To meet the high requirements of fatigue strength and thermal stability for the large forging dies, the complex strengthening process tests of new high thermal stability die steel 5Cr2NiMoVSi were done. This complex strengthening process was nickel plating the RE boron penetration→ pre-cool quenching → high temperature tempering. The results show that the surface micro-hardness, high temperature oxidation resistance, thermal fatigue resistance and wear resistance of 5Cr2NiMoVSi steel can greatly be improved by these processes. It has achieved significant results for auto front axle large forging dies by using the materials and processing technology.

High-energy shot-peening on H13 steel after quenched. The samples with or without high-energy shot-peening were ion-nitrided at 520°C for 3h．The Microstructure，nitriding depth, hardness gradient, surface phase and Corrosion resistance of the nitride layers were compared between the high-energy shot-peening samples and the original samples using optical microscope, micro-hardness tester, X-ray diffraction and CH1660A electrochemical test. Results show that the high-energy shot-peening greatly speeds up the nitriding on the H13 steel at 520°C for 3h.. The depth of ion-nitriding layer after shot peening is from 0.11mm to 0.16mm, micro-hardness of the surface layer is from 998HV0.5 to 1105HV0.5, The hardness gradient is slightly flat . Phase structure and content of the surface is different by Powerful shot-peening and not. Corrosion resistance of the samples by high-energy shot-peening is significantly improved because it is easier to form a stable passive film.

. In order to improve the high temperature stability of casting mold, we carried out the RE Ion nitro-carbonizing technology test on the 4Cr5MoSiVl steel. This test was done by using high-power pulsed supply for the 4Cr5MoSiVl steel casting mold surface treatment under different temperatures, time period, atmospheric pressure, and RE contents. The optimization of these parameters makes the layer structure dense, toughness increased, specifically the surface hardness, wear resistance, high temperature oxidation resistance, and thermal fatigue properties of the treated layer significantly improved. A test with the use of this technology has been done for the 4Cr5MoSiVl steel automotive lamp aluminum casting mold. The mold service life of each mold time increased from 30,000 to 100,000. The experimental results show that by using 4%RE 520oC×2h, and 1.05KPa atmospheric pressure, the treated layer has optimal qualities, which can meet the requirements in practice.

The laser cladding is used on the surface of 4Cr14Ni14NW2Mo heat-resisting steel, In the laser cladding added 0. 5% CeO2,Ni-based WC coating can be formed. The effects of rare-earth oxide CeO2 on the microstructure and microhardness and wear-resistance and corrosion-resistance of Ni-based metal-ceramic coatings are investigated. Observing and analying the microstructure, Measuring microhardness, Checking the dry friction and wear properties of high-temperature of the coating in different temperature. The results showed that the microstructure of Ni21+20%Wc+0.5%CeO2 cladding layer is even small, Hardness is more uniform and gentle. Wear mechanism of the laser cladding layer changes with temperature changes.Abrasion is the main mode under Low temperature , it was transformed into Adhesive wear and Oxidation wear along with the increase of the temperature.dry friction and wear properties of high-temperature is excellent.