Effect of QPQ Treatment on the Performance for H13 Die Steel

Abstract

QPQ salt bath treatment of H13 steel was conducted by nitriding at the same temperature of 565 ℃ for various times, followed by the same post-oxidation process. Optical microscope, microhardness tester, X-ray diffraction and wear resistance tester were employed to characterize the microstructure, phase constituents, micro-hardness and wear resistance of the treated specimens. The results showed a compound layer mainly composed of ε-Fe2-3N and diffusion layer were formed during salt bath nitriding and a thin oxide layer composed of Fe3O4 was formed by postoxidation, and the compound layer thickness increases with the nitriding time. The maximum surface hardness value of 1441 HV0.3was obtained after nitriding at 565℃ for 150 min, which is as three times high as that of untreated sample. Meanwhile the wear resistance of H13 steel is significantly improved by QPQ treatment, 150 min is the optimum nitriding time to improve the surface hardness and wear resistance of H13 steel.Keywords: QPQ treatment, H13 steel, Wear resistance, Hardness, Microstructure 1 Introduction H13 steel is a kind of widely used hot die steel due to its good mechanical properties at elevated temperature and moderate cost [1][2][3]. In real application, hot working tools are generally repeatedly subjected to high temperature and heavy loads [4,5], these severe conditions tend to result in failure of the tools due to wear or plastic deformation etc. [6][7][8][9][10][11][12]. In order to improve the related properties of H13 die steel, researchers have tried various surface modification methods, such as plasma nitriding, ion implantation, laser surface treatment and carbonitriding [13][14][15][16][17], among these technologies, plasma nitriding is currently widely adopted in real application to improve the wear resistance [18][19][20]. Unfortunately, it generally takes dozens of hours to obtain the required properties, which brings out low efficiency and high consumption of energy [21,22]. It has been reported that QPQ treatment is an effective surface modification technology, which has been widely used in manufacturing field to improve the wear and corrosion resistance of the components [23,24], since a compact oxide film can be formed on the top of a nitriding layer on the metal surface after QPQ treatment. More importantly, comparing with plasma nitriding, QPQ treatment has significant advantage of much higher efficiency; it generally takes only several hours for the whole process.