Laser Surface Alloying of Austenitic 316L Steel with Boron and Some Metallic Elements: Microstructure.

Michał Kulka,Natalia Makuch,Andrzej Miklaszewski,Piotr Dziarski,Damian Przestacki,Daria Mikołajczak,Dominika Panfil-Pryka,Adam Piasecki

doi:10.3390/ma13214852

Abstract

Austenitic 316L steel is known for its good oxidation resistance and corrosion behavior. However, the poor wear protection is its substantial disadvantage. In this study, laser surface alloying with boron and some metallic elements was used in order to form the surface layers of improved wear behavior. The microstructure was studied using OM, SEM, XRD, and EDS techniques. The laser-alloyed layers consisted of the only re-melted zone (MZ). The hard ceramic phases (Fe2B, Cr2B, Ni2B, or Ni3B borides) occurred in a soft austenitic matrix. The relatively high overlapping (86%) resulted in a uniform thickness and homogeneous microstructure of the layers. All the laser-alloyed layers were free from defects, such as microcracks or gas pores, due to the use of relatively high dilution ratios (above 0.37). The heat-affected zone (HAZ) wasn’t visible in the microstructure because of the extended stability of austenite up to room temperature and no possibility to change this structure during fast cooling. The use of the mixtures of boron and selected metallic elements as the alloying materials caused the diminished laser beam power in order to obtain the layers of acceptable quality. The thickness of laser-alloyed layers (308–432 μm) was significantly higher than that produced using diffusion boriding techniques.

Highlights

AISI 316L austenitic stainless steel is well-known for its excellent resistance to oxidation and good corrosion behavior
The laser surface alloying with boron and selected metallic elements was investigated in order to improve the wear behavior of austenitic 316L steel without sacrificing its corrosion resistance
Selected parameters of laser processing obtaining the homogeneous microstructure in the re-melted zone and the uniform thickness of the resulted in obtaining the homogeneous microstructure in the re-melted zone and the uniform formed layers [75] because of the relatively high overlapping

Summary

Introduction

AISI 316L austenitic stainless steel is well-known for its excellent resistance to oxidation and good corrosion behavior. This steel is often used in the aggressively corrosive environment in nuclear reactor applications as well as at high-temperature conditions. The important disadvantage of this steel is a relatively low hardness (about 200 HV). The typical thermochemical treatment, usually improving the wear behavior of the constructional or tool steels, such as nitriding, carburizing, or boriding, could be used for the austenitic steel under certain conditions.

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