Effect of Boron in welding.

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Boron is a lightweight element that has an enormous impact. It’s an essential mineral in the body and is added to many materials to alter their properties. In this post, we look at the effects of boron in carbon steel, where its presence can be a blessing or a curse.

The main benefit of adding boron to steel is hardenability, where minute amounts significantly improve hardness.

Depending on the type of steel and carbon content, the amount of boron can be as little as 3ppm to make a difference. Other substances can be added to steel to alter its characteristics, however using boron over other elements can improve steel properties at relatively low tempering temperatures, helping to reduce energy costs. Another benefit of boron is better machinability when compared with steels that have a similar hardness.

These properties mean that boron-containing carbon steels are used where the base steel meets most properties, such as wear resistance, but the hardenability is too low. In this case, boron is a less expensive option than using a different alloy. One of the main uses for boron steel is in the automotive industry, particularly within the European market. Safety bars, inner pillars and dash panels have used boron-containing steel.

Minute quantities of boron have a significant impact.

Problems arise when the amount of boron increases, or when the steel is used for load-bearing structures.

If too much boron is present, it segregates from the steel and settles in the grain boundaries, which lowers hardenability, reduces toughness and causes embrittlement.

It can also cause problems in welding. This is where the boron, due to its low melting point, congregates in the centre of the weld when cooling and causes a segregation crack.

Welding issues, lowered elasticity and potential deformation of large structures, could result in the collapse of bridges, buildings and drilling platforms. This is why there are regulations governing the amount of boron present in specified types of steel.

In the EU, low alloyed structural steel must not contain more than 8ppm boron – and for some applications this reduces to 5ppm.

We can see that in some cases boron is required, and in some it absolutely must not be present. The problem is that it’s not always declared on the certificate of conformance for the raw steel. And a simple material mix-up could have dire consequences if boron steel is used in the wrong application. Today’s complex supply chains can make it more likely that boron will end up in the wrong material.

The safest solution is to check incoming carbon steel yourself.

Analysis of boron in steel

In the past, boron has been relatively difficult to analyze. It has low mass, making it hard to detect, and you had to rely on destructive techniques that involved grinding and dissolving samples. Optical Emission Spectroscopy (OES) is a relatively simple technique that allows you to measure the steel directly without extensive preparation or the use of harsh chemicals. The only preparation required is to ensure the sample surface is completely flat before the measurement is taken.

Custody: Hitachi.