Study Of Thermal Fatigue About GRATE-KILN Steel And Analyse Of Oxidation Behavior

With the development of the society, there is an increasing demand for the use of materials. Materials are needed to possess of better performance when in practical environment. In practical use, fracture is one of the most important forms for materials to be invalided, which will cause great loss for people. A lot of fracture accidents take place because of material fatigue. Because of the sharp working circumstance and undergoing higher temperature, GRATE-KILN steel is more likely to be invalided. So thermal fatigue property is an important measuring method.The thermal fatigue samples with prefab crack have been chosen. The period from the initiation of the crack to the length reaches 0.1mm has been defined as the initiation period of thermal fatigue cracks. The period that the cracks propagate to more than 0.1mm and later has been defined as the propagation period of thermal fatigue cracks. The cold and hot cycle times when the length of the cracks reach to 0.1mm is used to measure the resistance to the initiation of thermal fatigue of different superalloys; The length of thermal fatigue cracks under same cycle times is used to measure the resistance to the propagation of the thermal fatigue cracks from different samples. Then we use the different heat treatment methods of solution and aging. Probing into the resistance of different samples thermal fatigue after heat treatment. Compare with the oxidation resistance of different treatments.The main conclusions that gained under the above conditions are as follows:Cracks are initiated in the defect of the samples which is near the gap,then extend to the stress centralized area. The thermal fatigue property of 30Cr24Nil2Mn2Si2RE is prior to Cr25Ni20, 30Cr24Ni7Mn3NRE and 30Cr21Mn8Ni4Si2Nre.And the process of phase change aboutγ→αis taking place during thermal fatigue. The resistance of thermal fatigue about different samples is improving after solution and aging. Reasons are as follow: Frist, we can obtain more alloying austenite after heat treatment. Second, it is more likely to spheroidized which can improve the plastic strain of sample. Third, the weeny carbide has the function of postponed the propagation of fatigue cracks At the temperature of 600℃, all the four samples have the ability of resist oxidation. The treated samples are porne to have better oxidation resistance at 800℃. But at 900℃. all samples have lower oxidation resistance. The thermal fatigue performance and oxidation resistance of alloy has been improved when added in proper amount of RE. The propagation mode of the cracks is mixed propagation: the cracks are propagated in grain boundary and intercrystalline cracking, the cracks with the trend of trancrystalline cracking quickly stopped then-propagation or trancrystalline cracking developed to a certain extent then turn to intercrystalline cracking.