The problem with welding grade 430 is that the weld zone loses its corrosion resistance, and 439 exists to fix precisely that. A small titanium addition ties up the carbon so chromium stays in solution through the heat of welding, which is why 439 goes into welded exhaust systems and hot water tanks where plain 430 would corrode at the seam. USA Piping Solution supplies SS 439 ERW pipes and tubes in this stabilized 18 percent chromium ferritic grade. For the non-stabilized general-purpose grade at lower cost, see our SS 430 ERW page.
How Stabilization Works
The enemy of a ferritic weld is chromium carbide. During welding, carbon in the steel grabs chromium at the grain boundaries and precipitates as carbide, which locally drops the chromium below the level needed for corrosion resistance, a condition called sensitization. Titanium is a stronger carbide former than chromium, so adding a little titanium means the carbon combines with titanium instead, harmlessly, and the chromium stays in solution doing its job. That is the whole trick, and it is why 439 keeps its corrosion resistance right through a weld where 430 would not.
Specifications
| Grade / UNS | 439 / UNS S43035 |
| Type | Titanium-stabilized ferritic stainless |
| Chromium | 17.0 – 19.0% (typical) |
| Stabilizer | Titanium (ties up carbon, prevents weld sensitization) |
| Tube Standard | ASTM A268; confirm against order |
| Construction | ERW welded |
| Key Property | Retains corrosion resistance after welding; good formability |
Applications
- Welded Exhaust Systems: the cooler and mid sections of automotive exhaust. See Automotive Steel Tubes.
- Hot Water Tanks & Heat Exchangers: welded vessels needing corrosion-tight seams.
- Condensing Heat Exchangers: moderate corrosion with welded construction.
- Automotive & Appliance Fabrications: any welded ferritic part that must stay corrosion-tight.
439 in the Ferritic Family
439 is the stabilized answer to 430's weld weakness. For high-temperature exhaust entry duty below where stabilization matters, 409 remains the classic lower-cost choice. Add molybdenum on top of 439 and you get 436, which resists exhaust condensate and road-salt corrosion better. Adjacent stabilized grades 441 and 444 carry dual stabilization and higher molybdenum for still tougher duty. Testing follows ASTM A268 with certificates and traceability; see our Quality Policy page. Send OD, wall, and length for availability.
Related Products
- SS 430 ERW Pipes & Tubes
- SS 436 ERW Pipes & Tubes
- Ferritic SS 441
- Automotive Steel Tubes
- Stainless Steel Pipes & Tubes
Frequently Asked Questions
What is the difference between 430 and 439?
439 is 430 made weldable. A titanium addition stabilizes the carbon so the weld zone keeps its corrosion resistance, which plain 430 loses when welded. Use 439 wherever a ferritic part is welded into corrosion service.
Why is 439 used in exhaust systems?
Exhaust systems are welded and see corrosive condensate. 439's stabilization keeps the welds corrosion-tight, and its ferritic structure handles the thermal cycling better than austenitic grades. For the hot end and salt exposure, 436 with molybdenum steps it up further.
Is 439 dual-stabilized?
439 is titanium-stabilized. Some related grades such as 441 use dual titanium-plus-niobium stabilization for higher-temperature strength. Tell us the service temperature and we will point you to the right grade in the family.