Question

7. Different time-temperature cooling paths for a 1080 steel on an isothermal transformation diagram will produce different microstructures. Use the IT diagram and other knowledge to determine the microstructure of the steel samples after each heat treatment. In each case assume that the specimen begins at 860ºC and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. (10 points) (1) Water-quench Ai 700 (2) Water-quench; reheat 1 h at 200°C, air-cool. 600 so (3) Quench in molten salt bath at 300°C, hold 5h, air-cool. 400 M (4) Quench in molten salt bath at 600°C; hold 3min; water quench. 200 100 10 10 101 (5) Quench in molten salt bath at 700°C; hold 2 h; water quench

Answer 1

(1) WATER QUENCH -

• We will get martensite.

(2) WATER QUENCH, REHEAT 1 Hr AT 200 C, AIR COOL -

• We will get tempered martensite.

(3) QUENCH IN MOLTEN SALT BATH AT 300 C, HOLD FOR 5 Hr, AIR COOL -

• We get AUSTEMPERING (BANITE).

(4) QUENCH IN MOLTEN SALT AT 600 C; HOLD FOR 3 MIN; WATER QUENCH-

• We get MARTEMPERING (martensite).

(5) QUENCH IN MOLTEN SALT BATH AT 700 c, HOLD 2 Hr; WATER QUENCH-

• We get SPHEROIDITE.
• Spheroidite structure is a microstructure that contains sphere-like cementitie particles.