罩式退火工艺对Ti-IF钢组织性能的影响

利用光学显微镜、伺服拉伸实验机和X射线衍射仪研究了不同退火温度和保温时间对Ti-IF钢组织、性能及r值的影响规律,分析了工艺优化后的再结晶织构. 结果表明,8 h为实验Ti-IF钢从部分饼形晶粒到绝大部分等轴晶粒演变过程中的一个时间界限,冷轧板在710℃下保温8 h退火后,再结晶晶粒为均匀的等轴晶粒,r值为2.347,抗拉强度312 MPa,延伸率44.7%,{111}面织构密度水平达到13.1. 在此工艺条件下,Ti-IF钢得到优良的深冲性能,该实验结果可为Ti-IF钢罩式退火工艺的优化提供理论依据.     

IF钢织构形成与演化影响因素

归纳分析了影响IF钢深冲性能（r值）的织构类型,介绍了IF钢中化学成分、第二相粒子、加工工艺等对织构形成与演化的影响,为提高IF钢的深冲性能指明了方向,指出关于晶粒大小、晶界对织构的影响机理有待进一步研究。     

Effect of Processing Condition on Texture and Drawability of a Ferritic Rolled and Annealed Interstitial-Free Steel

The processing conditions of the texture formation and deep drawability of a Ti-IF steel strip hot-rolled in ferritic region and subsequently annealed were investigated. The r-value increases with the decrease of reheating temperature, and finish rolling temperature and the increase of reductions in ferritic region. For lubricated ferritic rolling and annealing, the r-value is raised up to 1.75, and elongation rate is over 50% at the finish rolling temperature of 650 ℃, which is suitable for DDQ grade products. However, the r-value is below 1.0 in the case of unlubricated rolling. The X-ray diffraction was used to analyze the textural characteristic of samples. For samples subjected to lubricated rolling and annealing, the strong { 111 }//ND recrystallization texture is distributed homogeneously along the thickness direction, and the intensity of { 110} recrystallization texture is very low even in surface. However, for unlubricated samples, the {111} texture is distributed inhomogeneously and is weak along the thickness direction, and （110}//ND recrystallization texture is strong, which deteriorates the formability.     

Improvement of the drawability based on the surface friction stir process of AA5052-H32 automotive sheets

Based on the imperative social demand for lighter vehicles, lightweight materials such as aluminum alloys are expected to replace conventional steels in many automotive applications. In automotive parts manufacturing, most of the components produced in conventional stamping operations are geometrically complex as the blanks are subjected to both stretching and drawing deformations. However, aluminum alloys have intrinsic drawbacks, such as the inferior formability of these materials, although the effects of the weight reduction in terms of performance are highly promising. In an effort to improve the formability of aluminum alloy sheets, the surface friction stir process is proposed in this study. This process locally modifies the surface of automotive aluminum alloy sheets via stirring and advancing on the surface of the sheet, similar to the Friction Stir Welding (FSW) process that utilizes a probe without a pin. When the surface of the sheet is modified locally by stirring, dynamic recrystallization due to the severe shear deformation along with heat resulting from the friction occur due to changes in the micro-structure and mechanical properties in the stirred zone, while the dislocation density and grain size refinement are curtailed. In this work, the drawability performance of AA5052-H32 sheets (thickness 1.5 mm) that were welded using the surface friction stir process was experimentally and numerically investigated in cylindrical cup drawing tests. When applied to AA5052-H32 automotive sheets, the surface friction stir process improved the drawability of the entire aluminum alloy sheet. For numerical simulations, the non-quadratic anisotropic yield function Yld2000-2d was employed along with isotropic hardening, while the formability was evaluated by utilizing theoretical forming limit diagrams (FLD) based on Hill's bifurcation and M-K theories.     

AZ31镁合金板的热拉深性能

通过热轧工艺制备了厚度为0.8 mm的AZ31镁合金薄板. 在不同温度和应变速率条件下进行了单向拉伸试验. 在50～240 ℃的温度范围内, 采用平底杯形冲头拉深试验研究了成形温度、拉深速度以及冲头温度对AZ31镁合金板热拉深工艺的影响. 结果表明 AZ31镁合金热轧薄板的RLD随温度的升高而明显增大; 在成形温度为200 ℃, 拉深速度为30 mm/min的条件下, 最大RLD可达2.65, 相应的高径比为1.4, 证明AZ31镁合金板具有良好的热拉深性能; 此外, 拉深速度和冲头温度对AZ31镁合金的拉深成形也有重要影响.     

TEXTURE DEVELOPMENT IN EXTRA LOW CARBON (ELC) AND INTERSTITIAL FREE (IF) STEELS DURING WARM ROLLING

The warm rolling and subsequent annealing textures of an extra low carbon (ELC) and two interstitial free (IF) steels have been investigated using both single pass and multipass rolling in the ferritic temperature range. A total amount of 80% deformation by rolling was given in each case. It was observed that texture development in ELC and IF steels during warm rolling displays striking differences. In general, ELC steels acquire only a weak texture after finish rolling in the upper ferritic range, for both single and multipass rolling. Single pass warm rolling in the lower ferritic range, however, produces very sharp γ fiber in this alloy, as an exception. Recrystallization anneal after warm rolling, in general, has been found to decrease the overall texture. By contrast, much sharper overall texture (and γ fiber) develops in the IF steels during warm rolling, and it generally sharpens after subsequent recrystallization anneal. This is true for both single pass and multipass rolling. The best texture results (highest intensities of γ fibers) are invariably obtained when most of the rolling deformation is given in the ferritic regime. Thus, between the two grades, the IF steels are definitely far better than the ELC steels for the purpose of developing sharp γ fibers by warm rolling process. Out of the two IF steels, the Ti-containing steel appears to develop a perceptibly sharper γ fiber after warm rolling and annealing as compared to the Nb-containing one.     

Ultradrawing behavior of one- and two-stage drawn gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends

The ultradrawing behavior of gel films of plain ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE/low molecular weight polyethylene (LMWPE) blends was investigated using one- and two-stage drawing processes. The drawability of these gel films were found to depend significantly on the temperatures used in the one- and two-stage drawing processes. The critical draw ratio (λ_c) of each gel film prepared near its critical concentration was found to approach a maximum value, when the gel film was drawn at an “optimum” temperature ranging from 95 to 105°C. At each drawing temperature, the one-stage drawn gel films exhibited an abrupt change in their birefringence and thermal properties as their draw ratios reached about 40. In contrast, the critical draw ratios of the two-stage drawn gel films can be further improved to be higher than those of the corresponding single-stage drawn gel films, in which the two-stage drawn gel films were drawn at another “optimum” temperature in the second drawing stage after they had been drawn at 95°C to a draw ratio of 40 in the first drawing stage. These interesting phenomena were investigated in terms of the reduced viscosities of the solutions, thermal analysis, birefringence, and tensile properties of the drawn and undrawn gel films. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 149–159, 1998     

铁素体轧制生产超深冲冷轧板

通过铁素体轧制生产超深冲冷轧Ti-IF钢的工业试验,研究了化学成分、工艺制度对热轧IF钢金相组织、织构和第二相粒子析出的影响,分析了热轧IF钢再结晶状态与产品性能的关系,阐述了提高冷轧Ti-IF钢深冲性能的生产控制要素.试验结果表明:在采用适宜的成分、低的加热温度、高的卷取温度和铁素体区强润滑轧制时,热轧板具有粗大的二相粒子和强的{111}织构;与常规轧制相比,冷轧板的r值在横向和45.方向平均提高1.3和1.0,试验冷轧板的最高r值达到了3.23.     

冷轧压下率对铁素体区热轧Ti-IF钢冷轧板深冲性能的影响

研究了于铁素体区润滑热轧的Ti-IF钢在随后的冷轧及退火工艺中深冲性能的变化.结果表明,在冷轧压下率为75 %时IF钢所获得的r值最高.织构分析表明,于铁素体区润滑热轧的IF钢具有较强的{111}∥ND再结晶织构组分;冷轧时采用75 %的压下率和随后的退火工艺可获得最强的{111}∥ND再结晶织构;冷轧压下率进一步增加时,{111}∥ND再结晶织构将会削弱.这种织构变化与冷轧时ND纤维晶粒内部的剪切带变化有关.     

On Optimizing Batch Annealing for the Production of IF Steels

Batch annealing characterized by a long heating cycle and low heating temperature is widely used to produce sheet steels including interstitial-free (IF) steels. Optimizing batch-annealing conditions would be helpful in cutting lead time and saving energy while keeping the necessary deep drawability; however, little research has been done on it. The effects of batch-annealing parameters on the deep drawability of a Ti-stabilized IF steel and Nb+Ti-stabilized IF steel have been investigated. In general, a slight improvement in r_mvalue was found with the increase of annealing temperature. Because of the higher recrystallization temperatures of Nb+Ti-IF steel, it showed higher sensitivity to annealing temperature than Ti-IF steel. In addition, greater dependency of mechanical properties and deep drawability on soaking time was observed when annealing temperature was lower. Moreover, a heat transfer analysis showed that the annealing time could be reduced by 40% if the temperature decreases from 730°C to 650°C. The industrial production has verified that the analytical results are in good agreement with the recorded annealing temperature curve. Meanwhile, it has been shown that Ti-IF steels annealed at 650°C have very close deep drawability and other tensile properties compared with these annealed at 730°C.