The deformation process of H-beams was simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece was obtained. The results show that the flange width, elongation rat...The deformation process of H-beams was simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece was obtained. The results show that the flange width, elongation ratio between flange and web and flange thickness are the maior influencing factors on the spread of rolling piece, and the inclination and diameter of vertical roll together with web inner width can also influence to some extent on the spread of rolling piece.展开更多
The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-...The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.展开更多
It has been observed that H^- current could be improved by adding Ar to H2 plasma. But due to a slower pumping speed for Ar with the existing pumping scheme, the tank pressure will increase quickly during the length o...It has been observed that H^- current could be improved by adding Ar to H2 plasma. But due to a slower pumping speed for Ar with the existing pumping scheme, the tank pressure will increase quickly during the length of a beam pulse. Since H^- stripping loss depends on the tank pressure and gas species, part of the H^- beam can be converted to H^0 and then H^0 can be converted into H^＋ with background H2 and Ar gas thickness. Therefore, the H^- beam current, measured by a Faraday cup, situated at a distance L from GG （ground grid）, will decrease because it will be converted into a H^＋ current. This gives a ratio of the Faraday cup net current to the H^- beam current before stripping at background partial pressure of Ar.展开更多
Small H-beams such as the No.14–20 I-steel can be inserted into soil-cement retaining walls to form small H-beam soil-cement compound walls, functioning both as a retaining wall and a cutoff wall for braced structure...Small H-beams such as the No.14–20 I-steel can be inserted into soil-cement retaining walls to form small H-beam soil-cement compound walls, functioning both as a retaining wall and a cutoff wall for braced structure excavations. Being different from the mixed soil-cement wall (SMW), the interaction between soil-cement and small H-steel is very good. We have carried out a series of bending experiments on small H-beams in soil-cement model compound beams to study the mechanism of interactions. The results show that the interaction between H-beams and soil-cement is very good, whether the H-beam is single or double. Joint forms of double H-beams at one end have little effect on both the contribution coefficient and on ultimate deflection before cracking. But after cracking, the joint forms greatly affect the contribution coefficient. We conclude that the rigid joint girder for double H-beams is a better choice in practice.展开更多
Based on ANSYS, an analytical model was established for H beam during controlled cooling. The tempera-ture fields during controlled cooling and air cooling were analyzed and the microstructure and mechanical propertie...Based on ANSYS, an analytical model was established for H beam during controlled cooling. The tempera-ture fields during controlled cooling and air cooling were analyzed and the microstructure and mechanical properties for different parts of H-beam were discussed in detail. After the H-beam was controlled cooled for 4.5 s, its mean surface temperature decreased from 850 to 460 ℃, and the lowest and the highest temperatures were measured at edge of flange and at R corner, respectively. Whereas, for the H-beam air cooled for 30 s, the mean temperature at R corner and web was 700 and 540 ℃, respectively. The microstructures for different parts of H-beam consisted of ferrite and pearlite, and the grain size at R corner was coarser than those at flange and web. The difference of yield and tensile strengths of web, flange and R corner was within 30 MPa, and the elongation was similar. The changes of microstructure were in good agreement with that of temperature field. In addition, the results show that the uni formity of microstructure and mechanical properties can be improved by increasing water flow rate at R corner.展开更多
Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy （HSLA） H-beams cooled at different cooling rate, with different deformation were investigated. C...Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy （HSLA） H-beams cooled at different cooling rate, with different deformation were investigated. Continuous cooling transformation （CCT） diagram of this new type of steel was obtained by using Gleeble 1500 ther- momechanical simulator. Microstructures and hardness, especially micro-hardness of the experimental steel were in- vestigated by optical microscopy （OM）, scanning electron microscope （SEM）, Rockwell and Vickers hardness tests. Phase analysis was also studied by X^ray diffraction （XRD）. The results indicated that with increase of cooling rate, microstructures of continuous cooled specimens gradually transformed from polygonal ferrite and pearlite, grain boundary ferrite and bainite, bainite and martensite to single martensite. The CCT diagram revealed that slow cool- ing was needed to avoid austenite-bainite transformation to ensure toughness of this steel. By plastic deformation of 40%, austenite-ferrite transformation temperature increased by 46℃, due to deformation induced ferrite transfor- mation during continuous cooling, but Rockwell hardness has little change.展开更多
文摘The deformation process of H-beams was simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece was obtained. The results show that the flange width, elongation ratio between flange and web and flange thickness are the maior influencing factors on the spread of rolling piece, and the inclination and diameter of vertical roll together with web inner width can also influence to some extent on the spread of rolling piece.
基金Funded by the "11th Five" National Science and Technology Support Project(No.2006BAE03A13)
文摘The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.
文摘It has been observed that H^- current could be improved by adding Ar to H2 plasma. But due to a slower pumping speed for Ar with the existing pumping scheme, the tank pressure will increase quickly during the length of a beam pulse. Since H^- stripping loss depends on the tank pressure and gas species, part of the H^- beam can be converted to H^0 and then H^0 can be converted into H^＋ with background H2 and Ar gas thickness. Therefore, the H^- beam current, measured by a Faraday cup, situated at a distance L from GG （ground grid）, will decrease because it will be converted into a H^＋ current. This gives a ratio of the Faraday cup net current to the H^- beam current before stripping at background partial pressure of Ar.
文摘Small H-beams such as the No.14–20 I-steel can be inserted into soil-cement retaining walls to form small H-beam soil-cement compound walls, functioning both as a retaining wall and a cutoff wall for braced structure excavations. Being different from the mixed soil-cement wall (SMW), the interaction between soil-cement and small H-steel is very good. We have carried out a series of bending experiments on small H-beams in soil-cement model compound beams to study the mechanism of interactions. The results show that the interaction between H-beams and soil-cement is very good, whether the H-beam is single or double. Joint forms of double H-beams at one end have little effect on both the contribution coefficient and on ultimate deflection before cracking. But after cracking, the joint forms greatly affect the contribution coefficient. We conclude that the rigid joint girder for double H-beams is a better choice in practice.
基金Item Sponsored by National Science and Technology Support Project of China(2007BAE30B05)
文摘Based on ANSYS, an analytical model was established for H beam during controlled cooling. The tempera-ture fields during controlled cooling and air cooling were analyzed and the microstructure and mechanical properties for different parts of H-beam were discussed in detail. After the H-beam was controlled cooled for 4.5 s, its mean surface temperature decreased from 850 to 460 ℃, and the lowest and the highest temperatures were measured at edge of flange and at R corner, respectively. Whereas, for the H-beam air cooled for 30 s, the mean temperature at R corner and web was 700 and 540 ℃, respectively. The microstructures for different parts of H-beam consisted of ferrite and pearlite, and the grain size at R corner was coarser than those at flange and web. The difference of yield and tensile strengths of web, flange and R corner was within 30 MPa, and the elongation was similar. The changes of microstructure were in good agreement with that of temperature field. In addition, the results show that the uni formity of microstructure and mechanical properties can be improved by increasing water flow rate at R corner.
文摘Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy （HSLA） H-beams cooled at different cooling rate, with different deformation were investigated. Continuous cooling transformation （CCT） diagram of this new type of steel was obtained by using Gleeble 1500 ther- momechanical simulator. Microstructures and hardness, especially micro-hardness of the experimental steel were in- vestigated by optical microscopy （OM）, scanning electron microscope （SEM）, Rockwell and Vickers hardness tests. Phase analysis was also studied by X^ray diffraction （XRD）. The results indicated that with increase of cooling rate, microstructures of continuous cooled specimens gradually transformed from polygonal ferrite and pearlite, grain boundary ferrite and bainite, bainite and martensite to single martensite. The CCT diagram revealed that slow cool- ing was needed to avoid austenite-bainite transformation to ensure toughness of this steel. By plastic deformation of 40%, austenite-ferrite transformation temperature increased by 46℃, due to deformation induced ferrite transfor- mation during continuous cooling, but Rockwell hardness has little change.
