Composite heat treatment strengthening process for low-carbon steel

The invention discloses a composite heat treatment strengthening process for low-carbon steel, which relates to the field of manufacturing of electric automobile parts, and comprises the following steps: 01, normalizing: adopting different powers according to the specification difference of steel pipes, enabling the temperature of the steel pipes to uniformly reach 960-1010 DEG C and the heating speed to be 50-100 DEG C/S, and directly carrying out air cooling or air cooling to carry out temperature-controlled cooling after the steel pipes reach the temperature of 960-1010 DEG C and the heating speed to be 50-100 DEG C/S; 02, quenching is conducted, specifically, the rectangular steel pipe normalized in the step 01 is subjected to induction heating again till the quenching temperature is reached, then spraying rapid cooling is conducted, the quenching temperature is controlled to be 870-900 DEG C, the heating speed is 50-100 DEG C/S, and the water spraying pressure is 0.1-0.3 MPa; induction tempering is added