The resistance spot weldability of galvanized ultra-high-strength steels is not satisfed,the joints are prone to interfacial fracture and the weldable current range is narrow.To solve the problems,a novel method calle...The resistance spot weldability of galvanized ultra-high-strength steels is not satisfed,the joints are prone to interfacial fracture and the weldable current range is narrow.To solve the problems,a novel method called resistance spot welding with double-sided cover sheets was introduced to weld a galvanized Q&P980 steel with the thickness of 1.2 mm.Two thin SPCC mild steel sheets were chosen as cover sheets and were placed symmetrically at both sides between the Q&P980 steels and the electrodes,then the RSW process was carried out.Compared with the traditional RSW method,the joints obtained by using the novel method achieved larger tensile shear strength and energy absorption,which increased by 26.9%and 52.6%,respectively.With increasing the welding current,the failure mode transferred from interfacial fracture to nugget pull-out fracture or base metal tearing fracture.By contrast,the joints always showed interfacial fracture without cover sheets.The improvement of the joint performance was mainly attributed to the enlargement of the nugget.With the help of fnite element simulation,it was found that the cover sheets helped increase the contact area and reduced the current density during welding,which postponed the expulsion,and a larger area could be evenly heated.The application of the novel method can be easily extended to the resistance spot welding of other ultra-high-strength steels with various thicknesses.展开更多
Ballistic impact response of resistance-spot-welded(RSW)double-layered(2×1.6 mm)plates(190 mm×150 mm)for Q&P980 steel impacted by a round-nosed steel bullet(12 mm diameter and 30 mm length)was investigat...Ballistic impact response of resistance-spot-welded(RSW)double-layered(2×1.6 mm)plates(190 mm×150 mm)for Q&P980 steel impacted by a round-nosed steel bullet(12 mm diameter and 30 mm length)was investigated by using gas gun and high-speed camera system.The RSW specimens were spot welded using a 6 mm diameter electrode face producing a 7.2 mm diameter fusion zone of the spot weld.The ballistic curve and energy balance for the tests of the spot weld of the RSW specimens at different velocity were analyzed to characterize the ballistic behavior of the RSW specimens under bullet impact.The fracture mechanisms of the RSW specimens under bullet impact were presented.For the tests below the ballistic limit,the cracks initiated from the notch-tip and propagated along the faying surface or obliquely through the thickness depending on the impact velocity.For the tests above the ballistic limit,the plug fracture in the front plate of the RSW specimen could be caused by the thinning-induced necking in the BM near the HAZ,while the plug fracture in the rear plate of the RSW specimens may be consist of the circumferential cracking from the rear surface and the bending fracture of the hinged part of material.The effects of the electrode indentation and the weld interfaces on deformation and fracture of the RSW specimens under bullet impact were revealed.For the tests above the ballistic limit,the circumferential fracture from the rear surface of the RSW specimens was always initiated along the interior periphery of the electrode indentation and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.When the circumferential crack also formed outside the electrode indentation,the fracture on the BM/HAZ interface could be found.On the front plate of the RSW specimens,the shear/bending induced cracking from the notch-tip were observed and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.展开更多
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
采用摆动电弧窄间隙GMAW方法对42 mm厚的10Ni5Cr Mo V钢进行了焊接,并对其接头形貌、显微组织、硬度分布、拉伸性能和冲击韧性进行了测试分析。结果表明,该方法得到了成形良好、无任何宏观缺陷的窄间隙焊缝;焊缝组织由针状铁素体和粒状...采用摆动电弧窄间隙GMAW方法对42 mm厚的10Ni5Cr Mo V钢进行了焊接,并对其接头形貌、显微组织、硬度分布、拉伸性能和冲击韧性进行了测试分析。结果表明,该方法得到了成形良好、无任何宏观缺陷的窄间隙焊缝;焊缝组织由针状铁素体和粒状贝氏体及少部分马氏体组成;热影响区中的过热区以粗大的板条状马氏体组成,是整个焊接接头最薄弱区域,但其宽度较窄;窄间隙焊接接头具有较好的强度和韧性,无软化及脆化现象,满足使用要求。展开更多
980 high-strength steel has been widely used in marine engineering structures due to its high strength and toughness.However,it is easily affected by the harsh environmental conditions(such as the presence of sulfate-...980 high-strength steel has been widely used in marine engineering structures due to its high strength and toughness.However,it is easily affected by the harsh environmental conditions(such as the presence of sulfate-reducing bacteria,SRB),leading to the risk of stress corrosion cracking(SCC).In this paper,the effects of SRB and its metabolites on hydrogen permeation and SCC mechanism of 980 steel in seawater solution were investigated by slow strain rate tensile test,scanning electron microscope,Xray energy spectroscopy,Raman spectroscopy and Devanathan-Stachurski double electrolytic cell.Results demonstrated that the SCC susceptibility of 980 steel was promoted in the presence of SRB,which was related to the cultivation time of the bacteria.When SRB were cultivated for 3 d and 6 d,the SCC mechanism was controlled by hydrogen-induced cracking(HIC);while the cultivation time extended to 11 d,the SCC of 980 steel was under the combined effect of the anodic dissolution(AD) and HIC mechanism.When cultivated for 16 d,the SCC of 980 steel was caused by the dominant AD.Both the SRB accelerated hydrogen permeation under cathodic depolarization process and SRB assisted AD(pitting corrosion)played an enhancing role in promoting SCC susceptibility of 980 steel.展开更多
基金Supported by National Key Research and Development Program of China(Grant No.2017YFB0304403)National Natural Science Foundation of China(Grant No.51871154).
文摘The resistance spot weldability of galvanized ultra-high-strength steels is not satisfed,the joints are prone to interfacial fracture and the weldable current range is narrow.To solve the problems,a novel method called resistance spot welding with double-sided cover sheets was introduced to weld a galvanized Q&P980 steel with the thickness of 1.2 mm.Two thin SPCC mild steel sheets were chosen as cover sheets and were placed symmetrically at both sides between the Q&P980 steels and the electrodes,then the RSW process was carried out.Compared with the traditional RSW method,the joints obtained by using the novel method achieved larger tensile shear strength and energy absorption,which increased by 26.9%and 52.6%,respectively.With increasing the welding current,the failure mode transferred from interfacial fracture to nugget pull-out fracture or base metal tearing fracture.By contrast,the joints always showed interfacial fracture without cover sheets.The improvement of the joint performance was mainly attributed to the enlargement of the nugget.With the help of fnite element simulation,it was found that the cover sheets helped increase the contact area and reduced the current density during welding,which postponed the expulsion,and a larger area could be evenly heated.The application of the novel method can be easily extended to the resistance spot welding of other ultra-high-strength steels with various thicknesses.
基金supported by the National Natural Science Foundation of China,China under the grant No.11372149K.C.Wong Magna Fund in Ningbo University。
文摘Ballistic impact response of resistance-spot-welded(RSW)double-layered(2×1.6 mm)plates(190 mm×150 mm)for Q&P980 steel impacted by a round-nosed steel bullet(12 mm diameter and 30 mm length)was investigated by using gas gun and high-speed camera system.The RSW specimens were spot welded using a 6 mm diameter electrode face producing a 7.2 mm diameter fusion zone of the spot weld.The ballistic curve and energy balance for the tests of the spot weld of the RSW specimens at different velocity were analyzed to characterize the ballistic behavior of the RSW specimens under bullet impact.The fracture mechanisms of the RSW specimens under bullet impact were presented.For the tests below the ballistic limit,the cracks initiated from the notch-tip and propagated along the faying surface or obliquely through the thickness depending on the impact velocity.For the tests above the ballistic limit,the plug fracture in the front plate of the RSW specimen could be caused by the thinning-induced necking in the BM near the HAZ,while the plug fracture in the rear plate of the RSW specimens may be consist of the circumferential cracking from the rear surface and the bending fracture of the hinged part of material.The effects of the electrode indentation and the weld interfaces on deformation and fracture of the RSW specimens under bullet impact were revealed.For the tests above the ballistic limit,the circumferential fracture from the rear surface of the RSW specimens was always initiated along the interior periphery of the electrode indentation and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.When the circumferential crack also formed outside the electrode indentation,the fracture on the BM/HAZ interface could be found.On the front plate of the RSW specimens,the shear/bending induced cracking from the notch-tip were observed and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.
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.
文摘采用摆动电弧窄间隙GMAW方法对42 mm厚的10Ni5Cr Mo V钢进行了焊接,并对其接头形貌、显微组织、硬度分布、拉伸性能和冲击韧性进行了测试分析。结果表明,该方法得到了成形良好、无任何宏观缺陷的窄间隙焊缝;焊缝组织由针状铁素体和粒状贝氏体及少部分马氏体组成;热影响区中的过热区以粗大的板条状马氏体组成,是整个焊接接头最薄弱区域,但其宽度较窄;窄间隙焊接接头具有较好的强度和韧性,无软化及脆化现象,满足使用要求。
基金supported by the National Natural Science Foundation of China (Nos. 51871204 and U1706221)。
文摘980 high-strength steel has been widely used in marine engineering structures due to its high strength and toughness.However,it is easily affected by the harsh environmental conditions(such as the presence of sulfate-reducing bacteria,SRB),leading to the risk of stress corrosion cracking(SCC).In this paper,the effects of SRB and its metabolites on hydrogen permeation and SCC mechanism of 980 steel in seawater solution were investigated by slow strain rate tensile test,scanning electron microscope,Xray energy spectroscopy,Raman spectroscopy and Devanathan-Stachurski double electrolytic cell.Results demonstrated that the SCC susceptibility of 980 steel was promoted in the presence of SRB,which was related to the cultivation time of the bacteria.When SRB were cultivated for 3 d and 6 d,the SCC mechanism was controlled by hydrogen-induced cracking(HIC);while the cultivation time extended to 11 d,the SCC of 980 steel was under the combined effect of the anodic dissolution(AD) and HIC mechanism.When cultivated for 16 d,the SCC of 980 steel was caused by the dominant AD.Both the SRB accelerated hydrogen permeation under cathodic depolarization process and SRB assisted AD(pitting corrosion)played an enhancing role in promoting SCC susceptibility of 980 steel.
