The main types of steel plate are mild (low-carbon) plate, structural grade plate, high-strength and quenched and tempered plate, abrasion-resistant (AR) plate, checker or floor plate, weathering plate, stainless plate, pressure vessel plate, and coated plate such as galvanized or primed. For building work, almost all plate is mild steel ordered to a structural grade (CSA G40.21 300W or 350W, or ASTM A36 or A572 Grade 50) and cut into base plates, cap plates, gussets and connection plates. The other types serve wear, corrosion, traction or pressure jobs.
This guide explains each type, what it is for, and how to tell which one your job needs.
Steel plate types at a glance
| Type | What makes it different | Typical uses |
|---|---|---|
| Mild steel plate | Low carbon; soft, ductile, easy to weld | General fabrication, brackets, plates of all kinds |
| Structural grade plate | Mild or HSLA steel certified to a grade (300W, 350W, A36, A572 Gr 50) | Base plates, gussets, shear tabs, embed plates, built-up members |
| High-strength low-alloy (HSLA) | Small alloy additions raise strength while keeping it weldable | 350W and A572 Grade 50 plate, heavier structural parts |
| Quenched and tempered (Q&T) | Heat treated for very high strength | Cranes, heavy equipment, special structures |
| Abrasion-resistant (AR) | Hardened for wear resistance | Chutes, liners, buckets, dump bodies |
| Checker (floor, tread) plate | Raised pattern on one face | Stair treads, platforms, trench covers, ramps |
| Weathering plate | Forms a protective rust layer | Bridges, exposed structures left unpainted |
| Stainless plate | Chromium alloy, corrosion resistant | Food, chemical and marine settings, architectural work |
| Pressure vessel plate | Made and certified for pressure equipment | Boilers, tanks, pressure vessels |
| Coated plate | Galvanized, primed or painted | Exterior and corrosive environments |
A related split is by how the plate is supplied: hot-rolled (the normal state for plate, with mill scale on the surface), pickled and oiled (scale removed for a cleaner surface), and normalized or heat treated (for toughness or strength). Thin flat steel is sheet rather than plate; see steel plate vs sheet vs flat bar for where one ends and the other begins.
Mild steel plate and carbon steel plate
These two names cause the most confusion, so here is how they relate:
- Carbon steel is any steel whose properties come mainly from carbon, without significant chromium, nickel or other alloys. It ranges from low to high carbon.
- Mild steel is the low-carbon end of carbon steel. It is soft enough to bend and form, tough, and easy to weld, which is why it is the everyday plate in every fabrication shop.
- Medium and high carbon plates are harder and stronger but less ductile and harder to weld. They are used for wear parts, blades and tooling, not building structures.
The catch is that "mild steel" describes a type of steel, not a guaranteed strength. A structural drawing never says "mild steel plate". It names a grade, and the plate must come with a mill certificate showing it meets that grade. In practice most plate stock is already certified to a structural grade, because that is what mills produce. Our post on structural steel vs mild, carbon and stainless goes deeper.
Structural plate grades
For buildings in Canada, the plate grades you will see on drawings are:
- CSA G40.21 300W (44W): 300 MPa minimum yield, common for general plate work.
- CSA G40.21 350W (50W): 350 MPa minimum yield, matching most HSS and many connections.
- ASTM A36: 250 MPa minimum yield, on older and US-based drawings.
- ASTM A572 Grade 50: 345 MPa minimum yield.
Which grade to use, and what the letters mean, is covered in our steel plate grades guide. Substituting a lower grade for a higher one needs the designer's approval.
AR plate (abrasion-resistant)
AR plate is hardened steel plate made to resist wear, not to carry structural load. The number in grades such as AR400 and AR500 refers to the plate's nominal Brinell hardness; the higher the number, the harder and more wear-resistant the plate. Several mills sell their own branded wear plates in the same hardness classes.
Where it is used: dump truck bodies, excavator and loader buckets, chute and hopper liners, conveyor transfer points, scrap handling and aggregate equipment.
What to know before ordering AR plate:
- It is harder to cut, drill, bend and weld than mild plate. Bending needs larger radii, and welding needs the mill's recommended procedures.
- It is not a structural grade. Don't use it in place of 350W or A36 in a structural connection, and don't assume hardness means strength in the sense a designer uses.
- Hardness affects machining and tooling, so tell your fabricator up front if parts are AR.
Checker plate, weathering, stainless and pressure vessel plate
Checker plate (also called floor plate, tread plate or diamond plate) has a raised pattern rolled into one face for grip. It is used for stair treads, landings, platforms, ramps and trench covers. Sizes, thicknesses and uses are covered in our steel checker plate guide. It is widely sold in imperial thicknesses, so confirm what will be supplied against a metric thickness on the drawings.
Weathering plate (CSA G40.21 350A or ASTM A588, for example) forms a tight, stable rust layer that protects the steel underneath. It is used for bridges and exposed structures left unpainted. It needs good drainage and is not suited to every environment.
Quenched and tempered plate is heat treated for very high strength. ASTM A514, for example, has a minimum yield of 690 MPa, roughly twice that of 350W. It is specified by engineers for cranes, heavy equipment and special structures, and must be welded with matching procedures.
Stainless plate (commonly grades 304 and 316) contains chromium for corrosion resistance. It is used in food processing, chemical, marine and architectural settings. It needs its own fabrication practice: separate tools and handling so that carbon steel contamination does not cause rust spots.
Pressure vessel plate (such as ASTM A516) is made and certified for boilers, tanks and pressure equipment under separate codes. It is not interchangeable with structural plate in either direction without engineering approval.
Galvanized and primed plate
Plate can also be described by its finish:
- Black (bare) plate: as rolled, with mill scale. Fine indoors where it will be covered or painted.
- Primed or painted plate: shop primer or a full paint system, often applied after fabrication.
- Hot-dip galvanized plate: zinc coated for corrosion resistance, usually galvanized after fabrication so cut edges and welds are covered too.
For fabricated parts it is normally better to cut, drill and weld first, then prime or galvanize the finished piece. Our post on galvanized vs painted structural steel compares the two.
Which type of steel plate for which job
| Job | Usual plate type |
|---|---|
| Column base plates, cap plates, gussets, shear tabs | Structural grade plate (300W, 350W, A36 or A572 Gr 50) |
| Embed plates cast into concrete | Structural grade plate, often with welded studs |
| Exterior brackets and plates | Structural grade plate, galvanized or primed and painted |
| Stair treads, platforms, covers | Checker plate |
| Chutes, liners, buckets | AR plate |
| Food, chemical or marine exposure | Stainless plate |
| Tanks and pressure equipment | Pressure vessel plate to the governing code |
If your drawings name a grade, order that grade. If they don't, and the part is structural, ask the designer before choosing.
Plate cut and fabricated to your details
We cut, drill and weld steel plate into base plates, cap plates, connection plates, gussets and embed plates in our CWB certified shop, to the grade on your drawings, and can prime or galvanize the finished parts. Send your details for a free quote, or see our steel products.
Frequently asked questions
What is mild steel plate?
Mild steel plate is flat, hot-rolled, low-carbon steel. It is easy to cut, bend and weld and is the everyday plate in fabrication shops. For structural parts it is ordered to a named grade such as CSA G40.21 300W or 350W, or ASTM A36, so it has a guaranteed strength.
What is carbon steel plate?
Carbon steel plate is plate whose properties come mainly from its carbon content rather than from alloys like chromium or nickel. Mild steel plate is the low-carbon end of carbon steel; medium and high carbon plates are harder and stronger but less ductile and harder to weld.
What is AR steel plate?
AR (abrasion-resistant) plate is hardened steel plate made to resist wear from sliding rock, sand, gravel and scrap. Grades such as AR400 and AR500 are named for their nominal Brinell hardness. It is used for liners, chutes, buckets and truck bodies, not for structural members.
Is checker plate the same as mild steel plate?
Checker plate (floor or tread plate) is usually a mild or structural steel plate rolled with a raised pattern on one side for grip. The pattern is about traction; it does not make the plate stronger.
