About wear steel

At Partrex, we are careful and selective when choosing which wear steel we sell and what we recommend to you as a customer depending on what you will use the steel for. We weigh in all crucial aspects based on the area of use when choosing wear steel: wear resistance, toughness, weldability and price.

Various brands of hardened wear steels abound in the market, but most wear steels used in buckets, plows and flatbeds in Sweden are in hardened boron steel. Examples of brands of hardened boron steels are Hardox, Swebor, Bruxite, Borox, Olofsfors, RAEX, Fora and Dillidur. Different producers may differ in the quality of their production processes and all manufacturers may in individual batches fail with the quality of the steel. But many manufacturers today have equally good manufacturing processes and a consistent level of quality. However, they may differ in how they have adjusted their boron steel alloys on individual products and dimensions, for example, the carbon content of the steel. Particularly on thicker steels (+40 mm), manufacturers also differ in how they name their wear steels. For example, wear steel marked "500" can have different qualities at different manufacturers that, among other things, affect the weldability. From the manufacturers' data sheets, you can read a lot about the steel's weldability and wear resistance.

Common to all hardened boron steels, regardless of brand, is that:

Increased hardness gives increased resistance to abrasive wear (buckets and plow steel wear).
Lower carbon and alloy content provide better weldability.

The latter is a decisive reason for the boron steel's great success as a wear steel. With only 0.0035% boron, added to the steel melt in the right way, a relatively low-alloy steel with good weldability and good hardenability is obtained at a reasonable price. Without this fantastic discovery, our buckets, flatbeds and plow steel would be both heavier and more expensive. Swedish steel producers have also been pioneers in the field of boron steel since the 1970s, which has also influenced the design of Swedish construction machine tools. Today, boron alloys are used by steel mills all over the world. Partrex sells wear steel products specially developed and selected for Swedish buckets, plows and flatbeds. Ask us and we will help you make the right steel choice based on your use and need.

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Wear steels such as bucket steel / cutting edge and wear plate are more difficult to weld than ordinary weldable structural steels, such as S355. This is because wear steel has good hardenability. Your biggest enemies when welding wear steel are moisture and too short transitions between unhardened and hardened steel at your weld. Therefore, there are some things to keep in mind when welding wear steel such as bucket steel / cutting edge and wear plate.

The mechanical qualities of wear steel change a lot with temperature changes in the steel. The hardened steel has a very high yield strength and low impact resistance. When the same steel is normalized (hardened), it shrinks slightly in size and has a low yield strength. The difference is due to the fact that the structure of the steel inside has changed from martensite (hardened) to ferrite (unhardened). If the transition from martensite to ferrite in the wear steel is short, there will be a crack-prone "scarring" that can crack immediately after the weld has cooled, a few days later or when it begins to load.

Soft hardness transitions at the weld - let the heat spread

Directly at the weld itself, the bucket steel or wear plate becomes unhardened and mostly ferritic. In order for the transition to unhardened to not be too short, the heat from the joint must be spread in the wear steel, ie do not weld too quickly and do not let the steel cool too much before you lay the next joint. But at the same time keep in mind that the wear steel loses its wear resistance when it softens so you must not burn too hard either. The balance with it is a craft that every welder must learn and it is a little different for different types of wear steel (depending on carbon content and alloy). A rule of thumb, however, is that the steel about 7-10 cm from the weld should be at about 150-200 degrees when you weld.

In order for the transition from hardened to unhardened to be smooth, the surrounding steel cannot be too cold. Thinner steel heats up quickly by the weld, but the thicker and larger it is, the more the steel cools against the weld and the more you may need to preheat the entire steel before welding. Also keep in mind that the steel can quickly cool below 150 degrees, for example when the bucket has to be turned, the steel may need to be preheated again before further welding.

How quickly the wear steel loses hardness with increasing temperature depends on its carbon content and alloy, but roughly it can be said that weldable wear steels begin to soften when they become above 200 degrees. The hardness does not disappear immediately and completely above 200 degrees, but the softening of eg wear steel with 0.27% carbon content begins approximately there and increases with increasing temperature and the time that the steel is above 200 degrees. At 900 degrees, the steel is red annealed and then the steel is as soft as it can be before it melts. Even if reduced hardness reduces the wear resistance of the steel, you should primarily prioritize a soft hardness transition so that you get a strong weld. Reduced wear resistance of the wear steel around the welds is usually preferable to cracked welds.

Moisture is the enemy of welding - keep it dry and clean

Your second enemy when welding, moisture, is everywhere present when you are going to weld. Moisture, ie water, is present in the air, on the steel, in dirt on the steel and in welding rods. Water consists of oxygen and hydrogen, it is the hydrogen that is the enemy of steel. When the steel melts, the hydrogen is drawn into the steel and when the steel solidifies, it can cause the steel to crack.

Things to keep in mind to minimize moisture when welding:

Store welding rods in tight and closed packaging,
Clean the welding surfaces from slag, paint and embers,
Preheat the bucket steel and wear plate with gas to drive away the moisture that is present on the surface,
Have low humidity in the room, ie ventilate (especially important if you often drive wet/snowy tools and machines into the workshop).

Wear steel and carbon equivalent

Manufacturers of bucket steel and wear plate generally state in their data sheets instructions for welding specific types of wear steel. How the steel reacts in heat, which directly affects the weldability, depends, as stated above, on its hardenability. The higher the carbon content and the higher the content of alloying elements, the more reactive in heat the steel is and the more difficult it is to weld. The data sheets usually state a value for weldability, the "carbon equivalent tent", a mathematical formula for estimating the weldability of steel. The higher the value of the carbon equivalent, the worse the weldability. The higher the carbon content and the higher the content of alloys the higher the carbon equivalent. For structural steel, the norm is that the carbon equivalent may be a maximum of 0.45. But the thicker the steel, the lower the carbon equivalent should be to have good welding properties. The carbon equivalent is not an exact science and therefore there are also different ways to calculate it. However, it is the carbon that mainly impairs the welding qualities, the alloying elements have less effect. The harder the wear steel is, the more carbon it usually contains and the deeper it is hardened, the greater the amount of alloying elements it usually contains. "Hardened" wear steels with high hardness are good for wear resistance, but for welding it is more difficult and becomes increasingly difficult with increasing thickness. To maximize both wear resistance and weldability in thicker steel, it is better with lower carbon content and higher alloy content than the other way around.

No standard for designations - look in the data sheets

For structural steels, there are standards and general designations for the steels that mean the same thing from different manufacturers. This is not the case with bucket steel and wear plate. What manufacturers call their wear steels and what they state about the hardness of the steel are different between the manufacturers, especially in thicknesses over about 35 mm. Some manufacturers, for example, have very high carbon contents in their 400 Brinell wear plates in thicker dimensions. This is to be able to achieve high hardness, but it destroys the weldability. The same manufacturer may also have wear plates called "450" which in the same thickness have a lower carbon content than their own "400". In order to compare the wear steels of different manufacturers regarding weldability, one should therefore look at the carbon and alloy contents in the data sheets.

Choice of wear steel

At Partrex, we are careful and conscious when we choose bucket steel / cutting edge and wear plate to be welded, especially in thicker dimensions. For cutting edge in 60 mm, for example, in which tooth adapters are to be welded, a carbon content of a maximum of 0.22% can be a good choice. Feel free to ask us for advice on what can be a good choice for how you should use the wear steel. Regarding the choice of welding wire and welding rods and recommended preheating temperatures, we recommend that you start from the manufacturer's data sheet for the type of steel in question.

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Hardest wins. The resistance of a steel to the abrasive wear of stone materials to which buckets, crushers, plowshares and flakes are exposed depends mostly on the hardness of the steel. When two surfaces wear against each other, the side with the hardest material will wear out the other more.

Hard minerals with sharp structures that are pulled over a steel surface under pressure grip the surface of the steel and tear it off gradually; just like sandpaper on a tape set. The harder the steel surface, the worse the mineral gets and the slower the steel wears.

The mineral that wear steel is most often worn down by in Sweden is quartz. Quartz is much harder than the hardest weldable steel that can be produced. Granite and gneiss are the rocks that are most crushed in Sweden and used in roads and foundations. These rocks are composed of several types of minerals where quartz is the largest component. Natural sand, which is still also extracted and used in Sweden, contains a very high content of quartz. However, the natural sand grains are grinded against each other for millennia in water so they do not tear the steel in the same way as crushed material with the same high quartz content does. The level of quartz in the rock varies between different quarries and even within the same quarry there can be large differences.

How quickly a bucket steel or a wear plate wears down, for example crushed granite, are mostly depending on:

The hardness of the steel.
The amount of quartz content of the granite.
The pressure which the steel and the stone material wear against each other.
The density of the contact surface between the steel and the stone material - finer material - more contact surface - faster wear.
The heat of friction and the ability of the steel to maintain its hardness at the temperature the friction heats it to.

In practice, there are many things that cause the above factors. For example:

A lot of rain gives wet crushed stone which becomes heavier and thus increases the pressure and the wear on, for example, the wear surfaces of the loader bucket.
Dry roads with cold snow gives high friction and poor cooling and therefore faster wear of the plow steel than sludge.
The design of the tool or, for example, the bucket tooth affects how the pressure of the stone material is distributed and thus the wear speed.
How the implement is driven affects wear a lot, sometimes most of all, due to the reasons described above.

In Sweden, we usually measure hardness of steel with Brinell (HBW). Hardness of minerals is usually given in the Mohs hardness scale. Mohs scale is 1 to 10 where 10 is the hardest. The hardest mineral is diamond (10). Quartz is at a hardness of 7 Mohs. The hardest possible hardened steel, which has a Brinell hardness of 700 HBW (approx.), corresponds to about 5.5 Mohs, in other words softer than quartz. On the other hand, tungsten carbide is 9 in hardness on the Mohs scale and therefore wears much more slowly than hardened wear steel, which is very useful in snow plow edges, for example.

Even if no hardened wear steel is harder than the quartz-containing stone you break or plow snow on top of, the steel's wear rate decreases with increasing steel hardness. In some cases, 50 HBW higher hardness can double the wear time of, for example, a cutting steel on a rock bucket. The lower the quartz level in the stone material, the more the wear time for each brinell increases. The higher the quartz level in the crushing material, the less difference each brinell makes. In such extreme stone materials, for example, the design of the excavator and the teeth and the machine operator's technology can be more important for the wear time of the steel than Brinell.

Frictional heat is an additional factor that can dramatically increase the wear of the steel. This is because hardened steel loses hardness when it reaches the temperature limit. For example, 500 brinell boron alloy wear steel begins to soften at about 200 degrees. Ordinary 600 brinell boron alloy steel begins to soften at about 175 degrees. This becomes apparent on plow steel that is driven against asphalt at high speed. The higher the speed and pressure, the higher the friction, the higher the temperature and thus the steel softens and it wears very quickly.

Choosing the right steel is a consideration between different factors. Depending on what and how it is going to be used. That decision also includes the question of weldability.

Ask us about the choice of wear steel according to your specific needs and conditions and we will help you find a good solution. It all depends on how the wear steel is supposed to be used.

What is cemented carbide?

Carbide consists of tungsten carbide as a hard substance and cobalt as a binder metal. The cemented carbide is extremely hard, about 2600 Vickers, many times harder than the hardest possible hardened wear steel (about 650 Vickers) and also harder than most rock minerals, including quartz and porphyry, which are very common minerals in our Nordic roadways. On the mineral hardness scale Moh, where diamond is the hardest (10), quartz and porphyry are at 7 Moh and the cemented carbide is about 9 Moh, in other words harder than the hardest in the road surface, which gives carbide plows a very long wear time. The hardest wear steels in HBW600 are at about 5.5 Moh, ie softer than the material in the road surfaces, which means that the wear steel wears quickly.

Carbide has for long been used in mechanical processing, for example in concrete drills. Now the cemented carbide has also begun to have an impact on snow removal. More and more people are switching to plows with cemented carbide instead of hardened wear steels. The many advantages of cemented carbide edges simply provide better economy. More kilometers of plowing per crown for the plow edges, less overhead on steel replacements and reduced risk of damage to the plow that arises due to worn steel and incorrect plow settings. All in all, great advantages in an industry with a constantly squeezed economy.

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