Study On Microstructure And Properties Of H13 Steel Modified By Laser Quenching And Nitriding

Hot-working dies are usually used in environments such as rapid cooling,rapid heating,and high alternating stress.Under the action of alternating temperature and alternating stress,due to insufficient material surface properties,hot-working dies often exhibit early failure forms such as cracking,scratching,fatigue,and corrosion during use.Surface modification is the most effective measure to improve the surface performance of dies and prevent early failure of dies.Nitriding,as a typical surface strengthening technique,can significantly improve the hardness,wear resistance,and corrosion resistance of material surfaces.However,the nitriding layer obtained by a single nitriding treatment is relatively thin,and there is a larger hardness gradient between the nitriding layer and the substrate,which makes the material prone to cracking and wear during the grinding process.Although increasing the nitriding temperature and prolonging the nitriding time can increase the thickness of the nitriding layer and reduce the hardness gradient between the nitriding layer and the matrix,it is easy to increase the proportion of brittleε-Fe_2-3N phase in the nitriding layer.The increase ofεphase will lead to the increase of thermal shock stress on the die during the cold and hot cycle,and increase the opportunity of fatigue crack initiation and propagation.In addition,increasing the nitriding temperature or prolonging the nitriding time can also cause chromium depletion on the surface of the workpiece,leading to a decrease in its corrosion resistance and significantly reducing the overall performance of the material.Laser quenching,as a clean and convenient heat treatment process,is widely used for material surface modification treatment due to its special heating and cooling methods.Laser quenching process is easier to obtain a larger depth of hardened layer than plasma nitriding.At the same time,laser quenching can promote the formation of a large number of crystal defects such as vacancies,dislocations,and twinning on the material surface,accelerating the dynamic diffusion process of N atoms.However,compared to nitriding,the hardness of the laser quenched layer is relatively low,and the wear resistance is severely insufficient.Therefore,how to use compound modification technology to improve the shortcomings of single process performance and improve the comprehensive performance of materials is the focus of this topic.H13 steel is widely used in the hot-working die industry due to its high hardenability,toughness,and thermal fatigue performance.This article takes H13 steel as the research object and combines laser quenching with plasma nitriding surface modification technology to explore the influence process and mechanism of compound treatment on the comprehensive properties of H13 steel.The coupling mechanism and strengthening mechanism of laser quenching and plasma nitriding technology on the modified layer of H13 steel were revealed,and the surface characteristics of H13 steel were improved through compo und treatment,thereby improving the performance of the die.Research has shown that the compound treatment process can significantly improve the comprehensive performance of the modified layer.Compared with single laser quenching and single nitriding treatment,the thickness and wear resistance of the modified layer after compound treatment significantly increase,while the hardness gradient significantly decreases.Compared with conventional treatment and single laser quenching,the corrosion resistance of the modified layer after compound treatment is significantly improved,and the electrode potential is significantly increased.When the nitriding temperature is 440℃,the surface layer of a single nitriding sample forms a diffusion layer dominated byα’N-Fe.However,when laser quenching is followed by nitriding treatment,due to the dislocation and fine grain effects caused by laser quenching,the diffusion channel of N atoms increases,and the solid solution strengthening effect of nitrogen is significantly enhanced.And after compound treatment at lower temperatures,the corrosion resistance of the sample surface is significantly improved compared to conventional treatment,laser quenching,and single nitriding treatment.When the nitriding temperature increased to540℃,the brittleεin the compound layer decreased and the toughness ofγ’-Fe₄N increased,indicating that the compound treatment could inhibitεand promote the formation ofγ’.Compared with high-temperature compound treatment,the surface hardness,core hardness,and effective hardened layer depth of the sample significantly increase after low-temperature composite treatment.The modified layers H and H³/E² are larger,and the wear resistance and plastic deformation resistance are better.