Screw barrels are made from alloy steels chosen for strength, hardenability, and how well they take a hardened surface. The most common are 38CrMoAlA (1.8509) and 34CrAlNi7 (1.8550) for nitrided parts, 42CrMo (4140) and 31CrMoV9 (1.8519) for through-hardened work, 40Cr for bimetallic barrels, and SS304 / SS316 stainless for corrosive materials.
The grade is chosen together with the surface treatment — the steel gives the part its body and toughness; the surface treatment gives it wear resistance.
Ask three suppliers what steel a screw barrel "should" be made of and you may get three answers, because the honest answer is: it depends on the surface treatment and the material you process. This guide breaks down the grades EJS actually works in, what each one is, its international equivalents (so you can match a drawing from any market), and when it is the right choice.
01Which Steel Should a Screw Barrel Be Made Of?
There is no single "best" steel, because a screw barrel is a system: base steel plus surface treatment. A nitrided barrel needs a nitriding steel that forms a hard case; a through-hardened barrel needs a grade that responds to quench and temper; a bimetallic barrel needs a sound base under an alloy layer that does the real work. Pick the treatment for your material first, and the right base steel follows.
EJS commonly works in these grades: 42CrMo (4140), 38CrMoAlA (1.8509), 31CrMoV9 (1.8519), 34CrAlNi7 (1.8550), 40Cr, 45 steel, SS304, SS316, SKD11, SKD61, and W6Mo5Cr4V2. The sections below explain the workhorses.
02What Makes a Good Screw Barrel Steel
Before the grades, the properties that matter:
- Hardenability — how deep and how reliably the steel hardens through its section.
- Nitridability — for nitrided parts, the steel must contain nitride-forming elements (Cr, Mo, Al) so a hard case forms.
- Toughness — the core must resist the torque and pressure without cracking.
- Wear resistance — usually delivered by the surface treatment, not the base steel alone.
- Corrosion resistance — where the polymer is aggressive, the base steel (or a stainless grade) matters.
- Dimensional stability — the steel must hold its geometry through heat treatment to keep the screw-barrel clearance.
0338CrMoAlA (1.8509) — the Nitriding Steel
38CrMoAlA
DIN: 1.8509 / 41CrAlMo7 · GB: 38CrMoAlA · AISI: Nitralloy 135M (approx.)
The classic nitriding steel for screw barrels. Its high aluminium content lets it form a very hard, wear-resistant nitrided case, which is exactly what a screw or barrel surface needs. After nitriding, surface hardness can reach roughly 850–1100 HV depending on process and depth.
38CrMoAlA is used specifically for its nitriding behaviour — the case forms quickly and reaches high hardness. Reference literature lists wear-resistant parts on rubber and plastic extruders among its primary applications, which is precisely the screw-barrel use case. The trade-off is that the nitrided case is relatively brittle, so it is not the grade for parts taking heavy impact. On an EJS nitrided barrel, the nitriding layer runs 0.4–0.7 mm deep.
0442CrMo / 4140 — the Through-Hardening Workhorse
42CrMo (42CrMo4)
DIN/EN: 42CrMo4 / 1.7225 · AISI: 4140 · JIS: SCM440
A chromium-molybdenum low-alloy steel prized for high fatigue strength, good hardenability, and toughness. It is one of the most widely used engineering steels in the world, which makes it easy to source and match across markets.
42CrMo (equivalent to AISI 4140 and EN 1.7225) is a go-to for through-hardened screws and barrels, and for parts where core strength matters as much as surface hardness. In the quenched-and-tempered condition it offers an excellent balance of strength and toughness. It is functionally interchangeable with 4140 as long as the specified heat-treatment condition is respected — useful when you are matching an existing part from a European or American drawing.
0531CrMoV9 and 34CrAlNi7
31CrMoV9 (1.8519)
DIN/EN: 31CrMoV9 / 1.8519
A chromium-molybdenum-vanadium nitriding steel. The vanadium refines the structure and supports a hard, tough nitrided case, making it a strong choice for heavily loaded nitrided screws and barrels that need more core strength than 38CrMoAlA.
34CrAlNi7 (1.8550)
DIN/EN: 34CrAlNi7 / 1.8550
An aluminium-bearing nitriding steel, like 38CrMoAlA but with nickel for extra core toughness. Used where a hard nitrided case must sit on a tougher core.
06Stainless and Tool Steels
Beyond the standard alloy steels, some jobs call for something more specialised:
- SS304 / SS316 — stainless grades for corrosive polymers (PVC, fluoropolymers) where rust and chemical attack are the main threat.
- SKD11 (D2) / SKD61 (H13) — tool steels for high wear and high temperature, often used for screw elements and demanding sections.
- W6Mo5Cr4V2 (M2 high-speed steel) — for screw elements needing extreme wear resistance.
- 40Cr — commonly the base for bimetallic barrels. After years of production EJS finds 40Cr performs best here, because once the bimetallic alloy layer is worn the barrel is replaced regardless of base steel — so the base steel is not the life-limiting factor.
07Screw Barrel Steel Grades Compared
| Grade (GB) | DIN / EN | AISI / JIS | Type | Typical use |
|---|---|---|---|---|
| 38CrMoAlA | 1.8509 | ~Nitralloy 135M | Nitriding steel | Nitrided screws & barrels |
| 34CrAlNi7 | 1.8550 | — | Nitriding (Ni) | Nitrided, tougher core |
| 31CrMoV9 | 1.8519 | — | Nitriding (V) | Heavily loaded nitrided parts |
| 42CrMo | 1.7225 / 42CrMo4 | 4140 / SCM440 | Cr-Mo | Through-hardened, high strength |
| 40Cr | 1.7035 / 41Cr4 | 5140 | Cr | Bimetallic barrel base |
| SKD61 | 1.2344 | H13 | Hot-work tool | High-temp / elements |
| SKD11 | 1.2379 | D2 | Cold-work tool | High wear / elements |
| SS304 / 316 | 1.4301 / 1.4401 | 304 / 316 | Stainless | Corrosive materials |
08How to Choose the Right Steel
The decision chain is simpler than the grade list makes it look:
- Start with your material — clean, filled, abrasive, or corrosive? This sets the surface treatment.
- Pick the treatment — nitrided, through-hardened, bimetallic, or chrome-plated.
- The treatment points to the base steel — nitriding treatment → a nitriding steel (38CrMoAlA, 31CrMoV9, 34CrAlNi7); through-hardened → 42CrMo; bimetallic → 40Cr base; corrosive → stainless.
- Match any existing drawing — use the equivalents table so a European 1.8509 or American 4140 spec maps to the right grade.
In practice, you tell EJS the material you run and the machine, and our engineers specify the steel and treatment. EJS provides an inspection report and material certificate with every supplied screw barrel, so the grade on the order is the grade you receive.
09Frequently Asked Questions
What is the most common steel for screw barrels?
For nitrided screw barrels, 38CrMoAlA (DIN 1.8509) is the classic choice because its aluminium content forms a hard nitrided case. For through-hardened parts, 42CrMo (AISI 4140 / EN 1.7225) is the workhorse. The right one depends on the surface treatment.
Is 42CrMo the same as 4140 steel?
They are functionally equivalent. 42CrMo (42CrMo4, EN 1.7225) is the European/Chinese designation and AISI 4140 is the American one; they share very similar chromium-molybdenum chemistry and are interchangeable in most applications when the specified heat treatment is respected.
Why is 38CrMoAlA used for nitrided barrels?
Its high aluminium content lets it form aluminium nitrides during nitriding, producing a very hard, wear-resistant surface case. That hardness is ideal for a screw or barrel working surface. The case is relatively brittle, so it is not used where heavy impact is expected.
What steel is best for a bimetallic barrel?
The base steel matters less on a bimetallic barrel because the alloy layer does the work. EJS commonly uses 40Cr as the base, having found it performs best — when the bimetallic layer wears out, the barrel is replaced regardless of the base steel.
Which steel should I use for corrosive plastics like PVC?
For corrosive materials, a stainless base (SS304 or SS316) and/or a corrosion-resistant bimetallic alloy is the right route, rather than a plain alloy steel. Tell your supplier the exact polymer so they can match the grade and treatment.
How do I know I'm getting the steel I ordered?
Ask for a material certificate (MTC) with chemical composition. EJS provides an inspection report and material certificate with every supplied screw barrel, so the grade is verified rather than assumed.
Not sure which grade your job needs?
Tell us the material you process and your machine, or send a drawing with a steel spec from any standard. EJS engineers will confirm the right grade and treatment — and quote, usually within one working day.
Get a Quote- Otai Special Steel — 38CrMoAl special alloy steel: properties and applications (incl. rubber & plastic extruder wear parts)
- Hub of Steel — 38CrMoAl nitriding steel: surface hardness after nitriding (850–1100 HV) and heat treatment
- Industeel (ArcelorMittal) — AISI 4140 / W1.7225 / EN 42CrMo4 datasheet: composition & mechanical properties
- Otai Special Steel — 4140 steel DIN equivalent (42CrMo4 / 1.7225): standards cross-reference
- MakeItFrom — EN 1.7225 (42CrMo4) vs SAE-AISI 4140 property comparison
