| In this paper, the new IGF refined hot-forged and non-hardened-tempered steel with high strength and toughness was designed and its capability was studied. According to the theory of oxidizing metallurgy, through proper design of the components of the alloy, improvement of deoxidization in smelting, and control of the composition, distribution, shape and size of the fine oxide particles in steel, a great amount of fine and dispersed MnS would be produced. In the following cooling process, VN was separated out in the places of MnS. Due to the high coherency of VN and ferrite, VN became the best places for the separation of IGF. The result of the research on the microstructure showed that the designed steel obtained a lot of IGF after hot-forging and air cooling, the austenite grains were divided effectively, and the structure was refined. The result of the capability test indicated that after hot-forging and air cooling, the hardness of the tested steel was HRC26～31, the tensile strength was up to 1100MPa, and the impact toughness a_k value(V-notch) was between 50～70J / CM~2.After hot forging, the new IGF refined hot-forged and non-hardened-tempered steel was made into traction bolts and pivot centers of the Mt.Tai-12 tractors, instead of the original 40Cr quenched and tempered devices. It has worked well for over a year without showing any abnormal signs. The reduction gear's principal axis of plastic extruder made from the steel has worked well for over half a year. The new kind of mater has proved to have comprehensive mechanical property and to be able to meet the technical demands of mechine parts.The studied steel being made into structure parts instead of the tempered steel, is easiser in technics, lower in cost, and better in performance. It can save energy, reduce pollution,cut down cost, lessen reject rate and improve products' quality by canceling the quenching and tempering process, thus has great social and economical benefits, and good prospects of application, too. |
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