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21. The extracts from "Source Book on Forming of Steel Sheet" pages 93, 95, etc. is given below :-

"Cold Reduction, Annealing & Temper Rolling

1. The percentage of cold reduction to final thickness is important. A greater reduction results in a finer, harder grain; a lesser reduction results in a coarser, softer grain, Too fine a grain size can cause breakage; too coarse can cause surface-granulation (roughening) on forming. The amount of reduction is approximately 50% - 70% to produce an optimum ferritic grain size of ASTN numbers 6 to 8 (approx.). For example, the cold reduction of 0.100" thick hot rolled coil to 0.040" is 60%. Reduction to 0.020" is 80% and results in finer grain, harder sheet; to 0.060" is 40% and results in a softer, but coarser grain sheet. Likewise, reductions from thicker or from thinner hot bands to the same final thickness (e.g. to 0.040") results in finer and harder, or coarser and softer cold-rolled sheets.

2. Proper annealing temperature (approximately 1200° - 1300° F for drawing quality) along with proper heating, hold and cooling rate determines the optimum in properties, grain size and carbon spheroidization.

3. Although cold-rolled sheets are sometimes used in the annealed last or dead soft condition (for unexposed applications), most cold-rolled sheets are temper rolled (skin rolled), especially when used for exposed applications. The amount of temper rolling is important and is determined by the and part application. Where formability is not important but as much as 2.0% which decreases drawability. Where deep drawing is required the amount of temper rolling is approximately 1.0% or less but sufficient for sheets to be free from stretcher strains when drawn.

The actual percentages of temper rolling can be regulated very closely, for 0.50% or 0.75% or 1.25%. The amount is usually a compromise between drawability and non-straining propensity. With rimmed and capped steel the effects of temper rolling are temporary, therefore, for optimum results, the sheets should be used as promptly as possible.

Mechanical Properties Hot-rolled and cold-rolled sheets, when specified as commercial quality, drawing quality or drawing quality special killed, are generally produced to make identified parts without guarantees on mechanical properties as rejection limits. However, after years of experience, producers and consumers have established guidelines of inspection, testing and acceptance which are usually negotiated and mutually agreed upon, based upon knowledge of end part application.

Very careful consideration should be given to every individual job, and all the snags liable to be encountered during manufacture disposed of, as far as possible before starting to tool-up. Tentatively, the number of operations and the sequence in which they are to be performed should be laid down, taking into account such things as the size and shape of the finished product, and the finished required or to be applied.

Any draw tool, whether for first, second or subsequent metal is stressed past its yield point to cause plastic flow, any considerable variation in the material will have a serious effect on its performance. Variation may exist in the consistency of grain structure, temper ductility, strength, analysis and guage size."