Topic: Material Science / Manufacturing
Which of the following option is true for heat treatment of HSS 18:4:1?
- A. First specimen is heated to $1200^{\circ}C$
- B. First specimen is heated to $850^{\circ}C$
- C. First specimen is heated to $550^{\circ}C$
- D. None of the above
Answer: B. First specimen is heated to $850^{\circ}C$
Explanation: High-Speed Steel (HSS) 18:4:1 has high thermal expansion and low thermal conductivity. To prevent thermal shock and cracking, it is not heated directly to its austenitizing temperature ($1200^{\circ}C$). Instead, it is preheated slowly in stages, typically first around $550^{\circ}C$ and then to $850^{\circ}C$, before being rapidly heated to the final hardening temperature.