Summary

DC01 and DC04 are cold-rolled drawing steels; SPHC, SPHE and SPHF are hot-rolled. The difference between adjacent grades is mostly drawability rather than strength, and the difference between the two families is surface, thickness range and thickness band. A grade chosen from a previous project, or from a machined component, is the most common cause of both an over-specified material line and a crack at first-off. Draw ratio, final wall thickness, surface visibility and downstream welding or plating decide the grade; a first-article trial on the real sequence confirms it.

The Grade Ladder: Two Families, One Direction of Formability

DC01 and DC04 are cold-rolled drawing steels. SPHC, SPHE and SPHF are hot-rolled, and in the JIS G3131 designation the trailing letter is a formability claim: C for commercial quality, E for drawing quality, F for deep drawing quality. The five names are not five quality levels of one material. They are two mill routes, two surface conditions and two thickness ranges, with a ductility ladder running through each. What separates adjacent rungs inside a family is narrow and measurable: maximum carbon content, the plastic strain ratio r measured at 0, 45 and 90 degrees to the rolling direction, the work-hardening exponent n, and the minimum elongation. What separates the families is wider and mostly geometric: how the strip was rolled, how thick it is, and what its surface looks like at the press.

Carbon is the first number to read, because in low-carbon sheet it sets strength and ductility at the same time. Typical maximum carbon contents run near 0.12% for DC01, 0.08% for DC04, 0.15% for SPHC, 0.08% for SPHE and 0.06% for SPHF. The overlap between the families is the interesting part: SPHE is not a poorer grade than DC01, it is a hot-rolled grade with comparable chemistry and a different surface, thickness range and thickness tolerance. Reading the five names as one ladder from worst to best produces the wrong decision at quotation, which is where most grade problems are created.

Grade	Mill route	Typical max. carbon	Formability character	Typical thickness range	Where it earns its place
DC01	Cold-rolled	0.12%	Lowest r-value in the cold-rolled drawing ladder; adequate for shallow cups and gentle radii	About 0.4-2.0 mm	Shallow draws, flat formed parts, covers and brackets where surface and thickness band matter more than depth
DC04	Cold-rolled	0.08%	Higher r-value and n-value than DC01; carries a deeper reduction per stage before the wall tears	About 0.4-2.0 mm	Deep cups, small die radii, walls that must stay tight, routes that should avoid an extra anneal
SPHC	Hot-rolled, usually pickled	0.15%	Commercial quality; forms to gentle curvature and shallow recesses, not to a deep cup	About 1.2-6.0 mm	Thick shallow formed parts, structures, parts that will be painted or hidden in an assembly
SPHE	Hot-rolled, usually pickled	0.08%	The drawing grade of the hot-rolled family; behaves predictably when a thick part has real draw depth	About 1.2-6.0 mm	Thick drawn housings and formed plates where the radius is generous and the wall is not dimensionally critical
SPHF	Hot-rolled, usually pickled	0.06%	Deep drawing quality; the most formable hot-rolled strip, and the hardest of the five to source at short notice	About 1.2-4.0 mm	The deepest hot-rolled draws, or where an interstage anneal has to be avoided for surface reasons

Read the table as a starting point rather than a specification. Two mills can supply the same designation against different guaranteed minima, and a certificate that quotes a typical value instead of a minimum is not a guarantee at all. Family first, rung second: cold-rolled or hot-rolled changes the surface, the thickness band and the downstream operations, while the rung inside the family changes how deep the part can be drawn before something has to give.

DC01 vs DC04: The Difference Is Drawability, Not Strength

The two cold-rolled grades sit in a similar band of yield and ultimate strength, so choosing between them is not a strength decision. What changes is the plastic strain ratio, which measures how well the sheet resists thinning while it is pulled in its own plane. A higher r-value means the material flows from the flange into the wall while holding its thickness, which is exactly the deformation a drawn cup needs. In practice DC04 accepts a deeper single-stage reduction and reaches a smaller die radius before the wall tears below the radius, and it tolerates more accumulated reduction before the work-hardened wall needs softening again. DC01 is not a poor material. It is the wrong one for a deep cup and the right one for a shallow part.

The commercial consequence is not confined to the material line. A deeper draw in DC04 can remove an interstage anneal from the route, and that is usually worth more than the sheet itself: a furnace step adds a queue, a transport move, a distortion allowance to compensate in the die, and another chance to damage a finished surface. Read the other way, specifying DC01 often adds a drawing stage or an anneal, and both show up in the tool rather than on the purchase order. Where the sequence already includes ironing to set the final wall, the grade has a narrower job: it has to survive the draw, not set the thickness, and DC01 becomes more defensible.

SPHC vs SPHE: The Hot-Rolled Family, Thicker and Coarser

Hot-rolled strip is rolled above the recrystallisation temperature and is not cold-reduced afterwards, which is why it is available in thicker gauges and why it is less expensive per kilogram than cold-rolled sheet of comparable chemistry. It is also coarser. A pickled hot-rolled surface is rougher than a cold-rolled one, the thickness band is wider, and flatness is less tightly controlled. Within the family, SPHC is commercial quality and SPHE is the drawing grade; on a thick part with real draw depth, SPHE is the first rung that behaves predictably rather than approximately. SPHF sits above it and is genuinely more formable, but thickness and width availability are practical constraints, so it is not a grade to write on a drawing without confirming the coil can be obtained.

The thickness is not free either. A hot-rolled blank is stiffer, so it needs more tonnage and more blank-holder force for the same blank outline; the deep draw force calculator is the right place to check that before a press is booked. A thicker wall also carries residual stress over a larger section, which raises springback and leaves the flange less flat after trimming. On thick hot-rolled parts the workable approach is to design a generous radius and a modest draw ratio and accept that the wall will not be dimensionally tight, rather than to specify SPHE and then ask it to hold a cold-rolled thickness band.

The Specification Trap: A Grade Copied From the Wrong Project

The most common grade error never reaches a press. A grade is copied from the drawing of an earlier part, from a material list in a project file, or from a machined component, and it is carried into a new enquiry without being re-derived. Three variants follow, and they fail in different ways:

Over-specified: a shallow cap with a draw ratio near 1.3 is called out in DC04 or SPHF because the previous part in the family was deep. The extra formability is paid for and never used.
Under-specified: a grade that cannot carry the planned reduction per stage opens a crack at the die radius on the first draw, or forces an unplanned extra draw or anneal into the sequence after the tool has been cut.
Category error: a grade lifted from a machined or bar component. A bar grade is specified for machinability and hardenability and carries no r-value guarantee for strip forming, so chemistry that looks equivalent on paper says nothing about how the sheet will flow over a die radius.

Over-specification is the quieter failure and it is not always harmless. A softer, lower-yield grade wrinkles more readily in the flange and dents more easily in handling, so a blank-holder setting that ran clean on the previous grade has to be re-tuned, and a part that was dimensionally stable in a lower rung can start moving because the flange has less restraint. Under-specification is the expensive direction, and it announces itself at first-off rather than at quotation. Both are avoided by the same question: which property of this grade is actually doing work in this part? The wider catalogue of failure modes that point at the process rather than the material sits under metal working defects.

Symptom at first-off or in the trial	What it usually means for the grade	What to check before changing the tool
Crack in the wall just below the die radius on the first draw	Reduction per stage is higher than the grade can carry	r-value and carbon content against the planned reduction; split the stage or move up the ladder
Crack at the punch nose or across the bottom radius	Stretchability limit rather than drawability; n-value too low for the geometry	Corner radius against thickness, punch nose radius and lubrication
Wrinkles in the flange that are ironed flat into folds in the wall	Yield strength too low for the blank-holder restraint, or the grade was traded in the softer direction	Yield strength of the delivered coil against the certificate, blank-holder force and pad area
Wall below specification at mid-wall after the last draw	Total reduction is too much for the grade without an anneal, or the sequence is one stage short	Reduction history by stage, and whether an interstage anneal belongs in the route
Rough, orange-peel surface on the drawn wall	Coarse grain, typically a hot-rolled grade used in a stretching operation	Grain size on the material certificate, and whether the part was specified hot-rolled for thickness reasons only
Cracking only after an interstage anneal and a further draw	The grade was already at its limit before the anneal; the anneal was treating a symptom	Reduction by stage and the strain carried into the anneal; the grade itself may be the constraint
Parts crack days after forming with no load applied	Residual stress, and hydrogen from pickling or plating, in a higher-carbon or hot-rolled grade	Carbon content, forming strain, and whether the part should be annealed before it is released

The Go-Thinner, Cheaper-Grade Lever, and Where It Stops

There is a legitimate commercial lever here: reduce the starting thickness, or trade down a rung, and the material line falls. The limits on it are geometric rather than commercial. Thinning the blank lowers the bending strain at the die radius, because the outer-fibre strain from bending scales with thickness divided by roughly twice the radius. That is a real gain at the radius and the punch nose, which is why a thin blank can sometimes be drawn where a thick one would crack. The gain is paid for in the flange. Bending stiffness falls with the cube of thickness, so a thinner blank wrinkles under less restraint, and the blank holder has to be pushed harder to keep the flange flat. Higher restraint raises the tangential compression in the flange and the tension in the wall where it leaves the radius, so the window closes from the other side. Thinning does not move the limit; it narrows the band between wrinkling and tearing.

Trading the grade down acts on both sides at once. A lower r-value means the wall thins further as material is pulled out of the flange, so it arrives at the die radius with less section to carry the load and a steeper through-thickness stress gradient across the bend for that section to distribute. A lower yield strength makes the flange easier to over-restrain, which is how a part that ran clean in DC04 can wrinkle in DC01 on the same blank-holder setting, with the same blank and tool. The interaction between thickness, restraint and the radius is the same mechanism that governs deep drawing technology, and it is why a grade change and a gauge change should never be trialled together - one variable at a time, or the result cannot be attributed.

The floor no grade change can remove: The wall has to survive its ironing clearance, carry whatever load, pressure or magnetic flux the application puts on it, hold a thread, a stake or a weld, and be thick enough to be fed and handled without damage. Below that floor the part is not a cheaper version of itself, it is a different design. Set the floor from the function first, then choose the cheapest grade and gauge that clear it.

Cold-Rolled vs Hot-Rolled Surface, Die Wear and What Happens Downstream

Surface is the part of the grade decision that reappears in operations which have nothing to do with drawing. A cold-rolled grade arrives with a fine, uniform surface and a narrow thickness band, which is why it can be plated, painted or left as-drawn without extra preparation. A pickled hot-rolled grade arrives rougher, and that texture carries through the draw rather than being erased by it. Two consequences follow. The first is cosmetic: a visible part drawn in a hot-rolled grade will not match a cold-rolled surface, and no amount of polishing recovers a surface formed from a coarse substrate. The second is wear. A rougher, harder surface abrades the die radius and the punch nose, so the tool needs maintenance sooner and the wall drifts earlier in the run - a tooling cost that arrives months after the material saving.

For a part that will be plated, the substrate matters more than a roughness number. A coarse surface needs more coating to close into a continuous, pore-free layer, so plating thickness and substrate texture are coupled: the rougher the steel, the more of the dimensional budget the coating consumes. For a welded assembly, hot-rolled chemistry is usually unproblematic, but the wider thickness band has to be absorbed by the welding schedule rather than by the fit-up. The die-side consequences of that wear are covered under stamping die design, where insert material, coating and the radius it protects are chosen together.

Cold-rolled and hot-rolled deep drawn steel parts with visibly different surface texture — The surface a drawn part carries is decided by the substrate, not by the last operation. A coarse hot-rolled strip produces a coarse drawn wall, and downstream coating has to cover it rather than correct it.

How to Decide: Five Questions and a Starting Grade

Grade selection collapses quickly once five facts are on the table, and all five can be answered before any tooling work starts. Draw ratio and the reduction planned per stage set the family and the rung. Final wall thickness and what the wall has to carry set the floor. Whether the part is visible, and whether it is welded or plated afterwards, decides cold-rolled against hot-rolled. Annual volume decides whether an extra stage or an extra anneal is an acceptable answer or a project delay. The mechanics behind each row are set out in the deep draw stamping materials guide; the questions themselves are these:

What is the draw ratio, blank diameter divided by finished diameter, and what reduction per stage does the sequence assume?
What is the final wall thickness, and what does that wall have to carry: pressure, a magnetic circuit, a thread, a stake, a weld, or nothing but appearance?
Is the surface visible after assembly, and is it painted, plated or left as-formed?
What thickness band can the design absorb, given that a hot-rolled band is wider than a cold-rolled one?
What is the annual volume and batch pattern, and does it justify an additional draw stage or a furnace operation if the cheaper grade needs one?

Part and process situation	Starting grade	Reason and the caveat
Cold-rolled, 0.4-2.0 mm, draw ratio up to about 1.4, no radius tighter than about three times the thickness	DC01	No deep drawing grade is required; a cold-rolled surface and thickness band are the reasons to stay cold-rolled
Cold-rolled, draw ratio about 1.5-1.8, two or three draws, visible surface	DC01 or DC04, decided by the trial	The grades overlap in this band; the deciding evidence is wall thinning measured on the trial part, not the certificate
Cold-rolled, draw ratio above about 1.9, small die radius, or a route that must avoid an anneal	DC04 or the next rung of the cold-rolled ladder	Plan the reduction per stage before choosing; the higher rung buys drawability and not strength
Hot-rolled, 2.0 mm and above, draw ratio up to about 1.5, part is painted or hidden	SPHC	Accept the coarser surface and the wider thickness band, and design a generous radius into the part
Hot-rolled, 2.0 mm and above, draw ratio about 1.6-1.9	SPHE	This is the rung where the hot-rolled family starts behaving predictably on a genuine draw rather than a shallow recess
Hot-rolled, deepest hot-rolled draw, or an anneal has to be avoided	SPHF, or reconsider the family	Confirm thickness and width availability first; a thinner cold-rolled grade is sometimes the cleaner answer at a similar wall
Any part whose grade came from a machined, bar or plate specification	Re-derive the grade from the drawing	Bar and plate grades carry no r-value guarantee for strip forming, so chemistry alone does not predict behaviour over a die radius

Two rows deserve reading twice. The overlap row - DC01 or DC04 across the middle of the range - is genuinely settled by trial, because at a draw ratio around 1.6 the difference between the grades may be a tenth of a millimetre of wall thinning rather than a pass or a crack. The last row prevents the most expensive class of error, because a grade lifted from a machined component has no relationship to how sheet metal flows through a die radius.

Validate by First-Article Trial, Not by Datasheet r-Values Alone

A material certificate gives a minimum r-value measured in a tensile test at one strain level in one direction, and it is a useful filter but a poor predictor. Forming a cup involves bending and unbending over a die radius, through-thickness compression under the blank holder, thickening in the flange and thinning in the wall - a strain path a uniaxial tensile test does not reproduce. Planar anisotropy, the difference between r-values at 0, 45 and 90 degrees to the rolling direction, is not captured by a single number either, and it is what produces ears on a drawn cup and forces the tool designer to choose a blank outline and a trim allowance. Batch-to-batch variation adds further spread. The only reliable confirmation is a first-article trial on the production tool, with the production blank and lubricant.

The trial does not need to be elaborate, but it has to be representative, and it has to be recorded:

Run the intended grade on the intended sequence, including the number of draws and any interstage anneal, at the production press speed.
Measure wall thickness at three positions on the finished part: at the bottom radius, at mid-wall and near the mouth. Section the part if the geometry allows it.
Measure ten consecutive pieces rather than one. Ten pieces show the spread and the direction of drift; a single sample shows neither.
If the risk is forming rather than dimension, run a circle-grid strain analysis on one trial blank to locate the peak strain and see how much margin remains.
Repeat the check on the first production coil, not only on trial material, because coil-to-coil variation in r-value and thickness is real.

A grade substitution is a process change, so it earns the same evidence as any other change: same blank, same lubricant, same sequence, and a measured result before release. What can be committed on a drawn feature is finite, and our own statement of that limit is in our capability boundaries; it applies to a grade change as much as to a new part. Trading a rung down to reduce the material line is a legitimate decision. Making it on the strength of a certificate, without a trial, is an experiment run on production.

DC01 vs DC04 vs SPHC vs SPHE: Which Steel Grade Does a Deep Drawn Part Actually Need?