固溶温度对超纯净18Ni(350)马氏体时效钢断裂韧性及微观组织的影响

研究了在1083—1483K温度范围内，固溶温度对超纯净18Ni(350)马氏体时效钢断裂韧性(KIC)的影响．通过透射电镜(TEM)研究了马氏体时效钢微观组织的变化，结合相变曲线和断口扫描电镜(SEM)观察，探讨了固溶温度对断裂韧性的影响机理．结果表明：超纯净马氏体时效钢的断裂韧性(KIC)随着固溶温度的升高或再结晶晶粒尺寸的长大而增加，不存在常见的Ti(C，N)在晶界偏聚而引起的“热脆”现象．固溶态马氏体时效钢由单一的马氏体板条组成，其形貌、间距以及位错密度不受固溶温度的影响．在时效过程中，随着固溶温度的升高或再结晶晶粒的粗化，Ni3(Mo，Ti)等时效析出相在晶界或板条界的偏聚程度逐渐加重并导致基体软化，合金元素Ni，Mo的富集诱发了逆转变奥氏体形成．这使裂纹尖端易于钝化而表现出韧窝状穿晶断裂和保持较高的断裂韧性．

EFFECT OF SOLUTION TEMPERATURE ON FRACTURE TOUGHNESS AND MICROSTRUCTURE OF ULTRA-PURIFIED 18Ni(350) MARAGING STEEL

Variation of fracture toughness (KIC) of an ultra-purified 18Ni (350) maraging steel in the solution temperature range of 1083-1483 K was investigated, and its mechanism was discussed on the base of TEM examination of microstructure in both solution and aging conditions, along with phase transformation and SEM fractographic analysis. The results show that the value of KIC consistently increases with increasing solution temperature or coarsening of prior austenite grain, and there is no thermal embrittlement resulted from segregation of Ti(C,N) at high solution temperature. Solution treated maraging steel consists of invariable martensite lathes. In aging process, the segregation of precipitates Ni3(Mo,Ti) at the prior austenite grain boundaries and lath boundaries becomes more and more serious with the increase of solution temperature or coarsening of prior austenite grain, which leads to the martensite matrix softening and the reverted austenite forms because of enrichment of Ni and Mo at the prior austenite grain boundaries and lath boundaries. The softening matrix and reverted austenite blunt the crack tip and prevent its propagation, so the maraging steel shows a dimpled transgranular fracture and good toughness after high temperature solution treatment.