Ferritic SS 446
Ferritic SS 446 has the best corrosion resistance among all the grades in 400 series, notably due to its high chromium content (26%). It is commonly used in applications having a high-temperature range about 1500°F to 2100°F because it has exceptional high-temperature resistance to oxidation and corrosion.
The strength of the metal might decrease a little at elevated temperatures but finds its place due to its resistance to oxidation in air, and resistance to various other media at elevated temperatures.
The alloy can also suitably resist cyclic oxidation. The grade has superior scaling resistance than the majority of 400 and 300 series alloys.
The welding material needs to be considered during processing since the material does not have equal scaling resistance compared to the base metal. The alloy is heat-resistant, and normally non-heat treatable. High-temperature applications require the metal to be stable with an imperturbable grain structure, this is made possible by the exceptional chemical composition of 446.
For forging the alloy, it needs to be hot-worked, particularly beginning at a temperature of 1100°C. By the end of the process, the temperature should be below 870°C for grain refinement and prevention of embrittlement. In the Sigma phase, (intermetallic phase in the metal around 560- 980°C) embrittlement is common in the alloy with long term exposure at elevated temperature.
The cold working becomes very difficult in the grade due to very high chromium content, hence, processes like bending, drawing and spinning will be difficult for the grade. For convenient forming and bending, the alloy will require slow forming speeds, edge preparation and suitable preheating. The alloy grade also has lesser ductility due to the chromium content, with carbon content restricted to 0.20%. The grade’s resistance to reducing sulphurous gases, and metals like molten copper, lead and tin, might find its uses into respective applications.
CHEMICAL PROPERTIES
Grade | C | Ni | Mn | Si | Cr | Fe | P | S | N | |
SS 446 | Min. | – | – | – | – | 23.0 | 69.22 | – | – | – |
Max. | 0.020 | 0.75 | 1.50 | 1.00 | 27.0 | – | 0.040 | 0.030 | 0.25 |
PHYSICAL PROPERTIES
Density | 7.7 g/cm 3 / 0.28 lb/in 3³ |
Melting Point | 1510 C°/2750 F° |
Thermal Conductivity @ 70°F | 21.6 W/mK 150 BTU in/hr.ft².°F |
Specific Heat | 20 C ° J/Kg C° |
Electrical Resistivity | 20 C° |
Modulus of Elasticity | 200 GPa 29000 ksi |
Annealing | 800 – 860 (°C) / 1650 – 1700 (°F |
Poisson’s Ratio | 0.27-0.30 |
Quench | Rapid Water |
APPLICATIONS
Furnace parts, x- ray tube bases, oil burner parts, neutral salt pot electrodes, kiln linings, glass moulds, boiler baffles, stack dampers, annealing boxes, soot blowers, spouts, recuperators, industrial mufflers.
FORMS OF SUPPLY
Pipes and fittings, fittings and flanges, washers.