SGER: Paraequilibrium Carburization of Ferritic and Martensitic Stainless Steels

技术：将针对铁素体不锈钢的低温准平衡渗碳进行研究。这里的准平衡是指碳间隙是可移动的，而替代溶质，如铬和镍，由于渗碳热处理的低温而有效冻结。以前的研究表明，奥氏体不锈钢(如316L)的渗碳可以实现~14at%的表面碳浓度，而不会形成碳化物，并且渗层厚度~25um，维氏硬度为1200。这种硬化的奥氏体不锈钢改善了耐磨性和耐腐蚀性，而不会显著降低奥氏体钢的固有延展性。此外，由于渗碳过程中产生的残余压应力，含有这种硬化层的奥氏体钢的疲劳寿命显著提高。这项高风险、高收益的研究旨在探索铁素体不锈钢准平衡渗碳的潜力。用PH13-8Mo不锈钢进行的初步实验表明，维氏硬度达到1400是可能的。关于铁素体材料的准平衡渗碳的知识几乎为零。PIS将对EBRITE(注册)进行实验，EBRITE是一种化学成分特别简单的商业合金，以确定铁素体不锈钢在低温碳化时不会形成碳化物的条件。此外，本探索性项目还将考察两种马氏体不锈钢M152和Ph-17-4的响应情况。非技术性：这项研究的更广泛影响涉及扩展铁素体不锈钢在许多应用中的用途。特别是，通过一种可应用于成品部件的低成本保形工艺，能够在不影响其他性能的情况下提高其耐磨性、抗疲劳性和耐腐蚀性，因为渗碳几乎不涉及尺寸变化，可以被认为是一种破坏性技术。随着准平衡渗碳带来的性能改善，成本：效益比发生了变化，铁素体不锈钢将成为许多应用的首选材料，这些应用现在需要更昂贵的材料，或者将延长目前由不锈钢制造的部件的寿命。在教学方面，材料科学子学科的结合-热力学、动力学、微观结构表征和力学行为-使这一主题成为材料科学研究生教育的理想主题。

TECHNICAL: Research directed towards low temperature paraequilibrium carburization of ferritic stainless steels will be done. Paraequilibrium here refers to conditions where carbon interstitials are mobile, whereas substitutional solutes such as Cr and Ni are effectively frozen because of the low temperatures of the carburization heat treatment. Prior studies have demonstrated that carburization of austenitic stainless steels, e.g. 316L, allows surface carbon concentrations of ~ 14 at % to be realized but absent carbide formation, and with a case ~ 25 um thick, having a Vickers hardness of 1200. Such hardened austenitic stainless steels have improved wear resistance and enhanced corrosion resistance, without significant attenuation of the inherent ductility of austenitic steels. Further, fatigue life of these austenitic steels containing such hardened cases are significantly increased, because of the residual compressive stresses generated during carburization. The high risk, high profit payoff research is intended to explore the potential for paraequilibrium carburization of ferritic stainless steels. Preliminary experiments involving a PH 13-8 Mo stainless steel which has a bcc matrix indicate that Vickers hardnesses up to 1400 may be possible. Knowledge of paraequilibrium carburization of ferritic materials is virtually nil. PIs will undertake experiments with EBRITE (Registered), a commercial alloy with a particularly simple chemistry, to establish conditions under which low temperatures carburization absent carbide formation may be possible for ferritic stainless steels. In addition the response of two martensitic stainless steels, M152 and Ph-17-4, will be examined in this exploratory project. NON-TECHNICAL: The broader impact of the research concerns extending the utility of ferritic stainless steels in many applications. In particular, being able to improve their wear resistance, fatigue resistance and corrosion resistance, without attenuation of other properties, by a low cost conformal process that can be applied to finished components, as carburization involves virtually no dimensional changes, can be considered a disruptive technology. With the improved properties resulting from paraequilibrium carburization, the costs: benefit ratio changes in such a way that ferritic stainless steel will be preferred materials in many applications that now require more expensive materials, or will extend the lifetime of components currently fabricated from stainless steels. On the pedagogical front, the combination of materials science subdisciplines that have to be brought to bear on this research - thermodynamics, kinetics, microstructural characterization, and mechanical behavior - makes this topic an ideal topic for graduate education in materials science.