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Plate steels

  7 of 9
 
QuestionWhat is the carbon equivalent of this steel and what processing route would you use to achieve a grain size of about 7µm in a structural (HSLA) steel plate?  (TMCR - thermo-mechanically controlled rolling) ;

Red cross CDequiv of 0.36 and (TMCR) - - incorrect, you are right that TMCR processing will give you a fine grain size as the finish rolling passes usually occur in the non recrystallisation range resulting in a deformed austenite grain structure which transforms to a fine grained ferritic structure, however your carbon equivalent is incorrect - check you have used the right equation. Try again.

Red cross Cequiv of 0.36 and (TMCR) - incorrect, you are right that TMCR processing will give you a fine grain size as the finish rolling passes usually occur in the non recrystallisation range resulting in a deformed austenite grain structure which transforms to a fine grained ferritic structure, however your carbon equivalent is incorrect - we are using a modern low carbon microalloyed steel and therefore must use the other equation. Try again

Green tick CDequivof 0.21 and (TMCR) - Correct.

Red cross Cequivof 0.21 and (TMCR) - incorrect, you are right that TMCR processing will give you a fine grain size as the finish rolling passes usually occur in the non recrystallisation range resulting in a deformed austenite grain structure which transforms to a fine grained ferritic structure, however your carbon equivalent is incorrect - we are using a modern low carbon microalloyed steel and therefore must use other equation. Try again.

Red cross CDequivof 0.36 and hot rolling - incorrect, both your choice of processing route and your maths are wrong I'm afraid, try again.

Red cross Cequivof 0.36 and hot rolling - incorrect, both your choice of processing route and equation are wrong I'm afraid, try again.

Red cross CDequivof 0.21 and hot rolling - incorrect, your choice of processing route is wrong but you have got the right carbon equivalent. Try again.

Red cross Cequivof 0.21 and hot rolling incorrect, your choice of processing route is wrong and as we are using a modern low carbon microalloyed steel we must use the other equation. Try again.

    

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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:CDequiv of 0.21 and (TMCR)
For low alloy C-Mn steels with a ferrite + pearlite structure the appropriate equation is:

(alloying additions in wt%)

For modern low carbon steels then we need to use: 

(alloying additions in wt%)

 
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