To investigate the formation of internal cracks in GCrl 5 bearing steels during the soft reduction process in rectangular bloom con- tinuous casting, fully coupled thermomechanieal finite element models were developed...To investigate the formation of internal cracks in GCrl 5 bearing steels during the soft reduction process in rectangular bloom con- tinuous casting, fully coupled thermomechanieal finite element models were developed using the commercial software MSC.MARC, and microstructures and fractographs were also observed. With the finite element models, the contours of temperature, equivalent plastic strain, and equivalent vun Mises stress were simulated. It is observed that the fracture surfaces of internal cracks are covered by cleavage or quasi-cleavage facets. The region of internal cracks in the intergranular brittle fracture mode is in the mushy zone between the zero ductility temperature （ZDT） and the zero strength temperature （ZST）. The simulated equivalent plastic strain in the crack region is 2.34%-2.45%, which is larger than the critical strain （0.4%-1.5%）, and the equivalent von Mises stress is 1.84-5.05 MPa, which is within the range of criti- cal stress （3.9-7.2 MPa）, thus resulting in the occurrence of internal cracks. Reducing the soft reduction amount from 3 to 2 mm can lower the stress under the critical value.展开更多
To investigate the formation of internal cracks in steel billets during soft reduction, fully coupled thermo-mechanical finite element models were developed using the commercial software ABAQUS, also casting and soft ...To investigate the formation of internal cracks in steel billets during soft reduction, fully coupled thermo-mechanical finite element models were developed using the commercial software ABAQUS, also casting and soft reduction tests were carried out in a laboratory strand casting machine. With the finite element models, the temperature distribution, the stress and strain states in the billet were calculated. The relation between internal cracks and equivalent plastic strain, as well as maximal principal stress was analyzed. The results indicate that tensile stresses can develop in the mushy zone during soft reduction and the equivalent strain nearby the zero ductility temperature （ZDT） increases with decreasing solid fraction. Internal cracks can be initiated when the accumulated strain exceeds the critical strain or the applied tensile stress exceeds the critical fracture stress during solidification.展开更多
Center segregation is the main reason for cup fracture of high-carbon wire rod during drawing. Therefore, to continuously produce cast billets with very low center segregation is an important objective. The soft reduc...Center segregation is the main reason for cup fracture of high-carbon wire rod during drawing. Therefore, to continuously produce cast billets with very low center segregation is an important objective. The soft reduction technology is considered to be an effective method to minimize center segregation. To elucidate the effect of soft reduction on the internal quality of high-carbon steel billets, soft reduction was applied with different solid fractions in the core area of billets in a laboratory casting machine. A coupled temperature/displacement finite element model was developed to calculate the solid fraction using the commercial software ABAQUS. Center segregation, center porosity, homogeneity of elements, and equiaxed crystal zone were obviously improved by applying soft reduction, especially when the solid fraction was less than 1.0. The optimal results were obtained when the solid fraction was approximately 0.9.展开更多
At the initial operation stage of the continuous bloom caster at Baosteel, a lot of central porosity and cracks occurred in blooms, especially in the blooms of high-pressure boiler steel. In this study, a model of hea...At the initial operation stage of the continuous bloom caster at Baosteel, a lot of central porosity and cracks occurred in blooms, especially in the blooms of high-pressure boiler steel. In this study, a model of heat transfer and solidification was set up to analyze the process of continuous bloom casting. Based on the model, the distributions of temperature field and shell thickness were obtained, the mushy zone was defined, and thereby the technology of soft reduction for blooms was developed. After several tests were conducted, a reasonable test plan was developed, which led to the determination of the optimal reduction zone and gauge reduction. Now, central porosity and cracks in blooms are almost avoided and the inner quality has been obviously improved.展开更多
The propagation form of internal cracks induced by continuous casting soft reduction and the control strategy for enhancing the internal quality of 45 steel through industrial trials and a three-dimensional flow-heat ...The propagation form of internal cracks induced by continuous casting soft reduction and the control strategy for enhancing the internal quality of 45 steel through industrial trials and a three-dimensional flow-heat transfer-solidification coupling model were investigated.The results showed that the internal cracks induced by soft reduction exhibited a characteristic of being"coarse in the middle and fine at both ends",and displayed an elliptical arc distribution on the loose side of the strand cross section.The cracks originated within the brittle temperature range and propagated inward to the liquid impenetrable temperature and outward to the zero ductility temperature or below.The control strategy for enhancing the internal quality of the 45 steel strand through soft reduction is to adjust the casting speed or the reduction zone appropriately,ensuring that the central solid fraction of the reduction zone falls within the range of 0.33-0.99.At this point,a reasonable reduction amount is allocated to eliminate the center shrinkage cavities and center segregation,even if it results in minor reduction-induced cracks.展开更多
During the solidification of high-alloy steel(0.4C–1.5Mn–2Cr–0.35Mo–1.5Ni),the high temperature gradient of solidified shell as well as the columnar crystal development would contribute to the centre segregation a...During the solidification of high-alloy steel(0.4C–1.5Mn–2Cr–0.35Mo–1.5Ni),the high temperature gradient of solidified shell as well as the columnar crystal development would contribute to the centre segregation and cracking due to the high carbon and alloy contents.The effect of soft reduction process on the segregation of a 400 mm thick high-alloy steel slab was analysed.Industrial trials in a steel mill were performed combining with segregation analysis.The inner quality of the high-alloy steel slab produced through the optimised soft reduction procedures and had a significant improvement in centre segregation.The reduction amount is increased from 20%of solid phase fraction,to avoid the segregation due to the long liquid core,and the reduction rate is deceased from 1.35 to 0.88 mm/m as well.This operation would contribute to the symmetrical distribution of solute element and decrease the segregation to avoid the cracking.An obvious improvement in centre segregation to mainly 1.0 class of high-alloy slab after procedure optimization was achieved.The quality improvement of slab would ensure the quality of downstream forging.展开更多
基金financially supported by the Key Science and Technology Program of Liaoning Province, China (No.2007414003)
文摘To investigate the formation of internal cracks in GCrl 5 bearing steels during the soft reduction process in rectangular bloom con- tinuous casting, fully coupled thermomechanieal finite element models were developed using the commercial software MSC.MARC, and microstructures and fractographs were also observed. With the finite element models, the contours of temperature, equivalent plastic strain, and equivalent vun Mises stress were simulated. It is observed that the fracture surfaces of internal cracks are covered by cleavage or quasi-cleavage facets. The region of internal cracks in the intergranular brittle fracture mode is in the mushy zone between the zero ductility temperature （ZDT） and the zero strength temperature （ZST）. The simulated equivalent plastic strain in the crack region is 2.34%-2.45%, which is larger than the critical strain （0.4%-1.5%）, and the equivalent von Mises stress is 1.84-5.05 MPa, which is within the range of criti- cal stress （3.9-7.2 MPa）, thus resulting in the occurrence of internal cracks. Reducing the soft reduction amount from 3 to 2 mm can lower the stress under the critical value.
基金This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Centre (SFB) 289.
文摘To investigate the formation of internal cracks in steel billets during soft reduction, fully coupled thermo-mechanical finite element models were developed using the commercial software ABAQUS, also casting and soft reduction tests were carried out in a laboratory strand casting machine. With the finite element models, the temperature distribution, the stress and strain states in the billet were calculated. The relation between internal cracks and equivalent plastic strain, as well as maximal principal stress was analyzed. The results indicate that tensile stresses can develop in the mushy zone during soft reduction and the equivalent strain nearby the zero ductility temperature （ZDT） increases with decreasing solid fraction. Internal cracks can be initiated when the accumulated strain exceeds the critical strain or the applied tensile stress exceeds the critical fracture stress during solidification.
文摘Center segregation is the main reason for cup fracture of high-carbon wire rod during drawing. Therefore, to continuously produce cast billets with very low center segregation is an important objective. The soft reduction technology is considered to be an effective method to minimize center segregation. To elucidate the effect of soft reduction on the internal quality of high-carbon steel billets, soft reduction was applied with different solid fractions in the core area of billets in a laboratory casting machine. A coupled temperature/displacement finite element model was developed to calculate the solid fraction using the commercial software ABAQUS. Center segregation, center porosity, homogeneity of elements, and equiaxed crystal zone were obviously improved by applying soft reduction, especially when the solid fraction was less than 1.0. The optimal results were obtained when the solid fraction was approximately 0.9.
文摘At the initial operation stage of the continuous bloom caster at Baosteel, a lot of central porosity and cracks occurred in blooms, especially in the blooms of high-pressure boiler steel. In this study, a model of heat transfer and solidification was set up to analyze the process of continuous bloom casting. Based on the model, the distributions of temperature field and shell thickness were obtained, the mushy zone was defined, and thereby the technology of soft reduction for blooms was developed. After several tests were conducted, a reasonable test plan was developed, which led to the determination of the optimal reduction zone and gauge reduction. Now, central porosity and cracks in blooms are almost avoided and the inner quality has been obviously improved.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant No.U1860111).
文摘The propagation form of internal cracks induced by continuous casting soft reduction and the control strategy for enhancing the internal quality of 45 steel through industrial trials and a three-dimensional flow-heat transfer-solidification coupling model were investigated.The results showed that the internal cracks induced by soft reduction exhibited a characteristic of being"coarse in the middle and fine at both ends",and displayed an elliptical arc distribution on the loose side of the strand cross section.The cracks originated within the brittle temperature range and propagated inward to the liquid impenetrable temperature and outward to the zero ductility temperature or below.The control strategy for enhancing the internal quality of the 45 steel strand through soft reduction is to adjust the casting speed or the reduction zone appropriately,ensuring that the central solid fraction of the reduction zone falls within the range of 0.33-0.99.At this point,a reasonable reduction amount is allocated to eliminate the center shrinkage cavities and center segregation,even if it results in minor reduction-induced cracks.
文摘During the solidification of high-alloy steel(0.4C–1.5Mn–2Cr–0.35Mo–1.5Ni),the high temperature gradient of solidified shell as well as the columnar crystal development would contribute to the centre segregation and cracking due to the high carbon and alloy contents.The effect of soft reduction process on the segregation of a 400 mm thick high-alloy steel slab was analysed.Industrial trials in a steel mill were performed combining with segregation analysis.The inner quality of the high-alloy steel slab produced through the optimised soft reduction procedures and had a significant improvement in centre segregation.The reduction amount is increased from 20%of solid phase fraction,to avoid the segregation due to the long liquid core,and the reduction rate is deceased from 1.35 to 0.88 mm/m as well.This operation would contribute to the symmetrical distribution of solute element and decrease the segregation to avoid the cracking.An obvious improvement in centre segregation to mainly 1.0 class of high-alloy slab after procedure optimization was achieved.The quality improvement of slab would ensure the quality of downstream forging.
