Fasteners mechanical properties. What is the influence of elevated temperatures on mechanical properties of fasteners?
What is the effects?
The fasteners mechanical properties and its functional performance could be affected to the elevated temperatures.
Service temperatures:
- up to 150°C: no detrimental effects due to a change of mechanical properties of fasteners are know
- over 150°C – up to a maximum temperature of 300°C: the functional performance of fasteners should be ensured by careful examination.
What can we check with the encreasing temperatures?
May occur respectively:
- a progressive reduction of:
– lower yield strength
– stress at 0,2% non-proportional elongation
– stress at 0,0048d non-proportional elongation for finished fasteners
- a reduction of tensile strength can be experienced.
And a prolonged exposure to high temperatures?
This can cause relaxation phenomena under load that higher temperatures increase. Stress relaxation accompanies a loss of clamp force and a decrease in preload.
Work-hardened fasteners are more sensitive with regard to stress relaxation compared with quenched and tempered or stress-relieved fasteners.
Some foresights.
Care should be taken when lead-containing steels are used for fasteners at elevated temperatures. For such fasteners, a risk of liquid metal embrittlement should be taken into consideration when the service temperature is in the range of the melting point of lead.
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