Decoding the Designation: DC01, Non-Alloy, CRCA, Skin Passed
Every word in the product name carries information. DC01 identifies the base grade of the cold rolled low carbon family in EN 10130, formerly known as St12 or FeP01. Non-alloy confirms that corrosion resistance must come from a coating or paint system rather than from alloying elements. CRCA, meaning cold reduced close annealed, confirms that the strip was rolled cold and then annealed to restore ductility. Skin passed records the final light temper pass that follows annealing.
A thickness of 0.5 mm combined with a width of 1522 mm describes wide thin strip in coil, which is the natural feedstock for slitting into tube strip, strapping and panel widths. The metallurgy behind that strip, rather than its dimensions alone, decides how it behaves in the forming line.
Annealing Routes and Their Effect on the Strip
Two industrial routes produce CRCA material, and each leaves a different fingerprint on the finished coil.
| Route | How it works | Effect on the strip |
|---|---|---|
| Batch annealing | Coils stacked in a furnace under a protective atmosphere and held for many hours | Uniform and soft, low yield strength, forgiving on simple press work |
| Continuous annealing | Strip reheated and cooled in line at high speed | High throughput with tight property control, up to the most demanding drawing grades |
Whichever route is used, the aim is the same: recrystallise the structure that cold reduction has work hardened, so that yield strength falls and elongation rises enough for forming. Batch annealed coil is characteristically softer, while continuously annealed coil can reach the higher r and n values required by deep drawing grades such as DC04.
What Skin Passing Changes in the Metal
After annealing, low carbon steel shows a pronounced upper and lower yield point. Formed in that condition, it stretches unevenly and leaves visible bands across the part. A temper pass of roughly 0.5 % to 1.5 % extension suppresses the behaviour and produces a smooth yield curve.
Surface roughness. The work roll texture is transferred to the strip, giving a controlled Ra that holds lubricant in the die.
Flatness. Tension applied during temper rolling pulls out residual shape defects left by rolling and annealing.
Strength. A small but real rise in yield strength, which has to be allowed for in the forming calculation.
Ageing. Material stored for months before forming is often ordered to an anti-ageing specification so that the yield point does not creep back.
Inspection Points on a CRCA Skin Passed Coil
| Property | Method |
|---|---|
| Tensile properties and elongation | Tensile test on longitudinal samples |
| Forming indices r and n | Evaluated from tensile data where the grade requires them |
| Chemical composition | Heat analysis and product analysis against EN 10130 limits |
| Dimensions | Thickness and width measured against the EN 10131 tolerance class |
| Surface roughness | Profilometer reading taken at intervals along the coil |
| Surface defects | Visual inspection for scale, scratches, roll marks and edge damage |
| Coil build | Check of wrap tightness, telescope and edge alignment |
Two details are worth insisting on when the strip will be formed on a continuous line. First, that the surface roughness figure on the certificate is given as a range rather than a single point value. Second, that the coil is wrapped and protected for the sea leg of the journey, because edge rust on the outer wrap is the most common complaint raised on arrival.
Forming and Handling Thin Wide Strip
At 0.5 mm thickness, handling discipline matters as much as steel quality. Coil should be stored indoors on a saddle or pallet, never stood on edge and never lifted directly against the wrap. Decoiling tension has to be high enough to keep the strip flat but light enough not to stretch a thin gauge, and slitting burrs should be kept low because a burr becomes a stress raiser as soon as the strip is bent. In tube welding, a coil with even thickness across the full 1522 mm width tracks better through the forming rolls and gives a straighter seam.
Questions on CRCA Skin Passed Coil
Q: Is CRCA the same as annealed?
CRCA stands for cold reduced close annealed, so annealing is part of it. The practical point is that the coil is delivered in the soft annealed condition rather than full hard.
Q: Why do faint bands appear on pressings?
They are stretcher strains from discontinuous yielding in annealed steel that has not been temper rolled. An adequate skin pass, roughly 0.5 % to 1.5 % extension, prevents them.
Q: Which annealing route suits deep forming best?
Continuous annealing reaches the highest r and n values needed for deep drawing grades such as DC04, while batch annealing gives a soft uniform coil that performs well in simpler forming.
Q: Does skin passing reduce ductility?
It raises yield strength slightly and removes a little total elongation, but the gain in surface quality and forming consistency normally outweighs the small loss.
Q: How should 0.5 mm coil be stored?
Indoors, on a saddle or pallet, with the wrap intact and the coil kept clear of standing water. Stacking on edge should be avoided.
Q: Can CRCA coil be used for tube making?
Yes. Skin passed DC01 strip is a common feedstock for longitudinally welded tube, provided thickness is even across the width and burr height at the slit edge is controlled.