23. What is the cause of for the part in this graph? h) excessive compression st

Question

23. What is the cause of for the part in this graph? h) excessive compression stress (C) excessive heading stress D) futigue 24 A hoo-phase misture of ferise and cementite layers is called (B) Steel D) Ledeburite (C) Pearlite 25. One of the given phases/micro-constituents is best described by the following Low yield strength very ductile, low carbon solubiliry (A) Cementite C) Austenite (B) Pearlite (D) Ferrite s is best described by the following (B) Pearlite (D) Ferrite 26. One of the given phases/mic FCC anit cel (C) Austenite 27 Carbon content of cast iron ranges roughly from (B) 0.6 to 1.0 wt.s (D) 4to6wtSk (A ) 0.022 10 0 77 wt.% (C) 2 to 4.5 ut.% 28. Which of the following aluminium alloys (identified by Aluminium Association Number) the most suitable for highly stresses applications (A) 1100 (B) 2024 (C) 6064 (D) 7075 29An AlSI number 1080 is designated for steel with carbon composition of (A) 0.1% (B)0.8% (C) 1% (D) 10% 30. The type of heat treatment process in which the metal is rapidly cooled is called (A) Annealing (B) Carburizing (C) Quenching (D) Normalizing 31 Heat treatment of steels that yields maximum machinability, minimum hardness, and maximum ductility (A) Tempering (B) Annealing (D) Austenitizing 32. Fatigue limit is stress: (A) under no cycling (B) below which failure will not occur (C) cause failure for some specified number of cycles (D) cause failure for minimum number of cycles

Explanation / Answer

Solution:-

25) Overall, the mechanical properties can be influenced by the various constituents of the pearliticmicrostructure, including the nodule and colony size, as well as the thickness and spacing of the cementite lamellae.

ans:- (B)

26) As pointed out on the previous page, there are 14 different types of crystal unit cell structures or lattices are found in nature. However most metalsand many other solids have unit cell structuresdescribed as body center cubic (bcc), face centered cubic (fcc) or Hexagonal Close Packed (hcp).

Austenite- It is a phase of FCC structure which exists above 723°C.

ans :- (C)

27) 2 to 4.5%,because cast iron is alloy of iron and carbon and in which carbon percentage varies between 2 to 4.5%

ans:- (C)

28) 7075 aluminium alloy is an aluminium alloy, with zinc as the primary alloying element. It is strong, with a strength comparable to many steels, and has good fatigue strength and average machinability. It has lower resistance to corrosion than many other aluminium alloys, but has significantly better corrosion resistance than the 2000 alloys. Its relatively high cost limits its use.

ans :- (D)

29) ans (B)

30) In materials science, quenching is the rapid cooling of a workpiece in water, oil or air to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phase transformations, from occurring. It does this by reducing the window of time during which these undesired reactions are both thermodynamically favorable, and kinetically accessible; for instance, quenching can reduce the crystal grain size of both metallic and plastic materials, increasing their hardness.

ans :- (c)

31) Annealing, in metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature, and then cooling.

In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness. As the material cools it recrystallizes. For many alloys, including carbon steel, the crystal grain size and phase composition, which ultimately determine the material properties are dependent on the heating and cooling rate. Thus a skilled metalworker can tune the material from hard and brittle to soft and ductile by controlling the anneal process.

In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming.

ans :- (B)

32)  Fatigue limit, endurance limit, and fatigue strengthare all expressions used to describe a property of materials: the amplitude (or range) of cyclic stressthat can be applied to the material without causingfatigue failure.

ans :- (C)

Carbon, C 0.75 - 0.88

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