DC04 Deep Drawing Steel: Why Yield Strength Has an Upper Limit, Not a Lower One

DC04 is the deep-drawing quality of EN 10130, and it is specified with a maximum yield strength of 210 MPa rather than a minimum. That inversion is the entire logic of the grade. A steel that has to flow into a die cannot be sold on strength, so the standard caps yield, holds tensile strength in a narrow 270–350 MPa band, and guarantees ductility instead: elongation A80 of at least 38 %, a plastic strain ratio r90 of at least 1.6, and a strain hardening exponent n90 of at least 0.18.

Asking for "minimum yield 210 MPa" on a DC04 line is the single most common error in cold rolled enquiries. DC04 has no minimum to give.

1.The DC Ladder

The ladder is a softening ladder: each step up buys formability and gives away strength. Material numbers run 1.0330 (DC01) through 1.0338 (DC04) to 1.0873 (DC06).

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2.What r90 and n90 Actually Tell You

Both numbers describe behaviour in the die, and both are more useful than elongation when a part is difficult.

r90 measures resistance to thinning. Steel with a high r-value thickens in the flange instead of thinning in the wall, so the corner of a drawn cup survives. DC04 at r90 ≥ 1.6 holds wall thickness where DC03 starts to neck.

n90 measures how quickly the steel work-hardens as it stretches. A high n-value spreads strain evenly instead of letting it concentrate, which delays a visible neck.

If a part fails by wall thinning, look at r90. If it fails by local necking, look at n90. Neither value is reported unless you ask for it at order stage.

3.The Thickness Caveat

EN 10130 defines these figures within a thickness band, and the guaranteed values step down outside it. Below about 0.50 mm and above about 2 mm, the minimums that apply are lower than the headline numbers. Read the certificate against the gauge you actually ordered, not against the grade name. At 0.8 mm, DC04 sits inside the main band.

4.Annealing, Skin Pass and Lüders Lines

DC04 is annealed to a soft, recrystallised structure. It is then skin-passed, a light temper roll with three consequences that matter in production:

It removes yield-point elongation, the root cause of Lüders lines - the stretcher-strain bands that appear on formed panels.

It sets surface roughness, which controls oil behaviour in the die and coating adhesion.

It slightly raises strength and lowers elongation. The softer the material, the more likely it is to show stretcher strains; the harder, the less it draws.

5.Surface Quality and Finish

EN 10130 gives two surface quality classes. Class A permits minor defects that do not impair forming or coating adhesion; class B requires the better face to be free of anything that would spoil a quality coating or an electrolytic deposit, with the reverse face at least class A. Finishes run from extra smooth (b, Ra ≤ 0.40 µm) through smooth (g) and matt (m) to rough (r). Deep-drawn visible parts normally get class B with a smooth finish; hidden brackets do not need it.

6.What to Check on the Certificate

An EN 10204 3.1 document for DC04 should show heat or ladle analysis, actual Rp0.2 and Rm, measured A80, and r90/n90 where ordered, plus surface quality, finish and oiling state. Two things are worth reading twice: that the measured yield sits below the cap with a sensible margin, and that the values are quoted for your thickness.

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FAQ

Q: Does DC04 have a minimum yield strength?

A: No. EN 10130 sets a maximum of 210 MPa because the grade is sold on formability.

Q: Is DC04 weldable?

A: Yes, by spot, MIG and TIG without preheat, thanks to the low carbon content.

Q: Why does r90 matter more than elongation for deep drawing?

A: r90 predicts thinning resistance in the die wall, which is usually what limits draw depth; elongation is measured in a straight pull and misses that behaviour.

Q: Can I order DC04 without r90 and n90 guarantees?

A: Yes, and that is the default. The values are only supplied when agreed at the time of enquiry and order.

We supply DC04 with full EN 10204 3.1 documentation and can report r90 and n90 against your gauge. Send your part geometry and we will tell you whether DC04 is enough or whether the draw needs DC05.