439 - UNS S43035:
AISI Type 439 (also known as ASTM XM-8) is a ferritic stainless steel designed to resist corrosion in a variety of oxidizing environments from fresh water to boiling acids. Type 439 is a titanium stabilized, 18 percent chromium alloy that may be used in many oxidizing environments where Type 304 is considered adequate in terms of general corrosion resistance but is subject to chloride stress corrosion cracking. It is often used in place of Type 409 where higher thermal conductivity is required. Type 439 does not require annealing after welding to restore ductility or to provide intergranular corrosion resistance. Type 439 also has superior formability capabilities and is heavily used in the automotive industry; it can be work hardened slightly to increase tensile strength.
- Melting Point: 2741°F (1505°C)
- Density: 0.278 lbs/in3 / 7.70 g/cm3
- Modulus of Elasticity in Tension: 28 X 106 psi / 193 GPa
- Tensile Strength Minimum (psi): 66,000 - 70,000
- Yield Strength Minimum 0.2% offset (psi): 43,000 - 48,000
- % Elongation in 2” Minimum: 32 - 36%
- Hardness: Rockwell B74 - 78
- Carbon: 0.025 max
- Manganese: 0.50
- Silicon: 0.75
- Chromium: 17.00 - 19.00
- Nickel: 0.50
- Titanium: ≥ 0.20+4(C+N)min - 0.50 max
- Iron: Balance
All values are maximum values unless otherwise specified. Values derived from applicable AMS and ASTM specifications.
Heat Treatments: Type 439 is not hardenable by heat treatment
- Heat slowly to 1450 -1600°F (790 - 871°C), quickly cool. Slow cooling produces less desirable impact transition behavior. Ferritic stainless steels containing more than about 12% chromium have a susceptibility to a phenomenon known as 885°F (475°C) embrittlement. This embrittlement is observed as a degradation of impact properties at room temperature resulting from very long exposures in the temperature range of 700 to 1000°F (371 to 537°C). If service temperatures are cycling through this range, exposure above, about 1050°F (565°C), restores the room temperature toughness properties. When there have been long dwell times near 885°F (475°C), service temperatures that cycle above, about 1050°F (565°C), are beneficial rather than detrimental.
AISI Type 439 is resistant to attack by potable water and many mildly or moderately corrosive chemical environments which are oxidizing in nature. In various chloride solutions, studies have shown pitting resistance of Type 439 to be superior to that of Type 304. In addition, Type 439 is not subject to stress corrosion cracking which may cause premature failure of austenitic steels in chloride bearing environments such as hot waters used in heat exchangers.