Through-thickness quality
Thick plate loaded across its thickness by a big T or corner weld can tear in layers. Order Z25 or Z35 plate to EN 10164 at those joints.
Materials · Heavy fabrication sourcing
Steel grades and plate for heavy frames.
Most heavy frames are built from a handful of structural grades. The differences that matter sit in the impact test, the thickness steps and the certificate, not in the name. Values below are minimums from the standards, credited to each one.
01 · Structural steels
The grades that show up on frame drawings
Minimum yield is for the thinnest thickness band. Tensile range and impact requirement are as the standard states them for plate. Always check the current edition of the standard named on your drawing. Background on the material family is onWikipedia.
| Grade | Standard | Min yield, MPa | Tensile, MPa | Impact test | Typical use |
|---|---|---|---|---|---|
| S235JR | EN 10025-2 | 235 | 360 to 510 | 27 J at +20 °C | Light frames, brackets, secondary members |
| S355J2 | EN 10025-2 | 355 | 470 to 630 | 27 J at -20 °C | The default for heavy frames and machine bases in Europe |
| A36 | ASTM A36 | 250 | 400 to 550 | Not required unless ordered | General structure, base plates, US drawings |
| A572 Gr 50 | ASTM A572 | 345 | 450 min | Supplementary, when ordered | US equivalent of S355 for loaded members |
| Q235B | GB/T 700 | 235 | 370 to 500 | 27 J at +20 °C | Plate commonly stocked in Asia, light structure |
| Q355B (was Q345B) | GB/T 1591 | 355 | 470 to 630 | 34 J at +20 °C | Plate commonly stocked in Asia, loaded members |
| SS400 | JIS G3101 | 245 | 400 to 510 | Not specified | Japanese drawings, general structure |
| SM490A | JIS G3106 | 325 | 490 to 610 | Not required for grade A | Japanese drawings, welded loaded members |
Q345 was renamed Q355 in GB/T 1591-2018. Older drawings and mill certificates still use Q345B, and the two are often quoted against each other. Weathering steel (S355J2W to EN 10025-5, ASTM A588) and stainless (304, 316L) are placed on request. How the common grades compare in practice is in steel grades for heavy weldments.
02 · Thickness
Yield falls as plate gets thicker
A heavy base plate is not as strong as the grade name suggests. EN 10025-2 steps the minimum yield of S355 down as the plate thickens, and the other standards do the same in their own bands. A design checked at 355 MPa on an 80 mm plate is checked against the wrong number.
Thicker plate also needs more preheat. Preheat follows from thickness, hydrogen level and carbon equivalent (CEV), which EN 10025-2 caps for S355 at typically 0.45 to 0.47 depending on thickness. The calculation is explained underequivalent carbon content.
| Nominal thickness, S355 | Min yield, MPa |
|---|---|
| Up to 16 mm | 355 |
| Over 16 to 40 mm | 345 |
| Over 40 to 63 mm | 335 |
| Over 63 to 80 mm | 325 |
| Over 80 to 100 mm | 315 |
| Over 100 to 150 mm | 295 |
03 · Plate ranges
Typical plate thickness by frame member
The network works plate from 6 mm to 100 mm. Inside a frame the range splits by job. These are typical ranges seen on heavy frames and skids, not design values. The load case decides yours.
| Member | Typical thickness | Notes |
|---|---|---|
| Base and mounting plates | 30 to 100 mm | Thick enough that machining stock and flatness survive. Often the heaviest part of the frame. |
| Main girder webs and flanges | 12 to 40 mm | Sized by the load case. Box sections are common where torsion matters. |
| Stiffeners and diaphragms | 10 to 25 mm | Spaced to stop local buckling and to stiffen under machined pads. |
| Gussets and brackets | 8 to 20 mm | Laser or plasma cut. Thin enough to weld without heavy preheat. |
| Lifting lugs and padeyes | 20 to 60 mm | Sized and checked for the rigging load. Often a through-thickness quality plate. |
Ultrasonic tested plate
Base plates that are machined deep can expose laminations. Plate tested to EN 10160 or ASTM A578 lowers that risk where it matters.
Mill certificates
EN 10204 type 3.1, traceable to heat numbers marked on the plate, for every loaded member. Ask for them with the weld map.
04 · Castings
When a casting belongs in the frame
Castings come from a foundry, then are machined and either welded or bolted into the fabricated frame. Mention them on the RFQ so the shortlist covers the whole assembly. The trade-off for a full machine base is set out inmachined weldment vs casting.
| Type | Typical grades | Where it fits |
|---|---|---|
| Cast steel, weldable | G20Mn5 (EN 10293), ASTM A216 WCB | Nodes, bearing housings and lugs welded into a fabricated frame |
| Ductile iron | EN-GJS-400-15, ASTM A536 65-45-12 | Housings and brackets bolted to the frame. Not for structural welding. |
| Gray iron | EN-GJL-250, ASTM A48 Class 35 | Machine tool beds where damping matters. Bolted, never welded into steel. |
05 · On the drawing
What the material call-out should say
- One grade with its standard and edition, for example S355J2 to EN 10025-2.
- Whether an equivalent grade is acceptable, and which one.
- The impact test temperature if the frame sees cold service or dynamic load.
- Z-quality and ultrasonic testing on the specific plates that need it, not the whole frame.
- The certificate type, normally EN 10204 3.1, and heat number traceability.
Cost moves with these choices. See design for fabricationfor where the grade and the plate list change the price.
FAQ
Questions about frame materials
- Is S355 the same as A572 Grade 50 or Q355B?
- They are close in minimum yield, about 345 to 355 MPa, but not identical. Impact test temperature, chemistry limits and the thickness steps for yield all differ. Name one grade on the drawing and say whether an equivalent is acceptable, and on what terms.
- What does the J2 or JR suffix mean?
- It is the Charpy impact test temperature in EN 10025: JR at +20 °C, J0 at 0 °C, J2 at -20 °C, each with 27 J minimum. Frames under dynamic load or in cold service usually call for J2 or K2.
- When do I need Z-quality plate?
- When a thick plate is loaded through its thickness by a large T or corner weld, for example a heavy lug or a flange welded to a thick base. Through-thickness quality to EN 10164, Z25 or Z35, reduces the risk of lamellar tearing.
- What material certificates should I ask for?
- An EN 10204 type 3.1 inspection certificate for every plate and section in a loaded member, traceable to heat numbers marked on the material. Ask for the certificates in the quality documents with the weld map and NDT reports.
- Do you supply the steel?
- No. We are a matching service. The fabricator that quotes you buys the steel and supplies the mill certificates. We match your drawing with up to three vetted Vietnamese shops and they quote you directly.
Not sure which grade your drawing should name? Email it to and we will tell you plainly what the shops will ask about.
Grade and plate list settled?
Send the drawing with the material call-out. Within 24 business hours we tell you which shops clear the envelope, and up to three of them quote you directly.
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