439 vs 444 Stainless Steel: Choosing Between Two Titanium-Stabilized Ferritic Grades

What 439 and 444 Have in Common

Grades 439 (UNS S43035, EN 1.4510) and 444 (UNS S44400, EN 1.4521) are both titanium-stabilized ferritic stainless steels with a body-centered cubic structure. Neither contains nickel as an intentional alloying addition, which gives both grades three useful characteristics: they are magnetic, they cost substantially less than austenitic grades such as 304 or 316, and they are inherently resistant to chloride stress corrosion cracking, a failure mode that austenitic grades can suffer in hot chloride environments. Both are stabilized with titanium so that welded and annealed sections resist sensitization and intergranular corrosion.

Chemical Composition Comparison (ASTM A240)

Element (% by mass)	439 (S43035)	444 (S44400)
C	0.07 max	0.025 max
Cr	17.0-19.0	17.5-19.5
Ni	0.50 max	1.00 max
Mo	None required	1.75-2.50
Ti	0.20 + 4 x (C + N) min, 1.10 max	0.20 + 4 x (C + N) min, 0.80 max
Mn	1.00 max	1.00 max
Si	1.00 max	1.00 max
N	0.04 max	0.035 max

How Molybdenum Changes 444's Corrosion Performance

The decisive alloying difference is molybdenum. Grade 444 carries 1.75-2.50% molybdenum, which integrates into the passive chromium-oxide film and makes it far more resistant to breakdown by chloride ions. The practical effect is measured with the pitting resistance equivalent number, PREN = Cr + 3.3 Mo + 16 N: approximately 17-18 for 439 versus about 24 for 444. In plain terms, 444 can tolerate stagnant or slow-moving chloride-containing water, including heated domestic water, while 439 will eventually pit in the same service. Grade 444 effectively sits between standard ferritics and 316 austenitic in chloride resistance, at a lower cost than 316 because it contains no nickel.

Mechanical Properties and Fabrication

Property (plate, ASTM A240)	439 (S43035)	444 (S44400)
Tensile strength, min	450 MPa	415 MPa
Yield strength, min	205 MPa	275 MPa
Elongation, min	22%	20%

Both grades have moderate strength and good thermal conductivity, roughly 25 W/(m.K) at room temperature, which is about 50% higher than austenitic grades. Fabrication practices are similar: both are welded with matching ferritic filler or austenitic filler such as ER309L, with controlled heat input to limit grain growth, and both benefit from clean, scale-free surfaces before welding to preserve corrosion resistance in the joint. The molybdenum in 444 does not complicate welding. Neither grade should be used in heavy sections for load-bearing cryogenic service, since ferritics can lose impact toughness at low temperature.

Application-by-Application Selection Guide

Automotive exhaust systems and heat shields: 439, because the service is hot gas rather than chloride-laden water.

Domestic and commercial hot-water tanks, water-heater linings: 444, because heated water with any chloride content pits unstabilized and low-alloy ferritics.

Solar thermal collectors and heat-pump tanks: 444, for long-term immersion in treated water.

Coastal architectural panels, cladding, and fixtures: 444, for salt-spray exposure.

Dry interior trim, appliances, and fresh-water piping without chlorides: 439 remains adequate and lower cost.

The Final Selection Rule

Follow the chloride-and-temperature rule. If the component contacts heated water with any chloride content, or stands in a coastal atmosphere, choose 444. If the service is hot gas, dry heat, or fresh water without chlorides, choose 439. During design, verify the water chemistry, chloride level, and pH, because even 444 has limits: it is not intended for strong acids or for permanently immersed seawater, where duplex or super-austenitic grades are required.

FAQ

Is 439 or 444 magnetic?

Both are ferritic and therefore magnetic, and both retain magnetism after welding and annealing because their body-centered cubic structure is stable.

Why is 444 better than 439 for hot water tanks?

Grade 444 contains 1.75-2.50% molybdenum, which resists chloride pitting and crevice corrosion in heated water. Grade 439 has no molybdenum and will pit over time in the same service.

Are 439 and 444 cheaper than 316?

Yes. Neither contains nickel as a significant alloying addition, and nickel is the main cost driver in austenitic grades. For hot-water and coastal applications where 316 would be over-specified, 444 provides comparable chloride resistance at lower material cost.

Can 439 be welded without losing corrosion resistance?

Yes, when the correct practice is followed: titanium stabilization prevents sensitization, so the welded joint keeps its corrosion resistance provided heat input is controlled and the surface is cleaned of scale and contamination before welding.

What standards define 439 and 444?

In North America, ASTM A240 (plate/sheet/strip) and A268 (tube) define UNS S43035 and S44400. In Europe, EN 10088 defines 1.4510 (X3CrTi17) and 1.4521 (X2CrMoTi18-2). Always confirm composition and mechanical limits against the governing standard for the product form.