| Fe-Bi/Pb-Mn alloy is a new free-cutting stainless steel, and widely used in high precision machining, such as written material, automotive parts and machinery important parts. Especially Fe-Bi-Mn alloy is a new type environmentally free-cutting stainless steel. Properties of stainless steel have a close relationship with Bi/Pb shape. Fe-Bi/Pb-Mn alloy shows excellent free cutting when Bi/Pb and Mn S dispersed in the matrix steel. But Bi/Pb phase occur liquid→vapor→liquid→Solid phase transition and Mn S phase only occur liquid→Solid phase transition. Phase of Bi / Pb easily enriched in the bottom of the ingot and vapor phase of Bi/Pb easy volatile floating, Bi/Pb have severe segregation in the ingot. The three-dimensional mathematical model for a three-phase flow during the solidification of fluid dynamics method based on Eulerian-Eulerian and volume of fraction methods, in which the mass, momentum, species and enthalpy conservation equations of the Fe-Bi/Pb-Mn alloy solidification process are solved simultaneously. The principal elements are listed as follows:1. The effects of Pb area quadratic gradient(()Pb? ?S) and Pb concentration quadratic gradient(()Pb? ?C) on the segregation formation were investigated. The results show that the segregation mode is manifested as X-segregates in upper and V-segregates in lower during flow-solidification of liquid phase and gas phase. The X-segregates results from phase transformation driving force of gas phase and "scattering" due to orientation of phase transition. When t>tc the lower()Pb? ?S and()Pb? ?C curves cause larger Yielding rate of Pb with larger down angle of X-segregates and smaller up angle of X-segregates and V-segregates angle. All these are favorable for the formation of a well dispersed microstructure. In addition, the gas-liquid two-phase flow interaction term have an effect on channel segregation, showing that channels occur only in the region where the flow-phase transition interaction term( llu ×?c and ggu ×?c) is negative. With a negative flow-phase transition interaction term the increase in flow velocity due to a flow perturbation flow-phase transition interaction term becomes more negative, thus the channel continues to grow and becomes stable.2. Results show that the multiphase transformation-diffusion is strongly influenced free-cutting phases precipitation behavior: Mn S has a relatively large partition coefficient and small diffusion coefficient with larger ls,Mn SM. During the solidification, *s,Mn Sc may become even larger than l,Mn Sc cause Mn S in liquid is assumed to be fully ?trapped‘ in the solid and there is no longer any enrichment of Mn S; Bi has a relatively small partition coefficient and large diffusion coefficient with smaller ls,BiM and negative gl,BiM. During the solidification, l,Bic always greater than * s,Bic. In addition, the existence of Bi-gas phase, Bi continuous flow enriched in the solidified around Mn S.3. Results show that columnar crystal/equiaxed crystal formation model of Bi and Mn S in alloy solidification is strongly influenced by convection diffusion and multiphase transformation terms; The large multiphase mass transfer rate and small enrichment degree of species easy to form columnar crystal where the convection diffusion term is positive; The small multiphase mass transfer rate and large enrichment degree of species appeared at where the convection diffusion term is negative. The tip of columnar crystal breaking is caused by turbulence from convection diffusion and multiphase transformation when the species enriched to some degree, and which becomes the nucleation center of columnar crystal and the equiaxed crystal continues to grow and tends to be stable.4. The friction and wear characteristics of Fe-0.03Te-0.3Pb-0.9Mn free-cutting stainless steel were investigated using a lubricated rolling wear testing apparatus. The wear morphology, hardness, friction coefficient and wear volume of alloy surface were compared in different wear time, its mechanism of lubricated rolling wear was studied further. The results show that, at the beginning of wear, the performance of alloy surface wear is relatively stable, under the interaction of free-cutting phase, such as Mn S and Pb, that cracks happened at the alloy surface plough bottom; When the wear is stable, the performance of alloy surface changed gradually, the cracks of plough bottom continued, interweaved cracks begin to generate flake or block convex parts; When the wear is over, the alloy surface lubrication film and exfoliation numerous are flaking off, exfoliation formed abrasive wear, plough disappeared step by step, the alloy surface system is collapsed rapidly. |
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