Selection summary
Overview
439 is a low-carbon, titanium-stabilized ferritic stainless steel developed to improve weld durability and elevated-temperature performance over basic 430-type material. It is widely considered for automotive exhaust and heat-transfer components, while formability, weld procedure, surface condition, and the exact product specification remain purchase-critical.
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 | ≤ 0.030% | Weldability and stabilization control |
| Chromium | 17.0–19.0% | Oxidation and corrosion resistance |
| Titanium | Stabilized per specification | Binds carbon and nitrogen for weld durability |
| Nickel | ≤ 0.50% | Residual alloy control |
Concise grade-family reference only. Confirm every element limit against the current standard for the exact product ordered.
Condition matters
Reference properties
Annealed flat-product reference; verify thickness and standard
Annealed flat-product reference, not a formed-part guarantee
Typical room-temperature engineering reference
Environment first
Corrosion behavior
Provides useful atmospheric and mildly corrosive resistance with improved weld-zone stability over unstabilized ferritic grades.
It does not provide the broad chloride or reducing-acid resistance associated with higher-alloy austenitic or duplex grades.
Temperature, concentration, deposits, crevices, stress, surface finish, cleaning, and fabrication quality can change service performance.
Service limits
Temperature & service
Oxidation and thermal-fatigue performance depend on temperature cycle, atmosphere, thickness, and joint design.
Delivery condition
Heat treatment & condition
439 is supplied annealed; titanium stabilization supports weld durability, but a final anneal may be required after severe processing under the product specification.
It cannot be hardened by heat treatment; cold work raises strength while grain growth from excessive heat can reduce toughness and formability.
Process route
Fabrication
Ferritic grain growth and weld-zone toughness require controlled heat input and qualified procedures.
Forming behavior and springback differ from austenitic grades; surface protection is important for visible components.
Magnetic response: Ferromagnetic in annealed and fabricated conditions.
Decision boundaries
Comparisons & substitution
439 offers stabilization and welded thermal-cycle capability beyond basic 430 for many exhaust and heat-transfer components.
441 adds niobium-assisted stabilization for more demanding thermal fatigue, while austenitic or higher-alloy grades may be required for severe forming or corrosion.
Where it is used
Applications
Ordering scope
Product forms & standards
Plate, sheet, and strip under the applicable flat-product specification, exact UNS designation, finish, and delivery condition.
Welded or seamless tube, pipe, bar, wire, forgings, or components only under their own product-specific standards and condition requirements.
Decision support
Selection guidance
Choose this grade when
- A stabilized ferritic sheet is needed for welded or thermally cycled service.
- Low thermal expansion and nickel-independent alloying are useful design factors.
Review another grade when
- Deep drawing, severe stretch forming, or low-temperature toughness dominates.
- Chlorides or aggressive process media require a higher corrosion-resistance class.
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