Papers by Author: Hui Min Chen

Abstract: The frictional resistance and abrasion mechanism of high vanadium high speed steel were studied by the self-made friction wear testing machine under the conditions of 10% slip-roll ratio. Results show that the frictional resistance increases with the increase of carbon content and is optimal when the carbon content is 2.92%. The carbon content affect the wear resistance by changing the amount of the retained austenite and the shapes of carbides, the moderate quantities of retained austenite makes the matrix have better impact toughness and hardness; The spherical VC can prevent the initiation and expansion of cracks forming and make the frictional resistance increase. The abrasion mechanism is fatigue flake under the condition of rolling and sliding.

Abstract: The frictional resistance and abrasion mechanism of high vanadium high speed steel were studied by the self-made friction wear testing machine under the conditions of 0.5% slip-roll ratio. Results show that the frictional resistance increases with the increase of carbon content. The retained austenite and the shapes of carbides will change when the carbon content alters, which make the frictional resistance of the material change, and the proper quantities of retained austenite makes the impact toughness the matrix better; The spherical VC can prevent the initiation and expansion of cracks forming and make the frictional resistance increase. The abrasion mechanism is fatigue flake under the condition of rolling and sliding.

Abstract: The morphology and distribution of in-situ VC ceramics in cast high speed steel with about 5-10wt.% vanadium and 1.7-3.2wt.% carbon were studied. The results show that the elementary morphology of in-situ VC ceramics has six kinds: spherical, lumpy, flower shaped, strip, short rod shaped, and vermicular. The in-situ VC in high-speed steel has three kinds of distributions: grain boundary, chrysanthemum-like and homogeneous distributions, depending on the chemical composition of high-speed steel. The in-situ VC ceramics grows up along grain boundaries if the high-speed steel is hypoeutectic, leading to grain boundary distribution of VC ceramics. On the contrary, it distributes homogeneously when the high-speed steel is hypereutectic. Whereas, the in-situ VC ceramics takes on chrysanthemum distribution if the high speed steel is just eutectic. Modification can improve the morphology of primary VC ceramics, but has not obvious effect on the morphology of eutectic VC.

Abstract: The expansion curves during the procedure of continuous cooling which high vanadium high speed steel (HSS) was tempered with 250°C, 550°C and 600°C after 1050°C quenching were determined by the Gleeble-1500D thermal simulation test device, and the curves were analyzed subsequently. The hardness and microstructure of high vanadium HSS under different tempering temperatures were analyzed by means of SEM, TEM and X-ray diffraction, and the influence of tempering temperature on the hardness and retained austenite were discussed. At the same time, the wear resistance of the material at different tempering temperatures was studied by the HST-100 friction wear testing machine, and the influence of microstructure on wear resistance was analyzed further. The studies show that the structures are not transformed at 250°C tempering with cooling rate of 0.5°C/s; The retained austenite transformed to martensite at about 390°C when 550°C and 600°C tempering. Wear test shows that the abrasive wear performance is excellent with 550°C tempering after 1050°C quenching because of the decrease of the amount of retained austenite, therefore the heat treatment of 550°C tempering after quenching of high vanadium HSS is optimal.