Page 57 - MetalForming-Mar-2018-issue

The Science of Forming
in determining tensile properties. Suppose that you order grade-1008 or grade-1010, where only chemistry limits are specified, but you also require flatness tolerances. A mill may have produced a coil that meets chemistry requirements, but with buckles or waves. Though correctable, processing to eliminate these defects involves bending and unbending over rolls, which increases strength and decreases elongation. Take two identical paper clips, then bend one of them back and forth to straighten it out. While both have the same chemistry, formability is reduced for the clip that was shape-
corrected.
Since there are no tensile require-
ments associated with grades 1008 or 1010, the mill almost certainly will ship to you this re-rolled coil that meets the necessary flatness standards as long as order requirements are satisfied. Not only may stamping performance differ, but under most circumstances, the mill is not required to inform you of this change.
To ensure some consistency in ten- sile properties, you cannot order SAE J403 grade-1008 or grade-1010 steel. SAE J2329 is the low-carbon-sheet-steel specification with requirements for strength, elongation and n-value (see Table). In this spec., grade 1 represents the least restrictive steel (widest allow- able properties) while grade 3 for hot- rolled or grade 5 for cold-rolled ensures shipment of the highest-formability steel.
If your company has been working with the same supplier, maybe it knows what’s needed for each part or at least has a history of what has been shipped. On the other hand, when buying from various service centers, expect significant variation in the products received, even though the orders are the same.
If you experience high scrap costs, consider changing how you order your raw materials in order to better control what you receive. MF
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