In engineering construction, the rock drill bit is an important part. It directly contacts the rock, breaks the rock mass, and achieves the purpose of drilling rock holes. During the drilling process, the rock drill bit must withstand the cyclic stress of tension, compression, bending, and torsion imposed by a high-frequency, high-impact rock drill under intensified abrasion and corrosive media conditions. According to load and rock sturdiness, the service life of the drill bit is often only a few minutes to a few hours. Such harsh working conditions and short service life are rare in all machine tools. Rock drill bits are made of steel, and the rationality of their design and manufacture directly affects the progress and quality of the project. Therefore, the principle of steel for rock drill bits should be based on its usage characteristics.
Steel selection principles for rock drill bits
Toughness and wear-resistant
①Wear-resistant.
The rock drill bit rubs against the rock during the drilling process, requiring the steel to possess excellent wear resistance. Steel with good wear resistance can effectively reduce the wear of the rock drill bit and extend its service life. When selecting steel, we should focus on its hardness, wear resistance, and other indicators.
②Impact resistance and fatigue resistance.
Rock drill bits endure significant impact and vibration during use, necessitating steel with superior impact resistance and fatigue resistance. Steel with good impact resistance can resist damage when hit, while steel with good fatigue resistance can maintain stable performance during long-term use. When selecting steel, we should focus on its impact absorption capacity, fatigue life, and other indicators.
It has a high yield limit, fatigue strength, impact toughness, and fracture toughness, which can effectively prevent the deformation and brittle fracture of the drill bit shell, which can greatly ensure the stability of the drill bit geometry and the durability of the work.
Good manufacturability.
It should have good processing performance.
①Easy cutting. The hardness after annealing is not greater than HB260, but it should not be too soft, so as not to stick to the knife and affect its processing quality.
②Good hardenability and hardenability. Appropriately control the heating temperature and brazing process. Air cooling hardness should reach HRC35~50.
③Good weldability. It has a strong affinity for general copper-based or silver-based solders, the interface of the welded shell can form a solid solution, and the linear expansion coefficient and hardness alloy are relatively close to reducing welding stress.
In line with local resources
Because of the harsh stress conditions of the drill bit, Ni, Cr-Mo ultra-high-strength alloy steels are used for the more popular brand drill bit in the world. Ni and Cr resources are different in different regions. Therefore, in the necessary drilling conditions, alloy steels such as Ni, Cr, and Mo should be used. In general, Si, Mn, Mo steel series or other alloy steels with low Ni, Cr, and Mo steel series can be appropriately selected according to the actual situation.
Cost-effectiveness
On the premise of meeting the above principles, we should also consider the cost-effectiveness of steel. High-quality steel is generally more expensive, but its long service life and low maintenance costs may mean a lower overall cost. Therefore, when selecting steel for rock drill bits, the relationship between cost and performance should be considered according to project needs and budget constraints, opting for cost-effective steel.
How to choose the appropriate steel for rock drill bits
Knowledge of market availability
Before selecting steel for rock drill bits, it’s essential to understand the market supply situation. Different brands and models of steel may vary in performance, price, and other aspects. Therefore, we should choose steel with stable performance and reasonable price according to our needs and budget.
Consult a professional
When selecting steel for rock drill bits, consulting professionals or manufacturers can be beneficial. They can recommend suitable steel types and specifications based on your specific needs and project circumstances.
Conduct field visits and experiments
After selecting the type and specification of steel, we can conduct field visits and tests. By observing and testing the steel’s appearance, performance, and other indicators, we can further verify whether it meets the requirements.
Recommended steel for rock drill bit shell
The service conditions of the rock drill bit are similar to those of the drill rod, which are resistant to wear and have a high impact bearing capacity under fatigue load and corrosion conditions. The fracture shape of the drill rod and the rock drill bit is slightly different. The drill rod is mainly fractured by stress corrosion fatigue, while the rock drill bit shell is worn and deformed, losing the ability to fix buttons, plastic deformation, shell plastic deformation, and fatigue or brittle fracture.
Therefore, the requirements for the hardness and cyclic toughness of the drill bit shell should be higher than that of the drill rod. For commonly used induction brazing drill bit with a fixed button, the drill bit shell is recommended to use 40MnMoV, 24SiMnNi2CrMo, 25SiMnNiCrMoV, and 30CrNi4Mo steel grades. According to tape of rock and rock drilling, some 35SiMnMoV, 40SiMnCrMoV, and other medium carbon bainite alloy steels with good air cooling hardening ability can also be used. For button bits for the hot-clamping button, it is recommended to use Q45NiCrMoV and 24SiMnNi2CrMo steel grades.
Conclusion
Choosing the appropriate steel for rock drill bits is crucial for enhancing project efficiency and reducing costs. During the selection process, it’s important to adhere to principles of high strength, toughness, wear resistance, impact resistance, and fatigue resistance, while comprehensively considering the relationship between cost and performance. At the same time, by understanding the market supply situation, consulting professionals, and conducting on-site inspections and tests, steel types and specifications that meet the requirements can be selected more accurately.
