a.) What is the cooling rate from 800°C to 500°C for a steel part with 20 % bain

Question

a.) What is the cooling rate from 800°C to 500°C for a steel part with 20 % bainite?

b.) What is the room temperature hardness of this steel part?

c.) Which microstructure do you expect (in percentage) in a steel part with 41 HRC?

d.) How fast do you need to cool a steel part below Ms in order to achieve a 100 % martensitic microstructure?

%Ni |%Cu| %V | Method of MC Quoid-Ehn meltin b.S.-M 4 1 0.43 0.41 0.820.0410.015 1.22 0.04 0.14 0.11 Austenitizing temp. 880°C Grain size (ASTM) 10-11 800 700 600 25% Ferrite AC3 (0.25° min) 25 % Pearlite AC1 15 20 10 76 80 85 D 500 400 300 200 100 - Hardness HRC 5 10 20 30403030 % Bainite 50 00 Martensite 90 58 0 10 10 10 60 102 10 10 1 2 4 8 15 30 60 min 1 2 468 1624 1 2 34 6 10 Days

Explanation / Answer

a) At 500 degree Celsius, bainite forms after 51 s. The 100% transformation to bainite is occures in 3 min. So total time required for 20% transformation to bainite is 51+(180-51)×0.2=77s.

b) Haednes of steel lie between 170-210 HRB. The hardness of quenched>quenched&tempered>normalized>annealed

c) Tempered martensite. Hence a microstructure with ferrite and cementite is going to be observed.

d) We need to cool rapidly austenite to room temperature for 100% formation of martensite. Hence cooling rate is (880-25)/100)= 8.555 o C/s. Please note that 100s is the time required to bypass formation if Bainite at room temperature.

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