铁素体区轧制对超低碳钢和无间隙原子钢组织和力学性能的影响

本文研究了铁素体区轧制工艺条件对超低碳(ULC)钢和钛处理的无间隙原子(Ti-IF)钢组织和性能,特别是对深冲性能的影响,并分析了Ti-IF钢中的析出物.结果表明,润滑条件对Ti-IF钢的塑性应变比(r)值和深冲性能影响显著,但对ULC钢的r值影响很小.随铁素体区轧制温度的降低,Ti-IF钢的深冲性能得到提高,但ULC钢即使在铁素体区低温轧制其r值仍小于1,深冲性能较差.     

Tool temperature control to increase the deep drawability of aluminum 1050 sheet

A feasibility study on the tool temperature control to increase the deep drawability of Al-1050 sheet is performed. The conventional deep drawing process is limited to a certain limit drawing ratio (LDR) beyond which failure will ensue. The purpose of this study is to examine the possibilities of relaxing the above limitation through the tool temperature control, aiming towards a process with an increased LDR. The idea which may lead to this goal is strengthening the punch-nose radius part by cold punch which has frequently been potential failure area in cup drawing process, while heating the remainder of the blank to reduce the stress on the cup sidewalls. Over the ranges of conditions investigated, the deep drawability of Al-1050 is found to be strongly sensitive to the temperature of the die and punch. The experimental implementation shows that the tool temperature control is very effective way to promote deep drawability of Al-1050.     

基于可控拉深筋的高强度板盒形件拉深性能优化

针对高强度钢板等低塑性板材的成形需要,提出了可控拉深筋拉深成形优化设计.以JAC590Y高强度钢板作为研究对象,根据材料流动的要求设计了上升-静止-下降的拉深筋运动轨迹;通过正交试验确定试验方案,采用板料数值模拟软件Dynaform对试验方案进行模拟,以零件的极限拉深深度为评判标准,研究这些拉深筋运动轨迹对高强度平底盒形件拉深性能的影响.结果表明,采用可控拉深筋技术能显著提高高强度钢板的拉深性能,并获得了优化的拉深筋运动轨迹,最后从应变路径变化方面讨论了可控拉深筋最优运动轨迹相对于固定拉深筋能提高高强度钢板拉深成形性能的原因.     

Heating rate effects during non-isothermal annealing of AIK steel

The effects of heating rate on microstructural size and shape parameters during annealing of cold rolled aluminum killed steel strips have been examined under non-isothermal condition. It is shown that decrease in the heating rate results in accelerated grain growth behavior compared with the prediction by quasi-isothermal based kinetics. The {111} and {112} crystallographic orientations, which enhance the normal anisotropy and deep drawability of cold rolled annealed sheets, are found to exhibit a strong correlation with the grain shape anisotropy. This grain shape anisotropy itself is strongly dependent on heating rates. Lower heating rates result in higher aspect ratios and thus better drawability of the cold rolled sheets. A Hall-Petch type relationship is observed between grain size and hardness of the annealed samples.     

节镍型奥氏体不锈钢的组织性能对比

针对200系J5A、J5两种牌号节镍型奥氏体不锈钢冷轧压延性能的差异,对比分析J5A、J5钢成分设计、组织、力学性能和马氏体含量,研究冷加工性能差异产生的机理。结果表明:由于J5A钢成分设计不合理,镍当量较低,奥氏体稳定性较差,马氏体转变点M_d(30/50)高,在轧制过程中产生大量冷加工变形诱变马氏体,加工硬化程度严重,压延性能差。     

Role of counterpunch for square-cup drawing of tailored blank composed of thick/thin sheets

The deep drawability of tailored blanks (TBs) composed of thick and thin sheets is considerably lower than that of their component sheets, since the plane-strain stretching mode is more likely to occur in such TBs as a result of the movement of the weld line at the bottom of the cup during forming. To improve the deep drawability of TBs, a new forming technology using a counterpunch is proposed, where the movement of the weld line during forming is strongly constrained by the counterpunch pressure. From the results of square-cup drawing experiments on several types of TB of mild steel/high-strength steel sheets, it was found that the limiting cup height increases markedly with increasing counterpunch pressure. One good feature of this forming technology is that the action of counterpunch pressure is necessary only on the thicker (or stronger) sheet part, not on the entire cup bottom.     

Simulation and measurement of aluminium–nitride precipitation in hot rolled Al killed low carbon steel coil

Abstract

Aluminium–nitride precipitation is of great importance in the deep drawability of Al killed low carbon steels. The industrial processing of Al killed steel has some critical points at which the drawability of the final product is strongly influenced by the processing parameters (hot rolling end temperature, coiling temperature). The nitrides are dissolved at the slab reheating temperature (1250°C), and most of the nitrogen remains in solid solution until the hot rolling finishes. The precipitation of nitrides in ferrite occurs more quickly than in austenite, consequently the coiling temperature must be enough low to keep the nitrogen in solid solution. The main purpose of this paper is to describe the aluminium–nitride precipitation process in hot rolled coil. Moreover, on the basis of a phenomenological model of the precipitation process the precipitated fraction of nitrides coiling has been calculated.     

Friction aided deep drawing of sheet metals using polyurethane ring and auxiliary metal punch. Part 1: experimental observations on the deep drawing of aluminium thin sheets and foils

Friction aided deep drawing based on the Maslennikov process is investigated as a method to facilitate the deep drawing of sheet metals with poor drawability. Aluminium foils and thin sheets of 0.1–0.4 mm in thickness are used as a model for the material with poor drawability. An auxiliary metal punch is used together with a polyurethane ring to increase the drawing efficiency and to improve the dimensional accuracy of the drawn cup. The effect of drawing conditions such as thickness, hole diameter and the hardness of the polyurethane ring on the cup height are mainly investigated. Also, the optimum number of drawing operations required to achieve a given drawing ratio is examined by repeating compression and unloading the polyurethane ring. The experimental results show that even for foil and thin sheets, deep cups with drawing ratios of 2.25 and with good shape and dimensional accuracy can be obtained by repeating the drawing operation about ten times. The achievable drawing ratio is appreciably larger when compared with that obtained by the conventional deep drawing process.     

Formability of AZ31 magnesium alloy sheets at warm working conditions

Fine-grained AZ31 magnesium alloy sheets were prepared through hot-rolling process. To investigate the mechanical properties of the sheets, uniaxial tensile tests were conducted at various temperatures and strain rates. The formability of AZ31 alloy sheets at warm working conditions was evaluated by limit drawing ratio (LDR) tests and limit dome height (LDH) tests at temperatures from 50 to 240 °C. It is demonstrated that LDR increases remarkably with temperatures, whilst LDH does not seem to increase much with temperatures. The maximum LDR reaches 2.65 at a punch speed of 30mm/min at 200 °C, whereas the maximum LDH is only 10.8 mm, showing good deep drawability and poor stretchability of AZ31 alloy sheets. In addition, punch speeds and punch temperatures were found to have significant effects on the deep drawability of AZ31 magnesium alloy sheets.     

Electroconductive ceramic tooling for dry deep drawing

Large use and waste of lubricating oil has become a very serious environmental issue. Hence, oil-free metal forming is one of the most promising solutions to this issue. Among them, ceramic tooling is proposed because of its good tribological properties. Its feasibility for dry deep drawing has been studied in laboratory; ceramic tooling is thought to be applicable to dry deep drawing. However, the workability of ceramics in tooling preparation is inferior to that of alloy tool steel. In the present paper, electroconductive ceramics are proposed as an alternative tool material. The electroconductive ceramic tooling is shaped by electric discharge machining such as wire electric discharge machining, die sinking electric discharge, and so forth; any shape of tools can be easily accommodated by these methods. The workability of electroconductive ceramics by electric discharge machining as well as the deep drawability with electroconductive ceramics tooling is experimentally evaluated. Selection of electric conditions for electric discharge machining influences the surface finish quality of electroconductive ceramics. Zirconia-based electroconductive ceramic die has an equivalent deep drawability in dry to conventional SKD11 die with lubricant.     

Cold Deep Drawing of Commercial Magnesium Alloy Sheets

A cold deep drawing process for commercial AZ31 magnesium alloy sheets was developed. The commercial sheets were successfully formed into circular cups at room temperature by optimising the annealing temperature of the sheets, i.e. a limiting drawing ratio of 1.75 was attained for an annealing temperature of 500 °C. The increases in elongation, n-value and r-value, and the decrease in flow stress effective in the improvement of drawability were obtained for the annealing. The apparatus for cold deep drawing without heating becomes much simpler than that for the conventional warm deep drawing. The effects of the lubricant, the clearance between the die and the punch and the corner radius of the punch on the drawability were examined. The limiting drawing ratio was increased by applying force onto the edge of a blank through the die corner. In addition, cold deep drawing of magnesium alloy square cups was performed. It was found that comparatively shallow magnesium alloy cups are satisfactorily formed at room temperature without heating.     

Hot strip processing of low carbon enameling grades in the range of 600 to 700 °C

The processing of continuously cast low carbon steel grades for enameling usually requires a high coiling temperature. Low-temperature coiling, however, is required to ensure deep drawability. A steel composition characterized by low AIN leads to a material combining both good formability and enamelability ratio for hot strip coiling temperatures in the range of 600 to 700 °C. The influence of the coiling temperature on the mechanical properties, cementite morphology, H permeation, and enamel adhesion was studied in detail.     

Effect of reduction in cold rolling on the texture of sheet steel 08Yu

Conclusions The highest drawability of sheet steel reduced 70% in rolling results from the large [111] component, since cold plastic deformation occurs with displacement of individual sections of the crystal in planes and directions most densely filled with atoms.Zaporozhstal' Plant. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 5–9, October, 1970.     

Low-density low-carbon Fe–Al ferritic steels

Fe–Al solid-solution alloys, with interstitial-free matrix to avoid detrimental κ-carbides, have been investigated in the context of low-density steels for automotive applications. The mechanical properties of the 6.8 wt.% Al-containing alloy were found to be comparable to those of dual-phase steel but with the benefit of reduced density and better formability. Future work on these alloys should concentrate on improving the Young’s modulus and the deep drawability.     

拉深试验测试分析

极限拉深比用直观的方式反映了薄板材料的压延性能,它的测试可以用Swift试验方法完成,也可以用Engelhardt试验方法完成,且试验结果受润滑方式影响较大。采用两种试验方法、两种润滑方式测试了不锈钢薄板的极限拉深比,并对试验结果进行了分析。结果表明：拉深油润滑方式下测得的极限拉深比远远高于凡士林润滑方式,并且试验结果...     

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.     

Characteristics of the warm deep drawability of a transformation-induced plasticity steel sheet

Warm deep drawability in a square cup drawing was investigated using a newly developed high-strength steel sheet with retained austenite that was transformed into martensite during formation. For this investigation, six different temperatures between room temperature and 250°C, and five different drawing ratios ranging from 2.2 to 2.6 were considered. The results showed that the maximum drawing force and the drawing depth were affected by the change in temperature, and a more stable thickness strain distribution was observed at elevated temperatures. However, blue shortness occurred at over 200°C. FEM analysis using the LS-DYNA code was used to compare the experimental results with the numerical results for the thickness strain distribution.     

Role of shear band in texture control of Al-Mg alloys

Shear bands formed in Al-Mg alloys during cold rolling are nucleated on grain boundaries. Their mechanism of formation is different from that already proposed in the case of single crystals of the same alloy. Since recrystallized grains of non-cube orientations are nucleated on these shear bands during annealing, the development of cube recrystallization texture can be strongly suppressed by enhancing shear banding during cold rolling. Control of shear band thus provides a new fundamental technological tool to improve drawability of Al alloy sheets. In a microscopic scale, deformation in grain boundary regions also plays here a very important role, as in the case of the formation of {111}uvw recrystallization textures in low carbon steel sheets.     

Deep drawability of commercial purity aluminum sheets processed by groove pressing

Formability of aluminum alloys poses a major challenge for their wider application in automotive sheet metal components as the deep drawability of aluminum is low when compared to steel. This is indicated by the low limiting drawability ratio (LDR) of aluminum sheet blanks which is characterized by the poor r value or the plastic strain ratio. Recently, a number of techniques have been attempted to improve the r value of an FCC metal like aluminum by altering the texture. In the present study, a groove pressing process was carried out on commercial purity aluminum sheets under three different orientations to its rolling direction. The r, r_m and Δr values of the groove pressed specimens were experimentally determined. Improvements in these values were obtained. X-ray diffraction scans were carried out on the specimens to measure the relative intensities of the (1 1 1) and (2 0 0) peaks in the pattern. The LDR, determined by the Swift cup forming test shows an improvement for the aluminum sheet specimen groove pressed at 0° and 45° to the RD. This can be attributed to the improved r value due to the development of (1 1 1)//ND shear texture imparted to the specimen by groove pressing.     

Recrystallization texture characteristic and drawability of a warm rolled and cold rolled interstitial-free steel

The recrystallization textures and drawability in an interstitial-free (IF) steel were investigated as a function of cold rolling reduction. The hot bands for further cold rolling were obtained by lubricated hot rolling in the ferrite region. The orientation distribution function (ODF) was applied to analyze recrystallization textures. Texture analysis showed that hot bands rolled in the ferrite region had strong {111}//ND texture component. The {111}//ND recrystallization texture of the cold rolled steel with 73% reduction displayed the highest intensity, but weakened as more cold work was introduced. The highestr-value was obtained at a cold reduction of 73% when the hot band was previously rolled in the ferrite region.