WAEC SSCE Metalwork
Study notes for - Hardening - Tempering - Normalizing 4.3 Materials and Equipment for heat treatment of metals. - Materials used as cooling media for heat treatment of metals:coal, brine, water, air, oil and ash. - Equipment: furnaces, pyrometer, oven quenching tanks, blacksmith forge, oxy- acetylene flame. 4.4 Tempering colours and temperature ranges. 4.5 Safety precautions. — part of the WAEC SSCE Metalwork syllabus. 1 learning objectives with explanations and exam tips.
When you heat steel after hardening, it changes colour as the temperature increases. These colours tell you exactly how hot the metal is without needing a thermometer. The colour chart shows the progression: pale straw yellow appears around 220°C, dark straw at 230°C, brown at 250°C, purple at 280°C, and blue at 300°C. Each colour represents a specific temperature range and hardness level.
Think of a blacksmith in Oshogbo making cutlasses. After hardening the blade in water, he heats it gently until it turns purple, knowing this colour means the steel has reached the right temperature for a tough, flexible blade that won't shatter. Different tools need different colours—springs require blue, while cutting edges need straw yellow.
Understanding these colours helps you achieve the exact properties you need for your metal.