Rm decreases as the thickness increases
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In the note to Table 1 of GB150 (page 41): Rm decreases as the thickness increases. Why?
:For steels in which Rm decreases as thickness increases, the impact energy value is determined based on Rm at the minimum thickness range of that steel.
In actual manufacturing, the greater the thickness of the steel plate, the slower the cooling during normalizing, and the lower the required value for the strength Rm. This can be seen in GB713. If the requirements are not appropriately reduced, the qualification rate for thick plates will decrease.
This post was last edited by zhangjuhua on 2017-7-2 at 12:33. The thicker the steel plate, the more uneven the cooling rate during heat treatment; the center of the plate may cool more slowly, increasing the likelihood of defects and impurities. As a result, the Rm value is lower in thicker plates. However, it is stated that in many foreign materials, by controlling the alloy content and other factors, the Rm value remains unchanged even as the thickness increases
Indeed, for materials like SA516Gr70, the standards specify the same values for different thicknesses. However, the value is very low; it should be calculated based on thickness. The general requirements for our corresponding materials, Q345R and SA516Gr70, are equivalent to those for Q345R with a thickness of 100 mm. So, ASEM does not mean that Rm remains unchanged, but rather that a lower value is taken.