The predictability of hardness of the heat affected zone (HAZ) in aluminum weldments cooled in palm oil, based on hardness of similarly cooled mild steel and cast iron weldments has been ascertained. The general mode...The predictability of hardness of the heat affected zone (HAZ) in aluminum weldments cooled in palm oil, based on hardness of similarly cooled mild steel and cast iron weldments has been ascertained. The general model: α = 1.2769? indicates that HAZ hardness of aluminium weldment is dependant on the ratio of product to sum of HAZ hardness of mild steel and cast iron weldments cooled in palm oil under the same conditions. The maximum deviations of the model-predicted HAZ hardness values α, μ and β from the corresponding experimental values αexp, μexp and βexp were less than 0.04% indicating the reliability and validity of the model.展开更多
The microstructure and the characteristics of the inclusions embedded in ferrite matrix in simulated coarse-grain heat affected zone (CGHAZ) of a Ti-Zr-treated high strength low alloy (HSLA) steel have been investigat...The microstructure and the characteristics of the inclusions embedded in ferrite matrix in simulated coarse-grain heat affected zone (CGHAZ) of a Ti-Zr-treated high strength low alloy (HSLA) steel have been investigated. The microstructure of the simulated CGHAZ dominantly consisted of intragranular acicular ferrite (IAF) combining with a small amount of polygonal ferrite (PF), widmanst tten ferrite (WF), bainite ferrite (BF), pearlite and martensite-austenite (M-A) islands. The PF, WF and BF were generally observed at the prior austenite grain boundaries and the interlocking acicular ferrite was usually found intragranularly. It was found that the inclusions were composed of Ti2O3, ZrO2, Al2O3 locating at the center of the particles and MnS lying on the surface layer of the inclusions. The intragranular complex inclusions promoted the acicular ferrite formation and the refinement of microstructure whilst those at prior austenite grain boundaries caused PF formation on the inclusions. The simulated CGHAZ consisting of such complicated microstructure exhibited desired mechanical properties.展开更多
Effects of Zirconium on the chemical component and size distribution of Ti-bearing inclusions, favored the grain refinement of the welding reduced, coarse-grained heat affected zone （CGHAZ） with enhanced impact toug...Effects of Zirconium on the chemical component and size distribution of Ti-bearing inclusions, favored the grain refinement of the welding reduced, coarse-grained heat affected zone （CGHAZ） with enhanced impact toughness in Ti-killed steels, which were examined based on experimental observations and thermodynamic calculations. It indicated that the chemical constituents of inclusions gradually varied from the TiO oxide to the Ti-O＋Zr-O compound oxide and a single phase of the ZrO2 oxide, as the Zr content increased from zero to 0.0100%. A trace of Zr （0.0030%-0.0080%, depending on the oxygen content in liquid steel） provided a large amount of nucleating core for Ti oxide because of the larger specific density of ZrO2 oxide, and produced a small size distribution of the inclusions favorable for acicular ferrite transformation with a high nucleation rate in the CGHAZ, and a high volume fraction of acicular ferrite was obtained in the CGHAZ, with enhanced impact toughness. Otherwise, a high content of Zr （-0.0100%） produced a single phase Zr02, which was impotent to nucleate acicular ferrite, and a microstructure composed of ferrite side plate and grain boundary ferrite developed in the CGHAZ. The experimental results were confirmed by thermodynamic calculations.展开更多
One of the main problems during the welding of ferritic stainless steels is severe grain growth within the heat-affected zone （HAZ） In the present study, the microstmctural characteristics of tungsten inert gas （TI...One of the main problems during the welding of ferritic stainless steels is severe grain growth within the heat-affected zone （HAZ） In the present study, the microstmctural characteristics of tungsten inert gas （TIG） welded AISI409 ferritic stainless steel were investigated by electron backscattered diffraction （EBSD）, and the effects of welding parameters on the grain size, local misorientation, and low-angle grain boundaries were studied. A 3-D finite element model （FEM） was developed to predict the effects of welding parameters on the holding time of the HAZ above the critical temperature of grain growth. It is found that the base metal is not fully recrystallized. During the welding, complete recrystallization is followed by severe grain growth. A decrease in the number of low-angle grain boundaries is observed within the HAZ. FEM results show that the final state of residual sWains is caused by competition between welding plastic strains and their release by recrystallization. Still, the decisive factor for grain growth is heat input.展开更多
The austenite grain growth behavior in a simulated coarse-grained heat-affected zone during thermal cycling was investigated via in situ observation. Austenite grains nucleated at ferrite grain boundaries and then gre...The austenite grain growth behavior in a simulated coarse-grained heat-affected zone during thermal cycling was investigated via in situ observation. Austenite grains nucleated at ferrite grain boundaries and then grew in different directions through movement of grain boundaries into the ferrite phase. Subsequently, the adjacent austenite grains impinged against each other during the α→γtransformation. After the α→γ transformation, austenite grains coarsened via the coalescence of small grains and via boundary migration between grains. The growth process of austenite grains was a continuous process during heating, isothermal holding, and cooling in simulated thermal cycling. Abundant finely dispersed nanoscale TiN particles in a steel specimen containing 0.012wt% Ti effectively retarded the grain boundary migration, which resulted in refined austenite grains. When the Ti concentration in the steel was increased, the number of TiN particles de- creased and their size coarsened. The big particles were not effective in pinning the austenite grain boundary movement and resulted in coarse austenite grains.展开更多
In the wire bonding process of microelectronic packaging,heat affect zone(HAZ)is an important factor governing the loop profile of bonding.The height of loop is affected by the length of the HAZ.Factors governing the ...In the wire bonding process of microelectronic packaging,heat affect zone(HAZ)is an important factor governing the loop profile of bonding.The height of loop is affected by the length of the HAZ.Factors governing the HAZ were studied.To investigate this relationship,experiments were done for various sizes of wire and free air ball(FAB).Electric flame-off(EFO)current, EFO time,EFO gap and recrystallization were also studied.The results show that as the size of FAB becomes larger,the length of HAZ increases.With the increase of EFO current and time,the length of HAZ becomes longer.When FAB forms at the same parameter the length of HAZ becomes shorter with the high temperature of recrystallization.展开更多
The simulated heat affected zone （HAZ） of the high strength low alloy （HSLA） steels containing 0%, 0.047%, 0.097% and 0.151% vanadium, respectively, were studied with Gleeble-2000 thermomechanical simulator to det...The simulated heat affected zone （HAZ） of the high strength low alloy （HSLA） steels containing 0%, 0.047%, 0.097% and 0.151% vanadium, respectively, were studied with Gleeble-2000 thermomechanical simulator to determine the influence of vanadium addition on the mechanical properties of the HAZ. The HAZ simulation involved reheating the samples to 1350℃, and then cooling to ambient temperature at a cooling rate of 5℃/s ranging from 800 to 500℃ （△8/5=60s）. The mechanical properties including tensile strength and -20℃ impact toughness were conducted. The microstructures of the base steel and the simulated HAZs were investigated using optical microscope, scanning electron microscope （ SEM ） and transmission electron microscope （TEM）. Based on the systemutic examination, the present work confirmed that about 0.05% vanadium addition to low carbon low alloy steels resulted in expected balance of strength and toughness of the HAZ. And more than 0.10% levels addition led to detrimental toughness of the HAZ SEM study showed that the simulated 0.097% and 0.151%V HAZs consisted of more coarse ferrite plates with greater and more M-A constituents along austenite grain and ferrite plate bound- aries. The impact fracture surfaces of the simulated 0.097% and 0.151%V HAZs showed typically brittle mode with predominant cleavages. The size of the facet in the fracture surface increased with increasing vanadium level from 0.097% to 0.151%.As a result, the simulated 0.151% V HAZ has the lowest impact toughness of the four specimens.展开更多
Microstructure and mechanical properties of the heat affected zone(HAZ)in multi-pass gas metal arc(GMA)welded Al Zn Mg Cu alloy plates were investigated,based upon which the mechanical anisotropy and fracture mechanis...Microstructure and mechanical properties of the heat affected zone(HAZ)in multi-pass gas metal arc(GMA)welded Al Zn Mg Cu alloy plates were investigated,based upon which the mechanical anisotropy and fracture mechanism were analyzed.The microstructure and composition were analyzed by scanning electron microscope(SEM)and energy dispersive spectroscope(EDS).X-ray diffractometer(XRD),transmission electron microscope(TEM)and selective area electron diffraction(SAED)were used to analyze the phase composition.The distribution of microhardness was identified as gradual transition and tensile strength had a tendency to decrease first and then increase.The distribution of nano-sizedη(MgZn2)particles in theα(Al)matrix and Al2MgCu phase determined the tensile performances along the thickness direction and led to the formation of ductile/brittle composite fracture in the HAZ.The continuous distribution of Al2MgCu phase in the strip intergranular precipitates gave birth to premature cracks and the brittle fracture region.The precipitated particles coarsening also led to the deterioration of mechanical properties.展开更多
Coarsening, embrittlement and corrosion sensitization in a high temperature heat-affected zone （HTHAZ） are the major problems when 12% chromium low carbon stainless steel is being welded, which induce the deteriorat...Coarsening, embrittlement and corrosion sensitization in a high temperature heat-affected zone （HTHAZ） are the major problems when 12% chromium low carbon stainless steel is being welded, which induce the deterioration of the impact toughness at a low temperature and intergranular corrosion resistance property. This study investigates the corresponding microstructures in HTHAZ with different chemical compositions and heat inputs through thermal simulation tests. The results show that the martensite content increases with the descending of ferrite factor （FF） when FF is below 9.0 and heat input influences the microstructure of high FF steel in HTHAZ. Martensite of 12% Cr stainless steel in HTHAZ with only Nb stabilization reticularly distributes at ferrite grain boundaries.展开更多
Excellent heat affected zone(HAZ)toughness technology improved by strong deoxidizers(ETISI)technology has been developed by Baosteel.In the deoxidation process of molten steel by adding strong deoxidizers,the formatio...Excellent heat affected zone(HAZ)toughness technology improved by strong deoxidizers(ETISI)technology has been developed by Baosteel.In the deoxidation process of molten steel by adding strong deoxidizers,the formation of micrometer inclusions and nano-meter precipitates in steel plates can be effectively controlled by a precise control of oxygen concentration.In the welding process with a high-heat input,the formation of acicular ferrite can be selectively promoted with the aid of the micrometer inclusions;the growth of γ grains can also be selectively restrained by the pinning effect of the nano-meter precipitates.After welding with a high-heat input of 400 kJ/cm,excellent HAZ toughness can be obtained in the steel plates with both of the above microstructures,and the average absorbed energy is greater than 200 J for the V-notch Charpy impact test at-20℃.展开更多
Quantitative research on the heat affected zone （ HAZ） o f weave bead welding （ WBW） joint fo r Invar alloy is carried out in this paper. Based on the morphology and related data analysis of the weld se...Quantitative research on the heat affected zone （ HAZ） o f weave bead welding （ WBW） joint fo r Invar alloy is carried out in this paper. Based on the morphology and related data analysis of the weld seam, the width difference o f each layer and the forming mechanism are analyzed. Results show that the bottom layer （ Layer 1 ） has the widest HAZ and the smallest fluctuation, which reaches 1 200 ｜jLm. HAZ width o f layer 2 to 5 is relatively narrower which is basically below 600 jjim, while the amplitude fluctuation is greater. The main reason lies in the welding path. The long straight welding without weave causes the base metal near the groove fully melts which causes by the long straight welding without weave, while welding with weave leads to the uneven and inadequate melting of metal near groove.展开更多
The mechanical properties and microstructure features of the fine-grained heat-affected zone（FGHAZ） of ASTM4130 steel was investigated by optical microscope（OM）,scanning electron microscope（SEM）,transmission ele...The mechanical properties and microstructure features of the fine-grained heat-affected zone（FGHAZ） of ASTM4130 steel was investigated by optical microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,and welding thermal simulation test.It is found that serious embrittlement occurs in the FGHAZ with an 81.37% decrease of toughness,compared with that of the base metal.Microstructure analysis reveals that the FGHAZ is mainly composed of acicular,equiaxed ferrite,granular ferrite,martensite,and martensite-austenite（M-A） constituent.The FGHAZ embrittlement is mainly induced by granular ferrite because of carbides located at its boundaries and sub-boundaries.Meanwhile,the existence of martensite and M-A constituent,which distribute in a discontinuous network,is also detrimental to the mechanical properties.展开更多
The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was investigated.It was found that the HAZ has intermediate temperature transformati...The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was investigated.It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates,with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling regime.At relatively high cooling rates,which corresponded to low heat inputs,the hardness of the simulated HAZ was above that of the base metal.When the cooling rate was below 9C/s,the welding HAZ would have an obvious softening.The analysis of transformation rates in continuous cooling processes was completed by numerical differential method.The result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.展开更多
Microstructure evolution and impact toughness of simulated heat affected zone（HAZ） in low carbon steel have been investigated in this study. Thermal simulator was used to simulate microstructure evolution in HAZ wit...Microstructure evolution and impact toughness of simulated heat affected zone（HAZ） in low carbon steel have been investigated in this study. Thermal simulator was used to simulate microstructure evolution in HAZ with heat input of 10-100 kJ/cm welding thermal cycle. Results indicated that microstructure of HAZ mainly consisted of acicular ferrite（AF） inside grain and high volume fraction of grain boundaries ferrite（GBF） at prior austenite boundaries; the size of GBF and effective grain size increased with increasing heat input. Excellent impact toughness（more than 150 J at-40 ℃） was obtained in HAZ with heat input less than 50 k J/cm. When heat input was 100 kJ/cm, the impact toughness of HAZ decreased to 18 J because of the presence of large M-A constituent with lath-form in HAZ, assisting the micro-crack initiation and decreasing the crack initiation energy seriously. Effect of inclusions on acicular ferrite transformation in HAZ was also discussed.展开更多
The high-strength low-alloy（ HSLA ） steel heat-affected zone （HAZ）softening was predicted using a grey model. HSLA steel DILLIMAX690E, NK-HITEN61OU2 and BHW35 were taken as examples in the research on ultra-narrow...The high-strength low-alloy（ HSLA ） steel heat-affected zone （HAZ）softening was predicted using a grey model. HSLA steel DILLIMAX690E, NK-HITEN61OU2 and BHW35 were taken as examples in the research on ultra-narrow gap automatic welding technology. Test results turned out to be that the errors between the values calculated by the Grey Model （GM） （ 1,1 ） model and their actual value were less than 2%, indicating that the grey prediction method could accurately reflect the actual situation of the high-strength low-alloy steel heat-affected zone softening. This method will play a crucial role in guiding the applications of HSLA steel welded structures in the future.展开更多
Based on welding thermal simulation on Nb-microaUoyed XSO pipeline stee! using Gleeble-3500 thermal simulation equipment, microstlttcture and impact toughness in coarse grain heat-affected zone （CGHAZ） under differe...Based on welding thermal simulation on Nb-microaUoyed XSO pipeline stee! using Gleeble-3500 thermal simulation equipment, microstlttcture and impact toughness in coarse grain heat-affected zone （CGHAZ） under different welding parameters were investigated in this paper. The results show that high heat inputs with low preheats or low heat inputs with high preheats should be applied to achieve high impact toughness. Coarse original austenite grains may lower impact toughness. CGHAZ microstructure is mostly composed of upper bainite, granular bainite and lath bainite. The phase composition of microstructure and the quantity, size, shape of M/A constituents both have effects on impact toughness.展开更多
Models have been derived for assessment and computational analysis of the hardness of the heat affected zone (HAZ) in aluminum weldment. The general model;γ = 1.2714[(αβ/α + β)] was found to predict the HAZ hardn...Models have been derived for assessment and computational analysis of the hardness of the heat affected zone (HAZ) in aluminum weldment. The general model;γ = 1.2714[(αβ/α + β)] was found to predict the HAZ hardness of aluminum weldment cooled in water as a function of the HAZ hardness of both mild steel and cast iron welded and cooled under the same conditions. The maximum deviations of the model-predicted HAZ hardness values γ, α and β from the corresponding experimental values γexp, αexp and βexp were less than 0.02% respectively.展开更多
Shielded Metal Arc Welding (SMAW) in Ductile Irons (DI) is often required by foundries for practical manufacturing reasons. The mechanical properties of the welded structures are strongly dependent on their HAZ’s wid...Shielded Metal Arc Welding (SMAW) in Ductile Irons (DI) is often required by foundries for practical manufacturing reasons. The mechanical properties of the welded structures are strongly dependent on their HAZ’s width. A model based on the behaviour of the ferritic matrix of high-Si DIs in order to make an approach in measuring their HAZ’s width is developed in this study. A series of thermal treatments on 3.35 and 3.75 wt% Si as-cast DIs and spot SMAWs is applied on these materials. The applied SMAWs are done on non-preheated and preheated samples (150℃ - 300℃). For welding we modify the amperage (100 - 140A). The micro-hardness Vickers changes in the ferrite of the as-cast samples and inside the HAZ of the welded ones can be attributed to the existence of residual stresses (RS) in the ferritic matrix and assist in estimating the HAZ’s width.展开更多
The structural change in heat affected zone(HAZ)and its influence on properties of welded white cast iron have been investigated by means of thermal cycle simulation technique.The structure of the white cast iron at p...The structural change in heat affected zone(HAZ)and its influence on properties of welded white cast iron have been investigated by means of thermal cycle simulation technique.The structure of the white cast iron at peak temperature 800℃ was examined as cementite in pearlitic matrix,of which the hardness and impact toughness are the lowest,while the struc- ture after cyclic heating at high peak temperature is mainly cementite together with twin martensite,of which the hardness and impact toughness are rather higher.The phase bounda- ries in the structure of low hardness are smooth and regular as well as with fine precipitates. Both the cleavage and interphase fracture were revealed in the structure of low hardness,while the transgranular fracture was found in those areas of higher hardness.展开更多
For the machining of bladed ring parts of an aeroengine, experiments on Nd∶YAG pulsed laser cutting of TC1 titanium alloy sheet were carried out to investigate the influences of laser cutting parameters on heat-affec...For the machining of bladed ring parts of an aeroengine, experiments on Nd∶YAG pulsed laser cutting of TC1 titanium alloy sheet were carried out to investigate the influences of laser cutting parameters on heat-affected zone (HAZ). The selected laser cut samples were photographed by scanning electron microscopy. The results show that the microstructure in HAZ layers is characterized by metastable acicular martensite grains with a slight increase of hardness by 10%. The thickness of HAZ layers was studied as a function of laser cutting parameters. Medium pulse energy, higher pulse rate, higher cutting speed and argon at higher pressures help to reduce the thickness of HAZ layers.展开更多
文摘The predictability of hardness of the heat affected zone (HAZ) in aluminum weldments cooled in palm oil, based on hardness of similarly cooled mild steel and cast iron weldments has been ascertained. The general model: α = 1.2769? indicates that HAZ hardness of aluminium weldment is dependant on the ratio of product to sum of HAZ hardness of mild steel and cast iron weldments cooled in palm oil under the same conditions. The maximum deviations of the model-predicted HAZ hardness values α, μ and β from the corresponding experimental values αexp, μexp and βexp were less than 0.04% indicating the reliability and validity of the model.
文摘The microstructure and the characteristics of the inclusions embedded in ferrite matrix in simulated coarse-grain heat affected zone (CGHAZ) of a Ti-Zr-treated high strength low alloy (HSLA) steel have been investigated. The microstructure of the simulated CGHAZ dominantly consisted of intragranular acicular ferrite (IAF) combining with a small amount of polygonal ferrite (PF), widmanst tten ferrite (WF), bainite ferrite (BF), pearlite and martensite-austenite (M-A) islands. The PF, WF and BF were generally observed at the prior austenite grain boundaries and the interlocking acicular ferrite was usually found intragranularly. It was found that the inclusions were composed of Ti2O3, ZrO2, Al2O3 locating at the center of the particles and MnS lying on the surface layer of the inclusions. The intragranular complex inclusions promoted the acicular ferrite formation and the refinement of microstructure whilst those at prior austenite grain boundaries caused PF formation on the inclusions. The simulated CGHAZ consisting of such complicated microstructure exhibited desired mechanical properties.
文摘Effects of Zirconium on the chemical component and size distribution of Ti-bearing inclusions, favored the grain refinement of the welding reduced, coarse-grained heat affected zone （CGHAZ） with enhanced impact toughness in Ti-killed steels, which were examined based on experimental observations and thermodynamic calculations. It indicated that the chemical constituents of inclusions gradually varied from the TiO oxide to the Ti-O＋Zr-O compound oxide and a single phase of the ZrO2 oxide, as the Zr content increased from zero to 0.0100%. A trace of Zr （0.0030%-0.0080%, depending on the oxygen content in liquid steel） provided a large amount of nucleating core for Ti oxide because of the larger specific density of ZrO2 oxide, and produced a small size distribution of the inclusions favorable for acicular ferrite transformation with a high nucleation rate in the CGHAZ, and a high volume fraction of acicular ferrite was obtained in the CGHAZ, with enhanced impact toughness. Otherwise, a high content of Zr （-0.0100%） produced a single phase Zr02, which was impotent to nucleate acicular ferrite, and a microstructure composed of ferrite side plate and grain boundary ferrite developed in the CGHAZ. The experimental results were confirmed by thermodynamic calculations.
文摘One of the main problems during the welding of ferritic stainless steels is severe grain growth within the heat-affected zone （HAZ） In the present study, the microstmctural characteristics of tungsten inert gas （TIG） welded AISI409 ferritic stainless steel were investigated by electron backscattered diffraction （EBSD）, and the effects of welding parameters on the grain size, local misorientation, and low-angle grain boundaries were studied. A 3-D finite element model （FEM） was developed to predict the effects of welding parameters on the holding time of the HAZ above the critical temperature of grain growth. It is found that the base metal is not fully recrystallized. During the welding, complete recrystallization is followed by severe grain growth. A decrease in the number of low-angle grain boundaries is observed within the HAZ. FEM results show that the final state of residual sWains is caused by competition between welding plastic strains and their release by recrystallization. Still, the decisive factor for grain growth is heat input.
基金financially supported by the Postdoctoral Science Foundation of China (No. 2014M550415)the National Natural Science Foundation of China (No. 50734004)
文摘The austenite grain growth behavior in a simulated coarse-grained heat-affected zone during thermal cycling was investigated via in situ observation. Austenite grains nucleated at ferrite grain boundaries and then grew in different directions through movement of grain boundaries into the ferrite phase. Subsequently, the adjacent austenite grains impinged against each other during the α→γtransformation. After the α→γ transformation, austenite grains coarsened via the coalescence of small grains and via boundary migration between grains. The growth process of austenite grains was a continuous process during heating, isothermal holding, and cooling in simulated thermal cycling. Abundant finely dispersed nanoscale TiN particles in a steel specimen containing 0.012wt% Ti effectively retarded the grain boundary migration, which resulted in refined austenite grains. When the Ti concentration in the steel was increased, the number of TiN particles de- creased and their size coarsened. The big particles were not effective in pinning the austenite grain boundary movement and resulted in coarse austenite grains.
基金Project(50705027)supported by the National Natural Science Foundation of ChinaProject(2007AA04Z315)supported by the National High-Tech Research and Development Program of China。
文摘In the wire bonding process of microelectronic packaging,heat affect zone(HAZ)is an important factor governing the loop profile of bonding.The height of loop is affected by the length of the HAZ.Factors governing the HAZ were studied.To investigate this relationship,experiments were done for various sizes of wire and free air ball(FAB).Electric flame-off(EFO)current, EFO time,EFO gap and recrystallization were also studied.The results show that as the size of FAB becomes larger,the length of HAZ increases.With the increase of EFO current and time,the length of HAZ becomes longer.When FAB forms at the same parameter the length of HAZ becomes shorter with the high temperature of recrystallization.
文摘The simulated heat affected zone （HAZ） of the high strength low alloy （HSLA） steels containing 0%, 0.047%, 0.097% and 0.151% vanadium, respectively, were studied with Gleeble-2000 thermomechanical simulator to determine the influence of vanadium addition on the mechanical properties of the HAZ. The HAZ simulation involved reheating the samples to 1350℃, and then cooling to ambient temperature at a cooling rate of 5℃/s ranging from 800 to 500℃ （△8/5=60s）. The mechanical properties including tensile strength and -20℃ impact toughness were conducted. The microstructures of the base steel and the simulated HAZs were investigated using optical microscope, scanning electron microscope （ SEM ） and transmission electron microscope （TEM）. Based on the systemutic examination, the present work confirmed that about 0.05% vanadium addition to low carbon low alloy steels resulted in expected balance of strength and toughness of the HAZ. And more than 0.10% levels addition led to detrimental toughness of the HAZ SEM study showed that the simulated 0.097% and 0.151%V HAZs consisted of more coarse ferrite plates with greater and more M-A constituents along austenite grain and ferrite plate bound- aries. The impact fracture surfaces of the simulated 0.097% and 0.151%V HAZs showed typically brittle mode with predominant cleavages. The size of the facet in the fracture surface increased with increasing vanadium level from 0.097% to 0.151%.As a result, the simulated 0.151% V HAZ has the lowest impact toughness of the four specimens.
基金Project(51905126) supported by the National Natural Science Foundation of ChinaProject(2018M641822) supported by the China Postdoctoral Science Foundation-General ProgramProject(HIT.NSRIF.201703) supported by the Natural Scientific Research Innovation Foundation in HIT,China
文摘Microstructure and mechanical properties of the heat affected zone(HAZ)in multi-pass gas metal arc(GMA)welded Al Zn Mg Cu alloy plates were investigated,based upon which the mechanical anisotropy and fracture mechanism were analyzed.The microstructure and composition were analyzed by scanning electron microscope(SEM)and energy dispersive spectroscope(EDS).X-ray diffractometer(XRD),transmission electron microscope(TEM)and selective area electron diffraction(SAED)were used to analyze the phase composition.The distribution of microhardness was identified as gradual transition and tensile strength had a tendency to decrease first and then increase.The distribution of nano-sizedη(MgZn2)particles in theα(Al)matrix and Al2MgCu phase determined the tensile performances along the thickness direction and led to the formation of ductile/brittle composite fracture in the HAZ.The continuous distribution of Al2MgCu phase in the strip intergranular precipitates gave birth to premature cracks and the brittle fracture region.The precipitated particles coarsening also led to the deterioration of mechanical properties.
文摘Coarsening, embrittlement and corrosion sensitization in a high temperature heat-affected zone （HTHAZ） are the major problems when 12% chromium low carbon stainless steel is being welded, which induce the deterioration of the impact toughness at a low temperature and intergranular corrosion resistance property. This study investigates the corresponding microstructures in HTHAZ with different chemical compositions and heat inputs through thermal simulation tests. The results show that the martensite content increases with the descending of ferrite factor （FF） when FF is below 9.0 and heat input influences the microstructure of high FF steel in HTHAZ. Martensite of 12% Cr stainless steel in HTHAZ with only Nb stabilization reticularly distributes at ferrite grain boundaries.
文摘Excellent heat affected zone(HAZ)toughness technology improved by strong deoxidizers(ETISI)technology has been developed by Baosteel.In the deoxidation process of molten steel by adding strong deoxidizers,the formation of micrometer inclusions and nano-meter precipitates in steel plates can be effectively controlled by a precise control of oxygen concentration.In the welding process with a high-heat input,the formation of acicular ferrite can be selectively promoted with the aid of the micrometer inclusions;the growth of γ grains can also be selectively restrained by the pinning effect of the nano-meter precipitates.After welding with a high-heat input of 400 kJ/cm,excellent HAZ toughness can be obtained in the steel plates with both of the above microstructures,and the average absorbed energy is greater than 200 J for the V-notch Charpy impact test at-20℃.
基金the financial support of the project from Shanghai Municipal Commission of Economy and Informatization (15XI-1-15)Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘Quantitative research on the heat affected zone （ HAZ） o f weave bead welding （ WBW） joint fo r Invar alloy is carried out in this paper. Based on the morphology and related data analysis of the weld seam, the width difference o f each layer and the forming mechanism are analyzed. Results show that the bottom layer （ Layer 1 ） has the widest HAZ and the smallest fluctuation, which reaches 1 200 ｜jLm. HAZ width o f layer 2 to 5 is relatively narrower which is basically below 600 jjim, while the amplitude fluctuation is greater. The main reason lies in the welding path. The long straight welding without weave causes the base metal near the groove fully melts which causes by the long straight welding without weave, while welding with weave leads to the uneven and inadequate melting of metal near groove.
基金supported by the National High-Tech Research and Development Program of China (No.2006AA09A103-6)
文摘The mechanical properties and microstructure features of the fine-grained heat-affected zone（FGHAZ） of ASTM4130 steel was investigated by optical microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,and welding thermal simulation test.It is found that serious embrittlement occurs in the FGHAZ with an 81.37% decrease of toughness,compared with that of the base metal.Microstructure analysis reveals that the FGHAZ is mainly composed of acicular,equiaxed ferrite,granular ferrite,martensite,and martensite-austenite（M-A） constituent.The FGHAZ embrittlement is mainly induced by granular ferrite because of carbides located at its boundaries and sub-boundaries.Meanwhile,the existence of martensite and M-A constituent,which distribute in a discontinuous network,is also detrimental to the mechanical properties.
文摘The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was investigated.It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates,with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling regime.At relatively high cooling rates,which corresponded to low heat inputs,the hardness of the simulated HAZ was above that of the base metal.When the cooling rate was below 9C/s,the welding HAZ would have an obvious softening.The analysis of transformation rates in continuous cooling processes was completed by numerical differential method.The result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.
基金Funded by Doctoral Scientific Research Foundation of Liao Ning Province(No.201601167)
文摘Microstructure evolution and impact toughness of simulated heat affected zone（HAZ） in low carbon steel have been investigated in this study. Thermal simulator was used to simulate microstructure evolution in HAZ with heat input of 10-100 kJ/cm welding thermal cycle. Results indicated that microstructure of HAZ mainly consisted of acicular ferrite（AF） inside grain and high volume fraction of grain boundaries ferrite（GBF） at prior austenite boundaries; the size of GBF and effective grain size increased with increasing heat input. Excellent impact toughness（more than 150 J at-40 ℃） was obtained in HAZ with heat input less than 50 k J/cm. When heat input was 100 kJ/cm, the impact toughness of HAZ decreased to 18 J because of the presence of large M-A constituent with lath-form in HAZ, assisting the micro-crack initiation and decreasing the crack initiation energy seriously. Effect of inclusions on acicular ferrite transformation in HAZ was also discussed.
文摘The high-strength low-alloy（ HSLA ） steel heat-affected zone （HAZ）softening was predicted using a grey model. HSLA steel DILLIMAX690E, NK-HITEN61OU2 and BHW35 were taken as examples in the research on ultra-narrow gap automatic welding technology. Test results turned out to be that the errors between the values calculated by the Grey Model （GM） （ 1,1 ） model and their actual value were less than 2%, indicating that the grey prediction method could accurately reflect the actual situation of the high-strength low-alloy steel heat-affected zone softening. This method will play a crucial role in guiding the applications of HSLA steel welded structures in the future.
文摘Based on welding thermal simulation on Nb-microaUoyed XSO pipeline stee! using Gleeble-3500 thermal simulation equipment, microstlttcture and impact toughness in coarse grain heat-affected zone （CGHAZ） under different welding parameters were investigated in this paper. The results show that high heat inputs with low preheats or low heat inputs with high preheats should be applied to achieve high impact toughness. Coarse original austenite grains may lower impact toughness. CGHAZ microstructure is mostly composed of upper bainite, granular bainite and lath bainite. The phase composition of microstructure and the quantity, size, shape of M/A constituents both have effects on impact toughness.
文摘Models have been derived for assessment and computational analysis of the hardness of the heat affected zone (HAZ) in aluminum weldment. The general model;γ = 1.2714[(αβ/α + β)] was found to predict the HAZ hardness of aluminum weldment cooled in water as a function of the HAZ hardness of both mild steel and cast iron welded and cooled under the same conditions. The maximum deviations of the model-predicted HAZ hardness values γ, α and β from the corresponding experimental values γexp, αexp and βexp were less than 0.02% respectively.
文摘Shielded Metal Arc Welding (SMAW) in Ductile Irons (DI) is often required by foundries for practical manufacturing reasons. The mechanical properties of the welded structures are strongly dependent on their HAZ’s width. A model based on the behaviour of the ferritic matrix of high-Si DIs in order to make an approach in measuring their HAZ’s width is developed in this study. A series of thermal treatments on 3.35 and 3.75 wt% Si as-cast DIs and spot SMAWs is applied on these materials. The applied SMAWs are done on non-preheated and preheated samples (150℃ - 300℃). For welding we modify the amperage (100 - 140A). The micro-hardness Vickers changes in the ferrite of the as-cast samples and inside the HAZ of the welded ones can be attributed to the existence of residual stresses (RS) in the ferritic matrix and assist in estimating the HAZ’s width.
文摘The structural change in heat affected zone(HAZ)and its influence on properties of welded white cast iron have been investigated by means of thermal cycle simulation technique.The structure of the white cast iron at peak temperature 800℃ was examined as cementite in pearlitic matrix,of which the hardness and impact toughness are the lowest,while the struc- ture after cyclic heating at high peak temperature is mainly cementite together with twin martensite,of which the hardness and impact toughness are rather higher.The phase bounda- ries in the structure of low hardness are smooth and regular as well as with fine precipitates. Both the cleavage and interphase fracture were revealed in the structure of low hardness,while the transgranular fracture was found in those areas of higher hardness.
文摘For the machining of bladed ring parts of an aeroengine, experiments on Nd∶YAG pulsed laser cutting of TC1 titanium alloy sheet were carried out to investigate the influences of laser cutting parameters on heat-affected zone (HAZ). The selected laser cut samples were photographed by scanning electron microscopy. The results show that the microstructure in HAZ layers is characterized by metastable acicular martensite grains with a slight increase of hardness by 10%. The thickness of HAZ layers was studied as a function of laser cutting parameters. Medium pulse energy, higher pulse rate, higher cutting speed and argon at higher pressures help to reduce the thickness of HAZ layers.
