Effects of Nickel Content, Inclusion Type and Heat Treatment on the Microstructures and Strength and Toughness of New, Cobalt Free, Ultra-high Strength Steels of High Toughness

目前可用的高断裂韧性超高强度钢中含有大量的钴和镍。由于含有大量的钴和镍，这些钢的价格相对较高。这项研究的最终目标是进一步开发新的高断裂韧性超高强度钢，与现有的高断裂韧性超高强度钢相比，这种钢不含钴，镍含量低得多。显然，这项工作将使人们对成分和热处理对新钢材强度和韧性的影响有一个基本的了解。这一基本认识将有助于新型高断裂韧性超高强度钢的最终商业化开发，这种钢比目前可用的高断裂韧性超高强度钢要便宜得多。根据这项工作取得的初步结果，钢铁生产商和用户对新钢材产生了兴趣，因此认为新钢材有可能具有持久的技术和工程意义。由于新钢材不含必须进口的钴，新钢材在可持续性和国家安全方面也有好处。这项工作将有助于对一名将得到该项目支持的女研究生和几名本科生在学年和暑假期间通过NSF为本科生提供的研究经验补充补助金进行科学/工程培训。新的钢是中碳二次硬化钢，其中添加镍而不是钴通过二次硬化来强化，二次硬化是通过析出细小的合金碳化物来强化的。镍被用来代替钴，因为镍比钴便宜，而且镍降低了韧性到脆性的转变温度，而钴提高了韧性到脆性的转变温度。新钢材的强度和韧性都受到钢中镍加入量的强烈影响。因此，这项拟议工作的一个主要目标是了解镍的添加如何影响新钢的微观结构，从而影响其强度和韧性。拟议工作的第二个目标是研究夹杂物类型对新钢韧性的影响。钢中的夹杂物是第二相颗粒，用于从固溶体中去除某些杂质，如硫。当断裂方式为韧性时，夹杂物类型会影响韧性，也会影响韧脆转变温度。我们在这项工作中特别感兴趣的是评估夹杂物类型对新钢韧性到脆性转变温度的影响。

Currently available ultra-high strength steels of high fracture toughness contain large amounts of cobalt and nickel. Because of these large amounts of cobalt and nickel these steels are relatively expensive. The ultimate objective of this research is the further development of new ultra-high strength steels of high fracture toughness, which contain no cobalt and much less nickel than currently available ultra-high strength steels of high fracture toughness. Explicitly the work will provide a basic understanding as to the effects of composition and heat treatment on the strength and toughness of the new steels. This basic understanding will facilitate the eventual commercial development of a new class of ultra-high strength steels of high fracture toughness, which are much less expensive than currently available ultra-high strength steels of high fracture toughness. Based on the initial results obtained in this work there has been interest in the new steels from steel producers and users of such steels and thus it is felt that the new steels have the potential to be of lasting technological and engineering significance. As the new steel contains no cobalt, which must be imported, the new steels also have benefits in terms of sustainability and national security. This work will contribute to the scientific/engineering training of a woman graduate student who will be supported by the project, and several undergraduates during the school year and summers through the NSF Research Experience for Undergraduates supplemental grants. The new steels are medium carbon secondary hardening steels in which nickel additions, rather than cobalt, are used to enhance strengthening by secondary hardening, which is the strengthening by the precipitation of fine alloy carbides. Nickel is used instead of cobalt because nickel is less expensive than cobalt and because nickel lowers the ductile-to-brittle transition temperature while cobalt raises the ductile-to-brittle transition temperature. Both the strength and toughness of the new steels are strongly influenced by the amount of nickel added to the steel. Thus a major objective of the proposed work is to understand how nickel additions influence the microstructure and hence the strength and toughness of the new steels. The second objective of the proposed work is to examine the effects of inclusion type on the toughness of the new steels. Inclusions in steels are second phase particles used to remove from solid solution certain impurities such as sulfur. The inclusion type can influence the toughness when the fracture mode is ductile and can also influence the ductile-to-brittle transition temperature. Our specific interest in this work is to assess the effects of inclusion type on the ductile-to-brittle transition temperature of the new steels.