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Improving the toughness of ultrahigh strength steel.

机译：改善超高强度钢的韧性。

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摘要

The ideal structural steel combines high strength with high fracture toughness. This dissertation discusses the toughening mechanism of the Fe/Co/Ni/Cr/Mo/C steel, AerMet 100, which has the highest toughness/strength combination among all commercial ultrahigh strength steels. The possibility of improving the toughness of this steel was examined by considering several relevant factors.; Chapter 1 reviews the mechanical properties of ultrahigh strength steels and the physical metallurgy of AerMet 100. It also describes the fracture mechanisms of steel, i.e. ductile microvoid coalescence, brittle transgranular cleavage, and intergranular separation.; Chapter 2 examines the strength-toughness relationship for three heats of AerMet 100. A wide variation of toughness is obtained at the same strength level. The toughness varies despite the fact that all heat fracture in the ductile fracture mode. The difference originates from the inclusion content. Lower inclusion volume fraction and larger inclusion spacing gives rise to a greater void growth factor and subsequently a higher fracture toughness. The fracture toughness value, JIc, is proportional to the particle spacing of the large non-metallic inclusions.; Chapter 3 examines the ductile-brittle transition of AerMet 100 and the effect of a higher austenitization temperature, using the Charpy V-notch test. The standard heat treatment condition of AerMet 100 shows a gradual ductile-brittle transition due to its fine effective grain size. Austenitization at higher temperature increases the prior austenite grain size and packet size, leading to a steeper transition at a higher temperature. Both transgranular cleavage and intergranular separation are observed in the brittle fracture mode.; Chapter 4 examines the effect of inclusion content, prior austenite grain size, and the amount of austenite on the strength-toughness relationship. The highest toughness is achieved by low inclusion content, small prior austenite grain size, and a small content of stable austenite. The low inclusion content increases the strain at the fracture. The reduction in prior austenite grain size prevents the fast unstable crack propagation by cleavage. And the stable austenite decreases the strength of the intergranular separation at the prior austenite grain boundary, which provides the stress relief at the crack tip.
机译：理想的结构钢兼具高强度和高断裂韧性。本文讨论了铁/钴/镍/铬/钼/碳钢AerMet 100的增韧机理，该钢在所有商业超高强度钢中具有最高的韧性/强度组合。通过考虑几个相关因素，研究了提高这种钢的韧性的可能性。第1章回顾了超高强度钢的力学性能和AerMet 100的物理冶金学。还描述了钢的断裂机理，即韧性微孔聚结，脆性的经晶分裂和晶间分离。第2章研究了AerMet 100三种加热的强度-韧性关系。在相同的强度水平下，可获得各种韧性。尽管在延性断裂模式下所有热断裂的事实，韧性都变化。差异源自内含物含量。较低的夹杂物体积分数和较大的夹杂物间距导致较大的空隙生长因子，随后具有较高的断裂韧性。断裂韧性值， J Ic ，与大的非金属夹杂物的颗粒间距成正比。第3章使用夏比V型缺口试验研究了AerMet 100的韧性-脆性转变以及较高的奥氏体化温度的影响。 AerMet 100的标准热处理条件由于其有效的晶粒细小而显示出逐渐的延性-脆性转变。较高温度下的奥氏体化会增加先前的奥氏体晶粒尺寸和晶粒尺寸，从而导致较高温度下的陡峭转变。在脆性断裂模式下均观察到了跨晶分裂和晶间分离。第4章研究了夹杂物含量，奥氏体原晶粒度和奥氏体含量对强度-韧性关系的影响。通过低的夹杂物含量，小的奥氏体晶粒尺寸和少量的稳定奥氏体，可以获得最高的韧性。夹杂物含量低会增加断裂处的应变。先前奥氏体晶粒尺寸的减小防止了由于劈裂而导致的快速不稳定裂纹扩展。稳定的奥氏体降低了先前奥氏体晶界处晶间分离的强度，从而缓解了裂纹尖端的应力。

著录项

  • 作者

    Sato, Koji.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 144 p.
  • 总页数 144
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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