Effects Of Heat Treatment And Alloying Elements On Microstructure And Properties Of High Chromium Cast Iron

In this paper, the effects of the different heat treatment technology coordinating with the cryogenic treatment on the properties of high chromium cast iron (short for HCCI) were studied. By the means of the Rockwell hardness test, pendulum impact test, sliding abrasion test, rolling abrasion test, the properties of the materials have been tested. The results showed that the hardness of HCCI with cryo-treating enhanced 8~10 HRC, but the impact toughness dropped. HCCI with cryo-treating may obtain the well coordination of hardness and impact toughness when tempered in 250 ℃ for 4 hours. The hardness peak of the HCCI with cryo-treating appeared as the tempering temperature was about 450℃. Compared to HCCI without cryo-treating, the temperature of hardness peak is ahead about 100 ℃. The hardness peak of the HCCI after secondary preservation appeared in 450℃ tempered whether cryo-treated or not, and the materials also had good wear resistance. The Optical Microscope (OM), Environment Scanning Electron Microscope (ESEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) are applied to analyze the microstructure of HCCI. The results indicated that cryogenic treatment can cause the remaining austenite to transform further into the martensite, therefore the hardness is improving after treatment. But cryogenic treatment do little influence on the carbides of the matrix, so HCCI have similar wear resistance whether cryo-treated or not. The remaining austenites of the HCCI after secondary preservation were extremely few, so the effects of cryogenic treatment were insignificant. This article has also discussed the effects of alloying elements, such as Manganese (Mn),Titanium (Ti) and Nitrogen (N), coordinating with the cryogenic treatment on the properties of HCCI. The results showed that when Mn content increasing, the amount of the remained austenite in HCCI augmented, so that hardness reduced and toughness enhanced, and the sliding abrasion resistance became worse, but rolling abrasion resistance became better. It may caused by the increment of marstensite by cryogenic treatment. Titanium carbide can form heterogeneity crystal nucleus in melting HCCI, which can refine crystal grain and enhance the impact toughness. But too many Ti content resulted in the worse of hardness, wear resistance and corrosion resistance. The HCCI of 0.2%Ti had better wear resistance and corrosion resistance. The cryogenic treatment can enhance its wear resistance, but do not influence on the corrosion resistance. N can strengthen the matrix and enhance the hardness, so can improve the wear resistance. N can also boost the electrode potential of the matrix, and reduce the difference of electrode potentials between the metal matrix and the carbide, improve the corrosion resistance of HCCI.