high nitrogen austenitic stainless steel
Fang [6] used Ar + N2 as shielding gas for welding and found that with the increase in N2 ratio, arc shrank, arc column width decreased, welding spattered, and arc stability became worse. rough the investigation of the influence of different welding methods on weld microstructure, it is found that c dendritic structure existed in weld microstructure of shielded metal arc welding (SMAW), reverted c appeared in the martensite in the fusion zone of gas tungsten arc welding (GTAW), and weld of electron beam welding (EBW) is made up of c matrix and discontinuous net-like δ [7]

Summary

Introduction

Cr-Ni stainless steel has been widely used in many critical fields in China because of its good plasticity, corrosion resistance, and weldability. In δ ⟶ c phase transition, c precipitated along the direction of δ/δ grain boundaries with its longitudinal growth rate significantly faster than the transverse growth rate It is an economical and effective way to compensate for the loss of N by adding the appropriate amount of N2 to the shielding gas Ar [14], the effect of shielding gas on the microstructural change of weld has not been studied intensely and meticulously up to now. Is paper uses CLSM and electron backscattered diffraction (EBSD) to analyze the microstructural changes of low nickel high nitrogen austenitic stainless steel weld using different shielding gases. It provides a more detailed comparison of the effects of different shielding gases on the weld microstructure in the welding process. E microstructural changes on the surface and section of the sample are analyzed by using optical microscope (OM, Olympus, GX51), scanning electron microscope (SEM, Zeiss, EVO 18), energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD)

Results and Discussion

Nb Fe

Sample A Sample N Deposited metal

Conclusions