There are few relevant researches on coils by tempering,and the variations of microstructure and properties of steel coil during the tempering process also remain unclear.By using thermo-mechanical control process（T...There are few relevant researches on coils by tempering,and the variations of microstructure and properties of steel coil during the tempering process also remain unclear.By using thermo-mechanical control process（TMCP）technology,Mn-Ti typical HSLA steel coils with yield strength of 920 MPa are produced on the 2250 hot rolling production line.Then,the samples are taken from the coils and tempered at the temperatures of 220℃,350℃,and 620℃respectively.After tempering the strength,ductility and toughness of samples are tested,and meanwhile microstructures are investigated.Precipitates initially emerge inside the ferrite laths and the density of the dislocation drops.Then,the lath-shaped ferrites begin to gather,and the retained austenite films start to decompose.Finally,the retained austenite films are completely decomposed into coarse and short rod-shape precipitates composed of C and Ti compounds.The yield strength increases with increasing tempering temperature due to the pinning effect of the precipitates,and the dislocation density decreases.The yield strength is highest when the steel is tempered at 220℃because of pinning of the precipitates to dislocations.The total elongation increases in all samples because of the development of ferrites during tempering.The tensile strength and impact absorbed energy decline because the effect of impeding crack propagation weakens as the retained austenite films completely decompose and the precipitates coarsen.This paper clarifies the influence of different tempering temperatures on phase transformation characteristics and process of Mn-Ti typical multiphase steels,as well as its resulting performance variation rules.展开更多
Microstructural evolution,precipitation behavior,and tensile properties of four experimental Mo-bearing steels were studied to elucidate the effects of Nb and V on microstructural properties.The results indicated that...Microstructural evolution,precipitation behavior,and tensile properties of four experimental Mo-bearing steels were studied to elucidate the effects of Nb and V on microstructural properties.The results indicated that the microstructure of hot-rolled steels consisted of polygonal ferrite and degenerate pearlite,and the morphology remained same after holding at 600 ℃for 1h.The smallest grain size was obtained in Nb-V-Mo containing steel,followed by Nb-Mo and V-Mo steels.Precipitation was less in the hot-rolled Mo-bearing steel.The maximum volume fraction of precipitates was obtained in Nb-V-Mo bearing steel,and the Nb-V-Mo complex carbonitrides were highly stable at 600℃.In the Mo-bearing steel,the yield ratio was lowest at room temperature but highest at 600℃,which was attributed to the precipitation of Mo carbides and drag effect of Mo solute on dislocation movement.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51201154)
文摘There are few relevant researches on coils by tempering,and the variations of microstructure and properties of steel coil during the tempering process also remain unclear.By using thermo-mechanical control process（TMCP）technology,Mn-Ti typical HSLA steel coils with yield strength of 920 MPa are produced on the 2250 hot rolling production line.Then,the samples are taken from the coils and tempered at the temperatures of 220℃,350℃,and 620℃respectively.After tempering the strength,ductility and toughness of samples are tested,and meanwhile microstructures are investigated.Precipitates initially emerge inside the ferrite laths and the density of the dislocation drops.Then,the lath-shaped ferrites begin to gather,and the retained austenite films start to decompose.Finally,the retained austenite films are completely decomposed into coarse and short rod-shape precipitates composed of C and Ti compounds.The yield strength increases with increasing tempering temperature due to the pinning effect of the precipitates,and the dislocation density decreases.The yield strength is highest when the steel is tempered at 220℃because of pinning of the precipitates to dislocations.The total elongation increases in all samples because of the development of ferrites during tempering.The tensile strength and impact absorbed energy decline because the effect of impeding crack propagation weakens as the retained austenite films completely decompose and the precipitates coarsen.This paper clarifies the influence of different tempering temperatures on phase transformation characteristics and process of Mn-Ti typical multiphase steels,as well as its resulting performance variation rules.
基金Item Sponsored by National Key Technology Research and Development Program of the Ministry of Science and Technology of China(2012BAE04B01)Fundamental Research Funds for the Central Universities of China(N110402002,L1502045)
文摘Microstructural evolution,precipitation behavior,and tensile properties of four experimental Mo-bearing steels were studied to elucidate the effects of Nb and V on microstructural properties.The results indicated that the microstructure of hot-rolled steels consisted of polygonal ferrite and degenerate pearlite,and the morphology remained same after holding at 600 ℃for 1h.The smallest grain size was obtained in Nb-V-Mo containing steel,followed by Nb-Mo and V-Mo steels.Precipitation was less in the hot-rolled Mo-bearing steel.The maximum volume fraction of precipitates was obtained in Nb-V-Mo bearing steel,and the Nb-V-Mo complex carbonitrides were highly stable at 600℃.In the Mo-bearing steel,the yield ratio was lowest at room temperature but highest at 600℃,which was attributed to the precipitation of Mo carbides and drag effect of Mo solute on dislocation movement.
