农机用65Mn钢预热处理后激光强化组织及性能

    Microstructure and property of 65Mn steel preheated by laser strengthening

    • 摘要: 针对农机刀具易于磨损,且强化处理工艺较复杂、成本较高的现状,在正火和淬火-中温回火预热处理65Mn钢上,分别进行激光淬火和激光熔凝加工,研究了激光加工后的组织结构及显微硬度的变化规律,并探讨了其影响因素。研究结果表明:激光强化组织由表层熔凝区(激光熔凝)、完全淬火区、不完全淬火区、热影响区组成;正火预热处理后激光强化组织的显微硬度要高于淬火-中温回火预热处理后激光强化组织的显微硬度,激光熔凝处理后硬化区的显微硬度稍低于激光淬火硬化区的显微硬度。该研究为激光强化农机刀具的组织改善和性能提高提供了依据。

       

      Abstract: Abstract: At present, there exists a problem that the agricultural tools easily get worn. However, the common strengthening techniques have visible disadvantages, such as the complex process and comparatively high running cost. In order to solve the problem, the 65Mn steel was preheat-treated by the normalization or quenching + medium-temperature tempering. Subsequently, the preheat-treated 65Mn steel was strengthened by laser quenching or laser melting-hardening process with a YLR-6000 fiber laser. The microstructure was studied by optical microscope and scanning electronic microscope. The microhardness was measured using a Vickers-1000 microhardness tester with load of 1.96N and a dwelling time of 15s. Further, the controlling factors were investigated. The results showed that the preheat-treating and laser process had visible influences on the microstructure and property. In laser quenching, the microstructure was comprised of the entire quenching zone, part quenching zone and heat affected zone. The fine needle martensite was obtained in entire quenching zone by quenching + medium-temperature tempering + laser quenching. In the part quenching zone, the microstructures were fine needle martensite and troolstite. However, the fine needle martensite and a few ferrite were observed in entire quenching zone by normalization + laser quenching. In the laser melting-hardening process, the microstructure was made up of the surface melting zone, entire quenching zone, part quenching zone and heat affected zone. Compared with the microstructure of laser quenching, the surface melting zone was obtained in laser melting process, and the others were accorded with those in laser quenching. As for laser melting process, the depth of surface melting zone was within the range of 10-15 μm. In surface melting zone, the fine dendrite microstructure was got and the primary dendrite arm spacing was within the range of 4~6 μm. In addition, The microhardness of laser strengthening 65 Mn steel pretreated by normalization was relatively higher than that pretreated by quenching + medium-temperature tempering. It depended on the microstructure and its size. Moreover, the microhardness of laser melting-hardening was relatively lower than that of laser quenching. The microhardness of laser process could reach up to HV0.2830, about 1.5 times as much as that of common quenching + medium-temperature tempering. According to the working condition of agricultural tools, the surfaces needed to be hard and the interior parts needed to be with good toughness. The laser strengthening technique satisfied the request of steel property and simplified the running process. Therefore, in terms of agricultural tool strengthening approaches, the laser strengthening technique exhibits visible advantages and brings application prospects.

       

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