The QP980-DP980 dissimilar steel joints were fabricated by fiber laser welding.The weld zone(WZ)was fully martensitic structure,and heat-affected zone(HAZ)contained newly-formed martensite and partially tempered marte...The QP980-DP980 dissimilar steel joints were fabricated by fiber laser welding.The weld zone(WZ)was fully martensitic structure,and heat-affected zone(HAZ)contained newly-formed martensite and partially tempered martensite(TM)in both steels.The supercritical HAZ of the QP980 side had higher microhardness(~549.5 Hv)than that of the WZ due to the finer martensite.A softened zone was present in HAZ of QP980 and DP980,the dropped microhardness of softened zone of the QP980 and DP980 wasΔ21.8 Hv andΔ40.9 Hv,respectively.Dislocation walls and slip bands were likely formed at the grain boundaries with the increase of strain,leading to the formation of low angle grain boundaries(LAGBs).Dislocation accumulation more easily occurred in the LAGBs than that of the HAGBs,which led to significant dislocation interaction and formation of cracks.The electron back-scattered diffraction(EBSD)results showed the fraction of LAGBs in sub-critical HAZ of DP980 side was the highest under different deformation conditions during tensile testing,resulting in the failure of joints located at the sub-critical HAZ of DP980 side.The QP980-DP980 dissimilar steel joints presented higher elongation(~11.21%)and ultimate tensile strength(~1011.53 MPa)than that of DP980-DP980 similar steel joints,because during the tensile process of the QP980-DP980 dissimilar steel joint(~8.2%and 991.38 MPa),the strain concentration firstly occurred on the excellent QP980 BM.Moreover,Erichsen cupping tests showed that the dissimilar welded joints had the lowest Erichsen value(~5.92 mm)and the peak punch force(~28.4 kN)due to the presence of large amount of brittle martensite in WZ and inhomogeneous deformation.展开更多
The abrasive wear resistance of dual phase （DP） steels DP980 and DP600 was investigated by using an ASTM rubber wheel abrasion tester. At 2.40 m ·s-1 sliding speed under 19.9 N load with 180--355μm abrasive sa...The abrasive wear resistance of dual phase （DP） steels DP980 and DP600 was investigated by using an ASTM rubber wheel abrasion tester. At 2.40 m ·s-1 sliding speed under 19.9 N load with 180--355μm abrasive sands, the wear rates of DP980 and DP600 were 1.01 × 10^-11 and 0.86 ×10^-11 m3 · m-1 , respectively, correspond- ing to about 1.9 and 2.3 times of the relative wear resistance of normal low-carbon steel ASTM A283C. Using di- rectly water quenching from austenitic temperature, the abrasive wear resistance of DP980 samples under 19.9 N load could be improved by 1.65 times. The wear rates of DP980 and DP600 samples decreased respectively with in- creasing sliding speed and abrasive particle size and decreasing applied load. The experimental results reveal that the effect of martensite on the wear resistance not only depends on the volume fraction but also depends on the morphol- ogy, distribution and grain size.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51871010,51875129)Beijing Municipal Natural Science Foundation of China(Grant No.32020163212008).
文摘The QP980-DP980 dissimilar steel joints were fabricated by fiber laser welding.The weld zone(WZ)was fully martensitic structure,and heat-affected zone(HAZ)contained newly-formed martensite and partially tempered martensite(TM)in both steels.The supercritical HAZ of the QP980 side had higher microhardness(~549.5 Hv)than that of the WZ due to the finer martensite.A softened zone was present in HAZ of QP980 and DP980,the dropped microhardness of softened zone of the QP980 and DP980 wasΔ21.8 Hv andΔ40.9 Hv,respectively.Dislocation walls and slip bands were likely formed at the grain boundaries with the increase of strain,leading to the formation of low angle grain boundaries(LAGBs).Dislocation accumulation more easily occurred in the LAGBs than that of the HAGBs,which led to significant dislocation interaction and formation of cracks.The electron back-scattered diffraction(EBSD)results showed the fraction of LAGBs in sub-critical HAZ of DP980 side was the highest under different deformation conditions during tensile testing,resulting in the failure of joints located at the sub-critical HAZ of DP980 side.The QP980-DP980 dissimilar steel joints presented higher elongation(~11.21%)and ultimate tensile strength(~1011.53 MPa)than that of DP980-DP980 similar steel joints,because during the tensile process of the QP980-DP980 dissimilar steel joint(~8.2%and 991.38 MPa),the strain concentration firstly occurred on the excellent QP980 BM.Moreover,Erichsen cupping tests showed that the dissimilar welded joints had the lowest Erichsen value(~5.92 mm)and the peak punch force(~28.4 kN)due to the presence of large amount of brittle martensite in WZ and inhomogeneous deformation.
基金Item Sponsored by Fundamental Research Funds for Central Universities of China(2013B18314)National Natural Science Foundation of China(51475140)+1 种基金Natural Science Foundation of Jiangsu Province(BK20141155)Tribology Science Fund of State Key Laboratory of Tribology of Tsinghua University(SKLTKF13B03)
文摘The abrasive wear resistance of dual phase （DP） steels DP980 and DP600 was investigated by using an ASTM rubber wheel abrasion tester. At 2.40 m ·s-1 sliding speed under 19.9 N load with 180--355μm abrasive sands, the wear rates of DP980 and DP600 were 1.01 × 10^-11 and 0.86 ×10^-11 m3 · m-1 , respectively, correspond- ing to about 1.9 and 2.3 times of the relative wear resistance of normal low-carbon steel ASTM A283C. Using di- rectly water quenching from austenitic temperature, the abrasive wear resistance of DP980 samples under 19.9 N load could be improved by 1.65 times. The wear rates of DP980 and DP600 samples decreased respectively with in- creasing sliding speed and abrasive particle size and decreasing applied load. The experimental results reveal that the effect of martensite on the wear resistance not only depends on the volume fraction but also depends on the morphol- ogy, distribution and grain size.
