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Plate steels

  5 of 9
 
Question As you can see the yield strength of the candidate steel is less than the requirement for the application.  Rank the following strengthening mechanisms in order according to which you think can be used to provide the additional strengthening needed to meet the specifications. 1.  Grain size refinement; 2.  Solid solution strengthening; 3.  Dislocation strengthening; 4.  Precipitation strengthening;   5.  Microstructural strengthening through increasing pearlite content.

Red cross 1 2 3 4 5 - incorrect  -  whilst grain size refinement is indeed the best mechanism for improving the yield strength of this steel we cannot achieve all the additional strength by this method and your second and third choices are not  as effective as strengthening mechanisms as other possible choices.  Try again.

Red cross 5 2 1 4 3 - incorrect  -  dislocation networks, produced by work hardening, are not a strengthening mechanism seen for structural steels which are hot rolled, steel plate rolled to lower temperatures will have a degree of dislocation strengthening (10-20 MPa) however this is a relatively small contribution.  Try again.

Green tick 1 4 2 3 5 - Correct.

Red cross 4 2 1 5 3 - incorrect  -  precipitate strengthening is an extremely useful strengthening mechanism however there is another mechanism that, for this steel, we would rank more highly.  Try again.

Red cross 2 3 5 4 1- incorrect  -  solid solution strengthening would increase both the yield strength and tensile strength  almost equally and we are more concerned with increasing yield strength.  There are more effective mechanisms that can be used although solid solution strengthening will have a role to play.  Try again.

Red cross5 1 2 4 3 incorrect  -  the microstructure is ferrite +  pearlite and any increase in the amount of pearlite will increase the yield strength of the steel but not significantly compared to other mechanisms.  Also this would necessitate an increase of carbon content which is undesirable as this reduces the weldability of the steel by increasing its carbon equivalent.  Try again. 

    

Click on your answer to check and make a note of the answer on your notepad. If you have not already reviewed the section strength do so clicking here. 

 

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:1 4 2 3 5
 

 
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