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Engineering steels for gears

Q3: Measure of hardness

   3 of 5
 
QuestionSelect the correct statements from the following list.

 
Red cross a) correct - incorrect, TTT diagrams refer to samples that have been isothermally heat treated, i.e. held at a constant temperature. This is not very representative of many engineering processes. Try again.

Red cross a) and c) correct - incorrect, a) refers to TTT diagrams which relate to samples that have been isothermally heat treated, i.e. held at a constant temperature. This is not very representative of many engineering processes. c) refers to the Jominy Quench Test hardness curve for a 0.31% C and 0.8% Mn steel which shows an increase in hardness over 10mm not 30mm. Try again.

Red cross c) and e) correct - incorrect, whilst e) is correct c) refers to the Jominy Quench Test hardness curve for a 0.31% C and 0.8% Mn steel which shows an increase in hardness over 10mm not 30mm. Try again.

Red cross d) correct - incorrect, it is also possible to increase the hardenability of a steel through increasing the austenite grain size prior to cooling, for example by using a higher austenitising temperature. Try again.

Green tick b) and e) correct - Correct.

Red cross 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 on hardenability do so now by clicking here 

NOTEPAD

Three most important properties for an engineering steel for a gear in an automotive gear box: Surface Hardness, Wear Resistance and Fatigue Resistance

Technique used to determine the hardenability of a steel: Jominy End Quench

Correct statement (s) regarding the measure of hardness and hardenability of a steel:
Increasing the Mn content increases the hardenability of the steel but not the maximum hardness achieved. 
+ Controlled additions of alloying elements such as Cr, Ni, B and Mo can be used to increase the hardenability of a steel such that martensite can be obtained on air cooling of a 10mm bar.

a) TTT diagrams are more useful in defining operating process parameters to obtain a desired microstructure that CCT diagrams.
b) Increasing the Mn content increases the hardenability of the steel but not the maximum hardness achieved.
c) For a 0.31 wt% C, 0.8 wt% Mn steel the depth to which a Jominy Quench Test sample experiences a degree of hardening is 30mm.
d) Alloying additions are the only way in which the hardenability of a steel can be increased.
e) Controlled additions of alloying elements such as Cr, Ni, B and Mo can be used to increase the hardenability of a steel such that martensite can be obtained on air cooling of a 10mm bar.
 

 
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