Quantifying the Value of TP-CTL
A variety of thicknesses and material types were studied by Steel Warehouse Co. to characterize the effect and value of temper passing. For the study, material was processed on a temper-level line. To minimize experimental variability, the same coil of steel was used to produce both TP-CTL and non-temper-pass sheets and plates. This was accomplished by disengaging the temper mill once the required temper-passed, leveled quantity was produced, then running the balance of the coil as non-temper-passed, leveled-only steel. Both portions of the coil then were shipped to participants in the experiment for fabrication.
Two categories of parts were tested using both temper-passed, leveled and leveled-only sheet. The first category was composed of production parts familiar to the fabricator. The second category included difficult parts known to be highly sensitive to residual stresses in the steel. Some of these parts were long and narrow and, thus, subject to coil set. Others contained large windows that were sensitive to stresses in both length and width.
Low-carbon C1010 and high-strength, low-alloy (HSLA) grades 50 and 80 were tested. Material thicknesses were 10 gauge (0.134 in.), 7 ga. (0.179 in.), 1/4 in., and 1/2 in. The widths used were 36, 48, and 60 in.
After the parts were cut, they were measured on large, flat granite surface plates with a feeler gauge to determine the largest gaps on both the length and width. The results were recorded and converted to a flatness specification in inches per foot of deviation from flat.
