Why 4145H Outshines 35CrMo in Drilling Tool Innovation (part 3)

According to the relevant standards outlined in Sampling Location and Specimen Preparation for Mechanical Property Testing of Steel and Steel Products, heat-treated specimens were sampled and initially examined. After preliminary testing, they were machined into standard test pieces for mechanical property evaluation, including tensile and Charpy impact tests. The test results revealed notable differences in the mechanical behavior of 4145H and 35CrMo steels, particularly when tempered at different temperatures.

1. Comparative plots of yield strength versus impact energy were created for both 35CrMo and 4145H. These curves showed that, within the effective performance range, 4145H consistently delivers higher yield strength than 35CrMo at similar levels of impact energy. This indicates superior strength potential without compromising toughness.

1. The mechanical properties and tempering hardness values of both materials were assessed across a range of tempering temperatures. The data showed that 4145H demonstrates slightly better comprehensive mechanical performance than 35CrMo when tempered within appropriate temperature intervals. This suggests that 4145H may offer better adaptability in varying thermal treatment conditions.

To further evaluate its practical application, drilling tools were trial-manufactured using 4145H material. These tools underwent quenching and tempering heat treatment, followed by detailed inspection and metallurgical analysis of cross-sections.

1. The treated 4145H parts exhibited high hardness levels both at the surface and in the core. The hardness gradient was gradual and consistent, indicating excellent hardenability and uniform quenchability—critical factors for downhole tool applications, where both surface strength and core toughness are required.

1. Under a microscope at 500× magnification, the metallographic structure at the thickest section of the part showed that the surface consisted mainly of sorbite with minimal ferrite, while the core exhibited slightly more ferrite content. This distribution indicates a desirable and uniform microstructure, contributing to reliable performance under demanding conditions.

1. Mechanical testing of the finished 4145H tool parts confirmed that their tensile strength, yield strength, and impact energy not only met but significantly exceeded the relevant industry standards. This reinforces the material’s suitability for high-stress, high-impact applications such as drilling operations.

In conclusion, 4145H steel demonstrates superior mechanical performance compared to 35CrMo, particularly in terms of yield strength and impact resistance. Its excellent hardenability, favorable microstructure, and ability to meet stringent performance criteria make it a strong candidate for manufacturing high-performance drilling tools. The results confirm that 4145H exceeds industry expectations and offers reliable, high-strength performance in demanding operational environments.