HSS & Co. - Basic materials for taps

Every tap and die you handle began its journey as a simple, glowing piece of steel. If you haven’t paused to think about it, now’s the perfect moment to do so. What happens to a screw tap before it lands in your toolbox plays a crucial role in the quality and seamless functioning of your work.

You’ll fully grasp the significance of the steel used in screw taps when one of lesser quality snaps mid-use. To make smarter purchasing choices moving forward, let’s explore the primary material for drills, taps, and step drills: High-Speed Steel (HSS). We’ll look into its characteristics, the differences in how it’s manufactured, and how those differences are reflected in tool names.

What Properties Should the Steel for Screw Taps Have?

Before we dive deeper, let’s consider the demands placed on the steel used to craft taps.

Essentially, these can be boiled down to three key areas:

• Resistance to deformation
• Break resistance
• Wear behavior

Screw taps are precision tools that can endure extreme stresses. They mustn’t permanently distort under pressure but instead maintain their original shape. They also need to be robust enough to withstand breaking under strain. Lastly, taps should exhibit excellent wear resistance, reducing wear and tear over time.

Not All Steel is Created Equal: HSS & Beyond

In casual conversation, we often refer to “steel” without specifying its type. This overlooks the wide variety within this category. All steel starts with a carbon-iron alloy foundation. However, beyond that, factors like composition, purity, and production methods result in a vast range of steels. The steel used in high-quality taps falls under the category of High-Speed Steels (HSS), which itself has multiple variations. Let’s examine the distinctions between these types.

Alloying Elements

The type and concentration of alloying elements significantly impact High-Speed Steel’s properties. Each element brings both advantages and drawbacks that require careful consideration. For instance, while cobalt alloying boosts HSS’s heat resistance, it also raises the likelihood of breakage.

Common alloy types for High-Speed Steels include:

• Base alloy: Standard HSS with typical temperature and wear resistance.
• Vanadium-alloyed: Offers enhanced wear resistance.
• Cobalt-alloyed: Delivers greater hardness and heat resistance.
• Vanadium-cobalt alloyed: Provides improved wear resistance and heat resistance but reduced toughness.
• Reduced tungsten, increased vanadium: Highly wear-resistant but with lower heat resistance.

Manufacturing Processes

There are two main methods for producing HSS. The more widely used approach is melting metallurgical production. Here, steel is melted, mixed with desired alloying elements, and cast into bars. Subsequent processing steps aim to evenly distribute the components and improve the steel’s purity. The material is then rolled and forged.

The powder metallurgical production of HSS is less common. In this method, molten steel is atomized and hot isostatically pressed. This enables higher alloying concentrations and results in a particularly uniform composition of HSS.

High-Speed Steel also undergoes a heat treatment, which grants the necessary heat resistance and strength. The HSS is first heated, cooled, and then reheated in a process called tempering.

Further Processing

After initial production, various techniques can be applied to HSS to achieve additional desired properties. These include mechanical modifications like grinding, surface treatments such as nitriding, or coatings.

High-Speed Steel (HSS): The Material for Drills

With an understanding of what constitutes HSS, we can see why it provides excellent heat resistance, supports fast cutting speeds, and exhibits solid break resistance. Within the broader category of High-Speed Steels, there are many variants identifiable by specific codes. Let’s explore some of the most common ones.

HSS

HSS stands for High-Speed Steel. This is the standard form without any special alloying elements or treatments. It’s a versatile material, well-suited for general applications without extreme demands.

HSSE

HSSE refers to a screw tap made from HSS with an extra alloy, typically cobalt. HSSE taps are exceptionally hard, with good heat resistance. However, they come with a higher risk of breakage.

HSSE-V3

The V3 suffix indicates an added vanadium content along with cobalt. Vanadium increases hardness and reduces wear but is seldom used in concentrations exceeding 3% due to challenges during manufacturing.

HSSG

The G in HSSG doesn’t represent an alloying element but the manufacturing process. It stands for “ground.” HSSG taps are produced through grinding processes, making them highly precise. Grinding also extends tool life and improves chip evacuation.

HSSE-PM

The PM signifies powder metallurgy, a production method discussed earlier. Screw taps made from this type of HSS show remarkable wear resistance, heat resistance, and pressure resistance. They’re also tough and easy to grind. Their smooth surface after grinding minimizes friction when cutting threads.

Which HSS Steel is Best for Taps?

By now, you may be wondering which steel is truly the best. Generally, always ensure that HSS is used instead of inferior tool steel. Within the HSS category, no single variant stands out as the absolute best. Instead, each type is “the best” for its specific application. Therefore, always choose based on your needs.

Understanding the nuances of HSS can help you make more informed decisions. Whether you’re working on delicate projects or heavy-duty tasks, selecting the right HSS variant will ensure your tools perform optimally and last longer.