Cu-V双合金化3Mn钢的组织和力学性能

Microstructure and Mechanical Properties of Cu-V Dual Alloyed 3Mn Steel

研究了Cu-V双合金化的3Mn钢热轧板在550~650℃温轧和临界退火等制备工艺过程中(简称温轧退火样品)的组织演变与最终力学性能,并与热轧后在同样温度范围时效处理并临界退火的样品(简称热轧时效退火样品)进行对比。结果表明,温轧退火样品的塑性显著高于热轧时效退火样品,但2者屈服强度相似,这归因于温轧阶段引入大量缺陷,促进了临界退火时奥氏体逆转变过程,提高了残余奥氏体分数,最终可实现屈服强度高达1230~1320 MPa并保有23%~29%的延伸率,这一综合性能显著优于文献中Cu/V单一合金化的中锰钢,尤其是屈服强度大幅提高。这是由于采用了Cu-V双合金化并且在热轧后采用了温轧加临界退火的两段热变形处理工艺,除了在温轧阶段引入富Cu析出相以实现强化外,在临界退火阶段析出的VC还弥补了由于退火导致的软化,实现了高屈服强度;并形成25%~30%的残余奥氏体来提供相变诱导塑性,从而保证了高塑性。

Recently,medium Mn steels(MMnS)have been extensively investigated because of the excellent mechanical combination of strength and ductility achieved at the relatively low alloying cost.Intercritical annealing(IA)is a key process of MMnS to form intercritical austenite that can be retained fully or partially at room temperature,which can trigger transformation-induced plasticity and then improve work hardening during deformation.However,this process leads to a relatively low yield strength because the recovery,recrystallization,grain growth,coarsening,and dissolution of precipitates could occur during IA.In this study,the microstructural evolution and resultant mechanical properties of Cu-V dual alloyed 3Mn steel were examined during two manufacturing processes:hot rolling→warm rolling at 550-650℃→IA at 690℃ for 10 min(termed as WR-IA)and hot rolling→aging at 550-650℃ for 70 min→IA at 690℃ for 10 min(termed as Aging-IA).That is,the two processes differentiate in either the warm rolling or the aging process used as the intermediate process.WR-IA specimens exhibit significantly higher ductility than Aging-IA ones,but they both have the same yield strength.The former is attributed to a large quantity of defects introduced during warm rolling,which promoted austenite reverse transformation during IA and led to a large fraction of retained austenite.The resultant tensile properties include yield strength of 1230-1320 MPa and ductility of 23%-29%,which is superior to those of either V-or Cu-alloyed MMnS published in references.In particular,higher yield strength was achieved because the dual alloying of Cu-V and the two-stage thermomechanical process,that is,warm rolling plus IA,are adopted.The first warm rolling promoted Cu-rich precipitates dispersed for strengthening,and the precipitation of VC during subsequent IA could compensate for the softening caused by IA.Consequently,a high yield strength was achieved.Meanwhile,25%-30% fraction of austenite was retained,thereby providing transformationinduced plasticity during deformation,leading to high ductility.