Non-quenched and tempered steel for automobile fastener screws and production method thereof

The invention relates to a non-quenched and tempered steel for automobile fastener screws and a production method thereof, belonging to the technical field of ferrous metallurgy. The production method comprises the following steps: heating the non-quenched and tempered steel chemical components and a steel billet thereof, rolling, and carrying out post-rolling cooling. The non-quenched and tempered steel for automobile fastener screws comprises the following chemical components in percentage by mass: 0.35-0.45% of C, 0.45-0.65% of Si, 1.30-1.50% of Mn, 0.010-0.030% of P, 0.015-0.035% of S, 0.005-0.015% of Al, 0.10-0.30% of Cr, 0.05-0.15% of V, 0.0080-0.0150% of N, and the balance of Fe and inevitable inclusions. The steel billet heating temperature is controlled at 1150-1250 DEG C, the initial rolling temperature is kept at 1020-1100 DEG C, the finishing temperature is 800-900 DEG C, and the rolling reduction is greater than or equal to 15%. The post-rolling cooling speed is controlled at 1-10 DEG C/second. The production technique has the advantages of simple route and high operability, and is easy to control. The tensile strength of the produced non-quenched and tempered steel is greater than 900 MPa, the yield strength is greater than 650 MPa, the elongation percentage is greater than 20%, and the percentage reduction in area is greater than 45%. The method can finally obtain the high-strength high-toughness medium-carbon non-quenched and tempered steel for automobile fastener screws.