SS 347 — Stainless Steel (SS) Grade Specification, Properties & Equivalents
SS 347 stainless steel is a stabilized austenitic stainless steel grade, renowned for its excellent resistance to intergranular corrosion, especially after exposure to elevated temperatures. This stabilization is achieved by the addition of niobium (columbium), which forms chromi
SS 347 stainless steel is a stabilized austenitic stainless steel grade, renowned for its excellent resistance to intergranular corrosion, especially after exposure to elevated temperatures. This stabilization is achieved by the addition of niobium (columbium), which forms chromium carbides. In India, SS 347 is a critical material for industries dealing with high-temperature corrosive environments, such as the petrochemical, chemical processing, and power generation sectors. Its ability to withstand high temperatures without compromising mechanical integrity makes it a preferred choice for fabricating critical components like exhaust systems, furnace parts, and reactor vessels. Procurement engineers and QC professionals in India rely on SS 347 for its predictable performance and long service life in demanding operational conditions. The unique properties of SS 347 stainless steel ensure reliability and safety in high-heat industrial applications across the nation.
Chemical Composition of SS 347
Chemical Composition of SS 347 Stainless Steel
| Element | Weight % |
| Chromium (Cr) | 17.0 – 19.0 |
| Nickel (Ni) | 9.0 – 12.0 |
| Molybdenum (Mo) | - |
| Niobium (Nb) + Tantalum (Ta) | >= 10 * C % |
| Carbon (C) | 0.08 max |
| Manganese (Mn) | 2.0 max |
| Silicon (Si) | 0.75 max |
| Phosphorus (P) | 0.045 max |
| Sulfur (S) | 0.030 max |
| Iron (Fe) | Balance |
Mechanical Properties of SS 347
Mechanical Properties of SS 347 Stainless Steel
| Property | Value |
| Tensile Strength, Ultimate (UTS) | 515 MPa (75 ksi) min |
| Tensile Strength, Yield (YS) (0.2% offset) | 205 MPa (30 ksi) min |
| Elongation at Break | 35% min |
| Hardness, Rockwell B (HRB) | 92 max |
| Density | 8.0 g/cm³ |
| Modulus of Elasticity | 193 GPa (28 x 10⁶ psi) |
Available Forms of SS 347 Stainless Steel in India
| Shape | Typical Sizes | Standard Length |
| Plate | 3 mm to 25 mm thickness | Upto 3000 mm Width, 6000 mm Length |
| Sheet | 0.5 mm to 3 mm thickness | 1000 mm x 2000 mm, 1219 mm x 2438 mm |
| Bar | Round: 5 mm to 100 mm diameter | 3000 mm to 6000 mm |
| Wire | 0.5 mm to 6 mm diameter | Coils |
| Pipe (Seamless & Welded) | 1/2" NB to 6" NB | 6 meters |
| Tube (Seamless & Welded) | 1/2" OD to 4" OD | 6 meters |
Real-world Applications of SS 347 Stainless Steel
- Chemical Processing: Reactor vessels and heat exchangers
- Petrochemical Industry: High-temperature piping and furnace parts
- Power Generation: Boiler tubes, superheater elements, and exhaust stacks
- Aerospace: Aircraft engine exhaust systems and components
- Automotive: High-performance exhaust manifolds and catalytic converter parts
- Food Processing: Equipment handling corrosive substances at elevated temperatures
- Industrial Furnaces: Components requiring resistance to scaling and high heat
- Oil & Gas: Downhole tubulars and refinery equipment
Machinability & Weldability of SS 347 Stainless Steel
Machining SS 347 stainless steel requires careful consideration due to its work-hardening nature. Use rigid machine tools and heavy feeds to overcome this tendency. Slow cutting speeds, typically in the range of 10-15 m/min for turning with carbide tools, are recommended. Employ sharp, positive rake tools made of high-speed steel or cemented carbide. A constant flow of coolant is essential for chip lubrication and cooling to prevent tool overheating and ensure a good surface finish. For drilling, use stub drills and drill speeds around 10-20 m/min. Free-machining grades often offer slight improvements but are generally not available for SS 347.
Weldability of SS 347 stainless steel is considered good, especially with conventional welding methods like shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), and gas metal arc welding (GMAW). Due to its stabilized nature with niobium, SS 347 is less susceptible to intergranular corrosion in the heat-affected zone (HAZ) compared to unstabilized grades like SS 304 after welding. However, to maintain optimal corrosion resistance, it is recommended to use SS 347 filler metal or a matching composition. Preheating is generally not required, but maintaining interpass temperatures below 150°C helps minimize distortion. Post-weld heat treatment (PWHT) is typically not necessary if the welding procedures are correctly followed and the service temperature is below 800°C, as the niobium provides inherent sensitization resistance. If PWHT is performed, a solution anneal at 1040°C – 1150°C followed by rapid cooling is effective for SS 347.
Heat Treatment & Processing of SS 347 Stainless Steel
The primary heat treatment for SS 347 stainless steel is solution annealing, which is crucial for restoring ductility and forming a homogeneous microstructure, especially after cold working or welding. The recommended temperature range for solution annealing SS 347 is between 1040°C and 1150°C. This process dissolves carbides and stabilizes the structure. After heating to the solution temperature, rapid cooling (quenching) in water or air is essential to prevent re-precipitation of chromium carbides and maintain the material’s corrosion resistance. SS 347 is not hardenable by heat treatment; its strength is primarily derived from cold working.
Normalizing is not a typical heat treatment for austenitic stainless steels like SS 347 as it does not significantly alter the microstructure or properties in the same way it does for ferritic or martensitic steels. Tempering is also not applicable as SS 347 does not undergo hardening and tempering cycles. Cold working, such as rolling or drawing, can be used to increase the strength and hardness of SS 347. The presence of niobium in SS 347 stainless steel provides excellent resistance to sensitization during welding and high-temperature exposure, eliminating the need for post-weld heat treatment in many applications. Its inherent high-temperature strength and creep resistance make SS 347 a robust choice for demanding industrial environments.
Sourcing SS 347 Stainless Steel in India
SS 347 stainless steel is readily available across major industrial hubs in India, with significant stock often found in Mumbai, Pune, and Chennai. Leading Indian manufacturers such as Jindal Stainless, Tata Steel, and SAIL produce SS 347 in various forms. Minor manufacturers also contribute to the supply chain. For SS 347, the typical Minimum Order Quantity (MOQ) can vary, with smaller quantities (e.g., a few kilograms for bars or sheets) often available from distributors, while larger mill orders might require higher MOQs. The price band for SS 347 stainless steel typically ranges from INR 450 to INR 650 per kilogram, depending on the form, thickness, quantity, and prevailing market conditions. Buyers should always demand a Material Test Certificate (MTC) as per EN 10204 3.1 or 3.1.B, which confirms the chemical composition and mechanical properties of the supplied SS 347 material. Third-party inspections and Positive Material Identification (PMI) are also commonly requested by buyers to ensure compliance with specifications.
International Equivalents for SS 347 Stainless Steel
| Standard | Code |
| IS | X5CrNiNb18-10 (Implied) |
| ASTM | S34700 |
| EN | 1.4550 |
| JIS | SUS 347 |
| DIN | X12CrNiTi18-9 (Similar Application) |
| GOST | 12X18H10T (Similar Application) |
FAQs about SS 347
What is the primary advantage of SS 347 over SS 304?
The primary advantage of SS 347 stainless steel over SS 304 is its superior resistance to intergranular corrosion after exposure to elevated temperatures. This is due to the addition of niobium (columbium), which stabilizes the steel by forming chromium carbides, preventing sensitization—a phenomenon that weakens the grain boundaries and reduces corrosion resistance in unstabilized grades like SS 304 when heated between 425°C and 850°C. This makes SS 347 ideal for services involving high-temperature corrosive environments.
Can SS 347 be used in cryogenic applications?
While SS 347 stainless steel offers good high-temperature performance, it is not typically the primary choice for cryogenic applications. Its toughness decreases at very low temperatures compared to other austenitic grades specifically designed for cryogenic service, such as SS 304L or SS 310. Although SS 347 can be used at sub-zero temperatures, its impact strength may not be as robust as grades optimized for extreme cold, making SS 347 more suited for its high-temperature niche.
What is the typical hardness of SS 347?
SS 347 stainless steel exhibits a relatively low hardness in its annealed condition. The typical maximum hardness for SS 347 is around 92 on the Rockwell B (HRB) scale, which translates to approximately 200 on the Brinell scale. This low hardness contributes to its good formability and machinability. However, like other austenitic stainless steels, SS 347 work hardens significantly when subjected to cold working processes, increasing its hardness and tensile strength.
How does the niobium content in SS 347 affect its properties?
The niobium content in SS 347 stainless steel is its key differentiator. Niobium acts as a stabilizing element by forming stable niobium carbides. During heating, especially within the sensitization temperature range (425°C-850°C), niobium preferentially forms carbides over chromium carbides. This prevents the depletion of chromium at the grain boundaries, thereby significantly enhancing SS 347's resistance to intergranular corrosion, particularly after welding or high-temperature exposure, unlike grades such as SS 304.
Is SS 347 magnetic?
No, SS 347 stainless steel is non-magnetic in the annealed condition. Like other austenitic stainless steel grades (e.g., SS 304, SS 316), its crystal structure is face-centered cubic (FCC), which does not support ferromagnetic properties. However, SS 347 can become slightly magnetic after undergoing significant cold working. This induced magnetism is usually weak and does not affect the material's corrosion resistance or other key mechanical properties.
What is the difference between SS 347 and SS 347H?
The primary difference between SS 347 and SS 347H stainless steels lies in their carbon content. SS 347 has a maximum carbon content of 0.08%, whereas SS 347H has a higher specified carbon range, typically between 0.04% and 0.10%. The 'H' designation indicates a high carbon content, which enhances the high-temperature strength and creep resistance of the grade. Both grades are stabilized with niobium and offer similar corrosion resistance, but SS 347H is preferred for applications demanding superior elevated-temperature mechanical properties.
Tags: grade, stainless steel (ss), ss 347