Issues regarding the high-temperature mechanical properties of materials
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Hello everyone, I’ve been puzzled by a question recently: when it comes to the use of materials, at what design temperature do we need to specify high-temperature mechanical properties for the main materials? For example, with a material like duplex stainless steel S31803, whose design temperature is 275 degrees, is it necessary to specify requirements regarding the mechanical properties of this material at high temperatures? What is the basis? For this material, is the decrease in strength value upon temperature rise minimal due to the presence of ferrite? That person knows, thank you! This post was last edited by dam2930 on 2009-2-10 21:31.]
You just need to select from the temperature range specified for materials in GB150-1998; there are no special requirements, although there are some specifications in Chapter 4 regarding materials
The allowable stress for GB150 materials takes into account the material’s high-temperature properties; no special requirements are needed for the temperature ranges specified in the table
When austenitic steel is used at temperatures above 525°C, its carbon content should not be less than 0.04%; this is because at temperatures between 500–550°C, if the carbon content is too low, the strength and oxidation resistance of the steel decrease significantly. Therefore, the general application ranges for ultra-low carbon austenitic stainless steels are as follows: 18-9 up to 400°C, and 18-12-2 up to 450°C. When the operating temperature exceeds 650°C, foreign standards require that materials of type 304 and 316 be of grade H, meaning they should have a slightly higher carbon content; this is mainly to ensure better corrosion resistance, as well as improved heat resistance and thermal stability.
For the material S31803 (a duplex steel), there is no corresponding allowable stress specified in GB150; therefore, the allowable stress must be determined on its own in accordance with Article 3.6.1 of GB150. Hence, if the allowable stress is calculated based on the yield strength at room temperature or the standard tensile strength, then it is not necessary to specify requirements regarding mechanical properties at high temperatures. On the other hand, if the allowable stress is calculated based on the yield strength or tensile strength at the design temperature, then requirements regarding mechanical properties at that high temperature should be specified.
For the material S31803 (a duplex steel), there is no corresponding allowable stress specified in GB150; therefore, the allowable stress must be determined on its own in accordance with Article 3.6.1 of GB150. Thus, if the allowable stress is calculated based on the yield strength at room temperature or the standard tensile strength, then it is not necessary to specify requirements regarding mechanical properties at high temperatures. On the other hand, if the allowable stress is calculated based on the yield strength or tensile strength at the design temperature, then requirements regarding mechanical properties at high temperatures at that design temperature must be specified.
Thank you to everyone above. In the original GB6654, there is an appendix that specifies the high-temperature properties of materials, which need to be requested as special requirements when placing an order. Since it is designed in accordance with GB150, that is, based on the allowable stress values at corresponding temperatures, then why are high-temperature performance values specified in the material standards? Can’t it be specifically stated that the steel mill cannot meet the requirements?
The material shall be subject to retesting at high temperatures when the following conditions are met: HG20581-1998, 5.1 General technical requirements, 5.1.2 For the main pressure-bearing components of high-temperature pressure vessels that meet all the following conditions, their yield strength at the design temperature must be retested based on the furnace and vessel identifier; this value shall not be lower than 1.6 times the corresponding allowable stress value (1.5 times for austenitic steels). 1. The design temperature is greater than 300℃； 2. Design pressure greater than or equal to 1.6 MPa ； 3. The thickness of the steel material is greater than or equal to 20 mm ； 4. The main cross-section of the steel is designed to withstand primary membrane stresses, and its thickness is determined by the results of strength calculations.
Thanks to the person above for sharing the content of 5.1 in HG20581-1998
The temperature is not even 300 degrees, so it can’t be considered high. When high temperatures are actually reached, creep must be taken into consideration.