Ferrite stabilizer
Ferrite formers are metals such as chromium, molybdenum, or silicon that stabilize ferrite structure and narrow the austenite field. They promote finer grain and increase hardness and toughness.
Physicochemical mechanism of action
Ferrite formers are chemical elements that favor the body-centered cubic ferrite structure. They tie up oxygen and prevent the formation of austenite, a finer structure with higher toughness. This leads to a narrowed temperature range for austenite in the phase diagram.
Metallurgical relevance & welding risks
The use of ferrite formers can increase the hardness and toughness of the weld, which is especially beneficial in high-stress applications. However, excessive amounts of ferrite formers can lead to excessive hardness, making the structure glass-hard and reducing deformability. This increases susceptibility to cracking and hot cracking.
Workshop practice & actionable instructions
To effectively use ferrite formers, the content in the alloy must be precisely controlled. At too high a concentration of ferrite formers (e.g., over 0.4% chromium), the structure can become glass-hard and crack-prone. It is important to cool the weld slowly to achieve finer grain and higher toughness. The cooling time should be between 5 and 25 seconds to reach the critical temperature window for ferrite formation.