In the pursuit of efficient and precise modern engineering operations, hydraulic rock drills have become a powerful assistant in mining, road construction, tunnel excavation, and other fields with their excellent drilling capabilities. However, with the continuous improvement of engineering requirements, the critical component of hydraulic rock drills, the shank adapter, is often faced with the problem of fracture failure. Although 20CrNi3 is a high-strength alloy carburizing steel, such problems still occur. It affects the construction progress and increases maintenance costs and safety risks. So, what exactly causes the fracture of the 20CrNi3 shank adapter? This article will explore the reasons and solutions behind it for you, helping to improve the overall performance and durability of the hydraulic rock drill.
Analysis of fracture causes
High quenching temperature
Studies have shown that the main reason for the fracture of the 20CrNi3 shank adapter is that the quenching temperature is too high. At high temperatures, the carbon content of austenite in the carburized layer increases, and the undissolved carbides decrease, resulting in a large amount of residual austenite after quenching. These residual austenites will further undergo martensitic transformation during subsequent use, resulting in large residual stress and phase transformation instability, thereby reducing the fatigue resistance of the shank adapter and eventually causing fatigue fracture.
Residual stress and phase transformation instability
Due to the high quenching temperature, the residual austenite content in the carburized layer is high. During the grinding process, part of the high-carbon martensite + residual austenite + carbide layer on the surface is ground away, and the residual austenite undergoes further martensitic transformation under the action of grinding heat. These newly formed martensites increase the brittleness of the shank adapter due to the large residual stress and phase transformation instability, making it easy to break.
Grinding residual stress is not eliminated
After grinding, if the grinding residual stress is not effectively eliminated, the fatigue resistance of the shank will be further affected. The presence of residual stress will accelerate the initiation and expansion of cracks, resulting in fatigue fracture of the shank during use.
Use environment and stress state
The shank adapter in a hydraulic rock drill must handle significant impact loads and varying stress levels. It is especially true in harsh working conditions, such as extreme temperatures, high humidity, and heavy dust, which can shorten the shank’s fatigue life. Improper use and maintenance of the rock drill, including frequent overloading and inadequate lubrication, can further increase the shank adapter’s risks of wear and fracture.
Improvement strategy
Reduce quenching temperature
Appropriately reducing the quenching temperature is an effective method to lower the residual austenite content in the carburized layer. By optimizing the heat treatment process and maintaining the quenching temperature within a reasonable range, the residual austenite content can be significantly reduced, enhancing the fatigue resistance of the shank adapter.
Add cryogenic treatment
Cryogenic treatment is a method to further improve the structure and performance of materials through low-temperature environments. Cryogenic treatment after quenching can promote the transformation of retained austenite to martensite and reduce residual stress and phase transformation instability, thereby improving the shank adapter’s fatigue resistance and service life.
Stress relief annealing after grinding
After grinding, low-temperature stress relief annealing should be carried out in time to eliminate the residual stress generated during the grinding process. This step is crucial to stabilize the martensite structure formed during the grinding process and improve the fatigue resistance of the shank adapter.
Strengthen material testing
Strengthening material testing can guarantee the quality of the shank adapter. Through chemical composition analysis, hardness test, impact performance test, and other means, we can comprehensively evaluate the performance index of the shank adapter. Additionally, we should formulate strict microstructure acceptance standards to ensure that the metallurgical organization of the shank adapter meets the design requirements and reduces the risk of fracture caused by material defects.
Improve the use of the environment and conditions
When utilizing a hydraulic rock drill, it’s important to avoid operating in harsh environments. If it cannot be avoided, we should take corresponding protective measures. Additionally, it’s crucial to perform regular maintenance on the equipment, consistently check the wear of the shank adapter, and promptly replace any damaged parts. Moreover, it’s critical to control the operating load of the rock drill to prevent frequent overload operations and extend the service life of the shank adapter.
Technological innovation and upgrading
With the continuous development of science and technology, new materials and processes are constantly emerging. We encourage users to pay attention to industry trends, actively introduce new technologies and materials, and carry out technological innovation and upgrading of hydraulic rock drills and drill bits. Using more advanced materials and processes can further enhance the performance and extend the service life of the shank adapter, while also reducing the risk of breakage.
Conclusion
The problem of 20CrNi3 shank adapter fracture affects the hydraulic rock drills’ working efficiency and reliability. However, through scientific analysis, reasonable solutions, and continuous technological innovation, we can effectively deal with this problem and promote the progress and development of hydraulic rock drill technology.
