TheFe-CphasediagramisshowninFigureQ4.Fora0.25%wC steelatatemperaturejustbelowtheeutectoidtemperature(727°C),determine:(i)Thecompositionsofferriteandcementite.(2marks)(ii)Themassfractionofpearlite.(2marks)(iii)Themassfractionofeutectoidferrite.(2marks)TPC)160012004148°C~osi24000=8800f9oy727°C|oelnla+Fe,C2—)—400322O762344305.667:Cwt%CFigure Q4 Fe-C phasediagramGive twolimitationsof theFe-Cphasediagram.(4marks)Brieflydescribethedifferencesbetweenspheroidite andtemperedmartensiteinrespectofmicrostructureandmechanicalproperties.|(4marks)SketchtheheattreatmentofaQuenchingand Partitioning(Q&P)steelwithacarboncontentof C;.Pleaseindicatethemicrostructureandtherangeofcarboncontentineachphaseateachstep.(4marks)NamethesteelwhichistypicallyusedforB pillarand describeitsmicrostructure.(2marks)P.5 of 7
Question
TheFe-CphasediagramisshowninFigureQ4.Fora0.25%wC steelatatemperaturejustbelowtheeutectoidtemperature(727°C),determine:(i)Thecompositionsofferriteandcementite.(2marks)(ii)Themassfractionofpearlite.(2marks)(iii)Themassfractionofeutectoidferrite.(2marks)TPC)160012004148°C~osi24000=8800f9oy727°C|oelnla+Fe,C2—)—400322O762344305.667:Cwt%CFigure Q4 Fe-C phasediagramGive twolimitationsof theFe-Cphasediagram.(4marks)Brieflydescribethedifferencesbetweenspheroidite andtemperedmartensiteinrespectofmicrostructureandmechanicalproperties.|(4marks)SketchtheheattreatmentofaQuenchingand Partitioning(Q&P)steelwithacarboncontentof C;.Pleaseindicatethemicrostructureandtherangeofcarboncontentineachphaseateachstep.(4marks)NamethesteelwhichistypicallyusedforB pillarand describeitsmicrostructure.(2marks)P.5 of 7
Solution
The Fe-C phase diagram is shown in Figure Q4. For a 0.25% wC steel at a temperature just below the eutectoid temperature (727°C), determine:
(i) The compositions of ferrite and cementite. (2 marks) (ii) The mass fraction of pearlite. (2 marks) (iii) The mass fraction of eutectoid ferrite. (2 marks)
TPC) 1600 1200 4148°C ~ osi 24000 = 8800 f9oy 727°C | oelnla + Fe, C2 —) — 400 322O 7623 4430 5.667: Cwt% C
Figure Q4 Fe-C phase diagram
Give two limitations of the Fe-C phase diagram. (4 marks)
Briefly describe the differences between spheroidite and tempered martensite in respect of microstructure and mechanical properties. (4 marks)
Sketch the heat treatment of a Quenching and Partitioning (Q&P) steel with a carbon content of C;. Please indicate the microstructure and the range of carbon content in each phase at each step. (4 marks)
Name the steel which is typically used for B pillar and describe its microstructure. (2 marks)
P.5 of 7
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