Laser Quenching Process Parameter Research On45Steel

In recent years, there is not only a rapid development of technology of laser surfacetreatment in research and development, but also a lot of progress in the industrial applicationof surface engineering. Technology of laser surface treatment becomes very active inemerging field. Laser surface quenching is a kind of laser surface treatment technology. It’sprinciple is that the material surface is heated to above the phase transition by using laser,then as the material cools, austenite transforms into martensite, so that the quenching surfacehardening. Laser surface hardening technology solves the problem which many conventionalheat treatment process can not solve. And it has been widely used in automobile, metallurgy,mould, hardware, light industry, machinery manufacturing industry. Especially in theautomotive industry, laser surface quenched almost can be used for processing all wear partssuch as crankshaft, cylinder liner, cylinder, piston ring, the ring groove, the exhaust valve andvalve seat and other parts of the engine. However, many factors influence the process qualityof laser surface hardening. It results that is more difficult to control the quenching quality inthe actual operation and restricts the application of laser surface hardening technology. Inorder to strengthen the advantages of the laser surface quenching technology, further promoteits industrial application, it will need a better understanding of the physical process of laserquenching process in the laser interaction with materials, as well as the influence of processparameters on laser quenching processing quality, on the basis of the main process parametersof laser equipment testing and optimization, so as to realize the good industrial application.In this paper, according to the output power of the laser, scanning speed and light spotsize and other parameters on laser surface quenching effect, make a five experiment scheme,using Nd:YAG solid laser on45steel samples for five regimens of laser quenching. Then usethe X-350A type X ray stress instrument for measurement of45steel after laser quenchingresidual stress, and make into tissue observation of metallographic specimen by cutting linesalong and perpendicular to the scanning direction sampling; And make tissue observationwith metallographic microscope. Confirm the hardened layer depth with micro-hardnessmeasurement and metallographic observation. Through experimental observation we candiscover that laser processing before the original sample surface layer is tensile stress, thelaser quenching surface residual stress is compressive stress. Residual stress gets stronger bydecreasing the spot size and scanning velocity,and gets stronger too as the output powerincreases. The spot size and the current value make relatively greater influence to the residual stress values. Depending on heat conduction from the outside to the inside, Laser quenchingself-cold. This realizes high efficiency of quenching processing, and gains the hardened layerhardness and small grains, but in the depth direction is not uniform. By using of the Nd:YAGsolid laser device, laser surface quenching of45steel samples achieves that the surfacehardening effect can meet the requirement of production, the hardening depth of0.2～0.25mm, and at the same time the sample can be ensured to have better surface quality.Through the analysis under certain conditions,this article optimize the laser quenchingparameters.