For sample of 4340 steel, you with to form 100% bainite in the minimmm amount of
ID: 2086942 • Letter: F
Question
For sample of 4340 steel, you with to form 100% bainite in the minimmm amount of time The sample i beld at 800c for I hour and dhen rapidly cooled to a tempersture T. What is T, and bow long will i take to complete the bainite transformation? (See Fig, below). 800 1400 Eutectoid temperature 700 A+F 1200 t P 600 1000 500 800 400 A B 50% I 600 300Mstart) M +A M(90%) 200 100 200 t0 10 oo 10 1O Time (s) Adapted trom H. Boyer (Editor). Attas of isothermal Transformation and Cooling Transformation Diagrams. American Society tor Metals, 1977. p. 181 sothermal transformation diagram for an alloy steel (type 4340): A, austenite, B, bainite; P, pearlite, M martensite: F, arosutectoid ferrite. D (Ctri)-Explanation / Answer
As per the isothermal transformation diagram given, Bainite forms between 300 to 500 degree Celsius. The green coloured curve represent 100% completion or formation to Bainite. X axis is the time required for transformation. So rapidly bring down the homogezed austenite at 800 degree Celsius to 325 degree Celsius and hold for 1500 s for completely transform into Bainite.