ASTM 420 is a martensitic stainless steel defined by ASTM A276/A276M, commonly used for cutlery, surgical tools, and valves.
GB 2Cr13/3Cr13/4Cr13 are stainless steel under GB/T 1220. The prefix "2/3/4" indicates varying carbon content, while "Cr13" means ~13% chromium.
Grade | C (%) | Cr (%) | Si (%) | Mn (%) | P, S (max) |
ASTM 420 | 0.15Min | 12–14 | ≤1.0 | ≤1.0 | ≤0.04 |
2Cr13 | 0.16–0.25 | 12–14 | ≤0.60 | ≤1.0 | ≤0.035 |
3Cr13 | 0.26–0.35 | 12–14 | ≤0.60 | ≤1.0 | ≤0.035 |
4Cr13 | 0.36–0.45 | 12–14 | ≤0.60 | ≤1.0 | ≤0.035 |
The key difference between them is carbon content. ASTM 420 only have a minimum limit for carbon content (0.15 min), that means we can choose different carbon content according to our usage. From the chemical composition, we can know 2Cr13 3Cr13 and 4Cr13 are all equivalent with 420. We can call 2Cr13 as 420 Lower C, 3Cr13 as 420 Middle C, 4Cr13 as 420 Higher C.
Grade | +A hardness | Quenching media | +Q hardness |
ASTM 420 | HB241 Max | Air | HRC50 |
2Cr13 | HB223 Max | Oil | HRC40 |
3Cr13 | HB235 Max | Oil | HRC45 |
4Cr13 | HB235 Max | Air | HRC50 |
Even 420 only stipulate the minimum carbon content, that not means the higher carbon content, the better. With higher carbon content, the hardness will increase, but corrosion-resistant will decrease. We need to choose different carbon content range according to actual application.
ASTM 420: Surgical instruments, knife blades, and corrosion-resistant mechanical parts. It can have different kinds of usage according to different carbon content.
2Cr13: Low-stress components (e.g., bolts, bushings) requiring moderate corrosion resistance.
3Cr13: Cutlery, shafts, and pump parts needing higher hardness than 2Cr13.
4Cr13: High-hardness tools (e.g., scalpels, bearings) similar to ASTM 420.
ASTM 420 is the most special stainless steel from standard ASTM A276/276M, because all stainless steel have a maximum limit for carbon content. For other stainless steel, you can find just one equivalent steel from GB standard, but ASTM 420 is a series stainless steel, its equivalent steel can be 2Cr13 or 3Cr13 or 4Cr13 according to different usage.
The lower-carbon variants, it will be smaller hardness but better weldability /formability.
