(a) The camshaft shown opposite is to be induction hardened as part of a heat treatment procedure - Leaving Cert Engineering - Question 3 - 2016

Induction hardening presents several advantages:

1. Increased Hardness: This process significantly boosts the surface hardness of the camshaft, making it more resistant to wear and fatigue, which is crucial for automotive components.

2. Improved Mechanical Properties: The induced martensitic layer enhances tensile strength and decreases deformation under stress, thereby enhancing overall performance.

3. Localized Treatment: Induction hardening allows for targeted heating and hardening, preserving the dimensional integrity of the camshaft and preventing excessive warp or distortion.

4. Cost-Effectiveness: Compared to other heat treatment methods, induction hardening is often more economical due to its efficiency and speed.

In the iron-carbon equilibrium diagram:

• Region 1: Austenite and Ferrite (gamma + alpha iron)
• Region 2: Austenite (gamma iron)
• Region 3: Austenite and Cementite (gamma + Fe₃C)
• Region 4: Ferrite and Pearlite (alpha iron + lamellar structure)
• Region 5: Pearlite and Cementite (lamellar structure + Fe₃C)

To anneal 0.6% carbon steel, the following process is typically used:

1. Heating: The steel is heated to a temperature that is approximately 25°-50°F above the Upper Critical Temperature (UCT) for hypoeutectoid steels, ensuring uniform temperature throughout the component.

2. Soaking: The steel is maintained at this temperature for a set duration, allowing for a transformation of the microstructure without introducing excessive grain growth.

3. Controlled Cooling: Subsequently, the material is allowed to cool down slowly in a furnace. This gradual cooling enables new grains to form, resulting in a refined microstructure.

This process is essential for improving ductility and eliminating residual stresses.

An annealing process provides several benefits:

1. Improved Ductility: Annealing reduces the hardness and increases the ductility of the steel, making it easier to work with and shape for subsequent manufacturing processes.

2. Refined Grain Structure: The process helps refine the grain size, which enhances the overall mechanical properties of the steel, including strength and toughness, while also removing internal stresses that may have developed during prior processing.

A thermocouple pyrometer operates based on the principle of thermoelectricity. It consists of two dissimilar metal wires joined at one end (the hot junction), while the other ends are connected to a galvanometer (cold junction). The dataset below outlines the working principle:

1. Heat Detection: When the hot junction is exposed to high temperatures, a voltage is generated due to the difference in temperature between the junctions.

2. Voltage Measurement: This voltage is proportional to the temperature difference, and the galvanometer measures this current, displaying it in degrees of temperature.

A diagram would depict the hot junction, cold junction, dissimilar metals, and the galvanometer to illustrate this operation clearly.

One alternative method for measuring furnace temperature is the use of optical pyrometers. The operation can be described as follows:

1. Working Principle: An optical pyrometer measures the intensity of visible light emitted by the hot surface. As the temperature of the object increases, its brightness also increases.

2. Application: The intensity of light from a light source, typically a lamp, is compared to that of the hot object. The variable resistor adjusts the intensity of the light to match the brightness observed from the furnace.

3. Temperature Reading: When the filament seems to 'disappear' against the background, a temperature reading can be taken. Optical pyrometers are effective for measuring high temperatures without direct contact.