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Introduction
Stainless steels are high-alloy steels. They contain about 4-30% of chromium. They are further classified into three types such as martensitic, austenitic, and ferritic steels. Another group of stainless steels are precipitation-hardened steels. They are a combination of austenitic and martensitic steels.
Alloy 350 is a chromium-nickel-molybdenum stainless steel which can be hardnened by martensitic transformation and/or precipitation hardening. It has been used for gas turbine compressor components such as blades, discs, rotors, shafts, and similar parts where high strength was required at room and intermediate temperatures. Depending upon the heat treatment, alloy 350 may have an austenitic structure for best formability, or a martensitic structure with strengths comparable to those of martensitic steels. The alloy normally contains about 5 to 10% delta ferrite. The corrosion resistance of alloy 350 approaches that of the chromium-nickel austenitic stainless steel
Chemical Composition
The following table shows the chemical composition of grade 350 stainless steel alloy.
| Element | Content (%) |
| Iron, Fe | 72.69 - 76.29 |
| Chromium, Cr | 16-17 |
| Nickel, Ni | 4 - 5 |
| Molybdenum, Mo | 2.5-3.25 |
| Manganese, Mn | 0.5-1.25 |
| Silicon, Si | 0.5 |
| Nitrogen, N | 0.07-0.13 |
| Carbon, C | 0.07-0.11 |
| Phosphorus, P | 0.04 |
| Sulfur, S | 0.03 |
Grade Specification
| Grade | UNS | DIN | EN | AMS | ASTM | JIS | |
| AM 350 | S35000 | AMS 5745 AMS 5774 AMS 5775 AMS 5546 AMS 5548 AMS 5554 | ASTM A579 ASTM A693 | - | |||
Physical Properties
The physical properties of grade 350 stainless steel alloy are highlighted in the following table.
| Properties | Metric | Imperial |
| Density | 7.7-8.03 cm3 | 0.278-0.290 lb/in3 |
Mechanical Properties
The following table outlines the mechanical properties of grade 350 stainless steel alloy.
| Properties | Metric | Imperial |
| Tensile strength | 1105 MPa | 160266 psi |
| Yield strength | 415 MPa | 60190 psi |
| Elastic modulus | 190-210 GPa | 27557-30458 ksi |
| Poisson's ratio | 0.27-0.30 | 0.27-0.30 |
| Elongation | 30% | 30% |
| Hardness | 95 | 95 |
Thermal Properties
The thermal properties of grade 350 stainless steel alloy are displayed in the following table.
| Properties | Metric | Imperial |
| Thermal expansion co-efficient (@ 20-100°C/70-212°F) | 11.3 µm/m°C | 6.55 µin/in°F |
| Thermal conductivity (@ 38°C/100°F) | 14.5 W/mK | 100.7 BTU in/hr.ft².°F |
Processing method
Machinability
Grade 350 stainless steel alloy can be machined using practices applied on high strength stainless steels. It is recommended to use sharp tooling, positive feeds, slow speeds, and adequate lubricant.
Welding
Grade 350 stainless steel alloy can be welded using all common techniques except oxyacetylene welding method. After welding, this alloy is annealed to restore maximum properties.
Hot Working
Hot working of grade 350 stainless steel alloy is performed after heating at 1177°C (2150°F). This process is finished at 982°C (1800°F)
Cold Working
Grade 350 stainless steel alloy can be cold worked in the annealed condition. Radical deformation of this alloy is limited due to its high work hardening rate and the formation of martensite.
Annealing
Grade 350 stainless steel is annealed by soaking at 1010 to 1066°C (1850 to 1950°F) followed by quenching.
Tempering
Grade 350 stainless steel is soaked at -73°C (-100°F). It is then tempered at 454°C (850°F) to attain maximum strength or at 538°C (1000°F) to attain maximum toughness and corrosion resistance for 3 to 4 h.
Hardening
Grade 350 stainless steel can be hardened by sub zero or double aging. Before performing this process, this alloy is prepared by rapidly cooling at 932°C (1710°F).
Applications
