With the requirements of light-duty and high-performance automobile, the development of automobile industry puts forward new requirements for gear materials. Automotive gear steel is mainly developing in the direction of high purity, narrow hardenability band, fine grain, easy machining and easy cutting, and the lightweight of automotive gear material is also an urgent problem to be solved in the automotive industry.
1. Development of automotive gear steel with narrow hardenability
The heat treatment quality of mass-produced narrow hardenability belt automobile gears is stable, the matching meshing accuracy is improved, and the service life is prolonged. The key to smelting narrow hardenability belt gear steel is to strictly control the chemical composition, improve the composition and microstructure uniformity, establish the correlation between chemical composition and hardenability, and realize the accurate control of chemical composition (NCC) through computer-aided prediction and supplementary composition. At present, high-grade carburized gear steel for automobile has very strict requirements for hardenability band.
2. Development of infiltrated high toughness Automotive Gear Steel
It is required to increase the load of heavy-duty gear and improve the impact strength of steel. At the same time, in order to inhibit the large-scale of automobile gear, on the premise of high strength and toughness of the matrix, the key is to prevent the formation of infiltration layer crack and improve the toughness of infiltration layer. It is mainly used to reduce Si and P and add Ni and Mo elements. In addition, the most effective measure is to use ultra-low oxygen steel with oxygen content of no more than 10ppnl.
3. Development of free cutting Automotive Gear Steel
The use of high-speed CNC machine tools for high-speed cutting tooth profile puts forward higher requirements for the free cutting performance of automotive gear materials. At present, the common practice is to appropriately increase the sulfur content (s = 0.020% ～ 0.040%) in the traditional low sulfur content range, and improve the morphology and distribution of sulfide through appropriate smelting process, so as to improve the cutting performance. At present, Japan and other countries are developing free cutting automotive gear steels containing Bi, Mg and Ca without Pb.
4. Development of low oxygen content Automotive Gear Steel
By reducing the oxygen content in automobile gear steel and improving the purity of steel, the fatigue life of automobile gear will be greatly improved. Because of the decrease of oxygen content in steel, oxide inclusions are reduced, which reduces the adverse effect of inclusions on fatigue life. At present, the oxygen content of low carbon gear steel can be stabilized at 15.0 through if-vd vacuum degassing process × Within 10-6.
5. Develop precision forging and cold extrusion technology for automotive gear steel
The use of direct forming precision forging technology and cold extrusion technology can reduce the cutting cost and improve the production efficiency and material utilization. It requires that the deformation resistance of steel is small, the deformation ability is strong, and the grain is not easy to be coarse during carburizing. Therefore, it is necessary to develop special automotive gear steel to make its alloying, purity and dimensional tolerance meet the process requirements.
6. Development of lightweight automotive gear materials
Through the use of high-strength steel, multi-element alloy, carbon composite, composite plastic material, glass fiber reinforced material and the combination of new forming technology and new materials, the lightweight of automobile gears is realized. At present, metal matrix composites, such as particle reinforced metal matrix materials and carbon fiber reinforced composites, have been studied and applied in automobile gear manufacturing.