A2 Steel: Is A2 the Same as 304?
It depends on whether “A2” names a steel grade or a fastener marking.
As a steel grade, no. A2 tool steel and 304 stainless steel are completely different metals. A2 tool steel is a high-carbon, air-hardening cold work tool steel that is magnetic, hardens by heat treatment, and rusts if left unprotected.
As a fastener marking, yes. A bolt, nut, or washer stamped “A2” follows ISO 3506 property class A2, which is made from austenitic 304 stainless steel. It resists corrosion, cannot be hardened by heat treatment, and is generally non-magnetic.
To avoid confusion, always consider the context in which A2 appears. In practical terms, if you are dealing with a knife, mold block, die, or punch, it’s likely A2 tool steel. If you encounter a bolt, nut, or washer marked “A2,” it refers to A2 stainless (304). Now let’s take a closer look at each type.
A2 Tool Steel
A2 tool steel is a medium-alloy, air-hardening cold work tool steel. A typical composition is about 1.0% carbon, 5.0% chromium, 1.0% molybdenum, and 0.20% vanadium.
The 5% chromium is not enough to make it stainless, so the steel rusts or patinas when exposed to moisture. That same chemistry allows it to air-harden with minimal dimensional change, which is why it is chosen for parts that must maintain tight tolerances after hardening. Correct heat treatment brings A2 to 58-62 HRC, a balance of toughness and wear resistance. Common uses include blanking punches, trimming dies, forming tools, and custom knives.
Internationally, A2 tool steel also sells as DIN 1.2363 in Europe and JIS SKD12 in Japan.
A2 Stainless (304)
When “A2” is stamped on a bolt or screw, it indicates compliance with ISO 3506 for stainless steel fasteners. “A” stands for austenitic, and “2” identifies the alloy group, which in practice means Type 304 stainless steel.
A2 stainless contains roughly 18% chromium and 8% nickel, the composition known as “18-8” stainless. It cannot be hardened by heat treatment and is strengthened only by cold working. The high chromium and nickel content give it strong corrosion resistance in wet environments.
Equivalent grades for A2 fastener steel include AISI 304 in the United States and EN 1.4301 in Europe.
Side-by-Side Comparison
| Property | A2 Tool Steel | A2 Stainless / 304 |
| Type | Cold work tool steel | Austenitic stainless steel |
| Main alloying | 1.0% C, 5.0% Cr, 1.0% Mo, 0.20% V | ~18% Cr, ~8% Ni |
| Corrosion resistance | Low, will rust | High, rust-resistant |
| Hardenable by heat treatment | Yes, air hardening | No, only by cold working |
| Magnetic | Yes | No, mostly non-magnetic |
| Typical hardness | 58 to 62 HRC | Softer, measured in HRB |
| Equivalent grades | DIN 1.2363, JIS SKD12 | AISI 304, EN 1.4301 |
| Typical use | Punches, forming dies, molds, knives | Bolts, nuts, screws, washers |
How to Tell Which One You Have
Context gives the answer: Threaded hardware is almost always A2 stainless (304), while a heavy block of mold steel, die, or cutting tool is A2 tool steel.
If you still need to confirm, three quick checks:
- Magnet test: Hold a magnet against your sample. If the metal attracts the magnet strongly and snaps into place, it is likely A2 tool steel. If there is little or no attraction, especially in annealed pieces, it is A2 stainless (304). Cold-worked stainless steel may show a weak magnetic pull.
- Hardness test: Try to scratch a glass bottle with your sample. If the sample easily scratches the glass, it is hardened A2 tool steel (58-62 HRC). If it does not scratch glass, it is likely A2 stainless (304), which is softer.
- Rust test: Place a drop of water or acidic juice on your metal surface and leave it overnight. If the spot discolors or rusts, you have A2 tool steel. If the spot wipes clean, you have A2 stainless (304).
Frequently Asked Questions
No. It contains only 5% chromium, below the roughly 10.5% minimum required for stainless steel, so it rusts unless oiled or coated.
Generally no. A2 (304) is austenitic and non-magnetic, though heavy cold working can make it slightly magnetic. It never attracts a magnet as strongly as carbon or tool steel.