What is Type 347 stainless steel?
Type 347 stainless steel is a niobium-stabilized austenitic stainless steel with a niobium (columbium) stabilizer added to prevent the precipitation of chromium carbides. It maintains its integrity, particularly under intermittent heating and welding conditions, without the loss of strength and corrosion resistance seen in less-stable steels like Type 304. The alloy stands out for its excellent resistance to intergranular corrosion at high temperatures, particularly in the 800-1500°F range. It is commonly used in chemical processing, high-temperature exhaust systems, and boiler piping.
347 stainless steel standard
ASTM A240, ASTM A182, ASTM A276, ASTM A312, ASTM A358, ASTM A403
Chemical Composition of 347 Stainless Steel
| Element | Composition Range |
| Carbon (C) | ≤ 0.08% |
| Manganese (Mn) | ≤ 2.00% |
| Silicon (Si) | ≤ 1.00% |
| Chromium (Cr) | 17.0% – 19.0% |
| Nickel (Ni) | 9.0% – 13.0% |
| Sulfur (S) | ≤ 0.030% |
| Phosphorus (P) | ≤ 0.045% |
| Niobium (Nb) + Tantalum (Ta) | 10x C min – 1.0% max |
Physical Properties
| Property | Value |
| Density | 7.7 – 8.03 g/cm³ (0.278 – 0.290 lb/in³) |
| Melting Point | 1371 – 1400°C (2500 – 2550°F) |
| Thermal Conductivity | 16.3 W/m·K (212°F) |
| Coefficient of Thermal Expansion | 10.5 x 10⁻⁶/°C (20-600°C) |
| Electrical Resistivity | 72 µΩ·cm (20°C) |
| Specific Heat | 500 J/kg·K (0 – 100°C) |
Mechanical Properties
| Property | Value |
| Tensile Strength (UTS) | 515 MPa min (75 ksi min) |
| Yield Strength (0.2% Offset) | 205 MPa min (30 ksi min) |
| Elongation | 40% min |
| Hardness (Brinell) | 201 max |
| Hardness (Rockwell B) | 95 max |
| Modulus of Elasticity | 190 – 210 GPa (27557 – 30458 ksi) |
| Poisson's Ratio | 0.27 – 0.30 |
| Creep Strength (at 750°C) | 38 – 39 MPa (5510 – 5660 psi) |
| Rupture Strength (at 750°C) | 38 – 39 MPa (5510 – 5660 psi) (100,000 hours) |
| Impact Toughness (Charpy V-notch) | 60 J (Longitudinal) / 40 J (Transverse) |
| Fatigue Strength (Rotating Bending, at 20°C) | 240 MPa (34.8 ksi) |
Heat treatment
Annealing and stress relief are commonly used heat treatment processes for 347 stainless steel to restore the ductility of the material or eliminate internal stress.
Annealing: 1010°C to 1193°C (1850°F to 2000°F). Rapid cooling after annealing (usually water quenching) can prevent the precipitation of chromium carbides, thereby improving its corrosion resistance.
Welding
347 stainless steel is highly suitable for welding, with excellent resistance to intergranular corrosion after welding, thanks to its niobium stabilization.
Common welding methods include TIG, MIG, and resistance welding.
Post-weld heat treatment is usually not required, but 347 filler metals are recommended to maintain similar properties at the weld joint.
What is the difference between 347 and 316 stainless steel?
316 stainless steel is ideal for general-purpose corrosion and high-chloride environments due to its molybdenum content, while 347 stainless steel is superior for high-temperature applications because its niobium stabilization prevents intergranular corrosion during welding. In essence, 316 offers superior corrosion resistance, whereas 347 offers better high-temperature stability and corrosion resistance after welding.
What is the difference between SS 347 and 304 stainless steel?
304 stainless steel is the most commonly used stainless steel, and is well suited for general-purpose applications such as kitchen equipment and food processing, but it lacks the stability required for environments above 800°F (427°C). 347 contains niobium, which resists intergranular corrosion and is suitable for high-temperature service. While 304 is a more economical choice for everyday use, 347 is the preferred choice for high temperatures and corrosive environments.
Forms of 347 Stainless Steel
Bars: 347 stainless steel bars are mainly used for structural components, shafts, fasteners and machined parts. These bars are available in various shapes, including round, square and hexagonal.
Sheets and Plates: 347 stainless steel sheet and plate are ideal for applications like chemical processing equipment and heat exchangers. Their thin and flat form makes them easy to cut, bend and process into the required shape. 347 stainless steel sheets are thicker than sheets and are used in heavy-duty applications such as pressure vessels, heat shields and boiler components.
Tubes and Pipes: Tubes made of 347 stainless steel are commonly used in petrochemical, aerospace and power generation. They can transport liquids and gases under extreme conditions.
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