Chapter 12, Problem 12.63P

Interpretation Introduction

(a)

Interpretation:

The temperature at which austenite begins to transform needs to be determined.

Concept Introduction:

Austenite is defined as a gamma-phase iron, it is a metallic, non-magnetic iron allotrope or a solid solution of iron, containing an alloying element. Austenite which is known to exist above the eutectoid temperature of 1000K of plain carbon steel. Other alloys of the steel contain different eutectoid temperatures. Austenite can remain stable at room temperature only in the presence of austenite stability elements, e.g. Ni in adequate quantity.

Answer to Problem 12.63P

The temperatutre at which austenite will transform in Fe- $1.15\%$ C alloy is $880°C$.

Explanation of Solution

  

From the diagram cited above, the temperature at which austenite will start transforming on cooling in the Fe $1.15\%$ C alloy is calculated as $880°C$.

Interpretation Introduction

(b)

Interpretation:

The primary microconstituents that are formed needs to be determined.

Concept Introduction:

The microconstituent of iron carbide includes austenite ( $\gamma$ ), ferrite, etc. austenite is a solid solution formed from ferrite and iron carbide in gamma iron. It forms when the percentage of carbon in steel is up to 1.8% at 1130 $°$ C. Austenite starts converting into pearlite and ferrite when it cools below 723 $°$ C.

Answer to Problem 12.63P

The primary micro constituents that is formed in the alloy is primary Fe₃C.

Explanation of Solution

  

From the diagram mentioned above the microconstituent which is formed in the Fe- $\text{1}\text{.15\%C}$ alloy is primary Fe₃C.

Interpretation Introduction

(c)

Interpretation:

The amount and composition of phase at $728°C$ needs to be determined.

Concept Introduction:

The plain iron-carbon alloys contain the amount of steel between 0.002% and 2.14 % by weight. At atmospheric pressure, the phases of iron plays a vital role because of the differences in carbon which forms different types of steel. High pressure phases of iron are significant as the prototype of the solid parts regarding planetary cores. The standard pressure phases are as follows:

1) Delta iron

2) Gamma iron/ austenite

3) Beta iron

4) Alpha iron

Answer to Problem 12.63P

The amount and composition of phases in Fe- $1.15\%C$ are $6.4\%$ and $93.6\%$.

Explanation of Solution

  

Draw a line at which passes through Fe3Cand ofFe3C and r.

  $\begin{array}{l}\text{\%Fe3C=(}\frac{\text{\%Fe-1}\text{.15\%C-r\%c}}{\text{\%Fe3C-r\%C}}\text{×100)}\\ \\ \text{=}\frac{\text{1}\text{.15-0}\text{.77}}{\text{6}\text{.67-0}\text{.77}}\text{×100}\\ \\ \text{\%Fe3C=6}\text{.4\%}\\ \\ \text{\%r=100-6}\text{.4}\end{array}$

Interpretation Introduction

(d)

Interpretation:

The amount and composition of phases at $\text{726°C}$ needs to be determined.

Concept Introduction:

The plain iron-carbon alloys contain the amount of steel between 0.002% and 2.14 % by weight. At atmospheric pressure, the phases of iron plays a vital role because of the differences in carbon which forms different types of steel. High pressure phases of iron are significant as the prototype of the solid parts regarding planetary cores. The standard pressure phases are as follows:

1) Delta iron

2) Gamma iron/ austenite

3) Beta iron

4) Alpha iron

Answer to Problem 12.63P

The amount and composition of phases at $\text{726°C}$ are $83\%$ and $17\%$.

Explanation of Solution

  

Based on the digram we have the formula as mentioned above,

  $\begin{array}{l}\text{\%α=(}\frac{\text{\%Fe3C-Fe-1}\text{.15\%C}}{\text{\%Fe3C-α\%C}}\text{×100)}\\ \\ \text{\%α=}\frac{\text{6}\text{.77-1}\text{.15}}{\text{6}\text{.77-0}\text{.0218}}\text{×100}\\ \\ \text{\%α=83\%}\\ \\ \text{\%Fe3C=100-83}\\ \\ \text{=17\%}\end{array}$

Interpretation Introduction

(e)

Interpretation:

The amount and composition of microconstituent at $\text{726°C}$ needs to be determined.

Concept Introduction:

The plain iron-carbon alloys contain the amount of steel between 0.002% and 2.14 % by weight. At atmospheric pressure, the phases of iron plays a vital role because of the differences in carbon which forms different types of steel. High pressure phases of iron are significant as the prototype of the solid parts regarding planetary cores. The standard pressure phases are as follows:

1) Delta iron

2) Gamma iron/ austenite

3) Beta iron

4) Alpha iron

Answer to Problem 12.63P

The amount and composition of microconstituent are $726°C$ and $0.77\%C$.

Explanation of Solution

  

Based on the diagram mentioned above the microconstituent whichare present in the alloy at $726°C$ are primary Fe₃C and pearlite.

The amount of primary Fe₃C and composition are as follows:

Primary Fe₃C= $6.67\%C$

% primary Fe₃C= $6.4\%$

The amount and composition of pearlite are:

Pearlite= $0.77\%C$

% pearlite= $93.6\%$