Fig. 3 shows a piece of mild steel being heated in a furnace as part of a heat treatment process. It works in rain and sun. The shape is good. It is cheap t...
Question 1 Report
Fig. 3 shows a piece of mild steel being heated in a furnace as part of a heat treatment process.
It works in rain and sun. The shape is good.
It is cheap to make in large numbers. It sits on a flat base. The top is flat and smooth. The sides are straight and even. It keeps its shape well over time. It is made from mild steel. The edges are smooth and safe to touch.
A key advantage of using brass here is its natural impact resistance. The dimensions of the product have been determined by the needs of the intended user.
Describe the process of annealing mild steel. [3]
Answer Details
The process of annealing mild steel involves three stages:
- Heating: The mild steel workpiece is heated in a furnace to a cherry red colour, approximately 720 degrees Celsius (above its upper critical temperature). [1] At this temperature, the internal crystal structure of the steel transforms, and the internal stresses built up from previous working (bending, hammering, rolling) begin to relieve.
- Soaking: The steel is held at this temperature long enough for the heat to penetrate evenly throughout the full cross-section of the workpiece, ensuring a uniform transformation of the grain structure.
- Slow cooling: The steel is allowed to cool very slowly. [1] This can be achieved by turning off the furnace and leaving the workpiece inside to cool with the furnace (furnace cooling), or by burying the hot workpiece in dry sand, vermiculite, or ite ash, which acts as an insulator to slow the cooling rate. [1]
The result of annealing is that the steel becomes softer, more ductile, and easier to work. The slow cooling allows the grain structure to form large, even crystals (ferrite and pearlite), relieving internal stresses and making the metal less likely to crack during further shaping operations such as bending, pressing, or machining.
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