Here we present a novel approach of intercritical heat treatment for microstructure tailoring,in which intercritical annealing is introduced between conventional quenching and tempering.This induced a heterogeneous mi...Here we present a novel approach of intercritical heat treatment for microstructure tailoring,in which intercritical annealing is introduced between conventional quenching and tempering.This induced a heterogeneous microstructure consisting of soft intercritical ferrite and hard tempered martensite,resulting in a low yield ratio(YR)and high impact toughness in a high-strength low-alloy steel.The initial yielding and subsequent work hardening behavior of the steel during tensile deformation were modified by the presence of soft intercritical ferrite after intercritical annealing,in comparison to the steel with full martensitic microstructure.The increase in YR was related to the reduction in hardness difference between the soft and hard phases due to the precipitation of nano-carbides and the recovery of dislocations during tempering.The excellent low-temperature toughness was ascribed not only to the decrease in probability of microcrack initiation for the reduction of hardness difference between two phases,but also to the increase in resistance of microcrack propagation caused by the high density of high angle grain boundaries.展开更多
High strength low alloy（HSLA） steels have been widely used in pipelines,power plant components,civil structures and so on,due to their outstanding mechanical properties as high strength and toughness,and excellent w...High strength low alloy（HSLA） steels have been widely used in pipelines,power plant components,civil structures and so on,due to their outstanding mechanical properties as high strength and toughness,and excellent weldability.Multi-phase microstructures containing acicular ferrite or acicular ferrite dominated phase have been proved to possess good comprehensive properties in HSLA steels.This paper mainly focuses on the formation mechanisms and control methods of acicular ferrite in HSLA steels.Effect of austenitizing conditions,continuous cooling rate,and isothermal quenching time and temperature on acicular ferrite transformation was reviewed.Furthermore,the modified process to control the formation of multi-phase microstructures containing acicular ferrite,as intercritical heat treatments,step quenching treatments and thermo-mechanical controlled processing,was summarized.The favorable combination of mechanical properties can be achieved by these modified treatments.展开更多
基金This work was financially supported by the National Key Research and Development Program of China(No.2017YFB 0304800)One of the authors,H.Guo,would like to express her gratitude for the financial support of China Scholarship Council(award for one year visiting at Northwestern University in the USA,No.201706465056).
文摘Here we present a novel approach of intercritical heat treatment for microstructure tailoring,in which intercritical annealing is introduced between conventional quenching and tempering.This induced a heterogeneous microstructure consisting of soft intercritical ferrite and hard tempered martensite,resulting in a low yield ratio(YR)and high impact toughness in a high-strength low-alloy steel.The initial yielding and subsequent work hardening behavior of the steel during tensile deformation were modified by the presence of soft intercritical ferrite after intercritical annealing,in comparison to the steel with full martensitic microstructure.The increase in YR was related to the reduction in hardness difference between the soft and hard phases due to the precipitation of nano-carbides and the recovery of dislocations during tempering.The excellent low-temperature toughness was ascribed not only to the decrease in probability of microcrack initiation for the reduction of hardness difference between two phases,but also to the increase in resistance of microcrack propagation caused by the high density of high angle grain boundaries.
基金the China National Funds for Distinguished Young Scientists (Grant No.51325401)the National Magnetic Confinement Fusion Energy Research Project (Grant No.2015GB119001)the National Natural Science Foundation of China (Grant Nos.51501126,51474156 and U1660201) for grant and financial support
文摘High strength low alloy（HSLA） steels have been widely used in pipelines,power plant components,civil structures and so on,due to their outstanding mechanical properties as high strength and toughness,and excellent weldability.Multi-phase microstructures containing acicular ferrite or acicular ferrite dominated phase have been proved to possess good comprehensive properties in HSLA steels.This paper mainly focuses on the formation mechanisms and control methods of acicular ferrite in HSLA steels.Effect of austenitizing conditions,continuous cooling rate,and isothermal quenching time and temperature on acicular ferrite transformation was reviewed.Furthermore,the modified process to control the formation of multi-phase microstructures containing acicular ferrite,as intercritical heat treatments,step quenching treatments and thermo-mechanical controlled processing,was summarized.The favorable combination of mechanical properties can be achieved by these modified treatments.
