Urgent request: Why cannot the allowable temperature for 20MnNiMo exceed 426 degrees?
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The equipment has experienced local overheating due to accidental reasons. What is the reason why GB150 specifies an allowable temperature of 400 degrees for low-alloy high-strength steels such as 13MnNiMo and 20MnNiMo (which corresponds to the upper limit of the allowable stress value)? What are the mechanisms by which overheating causes damage to materials? I checked ASME Volume II, which specifies that the allowable maximum temperature is 426 degrees for this material, while it is 537 degrees for carbon steel. The notes indicate that care should be taken regarding graphitization at temperatures above 425 degrees; however, no such warning is given for 20MnNiMo. So what factors determine the allowable operating temperature for this material? ?
Since above 426, carbon steel exhibits a strong tendency to graphitize, which severely affects its mechanical properties; therefore, it is not possible to determine its allowable stress using conventional methods. Long-term testing must be employed, but this is time-consuming and labor-intensive, and the data variations are significant. To avoid misleading results, the upper temperature limit is simply set. If there is a reminder about graphitization, it means that tests have been conducted and data is available; if not, then it means that no tests have been done.
Thank you for your reply. The graphite content in 20MnNiMo is higher than that in 16Mn, and it also contains Ni, which promotes graphitization; therefore, graphitization is likely to be a factor that needs to be taken into consideration. Do you know what effect the Mo element has on graphitization? Additionally, aside from long-term effects such as graphitization, what other impacts does high temperature have on the material in the short term? Temper brittleness?
For these two materials, there is no need to consider temper brittleness; they should both fall within the category of high-strength steels. I’m not sure how short a period of time you mean by \"short term\" when it comes to high temperatures These two materials are generally used in situations with high pressure; then why not choose CrMo steel when the temperature is even higher?
It’s a testing device that has been built; the temperature is around 500 to 550 degrees. There is local overheating, but it’s not a situation where the entire cross-sectional thickness is affected. Thank you\ud83d\ude4f
It’s a testing device that has been built; the temperature is around 500 to 550 degrees. There is local overheating, but it’s not the case that the entire cross-sectional thickness is affected. Thank you\?\?