|Stainless Steel – Grade 431, UNS S43100, 1.4057, SUS431|
|Fe, <0.20% C, 15-17% Cr, 1.25-2.50% Ni, <1.00% Mn, <1% Si, <0.040% P, <0.03% S|
|This heat treatable martensitic, nickel-bearing grade has the best corrosion resistance properties of all the martensitic grades. It has excellent tensile and torque strength, and good toughness, making it ideally suited to shafting and bolt applications. It can be hardened to approximately 40HRC. Because of its high yield strength, this grade is not readily cold worked and is therefore not recommended for use in operations such as cold heading, bending, deep drawing or spinning.
Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.
Grade Specification Comparison
Possible Alternative Grades
Excellent resistance to a wide variety of corrosive media. Reasonable resistance to salt water in cold southern waters but less resistant than SUS316 in tropical waters. Overall the corrosion resistance of SUS431 is approximately the same as or slightly below that of SUS304.
Performance is best with a smooth surface finish, in the hardened and tempered condition.
Resists scaling in intermittent service to 925°C and in continuous service to 870°C, but is generally not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties.
Heat Treatment of sus431
Full anneal – not practical for this grade – it hardens even when cooled slowly.
Process Anneal – heat to 620-660°C and air cool.
Hardened by heating to 980-1065°C, holding for about 1/2 hour then quenching in air or oil. Pre-heating at 760-790°C may be useful for complex parts or those already hardened. Temper to suit mechanical requirements, at temperatures as indicated in the accompanying table.
The tempering range 425-600°C should be avoided due to reduced impact toughness, although the effect is less marked than in most other martensitic grades.
Typical applications include:
· Nuts and bolts
· Propeller shafting
· Pump shafts
· Beater bars
· Marine hardware
· Laboratory benches & equipment
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