Effects of Overlapping Distances on Steel Microstructure and Properties After Multi-track Laser Quenching
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JMEPEG DOI: 10.1007/s11665-017-2881-6
Effects of Overlapping Distances on Steel Microstructure and Properties After Multi-track Laser Quenching Yong Zhao, Chen Chen, Keng Yan, Jiasheng Zou, and Chuan Liu (Submitted February 21, 2017; in revised form July 26, 2017) In this study, multi-track laser quenching with different overlapping distances was used to assess SM45C microstructure and properties. Two overlapping distance types were evaluated, including overlapping distances in the transition and martensite regions, respectively. After multi-track quenching, hardness showed a threefold increase. With the overlapping distance in the transition region, surface hardness varied from 600 to 700 HV. There was a region of low hardness in each track. Hardness in the low hardness region was from 300 to 400 HV. The average hardness was basically over 500 HV with the overlapping distance in the martensite region, although there was a softening region. The increased hardness was mainly caused by the martensite. Microstructure in the overlapping region was self-tempered martensite, retained austenite and ferrite. Tempered sorbite and lowly tempered martensite were observed in heat-affected zones. Friction coefficients of quenched specimens varied between 0.275 and 0.325, with a 14% reduction relative to the base metal. The wear rate of the quenched specimen was only 40.8% of the base metal. With time, mass reduction in the quenched specimen was much smaller than that of the base metal. For specimens treated with laser quenching, slight fatigue wear was dominating. Keywords
laser surface quenching, overlapping distance, temper softening, wear resistance
1. Introduction Laser surface quenching is an important surface treatment technology with unique abilities to increase hardness locally, which helps resist wear and fatigue, leaving the remaining part intact (Ref 1-5). Many scholars have carried out related systematic studies, and its advantages have been acknowledged in recent years. After laser quenching, better performance in wear, corrosion and fatigue properties is achieved. The most obvious feature is increased hardness (Ref 6-10). However, if a track is operated in multi-track laser quenching, the martensite formed in the previous track is dissolved because of tempering. As a result, a lower hardness zone between the two overlapped tracks can be obtained (Ref 11-14). When components need larger areas of hardening, the softening zone adversely affects the surface performance (Ref 15-17). Currently, no systematic studies assessing the effects of overlapping distances in multi-track laser quenching have been reported. Whether different overlapping distances would prevent softening or reduce the softening zone remains largely unclear. In this study, multi-track laser quenching was performed with different overlapping distances after determining optimum parameters. The quenched region was divided into two parts, including the martensite and transition regions, and different overlapping distances were applied. First, the maxim
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