Foreign tests have proved that the supercooled austenite decomposition products during surface quenching of carburized steel are the main reason to reduce the fatigue resistance of truck gears, and internal oxidation just promotes this process. In order to reduce the effect of internal oxidation The content of Cr and Mn in the steel should be properly reduced and the content of Mo should be increased to improve the surface hardenability of the material and make the hardness distribution reasonable. Based on the above analysis, we believe that Cr Ni Mo steel is more suitable for large modulus heavy load truck gears.
Referring to the analysis of foreign brands, we believe that 17CrNiMo6 steel in Germany can be used as the preferred steel. In terms of performance, it can fully meet the application requirements, and the processability is better than 18crni8 steel; Compared with domestic 12crni3, 17CrNiMo6 not only has good hardenability, but also has low Ni content and correspondingly lower price, which is in line with the development direction of truck gear.
The application abroad shows that 17CrNiMo6 can not only be used as truck gear steel, but also replace the domestic 18Cr2Ni4W steel to produce large modulus heavy-duty gears for construction machinery, so it is a steel with great development prospect.
However, because the price of new steel is often too high, it is not easy for users to accept. In addition, the subsequent smelting processes need to be adjusted and transformed accordingly, and the application research of new materials in the factory is still not in-depth. Therefore, there are still great obstacles to the popularization and application of the imported new truck gear steel.
| Brand | C | Si | Mn | P | S | Cr | Ti | HRC/J9 | HRC/J15 |
| H1 | 0.18-0.23 | 0.17-0.37 | 0.8-1.1 | ≤0.03 | ≤0.035 | 1.0-1.3 | 0.04-0.1 | 26-32 | 22-29 |
| H2 | 0.18-0.23 | 0.17-0.37 | 0.8-1.1 | ≤0.03 | ≤0.035 | 1.0-1.3 | 0.04-0.1 | 30-36 | 24-31 |
| H3 | 0.18-0.23 | 0.17-0.37 | 0.8-1.1 | ≤0.03 | ≤0.035 | 1.0-1.3 | 0.04-0.1 | 32-38 | 26-33 |
| H4 | 0.18-0.23 | 0.17-0.37 | 0.8-1.1 | ≤0.03 | ≤0.035 | 1.0-1.3 | 0.04-0.1 | 25-41 | 28-35 |
| H5 | 0.18-0.23 | 0.17-0.37 | 0.9-1.25 | ≤0.03 | ≤0.035 | 1.1-1.45 | 0.04-0.1 | 37-43 | 32-38 |
| H6 | 0.18-0.23 | 0.17-0.37 | 0.9-1.25 | ≤0.03 | ≤0.035 | 1.1-1.45 | 0.04-0.1 | 39-45 | 35-41 |
At present, 20CrMnTi is the most widely used in truck gear industry in China, followed by 20Cr, 20CrMo and 20cemnmo steel. Due to the main reason of price, our company still uses the conventional gear steel 20CrMnTi or 20CrMnTiH steel with limited hardenability in heavy truck gears (see table).