Revealing the mechanical and microstructural performance of multiphase steels during tensile, forming and flanging operations
Revealing the mechanical and microstructural performance of multiphase steels during tensile, forming and flanging operations
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揭示多相钢在拉伸、成型和翻边操作过程中的机械和微观结构性能
DOI：
10.1016/j.msea.2017.06.056
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Efthymiadis P
中科院分区：
文献类型：
--
作者：
Efthymiadis P
通过SEM分析、拉伸试验、成形极限曲线研究和凸缘成形性试验，研究了双相钢和复相钢的力学性能。感兴趣的合金是双相（DP）未回火、双相（DP）回火和复相（CP）钢。相含量分析表明，铁素体和马氏体相的分布是相同的两种DP合金，但晶粒尺寸和条件（回火/未回火）的马氏体岛是在两种合金有很大的不同。在回火DP钢中，马氏体的较小晶粒尺寸和回火工艺导致增加的伸长率、更大的可成形性和形成凸缘（凸缘）的能力。在CP钢中，较软的铁素体相被较硬的贝氏体取代，产生贝氏体-马氏体显微组织。贝氏体降低了合金拉伸时的总延伸率，降低了合金的成形性（特别是在平面应变条件下），但改善了合金的翻边性。在翻边条件下，CP钢变形到更高的应变，在更小的回弹半径。在法兰试样的外径处的显微组织检查显示，在CP钢中，贝氏体变形类似于马氏体，因此，与DP钢相比，CP钢中的应变分配较小。CP钢在翻边时发生塑性变形，在马氏体和贝氏体中形成强滑移带。相比之下，DP钢中的马氏体和铁素体晶粒变形完全不同，导致强应变局部化。空洞形核和开裂发生在马氏体岛或紧邻马氏体岛的软铁素体相内。在CP钢中，在基体内没有观察到空隙或损伤。对一种更厚更强的合金--马氏体1400钢进行了特殊案例研究，以揭示先进高强度钢的法兰极限。在带凸缘的样本上，目视检查未观察到裂纹或损坏。然而，在凸缘样品的外径处的SEM观察显示在夹杂物位点处有显著的空隙生长，并且在与夹杂物相邻的基质内有裂纹成核。
The mechanical performance of Dual Phase (DP) and Complex Phase (CP) steels was investigated by SEM analysis, tensile testing, Forming Limit Curve investigation and flange formability testing. The alloys of interest were Dual Phase (DP) untempered, Dual Phase (DP) tempered and Complex Phase (CP) steels. Phase content analysis showed that the distribution of the ferrite and martensite phases was the same for the two DP alloys, but the grain size and condition (tempered/untempered) for the martensite islands was much different in the two alloys. In the tempered DP steel, the smaller grain size for the martensite and the tempering process resulted in increased elongation, more formability and ability to form a flange (flangeability). In CP steels the soft ferrite phase is replaced by harder bainite, yielding a bainitic-martensitic microstructure. Bainite reduced the total elongation of the alloy during tensile testing, reduced the formability (especially under plane strain conditions) of the alloy but improved the flangeability of the alloy. Under flanging conditions, CP steels deformed to higher strains, at tighter radii with minimum springback. Microstructural inspections at the outer radius of the flanged specimens revealed that in CP steels bainite deforms similarly to martensite, therefore the strain partitioning is smaller in CP steels in comparison to DP steels. Plastic deformation in CP steels upon flanging occurs with the formation of strong slip bands in both martensite and bainite. In contrast, the martensite and ferrite grains in DP steels deform quite differently leading to strong strain localisations. Void nucleation and cracking occurred at the martensite islands or within the soft ferrite phase next to the martensite islands. In CP steels no voids or damage was observed within the matrix. A special case study was done with a thicker and stronger alloy, a Martensitic 1400 steel to reveal the flangeability limits for advanced high strength steels. Neither cracks nor damage were observed visually on the flanged specimens. However SEM observations at the outer radius of the flanged samples revealed significant void growth at inclusion sites and cracks nucleating within the matrix adjacent to the inclusions.
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