双相不锈钢高温微观变形行为

 利用共聚焦激光扫描高温显微镜(CSLM)等设备对双相不锈钢的高温拉伸变形行为进行了研究,分析了双相不锈钢的热塑性变形机理,得出影响双相不锈钢热塑性的主要因素有：相界结合力、组织形貌和两相力学性能的差异。指出在双相不锈钢热加工时,增强相界结合力、优化组织形貌或减小两相力学性能差异,可有效改善双相不锈钢的热塑性。     

热连轧宽带钢中道次变形量的自动分配模型

对热连轧宽带钢轧制工艺中道次变形量的分配进行了探讨，提出了道次变形量的自动分配模型。该模型比传统的最优目标法简便，快捷，可为轧钢工艺设计（轧机数确定，轧机选型及电机选型）和在线控制中道次压下预设定提供理论参考。     

Effect of Residual Elements on Hot‐Crack Susceptibility of Austenitic Stainless Steel

After partial melting and solidification of cylindrical samples hot tensile tests were performed on austenitic stainless steels containing residual elements such as copper, tin and lead as well as calcium and magnesium. Using well controlled cooling conditions down to the testing temperature a radially solidified microstructure in the test zone of the samples was achieved. The testing material was prepared by remelting of base material from the industrial production and addition of single elements in the vacuum induction furnace. The maximum strength and the reduction of area were determined in the temperature range between liquidus and 1100°C. With regard to the reheating and hot rolling process some samples were thermally treated under industrial conditions. The ductility of the material at temperatures down to 950°C was tested and the effect of annealing was evaluated. Recommendations for material processing by continuous casting and hot rolling were derived from the tests performed.     

Effects of Temperature and Strain Rate on Flow Behavior and Microstructural Evolution of Super Duplex Stainless Steel under Hot Deformation

Hot compression tests were carried out in the temperature range of 1 223-1 473 Kand strain rate range of0.01-30s-1 to investigate the flow behavior and microstructural evolution of super duplex stainless steel 2507(SDSS2507).It is found that most of the flow curves exhibit a characteristic of dynamic recrystallization(DRX)and the flow stress increases with the decrease of temperature and the increase of strain rate.The apparent activation energy Qof SDSS2507 with varying true strain and strain rate is determined.As the strain increases,the value of Qdeclines in different ways with varying strain rate.The microstructural evolution characteristics and the strain partition between the two constituent phases are significantly affected by the Zener-Hollomon parameter(Z).At a lower lnZ,dynamic recovery(DRV)and continuous dynamic recrystallization(CDRX)of the ferrite dominate the softening mechanism during the compression.At this time,steady state deformation takes place at the last stage of deformation.In contrast,a higher lnZ will facilitate the plastic deformation of the austenite and then activate the discontinuous dynamic recrystallization(DDRX)of the austenite,which leads to a continuous decline of the flow stress even at the last deformation stage together with CDRX of the ferrite.     

Hot‐Rolling Experiments on Deformation Behaviour of Oxide Scale

A new test technique developed by the authors allows to investigate the brittle‐ductile behaviour of oxide scale during the hot‐rolling process. Sandwich specimens were pre‐oxidised and then welded so as to be gas‐tight. A micro‐alloyed deep‐drawing quality steel (interstitial free steel) and a fine‐grained low‐pearlite structural steel served as test material. The experiments were performed at temperatures up to 1050 °C. Optical metallography was used to describe the changes of the scale layers. The method is quite good to describe the results qualitatively whereas it is rather difficult to derive quantitative results.     

高应变率下00Cr23Ni4N双相不锈钢的热变形行为

 采用Gleeble-3800热力学模拟试验机对00Cr23Ni4N双相不锈钢进行了高温压缩试验,研究了其在900～1150℃、5～50s-1条件下的热变形行为,并利用Sellars双曲正弦模型建立了峰值流变应力与Zener-Hollomon（Z参数）之间的关系。研究结果表明,00Cr23Ni4N双相不锈钢的高温流变应力随变形温度的升高、应变速率的减小显著降低;在变形温度为1100～1150℃,材料均表现出良好的热加工性能;通过回归分析,00Cr23Ni4N双相不锈钢的应力指数为2.6,热变形激活能为263.4kJ/mol,Z参数能较好地描述该钢种的流变行为。     

Influence of Strain Rate on Hot Ductility of a V‐Microalloyed Steel Slab

The hot ductility and malleability of a vanadium‐microalloyed steel is investigated by means of tensile and compression tests at temperatures ranging from 700 to 850°C and strain rates of 3 × 10^?4 to 0.3 s^?1. The deformation tests are performed after austenitization and cooling to test temperature. The so‐called second ductility minimum is located around 750°C for all strain rates except for the highest one, where no ductility trough is observed. Ductility steadily increases with strain rate at a given temperature, and the fracture mode progressively changes from intergranular to transgranular. In the region of minimum ductility, intergranular cracking occurs at low strain rates by void nucleation, growth and coalescence within thin layers of deformation induced ferrite covering the austenite grain boundaries. Cracking is favoured by V(C,N) precipitation associated with the γ/α phase transformation. Ductility remains low above the temperature of minimum ductility, where no apparent ferrite formation is observed (790 °C). Void formation takes place as a result of grain boundary sliding in combination with matrix and grain boundary precipitation. These voids are able to grow and link up forming intergranular cracks. Ductility increases with strain rate mainly due to the short time available for precipitation as well as for intergranular void growth and coalescence.     

Aging Behaviour in Hot‐Rolled Low Carbon Steels

Lüders strain and aging index were employed to characterize the aging properties of hot rolled low carbon steels during production. The Lüders strain was found to increase with aging time while the aging index decreased. It is interpreted that the aging index represents the susceptibility of steels to aging, while the Lüders strain measures the effects of carbon and nitrogen atmosphere pinning on dislocations. By comparing accelerated aging with room temperature aging behaviours of low carbon steels for up to two years, an algorithm deriving the activation energy of solute carbon and nitrogen migration from aging property measurements was proposed. The equation derived for accelerated aging of hot‐rolled low carbon steels investigated was in reasonable agreement with that reported in the literature.     

Strain‐Rate Sensitivity in Hot Forming of Steels – Influence of Microstructure,Temperature and Chemical Composition

A methodology to determine the strain‐rate sensitivity index was developed, based on rolling of a set of samples with the same draught but different speed at defined temperatures. It was shown that initial grain size has nearly negligible influence on the investigated variable, in contrast to phase composition whose influence is very considerable. Combined influence of strain rate and temperature on deformation resistance of various types of steel was studied. For a selected group of steels a universal equation was set up, which described, with a good accuracy, impact of reciprocal temperature and chemical composition (expressed simply by nickel equivalent) on strain‐rate sensitivity in hot state.