Study on the Preparation and Properties of Laser Boron - Nitrogen Alloying Layer on 45 Steel

Abstract

In order to improve the wear resistance of the surface while maintaining the toughness of the commonly used parts in engineering, a binary-boron nitrogen alloying layer was prepared on the surface of 45 steel by laser alloying technology. The process parameters were optimized, and the microstructure and properties of the alloying layer were studied. Results showed that with the increase of laser power, scanning speed and lap ratio, the hardness of the alloying layer firstly increased and then decreased, and the maximum hardness was 954 HV2 N, 885 HV2 N and 882 HV2 N at 1.5 kW, 500 mm/min and 50%, respectively. As the content of B in B: N (mass ratio) increased, the hardness of the alloying layer increased gradually; the optimal process parameters were 1.5 kW of laser power, 500 mm/min of scanning speed, 50% of lap rate. The microstructure of the alloying zone in the coatings treated by the optimal process was composed of Fe2N, Fe2B, FeB, Fe7C3, γ-(Fe, N) and other compounds and solid solution, which were mainly columnar and cellular crystals with a thickness of about 600 μm. Furthermore, the average hardness was 1 023 HV2 N, and the heat affected zone was composed of a small amount of acicular martensite and retained austenite with a thickness of about 250 μm. The hardness distribution was gradient from 967 HV2 N to 265 HV2 N. In addition, the friction coefficient of the alloying layer was about 0.451 9, and the wear rate was 0.423 1×10-14 m3/(N·m), which was about 1/9 of that of the substrate. Besides, the wear mechanism was abrasive wear accompanied by adhesive wear.

Keywords

• laser alloying|boronitriding|45 steel|microhardness|abrasive resistance