This invention discloses a gear steel for automotive transmissions and its manufacturing method, comprising: C: 0.19%~0.21%, Si: 0.23%~0.28%, Mn: 0.95%~0.98%, Cr: 1.08%~1.12%, Ti: 0.05%~0.07%, S: 0.028%~0.035%, P≤0.015%, Als: 0.008%~0.025%, Ni≤0.05%, Cu≤0.05%, Mo≤0.01%, residual elements Sn≤0.01%, Pb≤0.005%, As≤0.02%, Bi≤0.008%, Sb≤0.008%, total
oxygen content: 0.001%~0.002%,
total nitrogen content ≤0.004%, with the balance being Fe and unavoidable
impurity elements, and the Mn / S ratio
ranging from 27 to 35. This application controls the carbon-
oxygen product at the end of the converter
smelting process, which helps reduce
residual oxygen in the steel; the aluminum-containing modifier modifies the
ladle top
slag, which helps improve aluminum yield; the high-basicity
slag operation in the early stage of refining effectively removes and controls
oxygen in the
molten steel, while the lower-basicity
slag operation in the later stage of refining stabilizes the
sulfur content and yield in the subsequent
sulfur feeding line; the sulfides are mainly composed of single
manganese sulfide sulfides, with a core of
calcium aluminate and an outer layer of
manganese sulfide composite sulfides, and are in a diffuse distribution state, which effectively ensures the
machinability of gear steel.