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.
Click image to enlarge
“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.”