1.4550, DIN X6CrNiNb18-10, AISI 347

1.4550, DIN X6CrNiNb18-10, AISI 347

Designation by Standards

 

Chemical Composition (in weight %)

Description
Similar to 321 stainless, 347 uses niobium (columbium) as a stabilizing element to maximize its principal feature: resistance to intergranular corrosion. It can be used in applications requiring repeated heating in the range of 427-899^oC.

Applications
High temperature gaskets and expansion joints, rocket engine parts, aircraft collector rings and exhaust manifolds and chemical production equipment. Component parts for the textile, food processing, paper, chemical, and leather industry.

Physical properties (avarage values) at ambient temperature
Modulus of elasticity [10³ x N/mm²]: 200, 186 (200^oC), 172(400^oC)
Density [g/cm³]: 7.70
Thermal conductivity [W/m.K]: 15.0
Electric resistivity [Ohm mm²/m]: 0.75
Specific heat capacity[J/g.K]: 0.50

Coefficient of Linear Thermal Expansion 10^{-6 o}C^-1

Hardening
Harden from a temperature of 1020-1120^oC followed by water or oil quenching. This procedure will result in maximum ductility. Structure is austenite.

Mechanical properties in solution-annealed condition and reistance to intercrystalline corrosion
0.2 % proof stress: 205 N/mm² (for d<=160, 160<d<=250)
1.0 % proof stress: 240 N/mm² (for d<=160, 160<d<=250)
Tensile strength: 510-740 N/mm²
Elongation: 40% (for d<=160, longit.), 30% (for 160<d<=250, transv.)
Notch impact energy (ISO-V): 100 J (for d<=160, longit.), 60 J (for 160<d<=250, transv.) Resistance to interystalline corrosion: yes (in as delivered condition), yes (in sensitised condition)
Note: Sensitisation treatment for 15 min at 700^oC with subsequent cooling in air.

Mechanical Properties At Elevated Temperatures

Forging
Hot forming temperature: 1150-850^oC.

Machinability
Slightly tougher than 304 stainless, this material will produce the same tough stringy chips. The use of slow speeds and constant positive feeds will minimize this alloy's tendency to work harden.

Corrosion Resistance
Organic media, atmospheric conditions, very weak acids, milk and other dairy products will have little affect on 347. Far superior to unstabilized chromium-nickel steels in terms of corrosion in the range of 427-816^oC.

Welding
347 may be welded by all commonly used fusion and resistance methods. Oxyacetylene welding is not recommended. When necessary, use AWS E/ER347 filler metal.

Cold working
Although this material requires higher initial forces than 304 stainless, it is quite tough and ductile and can be readily stamped, blanked, spun and drawn.