303 Stainless Steel Round Bar
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1.4305 – what kind of steel is it?
1.4305 (AISI 303), also designated X8CrNiS18-9, is an austenitic acid-resistant stainless steel. Its base chemistry is close to 304 – roughly 18% chromium and 9% nickel – but sulfur is deliberately added to the alloy. The sulfur forms fine manganese sulfide inclusions in the material that break the chips and reduce friction at the cutting edge. As a result, 303 bar can be turned, drilled and threaded much faster than 304 or 316L, with less tool wear and a better surface finish after machining. The trade-off for this machinability is somewhat lower corrosion resistance than 304 and 316L, and limited weldability. How to read EN numbers, AISI grades and older designations is explained in our article Stainless steel designations: AISI, EN, DIN, GOST.
Chemical composition and designations of 303
| Grade | C | Cr | Ni | S | Mo |
|---|---|---|---|---|---|
| 1.4305 / 303 | ≤ 0.10 | 17.0–19.0 | 8.0–10.0 | 0.15–0.35 | – |
| 1.4301 / 304 (for comparison) | ≤ 0.07 | 17.5–19.5 | 8.0–10.5 | ≤ 0.015 | – |
Values in wt.% per EN 10088-3. Equivalent designations: 1.4305 = X8CrNiS18-9 = AISI 303 = UNS S30300; closest GOST equivalent: 12Ch18N10E. The chemistry of each heat is confirmed by the 3.1 certificate.
Diameters from Ø 10.5 to Ø 95.25 mm, lengths and cutting
We offer 1.4305 round bar in diameters from Ø 10.5 to Ø 50 mm plus Ø 95.25 mm (3 3/4 in), in lengths from 10 cm up to full bar lengths. Bar can be ordered cut to length – convenient for production runs on automatic lathes, where a repeatable bar stock length matters. An EN 10204 3.1 certificate can be ordered with every shipment. Diameter deviations for each tolerance class are listed on the round bar tolerances page.
Machining and limitations
303 is chosen above all for machining: the short, brittle chips do not wrap around the tool, allowing higher speeds and unattended running on multi-spindle screw machines. The sulfide inclusions, however, are sites where pitting corrosion can start, so the steel is not suited to seawater, chloride environments or concentrated acids – 316L is the better choice there. Welding is not recommended – sulfur promotes hot cracking in the weld. Parts made from 303 also should not be cold-bent to tight radii, as the material has lower transverse ductility than 304.
What is 1.4305 round bar used for?
303 bar is used to turn small and medium-sized parts in high volumes: screws, nuts and spacers, shafts and axles, pneumatic and hydraulic connectors and fittings, components for valves, flow control equipment and measuring instruments, and parts for packaging and food machinery that do not come into contact with aggressive media. It is a typical material for CNC shops that want to cut cycle times while keeping parts rust-free in normal atmospheric conditions.
303, 304 or 316L?
If the part will be welded or operate in damp, chloride-bearing conditions, choose 304/304L stainless steel round bar or molybdenum-bearing 316L stainless steel round bar instead – they machine more slowly but are more corrosion-resistant and weldable. If the part needs to be hardened, e.g. knives, shafts or pins subject to wear, the right choice is 420 & 431 stainless steel round bar. 303 wins where the machining cost of a large production run matters and service conditions are moderate.
See also: the other grades in the stainless round bar category.