The Effects of Nickel and Carbon Content on the Toughness of an Ultra-High Strength Precipitation Strengthened Stainless Steel

商用和军用飞机起落架通常采用300M低合金钢生产，并镀镉以耐腐蚀。在几年内，由于环境问题，镀镉将不可能实现。一种可能的替代方案是使用强度可与300米相当的不锈钢，并且不需要镀镉。这种钢的开发引起了飞机制造商、起落架制造商和特种钢公司的极大兴趣。尽管进行了几年的工作，但仍未开发出用于起落架应用的具有足够韧性的超高强度不锈钢。本研究探索了一种超高强度、析出强化马氏体不锈钢的开发，该不锈钢具有高强度和高韧性，并通过R相颗粒的析出来强化。这些钢含有大约12重量%的铬、5重量%的钼、12重量%的钴和高达6重量%的镍。钢中这些元素的变化预计将导致屈服强度和极限抗拉强度分别为1475 MPa和1650 MPa，并具有良好的韧性。通过这一奖项，将检验钴、钼和碳对这些合金的强度和韧性的影响。为了获得良好的韧性，将主要通过镍含量来控制钢的合金化含量，使钢在淬火状态下含有6~8%的残余奥氏体量。成功地开发出用于起落架的超高强度不锈钢将满足重大工业需求。教育福利包括女研究生协助研究的经验。将培训学生使用扫描电子显微镜检查断口表面，并使用X射线衍射法测量残余奥氏体量。学生在从事提供这类体验的研究项目时，将学习如何使用这些设备和分析方法。

Commercial and military aircraft landing gears are often produced using low alloy steel, 300M, with cadmium plating for corrosion resistance. Within a few years, cadmium plating will not be possible because of environmental concerns. A possible alternative is the use of a stainless steel that has strength levels comparable to 300M and does not require cadmium coatings. The development of such a steel has been of great interest to airplane manufacturers, landing gear producers, and speciality steel companies. Despite several years of work, an ultra-high strength stainless steel with sufficient toughness for landing gear applications has not been developed. This research explores the development of an ultra-high strength, precipitation-strengthened martensitic stainless steel that has both high strength and toughness, and is strengthened by the precipitation of particles of R-phase. These steels contain approximately 12 wt. % chromium, 5 wt. % molybdenum, 12 wt. % cobalt, and up to 6 wt. % nickel. Variations of these in the steel are expected to result in yield strength and ultimate tensile strength of 1475MPa and 1650MPa, respectively, and also would have excellent toughness. With this award, the effects of cobalt, molybdenum and carbon are to be examined on the strength and toughness of these alloys. To have good toughness, the alloying content of the steels will be controlled, primarily through the nickel content, so that the steels contain 6 to 8 volume % retained austenite in the as-quenched condition.Successful development of an ultra-high strength stainless steel for landing gear applications will answer a major industrial need. Educational benefits include experience for a female graduate student to assist in the research. Students will be trained to use the scanning electron microscope to examine fracture surfaces and X-ray diffraction to measure retained austenite content. Students learn how to use such equipment and analysis methods when they are working on research projects that provides these types of experiences.