模锻变形对曲轴用非调质钢1538MV显微组织的影响

Influence of die-forging deformation on microstructure of 1538MV non-quenched and tempered steel for crankshaft

影响曲轴锻后组织的主要因素有变形量、终锻温度、金属流动及锻后冷却.本文采用数值模拟的方法研究了曲轴用非调质钢1538MV的锻造过程,并对轧材原料和曲轴成品的显微组织进行了分析,探讨了模锻变形对曲轴显微组织的影响.研究结果表明,曲轴较高的锻造温度和较小的变形量使得曲轴的锻后组织较轧材有所粗化.曲轴变形过程中的温度和应变分布不均导致了曲轴组织的不均匀.曲轴的铁素体含量和珠光体片层间距都低于轧材,且部分位置出现了贝氏体组织,这说明曲轴锻后的相变区冷速过快,应当进一步优化曲轴锻后冷却制度.另外,曲轴锻造过程中的偏析区金属流动对曲轴的锻后组织产生了明显的影响,也是造成贝氏体组织产生的原因,应严格控制轧材的质量.研究结果为轧材质量的提升和曲轴锻造工艺及锻后冷却制度的优化指明了方向.

Non-quenched and tempered steels offer many advantages such as energy saving,emission reduction,simple processing,short production time,and low cost. Demand for energy saving and emission reduction is increasing with the rapid increase of car production and ownership. As a result,the usage of non-quenched and tempered steel in automotive parts has attracted increasing attention. The main problem with non-quenched and tempered steel in actual production is the lack of a hot deformation process and a cooling process that can be used to precisely control the microstructure and properties of the material. The material 1538 MV is a type of pearlite ＋ ferrite non-quenched and tempered steel,and its use for building crankshafts has not been studied sufficiently thus far. The main factors affecting the structure of a crankshaft are deformation,final forging temperature,and metal flow and cooling after forging.In this paper,the forging process of 1538 MV non-quenched and tempered steel for building a crankshaft was studied by means of numerical simulation,microstructures of the rolled material and finished crankshaft were analyzed,and influence of deformation on the microstructure of the crankshaft was discussed. The results show that the microstructure of a crankshaft forged at a higher temperature and with smaller deformation is coarser than that of a crankshaft made of rolled material. The inhomogeneity of the microstructure is caused by unevenness of temperature and strain distribution during crankshaft deformation. The ferrite content of the crankshaft and the pitch of the pearlite were lower than those of the rolled material,and the bainite structure appeared in a few parts,which indicated that the cooling rate was too fast during phase transformation. Therefore,the cooling process should be optimized further. In addition,the metal flow in the segregation zone during the crankshaft forging process significantly influences the forged microstructure of the crank-shaft,which is another cause of the formation of bainite. Therefore,the quality of the rolled material should be strictly controlled. The above results provide directions for improving the quality of the rolled material,optimization of the crankshaft forging process,and optimization of the cooling process after forging.