Metallic Tensile Test Specimens

Manufacturers are continually searching for better materials and processes to enhance the product, improve health & safety aspects, and reduce costs. As an example, you will learn that the microstructure and mechanical properties of metals can be radically altered by a heat treatment process, opening up more areas where they could be used.

A series of tensile tests allows comparison of a batch of material, with or without heat treatment and/or between materials.

However, to ensure valid and consistent test results, certain criteria should be met;

• The test specimen shape and dimensions should be in accordance with a recognised standard. (BS EN ISO 6892, ASTM E8)
• Use a calibrated tensile test machine (tensometer) of sufficient load and displacement capacity with means to record the X-Y data.
• Choose suitable specimen holders giving good alignment throughout the test.
• Maintain a constant speed of test throughout.

Only then can tensile tests be replicated and their results stored and compared with confidence.

Normalising, Annealing, Quenching and Tempering are good examples of methods used to heat-treat carbon steels which are in the as drawn condition.

Normalising

For a carbon steel, heat to a suitable temperature, typically between 840 and 900 degrees Celsius, hold for 1 hour then air-cool.

Annealing

For a carbon steel, heat to a suitable temperature slightly lower than for normalising, hold for 1 hour, then cool in the switched-off furnace.

Quenching and Tempering

For a carbon steel 0.4% and above, heat to normalising temperature then cool rapidly by quenching in water, brine or oil. To temper, re-heat the quenched steel to below 723 degrees Celsius’ and then cool.