With the development of rock drilling technology and rock drilling conditions, shank adapters have become an indispensable and significant part of modern rock drilling tools. The shank adapter is not only an essential part of connecting other rock drilling tools but also has to withstand the harsh working environment, which requires higher requirements for its performance. The improvement of the performance of the shank adapter is inseparable from the materials and processes used to produce it, especially in the manufacturing process, if the appropriate heat treatment can improve the mechanical properties and wear resistance of shank adapters. Therefore, this article will introduce the heat treatment process of the En40B shank adapter.
What kind of material is En40B?
En40B is a high-strength low-alloy steel with high strength, good weldability, and good corrosion resistance, suitable for various mechanical parts and tools.
Heat treatment process of En40B shank adapter
carburizing – high-temperature tempering – isothermal quenching – low-temperature tempering
Carburizing
The carburizing process is a kind of chemical heat treatment. Chemical heat treatment is to put the steel workpiece in a chemical medium, through heating and heat preservation, infiltrate some elements of the chemical medium into the surface of the workpiece, thereby changing the chemical composition of the surface layer. The core and surface layers have different tissue and mechanical properties.
Isothermal quenching
Isothermal quenching is to put the heated shank adapter into a salt bath with a temperature slightly higher than the Ms point. Generally, the temperature holds for more than half an hour. After the lower bainite transformation occurs, the furnace is air-cooled, and the preheating is adopted in the initial heating to make the shank adapter heated uniform. Isothermal quenching can not only ensure that the shank adapter surface obtains much higher residual compressive stress than direct quenching but also, more importantly, the Ms point of En40B steel is decreased by more than 120 °C because of the carburizing result. The presence of an appropriate amount of retained austenite is very beneficial to improve the multi-impact bending fatigue resistance of the shank adapter. The lower bainite structure of medium carbon has good toughness and high strength, so it has lower crack sensitivity under the action of multiple shock loads, which can improve the service life of the rock drill shank adapter.
Low-temperature tempering
Because the performance of En40B is not high, it can meet the requirements through low-temperature tempering at 200°C. The tempering lasts 2 hours, and the tempering needs to be held for some time to make the core and surface temperature uniform, to ensure that the structure is fully transformed and the quenching stress is fully eliminated. If the tempering time is too short, it will lead to insufficient tempering and make the shank adapter crack in grinding. But too long time tempering will increase the production cost and reduce the utilization rate of the equipment.
In summary, the heat treatment of En40B shank adapters mainly includes two key steps: quenching and tempering. Quenching is rapidly cooling steel to achieve high hardness and strength. Tempering is the heat treatment of steel after quenching to reduce internal stress and improve toughness during quenching. After completing the heat treatment, other process steps, such as quenched and tempered and surface treatment, can be performed to make further improvements to the properties of the En40B shank adapter. Quenched and tempered can increase the strength and toughness of the shank adapter by heating and cooling at a suitable temperature. Surface treatment can adopt methods such as quenching, nitriding, or coating to improve the wear and corrosion resistance of En40B shank adapters.
Understanding the heat treatment process for shank adapters is crucial to ensure final product quality and performance for shank adapter manufacturers. Only with a deeper understanding of the heat treatment process of shank adapters for different materials can we produce shank adapters that better meet people’s needs and improve the service life of shank adapters.
