| This paper summarizes the steel-making qualities of gear steels, various gear steels around world and their steel-making processes. According to the characters of gear steels production by converter in PZH Steel and combining with the steel-making quality requirements of gear steels, the two aspects, the cleanliness and hardenability controls of the steels, have been systemically studied.On the cleanliness, these technologies including the final stage control of converter, deoxidization by P1 multiple deoxidant, LF plus RH refining, bloom and billet continuous casting with no-oxidization atmosphere protection have been applied to realize it.On the hardenability, the precise and homogenization of chemical composition have been paid more attention. For the accurate chemical composition control, firstly based on the influences of different alloying elements to hardenability, the chemical target has been decided; and then adjusted by alloying at converter and at RH refining slightly. For the homogenization of the chemical composition, it is mainly to control billet segregation, melt superheat, proper electromagnetic stirring, tapping velocity, reasonable secondary cooling and soft reduction at final stage of solidification.The real process flow of gear steel production by converter in PZH Steel has finally been plotted: 120t top and bottom combining blown converter — multi-alloying deoxidization — Ar blowing —LF+RH refining — bloom and billet continuous casting. Through one year production, it is indicated that the qualities and performances of 20CrMnTiH gear steel entirely meet the standard, GB5216-2004, and technology requirements of clients. The value of chemical composition was near middle of standard, good homogenization and high cleanliness (non-metallic inclusions A ≤2.0 grade, B and C≤1.0 grade, D≤1.5 grade; T[O]≤18.0 × 10-6, [H]≤1.8×10-6); good hardenability and its quenching belt width control ( J9:34-39HRC, band width: 6 HRC, J15:28-34HRC, the quenching belt width: 7HRC). |
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