Which drill for which type of steel? HSS-Co 5 and HSS-Co 8 in comparison

HSS stands for High Speed Steel or high-performance high-speed steel. This is a steel alloy that retains its hardness and cutting ability even at high cutting speeds. This is extremely important as high temperatures are generated at the cutting edges during machining. HSS is a proven material in metalworking that has been used for many years.

You can find more information about HSS in our article "High-speed steel: From which steel are drills made of".

The suffix "Co 5" means that the steel has a cobalt content of 5 %. This proportion ensures:

Higher hot hardness

HSS-Co 5 retains its dimensional stability even at high temperatures above 600 °C.

Increased toughness

Despite the increased hardness, good toughness is retained. The risk of breakage is also reduced.

Cobalt ensures that the steel becomes more heat-resistant. This means that the cutting edges retain their hardness and cutting performance even during intense heating caused by friction and the machining process.

This makes it particularly suitable for drilling in tough or poorly thermally conductive materials such as stainless steel or in difficult-to-machine materials with a strength of up to 1,100 N/mm².

Longer tool life

HSS-Co 5 tools show less wear under continuous load than HSS tools, which leads to a longer tool life.

Reduced chipping and burr formation

Thanks to the high stability of the cutting edges, cleaner results are achieved even with difficult-to-machine materials.

Universal applicability

Mild steel, stainless steel, aluminium, brass or plastic - HSS-Co 5 is an all-rounder, especially in manual and machine operation. The material is frequently used for twist drills, countersinks, step drills and taps.

Improved toughness

HSS-Co 5 is ideal for interrupted cuts and difficult-to-machine materials.

Better wear resistance

Tools made from HSS-Co 5 are more resistant to abrasion and wear. This leads to a longer tool life.

HSS-Co 5 is not always the better choice. An HSS drill is often sufficient for very soft materials (e.g. plastic or simple non-ferrous metals).

HSS-Co 5 is suitable when durability, material versatility and process reliability are important.

The slightly higher price is quickly offset by the longer tool life and better results - especially in demanding applications (stainless steel).

When do you not need HSS-Co 5?

A standard HSS drill is normally sufficient for machining mild steel, soft metals (such as aluminium and copper) or plastics, as it is more cost-effective. Using HSS-Co 5 would not bring any advantage here.

HSS-Co 8 is a cobalt-alloyed high-speed steel with a cobalt content of 8 %, which is used to increase hot hardness and tempering resistance.

The higher cobalt content leads to:

Very high high-temperature strength

The steel remains efficient even at temperatures above 650 °C.

Increased wear resistance

Perfect for long tool life in complex machining operations.

Less toughness

The steel is more brittle than HSS-Co 5, which can lead to chipping if the cut is interrupted.

Typical applications

High-alloy and difficult-to-machine materials (e.g. titanium, stainless steels), for applications with very high cutting speeds and dry machining or poor cooling.

Select HSS-Co 5 if:

• You machine a variety of materials.
• Tools should be inexpensive but durable.
• there may be interrupted cuts.

Choose HSS-Co 8 if:

• You are machining difficult-to-cut materials (e.g. high-alloy stainless steels, etc.).
• You have to work at very high temperatures or without cooling.
• Maximum tool life is required due to continuous cutting.

The price of HSS co-drills is higher - but only at first glance.

The longer service life means that you have to buy more drills less frequently. In addition, the need for spare parts is lower (e.g. chucks if non-round cheap drills are used).

HSS-Co tools are also easy to resharpen. They can be reused and are therefore much more sustainable than inexpensive drills.

Here are a few practical tips to help you realise the full potential of your HSS-Co 5 or HSS-Co 8 tools:

• Use the right cutting speed - cutting too slowly will lead to galling, if you cut too fast it can lead to overheating
• Use cooling - especially for longer holes in stainless steel or cast iron. Depending on the material, a single drop of cutting oil can make the difference between a dull drill and a long-lasting tool.
• Regularly deburr or resharpen twist drills - this way you can extend the service life of your tool
• Clean storage - keep drills separate, dry, not loose in the box (otherwise the coating or cutting edges may be damaged).
• Use centre drills in advance on smooth surfaces to prevent slipping.

With the right combination of drilling speed, cooling and tool selection, service life and results can be significantly improved.

Coated HSS drills are a popular alternative to HSS-Co. These are particularly common:

• TiN coating: Golden yellow lustre, ensures less friction and a harder surface. Ideal for unalloyed and alloyed steels, aluminium and non-ferrous metals.
• TiAlN coating: Dark grey to purple, offers very high heat resistance and is particularly suitable for dry machining or high-strength materials.

Both coatings significantly increase tool life and reduce wear. They are a cost-effective alternative to HSS-Co and may be the better choice depending on the material and conditions of use.

Find out more about coatings in our blog post TiN, TiAlN, AlTiN...a comparison of coatings.

Are HSS-Co drills better than coated drills?

Whether HSS-Co drills or coated HSS drills (with TiN or TiAlN) are better depends very much on the application, the material and the frequency of use.

The more often you will be drilling in stainless steel, for example, an HSS-Co 5 drills will make more sense.

Whether in the workshop, on the construction site or in industry - anyone who regularly drills with cobalt-containing HSS drills (HSS-Co 5 or Co 8) will notice the difference: in terms of quality, tool life and also costs.

HSS-Co 5 tools are a good choice if you regularly work with demanding, difficult-to-cut materials. The higher hot hardness and wear resistance due to the cobalt content leads to longer tool life, more precise results and more efficient machining. Although they are slightly more expensive to purchase than HSS tools, they quickly pay for themselves thanks to their durability and performance in the right applications.

The choice between HSS-Co 5 and HSS-Co 8 depends on the application. HSS-Co 5 impresses with its toughness and versatility, while HSS-Co 8 offers extreme heat resistance and a long tool life - but at the expense of breakage resistance and higher costs. To summarize, HSS-Co 5 is suitable for stainless steel and HSS-Co 5 for titanium-alloyed steels.