High speed steel tools retain their hardness upto a temperature of __________ °C.

ANS:C - 900

High-speed steel tools typically retain their hardness up to a temperature of around 600°C to 650°C (1112°F to 1202°F), not 750°C. This is the point at which high-speed steel starts to lose its hardness and temper, becoming softer and less effective for cutting or machining operations. Therefore, the correct answer would not be 900°C. Thank you for bringing that to my attention. To summarize:

• High-speed steel tools retain their hardness up to a temperature of around 600°C to 650°C (1112°F to 1202°F), not 900°C.