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
The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by ...The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by employing different thermomechanical processes and then carefully characterized.Their relation to yield strength and impact toughness was analyzed.We conclude that the refinement of martensitic structures could lead to the significant increase of yield strength,which follows the Hall-Petch relation with the effect grain size defined by high angle boundaries(HABs).Impact toughness of UHSSS depends on the frequency and capability for retained austenite(RA)grains at both HABs and martensite lath boundaries to trap the propagating cracks via strain-induced transformation,in which the film-like RA grains at lath boundaries appear to make the greater contribution.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 support from the National Key Research and Development Program of China(2016YFB0300202 and 2016YFB0300102)the Fundamental Research Funds for the Central Universities(No.FRF-TP-18-002C2)。
文摘The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by employing different thermomechanical processes and then carefully characterized.Their relation to yield strength and impact toughness was analyzed.We conclude that the refinement of martensitic structures could lead to the significant increase of yield strength,which follows the Hall-Petch relation with the effect grain size defined by high angle boundaries(HABs).Impact toughness of UHSSS depends on the frequency and capability for retained austenite(RA)grains at both HABs and martensite lath boundaries to trap the propagating cracks via strain-induced transformation,in which the film-like RA grains at lath boundaries appear to make the greater contribution.
