This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Normalizing & Tempering”.
1. In normalizing of hypoeutectoid steel, the component is heated to a temperature above _____
Explanation: Normalizing process consists of three steps. The first step involves heating the steel component above the 910⁰C temperature for hypoeutectoid steels and above Acm (upper critical temperature for cementite) temperature for hypereutectoid steels by 30⁰C to 50⁰C.
2. In normalizing, components are cooled _____
a) using water
b) using oil
c) in still air
d) in furnace
Explanation: The final step in normalizing involves cooling the hot steel component to room temperature in still air. Due to air cooling, normalized components show slightly different structure and properties than annealed components.
3. Normalizing is used for _____
a) alloy steels
b) high carbon steels
c) tool steels
d) aluminium alloys
Explanation: Normalizing is used for high-carbon (hypereutectoid) steels to eliminate the cementite network that may develop upon slow cooling in the temperature range from point Acm (upper critical temperature for cementite) to point A1 (lower critical point temperature).
4. Normalizing is not used for relieve internal stresses by which of the following processes?
Explanation: Normalizing is also used to relieve internal stresses induced by heat treating, welding, casting, forging, forming, or machining. Normalizing also improves the ductility without reducing the hardness and strength.
5. Martensite obtained after hardening is extremely _______
Explanation: The hardened steel is not readily suitable for engineering applications. It possesses few drawbacks, which are as follows:
• martensite obtained after hardening is extremely brittle and will result in failure of engineering components by cracking
• Formation of martensite from austenite by quenching produces high internal stresses in the hardened steel.
6. Structures obtained after hardening consists of _______
Explanation: Structures obtained after hardening consists of martensite and retained austenite. Both these phases are metastable and will change to stable phases with time which subsequently results in change in dimensions and properties of the steel in service.
7. Tempering is achieved by heating hardened steel to a temperature in the range of ______
a) 100⁰C – 150⁰C
b) 100⁰C – 680⁰C
c) 200⁰C – 375⁰C
d) 300⁰C – 835⁰C
Explanation: Tempering is achieved by heating hardened steel to a temperature below lower critical temperature, which is in the range of 100⁰C – 680⁰C, hold the component at this temperature for a soaking period of 1 to 2 hours (can be increases up to 4 hours for large sections and alloy steels), and subsequently cooling back to room temperature.
8. Highly alloyed tool steels are tempered in the range of ______
a) 100⁰C – 190⁰C
b) 180⁰C – 300⁰C
c) 450⁰C – 620⁰C
d) 500⁰C – 600⁰C
Explanation: The tempering temperature is decided based on the type of steel. Highly alloyed tool steels are tempered in the range of 500⁰C – 600⁰C. Low alloy steels are tempered above 400⁰C to get a good combination of strength and ductility. Spring steels are tempered between 300⁰C – 400⁰C.
9. Increase in the tempering temperature ______
a) increases hardness
b) increases ductility
c) decreases conductivity
d) increases toughness
Explanation: It is observed that the increase in the tempering temperature decreases the hardness and internal stresses while increases the toughness. But after a particular temperature there is no significant change in hardness and toughness.
10. Normalizing takes less time than that for annealing.
Explanation: The properties of normalized components are not much different from those of annealed components. However, normalizing takes less time and is more convenient and economical than annealing and hence is a more common heat treatment in industries.
11. Perlite formed during normalising is coarse in nature.
Explanation: Pearlite formed during normalizing is fine and usually appears unresolved with optical microscope. Whereas, pearlite during annealing is coarse and usually gets resolved by the optical microscope.
12. In normalizing, grain size distribution ______
a) is uniform
b) is less uniform
c) varies directly with temperature
d) varies with time
Explanation: If we compare annealing and normalizing, following point can be made:
• Grain size distribution is more uniform
• Internal stresses are least
• Less hardness, tensile strength and toughness
• Grain size distribution is slightly less uniform
• Internal stresses are slightly more
• Slightly more hardness, tensile strength and toughness.
Sanfoundry Global Education & Learning Series – Manufacturing Processes.
To practice all areas of Manufacturing Processes, here is complete set of 1000+ Multiple Choice Questions and Answers.