Papers by Author: Jian Dong Xing

Abstract: The microstructure, toughness, hardness and wear resistance of Fe-B-C cast wear-resistant alloy were studied. The results indicate that, the as-cast Fe-B-C alloy comprises pearlite, ferrite and eutectic phase Fe₂ (B, C), and that, with increasing boron and carbon contents, the boride volume fraction (BVF) and macrohardness increase; furthermore, when boron content increases from about 0.5 wt.% to 2.0 wt.%, the increase trend of the macrohardness will become smaller with increasing the carbon content. The results also indicate that, after heat-treatment, the Fe₂ (B, C) becomes coarser than that as cast condition, and the boron content has less effect on the martensite hardness at the same carbon content; with increasing boron and carbon contents, the hardness of the samples increases and inversely the toughness decreases. At a lower BVF, the matrix plays a dominant role on the impact toughness of Fe-B-C alloy; however, at a higher BVF, the BVF plays a dominant role. The wear test results indicate that, with increasing the boron and carbon contents, the weight loss of the samples decreases, namely, the increase of wear resistance.

Abstract: Boron-bearing high speed steels are widely used in roller materials because of their improved wear resistance and toughness. In present work, aluminum was added into boron high speed steel and the aging-hardening behavior and microstructures of tempered boron high speed steel at various tempering temperatures were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy dispersive spectrometry (EDS) and HR-150A Rockwell hardness tester. The results show that the bulk hardness of boron high speed steel gradually enhances with the increasing destabilized temperature. Aluminum addition cuts down the bulk hardness and delays the hardening process, thus leading to high the hardening value of boron high speed steel shifting to higher destabilized temperature. After tempering process, boron-bearing high speed steel displays precipitate-hardening behavior at the tempered temperature of about 520°C. The bulk hardness of boron-bearing high speed steel achieves 60.5 HRC as a maximum value when the aluminum addition is 0.6 wt.%. More aluminum addition can result in lower precipitate-hardening rate and bulk hardness. The microstructures of boron high speed steel tempered at 520°C consist of eutectic borides and tempered martensite dispersed a lot of secondary precipitates. XRD and TEM results indicate that the precipitate-hardening properties of boron high speed steel depend on precipitates and square degree of martensite

Abstract: The wettability between ceramic particles and metal play an important role in fabrication of ceramic particles reinforced metal matrix composites(PRMMCs). In present paper, Al₂O₃ particles were coated with nickel by chemical plating to modify the preparation and properties of Al₂O₃ particles reinforced steel matrix composites. Using the Al₂O₃ particles treated by chemical nickel-plating, Al₂O₃ particles reinforced steel matrix composites were fabricated by powder metallurgy process(PM). And the wear resistance of the composites was investigated. The results show that: the nickel coating can fully and tightly cover on the surface of Al₂O₃ particles, and the nickel coating thickness is uniform about 2~3 micron; The nickel coating can effectively improve the uniform distribution of Al₂O₃ particles in the composites. And the treated Al₂O₃ particles can be tightly bonded with steel matrix,which improve the wear resistance of composites. The wear resistance of composites reinforced treated and untreated Al₂O₃ particles each is 2.5 and 1.6 times of Hadfield steel.

Abstract: The effects of forging and heat treatment on microstructure and properties of high boron white cast iron were investigated in this paper. The results show that forging breaks up boride network and makes broken boride particles uniformly distributed in matrix. During subsequent heat treatment, spheroidized boride is able to be obtained. The hardness of high boron white cast iron increases slightly (from 51.4 HRC to 54.7 HRC) while the toughness increases obviously (from 5 J/cm2 to 107 J/cm2) by combined process of forging and heat treatment. Fracture morphology changes from brittle fracture to ductile fracture.

Abstract: The influence of boron concentration on corrosion resistance of high boron white cast iron dipped into a pure liquid zinc bath at 460°C was investigated. The results reveal that high boron white cast iron containing 3.5 wt.%B exhibits excellent corrosion resistance due to the dense continuous netlike or parallel Fe2B phase which hinders the Fe/Zn interface reaction. The corrosion rate decreases significantly when the boron concentration increases, but the corrosion rate declines slightly when the boron concentration exceeds 3.5wt.%. EDS results indicate the coarse and compact δ phase generated near the matrix and a large amount of massive and blocky  phase occurred close to the liquid zinc. The corrosion process includes Fe/Zn interface reaction and the spalling and fracture of Fe2B. The failure of Fe2B is mainly caused by the microcrack of phase transformation.

Abstract: This study investigates the effect of rare earth and aluminium composite modification on the structural variations of as-cast and heat treated medium carbon Fe–B cast alloys. The as-cast microstructure of Fe–B cast alloy consists of the eutectic boride, pearlite, martensite and ferrite. Moreover, compared to a netlike distribution of the coarse eutectic borides in the unmodified alloy, the eutectic boride structures in the modified alloy are greatly refined and less interconnected. After heat treatment, the phases in Fe–B cast alloy consist of the boride and martensite. The addition of rare earth helps to increase the number of the rod-shaped and round borides in Fe-B cast alloy during austenitizing. Compared to the unmodified alloy, the boride volume fraction and Rockwell hardness of the modified alloy have no significant change, however, the average area of each boride in the modified alloy is lower and the impact toughness is higher.

Abstract: Microstructure and properties of isothermally quenched high boron white cast iron were investigated in this paper. The results show that the microstructure of high boron white cast iron is mainly composed of many continuous and netlike eutectic borides, pearlite and ferrite under as-cast condition. The microhardness of Fe2B ranges in 1200-1600HV whose value seems to approximate that of (Fe,Cr)7C3–type carbide (HV1200~1800) in high chromium white cast iron. After isothermal quenching, the matrix transforms into lower bainite in which carbide precipitations are arranged in parallel rows at an angle of 60 deg to the long axis of the plates, but the morphology of boride remains nearly unchanged compared with its as-cast condition. Moreover, precipitation particles with the size of about 1~4 μm can be found in the matrix of isothermally quenched high boron white cast iron. Impact fracture morphology of isothermally quenched high boron white cast iron indicates that fracture propagated more easily through boride/matrix interface than through matrix.

Abstract: In order to improve the wear resistant properties, WC ceramic particles were used to reinforce Hadfield steel. WCp/Hadfield steel composites were fabricated by optimized solid state sintering process of powder metallurgy. Interface structure, constituent phase and the forming mechanism of the composites were investigated systematically. The results show that the WCp/Hadfield steel composites have uniformly distributed particles and well bonded interface between WC particles and Hadfield steel. In the WCp/Hadfield steel composites, the interface between WC particles and Hadfield steel matrix is of shell shape, in which W, Fe and Mn elements diffuse between the two phases. The interface is of metallurgical bond, in which a new phase, namely Fe3W3C is formed. The micro-hardness of the interface layer is between those of WC and the steel matrix, which can provide a guarantee for the property transition between WC particles and Hadfield steel matrix. The diffusion reaction mechanism of the interface was also systematically studied.

Abstract: To improve the wear resistance of high chromium white cast iron under severe abrasive conditions, a composites layer was designed for wear surface, which were locally reinforced with WC particles. And the local composites were successfully fabricated by optimized centrifugal casting process. Then the interface between WC and iron matrix was analyzed with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). And three body wear tests were carried out on a self-made rig to investigate the wear resistance of the composites. For comparison, the wear tests of high chromium white cast iron were also carried out under the same conditions. The results show that: There are no defects such as inclusion, crack, gas pore and so on in the obtained composites layer, which with a uniform thickness of 10 mm. WC particles are homogeneously distributed in the composites layer and tightly bonded with the iron matrix. The WC particles are partially dissolved in the iron matrix during centrifugal casting. The elements W, C and Fe react to form new carbides such as Fe3W3C or M23C6, which precipitate around former WC particles during subsequent solidification. So the interface between WC particles and the iron matrix is a strong metallurgical bonding. WC particles in the composites layer can effectively resist cutting by the abrasive, and then protect the matrix. The wear resistance of the composites layer is 7.23 times of that of high chromium cast iron.

Abstract: Seal materials often lose their effectiveness due to the wear of surface under the combined effect of environment and load. In this research, a metallurgical bonding composite coating reinforced with nickel -coated tungsten carbide (Ni -WC) particles was produced on 40Cr carbon steel substrate by plasma sprayed. The bond strength of the coating/substrate interface and the tensile strength of the coating itself reached 260–330 and 100–132MPa, respectively. Effects of Ni and WC contents on the wear behavior of the coating have been systematically investigated at two different wear conditions, namely the high stress pin-on-disk abrasion and three-body abrasive wear. The results show that the higher the Ni content in the coating, the lower the hardness and wear resistance. In stress pin-on-disk abrasive wear, the mass percent of Ni in the coating having the lowest wear amount was 40%, and which was 60% in three-body abrasion. In view of the above, the WC reinforcement of the composite coating plays an important role in protecting the matrix from being worn-out, whereas in the abrasive wear, the wear mechanism is mainly controlled by the scratching and micro-cutting of the matrix followed by the pull out of WC particles due to the scratching action of abrasives. The wear resistance of the 40Cr carbon steel composite coating (Ni -WC) is better than that of the flame overlaid coating.