Process of ensuring the rail precision constant-stress relief annealing (generally used in welding under phase transition of the Organization, in order to prevent internal stress caused deformation and cracking process, generally lower temperatures) to stress tempering process:
Cast iron Rails aging treatment:
Using stress relief annealing (also known as: Aging and tempering) or vibratory stress relief have reached remove internal stress effects. Tempering temperature 530 ° c, thermostat 2-3 hours, 48 hours, the temperature dropped below 200 ℃, make natural cooling, transferred to the next procedure. Machining, lapping and a final inspection after passing the factory. Cast iron rail stress relief annealing (also known as: Aging and tempering) steps:
1, charging: charging temperature should not be too high, generally less than 150 ℃. Should ensure the heating process furnace gas charge cycle flow.
2, heating: the heating rate should be controlled at less than 60 ° c/h.
3, insulation: insulation temperature 540-560 ℃, maintained 4H.
4, cooling: temperature after the cooling; the cooling speed of less than 30 ° c/h.
5, oven: oven temperature should be less than 200 ° c, should be less than 150 deg c in the winter.
HT250 material cast iron Rails ingredients: strictly according to the standard gray cast iron: ISO185-1988 implemented. Use lower-22# quality in Benxi iron and steel materials and various trace elements: 22# 60% Benxi iron, scrap 25~30%, allowance ar 60# 2% 75# 1% ferrosilicon furnace ferromanganese bred 75# Silicon 0.3% mobile. Hot metal temperature of 1400 ° c above (measured by thermocouple thermometer), take a small amount of liquid iron casting triangular test piece, after passing the review specimen, casting temperature 1300 c above, casting more than 24 hours after box, sand.