Railroad tracks made of 1025 steel are to be laid

Railroad tracks made of 1025 steel are to be laid during the time of year when the temperature averages 10째C (50째F). If a joint space of 4.6 mm (0.180 in.) is allowed between the standard 11.9-m (39-ft) long rails, what is the hottest possible temperature that can be tolerated without the introduction of thermal stresses?