This set of Tough Manufacturing Processes Questions and Answers focuses on “Annealing – 12”.
1. In thermal cycling stage of spheroidised annealing transforms _____ to ______
a) austenite to perlite
b) cementite to carbide
c) cementite from perlite to spheroidal
d) cementite from ferrite to spheroidal
Explanation: In this stage, the thermal cycling in the narrow temperature range around lower critical temperature transforms cementite lamellae from pearlite to spheroidal. During heating above lower critical temperature, cementite or carbides try to dissolve and during cooling they try to re-form. This repeated action spheroidises the carbide particles.
2. Spheroidised annealing is used for ______
a) medium carbon steel
b) hardened alloy steels
c) tool steel
d) stainless steel
Explanation: Spheroidised structures are softer than the fully annealed structures and have excellent machinability. This heat treatment is utilized to high carbon and air hardened alloy steels to soften them and to increase machinability and to reduce the decarburization while hardening of thin sections such as safety razor blades and needles.
3. In recrystallization annealing process, steel component is heated at the temperature in the range______
a) 300⁰C to 400⁰C
b) 455⁰C to 540⁰C
c) 590⁰C to 660⁰C
d) 625⁰C to 675⁰C
Explanation: Recrystallization annealing process consists of heating a steel component below lower critical temperature i.e. at temperature between 625⁰C and 675⁰C (recrystallization temperature range of steel), holding at this temperature and subsequent cooling.
4. Recrystallization annealing is applied before _____
a) hot working
b) cold working
c) stress relieving
d) full annealing
Explanation: This type of annealing is applied either before cold working or as an intermediate operation to remove strain hardening between multistep cold working operations. In certain case, recrystallization annealing may also be applied as final heat treatment.
5. Recrystallization annealing _____
a) improves ductility
b) improves hardness
c) decreases surface strain
d) decreases strength
Explanation: Recrystallization annealing relieves the internal stresses in the cold worked steels and weldments and improves the ductility and softness of the steel. Refinement in grain size is also possible by the control of the degree of cold work prior to annealing or by control of annealing temperature and time.
6. In stress relief annealing, steel is heated to a temperature between ______
a) 200⁰C to 250⁰C
b) 300⁰C to 325⁰C
c) 385⁰C to 440⁰C
d) 500⁰C to 550⁰C
Explanation: Stress relief annealing process consists of three steps. In the first step, the cold worked steel is heated to a temperature between 500⁰C to 550⁰C i.e., below recrystallization temperature. The second step involves holding the steel component at this temperature for1-2 hours. The final step is to cool the steel component to room temperature in air.
7. Stress relief annealing _____
a) decreases corrosion resistance
b) relieves stress at the loss of strength
c) improves corrosion resistance
d) improves yield strength
Explanation: The stress relief annealing partly relieves the internal stress in cold worked steels without loss of strength and hardness i.e. without a change in the microstructure. It reduces the risk of distortion while machining and increases corrosion resistance.
8. Stress relief annealing is applicable for _____
a) hypoeutectoid steel containing less than 0.4% carbon
b) hypoeutectoid steel containing less than 1% carbon
c) hypereutectoid steel containing less than 0.4% carbon
d) high speed tool steel
Explanation: Since only low carbon steels can be cold worked, the process is applicable to hypoeutectoid steels containing less than 0.4% carbon. This annealing process is also used on components to relieve internal stresses developed from rapid cooling and phase changes.
9. Spheroidal annealing produces globules of carbide in ferrite.
Explanation: Spheroidised annealing is one of the variants of the annealing process that produces typical microstructure consisting of the globules (spheroid) of cementite or carbides in the matrix of ferrite.
10. Holding the steel component at just below the lower critical temperature transforms the _____ to globular cementite particles.
Explanation: Holding the steel component at just below the lower critical temperature transforms the pearlite to globular cementite particles. But this process is very slow and requires more time for obtaining spheroidised structure.
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