High temperature low cycle fatigue behaviour of 4.2Cr-2.5Mo-V-Nb hot work tool steel

摘要

Hot work tool steels bearing 5% Cr are widely used for hot forging dies. These steels require high temperature strength, impact temghness, heat checking resistance, wear resistance etc. Many studies have been done in detail on the high temperature >!: strength and the impact toughness of hot work tool b. steels. A number of new types of hot work tool ii steels have been developed to improve such proper-iv ties [1-3]. However, there are few works relating to L> the high temperature low cycle fatigue life of hot ir, work tool steels [4-7]. We [8] have investigated the k-. low cycle fatigue behaviour of AISI Fill hot work lh tool steel under strain controlled conditions at 873 K iia in air. The study showed that cyclic softening was lh> caused by the decrease of dislocation density in the in: matrix and the coarsening of carbides during fatigue test, and that these processes were accelerated by the :o: increase of the applied strain. Therefore, we can j expect a tool steel with high resistance to temper ir4 softening to offer a good high temperature fatigue n, property. Accordingly, in this study, the high tempi- perature low cycle fatigue test of a new type of hot a; work tool steel was carried out in vacuum in order to to prevent oxidation problems. The effects of the cyclic 0 softening on the fatigue crack generation propaga-K tion were investigated.