1.What are the effects of a high elongation rate?
Deep-drawing grade (complex parts): Requires elongation ≥40%, even as high as 46-52% (e.g., DC04/BLD/SPCEN). This type of material is soft and has good plasticity, allowing it to be deep-drawn into deep-cavity parts such as mobile phone cases and automotive oil pans.
Medium-drawing grade (common forming): Elongation is typically around 31-34% (e.g., medium-drawing cold-rolled sheet). Suitable for shallow-drawing parts such as air conditioner housings.
Counterexample (ultra-high strength steel): When the elongation decreases by more than one-third due to process fluctuations, stamping will result in mass cracking, rendering the material unusable.
2.What are the effects of a low elongation rate (or a "fake" elongation rate)?
This is the most easily overlooked problem in the stamping process. If the elongation value of the steel sheet is qualified when it leaves the factory, but the flattening elongation is insufficient (i.e., the final straightening process is not done well), the steel sheet will have a "yield plateau". During stamping, this type of steel sheet does not deform uniformly, but suddenly slips locally, forming tensile strain marks (slip lines) - the part dimensions are qualified, but the surface is full of wrinkles, which cannot be covered after painting, and it is scrapped directly.
3.What is the relationship between elongation and hardness?
Soft materials (Grade A/S): Fully annealed, low hardness (HRB≤65), high elongation (>40%), best stamping performance.
Hard materials (1/2 hard, fully hard): High hardness (HRB>74), extremely low elongation, almost no plasticity; forced stamping will inevitably cause cracking.
Conclusion: If hardness exceeds the standard during acceptance, elongation will also be substandard, making it unsuitable for stamping.
4.What are some hard criteria for selecting materials for stamping?
Check elongation values: Complex parts must have an elongation of A80 ≥ 40% as stated on the quality certificate; ordinary parts must have at least ≥ 32%.
Check surface finish: When stamping samples, check for slip lines. The presence of slip lines indicates inadequate flatness; even if the surface finish is acceptable, the material should be returned.
Check corresponding grades: Directly select materials with grades ending in "D" (e.g., DC04, DC06, SPCD, BLD). These are high-elongation series materials specifically designed for stamping.
5.How does elongation affect stamping?
The higher the elongation, the stronger the material's plastic deformation capacity, and the better it can withstand complex stretching and bulging without cracking; insufficient elongation will inevitably lead to cracking or surface defects during stamping.