Both microstrueture and mechanical properties of low alloy steels treated by quenching and partitioning （Q＆P） process were examined. The mixed microstructure of martensite and large-fractioned retained austenite （...Both microstrueture and mechanical properties of low alloy steels treated by quenching and partitioning （Q＆P） process were examined. The mixed microstructure of martensite and large-fractioned retained austenite （about 27.3%） was characterized and analyzed, excellent combinations of total elongation of 19% and tensile strength of 1 835 MPa were obtained, and three-stage work hardening behavior was demonstrated during tensile test. The en hanced mechanical properties and work hardening behavior were explained based on the transformation induced plas ticity effect of large fractioned austenite.展开更多
The controlled cooling technology following hot rolling process is a vital factor that affects the final micro- structure and mechanical properties of the hot-rolled transformation induced plasticity （TRIP） steels. ...The controlled cooling technology following hot rolling process is a vital factor that affects the final micro- structure and mechanical properties of the hot-rolled transformation induced plasticity （TRIP） steels. In the present study, low alloy C-Si-Mn TRIP steel was successfully fabricated by hot rolling process with a 4450 hot roiling mill. To maximize the volume fraction and stability of retained austenite of the steel, two different cooling methods （aircooling and ultra-fast cooling ＂AC-UFC＂ and ultrmfast cooling, air cooling and ultra-fast cooling ＂UFC-AC-UFC＂） were conducted. The effects of the cooling method on the microstructure of hot-rolled TRIP steel were investigated via optical microscope, transmission electron microscope and conversion electron Mossbauer spectroscope. The mechanical properties of the steel were also evaluated by conventional tensile test. The results indicated that ferrite and bainite in the microstructure were refined with the cooling method of UFC-AC-UFC. The morphology of retained austenite was also changed from small islands distributing in bainite district （obtained with AC-UFC） to granular shape locating at the triple junction of the ferrite grain boundaries （obtained with UFC-AC-UFC）. As a result, the TRIP steel with a content of retained austenite of 11. 52%, total elongation of 32% and product of tensile strength and total elongation of 27 552 MPa·% was obtained.展开更多
A three-step cooling pattern on the runout table（ROT）was conducted for the hot rolled TRIP steel.Microstructural evolution during thermomechanical controlled processing（TMCP）was investigated.Processing condition o...A three-step cooling pattern on the runout table（ROT）was conducted for the hot rolled TRIP steel.Microstructural evolution during thermomechanical controlled processing（TMCP）was investigated.Processing condition of controlled cooling on a ROT in the laboratory rolling mill was discussed.The results indicated that the microstructure containing polygonal ferrite,granular bainite and a significant amount of the stable retained austenite can be obtained through three-step cooling on the ROT after hot rolling.TMCP led to ferrite grain refinement.Controlled cooling after hot rolling resulted in the stability of the remaining austenite and a satisfactory TRIP effect.Excellent mechanical properties were obtained through TMCP for the hot rolled TRIP steel.展开更多
文摘采用完全淬火+两相区再加热淬火-分配(IQ&P)热处理工艺对0.23C-1.8Mn-1.35Si钢进行处理,获得了具有亚温铁素体、马氏体以及广泛分布于原奥氏体晶界、相界等处的残余奥氏体等构成的多相组织.利用SEM,XRD以及EBSD等对不同热处理阶段钢的微观组织进行了表征.结果证实,该多相组织低合金钢中残余奥氏体的获得主要依赖于以下两点:一是两相区再加热阶段逆转变奥氏体组织中的富Mn富C,二是淬火-分配阶段残留奥氏体在分配过程中的二次富C,通过上述的两步元素富集处理可以使该低碳钢在室温下获得超过10%含量的残余奥氏体,而残留奥氏体在分配过程中的二次富C则对该类钢中残余奥氏体的形成及其在室温下的稳定化起到了至关重要的作用.由于广为分布的残余奥氏体在形变过程中的TRIP效应,使得该类钢种在拉伸变形过程中获得了持续的加工硬化能力,从而实现了强度与塑性的良好结合.测试结果表明,IQ&P钢的强塑积超过了26 GPa%,屈服强度大于600 MPa,抗拉强度超过900 MPa,均匀延伸在16%以上,常温半厚冲击韧性达到了39 J.
基金Item Sponsored by Youth Science Funds of China(51101036)National Basic Research Program of China(2010CB630803)National Key Technology Support Program of China(2013BAE07B05)
文摘Both microstrueture and mechanical properties of low alloy steels treated by quenching and partitioning （Q＆P） process were examined. The mixed microstructure of martensite and large-fractioned retained austenite （about 27.3%） was characterized and analyzed, excellent combinations of total elongation of 19% and tensile strength of 1 835 MPa were obtained, and three-stage work hardening behavior was demonstrated during tensile test. The en hanced mechanical properties and work hardening behavior were explained based on the transformation induced plas ticity effect of large fractioned austenite.
基金Key Projects in National Science and Technology Pillar Program During the Eleventh Five-Year Plan Period of China(2006BAE03A08)
文摘The controlled cooling technology following hot rolling process is a vital factor that affects the final micro- structure and mechanical properties of the hot-rolled transformation induced plasticity （TRIP） steels. In the present study, low alloy C-Si-Mn TRIP steel was successfully fabricated by hot rolling process with a 4450 hot roiling mill. To maximize the volume fraction and stability of retained austenite of the steel, two different cooling methods （aircooling and ultra-fast cooling ＂AC-UFC＂ and ultrmfast cooling, air cooling and ultra-fast cooling ＂UFC-AC-UFC＂） were conducted. The effects of the cooling method on the microstructure of hot-rolled TRIP steel were investigated via optical microscope, transmission electron microscope and conversion electron Mossbauer spectroscope. The mechanical properties of the steel were also evaluated by conventional tensile test. The results indicated that ferrite and bainite in the microstructure were refined with the cooling method of UFC-AC-UFC. The morphology of retained austenite was also changed from small islands distributing in bainite district （obtained with AC-UFC） to granular shape locating at the triple junction of the ferrite grain boundaries （obtained with UFC-AC-UFC）. As a result, the TRIP steel with a content of retained austenite of 11. 52%, total elongation of 32% and product of tensile strength and total elongation of 27 552 MPa·% was obtained.
基金Item Sponsored by National Natural Science Foundation of China(50334010)
文摘A three-step cooling pattern on the runout table（ROT）was conducted for the hot rolled TRIP steel.Microstructural evolution during thermomechanical controlled processing（TMCP）was investigated.Processing condition of controlled cooling on a ROT in the laboratory rolling mill was discussed.The results indicated that the microstructure containing polygonal ferrite,granular bainite and a significant amount of the stable retained austenite can be obtained through three-step cooling on the ROT after hot rolling.TMCP led to ferrite grain refinement.Controlled cooling after hot rolling resulted in the stability of the remaining austenite and a satisfactory TRIP effect.Excellent mechanical properties were obtained through TMCP for the hot rolled TRIP steel.
