Grade 444 is a low carbon, dual stabilised, molybdenum containing ferritic stainless steel with good ductility, toughness and resistance to sensitisation, even in the welds. With 18% chromium and 2% molybdenum, the steel has good pitting resistance and crevice corrosion resistance, similar to 316 and good general corrosion resistance and oxidation resistance, similar to 316 in most environments. Being a ferritic stainless steel, 444 is not susceptible to Stress Corrosion Cracking. Annealed 444 is ductile and can be formed using a wide range of roll forming or mild stretch bending operations as well as the more common drawing and bending operations. 444 does not harden excessively during cold working.The steel has limited weldability and should not be used in the as-welded condition for dynamic or impact loaded structures. As with most ferritic stainless steels, 444 can undergo grain growth in the heat affected zone of weldments, which may adversely affect the mechanical properties in these zones. Applications involving welded 444 are thus generally limited to a thickness of 2.5mm.444 has good pitting resistance and is thus suitable for roofing and cladding in marine environments, as well as hot water tanks and geysers, heat exchanger tubing and food processing equipment.
Chemical Composition of 444 stainless steel
1.75 - 2.50
17.5 - 19.5
Grade 444 is Molybdenum alloyed ferritc steel, and because of this, resistance to localized corrosion is close to grade 1.4404 / AISI 316 “acid-proof” austenitic. In chloride containing solutions pitting and crevice corrosion is possible, depending on various parameters like chloride concentration, temperature, pH value, redox potential, crevice geometry and others. Optimal material performance is usually achieved through efficient design, correct post-weld treatment and regular cleaning during use (if applicable).
The nickel-free ferritic grades have excellent resistances to chloride induced stress corrosion cracking.
444 can be readily cold-formed by all standard processes. It is particularly suitable for deep drawing. The deep drawability of 444 is comparable to that of deep drawing quality carbon steels.
444 has a lower work hardening rate than standard austenitic grades. This characteristic makes the grade 444 less suitable for applications involving stretch forming. For the same reason, 444 is more easily cold formed and machined. The forces needed in cold-forming and machining are similar to those needed for low-alloyed carbon steels.
Normally, 444 is not prone to the “ridging and roping” surface defect in deep drawing.
444 has low C and N contents. It is also stabilized with titanium and niobium which reduces or prevents the sensitation and formation of martensite. The stabilization gives this ferritic steel better weldability than many of the previously presented ferritic steels. The weldability is mainly limited by grain growth in the HAZ (heat affected zone), so the heat input must be kept to a minimum. Austenitic fillers are mostly used.