Measuring high-temperature hardness to save lives

With an ever-increasing number of steel constructions in residential and industrial buildings, fire safety remains a work of continuous improvement. The main parameter used is the ‘fire resistance period’ – which is the time in which all occupants must leave to avoid the risk of the building collapsing.

Standard steel constructions lose their strength around 600°C. With insulation and concrete protecting the steel beams, this temperature is reached after about 40 minutes of fire. However, this timeframe can be tight for emergency workers to clear out a building, certainly with response time taken into account. If the steel would keep its strength up to 700°C (and higher), the fire resistance period would be extended to at least 1 hour, providing extra time for everyone to get out safely.

Finding a screening method

The standard method for assessing fire resistance is to carry out a series of tensile tests at elevated temperature (ISO 6892-2:2018). Above a certain temperature, the steel will have lost 40% of its tensile strength, compared to its initial strength at room temperature. Comparing this temperature with the heating curve of a standard fire provides a value for the fire resistance period. However, this test method is highly time-consuming and requires large volumes of machined test samples for each grade – so it’s not really suited for screening 100+ novel grades.

That’s why OCAS has turned to high-temperature hardness measurement as an alternative to screen the loss of strength as a function of the temperature. The softening of a steel is well correlated with its loss of strength – and our automated test device can measure hardness up to 1000°C. The major advantage lies in the fact that only one sample of a few square centimetres is sufficient to plot the hardness evolution across the full temperature range. The most promising materials are then selected for further testing in the standard manner.

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“Our unique and flexible test device can perform several mechanical tests up to 1000°C. Hardness testing is just one of the many high temperature properties we can explore.”

Michiel Corryn, Expert Tribology Testing, OCAS