A Study of Microstructure and Mechanical Properties for the Autogenous Single-Pass Butt Weldment of a Ferritic/Martensitic Steel Using Gas Tungsten Arc Welding
来源期刊：Acta Metallurgica Sinica2021年第5期
论文作者：Dong Wu Shitong Wei Shanping Lu
文章页码：628 - 638
摘 要：A 12%Cr ferritic/martensitic steel,HT-9,has been used as a primary core material for nuclear reactors.The microstructure and mechanical properties of gas tungsten arc butt welded joints of HT-9 in as-welded,and as-tempered conditions have been explored.In as-welded condition,the fusion zone （FZ） contained a fresh martensite matrix with delta （δ）-ferrite.Theδ-ferrite was rich in Cr and depleted in C compared with the matrix.The heat-aff ected zone （HAZ） could be divided into three areas as the distance from the fusion line increased:δ-ferrite/martensite duplex zone,fully recrystallized zone,and partly recrystallized zone.Prior austenitic grains did not coarsen in theδ-ferrite/martensite duplex zone due to the newly nucleatedδ-ferrite grains and incompletely ferritizing （δ-ferrite） during the welding thermal cycle.The weldment microhardness distributed heterogeneously with values above 600 HV 1.0 in the HAZ and FZ and 250 HV 1.0 in the base metal （BM）.Solute C in the matrix,induced by the dissolution of carbide during the welding process,dominated the microhardness variation.Low toughness was observed in the FZ with a quasi-cleavage fracture tested from-80 to 20℃.The tensile fracture occurred in the relatively soft BM tested from 20 to 600℃.In as-tempered condition （760℃ for 1 h）,M 23 C 6-type carbides precipitated within the martensitic laths,the lath boundaries,and theδ-ferrite/martensite interfaces.Moreover,V,Cr,Mo-rich nitrides with very small size also precipitated in theδ-ferrite/martensite interface.The tempering treatment improved the homogenous distribution of weldment hardness significantly.Tensile fracture still occurred in the BM of the weldment specimens tested from 20 to 600℃.The impact toughness improved significantly,but the ductile–brittle transaction temperature was-12℃ which was higher than that of the normalized and tempered （N&T） BM.δ-ferrite was considered to be one of the major factors aggravating the impact toughness in the FZ.
Dong Wu1，Shitong Wei1，Shanping Lu2
1. CAS Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research,Chinese Academy of Sciences2. Shenyang National Laboratory for Materials Science, Institute of Metal Research,Chinese Academy of Sciences
摘 要：A 12%Cr ferritic/martensitic steel,HT-9,has been used as a primary core material for nuclear reactors.The microstructure and mechanical properties of gas tungsten arc butt welded joints of HT-9 in as-welded,and as-tempered conditions have been explored.In as-welded condition,the fusion zone （FZ） contained a fresh martensite matrix with delta （δ）-ferrite.Theδ-ferrite was rich in Cr and depleted in C compared with the matrix.The heat-aff ected zone （HAZ） could be divided into three areas as the distance from the fusion line increased:δ-ferrite/martensite duplex zone,fully recrystallized zone,and partly recrystallized zone.Prior austenitic grains did not coarsen in theδ-ferrite/martensite duplex zone due to the newly nucleatedδ-ferrite grains and incompletely ferritizing （δ-ferrite） during the welding thermal cycle.The weldment microhardness distributed heterogeneously with values above 600 HV 1.0 in the HAZ and FZ and 250 HV 1.0 in the base metal （BM）.Solute C in the matrix,induced by the dissolution of carbide during the welding process,dominated the microhardness variation.Low toughness was observed in the FZ with a quasi-cleavage fracture tested from-80 to 20℃.The tensile fracture occurred in the relatively soft BM tested from 20 to 600℃.In as-tempered condition （760℃ for 1 h）,M 23 C 6-type carbides precipitated within the martensitic laths,the lath boundaries,and theδ-ferrite/martensite interfaces.Moreover,V,Cr,Mo-rich nitrides with very small size also precipitated in theδ-ferrite/martensite interface.The tempering treatment improved the homogenous distribution of weldment hardness significantly.Tensile fracture still occurred in the BM of the weldment specimens tested from 20 to 600℃.The impact toughness improved significantly,but the ductile–brittle transaction temperature was-12℃ which was higher than that of the normalized and tempered （N&T） BM.δ-ferrite was considered to be one of the major factors aggravating the impact toughness in the FZ.
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