Heat Treatment And Toughness Of High Chromium Cast Iron

In this paper, the effects of heating treatment on the repeated impact-fatigue properties and the hardness of High-Chromium Cast Irons are discussed systematically. The results show that with the cooling rate enhancing, more Austenite arc transformed into Martensite, and the possibility of the initiating of fatigue crack turns larger, so the samples become hardener, and obtain poor repeated impact-fatigue properties. Obviously, slow cooling rate is beneficial to the integral properties of High-Chromium Cast Irons. In this paper, heating treatments with secondary preservation are developed to raise the ductile of High-Chromium Cast Irons. With the holding temperature increasing during secondary preservation, smaller and smaller secondary carbides precipitate evenly in the sample, which has a beneficial effect on the hardness of High-Chromium Cast Irons. On the contrary, the repeated impact-fatigue properties decrease because of the large possibility of the initiating of micro-cracks and the short distance of the propagation of cracks. After the first preservation, the samples continue to be hold at 8000C,900C,10000C for secondary preservation. Holding in the range of 13 hours, secondary carbides will keep on precipitating, with a result of the greater content of secondary carbides, which consequently produces a enhancement in the hardness of the samples and a drop in the repeated impact-fatigue properties. And when holding in the range of 3 hours, precipitated secondary carbides will agglutinate, causing a drop in hardness of the samples and an increase in the repeated impact-fatigue properties. When holding in the range of 62h, the alloying carbides begin to precipitate, which takes a beneficial effect on the hardness of the samples and a harmful influence for the repeated impact-fatigue properties. preserving at 7OOC for secondary preservation results in a significant drop in the hardness and the repeated impact-fatigue properties of the samples, which is related to the decomposition of matrix. To investigate the application of impact-fatigue test for the search of brittle materials, the experimental data include the repeated times of impact-fatigue, shock ductile, hardness and abrasion are regressed with liner relation. The result show that small energy repeated impact-fatigue test is appropriate for measuring the ductile of brittle materials.