Selection summary
Overview
431 is a chromium-nickel martensitic stainless steel selected for high strength, toughness, and better corrosion resistance than basic 410-type grades in suitable environments. It is supplied and used in specific hardened-and-tempered conditions, so section size, mechanical target, tempering temperature, straightness, machining sequence, and final surface condition must be controlled.
This page separates standard-oriented limits from typical reference data. Purchase acceptance comes from the ordered specification and certified material test report.
Names and systems
Identity & standards
Similar designations across ASTM, EN, JIS, and other systems are not automatically interchangeable. Product form and ordered standard control chemistry, properties, dimensions, condition, and testing.
Reference chemistry
Composition
| Element | Reference range | Why it matters |
|---|---|---|
| Carbon | ≤ 0.20% | Hardening response |
| Chromium | 15.0–17.0% | Corrosion resistance and hardenability |
| Nickel | 1.25–2.50% | Toughness and hardenability |
Concise grade-family reference only. Confirm every element limit against the current standard for the exact product ordered.
Condition matters
Reference properties
Specify hardened-and-tempered condition and section size
Acceptance requires the ordered condition, location, and test method
Typical room-temperature engineering reference
Environment first
Corrosion behavior
Higher chromium and nickel can provide more corrosion margin than 410 in many mild environments.
It remains a martensitic grade and is not equivalent to 304/316 for chloride, hygienic, or aggressive chemical service.
Temperature, concentration, deposits, crevices, stress, surface finish, cleaning, and fabrication quality can change service performance.
Service limits
Temperature & service
Select tempering and service temperature together to avoid unintended softening or toughness loss.
Delivery condition
Heat treatment & condition
431 is normally supplied or finished in a named hardened-and-tempered condition; austenitizing, quench, temper, and section size determine strength and toughness.
Stock removal, straightening, stress relief, and final grinding must remain compatible with the certified tempering condition and corrosion surface.
Process route
Fabrication
Usually machined before final hardening and tempering; stock allowance must consider scale and distortion.
Welding is difficult and requires control of hydrogen, preheat, heat input, cooling, and postweld treatment.
Magnetic response: Ferromagnetic.
Decision boundaries
Comparisons & substitution
431 generally offers more corrosion resistance and toughness than 410 at comparable high-strength intent because of its chromium-nickel balance.
17-4 PH or 15-5 PH may offer easier aging-based strength control, while austenitic or duplex grades are reviewed when welding or chloride resistance dominates.
Where it is used
Applications
Ordering scope
Product forms & standards
Bar and shapes ordered with the exact annealed or hardened-and-tempered condition, section, straightness, and test requirements.
Plate, sheet, strip, wire, forgings, or machined components under the form-specific standard with heat identity preserved through final treatment.
Decision support
Selection guidance
Choose this grade when
- High strength and moderate corrosion resistance are required in a heat-treatable shaft or fastener.
- The supplier can certify the exact hardened-and-tempered condition through the ordered section.
Review another grade when
- Continuous seawater immersion, welded fabrication, or high chloride exposure dominates.
- Fatigue, fracture toughness, or stress-corrosion requirements lack a qualified condition and test plan.
Before ordering
Procurement checklist
Name the governing product specification and edition, exact UNS designation, dimensions, tolerances, finish, and delivery or heat-treatment condition.
Require a traceable material test report and verify chemistry, mechanical tests, heat treatment, marking, and any supplementary examination against the purchase order.
State the service environment, design temperature, fabrication route, inspection plan, certification, packaging, and any regulatory or end-user approval before order release.
Traceable evidence