Chapter 8, Problem 8.69P

Interpretation Introduction

(a)

Interpretation:

The recovery, recrystallization and grain growth temperature when a cold work material is annealed needs to be determined.

Concept Introduction:

Recovery takes place at the low annealing temperature. Recrystallization is a process of formation of new defect-free grains. Grain growth is the process of increasing the size of grains at high temperature.

Answer to Problem 8.69P

Recover temperature is ${550}^{0}C$

Recrystallization temperature is ${750}^{0}C$

Grain growth temperature is ${950}^{0}C$

Explanation of Solution

Given Information:

The following data shows the properties of cold worked material after annealing.

Annealing temperature ${(}^{0}C)$	Electrical conductivity $({\mathrm{ohm}}^{-1}.c{m}^{-1})$	Field strength $\begin{array}{l}3.04\times {10}^5\\ {700}^{0}c\end{array}$	Grain size $(mm)$
400	$3.04\times {10}^5$	86	0.10
500	3.05	85	0.10
600	3.36	84	0.10
700	3.45	83	0.098
800	3.46	52	0.030
900	3.46	47	0.031
1000	3.47	44	0.070
1100	3.47	42	0.120

From the above data, one can plot a graph of tensile strength, residual stress and grain size of cold worked metal at the given annealing temperature.

  

• Recovering takes place at low annealing temperature and when there is no change in grain size thus, from figure recovery temperature should be near ${550}^{0}C$ .
• At recrystallization temperature, tensile strength is low and nucleation and growth of grain takes place.
• From the figure, ${750}^{0}C$ is the temperature where grain growth and nucleation takes place and tensile strength is minimum.
• Grain growth takes place at a high annealing temperature from the figure, grain growth occurs at ${950}^{0}C$ the annealing temperature.

Interpretation Introduction

(b)

Interpretation:

The allowable temperature of stress-relief heat treatment needs to be determined.

Concept Introduction:

Heat treatment in which residual stress is relieved from a material is known as stress-relief heat treatment.

Answer to Problem 8.69P

Allowable temperature for stress-relief heat treatment is ${700}^{0}C$.

Explanation of Solution

During stress-relieving, heat treatment material is heated to a temperature to relieve internal residual stresses.

Ductility and strength do not affect by this heat treatment.

From figure, suitable temperature for stress-relief heat treatment is ${700}^{0}C$.

Interpretation Introduction

(c)

Interpretation:

The appropriate temperature for hot working needs to be determined.

Concept Introduction:

Hot working is carried out above the recrystallization temperature of a material.

Answer to Problem 8.69P

Hot working takes place at ${900}^{0}C$.

Explanation of Solution

• Hot working is a process carried out above recrystallization temperature of a given material
• Hot working improves strength.
• Hence a suitable temperature for hot working is ${900}^{0}C$ .

Interpretation Introduction

(d)

Interpretation:

The melting temperature of the metal needs to be determined.

Concept Introduction:

Melting temperature is a temperature at which phase change from solid to liquid takes place.

Answer to Problem 8.69P

Melting temperature of the alloy is ${1875}^{0}c$.

Explanation of Solution

The relation between melting temperature and recrystallization temperature is as follows.

$T_r=0.4T_m$

Here,

$\begin{array}{l}{T}_r={\text{Recrystalization temperature=750}}^{\text{0}}\text{C}\hfill \\ T_m=\text{Melting temperature}\hfill \end{array}$

$\begin{array}{l}0.4T_m={750}^{0}C\\ T_m=\frac{750}{0.4}\\ T_m={1875}^{0}C\end{array}$