Retained Austenite Decomposition, and its Effect on Microstructure and Properties in Low-Alloy Steels.

低合金钢中残余奥氏体分解及其对显微组织和性能的影响。

• 批准号: 2879345
• 金额: --
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2879345
• 关键词: Retained; Austenite; Decomposition; its; Effect

It is critically important that the low-alloy steels used in energy applications have excellent strengths and toughnesses. These properties are determined by their microstructures, which are typically controlled by a processing route referred to as 'austenitise, quench and temper'. The austenitise step is a high-temperature hold, which homogenises the microstructure across the material as a single phase - austenite. The steel is then cooled in the quench step, to form strong microconstituents such as bainite and martensite. A tempering step is then required to increase toughness, by relieving internal stresses and precipitating carbides in the martensite/bainite. Recent work has indicated that the presence of large carbides in low-alloy steel microstructures, which are detrimental for toughness, may result of the decomposition of islands of carbon-enriched retained austenite during tempering (retained austenite = austenite retained after quenching). We have already measured that significant levels of retained austenite (>10%) are likely to be present in large forgings following the quenching step, but the effect of tempering on these islands remaining less well understood. For instance, it is not clear at what stage during the tempering heat treatment these islands decompose, and whether they form different microstructures when different tempering temperatures are used. This project aims to characterise the process of retained austenite decomposition in low-alloy steels (SA540, SA508 Grade 3 and SA508 Grade 4N) in detail, and understand the conditions under which coarse carbides form. It will use techniques such as scanning and transmission electron microscopy, optical microscopy, dilatometry and synchrotron X-ray diffraction to characterise the austenite decomposition and the resulting microstructures. It will use microhardness testing and Charpy impact testing to assess the change in mechanical properties brought about by different post-temper microstructures. If time permits, a comparison will be made between the retained austenite behaviours in material that is chemical heterogeneous (i.e., standard wrought material) and material that has been homogenised to ensure a consistent chemistry throughout.

至关重要的是，用于能源应用中使用的低合金钢具有出色的优势和韧性。这些属性取决于它们的微观结构，这些微结构通常由称为“ Austenitise，quench和penper”的处理路线控制。奥氏体的步骤是一个高温保持，它是单相 - 奥氏体的材料均匀的均匀固定。然后将钢在淬火步骤中冷却，以形成强大的微晶体，例如贝氏和马氏体。然后，需要通过缓解内部应力并在马氏体/贝氏体中降低碳化物来增加韧性。最近的工作表明，在低合金钢微观结构中存在大碳酸盐，这对韧性有害，这可能是由于在降温期间保留了碳富含碳的岛岛在降温期间保留了奥斯丁岩的岛化。我们已经衡量，在淬灭步骤之后，很可能会出现大量的保留奥氏体（> 10％），但是降温对这些岛屿的影响仍然不太了解。例如，在回火热处理期间，这些岛屿分解的阶段尚不清楚，以及当使用不同的回火温度时它们是否形成不同的微观结构。该项目旨在详细描述保留的奥斯丁岩分解过程（SA540，SA508 3级和SA508级4N级），并了解粗碳化物形式的条件。它将使用扫描和透射电子显微镜，光学显微镜，扩张法和同步加速器X射线衍射等技术来表征奥氏体分解和所得的显微结构。它将使用微硬度测试和夏比冲击测试来评估不同后宴会后微观结构带来的机械性能的变化。如果时间允许，将在化学异质（即标准锻造材料）的材料中保留的奥氏体行为进行比较，这些材料和材料已被均质，以确保整个化学性质一致。