Hardening

Process

• The piece is heated to a cherry red colour and then cooled rapidly in water oils and brine.
• At the cherry red colour the steel will have undergone structural changes (FCC to BCC, martensite) and the rapid cooling does not allow it to revert to its original condition.

Result

• Very hard and Brittle.

Tempering

Process

• It is done by heating the article to a suitable temperature (500°C) below the reddening point of steel and then cooling it in oil or water.
• The higher the temperature the greater the reduction in hardness and brittleness.
• The temperature is gauged by... (More)

MIG welding

• Semi automatic process.
• A consumable bare wire electrode fed continuously into the weld pool through torch by spool.
• An inert gas, e.g. argon, has a fluxing action and creates a protective shield around the weld pool.
• The feed and flow rate are set by the operator.
• Does not produce slag.
• Used on sheet metals.

TIG welding

• Utilises a non-consumable tungsten electrode
• An electric arc is formed between a non-consumable electrode and the metal being welded.
• An inert gas such as argon creates a protective gas shield.
• A filler metal is added manually.
• No slag is produced.

MIG vs.... (More)

Submerged Arc Welding

• Uses bare wire electrode.
• Fed automatically from spool.
• Generates electric arc to heat metal/
• Flux in powder form.
• Fed using a hopper.
• Electric arc melts joint, flux and electrode.
• Excess flux is collected and re-used.
• Fully automated process.
• Used on Low carbon steels.
• E.g. Ship building and bridge construction.

Resistance Spot welding

• Components to be joined are placed between two non consumable electrodes and pressed together.
• The current is passed through the electrodes which generates the required heat.
• A nugget weld (circular mark) is formed.
• It is used on sheet metals.
• The process is energy efficient and... (More)