Do you know why there are these regulations in GB/T150.2-2011?

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1. Clause 3.6.2 of GB/T150.2-2011 stipulates: Why is it necessary to consider the graphitization tendency of carbides in steel? The reason is that when carbon steel and carbon-manganese steel are used for extended periods at temperatures above 425°C, the cementite in the steel decomposes, turning Fe3C into 3Fe + C (graphite). This decomposition and graphitization eventually cause part or all of the pearlite in the steel to disappear, resulting in a decrease in both the strength and ductility of the material. The impact value drops significantly as well, and the steel becomes much more brittle. The ASME codes also have similar provisions on this. 2. Clause 3.6.3 of GB/T150.2-2011 states: The reason is that when austenitic steel is used at temperatures above 500°C–550°C, if its carbon content is too low, its strength and oxidation resistance will decrease significantly. Therefore, as a general rule, for ultra-low carbon (C≤0.03%) austenitic stainless steels, 18-9 grade materials (such as 0Cr18Ni9, S30408) can be used up to around 400°C, while 18-12-2 grade materials (such as 1Cr18Ni12Mo2Ti, S31603) can be used up to around 450°C. When the operating temperature exceeds 650°C, abroad it is generally required that 304 and 316 grades be of H grade, meaning they have a slightly higher carbon content; this is mainly to ensure better corrosion resistance as well as heat resistance, i.e., thermal strength. 3. Clause 4.1.4 of GB/T150.2-2011 stipulates: Why is it necessary to use it in the normalized state? The reason is that, mainly due to the limitations of domestic rolling equipment, the rolling ratio for thicker plates is lower, resulting in slightly poorer density within the steel plates as well as lower quality of the core structure ； Furthermore, normalizing the steel plate can refine the grain structure and improve its microstructure, thereby endowing the plate with better toughness, plasticity, and overall mechanical properties. 4. Clause A.2.1 d) of GB/T150.2-2011 stipulates: What is a \"heat treatment stress\"? A steel ingot (or a continuous casting slab) is rolled into a very long sheet, which is then heat-treated in a furnace depending on various requirements and orders. Those that are heat-treated in the same furnace are called heat-treated coils; those that are heat-treated in different furnaces but rolled together are called rolled coils. The rolling tension should be greater than or equal to the heat treatment tension. For example: if one rolled sheet of steel is cut into 4 pieces, one of which is hot-rolled, one is normalized, one is normalized + tempered, and one is quenched and tempered, then these 4 pieces belong to the same rolled sheet, but they are 4 pieces that have undergone different heat treatment processes. If that heat-treated steel plate that has undergone normalizing and tempering is cut into 2 pieces due to transportation issues after the heat treatment is complete, then those 2 pieces still belong to the same heat-treated batch. It is generally understood that steel plates from the same rolling batch should have identical chemical compositions, while steel plates from the same heat treatment batch should have similar mechanical properties.