The effect of the local hard zone (LHZ) distributed in the coarse grained HAZ (CGHAZ) has been analyzed by 2-dimensional FEM on a mechanical model of the weld CGHAZ. The existence of the LHZ elevates considerably the ...The effect of the local hard zone (LHZ) distributed in the coarse grained HAZ (CGHAZ) has been analyzed by 2-dimensional FEM on a mechanical model of the weld CGHAZ. The existence of the LHZ elevates considerably the stress in LHZ and causes the discontinuity of strain at the boundary between the LHZ and the matrix. The stress distribution in the LHZ is strongly affected by the shape of the LHZ. In a slender LHZ almost the whole region in the LHZ is exposed to elevated stress, whereas in the massive LHZ only the edge region sustains high stress. The longer the LHZ becomes, the more the highly stressed area, and the peak stress in the LHZ grows even under the same volume fraction of the LHZ. These results indicate that the slender LHZ brings about unstable fracture at a lower load level than the blocky LHZ. This tendency was confirmed by CTOD test results on the weld CGHAZ of a high-strength steel. The CGHAZ with elongated M-A constituents fractures at apparently lower critical CTOD than the CGHAZ with massive M-A constituents. In conclusion, the control of the shape of the M-A constituent has a striking effect on the toughness improvement of CGHAZ.展开更多
Charpy impact test and COD test were performed on the specimens subjected to simulated welded thermal cycle and the specimens taken from welded joint. The optical microscope, TEM, SEM, EDAX and XRD analysis have been ...Charpy impact test and COD test were performed on the specimens subjected to simulated welded thermal cycle and the specimens taken from welded joint. The optical microscope, TEM, SEM, EDAX and XRD analysis have been used to investigate the behaviors of second phase particles and the effects of microstructure on toughness separately. The results are as follows. The dispersed second phase particles can effectively retard the growth of austenite grain in the coarse grained HAZ (CGHAZ), and improve the toughness. When t 8/5 is different, the behaviors of the particles are also different in dissolving, coarsening and re precipitating. The ability of retarding the growth of austenite grain will be affected. When t 8/5 increases from 10 s to 70 s , the microstructure of CGHAZ will transform from upper bainite and granular bainite to granular bainite, and the size of austenite grain will grow a little, thus the toughness of the materials decreases slightly.展开更多
The Effect of A1 and Ti treatment on non-metallic inclusions and microstructures of coarse-grain HAZ in HSLA stee1 was investigated in this paper based on experiments and thermodynamic calculations.The results showed ...The Effect of A1 and Ti treatment on non-metallic inclusions and microstructures of coarse-grain HAZ in HSLA stee1 was investigated in this paper based on experiments and thermodynamic calculations.The results showed that the inclusions in A1 treated steel were mainly aluminum oxides and titanium nitrides which could not promote the formation of acicular ferrite microstructures.Microstructure of coarse-grain HAZ in A1 treated steels consists of heavy grain boundary ferrite and ferrite side plate.The inclusions in Ti treated steel were A1,Ti,Mg,Ca composite oxides with size in the range of 0.5-3μm and titanium nitrides with size less than 0.3μm.Ti composite oxide could promote the formation of acicular ferrite and microstructures of coarse-grain HAZ in Ti treated steel consists of grain boundary ferrite,small amounts of ferrite side plate and large amounts of intragranular acicular ferrite.The size of grain boundaries ferrite was increased and the amount of ferrite side plate was decreased with the increase of soaking time at the peak temperature.The amount of grain boundary ferrite and the size of acicular ferrite were also increased with the increase of cooling rate during ferrite phase formation.展开更多
文摘The effect of the local hard zone (LHZ) distributed in the coarse grained HAZ (CGHAZ) has been analyzed by 2-dimensional FEM on a mechanical model of the weld CGHAZ. The existence of the LHZ elevates considerably the stress in LHZ and causes the discontinuity of strain at the boundary between the LHZ and the matrix. The stress distribution in the LHZ is strongly affected by the shape of the LHZ. In a slender LHZ almost the whole region in the LHZ is exposed to elevated stress, whereas in the massive LHZ only the edge region sustains high stress. The longer the LHZ becomes, the more the highly stressed area, and the peak stress in the LHZ grows even under the same volume fraction of the LHZ. These results indicate that the slender LHZ brings about unstable fracture at a lower load level than the blocky LHZ. This tendency was confirmed by CTOD test results on the weld CGHAZ of a high-strength steel. The CGHAZ with elongated M-A constituents fractures at apparently lower critical CTOD than the CGHAZ with massive M-A constituents. In conclusion, the control of the shape of the M-A constituent has a striking effect on the toughness improvement of CGHAZ.
文摘Charpy impact test and COD test were performed on the specimens subjected to simulated welded thermal cycle and the specimens taken from welded joint. The optical microscope, TEM, SEM, EDAX and XRD analysis have been used to investigate the behaviors of second phase particles and the effects of microstructure on toughness separately. The results are as follows. The dispersed second phase particles can effectively retard the growth of austenite grain in the coarse grained HAZ (CGHAZ), and improve the toughness. When t 8/5 is different, the behaviors of the particles are also different in dissolving, coarsening and re precipitating. The ability of retarding the growth of austenite grain will be affected. When t 8/5 increases from 10 s to 70 s , the microstructure of CGHAZ will transform from upper bainite and granular bainite to granular bainite, and the size of austenite grain will grow a little, thus the toughness of the materials decreases slightly.
文摘The Effect of A1 and Ti treatment on non-metallic inclusions and microstructures of coarse-grain HAZ in HSLA stee1 was investigated in this paper based on experiments and thermodynamic calculations.The results showed that the inclusions in A1 treated steel were mainly aluminum oxides and titanium nitrides which could not promote the formation of acicular ferrite microstructures.Microstructure of coarse-grain HAZ in A1 treated steels consists of heavy grain boundary ferrite and ferrite side plate.The inclusions in Ti treated steel were A1,Ti,Mg,Ca composite oxides with size in the range of 0.5-3μm and titanium nitrides with size less than 0.3μm.Ti composite oxide could promote the formation of acicular ferrite and microstructures of coarse-grain HAZ in Ti treated steel consists of grain boundary ferrite,small amounts of ferrite side plate and large amounts of intragranular acicular ferrite.The size of grain boundaries ferrite was increased and the amount of ferrite side plate was decreased with the increase of soaking time at the peak temperature.The amount of grain boundary ferrite and the size of acicular ferrite were also increased with the increase of cooling rate during ferrite phase formation.
