JNTU
JNTU B.Tech III HEAT TREATMENT Previous Question Paper (May/June - 2019 - R16)
Part A is compulsory. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
List out the quenching media and its requirements.
Answer
Common quenching media include water, brine (salt water), oils (mineral or vegetable), molten salts, and forced air or gases. The requirements for an ideal quenching medium are high initial cooling rate to bypass the nose of the TTT diagram, slower cooling rate at lower temperatures to minimize distortion and cracking, chemical stability, low cost, and non-toxicity.
What is the importance of heat treatment?
Answer
Heat treatment is essential to modify the mechanical and physical properties of metals and alloys. It is used to increase hardness and wear resistance, improve ductility and toughness, relieve internal stresses induced by prior processing (like casting or welding), refine grain structure, and improve machinability or formability for subsequent manufacturing stages.
What are residual stresses and how they minimised?
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Distinguish between bainite and martensite.
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List out the factors which effects the hardenability.
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Distinguish the terms hardness and hardenability.
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Differentiate between cryoforming and ausforming.
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What are the limitations of martempering?
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What factors effects the chemical hardening techniques?
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Distinguish between mechanical hardening techniques and chemical hardening techniques.
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Unit I
Draw typical heat treatment cycles of subcritical annealing and isothermal annealing. Also describe the process.
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Discuss the merits and demerits of the following hardening processes:
Direct quenching
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Auto-Tempering
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Interrupted quenching.
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Unit II
Explain the construction of TTT diagram according to the first principle. Why it is called S-curve?
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Describe the mechanism of formation of upper and lower bainite.
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Austenite to bainite transformation is referred to as intermediate transformation. Why?
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Distinguish between upper and lower bainite with respect to microstructural features and mechanical properties.
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Unit III
Explain how alloying elements affect the TTT curves, Fe-Fe3C phase diagram? Why the alloying elements are added to steel.
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Explain the characteristics of austenite conversion to pearlite.
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How hardenability of a steel can be measured and list out the factors which effects it?
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Unit IV
List out thermo-mechanical treatments and its advantages and limitations.
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Distinguish between Sub-zeroTreatment and Spheroidzing.
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What is the significance of Patenting.
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Distinguish between cryoforming and austempering.
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Unit V
If some portions of a surface of a steel articles are not to be carburized and remaining portions require a case, how do you do.
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Carburized articles are subject to subsequent hardening heat treatment. However nitride articles will not be heated subsequently, Explain why?
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Distinguish between carbonitriding and cyaniding.
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Discuss the technological aspects of nitriding heat treatment.
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Discuss briefly about flame hardening technique.
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Compare pack carburising and gas carburising.
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