Materials & grades
303 / 1.4305 / SUS303 free-machining austenitic stainless steel (S30300, X8CrNiS18-9)
Type 303 is the free-machining version of 304-type austenitic stainless steel, with added sulphur for high-speed screw machining. It is UNS S30300 in the USA, X8CrNiS18-9 (1.4305) in Europe, 303S31 (old EN58M) in the UK and SUS303 in Japan.
Names by standard
What it is called in each region
| Region | System | Designation | 規格 | Match |
|---|---|---|---|---|
| USA | AISI/ASTM | 303303Se (UNS S30323) uses selenium instead of sulphur. | ASTM A582 (bar) | Same material |
| UNS | S30300 | — | Same material | |
| UK | BS (legacy) | 303S31Superseded British name, listed by Atlas, Aalco and Outokumpu. | — | Equivalent |
| BS 970 (1955 EN series) | EN58MSuperseded 1955 name. Aalco notes that old cross-references may not be exact. | — | Closest equivalent | |
| EU | EN 10027-1 name | X8CrNiS18-9 | EN 10088-3 | Equivalent |
| EN 10027-2 number | 1.4305 | EN 10088-3 | Equivalent | |
| DIN (legacy) | X10CrNiS18-9Superseded German name for 1.4305, still printed by some suppliers. | DIN 17440 (1985) | Equivalent | |
| Japan | JIS | SUS303JIS also lists SUS303Se (selenium) and SUS303Cu (copper added for cold working). | JIS G 4303 (bar) | Equivalent |
On equivalence
- 303 is a sulphur-bearing modification of the 18 8 family, so its closest everyday alternative for corrosion service is 304. A 304 improved-machinability grade trades some machining speed for better formability, welding and corrosion resistance (Atlas).
- EN 10088-3 holds carbon to 0.10 % and allows up to 0.10 % nitrogen (EN 10088-3:2014; the 2005 edition printed 0.11 %) and 1.00 % copper. ASTM A582 and JIS allow 0.15 % carbon and have no nitrogen limit.
- India: no free-machining austenitic grade was found in IS 1570 (Part 5):1985 or IS 6603:2001. Their free-cutting notes cover only the first four and five grades of those lists, none of them austenitic. Indian buyers normally order 303 to ASTM A582, or SUS303 or 1.4305, so no Indian designation is listed here.
- Some charts print X10CrNiS18-9 for 1.4305. That is the DIN 17440 (1985) name; the EN name is X8CrNiS18-9.
- 303 is a bar and wire grade. Atlas notes it is not produced in flat-rolled products.
Chemical composition
Composition limits, mass %
| Element | 303 (S30300)USA · ASTM A582 | X8CrNiS18-9 (1.4305)EU · EN 10088-3 (bar, rod, wire, sections) | SUS303Japan · JIS G 4303 (bar) |
|---|---|---|---|
| C | ≤0.15 | ≤0.10 | ≤0.15 |
| Si | ≤1.0 | ≤1.00 | ≤1.00 |
| Mn | ≤2.0 | ≤2.00 | ≤2.00 |
| P | ≤0.20 | ≤0.045 | ≤0.20 |
| S | ≥0.15 | 0.15–0.35 | ≥0.15 |
| Cr | 17.0–19.0 | 17.0–19.0 | 17.00–19.00 |
| Ni | 8.0–10.0 | 8.0–10.0 | 8.00–10.00 |
| Mo | — | — | ≤0.60 (optional) |
| Cu | — | ≤1.00 | — |
| N | — | ≤0.10 | — |
Mechanical properties
Strength and hardness
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Annealed bar (ASTM A582)Tensile and yield values are typical and not guaranteed; the standard specifies only the hardness maximumAtlas Steels 303 grade data sheet (23/04/2021) | 650 MPa94 ksi | 300 MPa44 ksi | 45 % | ≤262 HB |
| Solution annealed (+AT) bar (1.4305)Specified, bar up to 160 mm; hardness is a maximumEN 10088-3 as published by Aalco and tabulated by Roymech | 500–750 MPa73–109 ksi | ≥190 MPa≥28 ksi | ≥35 % | ≤230 HB |
| Solution treated (SUS303)Specified minimums per the JIS reference sheet; hardness is a maximumJIS reference sheet by Nose Stainless | ≥520 MPa≥75 ksi | ≥205 MPa≥30 ksi | ≥40 % | ≤187 HBW (≤90 HRBW) |
In practice
Behaviour, heat treatment and uses
Characteristics
- The most machinable of the standard austenitic stainless steels. The sulphur addition (0.15 % minimum) improves machining and reduces galling (Atlas).
- Corrosion resistance is clearly lower than 304 because the sulphide inclusions act as pit-initiation sites. Atlas says 303 should not be used in marine or similar environments.
- Weldability and formability are poor. Sharp bends should not be attempted. Where welding cannot be avoided, Atlas suggests 308L or 309 filler, with the weld annealed.
- Usually not a low-carbon grade, so it can sensitise at 425–860 °C. Outokumpu rates 1.4305 as not resistant to intergranular corrosion.
- Cannot be hardened by heat treatment.
- Oxidation resistance is good in intermittent service to 760 °C and continuous service to 870 °C (Atlas).
- Variants include 303Se (selenium, better hot and cold forming and a smoother machined finish), 303Cu (copper added, better cold workability) and mill improved-machinability grades.
Heat treatment
- Solution annealing: 1010–1120 °C then rapid cooling (Atlas); JIS gives 1010–1150 °C and Outokumpu 1050 ± 50 °C.
- Cannot be hardened by heat treatment.
主な用途
- Nuts, bolts and screws made on automatic screw machines
- Bushings and shafts
- Gears
- Electrical switchgear components
- Any heavily machined part where corrosion resistance and forming needs are modest
Stainless steels
Similar grades compared
| グレード | C % | Mn % | Cr % | Ni % | Tensile, first listed condition |
|---|---|---|---|---|---|
| 303 / 1.4305 | ≤0.15 | ≤2.0 | 17.0–19.0 | 8.0–10.0 | 650 MPa |
| 201 / 1.4372 | ≤0.15 | 5.50–7.50 | 16.0–18.0 | 3.5–5.5 | ≥515 MPa |
| 301 / 1.4310 | ≤0.15 | ≤2.00 | 16.0–18.0 | 6.0–8.0 | ≥515 MPa |
| 304 / 1.4301 | ≤0.08 | ≤2.00 | 18.0–20.0 | 8.0–10.5 | ≥515 MPa |
| 304L / 1.4307 | ≤0.030 | ≤2.00 | 18.0–20.0 | 8.0–12.0 | ≥485 MPa |
| 309 / 309S | ≤0.08 | ≤2.00 | 22.0–24.0 | 12.0–15.0 | ≥515 MPa |
| 310 / 310S | ≤0.08 | ≤2.00 | 24.0–26.0 | 19.0–22.0 | ≥515 MPa |
| 316 / 1.4401 | ≤0.08 | ≤2.00 | 16.0–18.0 | 10.0–14.0 | ≥515 MPa |
| 316L | ≤0.030 | ≤2.00 | 16.0–18.0 | 10.0–14.0 | ≥485 MPa |
| 321 | ≤0.08 | ≤2.00 | 17.0–19.0 | 9.0–12.0 | ≥515 MPa |
Composition from the US standard where one exists, otherwise the first standard listed on each grade's page. Strength conditions differ between grades; open a grade for its full table.
よくあるご質問
Common questions
What is the difference between 303 and 304 stainless steel?
303 has at least 0.15 % sulphur (and up to 0.20 % phosphorus) so it machines far faster, but its corrosion resistance, weldability and formability are lower than 304. Use 303 for machined parts in mild environments and 304 where the part will be welded, formed or exposed to moisture.
What is the equivalent of 303 stainless steel?
UNS S30300 in the USA, X8CrNiS18-9 (1.4305) in Europe, 303S31 (old EN58M) in the UK and SUS303 in Japan. No Indian IS designation was found, so Indian buyers usually specify ASTM A582 303 or EN 1.4305.
Can 303 stainless steel be welded?
It is not generally recommended. The sulphur causes poor weldability. If welding is unavoidable, Atlas suggests 308L or 309 filler and annealing the weld for best corrosion resistance, though the weld will still have poor properties.
Is 303 stainless steel suitable for marine use?
No. Atlas advises against exposing 303 to marine or similar environments because the sulphide inclusions cause rapid pitting. Choose 316 for chloride-bearing service.
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Related references
References
Sources
- Atlas Steels: Stainless Steel 303, 303Se Grade Data Sheet (revised 23/04/2021) — ASTM A582 composition, hardness, typical properties, corrosion, welding, machining, heat treatment and applications.
- Aalco: Stainless steel 1.4305 / 303 bar datasheet — EN 10088-3 composition and bar properties; UNS, BS and old EN cross-reference.
- Outokumpu: Steel grades, properties and global standards — Cross-reference, EN and ASTM properties, annealing temperature and intergranular corrosion rating for 1.4305.
- Roymech: BS EN 10088 stainless steels — EN 10088-3 composition and bar properties for 1.4305.
- Nose Stainless: steel types, composition and mechanical properties (JIS reference sheet) — SUS303, SUS303Se and SUS303Cu composition and properties.
- Wieland: X8CrNiS18-9 pulled round rod — States that X8CrNiS18-9 is comparable to X10CrNiS18-9 under DIN 17440:1985.
- Bureau of Indian Standards, IS 1570 (Part 5):1985 (Public.Resource.Org copy) — Checked for a free-machining austenitic grade; none listed.
- Bureau of Indian Standards, IS 6603:2001 Stainless steel bars and flats (Public.Resource.Org copy) — Checked for a free-machining austenitic grade; none listed.
Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.