Martensite is a structural change in the wire material caused by a very sudden cooling of the rope after a strong local heating generated by friction (fig. 46).
The friction may be caused by e.g. bad winding of the wire rope on winches. The martensite structure is very brittle and may cause fractures during normal operation or when spliced, even though the wire rope does not show any visible signs of external wear (fig. 47).
Precautions against martensite:
- The blocks must not be worn down and should turn easily.
- When a wire rope is wound on a drum, it should be in tight wraps without the layers crossing each other in order to prevent the top layer from cutting into the underlying layers.
- The wire rope should be lubricated at regular intervals in order to minimise the friction between wires and strands.
- The wire rope should be checked at regular intervals for crushing, minor cracks and mechanical damages, all of which might indicate martensite spots.
If a steel cable carries a current, there will often be sparks. The surface temperature where the sparks appear will be over 800°C, making it quite probable that Martensite will be formed. If there is a strong probability of sparks appearing, wire and cable fractures may occur quickly.