Grade dossier
430F Stainless Steel
430F stainless steel is a free-machining ferritic stainless grade identified as UNS S43020. It combines roughly 16–18% chromium with elevated sulfur to improve chip breakage and machining productivity, making it a practical choice for automatic-screw-machine and CNC parts such as gears, fasteners and magnetic components when moderate corrosion resistance is sufficient.
Identity before substitution
Specify 430F by product form, machining condition and governing chemistry
430F is the sulfur-bearing free-machining modification of the 17% chromium ferritic family. Sulfur improves machinability but reduces weldability and can reduce corrosion performance compared with cleaner 430 chemistry. Because UNS S43020 is cross-referenced to more than one EN free-machining ferritic grade, the RFQ should lock the exact standard, chemistry, product form, size, surface condition, machining route and service environment rather than relying on the grade name alone.
430F stainless composition
UNS S43020 free-machining chemistry reference
Sulfur is the machining lever
Carpenter publishes UNS S43020 with 16.00–18.00% chromium, sulfur at 0.150% minimum and molybdenum up to 0.60%. European cross-references such as 1.4104 and 1.4105 use different carbon and sulfur windows, so do not merge ASTM/UNS and EN limits on one order. State the controlling standard and verify the heat analysis on the MTC.
| C | 0.120 max |
|---|---|
| Mn | 1.25 max |
| Si | 1.00 max |
| P | 0.060 max |
| S | 0.150 min |
| Cr | 16.00–18.00 |
| Mo | 0.60 max |
| Fe | Balance |
430F stainless properties
Use condition-specific bar data—not a generic strength claim
Carpenter 25.4 mm round bar · cold-drawn finish
| Ultimate tensile strength | 621 MPa typical |
|---|---|
| 0.2% yield strength | 448 MPa typical |
| Elongation in 50.8 mm | 15% typical |
| Hardness | 190 HB typical |
Annealing and property-selection indicators
| Annealing | 677–760°C · air cool |
|---|---|
| Annealed hardness | about 170 HB |
| Heat hardening | Does not respond |
| Density | about 7.695 g/cm³ |
The 621 MPa tensile / 448 MPa yield / 15% elongation / 190 HB values are Carpenter typical data for a 25.4 mm round bar in cold-drawn finish, not universal acceptance limits. 430F does not harden by heat treatment; cold work can increase hardness. Use the actual ASTM or EN product specification plus the heat-specific MTC for lot acceptance.
Selection boundary
Use 430F for machined ferritic parts—and stop when welding, pressure or severe corrosion controls
430F is not simply “430 that machines faster.” The sulfur addition changes the design boundary. It is strong for repetitive machined parts in atmospheric, fresh-water and other reviewed mild environments, but should be escalated for seawater, pressure containment, critical welding or applications where free-machining sulfur inclusions are unacceptable.
Good reasons to evaluate 430F
Automatic screw-machine and CNC parts where chip control and tool life are major cost drivers.
Gears, fasteners, shafts and aircraft or industrial parts requiring extensive machining.
Magnetic components machined to shape when the magnetic requirement is compatible with standard 430F rather than a restricted solenoid-quality chemistry.
Moderately high-temperature parts where the ferritic low-expansion behavior is useful and the oxidation/service requirements have been reviewed.
Stop and review before release
Seawater or aggressive chloride exposure; Carpenter rates seawater resistance as restricted and salt-spray resistance only moderate.
Pressure vessels or high-pressure gas/liquid containment; Carpenter specifically does not recommend 430F for these vessels.
Welded fabrications where sulfur-related hot cracking, filler selection and post-weld annealing cannot be controlled.
Cold-upset parts or applications that depend on heavy cold forming; producer guidance does not recommend 430F for cold upsetting.
Machining and heat-treatment route
Build the process around free machining, surface cleanliness and welding limits
Use 430F where automatic screw machining or CNC productivity is the main value driver; producer guidance notes that it cuts very freely and behaves like familiar free-machining carbon steels in turning.
Anneal at about 677–760°C followed by air cooling when a softer condition is needed. Carpenter notes an annealed hardness of about 170 HB.
Do not specify a quench-and-temper hardening route: 430F does not harden by heat treatment. Cold work can increase hardness moderately, so the delivered condition should be stated on the order.
Welding is normally discouraged because high sulfur can cause hot cracking. If it cannot be avoided, qualify the filler, minimize heat input and base-metal dilution, and use post-weld annealing where required.
430F stainless supplier checklist
Order 430F as a free-machining ferritic product with traceable chemistry and condition
A 430F stainless supplier should state the exact product form, diameter or section, tolerance, surface condition, annealed/cold-drawn condition and governing standard. Carpenter lists bar-rounds, billet, wire and wire rod; Universal Stainless lists round bar, RCS billet, flat bar and ingot. These are attributable producer forms—not a claim of this website’s live inventory, and size availability should be confirmed against the current mill or stock source.
Carpenter: bar-rounds · billet · wire · wire rod
Universal Stainless: round bar · RCS billet · flat bar · ingot
Common references: ASTM A314 · A473 · A581 · A582 · A838
EN cross-reference: 1.4104 / X14CrMoS17 or 1.4105 / X6CrMoS17 · verify chemistry
MTC / test-report checkpoint
Verify heat number and traceability, UNS S43020 or the agreed EN designation, governing specification and edition, chemical analysis including sulfur and molybdenum, ordered diameter/section and tolerance, supplied surface condition, annealed or cold-drawn state, applicable hardness/tensile results and any supplementary inspection. A useful MTC excerpt should connect the heat identity, chemistry, mechanical result and delivered condition to the ordered lot.
Interactive procurement check
Test 430F against the controlling design question
Procurement FAQ
Questions to close before ordering 430F stainless steel
What is 430F stainless steel?
430F is a sulfur-bearing free-machining ferritic stainless steel identified as UNS S43020. It uses roughly 16–18% chromium and elevated sulfur to improve machinability compared with standard 430, while remaining magnetic and non-hardenable by heat treatment.
What is the EN equivalent of 430F stainless steel?
There is not one chemistry-identical EN substitute for every S43020 order. Swiss Steel cross-references S43020 to both 1.4104 / X14CrMoS17 and 1.4105 / X6CrMoS17, which use different carbon limits. Specify the exact EN designation and standard rather than treating the names as automatically interchangeable.
Can 430F stainless steel be hardened?
Not by conventional heat treatment. Carpenter states that 430F does not respond to heat hardening; hardness can be increased moderately through cold work. Annealing is used to restore a softer condition.
Is 430F stainless steel easy to weld?
No. Carpenter usually does not recommend welding 430F because the high sulfur level can cause hot cracking and weld-centerline problems. If welding is unavoidable, filler selection, low heat input/base-metal dilution and post-weld annealing require procedure qualification.
What should a 430F RFQ include?
State UNS S43020 or the required EN designation, governing standard and edition, product form, diameter or section, tolerance, surface condition, annealed/cold-drawn condition, machining route, corrosion and temperature environment, MTC requirement and any supplementary inspection or magnetic requirement.
Sources, scope and RFQ
Trace 430F chemistry, condition and source evidence before approving the machined part
UNS S43020 identity, 16–18% chromium / sulfur-bearing chemistry, bar-round/billet/wire/wire-rod forms, cold-drawn 25.4 mm bar properties, annealing guidance, machining behavior, corrosion ratings, welding limits and the high-pressure-vessel restriction.
Free-machining 17% chromium positioning, ASTM A314 / A473 / A581 / A582 / A838 references and application-market context for machined corrosion-resistant parts.
Shows S43020 against both 1.4104 / X14CrMoS17 and 1.4105 / X6CrMoS17, demonstrating why the EN cross-reference must be checked against carbon, sulfur and molybdenum chemistry rather than assumed from the 430F name alone.
Use the current ASTM A314/A473/A581/A582/A838 or applicable EN product requirements for the ordered form. The heat-specific MTC, agreed delivered condition, dimensions and acceptance tests—not a generic web table—control release.