The invention relates to an annealing-free
alloy cold heading steel
wire rod for a 12.9-grade bolt and a production method of the annealing-free
alloy cold heading steel
wire rod. The production process comprises the steps of molten iron pre-removal of P / S, electric furnace or converter
smelting, external refining, bloom
continuous casting, rolling into an intermediate billet and steel billet finishing, intermediate billet heating, high-pressure water descaling, rough rolling, intermediate rolling, pre-finish rolling, finish rolling,
spinning, coil collecting and cooling. The annealing-free
alloy cold
forging steel wire for the 12.9-grade bolt comprises the following components in percentage by
mass: 0.30%-0.35% of C, 0.10%-0.30% of Si, 0.70%-1.20% of Mn, 1.0%-1.5% of Cr, 0.15%-0.30% of Mo, 0.015%-0.030% of Al, 0.0030%-0.0080% of N, 0.01%-0.04% of Nb, less than or equal to 0.30% of Ni, less than or equal to 0.10% of Cu, less than or equal to 0.015% of P, less than or equal to 0.010% of S, less than or equal to 0.012% of (As + Sb + Bi), less than or equal to 0.0010% of O and the balance of Fe and inevitable
impurity elements, the
niobium-
nitrogen product (Nb * N) is greater than On the premise that main alloy components are not reduced, a
fine grain structure can be obtained under a certain condition by adding grain refining elements, and the
delayed phase change effect the same as that of a low-temperature finish rolling process is achieved by utilizing the
delayed phase change characteristic of the
fine grain structure.