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Heat treatments, microstructures and properties of TRIP steels without hold time during the Bainite transformation

贝氏体转变过程中无保温时间的 TRIP 钢的热处理、显微组织和性能

基本信息

批准号：
281456923
负责人：
Professor Dr.-Ing. Martin Franz-Xaver Wagner
金额：
--
依托单位：
Zapadoceska Univerzita v Plzni
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/281456923?language=en
关键词：
Heat treatments microstructures properties TRIP

项目摘要

This project, which we propose in collaboration with colleagues from Czech republic, considers TRIP steels. Their microstructure consists of a mixture of ferrite, bainite and retained austenite as a result of special thermo-mechanical treatments and suitable alloying. TRIP steels can reach combinations of strengths over 1000 MPa with ductility around 30%. However, to achieve these impressive properties, it is necessary to obtain about 10-15% of properly stabilized retained austenite. In practice one crucial problem in processing of TRIP steels is the holding at the bainitic transformation temperature in the 300 - 450 °C range, where bainite forms and retained austenite becomes stabilized: This holding stage represents an important technological constraint in utilizing TRIP steels. The objective of this project is to obtain a deeper insight into novel processing routes with continuous cooling to replace the existing procedures of TRIP steel processing, and to directly relate information on microstructural features with the resulting mechanical properties. Three low-alloyed steels with chemical compositions suitable for the TRIP effect will be selected for the experimental program: (i) alloyed with silicon and manganese; (ii) substitution of silicon by another element; (iii) micro-alloying with niobium for microstructural refinement. Conventional heat treatments will be systematically compared to novel continuous cooling approaches without the bainitic hold step. To fully utilize these new processing approaches, it is necessary to understand the influence of continuous cooling conditions on the stabilization of retained austenite and on the transformation of sufficient amounts of bainite. The morphologies of regions of retained austenite in particular need to be characterized in detail. While the development of alloying concepts and processing routes are the main focus of our partners in Pilsen, the main contributions of the project described here will be in the areas of microstructural analysis and mechanical characterization. This includes metallography, electron microscopy and X-ray diffraction for quantitative analysis of phase fractions and stability and morphology of retained austenite, and mechanical testing (also: first experiments on cyclic behavior) to fully characterize the macroscopic mechanical and transformation behavior. Special emphasis is placed on a characterization of retained austenite and its stability; nanoindentation will be used to further analyze the mechanical behavior of the individual microstructural constituents. This joint project will provide detailed information on the complex relationships between processing, microstructures and properties of the new TRIP steels and thus allow for an elimination of the isothermal holding step, which may eventually lead to substantial expansion in the use of these cost-effective steels.

这个项目是我们与来自捷克共和国的同事合作提出的，考虑了TRIP钢。经过特殊的热处理和适当的合金化处理，其显微组织为铁素体、贝氏体和残余奥氏体的混合。TRIP钢的组合强度可以达到1000兆帕以上，延展性在30%左右。然而，为了获得这些令人印象深刻的性能，需要获得约10-15%的适当稳定的残余奥氏体。在实践中，处理TRIP钢的一个关键问题是在300 - 450°C范围内的贝氏体转变温度下的保温，此时贝氏体形成，残余奥氏体变得稳定：这一保温阶段是使用TRIP钢的一个重要技术限制。该项目的目的是更深入地了解使用连续冷却的新型加工路线，以取代现有的TRIP钢加工程序，并将微观组织特征信息与所得力学性能直接联系起来。将为实验方案选择三种化学成分适合TRIP效应的低合金钢：(i)硅锰合金钢；（ii）用另一种元素取代硅；（iii）用铌进行微合金化以细化显微组织。传统的热处理将系统地与没有贝氏体保持步骤的新型连续冷却方法进行比较。为了充分利用这些新的加工方法，有必要了解连续冷却条件对残余奥氏体的稳定和足够数量的贝氏体转变的影响。残留奥氏体区域的形态尤其需要详细表征。虽然合金概念和加工路线的发展是皮尔森合作伙伴的主要关注点，但这里描述的项目的主要贡献将是在微观结构分析和力学表征领域。这包括金相、电子显微镜和x射线衍射，用于定量分析相组分、残余奥氏体的稳定性和形态，以及力学测试（也包括循环行为的首次实验），以充分表征宏观力学和转变行为。特别强调保留奥氏体的表征及其稳定性；纳米压痕将用于进一步分析单个微观结构成分的力学行为。这个联合项目将提供关于新型TRIP钢的加工、微观结构和性能之间复杂关系的详细信息，从而允许消除等温保温步骤，这可能最终导致这些具有成本效益的钢的大量使用。