Question Set 90

1.For which parts the Wahl factor and Lewis form factor used ?

Ans: For springs and gears respectively.

2.How oxygen can be removed from steel during melting? What are fully killed steels ?

Ans: Oxygen can be removed by adding elements such as manganese, silicon or aluminium which, because of their high affinity for oxygen, react with it to form non-metallic oxides which rise into the slag. Steels which have had most of their dissolved oxygen removed are called “fully killed steels”.

3.Hydrogen cannot be removed easily from molten steel. What harm hydrogen has on property of steel ?

Ans: Excessive hydrogen results in the formation of small fissures often described as hairline cracks or flakes in the steel. Large forgings in alloy steel are particularly sensitive to this phenomenon.

4.What is allotrope ? In what forms of cubic pattern, iron exists ?

Ans: Some elements exist in more than one crystalline form. Each form is known as “allotrope”. Iron exists in two forms of cubic pattern, namely body centered cubic (bcc) and face-centered cubic (fee).

5.What is the difference between alpha iron, delta iron and gamma iron ?

Ans: The bcc form of iron exists between room temperature and 910°C, and between 1400°C and the melting point at 1539°C. The lower temperature form is known as “alpha”-iron and the higher temperature form as “delta”-iron. The face-centered cubic form existing between 910°C and 1400°C is referred to as “gamma-iron”.

Metals, in general are of low strength and do not possess required physio-chemical and technological properties for a definite purpose. Alloys are therefore more than metals alone.

6.Discuss the arrangement of atoms and structures of alloys.

Ans: Alloys are produced by melting or sintering two ore more metals, or metals and a non-metal, together. Alloys possess typical properties inherent in the metallic state. The chemical elements that make up an alloy are called its components. An alloy can consist of two or more components. The phase and structures of alloys describe the constitution, transformations and properties of metals and alloys. A combination of phases in a

state of equilibrium is called a system. A phase is a homogeneous portion of a system having the same composition and the same state of aggregation throughout its volume, and separated from the other portions of the system by interfaces. For instance, a homogeneous pure metal or alloy is a single-phase system. A state in which a liquid alloy (or metal) coexists with its crystals is a two-phase system. Structure refers to the shape,

size or the mutual arrangement of the corresponding phases in metals or alloys. The structural components of an alloy are its individual portions, each having a single structure with its characteristic features.

7.What is the difference between isotropic material and homogeneous material ?

Ans: In homogeneous material the composition is same throughout and in isotropic material the elastic constants are same in all directions.

8.Explain the difference between the points of inflexion and contraflexure.

Ans: At points of inflexion in a loaded beam the bending moment is zero and at points of contraflexure in loaded beam the bending moment changes sign from increasing to decreasing.

9.What is the difference between proof resilience and modulus of resilience ?

Ans: Proof resilience is the maximum strain energy that can be stored in a material without permanent deformation. Modulus of resilience is the maximum strain energy stored in a material per unit volume.

10.What is the difference between column and strut ?

Ans: Both column and strut carry compressive load. Column is always vertical but strut as member of structure could carry axial compressive load in any direction.