Study On Grind-Hardened Layer And Its Uniformity

The grind-hardening is a new technology utilizing heat and mechanical composite effect to induce martensitic phase transformation during grinding to quench the surface of steel directly with a fast cooling. It is a green manufacturing and clean production mode which can replace the induction quenching, the flame quenching, and the laser-quenching integrating surface heat treatment with surface finishing, and reducing the manufacturing procedures, the input of special facilities as well as workers of heat treatment and pollution resulted from heating treatment.Basing on surface grind-hardening experiment, this paper focuses on grind-hardened layer and its uniformity of 65Mn steel according to principle of grinding and heat treatment using SEM, microhardness tester, and optical microscope. The research of this dissertation can be mainly summarized as follows.Firstly, the influence of three primary factors depth of cut, table speed, and grinding mode on structure of 65Mn steel grind-hardened layer in length and depth of workpiece were studied with single factor experiment. The results show that the entire grind-hardened layer can be divided into the entirely hardened zone and the transitional zone from ground surface to parent material by temperature distribution loading upon workpiece in grinding process, and the entirely hardened zone is of fine lathe martensites, residual austenite and a few carbide. Different grinding condition has little remarkable effect upon the delamination of the microstructure due to comprehensive action of grinding heat and grinding force.Secondly, the influence of three primary factors depth of cut, table speed, and grinding mode on microhardness of 65Mn steel grind-hardened layer in length and depth of workpiece were studied with single factor experiment. The results show that the grind-hardened layer microhardness under different grinding parameters has similar distribution from surface to inner. There is no obvious microhardness descent can be observed in the high microhardness zone whose average microhardness is up to 770HV0.5 with fair uniformity. The hardness of high microhardness zone mainly depends on carbon content of material and has little change by the grinding condition.Finally, on the basis of orthogonal experiment method, the influence of depth of cut a_p, table speed v_w, grinding mode gm, and interaction between depth of cut and table speed a_v on depth and its uniformity of grind-hardened layer of 65Mn steel were investigated. The results show that, the a_p is the significant factor influences the average depth of grind-hardened layer; the gm and the vw are the significant factors influence the depth uniformity of grind-hardened layer. The fairly uniformity of grind-hardened layer with good economy can be obtained when using grinding conditions that the a_p = 0.6mm, the v_w = 0.4m/min, and the g_m =up grinding + down grinding in practical applications.This paper is an important component of NSF of Fujian Province (2009J01260).