Selection of Heat Treatment Process for Threaded Extension Rod

Table of Contents

In the field of metal processing, the heat treatment process is a crucial step to enhance material performance. As a tool used in drilling, rock drilling, and other projects, the quality and service life of threaded extension rods directly affects the safety and efficiency of the project. Choosing the appropriate heat treatment process is crucial to ensure strength, toughness, and durability. This article will delve into the detailed process of selecting the proper heat treatment for threaded extension rods, considering material type and performance requirements. The aim is to enhance their overall performance and service life.

Understand the material types and performance requirements of threaded extension rods

First, choosing the appropriate heat treatment process requires understanding the type of material used in the threaded extension rod and the required performance requirements. Common threaded extension rod materials include carbon steel, alloy steel, and stainless steel. These materials’ chemical composition and microstructure determine their mechanical properties and heat treatment response. Therefore, comprehending the material’s chemical composition, microstructure, and performance requirements, such as the needed strength, toughness, and corrosion resistance, forms the foundation for selecting an appropriate heat treatment process.

extension rod

Selection of suitable heat treatment process

Depending on the material type and performance requirements, selecting the appropriate heat treatment process is the key to improving the performance of the threaded extension rod. Typical heat treatment processes include quenching, tempering, surface treatment, etc. The selection and application of these processes should be optimized based on the material type and performance requirements. For example, for high carbon steel or alloy steel materials, quenching and tempering treatments can significantly improve their hardness and strength, while for stainless steel materials, choosing appropriate surface treatments can enhance their corrosion resistance.

Control of heat treatment process parameters

The control of heat treatment process parameters is crucial to ensure the performance of threaded extension rods. Key parameters include heating temperature, holding time, cooling rate, etc. The selection and control of these parameters will directly affect the microstructure and mechanical properties of the threaded extension rod. Therefore, precise control of these parameters is the key to achieving the best heat treatment results.

Post-heat treatment processing and quality control

Post-heat treatment handling and quality control are equally crucial to ensure the performance and stability of threaded extension rods. It involves grinding, polishing, testing, and other processes applied to the threaded extension rod to guarantee its surface quality and dimensional accuracy. Additionally, regular maintenance and calibration of heat treatment equipment are essential to ensure the stability and accuracy of process parameters.

The best choice for threaded extension rod production process

Comprehensive domestic and foreign decades of research and production practice of threaded extension rods, the best production process route of the threaded extension rod is low-carbon high-strength alloy hollow steel, after forming and processing for overall carburizing treatment, controlled cooling in a special cooling tank, both ends re-quenched by medium-frequency heating and low-temperature tempering, and then the inner and outer surfaces are cleaned, followed by effective anti-corrosion treatment.

Carburizing process

The overall carburizing treatment of threaded extension rods requires a well-deep gas carburizing furnace. Drip injection gas carburizing adopts many infusion liquid formulas, generally methanol + acetone; kerosene + air has the lowest cost, but the carbon content on the surface is high, and carbon black is prone to appear. It is ideal to use methanol + acetyl acetate as the drip solution formulation and it is easy to control the carbon potential of the carburizing process.

The control of carbon content on the surface of the carburized layer is very important for threaded extension rods. The control of carbon content on the surface of the carburized layer is often controlled by the carbon potential in the furnace. The level of carbon potential is related to the selected infusion solution formula and also to the carburizing temperature. The carburizing temperature is high, the carbon potential is high, and the carburizing speed is fast; the temperature is low, the carbon potential is low, and the carburizing speed is slightly lower.

The application of computer control technology in the carburizing heat treatment process has solved a series of carburizing heat treatment quality control problems. It can be controlled by a microcomputer to ensure the high quality of carburizing drill rods.

Cooling after carburizing

The main purpose of controlled cooling after carburizing is to ensure that the drill rod obtains a relatively uniform hardness and prevent excessive oxidation or decarburization of the drill rod surface during the cooling process. The special carburizing furnace for foreign threaded extension rods is equipped with a specially designed control cooling device, which can control and adjust different cooling speeds to ensure the cooling requirements of different diameters and meet the specified hardness requirements and organizational requirements.

The long drill rod will have a large bending after cooling by the overall carburizing, which adds a lot of difficulties to drill rod straightening, and after cooling to ensure good rigidity and elasticity of drill rod, the required hardness is around HRC40, and the bent HRC40 drill rod is difficult to straighten, which increases the workload of straightening. High volume production should be equipped with high efficiency straightening machine.

Heat treatment after carburizing

After the overall carburizing of the drill rod, to improve the wear resistance and fatigue strength of the threaded parts at both ends, quenching and low-temperature tempering treatment should be carried out. It is best to use intermediate frequency induction heating for quenching heating. The heating length is slightly longer than the transition groove (or handle groove). After quenching, the surface hardness should be ≥ HRC58; for tempering, it is recommended to use a low-temperature salt bath furnace. After quenching and tempering, the drill rod is subjected to final fine straightening, surface cleaning, and anti-corrosion treatment.


Choosing a suitable heat treatment process for threaded extension rods requires a comprehensive consideration of many factors. By gaining a profound understanding of material characteristics, continually optimizing process parameters, and enhancing quality control standards, the threaded extension rods’ performance and service life can be further improved to meet the requirements of various application scenarios. Simultaneously, keeping an eye on industry trends and technological innovations and consistently enhancing and developing new heat treatment technologies are crucial avenues for advancing the continuous development of threaded extension rod heat treatment processes.

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