In cold roll forming, steel pipes are welded with different technology parameters in order to improve the steel pipe＇s quality, thus we should optimize the technology parameters for producing steel pipes. By means of...In cold roll forming, steel pipes are welded with different technology parameters in order to improve the steel pipe＇s quality, thus we should optimize the technology parameters for producing steel pipes. By means of metallographic examination, scanning electron microscope examination, hardness test, impact test, bend test, tensile test and so on, the microstructure and mechanical properties of the steel pipes were investigated. The test results show that welding defects such as crack and blowholes are not found. The microstructure of the welded metal is Widmanstatten ; the microstructure of the heat affected zone is Widmanstatten, pearlite and proeutectoid ferrite, and the base metal is pearlite and ferrite. The highest of the metal Brinell hardness is in the weld seam, followed by the heat affected zone, and the lowest is in the base metal. The microstructure of the weld metal is coarse, which results in that the toughness of the weld is the lowest, but the hardness of the welds is the highest in the weld zone. The bend angles of the weld metal present a mountainous shape with the surface energy. Only when the surface energy is of the best value, the mechanical properties of the weld metal is the best.展开更多
For QSTE700 high-strength steel rectangular welded tube,the mechanical properties of the weld zone vary with the distancefrom the centerline of the weld.Therefore,the accurate description of constitutive relationship ...For QSTE700 high-strength steel rectangular welded tube,the mechanical properties of the weld zone vary with the distancefrom the centerline of the weld.Therefore,the accurate description of constitutive relationship of the weld zone is of greatsignificance for the study of formability of QSTE700 rectangular welded tube.Firstly,the mechanical properties of parentand mixed specimens containing weld zone and parent zone were obtained by uniaxial tensile test.And based on the micro-hardness test,the width and the microhardness distribution of the weld zone were determined.Secondly,by subdividingthe weld zone into several small areas,and combining with the rule of mixtures and nanoindentation test,the continuous functional relationships of strength coefficient K,hardening coeffecient n and elastic modulus E were obtained,and then,the continuous constitutive relationship of QSTE700 rectangular welded tube was established.Finally,the validity and reliability of the continuous constitutive relationship of welded tube were verified by nanoindentation fest and rotary drawbending of rectangular welded tubc.Besides,it was found that the finite element model of rotary draw bending of QSTE700 rectangular welded tube established by using the continuous constitutive relationship can well simulate the cross sectiondeformation and wall thickness variation.展开更多
文摘In cold roll forming, steel pipes are welded with different technology parameters in order to improve the steel pipe＇s quality, thus we should optimize the technology parameters for producing steel pipes. By means of metallographic examination, scanning electron microscope examination, hardness test, impact test, bend test, tensile test and so on, the microstructure and mechanical properties of the steel pipes were investigated. The test results show that welding defects such as crack and blowholes are not found. The microstructure of the welded metal is Widmanstatten ; the microstructure of the heat affected zone is Widmanstatten, pearlite and proeutectoid ferrite, and the base metal is pearlite and ferrite. The highest of the metal Brinell hardness is in the weld seam, followed by the heat affected zone, and the lowest is in the base metal. The microstructure of the weld metal is coarse, which results in that the toughness of the weld is the lowest, but the hardness of the welds is the highest in the weld zone. The bend angles of the weld metal present a mountainous shape with the surface energy. Only when the surface energy is of the best value, the mechanical properties of the weld metal is the best.
基金The authors would like to thank the Science and Technology Plan Project of Shenzhen Science and Technology Innovation Committee(JCYJ20180306171058717)Natural Science Basis Research Plan in Shaanxi Province of China(2019JZ-03).
文摘For QSTE700 high-strength steel rectangular welded tube,the mechanical properties of the weld zone vary with the distancefrom the centerline of the weld.Therefore,the accurate description of constitutive relationship of the weld zone is of greatsignificance for the study of formability of QSTE700 rectangular welded tube.Firstly,the mechanical properties of parentand mixed specimens containing weld zone and parent zone were obtained by uniaxial tensile test.And based on the micro-hardness test,the width and the microhardness distribution of the weld zone were determined.Secondly,by subdividingthe weld zone into several small areas,and combining with the rule of mixtures and nanoindentation test,the continuous functional relationships of strength coefficient K,hardening coeffecient n and elastic modulus E were obtained,and then,the continuous constitutive relationship of QSTE700 rectangular welded tube was established.Finally,the validity and reliability of the continuous constitutive relationship of welded tube were verified by nanoindentation fest and rotary drawbending of rectangular welded tubc.Besides,it was found that the finite element model of rotary draw bending of QSTE700 rectangular welded tube established by using the continuous constitutive relationship can well simulate the cross sectiondeformation and wall thickness variation.
