Effects of TiC addition on microstructure, microhardness and wear resistance of 18Ni300 maraging steel by direct laser deposition

摘要

18Ni300 maraging steel with different TiC contents (0-10 wt.%), for the first time, have been fabricated by a direct laser deposition (DLD) technique. The microstructure and properties of the as-deposited and heat-treated samples have been carefully investigated. The obtained results show that the original 18Ni300 maraging steel exhibits extremely fine cellular microstructure with an average diameter of 3.7 mu m, composed of martensite (M) and Ti2N. In contrast, the microstructure of the TiC-reinforced composites is significantly refined, in which the volume fraction of TiC formed with different morphologies varies with the TiC addition content. However, some cracks exist in the composite sample with the TiC addition up to 10 wt.%. The average microhardness of the asdeposited samples increases initially and then decreases with increasing TiC content, and the maximum microhardness (444 HV0.2) is obtained after adding 5 wt.% TiC. In addition, the sample with 5 wt.% TiC has been experienced a solution treatment at 850 degrees C for 1 h and then a subsequent aging treatment at 500 degrees C for 3 h. A number of nano-precipitates Ni3(Mo,Ti) and a few austenite are formed, which are dispersed in the martensite matrix after the heat treatment. This results in a high microhardness of 576 HV0.2 and a low wear rate of 1.37 x 10-6 mm3/(N center dot m), compared with those of the TiC-free sample (368 HV0.2 and 5.61 x 10-5 mm3/(N center dot m)), respectively. The possible microstructural mechanisms accounting for the property changes of the TiC-reinforced 18Ni300 maraging steel have been discussed in detail.