The drill rod is a rock drilling tool mainly used to transmit the impact energy of the rock drill and is not directly used as a tool for breaking rocks. They play an integral role in various industrial fields such as construction, manufacturing, and infrastructure. In the manufacturing process of drill rods, choosing the appropriate material is crucial to ensure product quality and performance.

The manufacturing material of the drill rod is mainly hollow steel, which comes in various types due to the different needs of rock drilling. The classification according to the purpose is as follows.

Types of hollow steel

1. Hollow steel for manufacturing down-the-hole drill rods

For rock drilling operations with rock hole depth below 8m, most drilling works are carried out by single drill rods. Therefore,  from the stiffness, the effect of discharging powder, drilling speed, and other aspects of the drill rod, the hollow steel for such purposes adopts a regular hexagonal section. Because of the wide application range of DTH rock drilling, the requirements for drilling equipment, and other rock drilling conditions are low, hollow steel occupies a large proportion in drilling and blasting engineering, accounting for more than 70% of the total hollow steel consumption.

2. Hollow steel for the manufacturing of threaded extension rods for drilling medium and deep rock holes

For the rock drilling operation of drilling deep rock holes of more than 8m, it is necessary to drill by connecting multiple drill rods. Hollow steel with a circular section is often used to solve the connection structure and roll thread at both ends. To reduce the single weight of the drill rod and improve the power transfer efficiency of the rock drill, hollow steel with a normal hexagonal section is also used when the strength and stiffness permit. The amount of this kind of hollow steel accounts for about 20%-30% of the whole.

3. Hollow steel for manufacturing special purpose drill rods

Such as flexible drill rods and coal drill rods the amount of which is less.

Commonly used steel types for making drill rods

1. Carbon hollow steel

This category is mainly carbon tool steel with carbon content in the range of 0.7% to 1.00%, including improving the hardenability of steel, grain refinement, toughness, and adding 0.15% ~ 0.3% vanadium vanadium-containing high-carbon tool steel. This type of steel is mainly used to make small-section tapered drill rods or integral drill rods and is used with light rock drills to drill shallow holes in soft rocks.

2. Alloy hollow steel

If classified by carbon content, there are high carbon, medium carbon, and low carbon three categories; according to the classification of alloying elements, there are chromium-molybdenum steel, chromium-nickel-molybdenum steel, and chromium-manganese-molybdenum steel and so on.

High carbon chromium molybdenum steel contains about 1% chromium and 0.2%~0.4% molybdenum, and its main feature is its high hardenability.

The most commonly used representative steel grade of medium-carbon chromium-nickel-molybdenum steel is 30CrNi3Mo. Due to the combination of chromium and nickel elements, this steel has good stress, plasticity, and toughness under the condition of conditioning.

Medium-carbon chromium-manganese-molybdenum steel has high fatigue strength and impact toughness, and its hot rolled state of the comprehensive mechanical properties, forging properties, and hardenability are good, the air-cooled state to obtain martensitic organization.

The carbon content of low-carbon chromium-nickel-molybdenum steel is 0.13%~0.25%, which belongs to carburizing steel. The use of this steel type to manufacture drill rods requires surface carburizing treatment.

When selecting materials for drill rod manufacturing, there are some things to consider, such as the application environment (temperature, corrosivity), load requirements, and manufacturing process. Different materials will show various properties under varying conditions, so it is necessary to make a reasonable choice according to the actual situation. In addition, the manufacturing process of the drill rod is also critical, affecting the quality and performance of the final product.

In short, the choice of material for drill rods directly affects the performance, service life, and application range of drill rods. When manufacturing drill rods, choosing the appropriate material according to the specific application requirements can ensure the high quality and stable performance of drill rods.