Chamfered mould has gradually become a new technology equipment to eliminate transverse corner crack.However,longitudinal corner crack ratio of chamfered slab was very high.Solidification microstructure was detected i...Chamfered mould has gradually become a new technology equipment to eliminate transverse corner crack.However,longitudinal corner crack ratio of chamfered slab was very high.Solidification microstructure was detected in the area where the longitudinal corner crack occurred.Effect of narrow face shape and taper distribution of mould copper plate on longitudinal corner crack was studied by industrial tests.Water velocity distribution in the narrow copper plate was studied by numerical simulation.On the premise of preventing cooling water from nuclear boiling,improvement measures of mould cooling process and water seam structure were put forward through heat transfer calculation.The results showed that local taper of the meniscus region of mould should be increased to prevent generation of longitudinal corner crack.Chamfering slope length of narrow copper plate should be controlled within 55 mm,and chamfering angle should be controlled at about 30°.Average water velocity should be more than 7.0 m/s.The flat and chamfering regions of narrow copper plate working face should be designed as double taper and funnel structure,respectively.The water seam in the chamfering region should preferentially choose the combined cooling structure with two holes and one slot.In order to prevent the extension of longitudinal corner crack,chamfered narrow face foot roller should be used.展开更多
A mathematical model for simulating the fluid flow, heat transfer and solidification in the conventional mold and the chamfer mold, together with a finite element stress-strain model in the straightening process of bo...A mathematical model for simulating the fluid flow, heat transfer and solidification in the conventional mold and the chamfer mold, together with a finite element stress-strain model in the straightening process of both molds, were established for the typical niobium, vanadium, and titanium micro-alloyed steels. On the basis of both numerical analysis, the mold copper plate with an optimum chamfered shape was designed and applied in industrial tests. The predicted results from numerical simulation of fluid flow, heat transfer and solidification in the conven tional mold and the chamfer mold show that the increased chamfered angle leads to an approximately linear increase o[ the slab surface temperature, but it also causes strong flow near the slab corner. Very small chamfered length can lead to a significant increase of the temperature near the slab corner. However, with further increasing the chamfered length, the temperature of the slab corner increased slightly. The calculated results from the finite element analysis of stress-strain during the straightening process show that at the same slope width, the tangential strain on the slat） edges and corners is minimum when the chamfered angle is 30° and 45°, which is only 40° to 46° of rectangular slabs with the same cross-section area. At the same chamfered angle of 30°, when the chamfered length is controlled between 65-85 mm, the tangential strain on the part of the slab edges and corners is relatively smaller. Industrial test results show that the slab corner temperature at straightening segment increases about 100 ℃ by using chamfer mold compared to the conventional molds. The slab transverse corner cracks have been reduced more than 95° in comparison with those in the conventional mold.展开更多
The line-spring model of surface cracks is applied to the fully plastic analysis of corner cracks at a hole in a plate. The generalized fully plastic constitutive relations and the fully plastic J-integral, as well as...The line-spring model of surface cracks is applied to the fully plastic analysis of corner cracks at a hole in a plate. The generalized fully plastic constitutive relations and the fully plastic J-integral, as well as its coefficients in polynomial expressions are given. The model obtained is incorporated into a finite element program. The corner cracks at a hole in a plate subjected pure tensions are calculated by the present model. The fully plastic J-integral is then estimated. The results obtained show that the line-spring model is effective for the analysis of corner cracks. The influence of the crack depth and the hardening exponent on the fully plastic J-integral is also discussed.展开更多
The three-dimensional weight function method recently developed by the authors is used to determine stress intensity factors for two symmetric quarter-elliptical corner cracks at a hole in a wide finite-thickness plat...The three-dimensional weight function method recently developed by the authors is used to determine stress intensity factors for two symmetric quarter-elliptical corner cracks at a hole in a wide finite-thickness plate subjected to remote tensile loading. The geometry parameters considered are r / t = 0.5, 1, 2; a / c= 0.2, 0.5, 1, 2; a / t = 0.2, 0.5 within c/r= 2. The results are compared, where possible, with other solutions available in the literature. Generally good agreement is observed. The effect of an approximation of the two-dimensional unflawed stress distribution on the accuracy of stress intensity factors by the weight function method is discussed.展开更多
The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensiona...The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensional thermo-elasto-visco-plastic finite element model was developed to predict the mould gap evolution, temperature profiles and deformation behavior of the solidified shell in the mould region. Then, a three-dimensional model was adopted to calculate the shell growth, tempera- ture history and the development of stresses and strains of the shell in the following secondary cooling zones. Finally, another three-dimensional model was used to analyze the stress distributions in the straightening region, The results showed that the off-corner cracks in the shell originated from the mould owing to the tensile strain developed in the crack sensitive regions of the solidification front, and they could be driven deeper by the possible severe surface temperature rebound and the extensive tensile stress in the secondary cooling zone, especially upon the straightening operation of the bloom casting. It is revealed that more homogenous shell temperature and thickness can be obtained through optimization of mould corner radius, casting speed and secondary cooling scheme, which help to decrease stress and strain concentration and therefore prevent the initiation of the cracks.展开更多
Q355钢是中厚板领域中重要的低合金结构钢,其含碳量为0.12%~0.20%,具有良好的强度、韧性、可塑性和抗腐蚀性。钢板角部裂纹是中厚板生产中的一个常见问题,严重影响了产品的质量和使用性能,进而影响中板厂成材率。本文针对厚度8~20 mm Q3...Q355钢是中厚板领域中重要的低合金结构钢,其含碳量为0.12%~0.20%,具有良好的强度、韧性、可塑性和抗腐蚀性。钢板角部裂纹是中厚板生产中的一个常见问题,严重影响了产品的质量和使用性能,进而影响中板厂成材率。本文针对厚度8~20 mm Q355B钢板出现的角部裂纹的问题,采用金相观察形貌结合电子背散射衍射(EBSD)技术观察了晶粒尺寸和取向,探究了角部裂纹的微观组织演变特点,分析引起角裂的主要原因,提出了改善措施,并进行了生产性跟踪验证。结果表明:无角裂试样的晶粒组织均匀;有角裂试样的裂纹主要分布在表层及皮下,深度为0.1~0.5 mm,裂纹面晶粒粗大,存在明显的铁素体和再结晶组织。基于微观组织分析,确定中间坯厚度对角裂的影响较为严重,对于较小厚度的钢板,调整中间坯厚度影响不大,可适当增加精轧道次,减小角裂发生率。展开更多
文摘Chamfered mould has gradually become a new technology equipment to eliminate transverse corner crack.However,longitudinal corner crack ratio of chamfered slab was very high.Solidification microstructure was detected in the area where the longitudinal corner crack occurred.Effect of narrow face shape and taper distribution of mould copper plate on longitudinal corner crack was studied by industrial tests.Water velocity distribution in the narrow copper plate was studied by numerical simulation.On the premise of preventing cooling water from nuclear boiling,improvement measures of mould cooling process and water seam structure were put forward through heat transfer calculation.The results showed that local taper of the meniscus region of mould should be increased to prevent generation of longitudinal corner crack.Chamfering slope length of narrow copper plate should be controlled within 55 mm,and chamfering angle should be controlled at about 30°.Average water velocity should be more than 7.0 m/s.The flat and chamfering regions of narrow copper plate working face should be designed as double taper and funnel structure,respectively.The water seam in the chamfering region should preferentially choose the combined cooling structure with two holes and one slot.In order to prevent the extension of longitudinal corner crack,chamfered narrow face foot roller should be used.
基金Sponsored by National Natural Science Foundation of China(51204059)
文摘A mathematical model for simulating the fluid flow, heat transfer and solidification in the conventional mold and the chamfer mold, together with a finite element stress-strain model in the straightening process of both molds, were established for the typical niobium, vanadium, and titanium micro-alloyed steels. On the basis of both numerical analysis, the mold copper plate with an optimum chamfered shape was designed and applied in industrial tests. The predicted results from numerical simulation of fluid flow, heat transfer and solidification in the conven tional mold and the chamfer mold show that the increased chamfered angle leads to an approximately linear increase o[ the slab surface temperature, but it also causes strong flow near the slab corner. Very small chamfered length can lead to a significant increase of the temperature near the slab corner. However, with further increasing the chamfered length, the temperature of the slab corner increased slightly. The calculated results from the finite element analysis of stress-strain during the straightening process show that at the same slope width, the tangential strain on the slat） edges and corners is minimum when the chamfered angle is 30° and 45°, which is only 40° to 46° of rectangular slabs with the same cross-section area. At the same chamfered angle of 30°, when the chamfered length is controlled between 65-85 mm, the tangential strain on the part of the slab edges and corners is relatively smaller. Industrial test results show that the slab corner temperature at straightening segment increases about 100 ℃ by using chamfer mold compared to the conventional molds. The slab transverse corner cracks have been reduced more than 95° in comparison with those in the conventional mold.
基金The project is supported by Provincial Natural Science Foundation of Sichuan.
文摘The line-spring model of surface cracks is applied to the fully plastic analysis of corner cracks at a hole in a plate. The generalized fully plastic constitutive relations and the fully plastic J-integral, as well as its coefficients in polynomial expressions are given. The model obtained is incorporated into a finite element program. The corner cracks at a hole in a plate subjected pure tensions are calculated by the present model. The fully plastic J-integral is then estimated. The results obtained show that the line-spring model is effective for the analysis of corner cracks. The influence of the crack depth and the hardening exponent on the fully plastic J-integral is also discussed.
文摘The three-dimensional weight function method recently developed by the authors is used to determine stress intensity factors for two symmetric quarter-elliptical corner cracks at a hole in a wide finite-thickness plate subjected to remote tensile loading. The geometry parameters considered are r / t = 0.5, 1, 2; a / c= 0.2, 0.5, 1, 2; a / t = 0.2, 0.5 within c/r= 2. The results are compared, where possible, with other solutions available in the literature. Generally good agreement is observed. The effect of an approximation of the two-dimensional unflawed stress distribution on the accuracy of stress intensity factors by the weight function method is discussed.
文摘The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensional thermo-elasto-visco-plastic finite element model was developed to predict the mould gap evolution, temperature profiles and deformation behavior of the solidified shell in the mould region. Then, a three-dimensional model was adopted to calculate the shell growth, tempera- ture history and the development of stresses and strains of the shell in the following secondary cooling zones. Finally, another three-dimensional model was used to analyze the stress distributions in the straightening region, The results showed that the off-corner cracks in the shell originated from the mould owing to the tensile strain developed in the crack sensitive regions of the solidification front, and they could be driven deeper by the possible severe surface temperature rebound and the extensive tensile stress in the secondary cooling zone, especially upon the straightening operation of the bloom casting. It is revealed that more homogenous shell temperature and thickness can be obtained through optimization of mould corner radius, casting speed and secondary cooling scheme, which help to decrease stress and strain concentration and therefore prevent the initiation of the cracks.
文摘Q355钢是中厚板领域中重要的低合金结构钢,其含碳量为0.12%~0.20%,具有良好的强度、韧性、可塑性和抗腐蚀性。钢板角部裂纹是中厚板生产中的一个常见问题,严重影响了产品的质量和使用性能,进而影响中板厂成材率。本文针对厚度8~20 mm Q355B钢板出现的角部裂纹的问题,采用金相观察形貌结合电子背散射衍射(EBSD)技术观察了晶粒尺寸和取向,探究了角部裂纹的微观组织演变特点,分析引起角裂的主要原因,提出了改善措施,并进行了生产性跟踪验证。结果表明:无角裂试样的晶粒组织均匀;有角裂试样的裂纹主要分布在表层及皮下,深度为0.1~0.5 mm,裂纹面晶粒粗大,存在明显的铁素体和再结晶组织。基于微观组织分析,确定中间坯厚度对角裂的影响较为严重,对于较小厚度的钢板,调整中间坯厚度影响不大,可适当增加精轧道次,减小角裂发生率。
