Understanding and Controlling the Ductile-Brittle Transition in High-Strength Martensitic Steel

了解和控制高强度马氏体钢的韧脆转变

• 批准号: 1006160
• 负责人: John Morris
• 金额: $ 37.5万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1006160&HistoricalAwards=false
• 关键词: Understanding; Controlling; Ductile; Brittle; Transition

TECHNICAL SUMMARY: This research concerns the influence of microstructure on the ductile-brittle transition in lath martensitic steels. It specifically addresses the central role of the martensite "block" as the effective grain size in lath martensitic steel and the apparently very different influence of the block size on the strength and the cleavage fracture resistance. The research is technologically important since the high-strength steels now used or proposed for low-temperature, arctic or cryogenic service are lath martensitic steels. Technological advances in the properties and cost of these steels require understanding and exploiting the microstructural mechanisms that control low-temperature strength and toughness. The research is scientifically important since it promises to complete the emerging mechanistic theory of the microstructure-property relations that control the ductile-brittle transition in martensitic steels, a theory that has slowly developed through some forty years of international metallurgical research. The research will study a series of Fe-C, Fe-Ni and Fe-Mn steels with lath martensitic microstructures. Their grain, packet and block structures will be characterized, and modified using thermal treatments that are known to refine the effective block size. Appropriate strength and toughness tests will be done, and studied with high-resolution characterization techniques, including orientation imaging and profile fractography, to determine the influence of the block structure on the strength, toughness and cleavage fracture path. The results will provide new, probative information on the block structure of lath martensite and its specific influence on the strength and the ductile-brittle transition, suggesting new metallurgical approaches to design advanced alloys with superior properties.NON-TECHNICAL SUMMARY: The use of high-strength steel in low-temperature, arctic or deep-sea environments is severely restricted by the danger of catastrophic failure through brittle fracture. The relevant metallurgical problem is the ductile-brittle transition; steels that are tough and ductile at high temperature become almost glassy brittle when used below their ductile-brittle transition temperature. To avoid the problem the designers of low-temperature structures and devices have used relatively low-strength steels, which compromises engineering efficiency, or highly alloyed steels, which raise cost. The ductile-brittle transition temperature of steel is strongly influenced by its internal structure ("microstructure") - the way its atoms are arranged on the micro- and nanoscale. Through some fifty years of directed research in many laboratories around the world metallurgists have come to understand many features of the microstructure of high strength steels and how that microstructure can be engineered to control the ductile-brittle transition. The present research project is intended to fill out that theoretical understanding by applying the best modern tools for microstructure characterization to steels that have been broken under controlled conditions. The results will provide new, probative information on the fundamental mechanisms that govern the brittle transition, suggesting new metallurgical approaches to design advanced alloys with superior properties for low-temperature, arctic or deep-sea service. The PI will continue to teach a freshman seminar course on the history of weaponry, which he has used previously to interest students in the field of Metallurgy. The PI will also encourage the involvement of women and underrepresented groups in his research projects, as he has done in the past.

技术综述：本研究主要研究板条马氏体钢显微组织对韧脆转变的影响。具体论述了马氏体块作为板条马氏体钢中有效晶粒度的核心作用，以及块体尺寸对强度和解理断裂抗力的明显不同的影响。这项研究具有重要的技术意义，因为目前用于或建议用于低温、北极或低温服务的高强度钢是板条马氏体钢。在这些钢的性能和成本方面的技术进步要求了解和利用控制低温强度和韧性的微观结构机制。这项研究具有重要的科学意义，因为它有望完成控制马氏体钢延性-脆性转变的组织-性能关系的新兴机制理论，这一理论经过大约40年的国际冶金研究慢慢发展起来。本研究将研究一系列板条马氏体组织的Fe-C、Fe-Ni和Fe-Mn钢。它们的颗粒、包和块结构将被表征，并使用已知的细化有效块大小的热处理进行修改。将进行适当的强度和韧性测试，并使用高分辨率表征技术进行研究，包括取向成像和剖面断口分析，以确定块体结构对强度、韧性和解理断裂路径的影响。这些结果将为板条马氏体块状结构及其对强度和韧脆转变的具体影响提供新的验证性信息，为设计具有优异性能的先进合金提供新的冶金方法。非技术摘要：高强度钢在低温、北极或深海环境中的使用受到脆性断裂灾难性破坏危险的严重限制。相关的冶金问题是延性-脆性转变；在高温下韧性和延性的钢在低于其延性-脆性转变温度时几乎变成玻璃性脆性。为了避免这个问题，低温结构和装置的设计者使用了相对低强度的钢，这损害了工程效率，或者使用了高合金钢，这增加了成本。钢的延性-脆性转变温度受到其内部结构(“微结构”)的强烈影响--它的原子在微米和纳米尺度上的排列方式。经过世界各地许多实验室近50年的定向研究，冶金学者已经了解了高强度钢的许多组织特征，以及如何设计这种组织来控制塑性-脆性转变。本研究项目旨在通过将最好的现代显微组织表征工具应用于在受控条件下断裂的钢来填补这一理论上的理解。这些结果将为控制脆性转变的基本机制提供新的验证性信息，建议采用新的冶金方法来设计具有优异性能的先进合金，用于低温、北极或深海服务。PI将继续教授一年级的武器史研讨会课程，他以前曾用过这门课程来吸引冶金领域的学生。国际和平研究所还将鼓励妇女和代表性不足的群体参与他的研究项目，就像他过去所做的那样。