1. Preface
With the rapid development of materials science and technology at home and abroad, the selection of gear materials in the manufacturing industry is not limited to existing domestic materials.
More and more companies have introduced some gear materials with excellent comprehensive performance from abroad.
17Cr2Ni2MoA steel is a kind of carbureted gear material with excellent mechanical properties and processability.
After carburizing and quenching, the performance of this material is equivalent to that of 18Cr2Ni4WA steel gear material widely used in heavy machinery.
However, its processability in heat treatment is better and raw material savings are greater.
Compared with the latter, the cost per ton of raw materials is saved by about 6,000 yuan.
However, whether the potential performance of 17Cr2Ni2MoA steel can be fully realized depends on the technical level of each manufacturer's heat treatment process.
In order for this material to be successfully used in gear products, our company has conducted experimental research.
2. Comparison of the mechanical properties of two materials
2.1 Chemical composition
See Table 1 for the chemical composition of the two materials.
Table 1 Chemical composition (mass fraction) of 18Cr2Ni4WA Steel and 17Cr2Ni2MoA Steel (%)
| Material | 18Cr2Ni4WA | 17Cr2Ni2MoA |
| W | 0.13~0.19 | 0.14~0.19 |
| Cr | 1.35~1.65 | 1.5~1.8 |
| Ni | 4.0~4.5 | 1.4~1.7 |
| W | 0.8~1.2 | – |
| Mo | – | 0.25~0.35 |
| Mn% | 0.3~0.6 | 0.4~0.6 |
| Yes | 0.17~0.37 | 0.17~0.35 |
By comparison, it is found that the carbon content of these two gear materials is close, and they are carbon steel carbureted with low carbon alloy.
The surface hardness of the gear can be improved by carburizing and quenching.
2.2 Comparison of mechanical properties
To study the mechanical properties of the two materials, we put 17Cr2Ni2MoA steel and 18Cr2Ni4WA steel with the same size into production to compare the mechanical properties.
18Cr2Ni4WA steel is the material currently used by our company.
According to our production process, the manufacturing process of 18Cr2Ni4WA steel test bar is: normalizing after forging + tempering → machining → carburizing → high temperature tempering for 3 times → machining → quenching and tempering.
Since our company did not use 17Cr2Ni2MoA material, after consulting other manufacturers and various documents in terms of process, it is decided that the manufacturing process of 17Cr2Ni2MoA steel test bar is: normalization after forging + tempering → machining → carburizing → high temperature tempering → machining → quenching and tempering.
After heat treatment according to the above process, the test bar is processed into a sample according to the standard for inspection. See Table 2 for results.
Table 2 Mechanical properties of two materials after heat treatment
| Name | Material | Yield limit/MPa | Tensile strength/MPa | Stretching (%) | Area reduction (%) | Impact resistance / · cm -2 |
| φ 60 mm sample (not hardened at high temperature) | 17Cr2Ni2MoA | 810 | 954 | 10.5 | 61.25 | 121.4 |
| φ 60 mm sample | 18Cr2Ni4WA | 822.5 | 1003 | 16.5 | 67.2 | 169.7 |
| φ 82 mm sample | 17Cr2Ni2MoA | 789.4 | 947 | 17.3 | 65.4 | 144.8 |
| φ 82 mm sample | 18Cr2Ni4WA | 698 | 931.7 | 19.8 | 70.7 | 180.48 |
2.3 Analysis of test bar mechanical property test results
1) The yield strength and tensile strength of 17Cr2Ni2MoA steel and 18Cr2Ni4WA steel with the same size are similar after carburizing and tempering.
2) The impact resistance of 17Cr2Ni2MoA steel is slightly lower than that of 18Cr2Ni4WA steel.
3) The area reduction of 17Cr2Ni2MoA steel is slightly lower than that of 18Cr2Ni4WA steel, with a difference of 5% ~ 7%.
4) The elongation of 17Cr2Ni2MoA steel is slightly lower than that of 18Cr2Ni4WA steel, with a difference of 6%.
5) In this test, the φ 17Cr2Ni2MoA material of the 60mm sample is not subject to high-temperature tempering after carburizing due to special circumstances, which has little impact on the subsequent overall quenching hardness, strength and impact resistance, but It has a big impact on stretching.
Therefore, high temperature tempering after carburizing 17Cr2Ni2MoA steel is very important for the overall performance of the parts.
3 Results and discussion
To study the performance of the heat treatment process of the two materials, we put 17Cr2Ni2MoA steel and 18Cr2Ni4WA steel with the same size into production for comparison.
According to the existing carburizing process of 18Cr2Ni4WA steel, samples of the two materials are loaded into the furnace together with the parts in production.
Carburizing is carried out in two furnaces at the same time.
After carburizing, high temperature tempering is carried out once.
See Table 3 for carburizing results of test samples.
Table 3 sample carburizing results
| Furnace sample | Material | Carbide grade/grade | Class/class of retained martensite and austenite | Penetration depth/mm | Comments |
| φ25mm sample | 17Cr2Ni2MoA | 4 | two | 6.6 | High temperature tempered once after carburizing in the same furnace |
| sample φ25 | 18Cr2Ni4WA | 3 | 6 | 7.2 | |
| M7 tooth-shaped sample | 17Cr2Ni2MoA | 4 | two | 2.3 | High temperature tempered once after carburizing in the same furnace |
| M7 tooth-shaped sample | 18Cr2Ni4WA | 3 | 4 | 2.5 |
Analysis of inspection results after carburizing:
1) There are differences in the carbide grade (k), but the difference is not large, which can fully guarantee that the carbide grade meets the national standard of K ≤ 4.
2) 17Cr2Ni2MoA steel has excellent processability.
After high-temperature tempering, the retained austenite can be basically reduced to grade 2, and subsequent quenching and tempering or general quenching can be carried out;
The degree of retained austenite of 18Cr2Ni4WA steel is still large after high-temperature tempering and can be reduced only after two to four high-temperature tempering procedures.
3) The depth of the carburized layer is different, but the difference is small.
In this test, the depth of the carburized layer of 17Cr2Ni2MoA steel is slightly smaller than that of 18Cr2Ni4WA steel.
4. Conclusion
The mechanical properties of the 17Cr2Ni2MoA steel and 18Cr2Ni4WA steel used now are not much different, but the process performance is better and the cost is reduced.
It can completely replace the existing 18Cr2Ni4WA steel in our company.
The gear is the main part of the clipper, which accounts for a large proportion.
The application of 17Cr2Ni2MoA steel saves our company at least 3 million yuan in gear manufacturing costs every year.
In addition, due to the excellent process performance and the reduction of high temperature tempering times after carburizing, the material can shorten the processing cycle of gears, reduce the deformation of gear products, further improve the quality of heat treatment of gears and reduce subsequent machining costs. .
