Heat treatment method for improving percentage elongation after fracture of C-grade level

The invention relates to a heat treatment method for improving percentage elongation after fracture of C-grade steel. The method comprises the following steps of putting a C-grade steel casting into aheat treatment furnace, heating to 1100 DEG C, keeping the temperature for 4 hours, cooling to 500 DEG C along with a furnace, discharging, and air cooling to room temperature; recharging into the heat treatment furnace, heating to 910 DEG C, keeping the temperature for 3 hours, discharging and air-cooling; and then heating to 900 DEG C, keeping the temperature for 3 hours, quenching, discharging, carrying out water cooling, heating to 680 DEG C, tempering for 3 hours, cooling to 500 DEG C along with the furnace, discharging, and carrying out air cooling to obtain the percentage elongation after fracture of the C-grade steel. The heat treatment process disclosed by the invention has the advantages that compared with a traditional quenching and tempering process, the heat treatment processis uniform in component s