Samples of the cross section microstructures of galvannealed steel sheets that lack alloying were analyzed. X-ray diffraction （XRD） tests were carried out. The study discovers that the deficit of alloying was higher...Samples of the cross section microstructures of galvannealed steel sheets that lack alloying were analyzed. X-ray diffraction （XRD） tests were carried out. The study discovers that the deficit of alloying was higher on both sides of the steel sheet when compared to the center and the thickness of the coating on the sides was also higher than the center. The results of the XRD tests demonstrate that the microstructure of the coating with a lack of alloy is mainly composed of zinc,ζ and δ. They also indicate that the lack of alloying is mainly due to a lower galvannealing temperature and thicker coating. It is shown by the optical micrographs of coating that the δ phase forms first in a discontinuous manner at the interface and then rapidly pushes towards the coating and enlarges.展开更多
Since it has excellent tensile strength, the quenching and partitioning （Q ＆ P） treated steel has been widely acclaimed. Some researched is currently being conducted on Q ＆ P steel, but Q ＆ P techniques and relat...Since it has excellent tensile strength, the quenching and partitioning （Q ＆ P） treated steel has been widely acclaimed. Some researched is currently being conducted on Q ＆ P steel, but Q ＆ P techniques and related mechanisms have been mostly research based on conventional transformation-induced plasticity （TRIP） steel. This study researches the effect of Mn on the properties of Q ＆P sheet steel. Two kinds of steel sheet with different levels of Mn content （1.46% Mn and 2.75% Mn） are investigated. After being fully annealed, the steel sheets were quenched to a temperature between Ms and Mr. Allocation treatment then caused the carbon to be partitioned into the remaining austenite.The microstructure and tensile properties were analyzed. The results show that the increment of Mn content can increase the stability of the steel and decrease the sensitivity of the quenching temperature （QT）. The results also indicate that increasing the level of Mn can effectively suppress the formation of bainite.展开更多
The effects of the welding current mode in resistance spot welding on the microstructure and mechanical properties of advanced high-strength steel dual-phase 590(DP590)sheets were investigated.Results showed that a ro...The effects of the welding current mode in resistance spot welding on the microstructure and mechanical properties of advanced high-strength steel dual-phase 590(DP590)sheets were investigated.Results showed that a rough martensitic structure was formed in the weld zone of the sample welded via the single-pulsed mode,whereas the microstructure in the heat-affected zone consisted of a very rough martensitic microstructure and rough ferrite.However,using the secondary pulse mode led to the formation of tempered martensite in the weld zone.The maximum load and the energy absorption to failure of the samples with the secondary pulsed cycle were higher than those of the samples with the single-pulsed mode.Tensile shear results indicated that the secondary pulsed mode could significantly change the mode of failure upon shear tension testing.Therefore,the obtained results suggest that the use of secondary pulsed mode can improve the microstructural feature and mechanical properties of advanced high-strength steel DP590 welds.展开更多
The hot-deformation behavior of Fe-Mn-C twinning induced plasticity （TWIP） steel was investigated by conducting hot compression tests within a recommended hot rolling temperature range at various strain rates. Flow ...The hot-deformation behavior of Fe-Mn-C twinning induced plasticity （TWIP） steel was investigated by conducting hot compression tests within a recommended hot rolling temperature range at various strain rates. Flow resistance curves during hot-deformation were obtained, and strain rate sensitivities and activation energies for plastic deformation were calculated using the power law. It is found that the addition of Al and Si clearly increases the peak stresses for the present alloys, especially at 950℃. But Mn has a minor effect on the stress-strain curves and activation energy when its content varies from 15 mass% to 22 mass% for the present alloys.展开更多
This study researches cold rolled ultra high strength martensitic steel processed by water quenching. It is found that both the quenching and overageing temperatures greatly influence the mechanical properties of mart...This study researches cold rolled ultra high strength martensitic steel processed by water quenching. It is found that both the quenching and overageing temperatures greatly influence the mechanical properties of martensitic steel. A tensile strength of 1500 MPa can be obtained from 0.2% C-1.8% Mn steel by soaking at 840℃,quenching at 700℃ and overageing at 200℃ for several minutes. The continuous cooling transformation （CCT） diagram reveals that full martensite can be obtained at a cooling rate of 100℃/s or higher; and at a cooling rate of 3 - 10℃/s,austenite barely decomposes at 700℃. For steel with 0.2% carbon and less manganese, austenite decomposition occurs before it is cooled to 700℃ at a cooling rate of 3 - 10℃/s, which leads to lower tensile strength. It is possible to reduce the manganese content of the 1500 MPa martensitic steel by increasing the quenching temperature. To increase the quenching temperature,the control of flatness during water quenching becomes a major concern.展开更多
The feasibility of reducing the welding residual stress through local tensile loading is verified using the finite element method （FEM）. The mechanism and effect of reducing stress during and after welding are compa...The feasibility of reducing the welding residual stress through local tensile loading is verified using the finite element method （FEM）. The mechanism and effect of reducing stress during and after welding are compared. The results show that the effect of the former is better than that of the latter. Applying an external tension load of 200 MPa after welding, the maximum residual stress drops down from 235 MPa to about 90 MPa, moreover, it decreases to 30MPa when an external tension load of 200 MPa is applied during welding.展开更多
Mist jet impingement cooling is an enhanced heat transfer method widely used after the continuous galvanizing process. The key of a successful design and operation of the mist jet impingement cooling system lies in ma...Mist jet impingement cooling is an enhanced heat transfer method widely used after the continuous galvanizing process. The key of a successful design and operation of the mist jet impingement cooling system lies in mastering heat transfer coefficients. The heat transfer coefficients of high temperature steel plates cooled with multiple mist impinging jets were experimentally investigated, and the effects of gas and water flow rates on heat transfer coefficients were studied. The test results illustrate that the gas flow rate has little effect on the mist heat transfer rate. It is also found that the water flow rate has a great impact on the heat transfer coefficient. When the water flow rate ranges from 0.96m3/h to 1.59 m3/h, an increase in the rate will produce a higher heat transfer coefficient with a maximum of 5650 W/（m2 · K）. Compared with the conventional gas jet cooling, the heat transfer coefficient of the mist jet cooling will be much higher, which can effectively strengthen the after-pot cooling.展开更多
文摘Samples of the cross section microstructures of galvannealed steel sheets that lack alloying were analyzed. X-ray diffraction （XRD） tests were carried out. The study discovers that the deficit of alloying was higher on both sides of the steel sheet when compared to the center and the thickness of the coating on the sides was also higher than the center. The results of the XRD tests demonstrate that the microstructure of the coating with a lack of alloy is mainly composed of zinc,ζ and δ. They also indicate that the lack of alloying is mainly due to a lower galvannealing temperature and thicker coating. It is shown by the optical micrographs of coating that the δ phase forms first in a discontinuous manner at the interface and then rapidly pushes towards the coating and enlarges.
文摘Since it has excellent tensile strength, the quenching and partitioning （Q ＆ P） treated steel has been widely acclaimed. Some researched is currently being conducted on Q ＆ P steel, but Q ＆ P techniques and related mechanisms have been mostly research based on conventional transformation-induced plasticity （TRIP） steel. This study researches the effect of Mn on the properties of Q ＆P sheet steel. Two kinds of steel sheet with different levels of Mn content （1.46% Mn and 2.75% Mn） are investigated. After being fully annealed, the steel sheets were quenched to a temperature between Ms and Mr. Allocation treatment then caused the carbon to be partitioned into the remaining austenite.The microstructure and tensile properties were analyzed. The results show that the increment of Mn content can increase the stability of the steel and decrease the sensitivity of the quenching temperature （QT）. The results also indicate that increasing the level of Mn can effectively suppress the formation of bainite.
文摘The effects of the welding current mode in resistance spot welding on the microstructure and mechanical properties of advanced high-strength steel dual-phase 590(DP590)sheets were investigated.Results showed that a rough martensitic structure was formed in the weld zone of the sample welded via the single-pulsed mode,whereas the microstructure in the heat-affected zone consisted of a very rough martensitic microstructure and rough ferrite.However,using the secondary pulse mode led to the formation of tempered martensite in the weld zone.The maximum load and the energy absorption to failure of the samples with the secondary pulsed cycle were higher than those of the samples with the single-pulsed mode.Tensile shear results indicated that the secondary pulsed mode could significantly change the mode of failure upon shear tension testing.Therefore,the obtained results suggest that the use of secondary pulsed mode can improve the microstructural feature and mechanical properties of advanced high-strength steel DP590 welds.
文摘The hot-deformation behavior of Fe-Mn-C twinning induced plasticity （TWIP） steel was investigated by conducting hot compression tests within a recommended hot rolling temperature range at various strain rates. Flow resistance curves during hot-deformation were obtained, and strain rate sensitivities and activation energies for plastic deformation were calculated using the power law. It is found that the addition of Al and Si clearly increases the peak stresses for the present alloys, especially at 950℃. But Mn has a minor effect on the stress-strain curves and activation energy when its content varies from 15 mass% to 22 mass% for the present alloys.
文摘This study researches cold rolled ultra high strength martensitic steel processed by water quenching. It is found that both the quenching and overageing temperatures greatly influence the mechanical properties of martensitic steel. A tensile strength of 1500 MPa can be obtained from 0.2% C-1.8% Mn steel by soaking at 840℃,quenching at 700℃ and overageing at 200℃ for several minutes. The continuous cooling transformation （CCT） diagram reveals that full martensite can be obtained at a cooling rate of 100℃/s or higher; and at a cooling rate of 3 - 10℃/s,austenite barely decomposes at 700℃. For steel with 0.2% carbon and less manganese, austenite decomposition occurs before it is cooled to 700℃ at a cooling rate of 3 - 10℃/s, which leads to lower tensile strength. It is possible to reduce the manganese content of the 1500 MPa martensitic steel by increasing the quenching temperature. To increase the quenching temperature,the control of flatness during water quenching becomes a major concern.
文摘The feasibility of reducing the welding residual stress through local tensile loading is verified using the finite element method （FEM）. The mechanism and effect of reducing stress during and after welding are compared. The results show that the effect of the former is better than that of the latter. Applying an external tension load of 200 MPa after welding, the maximum residual stress drops down from 235 MPa to about 90 MPa, moreover, it decreases to 30MPa when an external tension load of 200 MPa is applied during welding.
文摘Mist jet impingement cooling is an enhanced heat transfer method widely used after the continuous galvanizing process. The key of a successful design and operation of the mist jet impingement cooling system lies in mastering heat transfer coefficients. The heat transfer coefficients of high temperature steel plates cooled with multiple mist impinging jets were experimentally investigated, and the effects of gas and water flow rates on heat transfer coefficients were studied. The test results illustrate that the gas flow rate has little effect on the mist heat transfer rate. It is also found that the water flow rate has a great impact on the heat transfer coefficient. When the water flow rate ranges from 0.96m3/h to 1.59 m3/h, an increase in the rate will produce a higher heat transfer coefficient with a maximum of 5650 W/（m2 · K）. Compared with the conventional gas jet cooling, the heat transfer coefficient of the mist jet cooling will be much higher, which can effectively strengthen the after-pot cooling.
