Answer Happy

There is a part made of eutectoid steel and its microstructure consists of 50% fine pearlite and 50% martensite. Recommend the best isothermal heat treatment processes that would convert its microstructure to the ones given below. Show the required heat treatment processes on the diagrams provided, and state the time, temperature, and resulting microstructure for each step of the process in the tables below the diagrams. a) 50% bainite and 50% tempered martensite [2 marks] b) 100% ferrite [2 marks] c) Equal percentages of all possible micro-constituents without a subsequent annealing/tempering operation [2 marks] Hints: There is no typo in the requested microstructures. Consider different types of pearlite (course, medium, fine) as one product. If any of the requested microstructures cannot be achieved, then explain the reason. The final products produced above should be cooled down to the room temperature. Answer to Part (a): 800 A Eutectoid temperature 1400 700 1200 600 1000 500 B 800 400 600 300 200 400 100 200 Step Example 1 2 3 4 5 Temperature (°C) A 1x1411 -8 A M(start) M(50%) M(90%) 10-1 1 10 10² Time (s) Heat treatment process (including temperature and time) At room temperature before processing M+A 50% TT Temperature (°F) 103 104 105 Resulting microstructure (include the % of micro-constituents) 50% fine pearlite + 50% martensite
Answer to part (b): Step 1 2 3 4 5 Temperature (°C) 800 700 600 500 400 300 200 100 A A Eutectoid temperature P A M(start) M(50%) M(90%) 0 10-1 1 10 10² Time (s) Heat treatment process (including temperature and time) M+A B I T 1400 1200 1000 800 600 400 200 T Temperature (°F) 50% 10³ 104 105 Resulting microstructure (include the % of micro-constituents)
Answer to c: Step 1 2 3 4 5 800 700 600 500 400 A 300 M(start) 200 M(50%) M(90%) 100 0 10-1 1 10 10² Time (s) Heat treatment process (including temperature and time) Temperature (°C) A A --B M+A -Eutectoid temperature P B T 50% 1400 1200 1000 800 Temperature (°F) 600 400 -200 10³ 104 105 Resulting microstructure (include the % of micro-constituents)