Boron in Steel – Definition and Applications

At BorTec, we make steel harder and wear resistant by diffusing boron into the surface layer of the material. But did you know that boron can also act as an alloying element in steel? It is one of the most useful alloying elements and can be found in many other materials, among which is steel. There, boron is used to significantly enhance hardenability and wear resistance.

Differences between boronizing and boron steel

The main difference between boronizing and boron steel is the degree in which boron is diffused into the material. When it comes to boronizing, the surface layer is coated in an agent (such as BoroCoat®) to change only the outer case of the material. This means that the core is left untouched by boron. Even a small amount of boron can crucially improve hardenability; concentrations of around 0.0015% to 0.0030% are accepted as the peak amount, but can vary depending on the hardening technique. 

Boron steel, on the other hand, contains boron in the entirety of the material as opposed to merely the surface layer. This means that the core contains boron as well. As an alloy, the amount of boron added to the material can vary, depending on how much hardness is required. Boron steel typically has inferior forging qualities and ductility in comparison to steels that do not contain boron. 

When it comes to deciding between boronized steel and boron steel, there is no universally correct answer. It depends on the end-use and application which material will fit best. While they both provide hardness, boron steel tends to be more brittle due to its through and through hardness. Boronized steel retains its soft core (assuming that the original material would count as such) and display better ductility. Futhermore, in boron steel, boron has to be worked into the material as an alloy, making it more suitable for parts that are to be made and formed. When it comes to already existing steel parts, boronizing would be the wiser choice because you only apply additional coating. It is not necessary to diffuse boron any deeper than a few nanometers into the surface. 

Which steel types can be alloyed with boron?

Boron can be added to low alloyed and unalloyed steels to increase their hardness. It can also be found in austenitic steels to improve their high-temperature strength. It prevents the formation of pearlite and ferrite structures within the material, causing increased hardness and strength. 

One of the most common boron steels is ferroboron, an alloy made of ferritic steel and relatively high levels of boron. They range between 12% and 24%, depending on the steelmaking practice. Ferroboron is known for its high hardness, wear resistance and other physical, chemical, mechanical and metallurgical properties. 

Boron is also found in another ferrous material other than steel. It is a key element in Neodymium magnets (FeNdB), the most common rare-earth magnet. It is made of neodymium, iron and boron, and it is known for being a very strong permanent magnet.