DC06 as the Ultra Deep Drawing Grade
DC06 is the highest grade in the ordinary cold rolled low carbon family defined by EN 10130. It is an interstitial-free, ultra low carbon steel produced by a fully stabilised route, and its purpose is to accept the kind of draw that would tear an ordinary cold rolled sheet: a deep, narrow, sharp-cornered automotive structural or closure panel pressed in a single stroke. Where DC04 handles high forming requirements and DC05 handles higher ones, DC06 is reserved for the extremes, which is why it appears most often in automotive outer panels, complex housings and parts with a large draw ratio.
Supplied as cold rolled sheet, plate, coil or blank, DC06 carries the European material number 1.0873 and is normally quoted with a skin-passed surface so that the flat areas of a panel remain free from yield-point elongation bands after painting.
Chemistry of an Ultra Low Carbon Steel
The design idea is simple to state and difficult to produce: drive carbon down to a level where no free solute remains, then tie up whatever is left with titanium or niobium so that the sheet cannot age. Manganese, phosphorus and sulphur are also held low, because each of them either hardens the ferrite or forms inclusions that would initiate a tear at the punch radius. A higher purity level is available for exposed panels where surface appearance and stretch formability both matter.
| Element | Typical limit | Why it is controlled |
|---|---|---|
| C | 0.03 % max, 0.006 % max for the highest purity class | Free carbon raises yield strength and causes ageing |
| Mn | 0.30 % max | Solid solution hardening reduces the draw depth |
| P | 0.020 % max | Strong hardening element, harmful to r-value |
| S | 0.020 % max | Forms inclusions that open into cracks |
| Al | 0.015 - 0.020 % min | Deoxidation and nitrogen fixing |
| Ti + Nb | 0.20 % max | Stabilises carbon and nitrogen in the interstitial-free route |
Mechanical Properties Behind the Deep Draw
The plastic strain ratio r and the work hardening exponent n are the two numbers that decide whether a part can be drawn at all. A high r-value means the sheet resists thinning in the wall of the cup, so the wall stays thick enough to carry the load; a high n-value means strain spreads over a wider area before local necking begins. Elongation increases with thickness, so the values below are quoted for the usual cold rolled thickness window and are used to compare grades rather than to guarantee a single coil.
| Property | Typical value for DC06 |
|---|---|
| Yield strength Re | 100 - 180 MPa |
| Tensile strength Rm | 270 - 370 MPa |
| Elongation after fracture A80 | 39 % min, rising with thickness |
| Plastic strain ratio r90 | 2.0 min |
| Work hardening exponent n90 | 0.22 min |
| Material number | 1.0873 |
Read across the family and the trade-off is clear. DC01 is the stiffest and least formable, DC03 and DC04 cover ordinary and deep drawing, DC05 adds margin, and DC06 sits at the top with the lowest carbon content, the lowest yield strength and the highest r-value and n-value of the group. Strength increases down the list; formability increases up it.
Surface Quality Classes FB, FC and FD
For exposed parts the surface class matters as much as the mechanical properties, because any defect that survives the press will be visible under a paint film. Three classes are normally quoted, and the automotive outer panel class is the one that drives most DC06 orders.
FB, sometimes written O3: minor scratches and indentations are permitted on the delivered face because the part will be formed and finished further.
FC, sometimes written O4: one face is free from visible defects and the reverse face meets the FB level, which suits parts painted after forming.
FD, sometimes written O5: one face is entirely defect-free to painting and electroplating requirements while the reverse meets FB, and this is the class used for automotive exterior body panels.
Where DC06 Is the Right Choice, and Where It Is Not
DC06 is wasted money on a part that only needs bending or a shallow draw, and it is the wrong answer when the finished component must carry load in service, because its very formability comes from a low yield strength. The grade earns its place where geometry, not strength, sets the limit.
Automotive outer and closure panels with large draw ratios and sharp character lines.
Complex appliance housings, sink bowls and drawn enclosures with deep side walls.
Parts formed in one stroke from a blank where a second annealing step is not economical.
Applications where a high r-value reduces the number of forming stations needed on a transfer press.
Where the part is both deeply drawn and required to carry structural load, the usual solution is to draw in DC06 and then assemble the component onto a higher strength member, rather than to attempt the draw in a stronger grade.
Frequently Asked Questions
Q: What makes DC06 different from DC04 and DC05?
DC06 is the ultra deep drawing grade, with the lowest carbon content and the highest r-value and n-value in the family. DC04 covers high forming requirements and DC05 covers higher ones, but neither reaches the draw depth that DC06 can accept.
Q: Why is a high r-value important for deep drawing?
The r-value measures resistance to thinning under tensile stress. A sheet with a high r-value keeps more thickness in the drawn wall, so the cup can be pushed deeper before the wall tears.
Q: Does DC06 need a coating?
The uncoated sheet is used for parts that are painted, phosphated or assembled inside a structure. For exposed service the same substrate chemistry is supplied with a zinc or 55% aluminium-zinc coating under the corresponding coated grade designation.
Q: What does the O5 surface class mean?
O5 corresponds to the FD class, in which one face is free from defects that would show through paint or plating. It is the class normally ordered for visible automotive body panels.
Q: Is DC06 difficult to weld?
Not particularly. The very low solute carbon leaves the weld zone soft and free from hardening peaks, and the grade is regularly joined by spot, seam and laser welding on automotive lines.
Q: Can DC06 be supplied as plate as well as coil?
Yes. Thicker cut lengths are supplied as plate or sheet alongside coil and slit strip, with the same grade and surface requirements applying to the cut product as to the coil it was cut from.