A new category of steel with excellent combi- nation of strength,toughness,strain-hardening ability and excellent resistance to high-stress,espec- ially to severe impact-loaded abrasion has been de- veloped with a new...A new category of steel with excellent combi- nation of strength,toughness,strain-hardening ability and excellent resistance to high-stress,espec- ially to severe impact-loaded abrasion has been de- veloped with a new idea of abrasion-resistant ma- terial design.The steels have the microstructures of austenite film and bainitic ferrite laths in arrange- ment of extremely fine lath spacing and are chemically high-carbon low alloy ones.The effects of austempering temperatures on microstructures, mechanical properties,wear-resistance and behaviour of the austenite-bainite steels in impact-abrasion system have been emphatically studied.展开更多
The fine microstructures of medium and medium-high carbon bainitic steels were observed and analyzed by high resolution electron microscope(HREM).The investigation results show that there are retained austenitic films...The fine microstructures of medium and medium-high carbon bainitic steels were observed and analyzed by high resolution electron microscope(HREM).The investigation results show that there are retained austenitic films with different appearances and sizes in bainitic ferrite laths.The boundaries of different structure levels are separated and encircled by retained austenitic films.The fine structure units and their sizes of different structure levels in the bainitic ferrite were determined by retained austenitic films.The bainitic ferrite laths are composed of different structure level sublaths,subunits and elementary units(or so called sub-subunits).The dimensions of most sublaths,subunits and elementary units are 25-80 nm,25-80 nm and 5.0-30 nm,respectively.展开更多
The effects of bainitic treatment on microstructure and mechanical properties of 0.10C-1.5Mn-l.5Al TRIP-aided cold-rolled steels have been investigated.The samples were heated by intercritical annealing at 820℃for 2 ...The effects of bainitic treatment on microstructure and mechanical properties of 0.10C-1.5Mn-l.5Al TRIP-aided cold-rolled steels have been investigated.The samples were heated by intercritical annealing at 820℃for 2 min and quenched in banitic temperature with different hoding time for 5 to 300s,two salt bath were used for the heat treatment.Experimental results show that the yield strength and elongation increase with the increasing of bainitic holding time,while the tensile strength decrease.The volume fraction of retained austenite rise at the beginning of bainitic holding and then reduce,the carbon content of retained austenite increase during the bainitic holding.The tensile strengthen multiply elongation reaches the highest value at 120s.The mechanical stability of retained austenite fits well with strain hardening during deformation.展开更多
Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and martensite exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/...Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and martensite exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/VHCF)regimes.The subsurface microstructural fatigue crack initiation,referred to as“non-inclusion induced crack initiation,NIICI”,is a leading mode of failure of bainitic steels within the HCF/VHCF regimes.In this regard,there is currently a missing gap in the knowledge with respect to the cyclic response of multiphase structure during VHCF failure and the underlying mechanisms of fatigue crack initiation during VHCF.To address this aspect,we have developed a novel approach that explicitly identifies the knowledge gap through an examination of subsurface crack initiation and interaction with the local microstructure.This was accomplished by uniquely combining electron microscopy,three-dimensional confocal microscopy,focused ion beam,and transmission Kikuchi diffraction.Interestingly,the study indicated that there are multiple micro-mechanisms responsible for the NIICI failure of bainitic steels,including two scenarios of transgranular-crack-assisted NIICI and two scenarios of intergranular-crack-assisted NIICI,which resulted in the different distribution of fine grains in the crack initiation area.The fine grains were formed through fragmentation of bainitic ferrite lath caused by localized plastic deformation or via local continuous dynamic recrystallization because of repeated interaction between slip bands and prior austenite grain boundaries.The formation of fine grains assisted the advancement of small cracks.Another important aspect discussed is the role of retained austenite(RA)during cyclic loading,on crack initiation and propagation in terms of the morphology,distribution and stability of RA,which determined the development of localized cyclic plastic deformation in multiphase structure.展开更多
文摘A new category of steel with excellent combi- nation of strength,toughness,strain-hardening ability and excellent resistance to high-stress,espec- ially to severe impact-loaded abrasion has been de- veloped with a new idea of abrasion-resistant ma- terial design.The steels have the microstructures of austenite film and bainitic ferrite laths in arrange- ment of extremely fine lath spacing and are chemically high-carbon low alloy ones.The effects of austempering temperatures on microstructures, mechanical properties,wear-resistance and behaviour of the austenite-bainite steels in impact-abrasion system have been emphatically studied.
基金Item Sponsored by National Natural Science Foundation of China(59971027)
文摘The fine microstructures of medium and medium-high carbon bainitic steels were observed and analyzed by high resolution electron microscope(HREM).The investigation results show that there are retained austenitic films with different appearances and sizes in bainitic ferrite laths.The boundaries of different structure levels are separated and encircled by retained austenitic films.The fine structure units and their sizes of different structure levels in the bainitic ferrite were determined by retained austenitic films.The bainitic ferrite laths are composed of different structure level sublaths,subunits and elementary units(or so called sub-subunits).The dimensions of most sublaths,subunits and elementary units are 25-80 nm,25-80 nm and 5.0-30 nm,respectively.
文摘The effects of bainitic treatment on microstructure and mechanical properties of 0.10C-1.5Mn-l.5Al TRIP-aided cold-rolled steels have been investigated.The samples were heated by intercritical annealing at 820℃for 2 min and quenched in banitic temperature with different hoding time for 5 to 300s,two salt bath were used for the heat treatment.Experimental results show that the yield strength and elongation increase with the increasing of bainitic holding time,while the tensile strength decrease.The volume fraction of retained austenite rise at the beginning of bainitic holding and then reduce,the carbon content of retained austenite increase during the bainitic holding.The tensile strengthen multiply elongation reaches the highest value at 120s.The mechanical stability of retained austenite fits well with strain hardening during deformation.
基金the funding by National Key Technologies Research and Development Program of China(2017YFB0304500)the support from National Natural Science Foundation of China(No.51771014)Joint Funds of National Natural Science Foundation of China(No.U1834202)。
文摘Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and martensite exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/VHCF)regimes.The subsurface microstructural fatigue crack initiation,referred to as“non-inclusion induced crack initiation,NIICI”,is a leading mode of failure of bainitic steels within the HCF/VHCF regimes.In this regard,there is currently a missing gap in the knowledge with respect to the cyclic response of multiphase structure during VHCF failure and the underlying mechanisms of fatigue crack initiation during VHCF.To address this aspect,we have developed a novel approach that explicitly identifies the knowledge gap through an examination of subsurface crack initiation and interaction with the local microstructure.This was accomplished by uniquely combining electron microscopy,three-dimensional confocal microscopy,focused ion beam,and transmission Kikuchi diffraction.Interestingly,the study indicated that there are multiple micro-mechanisms responsible for the NIICI failure of bainitic steels,including two scenarios of transgranular-crack-assisted NIICI and two scenarios of intergranular-crack-assisted NIICI,which resulted in the different distribution of fine grains in the crack initiation area.The fine grains were formed through fragmentation of bainitic ferrite lath caused by localized plastic deformation or via local continuous dynamic recrystallization because of repeated interaction between slip bands and prior austenite grain boundaries.The formation of fine grains assisted the advancement of small cracks.Another important aspect discussed is the role of retained austenite(RA)during cyclic loading,on crack initiation and propagation in terms of the morphology,distribution and stability of RA,which determined the development of localized cyclic plastic deformation in multiphase structure.
