1.Why are erosion pits fatal to deep boring?
Stress Concentration Effect: Pitfalls are microscopic notches; during tensile testing, the stress concentration factor at the notch root can reach 3-5 times the normal value. Even if the material elongation is acceptable, local strain can instantly exceed limits, leading to cracking.
Accelerated Die Wear: The rust layer is Fe₂O₃/Fe₃O₄, with a Mohs hardness of 5.5-6.5 (the substrate is only 4.5). This is equivalent to applying an abrasive layer to the steel plate. After thousands of punches, the die edge becomes dull, leading to burrs and cracking.
Irreversible Thickness Loss: Grade C and above rust is typically accompanied by a thinning of 0.02-0.05mm. For a 1.0mm plate, this represents a 2-5% tolerance loss. The die clearance is designed based on the nominal thickness; the thinned area cannot be contained, leading to wrinkling and cracking.
2.What solution is suitable for Grade A surface rust + non-visual parts?
No rust removal required, proceed directly with stamping (but mold adjustment is necessary).
The surface rust layer will partially peel off during stamping, not affecting the forming process, but only the weld conductivity (requiring subsequent grinding).
Operating recommendations: Reduce stamping speed by 10-15%, apply an anti-burring coating to the mold, and perform rust prevention treatment after stamping.
3.What are the options for offline rust removal with a 48-hour usage period?
Chemical Method: Organic acid rust remover (VCI-708 type), brush or soak. Hydrochloric acid/sulfuric acid are strictly prohibited-strong acids will penetrate grain boundaries, causing hydrogen embrittlement and delaying cracking during stamping.
Mechanical Method: Nylon abrasive brush roller (180-240 mesh), dry polishing, with single-sided removal controlled to ≤0.003mm.
Red Line: Abrasive wheel grinding and sandblasting are strictly prohibited-they will damage the sheet shape and surface roughness, drastically increasing resistance during stamping.
4.In what situations should we directly process the product as scrap or return the roll by agreement?
Do not attempt to pass through the pickling line again: Search results clearly show that 1.0mm thin plates are extremely prone to over-etching and burning through when passing through the pickling line, and the loss rate is uncontrollable.
Do not use inferior materials: Even if cold-rolled plates with etched pits are made into parts, their fatigue life is significantly reduced, and there is a recall risk if they are used in automotive structural components.
5.Under what circumstances should you refuse to accept the package?
Rust occurring in the middle of the steel coil (not at the beginning or end) indicates that water ingress or condensation has seeped into the core, making the internal corrosion uncontrollable.
Promising to "re-pass the pickling line" with rust present is a dangerous promise from an unqualified person; the pickling pass rate for 0.8-1.5mm cold-rolled sheets is extremely low.
For deep-drawn stamped parts (such as fuel tanks and clutch housings)-these parts have stringent requirements for surface continuity; rusted sheets are scrap and require no grade assessment.