Types of Metals and What They're Used For — And Where to Source Them

Whether you’re a fabricator, contractor, architect, or engineer, you’ve probably searched online for a specific grade of steel or metal — only to land on a supplier’s website that doesn’t actually stock what you need. It’s a common frustration. The good news? If you know the right terminology for the material you need, you can source it from a supplier who actually carries it. That’s exactly what this guide is for.

Below is a breakdown of the most common types of metals and steel grades, what they’re used for, and what to look for when requesting a quote.

The Four Main Categories of Steel

Steel is one of the most versatile materials in the world — and one of the most misunderstood. At its core, steel is an alloy of iron and carbon, but small changes in composition create dramatically different properties. The industry broadly organizes steel into four main types:

1. Carbon Steel

Carbon steel is the most widely used form of steel, accounting for roughly 90% of all steel manufactured globally. Its properties shift significantly based on carbon content, which is why it’s broken into three sub-categories:

Low Carbon Steel (Mild Steel)

Carbon content of 0.05%–0.29%. This is the most workable and weldable form of carbon steel. Common grades include A36, 1008, 1010, and 1018. You’ll find low carbon steel in structural beams, automobile doors, appliances, hardware, and general construction. It’s affordable, readily available, and easy to fabricate.

Medium Carbon Steel

Carbon content of 0.25%–0.60%. Stronger but less ductile than mild steel, medium carbon steel is used in shafts, axles, gears, and structural components that require higher wear resistance. Common grades include 1030, 1040, and 1045.

High Carbon Steel

Carbon content of 0.60%–1.0%+. High carbon steel is known for its hardness and ability to hold a sharp edge. It’s the go-to material for springs, cutting tools, punches, knives, and dies. Grades in the 1059–1080 range fall into this category.

2. Alloy Steel

Alloy steel is carbon steel enhanced with additional elements — manganese, chromium, nickel, molybdenum, copper, or aluminum — to achieve specific performance properties. These additions improve strength, toughness, corrosion resistance, or machinability depending on what the application demands.

Common Alloy Steel Grades and Their Uses:

4130 – structural frames for aircraft, fasteners for ships, bridges, and buildings. A strong, weldable grade used across aerospace and industrial construction.
4140 – high strength and hardness. Used heavily in automotive parts such as crankshafts, connecting rods, and gears. Also popular in oil and gas tooling.
4340 – offers excellent strength and toughness. Used in aircraft components, structural parts, and demanding industrial applications.
8620 – ideal for gears, bushings, bolts, and heavy-duty pins. Often used in the automotive and heavy equipment industries.

Alloy steels are also common in oil country tubular goods (OCTG), power generation, agriculture equipment, railways, mining, and defense applications.

3. Stainless Steel

Stainless steel contains a minimum of 10.5% chromium, which forms a passive oxide layer on the surface that resists corrosion. It’s prized for both its durability and its hygienic properties, making it a staple in medical, food processing, marine, and architectural applications.

Most Common Stainless Steel Grades:

Grade 304 – widely used stainless steel in the world. The classic 18% chromium / 8% nickel composition resists ordinary corrosion and is used in kitchen equipment, building facades, and chemical tanks.
Grade 304L – 304 but with lower carbon content for improved weldability.
Grade 316 – polybdenum for greater resistance to chloride corrosion. The preferred choice for marine environments, food processing, surgical instruments, and pharmaceutical applications. Often called “marine grade stainless.”
Grade 316 – low carbon variant of 316. Commonly used in marine applications, watches, and reactor pressure vessels.
Grade 430 – widely used ferritic stainless steel, popular in decorative and general-purpose applications.

4. Tool Steel

Tool steel is engineered specifically for manufacturing tools — drill bits, dies, punches, molds, and cutting implements. Its hardness, resistance to abrasion, and ability to retain shape under stress and heat make it the preferred material for fabrication shops. Tool steel is divided into five main groups:

W-Grade (Water-Hardening) steels, water-quenched. Most widely used in tool steels.
O-Grade (Oil-Hardening) steel, used for bushings, collets, and thread-cutting chasers.
A-Grade (Air-Hardening) and toughness. Used for cold extrusion dies, plastic molds, and lamination dies.
D-Grade (High-Chromium) it gives excellent wear resistance. Common in cold forming dies, woodworking knives, and forming rolls.
H-Grade (Hot-Working) and toughness at elevated temperatures. Used in hot forging, extrusion tooling, and plastic injection molds.
S-Grade (Shock-Resisting) used in tools that experience heavy impact.
HSS (High-Speed Steel) – strong at high speeds. Used in drill bits, saw blades, and milling cutters.

Weathering Steel (Corten) — A Specialty Category Worth Knowing

If you’ve ever searched for “Corten steel” and ended up on a supplier’s site that didn’t actually carry it, you’re not alone. Weathering steel is one of the most searched-for materials in the industry — and one of the most commonly misunderstood.

What Is Weathering Steel?

Weathering steel is a family of low-alloy steels that form a stable, rust-like protective patina when exposed to air and moisture. This natural oxidation layer actually prevents further corrosion, eliminating the need for paint or coatings over the life of the structure. The name “COR-TEN” is a registered trademark of U.S. Steel, referring to its two key properties: Corrosion resistance and Tensile strength.

The Key ASTM Grades

ASTM A588 – structurally robust weathering steel grade. Available in plate, angles, channels, beams, and flat bar. With a 50 ksi minimum yield strength and 70 ksi tensile strength, it’s used in bridges, transmission towers, highway structures, rail cars, and building frames. Most equivalent to Corten B.
ASTM A242 – the earliest weathering steels, similar to Corten A. Valued for its aesthetic appeal. Used in architectural panels, decorative walls, outdoor sculptures, and building cladding. Available in plate up to one-half inch thick.
ASTM A606 Type 4 – strength, low-alloy sheet and coil. The grade you need for roofing, siding, shipping containers, and applications where the steel needs to be formed or shaped. Available from 22 gauge through 3/16″ thickness.
ASTM A847 – ring steel in hollow structural sections — square and rectangular tubing and pipe.
ASTM A709-50W steel specification commonly dual-certified with A588.

A Note on COR-TEN®

The trademark COR-TEN is owned by U.S. Steel. When someone says they need “Corten,” they almost always mean ASTM A606-4 (for sheet/coil) or ASTM A588 (for plate and structural shapes). If a supplier tells you they’re providing COR-TEN, ask if it was purchased from U.S. Steel — because most of the time, it’s an equivalent ASTM grade, not the trademarked product.

Common Applications of Weathering Steel

Bridges and highway structures
Building facades and architectural cladding
Outdoor sculptures and public art
Rail cars and transit infrastructure
Roofing and siding panels
Retaining walls and landscaping

High-Strength Low-Alloy (HSLA) Steel

HSLA steel is engineered to meet specific mechanical properties — primarily strength — without the weight penalty of heavier structural sections. Small additions of niobium, vanadium, or titanium give these steels their strength without excessive carbon content. Common grades include 45, 50, 60, 70, and 80.

Where you’ll find HSLA steel:

Bridges and cranes
Automotive frames and structural components
Heavy trucks and transportation equipment

Why You Can’t Always Find What You Need From a Basic Google Search

Here’s the honest reality of the steel market: many suppliers show up in search results for materials they don’t actually stock. Their websites may reference a grade to capture web traffic — but when you send an RFQ, they come back empty-handed.

The difference between a general steel distributor and a metal sourcing partner is the ability to find and supply specialty grades. Materials like ASTM A588, A606-4, 4340 alloy steel, or tool steel grades aren’t always sitting in a local warehouse. They often require sourcing from specific mills or specialty distributors.

When you’re looking for a hard-to-find grade, here’s what to include in your RFQ:

The specific ASTM or AISI/SAE grade (e.g., ASTM A588, 4140, 316L)
The product form (plate, sheet, coil, bar, structural shape, tube)
Thickness, width, and length requirements
Quantity and delivery timeline
Any certifications or test reports required (MTRs, dual certs, etc.)

Can We Source It?

If you’ve searched for a material and found this page, there’s a good chance we can help. We specialize in sourcing and supplying a wide range of steel grades — including specialty materials that the big distributors don’t keep in stock. Send us your RFQ with the grade and specs, and we’ll tell you exactly what we can do.

Request a Quote Today →

Have a material grade you don’t see listed here? Contact us — chances are we can source it.