The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles du...The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles during welding.The chaotically oriented IAF and refined PAGs inhibit crack initiation and propagation in the steel,resulting in high impact toughness.This work summarizes the com-bined effect of deoxidizers and alloying elements,with the aim to provide a new perspective for the research and practice related to im-proving the impact toughness of the heat affected zone(HAZ)during the high heat input welding.Ti complex deoxidation with other strong deoxidants,such as Mg,Ca,Zr,and rare earth metals(REMs),can improve the toughness of the heat-affected zone(HAZ)by re-fining PAGs or increasing IAF contents.However,it is difficult to identify the specific phase responsible for IAF nucleation because ef-fective inclusions formed by complex deoxidation are usually multiphase.Increasing alloying elements,such as C,Si,Al,Nb,or Cr,con-tents can impair HAZ toughness.A high C content typically increases the number of coarse carbides and decreases the potency of IAF formation.Si,Cr,or Al addition leads to the formation of undesirable microstructures.Nb reduces the high-temperature stability of the precipitates.Mo,V,and B can enhance HAZ toughness.Mo-containing precipitates present good thermal stability.VN or V(C,N)is ef-fective in promoting IAF nucleation due to its good coherent crystallographic relationship with ferrite.The formation of the B-depleted zone around the inclusion promotes IAF formation.The interactions between alloying elements are complex,and the effect of adding dif-ferent alloying elements remains to be evaluated.In the future,the interactions between various alloying elements and their effects on ox-ide metallurgy,as well as the calculation of the nucleation effects of effective inclusions using first principles calculations will become the focus of oxide metallurgy.展开更多
The characteristics of inclusions in two types of low-carbon steels by different deoxidization methods have been investigated by using the welding thermal simulation,the optical microscopy and scanning electron micros...The characteristics of inclusions in two types of low-carbon steels by different deoxidization methods have been investigated by using the welding thermal simulation,the optical microscopy and scanning electron microscopy.In addition,the effects of inclusions on microstructure and properties of heat-affected-zone were studied.The nucleation and growth of intragranular acicular ferrite was observed in situ by the laser scanning confocal microscopy.The distribution of Mn element near the inclusion was also analyzed by the auger electron spectroscopy.The results showed that the inclusions in Al killed steel are mainly aluminum oxides,manganese sulfide and titanium nitrides,and that the inclusions in Ti killed steel are mainly titanium oxide,manganese sulfide complex inclusion and single manganese sulfide.The auger electron spectroscopy showed that there is an Mn-depleted zone near the interface of TiO x /MnS complex inclusion in the size of 1-3 m.It could be the effective nucleus of intragranular acicular ferrite which could divide the prior austenite grains,inhibit the growth of low-temperature microstruc-ture,and refine the final microstructure,so as to improve the toughness of heat-affected-zone significantly.展开更多
Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed.It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles.This ...Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed.It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles.This phenomenon can be explained by the following aspects.As we know,welding thermal cycle include a rapid heating process and a cooling process.During the heating-up period,high melting TiO x particles which contains NbC with the size below 1μm can make a stronger pining force on the gain boundary migration than pure NbC ones,this effect restrain the austenite growth and control the austenite grain size to a certain extent.Then,when the cooling process begins,TiO x particles containing MnS with the size between 1 to 3μm act as a nucleation site for the intragranular acicular ferrite (IAF).Although the growth of bainite would extrude the IAF and make the smooth edge of IAF deformed,it still can not grow through the IAF.Just owing to the pining effect of TiO x-NbC particles and the hindering effect of IAF induced by the TiO x-MnS particles,prior austenite grains haven't undergone a rapid growth during the heating process and these austenite grains are divided into small regions by the IAF finally.展开更多
基金supported by the National Natural Science Foundation of China(No.U1960202).
文摘The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles during welding.The chaotically oriented IAF and refined PAGs inhibit crack initiation and propagation in the steel,resulting in high impact toughness.This work summarizes the com-bined effect of deoxidizers and alloying elements,with the aim to provide a new perspective for the research and practice related to im-proving the impact toughness of the heat affected zone(HAZ)during the high heat input welding.Ti complex deoxidation with other strong deoxidants,such as Mg,Ca,Zr,and rare earth metals(REMs),can improve the toughness of the heat-affected zone(HAZ)by re-fining PAGs or increasing IAF contents.However,it is difficult to identify the specific phase responsible for IAF nucleation because ef-fective inclusions formed by complex deoxidation are usually multiphase.Increasing alloying elements,such as C,Si,Al,Nb,or Cr,con-tents can impair HAZ toughness.A high C content typically increases the number of coarse carbides and decreases the potency of IAF formation.Si,Cr,or Al addition leads to the formation of undesirable microstructures.Nb reduces the high-temperature stability of the precipitates.Mo,V,and B can enhance HAZ toughness.Mo-containing precipitates present good thermal stability.VN or V(C,N)is ef-fective in promoting IAF nucleation due to its good coherent crystallographic relationship with ferrite.The formation of the B-depleted zone around the inclusion promotes IAF formation.The interactions between alloying elements are complex,and the effect of adding dif-ferent alloying elements remains to be evaluated.In the future,the interactions between various alloying elements and their effects on ox-ide metallurgy,as well as the calculation of the nucleation effects of effective inclusions using first principles calculations will become the focus of oxide metallurgy.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2010CB630801)
文摘The characteristics of inclusions in two types of low-carbon steels by different deoxidization methods have been investigated by using the welding thermal simulation,the optical microscopy and scanning electron microscopy.In addition,the effects of inclusions on microstructure and properties of heat-affected-zone were studied.The nucleation and growth of intragranular acicular ferrite was observed in situ by the laser scanning confocal microscopy.The distribution of Mn element near the inclusion was also analyzed by the auger electron spectroscopy.The results showed that the inclusions in Al killed steel are mainly aluminum oxides,manganese sulfide and titanium nitrides,and that the inclusions in Ti killed steel are mainly titanium oxide,manganese sulfide complex inclusion and single manganese sulfide.The auger electron spectroscopy showed that there is an Mn-depleted zone near the interface of TiO x /MnS complex inclusion in the size of 1-3 m.It could be the effective nucleus of intragranular acicular ferrite which could divide the prior austenite grains,inhibit the growth of low-temperature microstruc-ture,and refine the final microstructure,so as to improve the toughness of heat-affected-zone significantly.
文摘Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed.It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles.This phenomenon can be explained by the following aspects.As we know,welding thermal cycle include a rapid heating process and a cooling process.During the heating-up period,high melting TiO x particles which contains NbC with the size below 1μm can make a stronger pining force on the gain boundary migration than pure NbC ones,this effect restrain the austenite growth and control the austenite grain size to a certain extent.Then,when the cooling process begins,TiO x particles containing MnS with the size between 1 to 3μm act as a nucleation site for the intragranular acicular ferrite (IAF).Although the growth of bainite would extrude the IAF and make the smooth edge of IAF deformed,it still can not grow through the IAF.Just owing to the pining effect of TiO x-NbC particles and the hindering effect of IAF induced by the TiO x-MnS particles,prior austenite grains haven't undergone a rapid growth during the heating process and these austenite grains are divided into small regions by the IAF finally.
