Introduction To Ferritic Stainless Steel Casting Parts

Chromium is the primary alloying element in this type of steel, with a chromium content typically ranging from 13% to 30%. It possesses excellent resistance to oxidation and corrosion in various media, as well as the ability to withstand air oxidation at high temperatures, making it suitable for heat-resistant applications. However, the welding performance of this steel is relatively poor. When the chromium content exceeds 16%, the as-cast structure becomes coarse. Prolonged exposure to temperatures between 400-525°C and 550-700°C can lead to the formation of "475°C" embrittlement and σphase, causing the steel to become brittle. The 475°C embrittlement is related to the ordering phenomenon of the chromium-containing ferrite. To improve the brittleness caused by the 475°C embrittlement and σ phase, the steel can be heated above 475°C and then rapidly cooled. Room temperature brittleness and brittleness in the heat-affected zone after welding are also fundamental issues with ferritic stainless steel. These can be improved by methods such as vacuum refining, adding trace elements (such as boron, rare earths, and calcium), or introducing austenite-forming elements (such as nickel, molybdenum, nitrogen, copper, etc.). 

To enhance the mechanical properties of the weld zone and heat-affected zone, small amounts of titanium and niobium are often added to prevent grain growth in the heat-affected zone. Commonly used ferritic steels include ZGCr17 and ZGCr28. However, in many applications, these steels are being replaced by austenitic stainless steels with high nickel content and good impact resistance, which have a nickel content exceeding 2% and a nitrogen content exceeding 0.15%.