Abstract
As an emerging composite processing technology, the grind-hardening process implements efficient removal on workpiece materials and surface strengthening by the effective utilization of grinding heat. The strengthening effect of grind-hardening on a workpiece surface is principally achieved by a hardened layer, which is chiefly composed of martensite. As a primary parameter to evaluate the strengthening effect, the hardness of the hardened layer mostly depends on the surface microstructure of the workpiece. On this basis, this paper integrated the finite element (FE) and cellular automata (CA) approach to explore the distribution and variation of the grinding temperature of the workpiece surface in a grind-hardening process. Moreover, the simulation of the transformation process of “initial microstructure–austenite–martensite” for the workpiece helps determine the martensite fraction and then predict the hardness of the hardened layer with different grinding parameters. Finally, the effectiveness of the hardness prediction is confirmed by the grind-hardening experiment. Both the theoretical analysis and experiment results show that the variation in the grinding temperature will cause the formation to a certain depth of a hardened layer on the workpiece surface in the grind-hardening process. Actually, the martensite fraction determines the hardness of the hardened layer. As the grinding depth and feeding speed increase, the martensite fraction grows, which results in an increase in its hardness value.
Highlights
Grind-hardening can achieve efficient material removal at a greater grinding depth but can form a hardened layer dominated by martensite on the workpiece surface, which effectively makes use of the grinding heat
From the literature outlined above, it can be seen that the hardened layer is mainly produced by microstructure transformation on the workpiece surface with the grinding heat effect
Based on the theory of phase transformation, the austenite on the workpiece surface transforms into martensite and forms a martensite lath with the driving force effect when the grinding temperature is lower than Ms In martensitization process, the formation of martensite lath mainly contains two processes—namely martensite nucleation and grain growth
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Presented a temperature-dependent finite element (FE) heat transfer model, which analyzed the influence of grinding temperature distribution and different cooling modes on the formation of the hardened layer. From the literature outlined above, it can be seen that the hardened layer is mainly produced by microstructure transformation on the workpiece surface with the grinding heat effect. It is known that the CA approach is capable of simulating the microstructure transformation, which is helpful to study the formation of hardened layer in grind-hardening process. The hardness of the hardened layer, whose value mainly depends on the surface microstructure, is a key to evaluate the strengthening effect on the surface From this consideration, the integration of FE and CA approaches is helpful to discover the distribution and variation of the grinding temperature of the workpiece and simulate microstructure transformation. Where λs , ρs , and Cs are the heat conductivity, density, and specific heat of the wheel material, respectively; λw is the thermal conductivity of the workpiece material
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