Grade selection is a system decision
Choosing a steel for a cylinder is usually reduced to a strength comparison. Strength matters, and it is the wrong starting point. The parts of a cylinder ask different things of the same material, and the grade that suits a barrel can be the wrong grade for a rod eye or a piston.
| Part | What the material has to do | What usually governs |
|---|---|---|
| Barrel / tube | Contain pressure, hold a honed bore, accept welding | Honeability, weldability, dimensional consistency of the starting tube |
| Piston rod | Resist wear, corrosion and buckling | Surface hardness route, core strength, straightness |
| Piston | Take pressure load, guide in the bore | Machinability, wear bearing surface |
| Gland / end cap | Take rod side load, thread strength | Toughness, machinability, weld compatibility with barrel |
The grades you will meet
| Grade | Character | Typical home |
|---|---|---|
| E355 / ST52 (S355) | Normalised or stress-relieved fine-grain carbon-manganese. Good weldability, good cold formability, the default for honed and skived tube. | Cylinder barrels, welded cylinder construction |
| 20# / 1020 | Low carbon. Soft, very weldable, lower strength. | Low-pressure welded barrels, non-pressure parts |
| CK45 / C45 / 1045 | Medium carbon. Responds to quenching and tempering and to induction hardening. | Piston rods, pistons, gland components |
| 27SiMn | Low-alloy silicon-manganese with higher hardenability and good strength after Q&T. | Heavy-duty mining and construction barrels |
| 42CrMo4 / 4140 | Chrome-molybdenum alloy, through-hardenable, high fatigue strength. | High-load rods, tie rods, clevis and rod eye forgings |
How the numbers move after treatment
| Material and condition | Typical hardness | Where it lands |
|---|---|---|
| 20# quenched and tempered | HB 170 – 210 | Low-pressure, low-frequency cylinders |
| 45# quenched and tempered | HB 220 – 260 | Standard medium to high pressure barrels |
| 27SiMn quenched and tempered | HB 240 – 280 | Heavy duty with impact loading |
| Bore after roller burnishing or induction hardening | HRC 45 and above | High-cycle, long-life barrels |
Harder is not automatically better for a barrel. A very hard bore abrades seals and is harder to hone to a consistent plateau finish. Surface strengthening earns its place under high-frequency reciprocation and long-life requirements, and it is an added cost on a standard-duty cylinder.
The standards behind the tube
When a supplier quotes a tube grade without a standard, the quote is incomplete. Three families dominate precision tube.
- EN 10305-1, seamless cold drawn tubes for precision applications, the common European reference for honed and skived tube.
- DIN 2391, the older German seamless precision tube specification still widely quoted on honed tube.
- ASTM A519, seamless carbon and alloy mechanical tubing, the usual North American reference, with A513 covering welded.
The delivery condition suffix matters as much as the grade. Cold finished, stress relieved, annealed, normalised and quenched and tempered produce different machinability, different straightness after machining, and different dimensional stability. A tube supplied +C will move more during machining than one supplied +SR.
Weldability, the constraint that quietly rules
Welded cylinder construction dominates mobile hydraulics because it is compact and light. It imposes a carbon equivalent limit on the barrel material, since every end cap weld is a heat-affected zone in the pressure boundary. Micro-alloyed and higher-carbon grades weld less forgivingly and may need preheat and controlled interpass temperature. If your design is welded, declare it at the material selection stage rather than after the grade is fixed.
Specifying the grade on a drawing without ambiguity
A grade name alone leaves too much open. Two drawings that both name ST52 can describe material that machines and welds differently, because the delivery condition is missing. Write the standard edition, the grade, the delivery condition suffix, and the certification type on the drawing. “EN 10305-1 E355 +SR, EN 10204 3.1” closes the gaps a bare grade name leaves open. On a corrosive site, name the corrosion allowance and the coating along with the grade. The structural grades here are carbon and alloy steels, none of them stainless, so the corrosion resistance comes from the finish and the coating, with the grade supplying the structure.
How we handle grade selection
Our routine barrel grades are [ORISE: confirm default grades, e.g. E355 / ST52 / 27SiMn] and our rod grades are [ORISE: confirm, e.g. C45 and 42CrMo4]. We confirm the mill certificate against the ordered grade and delivery condition on every batch, and we record heat numbers so the certificate traces to the material actually shipped. Grades and routes we have not run on our own line are marked not published.
See heat treatment for the routes we run, cylinder tubes and barrels for tube scope, and certifications for the documentation we issue. Material questions go to the RFQ page with the standard edition named.