Question

1. Does recrystallization eliminate mechanical fibering in a workpiece? Explain.

2. Explain advantages of the cold, warm and hot working of metals, respectively.

Answer 1

answer-

1). Mechanical fibering involves the alignment of impurities, inclusions, and voids in the workpiece during deformation. Recrystallization generally modifies the grain structure, but will not eliminate mechanical fibering.

(a) Two pieces of the same metal can have different recrystallization temperatures if the pieces have been cold worked to different amounts. The piece that was cold worked to a greater extent will have more stored energy to drive the recrystallization process, and hence its recrystallization temperature will be lower.

(b) Recrystallization may occur in some regions before others if i. the workpiece was unevenly worked, as is generally the case in deformation processing of materials, since varying amounts of cold work have different recrystallization temperatures, or ii. the part has varying thicknesses; the thinner sections will heat up to the recrystallization temperature faster.

2).

The processes working above recrystallisation temperature,are termed as Hot Working processes.

In Hot working the temperature at which the working is completed is important since any extra heat left after working will aid in grain growth, thus giving poor mechanism properties.

ADVANTAGES:

1. The porosity of the metal is almost eliminated.

2. The partical structure of the metal is refined.

3. mechanical properties such as ductility, toughness, percentage elongation , percentage reduction are better due to refinement of grains.

4. Since the shear stress gwts reduced at higher temperatures ,the hot working required much less force to acheive the necessary deformation.

5. At high temperatures ,the material would have higher amount of ductility and therefore there is no limit on amount of hot working that can be done on a material. Even brittle materials can be hot worked.