A36, S355 or A514: What the Grade Does to Your Weldment Price

Published September 21, 2026. How we research this.

Material is the easiest line on a weldment quote to read and the one buyers most often over-weight. The plate price is visible. What the grade does to welding, preheat, distortion and machining is not, and it is usually bigger.

The families

Mild structural steel: ASTM A36, EN S235JR. The default. Cheap, available everywhere, forgiving to weld, no preheat on normal sections. Yield around 235 to 250 MPa. Loose as-rolled flatness, so leave machining stock.

Higher strength structural: ASTM A572 Grade 50, EN S355J2. Roughly 50 per cent more yield strength for a modest price increase. Still weldable with the same processes, with more attention to heat input on thicker sections. S355J2 carries a specified impact test at minus 20 degrees C, which matters when the drawing or the application calls for toughness. This is the workhorse grade for machine frames and heavy structures.

Quenched and tempered: ASTM A514, EN S690QL. Yield around 690 MPa. Bought when weight matters: lifting structures, booms, mobile equipment. It brings real welding requirements. Preheat and interpass temperature are controlled and not optional, consumables are matched and hydrogen controlled, and heat input is limited at both ends because too little cools the joint too fast and too much softens the heat affected zone. Post-weld heat treatment can undo the temper, so the stress relief plan has to be decided with the grade in mind.

Abrasion resistant: Hardox 400 and 450, AR400. Bought for wear life, not strength. Welded with heat input and preheat limits published by the plate maker, because exceeding them removes the hardness at the joint you paid for. Usually used as a wear face on a mild steel structure rather than for the whole part.

Stainless 304L and 316L. A different conversation entirely, covered in the stainless weldments guide.

Aluminium 6061 and 5083. Also different, and the heat affected zone problem is covered here.

Strength versus stiffness, the mistake worth avoiding

This one costs real money.

All structural steels have essentially the same elastic modulus, about 200 GPa. Yield strength varies by a factor of three across the grades above. Elastic stiffness does not vary at all.

So:

• If the part is governed by strength, going to a higher grade lets you use thinner plate and save weight, weld metal and machining.
• If the part is governed by stiffness or deflection, a higher grade buys you nothing. Thinner high strength plate will deflect more, not less. You need section depth and geometry, not a better grade.

Machine bases, gantries and anything where accuracy under load matters are usually stiffness driven. Lifting structures and load bearing members are usually strength driven. Getting this the wrong way round produces either a heavy, expensive part or a frame that flexes.

What the grade does downstream

Grade family	Welding	Distortion	Machining
A36, S235	Simple, no preheat on normal sections	Moderate	Easy, but mill scale is abrasive
A572 Gr 50, S355	Same processes, tighter heat control	Similar to mild	Similar, slightly harder
A514, S690QL	Preheat and interpass control, matched consumables, hydrogen control	Similar, but repairs are more restricted	Harder, slower, more tool wear
Hardox, AR400	Heat input limits, preheat per plate maker	Moderate	Hard. Often ground rather than milled

The practical point is that moving from A36 to A514 does not add 30 per cent to the job because the plate costs 30 per cent more. It adds preheat time, supervision, consumable cost, slower machining and a more restricted repair route.

Mixing grades on purpose

It is common and it is usually right. A mild steel structure with an abrasion resistant wear face, or an S355 frame with A36 guarding and brackets, puts the expensive material only where it is doing work.

It does need the drawing to be explicit about which part is which grade and which procedure applies to the joints between them, because a dissimilar joint is its own qualification case.

Plate flatness and thickness tolerance

Two facts that catch people out:

Hot rolled plate arrives with a flatness tolerance that is loose compared with anything you would machine to. That tolerance is in the part before a single weld is made, and it is one reason machining allowance is not optional.

Plate thickness has a tolerance too. If a design needs a precise thickness on a face, it gets machined. Specifying a nominal plate thickness as a finished dimension is a common drawing error.

A short selection rule

• Stiffness driven, size not constrained: A36 or S355, more section depth.
• Strength driven, weight matters: S355, or A514 if the weight saving justifies the welding cost.
• Wear surface: mild steel structure with an abrasion resistant face.
• Corrosion matters: 316L, and budget for what stainless brings with it.
• Toughness at low temperature specified: a grade with the impact test, such as S355J2, and say so on the drawing.

Send your drawing with the grade named and we will match it with shops qualified to weld it.

Frequently asked questions

Keep reading

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