Martensite microstructure,which is compatible to multiple strengthening mechanisms,is the ideal matrix for high-strength steel seeking ultimate strength and ductility.Traditional martensite is of lath or lenticular shape,but as for additive manufacturing(AM)high-strength steel,its ultra-high cooling rate,cyclic heat input and scanning mode makes the microstructure highly non-equilibrated.The massive energy input leads to cellular structure,alloy-ing elements segregation,dislocation piling-up and prior austenite distinct from conventional high-strength steel.Such differences from traditional subtractive processing bring new challenges to performance control and microstruc-ture design of AM high-strength steel.Conventional post-processing methods fit poorly with AM high-strength steel,and there is an urgent need for more appropriate microstructure and processing deign based on microstructural characteristics of AM steel.A brief analysis concerning current development of metal AM techniques and trade-off between strength and ductility were made,along with a summary on the multiphase,metastable,and multiscale char-acteristics of martensite structure in AM high-strength steel compared to traditional martensite laths.Starting from the two transformation stages involved in metal additive processing(i.e.solidification and martensite transforma-tion),the differences from the processing characteristics like high cooling rate and cyclic energy input were explained,as well as microstructure characteristics such as composition gradient and dislocation distribution.Additionally,plau-sible methods for microstructural design and modification of AM high-strength steel including chemical processing and optimization were concluded,and current research progress and heated directions in AM high-strength steel were inducted,which may provide guidance for the promotion of AM martensitic high-strength steel in a foreseeable future.
metal additive manufacturingadvanced high-strength steelmartensitic transformationmicrostructure designmechanical performance modification
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