A solenoid valve housing usually carries one material line on the drawing, DC04 or DT4E, and that single line decides three things at once: how the valve behaves magnetically, how many drawing stages the part needs, and whether the finished housing has to be magnetic annealed. The two grades are not two versions of the same steel. One is a European cold-rolled deep drawing steel chosen for formability; the other is a Chinese electromagnetic pure iron chosen for soft magnetic performance, with a chemistry ceiling that exists to keep coercivity low. This comparison separates the two on the questions that actually decide a production route: what the material does in a magnetic circuit, and what it does under the press.
DC04 vs DT4E pure iron — which grade belongs in a solenoid valve housing?
DC04 is a cold-rolled low-carbon deep drawing steel to EN 10130, while DT4E is an industrial electromagnetic pure iron to GB/T 6983, known as soft magnetic pure iron or electrical pure iron; the two are separated by carbon content and by what the housing is asked to do. DC04 allows up to about 0.08 per cent carbon and forms easily — typically a yield strength of 210 MPa or less with 38 per cent elongation or more — so it suits a housing that is structural and carries no specified magnetic duty. DT4E holds about 99.5 per cent iron or better with a carbon ceiling near 0.025 per cent, which typically brings coercivity down to roughly 48 A/m or less and maximum permeability up to about 12.5 mH/m; it is the choice where the housing is part of the magnetic circuit and coercivity or permeability is specified. The grade name alone proves nothing — the mill certificate and the agreed Hc and permeability limits govern, together with the anneal cycle.
What DC04 is — and what it is not
DC04 is a non-alloy, low-carbon, cold-rolled flat steel produced to EN 10130 for cold forming. Its specification controls chemistry and mechanical behaviour: a carbon ceiling of about 0.08 per cent, manganese at 0.40 per cent or less, phosphorus and sulphur at 0.030 per cent or less, a yield strength typically at or below 210 MPa, a tensile strength in the 270 to 350 MPa band and an elongation of 38 per cent or more in the longitudinal direction. It is ductile, it is consistent in thickness, and it is cheap to buy and to form — which is exactly why it became the default shell material for housings whose magnetics are not critical. What EN 10130 does not do is constrain coercivity, permeability, saturation or magnetic aging. DC04 is a structural forming grade that happens to be soft and low in carbon. A housing drawn from it is magnetic, but the magnetic behaviour of any given coil is not a number the grade guarantees, because carbon content within the allowed band and the amount of cold work left in the wall both move it.
What DT4E pure iron is
DT4E belongs to the DT4 family of industrial electromagnetic pure iron specified in GB/T 6983, and the numeric part of its name is not the interesting one — the letter is. The grades in that family are separated mainly by how tightly the magnetic properties are held: a lower coercivity and a higher maximum permeability, bought by pushing interstitial carbon and nitrogen down. In practice that means an iron content of roughly 99.5 per cent or better, a carbon ceiling near 0.025 per cent instead of 0.08 per cent, coercivity held around 48 A/m or lower and maximum permeability from about 12.5 mH/m upwards. Those are the numbers that decide whether a given coil current produces the flux the valve needs at the armature. Carbon and nitrogen left in solution pin the domain walls, so the carbon ceiling is the first figure to read on a certificate; it is also the reason the material is normally bought against a magnetic property certificate, and often against an aging requirement, rather than against chemistry on its own. Confirm the exact revision of the grade with the mill, because the letters inside the DT4 family are not used identically by every supplier.
DC04 vs DT4E: the magnetic difference in four numbers
- Coercivity (Hc): DT4E is specified at roughly 48 A/m or lower; DC04 carries no controlled coercivity at all, so a housing drawn from it can sit several times higher, depending on where its carbon falls in the permitted band and how much cold work the wall retains.
- Maximum permeability (μmax): about 12.5 mH/m and upwards for DT4E. For DC04 the value varies with heat, thickness and forming history, so it cannot honestly be quoted as a design number from the grade name.
- Carbon and nitrogen: up to 0.08 per cent carbon in DC04 against a ceiling near 0.025 per cent in DT4E. This is the single number behind the coercivity gap, and the one that decides whether the magnetics stay stable in service rather than drifting with time and temperature.
- Saturation: both materials are ferritic and iron-based, so the difference in saturation flux density is much smaller than the difference in low-field behaviour. Where a design pushes close to saturation, coercivity and permeability are still what decide coil current at the working point.
DC04 vs DT4E: the forming difference
Under the press the ranking reverses. DC04 is bought for forming: its specification includes mechanical properties and a mill-controlled normal anisotropy that keeps a cup from earing badly and lets a single draw take a larger reduction, which usually means fewer stages and less interstage annealing. DT4E is also soft and it draws well, but the certificate you receive describes magnetics, not formability, so the drawing route has to be agreed rather than assumed. Two consequences follow. First, when a pure iron housing is deep drawn and then ironed to bring the bore, the outside diameter and the wall thickness onto one axis, every pass adds cold work and raises coercivity — the wall thinning that saves a machining operation is also the operation that degrades the property the material was bought for. Second, when the route needs more reduction than the material will take in one pass, the decision is whether to add a stage or to add an interstage anneal, and that is a tooling decision with a cost on both sides.
The process trap: the magnetics belong to the finished part
The coercivity and permeability that matter are the ones measured on the finished, annealed housing, not the ones on the incoming strip. Drawing, ironing, coining and trimming all raise dislocation density, and a scored or poorly lubricated ironing surface raises coercivity further, so a route that produces a dimensionally perfect housing can still fail the magnetic requirement. The sequence that protects the result is to form to size, then run a magnetic anneal specified by the property to be reached — coercivity or permeability after the cycle, not the word annealing on its own — and then to keep that geometry through any secondary operation. Because bulk heat treatment is outsourced for us, the furnace atmosphere, the cycle and the batch traceability sit with a qualified external partner rather than in our own plant, and that partner's process control is part of what the customer is buying. Anything the anneal cannot repair, such as a torn wall or a contaminated surface, has to be solved in the tool.
How to specify either grade so it can be quoted and verified
- Name the standard and the grade — EN 10130 DC04, or GB/T 6983 DT4E. The trade word pure iron on its own is not a specification and cannot be inspected against.
- Put the magnetic requirement on the drawing where the housing carries flux: coercivity, permeability, or flux at a stated coil current, measured after the finished anneal, with the test method and the sample location named.
- Say whether the housing is structural or magnetic. If it is structural, DC04 is normally the cheaper and easier answer and the magnetic numbers do not need to be controlled at all.
- Write the anneal as a process step with a property target and a position in the route, including whether it comes before or after plating, threading or any press operation that adds cold work.
- Agree what replaces the mill certificate if it is missing. For DC04, chemistry and mechanical values are enough to confirm the grade; for DT4E they are not, because a chemistry reading inside the band does not tell you the coercivity.
What Balford runs
Balford deep draws and irons housings up to 250 mm in diameter in Zhuji, Zhejiang, on presses from 25 t to 350 t, with the tooling designed and built in house, so the draw schedule, the ironing pass and the anneal position are one engineering decision rather than three purchase orders. We run DC01 and DC04 mild steel, 304 and 316L stainless steel, 65Mn spring steel, 5052 and 6061 aluminium, and copper and brass, and we form DT4E pure iron where the drawing calls for it. Two statements to keep the picture honest: we hold ISO 9001:2015 and our quality controls are aligned with the requirements of IATF 16949, but we do not claim IATF 16949 certification; and bulk heat treatment, including magnetic annealing, is carried out by qualified external partners and is declared as outsourced, as is plating. Forming, machining, assembly and inspection of the part itself are done in our own plant, and the drawing is reviewed for feasibility before tooling is cut.
Key point
Answer the design question before the material question: is this housing structural, or is it part of the magnetic circuit? DC04 is the cheaper and easier answer to the first, and DT4E is the answer to the second — with the cost of a magnetic certificate and a controlled anneal attached. Then write the magnetic number you actually need on the drawing, because the grade name is a starting point and the finished, annealed part is what has to pass.
Frequently asked questions
Is DC04 magnetic?
Yes. DC04 is a ferritic low-carbon steel, so it is magnetic. What it is not is a specified soft magnetic material: EN 10130 controls chemistry and mechanical properties, not coercivity or permeability, so the magnetic behaviour of a DC04 housing varies with where its carbon falls inside the permitted band and with how much cold work the wall has seen. A DC04 housing will function in a magnetic circuit, but the flux produced at a given coil current cannot be predicted from the grade name the way it can for DT4E.
Can DT4E and DC04 be substituted for each other?
Not as a straight drop-in, because the two are specified against different things. Moving from DC04 to DT4E gains a controlled coercivity and permeability, but it also changes what the mill guarantees, so the draw schedule and the number of stages have to be re-checked and the anneal cycle established on the finished part. Moving the other way loses the controlled magnetics and the certificate behind them. If the change matters, change one variable at a time: material first, then anneal cycle, then verify coercivity on the finished housing.
Does deep drawing change the magnetic properties of DT4E?
Yes. Every cold-forming step raises dislocation density, which raises coercivity and lowers permeability, and ironing with a damaged or poorly lubricated surface makes it worse. That is why a DT4E housing is normally magnetic annealed after forming: the values that must be met belong to the finished, annealed part rather than to the incoming strip. The drawing should therefore state the magnetic requirement after the anneal, with the test method and the measurement position, not as an incoming material property.
How do I check that the grade delivered is actually DT4E?
Read the mill certificate for the finished, annealed properties and not only for chemistry. For DT4E the figures that decide performance are coercivity and maximum permeability, plus any aging requirement agreed for the programme; a chemistry reading inside the band does not tell you the coercivity, because anneal cycle and cold work move it as well. Batch traceability matters for the same reason — the anneal is where the magnetic value is set, so the record has to follow the batch through that step.