UFG-Microstructures by Linear Flow Splitting
UFG-Microstructures by Linear Flow Splitting
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线性流分裂的 UFG 微观结构
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
P. Groche
中科院分区：
文献类型：
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作者：
C. Müller;T. Bohn;E. Bruder;P. Groche
线性分流是一种新型的连续冷成形工艺，通过分流和支承辊将板材边缘成形成两个凸缘。因此，从板材生产分叉型材成为可能，而不需要材料的叠层。这种结构的生产是在改进的辊成型机中增量地进行的。对一种低合金钢的试验研究表明，即使在板边表面增加约1800%的情况下，型材中也没有裂纹形核。在分裂中心的EBSD测量表明，与其他SPD工艺类似，UFG微结构在加工区发展。因此，在加工区达到稳定状态，在该状态下，增加应变不会更多(或更少)地影响材料的性能，即其变形能力，这是典型的SPD工艺。UFG微观组织的形成被认为是线性分流工艺的强制性条件，因为它将材料的成形性提高到该工艺所需的极高水平。由线性分流产生的型材的力学性能具有大梯度的特点，这取决于局部变形和由此产生的微观结构。在前加工区，即劈裂中心和凸缘表面，测量到非常高的硬度，那里发生了严重的塑性变形，存在超细晶组织。在降低变形的方向上，即随着离劈开磨削面或法兰表面距离的增加，硬度下降到接近未变形材料的水平。本文介绍了线性分流工艺，并在对ZStE-500钢断面进行EBSD测量的基础上，讨论了加工区组织的发展。通过详细的硬度测量，证明了分叉轮廓中的力学性能的重新分配。
Linear flow splitting is a new continuous cold forming process where the edge of a sheet metal is formed into two flanges by splitting and supporting rolls. Thus the production of bifurcated profiles from sheet metal without lamination of material becomes feasible. The production of such structures takes place incrementally in a modified roll forming machine. Experimental investigateons on a HSLA steel show, that even at a surface increase of the sheet edge of about 1800% no cracks were nucleated in the profiles. EBSD measurements in the splitting centre reveal that similar to other SPD processes UFG microstructures develop in the processing zone. Thus a steady state is reached in the processing zone where increasing strain has no more (or little) influence on the materials properties i.e. its deformability, as it is typical for SPD-processes. The formation of UFG microstructures is considered to be a mandatory condition for the linear flow splitting process, as it improves the formability of the material to the extremely high level required for this process. The mechanical properties of profiles produced by linear flow splitting are characterised by large gradients, depending on the local deformation and the resulting microstructure. Very high hardness is measured at the former processing zone, i.e. the splitting centre and the flange surface, where severe plastic deformation takes place and UFG microstructures are present. In direction to lower deformation i.e. with increasing distance to the splitting ground or flange surface the hardness decreases close to the level of the undeformed material. In the present paper the linear flow splitting process is introduced and the microstructural development in the process zone is discussed on the base of EBSD measurements on profiles of the steel ZStE 500. The repartition of mechanical properties in a bifurcated profile is demonstrated by detailed hardness measurements.