In the last few years,substantial experimental simulation and mumerical modelling hare been carried out in IMMPETUS to characterise the interfacial heat transfer and friction conditions during hot forging and rolling ...In the last few years,substantial experimental simulation and mumerical modelling hare been carried out in IMMPETUS to characterise the interfacial heat transfer and friction conditions during hot forging and rolling of steels. Emphasis has been placed on the influence of the oxide scale which forms on the steel workpiece. In the present paper, the experimental methods used for investigating interfacial heat transfer and friction conditions are described. Theses include hot flat rolling of steel slabs and hot axi- symmetric forging of steel cylinders and rings.Temperature measurements and computations demon- strate that for similar conditions, similar conditions, the effective interfacial heat transfer coefficients (IHTC) derived for hot rolling are significantly higher than those for forging, mainly due to the contribution of scale cracking during rolling. On the basis of experimental observations and numerical analysis,physical models for interfacial heat transfer in forging and rolling have been established. In addition, hot' sandwich' rolling and hot tensile tests with finite element modelling have been carried out to evaluate the hot ductility of the oxide scale.The results indicate that the defomation, cracking and decohesion behaviour of the oxide scale depend on deformation temperature, strain and relative strengths of the scale layer and scale - steel interface.Finaly, friction results from hot ring compression tests and from hot rolling with forward/backward slip measurements are reported.展开更多
The superplastic behavior of a commercial duplex stainless steel has beenstudied by means of isothermal hot tensile test at temperatures of 850-1050 deg C for the initialstrain rates ranging from 3X10^(-4) s^(-1) to 5...The superplastic behavior of a commercial duplex stainless steel has beenstudied by means of isothermal hot tensile test at temperatures of 850-1050 deg C for the initialstrain rates ranging from 3X10^(-4) s^(-1) to 5X10^(-2) s^(-1). At 960 deg C, the best superplasticdeformation that caused the maximum elongation greater than 840 percent was obtained for an initialstrain rate of 1.2X10^(-3) s^(-1). At 850 deg C, the best elongation 500 percent was achieved for aninitial strain rate of 2.5X10^(-3) s^(-1) During the deformation in higher temperature region,coarse gamma grains formed during the prior treatments were broken into spherical particles,resulting in a homogeneous dispersion of gamma particles within the delta-ferrite matrix. However,at lower temperatures between 800 and 950 deg C, the sigma phase was formed through the eutectoiddecomposition of delta->gamma+sigma, resulting finally in the stable equiaxed micro-duplexstructures with delta/gamma and gamma/sigma respectively. The precipitation of the sigma phaseplayed an important role in improving the superplasticity at 850 deg C. The strain-rate sensitivitycoefficient, m-values, were also determined by the strain rate change tests. The microstructurestudies show that the superplastic process occurs mainly by the local work hardening and thesubsequent dynamic recrystallization and a grain boundary sliding and grain switching mechanism.展开更多
文摘In the last few years,substantial experimental simulation and mumerical modelling hare been carried out in IMMPETUS to characterise the interfacial heat transfer and friction conditions during hot forging and rolling of steels. Emphasis has been placed on the influence of the oxide scale which forms on the steel workpiece. In the present paper, the experimental methods used for investigating interfacial heat transfer and friction conditions are described. Theses include hot flat rolling of steel slabs and hot axi- symmetric forging of steel cylinders and rings.Temperature measurements and computations demon- strate that for similar conditions, similar conditions, the effective interfacial heat transfer coefficients (IHTC) derived for hot rolling are significantly higher than those for forging, mainly due to the contribution of scale cracking during rolling. On the basis of experimental observations and numerical analysis,physical models for interfacial heat transfer in forging and rolling have been established. In addition, hot' sandwich' rolling and hot tensile tests with finite element modelling have been carried out to evaluate the hot ductility of the oxide scale.The results indicate that the defomation, cracking and decohesion behaviour of the oxide scale depend on deformation temperature, strain and relative strengths of the scale layer and scale - steel interface.Finaly, friction results from hot ring compression tests and from hot rolling with forward/backward slip measurements are reported.
文摘The superplastic behavior of a commercial duplex stainless steel has beenstudied by means of isothermal hot tensile test at temperatures of 850-1050 deg C for the initialstrain rates ranging from 3X10^(-4) s^(-1) to 5X10^(-2) s^(-1). At 960 deg C, the best superplasticdeformation that caused the maximum elongation greater than 840 percent was obtained for an initialstrain rate of 1.2X10^(-3) s^(-1). At 850 deg C, the best elongation 500 percent was achieved for aninitial strain rate of 2.5X10^(-3) s^(-1) During the deformation in higher temperature region,coarse gamma grains formed during the prior treatments were broken into spherical particles,resulting in a homogeneous dispersion of gamma particles within the delta-ferrite matrix. However,at lower temperatures between 800 and 950 deg C, the sigma phase was formed through the eutectoiddecomposition of delta->gamma+sigma, resulting finally in the stable equiaxed micro-duplexstructures with delta/gamma and gamma/sigma respectively. The precipitation of the sigma phaseplayed an important role in improving the superplasticity at 850 deg C. The strain-rate sensitivitycoefficient, m-values, were also determined by the strain rate change tests. The microstructurestudies show that the superplastic process occurs mainly by the local work hardening and thesubsequent dynamic recrystallization and a grain boundary sliding and grain switching mechanism.
