Papers by Author: Zhong Hou Li

Abstract: Cobalt- superhard high speed steel layer has been formed on the surface of low alloy steel 20Cr2V by tungsten-molybdenum-cobalt plasma surface alloying and following plasma carbonizing. After plasma surface alloying, a homogeneous and dense surface alloying layer was formed, thickness of which is 200μm. Composition, microstructure and properties of the alloying layer were investigated. Contents of W, Mo, Co, Cr, V and C in the surface layer reach 8%,5%, 6% ,4%,1.5% and 1.5% or so respectively. The concentrations of alloy elements basically meet the requirements of high cobalt type superhard high speed steel. Constituent phases of the surface layer were martensite, M7C3 ,M2C and Cr3C2 carbides and μ phase after quenching treatment. The advanced gradient superhard high speed steel possesses not only high surface hardness, high anti-temper softening ability but also enough toughness.

Abstract: The objective of this research was to develop methods for improved the uniformity of temperature distribution within plasma surface alloying furnace by simulating the heat transfer process and numerical calculation. Results show that the structure of charging basket, hanging auxiliary cathode plates in both sides of charging basket and blackness of material influence strongly temperature distribution within the plasma surface alloying furnace. Discharge intensity of the center zone can be weakened through increasing the distance between backs both column blades in center of the furnace, which decreased the consumption of discharge power in center, depressed temperature of the center zone of the furnace. Intensity of discharge in fringe of the charging basket can be reinforced and that of discharge in center can be weakened when auxiliary cathode plates were hanged to outer flank of the charging basket, which increased boundary temperature of the system, at the same time the auxiliary cathode plate plays a heat preservation role. Decreasing the blackness of outside material of charging basket may decrease heat dissipating capacity of outside, decrease temperature difference of outside and center of the furnace and improve the uniform of temperature distribution in the furnace.

Abstract: The surface age alloy of Fe-Co-W-Mo was formed on 25Cr2Mo2V steel by double glow plasma surface alloying technique. The effects of processing parameters on the depth, composition and constituent phases of surface alloying layer were investigated. Results indicate that the plasma processing parameters influenced significantly the surface alloying process. The composition of the surface layer nears W11Mo7Co23Fe59wt%, the depth of the surface alloying layer is 150μm after processing at 1100°C for 6hr. The microstructure of the cross section was composed of three sub-layers, that is, the deposition layer, the diffusion layer and the matrix. The constituent phases of the deposition layer were Fe7W6 type μ phase Fe2W type laves phase, Fe3Mo and a little amount of M2C type carbide, that of the diffusion layer were α-Fe and some intermetallics.

Abstract: Tungsten, molybdenum and cobalt were co-diffused into the surface of undecarburized 45 steel at 1150 °C for 6 hours by a double glow plasma surface alloying technique. A Fe-W-Mo-Co type gradient surface alloyed layer with very low carbon content was formed. Thickness of the surface alloyed layer is 225.2μm. Concentrations of alloying elements Co, W and Mo in the alloyed layer are mostly ranged from 21 to 14 wt.%, 12 to 6 wt.% and 7 to 5 wt.%, respectively. The concentrations of alloying elements basically meet the requirements of W11Mo7Co23 type age-hardened high speed steel. The alloyed samples were solution heat treated, ageing and high-temperature tempering. The results show that the surface alloyed layer formed on 45 steel exhibits very strong age-hardening property and anti-temper softening ability as the metallurgical age-hardened high speed steel, the surface age-hardened high speed steel on ingot and decarburized carbon steel.