06Cr19Ni10 vs SUS304: Welding, Bending and Surface Treatment Practice
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One Alloy, Three Designations
06Cr19Ni10 is the Chinese designation for the standard 18-8 austenitic grade, listed with its chemistry in GB/T 20878. SUS304 is the Japanese designation under JIS G4303 for bars, G4304 for hot-rolled plate and G4305 for cold-rolled sheet and coil. Type 304 is the ASTM and AISI designation under ASTM A240 for plate and ASTM A276 for bar. All three describe the same basic alloy: nominally 18 % chromium, 8 % nickel, carbon capped at 0.08 %. International equivalence is indexed in ISO 15510, and the European counterpart is 1.4301, or X5CrNi18-10, under EN 10088-2 and EN 10088-3.
Because the designations are near-equivalent, cross-standard substitution is common in fabrication. The differences that matter in practice sit in dimensional tolerances, surface finish definitions, test requirements and the documentation supplied with the mill certificate.
Welding: Filler Metal and Parameter Control
| Item | Chinese system | US and Japanese system |
|---|---|---|
| Covered electrode | E308-16 to GB/T 983 | E308-16 to AWS A5.4 |
| Solid wire | H0Cr21Ni10 to GB/T 14957 | ER308 to AWS A5.9 |
| Shielding gas | Argon 99.99 % or Ar + 2 % O2 | Same practice |
| Typical current, 3.2 mm electrode | 100-150 A | 100-150 A |
| Interpass temperature | 150 degrees C maximum | 150 degrees C maximum |
Both systems aim at the same weld metal: a deposit of about 19 % Cr and 10 % Ni carrying a small amount of delta ferrite, typically a few FN, which prevents solidification cracking without pushing ferrite high enough to harm ductility and corrosion resistance. Heat input should be kept low and interpass temperature controlled, because slow cooling through the sensitisation band between roughly 450 and 850 degrees C precipitates chromium carbides at grain boundaries in the heat-affected zone. Low-carbon or stabilised variants remove that risk for aggressive service; the standard grade is adequate for ordinary indoor duty.
On thin sheet, distortion control matters more than joint strength. Tack spacing, a balanced welding sequence, copper backing and low current all help, and dressing a neat cap generally beats adding extra passes on both finish and heat input.
Bending and Cold Forming
Annealed Type 304 and 06Cr19Ni10 both deliver a minimum 0.2 % proof strength of 205 MPa, a minimum tensile strength of 515 MPa and a minimum elongation of 40 % under ASTM A240, with the EN grade specified at comparable levels. Both work-harden rapidly, so strength rises and ductility falls with each forming pass and a part formed in several operations behaves differently from one formed in a single stroke.
| Condition | Practical guidance |
|---|---|
| Thickness up to 3 mm | Minimum inside bend radius near one times thickness, bending transverse to the rolling direction |
| Thickness above 3 mm | Increase the radius progressively and allow for springback |
| Bend line parallel to rolling direction | Use a larger radius; the risk of surface orange peel rises |
| After heavy cold work | Consider annealing before a second forming operation |
Springback is substantial on 304 because of the high strain-hardening rate, so tooling is normally overbent or the bend line is coined. Drawing lubricants must be chloride-free: chlorides trapped in a scratch or a lap become pitting initiation sites and are a frequent cause of field failures wrongly attributed to the base metal.
Surface Treatment and Passivation
Finish selection starts at the mill. 2B cold-rolled sheet is the general-purpose supply condition, BA is brighter and used for visible parts, and No. 4 or hairline finishes are produced with abrasive belts for architectural work. Fabrication then destroys the passive film along welds, heat tint and grinding marks, and it must be restored.
Pickling followed by passivation is standard practice: acid pickling dissolves the chromium-depleted layer, and a nitric or citric passivation treatment to ASTM A380 and ASTM A967 rebuilds the oxide film. Electropolishing goes further and is common on pharmaceutical, food and semiconductor components where low surface roughness and easy cleaning are required. Where intergranular corrosion is a service risk, sensitisation can be checked using the test methods of GB/T 4334.
Contamination causes most poor results. Carbon steel grinding dust, iron particles from a shared wire brush and chloride-bearing marking pens all leave free iron on the surface, which rusts and stains. Dedicated stainless tools, controlled pickling baths and thorough rinsing solve the problem; additional passivation does not.
Frequently Asked Questions
Q: Are 06Cr19Ni10 and SUS304 interchangeable?
A: Chemically they are equivalent and either can normally be substituted. Check thickness and width tolerances, surface finish definitions and the test certificates, because these differ between GB/T 3280, JIS G4305 and ASTM A240 even when the chemistry matches.
Q: Is 304 the same as SUS304?
A: Yes. SUS304 is the JIS designation, Type 304 the ASTM and AISI designation, 06Cr19Ni10 the Chinese designation and 1.4301 the EN designation for the same nominal composition.
Q: Can 304 be hardened by heat treatment?
A: No. It is austenitic and cannot be hardened by quenching. Strength is raised only by cold work, which is why formed or drawn parts are stronger and less ductile than the annealed sheet they came from.
Q: How should weld discolouration be removed?
A: Mechanical removal followed by pickling and passivation, or electropolishing. Heat tint is a chromium-depleted oxide, so leaving it in place removes the corrosion protection exactly where the weld is most vulnerable.
Q: What test verifies the delivered material?
A: Positive material identification or a chemical analysis per heat, supported by an EN 10204 3.1 inspection certificate. Add tensile, hardness and intergranular corrosion tests when the application demands them.
Q: Do the two designations differ in welding consumables?
A: No. E308-16 covered electrodes and ER308 or H0Cr21Ni10 wire are used for both, and the two systems can be mixed provided the deposit chemistry and ferrite level remain within the agreed range.
