Fabrication Of Locally Reinforced Manganese Steel Matrix Composite And Study On Stability Of Low Temperature Martensite

With the rapid development of modern industry, wear resistant materials need represent good wearability not only on the condition of strong impact, it is also necessary, under the conditions of medium or low stress. The ordinary wear resistant materials have been unable to adapt to harsh working conditions, therefore, the exploitation of new wear resistant materials has become an important issue to be resolved in the process of industrial production.For a long time, high manganese steel because of high stress, a good strong impact and the wear resistance of metals are widely used in the area of metal wear-resistant materials. However, in the low-stress service environment, high manganese steel with the effect of work hardening inadequately lead to the poor wear resistance appeared. To improve the wear resistance of manganese steel, in particular the wear resistance under the conditions of lack the Surface impact hardening, there was a substantial amount of research work, such as the addition of different alloying elements to improve the original hardness of the high manganese steel and adjust the steel alloy component of high manganese. These modification methods generally tend to undermine the high manganese steel toughness. And austenite manganese steel under the low stress abrasion conditions, using the strong strain hardening ability of the manganese steel metastable austenite not only has better wear resistance, and has good strength and toughness, has a good prospect as a new type of wear resistant material. The hard TiCp is deposited on the surface of austenite manganese steel, not only can increase the wear evidently, but also to ensure strength and toughness and keep the components operating safely and reliably. Even if the surface layer is worn, the matrix still has a high wearability, the wear resistance will continue to play a important role. Therefore, in this paper, the austenite manganese steel has been chosen as the matrix materials.Deep-Cryogenic treatment is an effective way to improve the material hardness and wear resistance. Through appropriate technology,there could be high hardness of martensite with deep-colding austenitic manganese steel matrix.However, Manganese steel was tempered ,which contains deep-cryogenic martensite, for studying the stability of this amterial in the actual conditions. And then,I analysed the change of microstructure and wear resistance for manganese steel under different conditions.So the preliminary results have achieved in this thesis:(1)The results show that TiC had formd before Fe3C ,Fe2Ti and FeTi.in the (Ti, Fe)-C system. Moreover, the thermodynamic stability of TiC is much larger than such as Fe3C ,Fe2Ti and FeTi.(2) In this experiment, the starting temperature of martensite transformation, Ms is 225(K),that is in austenitic manganese steel which contains 8.8%Mn,0.7%C(weight percentage) .Moreover,the temperature Ms is much higher than that in liquid nitrogen which is 77(K) .A large nunber of needle-like martensites generate in austenitic manganese steel with deep-cryogenic treatment.And they tend to parallel in the austenite grains.(3) The influenced factors of growing and distribution of TiC,which is impacted by the (Mn,Fe)particles in the pre-preparational piece : Close to interface,there are reinforced areas with lots of small dense TiC particles,because the melted (Mn,Fe)particles have provided enough Fe element for the reaction,and inhibited the growing of TiC.Close to the center of the pre-preparational piece, the melted (Mn,Fe)particles have absorbt much heat,and then delayed the SHS reaction. (Mn,Fe)particles made the TiC particles bigger and accumlativer,because they formed tree-shaped crystal,and then reduced Fe element in the solidification process.(4) In this experiment,there are martensites by deep-cryogenicing the samples.The martensites did not decompose completely under tempering with high temperature and short time(600℃,two hours),or low temperature and long time(200℃,six hours).The martensites would decompose completely under under tempering with high temperature and long time. Hardness of the sample reduce gradually with the raising of the tempering temperature or prolonging of the holding time.(5) The wear resistance of the district in the composite materials is better then that in manganese steel matrix..Furrows are deep and wide in manganese steel matrix,however,they are narrow and shallow. It proves that the in-situ TiC particles possess good ability for bearing load,strengthening matrix and hindering the deformation.(6) The wear resistance of the sample under deep-cryogenic treatment without tempering is better than that under deep-cryogenic treatment with tempering. The wear resistance of the sample without deep-cryogenic treatment is the worst. The wear resistance of the sample under deep-cryogenic treatment is lower gradually accompanied by higher tempering tempreture or longer holding time.