Effects Of Alloying Elements On The Solidification Structure And The Sub-critical Treat Hardening Behavior Of The High Chromium Cast Irons

In the microstructures of as-cast High Chromium Cast Irons (HCCIs), there is the eutectic type M7C3 carbide that has high hardness, doesn't join into net and is isolated distribution in the matrix, which has high strength and good toughness. The HCCIs have excellent wear resistance because it's particular microstructure and being widely applied in the miner areas, metallurgy, manufacture of building materials, power plant and chemical industry and so on. The as-cast HCCIs have not well abrasion resistance and they must be properly heat-treated, then has the finer wear resistance, commonly. The sub-critical treatment is an appropriate heat treatment method and through it, the HCCIs have good mechanical properties. With the development of industry technology, the alloying elements are added into HCCIs to achieve favorable performance .The study on the effect of the alloying element on solidification microstructure and the sub-critical treat hardening behavior of HCCIs is needed for reasonably and availably utilization of the precious alloy resource. Our task is to study the effects of manganese, copper and vanadium on the HCCIs through some contrastive experiment.In this paper, the solidification microstructure and sub-critical heat treatmenthardening behavior of a series of different composition HCCIs has been researched by using electron probe analyzer, X-ray diffraction, SEM, DTA, magnetic method and hardness test, and the influence of different content of manganese, copper and vanadium on HCCIs is gone into particular.The results indicate that, the microstructure of as-cast HCCIs is composed with austenite, martensite and type MiCj, carbide. And with the manganese, copper, or vanadium is added into HCCIs, the retained austenite of the HCCIs increases based on distinct mechanism, respectively. Copper can increase the amount of carbide when it been added into HCCIs and vanadium can fine the microstructure of HCCIs that can bring on HCCIs hardening. HCCIs will appear secondary hardening in the sub-critical treatment, and the more austenite content HCCIs have, the more obvious the phenomenon is. The mechanism of secondary hardening is that with the precipitation of carbide from austenite, the Ms point of HCCIs increase, and occurs martensite transformation and hardening in the course of cooling. The HCCIs contented copper or vanadium will precipitation the e-Cu phase or VC, respectively, in the process of sub-critical treatment, which will lead to dispersion strengthening and HCCIs hardening. Because the precipitation of e-Cu or VC will last longer time, the secondary hardening peak owing to that will posterior to the first hardening peak due to martensite transformation. Through experiment with the cryogenic treated sample also confirm that the first hardening peak of hardening curve results from martensite transformation. And through cryogenic treatment, the hardness of HCCIs augments as a result of retained austenite changed into martensite.