Stabilised Ferritics with Mo 436 444 470LI

Grades which compete with 316/316L in corrosion resistance. The absence of nickel produces a lower cost alternative. The ferritic structure gives excellent deep drawability and stress corrosion cracking resistance but disadvantages in welding of thick sections and stretch forming.

Equivalent EN and UNS Grades - 1.4526 1.4521 1.4613 S43600 S44400

Approximate Composition – 17-20% Cr, 1.0-2.0% Mo, plus combinations of stabilising elements like Ti and Nb.  470LI uses 24% Cr instead of Mo additions to achieve comparable corrosion resistance to 316. (Exact composition ranges vary between EN and ASTM standards).

These grades combine the following characteristics:

• Good corrosion resistance similar to or just below that of 316
• Excellent resistance to stress corrosion cracking better than standard austenitic grades 304 and 316
• Higher 0.2% PS compared to 316. 280/300 MPa compared to 240 MPa
• Excellent deep drawing properties slightly better than austenitic grades
• Reduction in ridging and roping during forming compared to unstabilised ferritic grades like 430
• Lower thermal expansion and higher thermal conductivity than austenitic grades
• Limited stretch formability compared to austenitic grades due to lower ductility
• Limit on welding to about 5 mm due to poor weld toughness from rapid grain growth
• Loss of toughness at sub-zero temperatures

These grades have been used extensively over the years for a number of familiar applications such as exhaust systems. They are being targeted at competing with 316 in applications where the limitations on weld thickness and stretch forming are not an issue. 

Applications which illustrate these features include:
Cladding, wall panels, exhaust systems, roofing, handrails, catering equipment, domestic plumbing, hot water tanks, sugar processing, electrical motor housings.