AISI 420B and AISI 420C are two members of the same family: both are 13 % chromium martensitic stainless steels and both are hardened by quenching. The one deliberate difference is carbon content — and that difference sets the achievable hardness.
Carbon equals hardness
In martensitic stainless steels the hardness obtained after quenching rises with the dissolved carbon. The 420 family is built on exactly that logic: different carbon steps at the same chromium level.
Speaking in material numbers: 1.4028 has 0.26–0.35 % carbon and 1.4034 has 0.43–0.50 %. As carbon rises, so does the hardness after quenching; for 1.4034 Notz Metall, Deutsche Edelstahlwerke and Carpenter/Latrobe report a band of about 52–55 HRC. The price is lower toughness and formability.
Compared in figures
The values are EN 10088-3 cast analysis limits.
| PROPERTY | AISI 420B (1.4028) | AISI 420C (1.4034) |
|---|---|---|
| EN name | X30Cr13 | X46Cr13 |
| Carbon (C) | 0.26 – 0.35 % | 0.43 – 0.50 % |
| Chromium (Cr) | 12.00 – 14.00 % | 12.50 – 14.50 % |
| Manganese (Mn) | 1.50 % max | 1.00 % max |
| Hardening temperature | approx. 980 – 1050 °C | approx. 980 – 1050 °C |
| Tempering for maximum hardness | 150 – 350 °C | 150 – 250 °C |
| Achievable hardness | lower | higher |
| Toughness | better | lower |
Heat treatment
Both grades are hardened from roughly 980 to 1050 °C in oil or air (the exact range varies by mill). If maximum hardness is wanted, tempering is kept low: Notz Metall gives 200–350 °C for 1.4028 and 150–250 °C for 1.4034; Carpenter/Latrobe typically uses 149 °C.
In this family corrosion resistance is best in the hardened and polished condition, not annealed. Neither grade is a chloride-service steel.
What to watch when ordering — read this part
“420A / 420B / 420C” is not defined in any standard.
These letter suffixes do not appear in EN 10088-3 (which uses the names X20Cr13, X30Cr13, X39Cr13 and X46Cr13), nor in BS 970 (which used the S-number system: 420S29, 420S37), nor in ASTM/UNS — the American system has a single Type 420 / UNS S42000. The letters are a trade shorthand from the cold-rolled strip and blade sector.
And not everyone applies the same letter to the same material. The strip market uses 420C for 1.4034; Ugitech puts “420C” against 1.4031 (X39Cr13) in its own bar catalogue. That is 0.07 % carbon apart, with a different chromium band.
So put the material number on your order: not “420C” but 1.4034 — or state the carbon range you need directly.
One more point: in ASTM Type 420, carbon has a minimum (0.15 % min) and no maximum. A certificate reading “420” is therefore not by itself a guarantee of hardness. Suppliers publish different upper limits — Rolled Alloys 0.15–0.30 %, Jacquet 0.15–0.40 %. If hardness is critical, write the carbon range into the contract.
Where are they used?
Both grades are used for cutlery and blades, surgical and dental instruments, valve parts, moulds and dies, bearings and wear parts. If wear resistance and cutting edge are your priority, 420C (higher carbon, higher hardness); for parts that will take impact and need toughness, 420B is preferred.
Designations, standards and AMS equivalents
The same steel is called different things depending on which system you are speaking in. Most ordering and certification confusion starts here, so a short summary:
- AISI — the American Iron and Steel Institute’s grade naming (410, 316L and so on). It is the most widely used name in everyday use, but on its own it is not a purchasing specification: composition and mechanical requirements are defined in the ASTM standards.
- UNS — the Unified Numbering System operated jointly by ASTM and SAE (S41000 and so on). It is the number used for ordering and certification in North America, and it is more precise than the AISI name.
- W.Nr / EN — the European material number (1.4006 and so on) and EN name (X12Cr13 and so on). This is the governing designation in Europe. It is usually only an approximate equivalent of the AISI grade; carbon, sulphur or molybdenum limits frequently differ.
- AMS — SAE’s Aerospace Material Specifications. An AMS specification binds not only the composition but also the melting practice, the product form, the heat treatment condition and the inspection requirements. In aerospace and defence orders this is the designation that governs.
| DESIGNATION | AISI 420B | AISI 420C |
|---|---|---|
| AISI / trade name | AISI 420B | AISI 420C |
| EN material no. (W.Nr) | 1.4028 | 1.4034 |
| UNS number | S42000 | S42000 |
| AMS specifications | AMS 5506 · AMS 5620 | AMS 5506 · AMS 5620 |
| Product page | AISI 420B technical page | AISI 420C technical page |
Two reminders. First: an AMS number is specific to a product form and condition. The same grade may have separate AMS specifications for bar, sheet and forgings, so establish which product form you need before calling up an AMS number.
Second: the AISI name, material number, UNS and AMS data in the table above are the designations shown on Defence Metal’s product pages. If you are working to a different edition of a standard or to a different product form, state the material number and the specification edition explicitly on your order.