What temperature range does blue brittleness occur?

What temperature range does blue brittleness occur?

• A. 300-700F (150-370C)
• B. 0-100F ( -18 to 38C)
• C. 600-900F (316-482C)
• D. 100-300F (38-149C)

Answer: (A)

Blue brittleness shows up when steel is heated into a moderate tempering range, where the microstructure changes enough to reduce notch toughness even though hardness may be high. In this window, impurities can diffuse and brittle phases can form at grain boundaries, making the metal more prone to brittle fracture under impact. The familiar blue temper color appears in this same temperature zone, which is why it’s associated with blue brittleness. That’s why the temperature range around 150–370°C (300–700°F) is the correct one. At lower temperatures, the steel hasn’t entered this tempering window, and at higher temperatures you generally get softening and increased ductility rather than brittleness from this mechanism.

Blue brittleness shows up when steel is heated into a moderate tempering range, where the microstructure changes enough to reduce notch toughness even though hardness may be high. In this window, impurities can diffuse and brittle phases can form at grain boundaries, making the metal more prone to brittle fracture under impact. The familiar blue temper color appears in this same temperature zone, which is why it’s associated with blue brittleness. That’s why the temperature range around 150–370°C (300–700°F) is the correct one. At lower temperatures, the steel hasn’t entered this tempering window, and at higher temperatures you generally get softening and increased ductility rather than brittleness from this mechanism.