Orientation relationships (ORs) play a crucial role in the phase transformation of face-centered cubic austenite (γ-fcc) to body-centered cubic martensite (α′-bcc) upon plastic deformation. So far, ORs between γ-fcc and α′-bcc are reported frequently; however, the correlation to the transformation sequences is not clear. Here, the gradient structured austenitic stainless 304 steel prepared by ultrasonic nanocrystalline surface modification was examined to clarify the ORs that were involved in the strain-induced martensitic transformation (SIMT) behaviors. The results showed changes in the ORs from Nishiyama–Wassermann (N-W) to Kurdjumov–Sachs (K-S) and Pitsch with an increase in depth from the top-treated surface. The OR of α′-bcc formed directly on γ-fcc was identified as N-W, while those via the hexagonal closed packed ε-plate (ε-hcp) were the K-S and Pitsch as they were nucleated at the single and two ε-plates intersections, respectively. Thus, the SIMT sequence was the direct γ → α′ with the presence of the N-W OR in the high strain depth, while it was the γ → ε → α′ as the existence of K-S and Pitsch ORs in the low strain depth. The findings provide essential data for the in-depth and comprehensive study of the polymorphic martensitic transformation mechanisms in various steels and alloys.

中文翻译：

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梯度奥氏体不锈钢取向关系与应变诱发马氏体相变序列的相关性

取向关系（ORs）在塑性变形时面心立方奥氏体（γ-fcc）到体心立方马氏体（α'-bcc）的相变中起着至关重要的作用。迄今为止，γ-fcc 和 α'-bcc 之间的 OR 被频繁报道；然而，与转换序列的相关性尚不清楚。在这里，研究了通过超声纳米晶表面改性制备的梯度结构奥氏体不锈钢 304 钢，以阐明参与应变诱导马氏体转变 (SIMT) 行为的 OR。结果显示从 Nishiyama-Wassermann (NW) 到 Kurdjumov-Sachs (KS) 和 Pitsch 的 OR 发生变化，从顶部处理的表面开始增加深度。直接在 γ-fcc 上形成的 α'-bcc 的 OR 被鉴定为 NW，而通过六边形密堆积 ε 板 (ε-hcp) 的那些是 KS 和 Pitsch，因为它们分别在单个和两个 ε 板相交处成核。因此，SIMT 序列是直接 γ → α'，在高应变深度存在 NW OR，而在低应变深度存在 KS 和 Pitsch OR 时，它是 γ → ε → α'。研究结果为深入和全面研究各种钢和合金的多晶型马氏体转变机制提供了重要数据。