What is the reason why the allowable stress for sheets is higher than that for forgings, given the ratio of strength between forgings and sheets?
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Hello, teachers! After being forged, the sheet metal forms forgings, which possess superior comprehensive properties compared to the sheet metal. However, in GB/T150.2, by referring to the tables – “Table 2 Allowable stresses for carbon steel and low-alloy steel plates” and “Table 9 Allowable stresses for carbon steel and low-alloy steel forgings” – it can be seen that the strength of Q345R is higher than that of 16Mn, and the strength of 15CrMoR is higher than that of 15CrMo. “Table 5: Allowable stresses for high-alloy steel plates; Table 11: Allowable stresses for high-alloy steel forgings. The strength of S30403 plates is higher than that of S30403 forgings. It follows that after the sheet metal is processed into forgings, the allowable stress does not increase; instead, it decreases. Why is this?
Since there are many factors that affect the quality of forgings, these forgings may develop defects such as laminations and cracks
Large forging manufacturers use steel ingots for production, while smaller manufacturers use steel plates with a thickness of 200–300 to carry out forging; these are the scrap materials
The allowable stress of a material is related to its thickness; in the tables showing the allowable stress for forgings, the range of thicknesses is quite wide. If sheet metal and forgings are compared using the upper limit of thickness, their allowable stresses are roughly the same.
I hadn’t noticed this issue yet.
The impact of thickness is significant; the difference isn’t much