Q8: Ductile Brittle Transition Temperature (DBTT)


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Plate steels

8 of 9

What is the ductile brittle transition temperature (DBTT) of the HSLA steel?

DBTT = -19 + 44 (%Si) + 700 (%Nf^1/2) + 2.2 (%pearlite) - 11.5(d^-1/2)

-55 °C - incorrect, you probably have forgotten to recalculate how much pearlite is in the HSLA steel (you will have to assume equilibrium conditions and that all the carbon is present as pearlite). Try again.

-81 °C - Correct.

-20 °C - Incorrect. Try again.

52 °C - incorrect, you have probably forgotten to use grain size in mm instead of µm. Try again.

Try again.

Click on your answer to check and make a note of the answer on your notepad.

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NOTEPAD

The 3 most important properties for plate steel for structural applications:
Strength, Toughness and Weldability

Typical yield strength level for a family saloon car panel (roof or wing) is: 350 - 500 MPa (more accurately 400 MPa)

Maximum pearlite content in the steel:23%

Yield strength and tensile strength levels in the candidate steel: 238 MPa and 502 MPa respectively.

Strengthening mechanisms to increase the yield strength of the candidate steel in order of preference: Grain size refinement, precipitation strengthening, solid solution strengthening, dislocation strengthening, microstructural strengthening

Grain size require to achieve a 400 MPa yield strength in the candidate steel: 4.4 µm

Carbon equivalent of the steel and processing route to obtain a fine ferrite grain size:C^D_equiv of 0.21 and (TMCR)

DBTT of the HSLA steel:-81 °C (note)