The Effects of Carbon Content on the Formation of Ti2CS and the Fracture Toughness of Ultra-High Strength Steels

本研究的目的是研究碳含量对钛改性钢中硫化物形成和空穴成核阻力的影响。假设增加钛改性钢的碳含量会导致Ti2CS硫化物的沉淀颗粒在更高的温度下形成，从而产生更大的硫化物尺寸。由于Ti2CS颗粒的空穴成核阻力随着颗粒尺寸的增加而降低，因此随着碳含量的增加，将硫作为Ti2CS捆绑在一起对提高断裂韧性的效果应该不那么有效。如果证实增加碳含量增加了钛改性钢中硫化物的尺寸并降低了空泡成核阻力，那么将探索以下方法：(1)在硫作为Ti2CS获得时细化硫化物的尺寸，或者(2)创造新的方法将硫获得为在高碳水平下仍然有效的抗空泡成核颗粒。将考虑的一种方法是溶解硫化物，然后在较低的温度下在奥氏体中再沉淀它们。如果用这种方法细化硫化物尺寸，再析出的硫化物为Ti2CS，那么将研究含再析出硫化物的高碳钢的韧性以及这些更细的再析出硫化物的抗空穴成核行为。还将考虑以Nb2CS而不是Ti2CS来获得硫。最近的研究结果表明，这是可行的，而且这种粒子能够抵抗空穴成核。本研究探讨了影响结构钢断裂行为的微观组织因素。它对抗断裂金属合金的设计具有潜在的影响，可以用于提高寿命和安全性的结构。＊＊＊

9712620 Garrison The objective of this research is to investigate the effects of carbon content on sulfide formation and void nucleation resistance in titanium-modified steels. It is hypothesized that increasing the carbon content of titanium-modified steels causes the precipitate particles of the Ti2CS sulfide to be formed at higher temperatures, thereby producing larger sulfide sizes. Since the void nucleation resistance of Ti2CS particles is expected to decrease with increasing particle size, tying up sulfur as Ti2CS should be less effective in improving fracture toughness as the carbon content increases. If it is confirmed that increasing the carbon content increases the sulfide size and diminishes the void nucleation resistance in the titanium-modified steels, then methods will be explored to: (1) refine the sulfide size when the sulfur is gettered as Ti2CS, or (2) create new methods of gettering the sulfur into void nucleation resistant particles that remain effective at higher carbon levels. One approach that will be considered is to dissolve the sulfides and later reprecipitate them at lower temperatures in the austenite. If the sulfide size is refined by this approach and the reprecipitated sulfides are Ti2CS, then the toughness of higher carbon steels which contain reprecipitated sulfides will be investigated as well as the void nucleation resistance behavior of these finer reprecipitated sulfides. Gettering sulfur as Nb2CS rather than as Ti2CS will also be considered. Recent results suggest that this is feasible and that such particles are resistant to void nucleation. %% This research explores microstructural factors that influence the fracture behavior of structural steels. It has potential impact on the design of fracture-resistant metal alloys that could be employed in structures with improved lifetimes and safety. ***