And The Mechanism Of High-temperature Wear Properties Of Carbon And Boron Alloy

As a new type of wear resistant materials, high boron iron-base alloy have been applied gradually, and its room temperature wear research is more mature compared to the less in high temperature. Taking advantage of the charateristic that high temperature oxidation-resistance of the metallic boride is batter than those corresponding matallic carbide, the use of high temperature wear resistant alloys can be partly replaced by high boron medium carbon alloy(HBMCA). The dissertation has been supported by the Yunnan ShengYuan provincial universitiy science and technology cooperation project(Research and Industrialization of the High Boron Low Alloy High Speed Steel Compound Roll). The preliminary study on high temperature wear of the HBMCA contain1.7%B was carried out in this paper.The X-ray diffraction(XRD), optical microscope(OM), scanning electron microscopy (SEM) and energy disperse spectroscopy(EDS), etc, were adopted to investigating the two heat treatment process elements i.e. quenching cooling way and quenching temperature, that effect on the microstructure transformation of the HBMCA, then researched the relationships between the microstructure and its temperature wear properties, and also discussed the high temperature wear charateristics that from200℃to600℃in different environment. The resluts show that, when the alloy quenched in three media, i.e, air, oil and water, as the quenching cooling velocity accelerating, the granular precipitates of boron carbon compounds in the matrix is increased, the hardness and wear resistance are improved, the spalling in the friction surface reduces significantly, and micro-cutting is more serious. The eutectic boron carbon compounds experiences oxidation and fracture wear. When quenched by water from950-1100℃, the granular precipitates of boron carbon compounds in the matrix is more and the hardness improves, but the wear resisitance reduces as improving the quenching temperature. Wear resistance of the HBMCA is similar to the high speed steel using for roller, the sample quenched at950℃experiences plastic deformation and oxidation wear, abrasive wear and adhesive wear, and as improving the quenching temperature, plastic deformation wear alleviates but adhesive wear becomes more serious. The results also show that, as the wear temperature increased, volatility of the friction coefficient in rough vacuum becomes severe, but less in the air environment and is very severe and no regular pattern in abrasive environment. In rough vacuum, the wear loss is increased linearly with temperature under500℃, and to600℃increased by one order of magnitude. The loss is low in air environment at200℃,300℃and600℃but is higher in400℃and500℃, and the abrasive wear loss at200℃is much higher than that gradually increasing from300to600℃. As the friction heat relies mainly on the heat conduction to be lost in rough vacuum, thus, it experiences local plastic deformation and fatigue, and oxidation wear in lower temperature, and then it loss much more by the stronger plastic flow, oxidation wear and adhesive wear as it becomes softer and even appears banded structure at higher temperature, then, when the wear temperature reach600℃, the eutectic structures fractured severely as the friction surface layer of the alloy is marked softing. In the air environment, it experiences local plastic deformation, oxdiation, adhesive and abrasive wear at200～300℃, and these types of wear become more severe at400-500℃, but at600℃, both the matrix and boron carbon compounds oxidate severely and the uniformity oxidation film forms quickly, thus, this oxidation film experiences fatigue and shear tear wear. In the abrasive condition, the alloy suffers from severe micro cutting and the deep and wide cutting groove is in different direction, then as the temperature increased, the micro cutting in the friction surface gradually reduces but the fatigue wear and tear gradually increases, up to600℃, the thick and homogeneous oxidation film in a large area experiences fatigue failure, and the new fatigue spalling surface begin to suffer from a lot of small but obvious micro cutting.