Research Of Laser Quenching Performance Of 40Mn

Laser quenching is a surface hardening technology which use laser as heat source. In laser quenching, a thin layer of the material is rapidly heated well into the austenitizing temperature range by laser beam and is cooled subsequently at a rapid speed, due to self-quenching by the conduction of heat into the base metal, to realize phase transformation and quenching strengthen. Laser quenching technology has many advantages, such as good strengthening effect, strong applicability, high controllable degree and so on. So this technology not only attracts much attention among the material surface strengthening techniques, but also has the trend of accelerate its popularization and applications in automobile manufacturing, mold, heavy machinery and many other manufacturing industry field.40Mn is premium carbon steel and is a common material for parts worked under fatigue load. In order to improve the wear resistance of 40 Mn steel body, this paper operate laser quenching experiment on 40 Mn steel using YLS-6000 fiber laser. This thesis mainly studied the effect of laser power, scanning speed and spot size on surface hardness, width and depth of the quenched layer; Based on the optimum process parameters acquired in single track laser quenching experiment, conducted the multiple tracks laser quenching experiment and obtained qualified quenched layer with good forming surface. By using metallographic microscope(OM), scanning electron microscopy(SEM) and X-ray diffraction(XRD), analyzed the organization structure and phase composition of quenched layer, meanwhile the hardness distribution and wear resistance under the optimum parameters were investigated with hardness tester and wear testing machine.The experiment results show that for single track laser quenching, when the power is lower, the optimum parameters: the laser output power 1500 W, scanning speed 5mm/s, spot size 10×4mm2; when the power is higher, the laser output power 2500 W, scanning speed8mm/s, the spot size 15×7mm2. For multiple tracks laser quenching, the optimum parameters:the spot size 15×7mm2, laser output power 2500 W, scanning speed 8mm/s and overlapping amount 3mm.After laser quenching, from the surface of quenched layer to the base metal consists ofthree regions, namely the completely quenched zone, transition zone(incomplete quenched zone), and the base metal. The microstructure of completely quenched zone is mainly lath martensite. The transition zone consists of martensite and ferrite. The base metal consists of pearlite and ferrite. Under optimal laser quenching parameters condition, the effective hardening depth is about 1.3mm, the surface hardness is above 512HV(50HRC). Through laser quenching, the surface hardness of material increased above 2 times compared with base metal and the wear resistance about increased by 90 times.