The electric roller roll excavator roller produced by China First Heavy Machinery Co., Ltd. is made from P&H107 material, a type of steel developed by the American P&H Company (material code 4350 under the American Iron and Steel Association). However, this specific material standard is not available in China. While the 50CrNiMo component in the JB/T6401-1992 standard is somewhat similar, its performance parameters are significantly lower than those of P&H107. As a result, there are no established empirical data to guide production. Based on previous domestic experience, it was possible to achieve strength and hardness close to the required specifications, but the plasticity and toughness failed to meet foreign design standards, which affected the workpiece’s overall performance and service life.
To address this issue, the company sent technical experts to inspect domestic manufacturers in search of potential collaboration, but none could meet the rigorous inspection criteria of P&H products. In response, the company initiated research into the heat treatment process for the roller, aiming to determine suitable parameters based on their own equipment capabilities.
**1. P&H107 Roller Roll**
The chemical composition of the P&H107 roller roll is detailed in Table 1. The production process includes smelting, forging, rough machining, tempering heat treatment, and finishing. During forging, the rod is first formed, and rough machining is carried out according to process requirements. Hardness upper and lower limits are set for rolls from the same smelting and heat treatment batch. Mechanical property samples are taken from the roughed section (as shown in Figure 1), including two tensile specimens and three longitudinal and tangential impact samples. If several consecutive furnace batches pass the test, mechanical properties can be accepted. The technical requirements after quenching and tempering are listed in Table 2.
The critical point of the P&H107 material was measured using a DT-1000 automatic thermal dilatometer on a post-forged annealed specimen. The sample tested was mainly pearlitic with a size of φ3 mm × 50 mm. The heating rate was 200°C/h, austenitizing temperature was 880°C, and the holding time was 20 minutes. The vacuum level was maintained at ≤10â»Â³ Pa. To prevent decarburization, the furnace was evacuated and then filled with nitrogen for protection. The critical point test results are summarized in Table 3.
**2. Development of Heat Treatment Process Parameters**
Currently, cooling parameters for structural steel quenching and tempering are selected based on carbon equivalent. According to these guidelines:
1. When wC ≤ 0.31% and CE ≤ 0.75%, water quenching is safe.
2. When wC = 0.32–0.36% and CE = 0.75–0.88%, water quenching is allowed with caution.
3. When wC ≥ 0.36% and CE ≥ 0.88%, water quenching is prohibited unless special guidance is provided.
P&H107 has a carbon content of approximately 0.50%, so oil quenching is necessary. To ensure high strength, the austenitizing temperature was increased by 20–30°C above the standard (Ac3+50°C) to enhance hardenability. Tempering temperature was also reduced as much as possible. Raising the quenching temperature for medium-carbon alloy steel reduces flake martensite and improves toughness, but excessive temperatures may increase retained austenite, reducing hardness.
Other parameters were determined based on the roller’s effective cross-section size of 200 mm, considering the number of parts per furnace and attachments. The specific heat treatment parameters are shown in Figure 2.
Heat treatment was conducted on two smelting furnaces (a total of 12 pieces). The actual chemical composition is listed in Table 4. After heat treatment, four hardness limits were tested. The results showed that while strength was slightly below expectations, plasticity, especially low-temperature impact toughness, did not meet the design requirements. Subsequent tests confirmed similar outcomes.
**3. Optimization of Heat Treatment Parameters**
Increasing the quenching cooling speed leads to more martensite formation and a deeper hardened layer, significantly improving the mechanical and low-temperature impact properties of the workpiece. However, due to the risks associated with water cooling for P&H107, strict control is necessary.
The design of the quenching tank and agitation system greatly influences the cooling effect. By optimizing water-cooling conditions, the desired quenching effect for P&H107 rollers was achieved. Figure 3 shows the cooling capacity of water at different temperatures compared to N46 oil.
Due to the increased quenching speed, the austenitizing temperature could be slightly lowered, and the tempering temperature raised, which improved the roller's plasticity and toughness. Considering the use of a trolley furnace, the time between quenching and entering the water tank must be accounted for. The austenitizing temperature was set at Ac3 + (60–70)°C. Our smallest trolley furnace measures 2600×1300×800 mm, capable of holding over 12 rollers per batch. The smallest quenching tank is 5000×3000×5000 mm, with a maximum cooling capacity of 20 tons. The water temperature before quenching was controlled at 30–40°C, offering a cooling rate faster than oil without causing excessive stress. The water tank was not ventilated or circulated, and the roller was oscillated during quenching to enhance cooling efficiency. The surface temperature after quenching was controlled at 100–150°C. The specific process parameters are shown in Figure 4.
Using the process in Figure 4, the first two smelting furnaces were treated. The chemical composition is shown in Table 6. After heat treatment of 12 pieces, four hardness limits were tested, showing results similar to Table 7. The microstructure was tempered sorbite.
Subsequently, over 40 batches (more than 500 pieces) were processed following this method. Mechanical properties remained consistent with Table 7. Only the radial performance of two parts was slightly below the requirements due to obvious forging fibers and uneven riser placement during forging. Adjustments were made to the forging process, and after quenching and tempering, all performance metrics met the US P&H standards, gaining recognition from the foreign partner.
**4. Conclusion**
1. Forged fibers resulting from long bar cutting can negatively affect the radial performance of the roller after heat treatment.
2. By controlling water quenching parameters and optimizing the process, the roller can achieve mechanical properties far exceeding domestic standards, fully realizing the material's potential.
Classic Composite Decking,Wood Plastic Composite Decking,Composite Wood Decking,Wood Plastic Composite
Jinhu Jusheng Plastic Wood New Material Co.,Ltd , https://www.goldenlakewpc.com