Ultrahigh-strength automobile suspension guide arm steel and smelting method thereof

The invention discloses ultrahigh-strength steel for an automotive suspension guide arm and a preparation method of the ultrahigh-strength steel, and the ultrahigh-strength steel comprises the following components in percentage by weight: 0.57%-0.61% of C, 1.25%-1.45% of Si, 0.90%-1.10% of Mn, less than or equal to 0.012% of P, less than or equal to 0.010% of S, 1.05%-1.15% of Cr, 0.015%-0.025% of Nb, 0.25%-0.35% of Ni, 0.012%-0.027% of Al, 0.0035%-0.075% of N, 0.15%-0.25% of Cu, 0.010%-0.020% of Ti and the balance of Fe and inevitable impurities. The smelting production process comprises the steps of combined blown converter smelting, refining slag washing and deoxidation, external refining, vacuum degassing and continuous pouring. The continuous casting blank produced by smelting is high in purity, uniform and stable in component, good in internal compactness, low in non-metallic inclusion and total oxygen content, the range of macrosegregation main components of the section of the casting blank is controll