Working With Boron-Alloyed Steel - What's In A Name? (UHSS)

Vehicle makers each have there own way of organizing their repair information. The names of the materials and even the names of different parts of vehicles may vary.

376(Figure 1) This chart shows that steel types can have a wide range of strength.

Within the collision repair industry, we use terms like advanced high-strength steel (AHSS), ultra-high-strength steel (UHSS), and Boron steel. What does AHSS mean? It has no meaning in regards to repairs, all it tells us is how the steel is made. What about UHSS? This means that the steel is probably 600 MPa and higher, but it doesn't give us any more information. (See Figure 1) Boron is a term that is often used to describe all high-strength steel, but it does not tell us enough information to make a informed decision. These terms are appropriate for general conversation, however, when it comes to repair plans, we need a lot more information to help us make repair decisions.

With steel that is 600-800 MPa, there are some possibilities for repairs. However, it is usually limited to straightening minor damage. Once the steel goes over 800 MPa, repair options are usually limited to part replacement at factory seams. So when building a repair plan, you need to look into the repair information and look for the MPa rating of the steel, not just the name.  

13159(Figure 2) Chrysler use color-coded images to identify the different steel strengths in their collision repair information. (Image Courtesy of Chrysler)

Nissan repair information, for example, calls out 370-590 MPa steel as high-strength steel. Nissan also calls out 790-1,350 MPa steel as high-strength steel. So in this example, the name called out in the repair information would not tell you what repair options are possible. 

Chrysler calls out 600 MPa steel and above as very high-strength steel, which is shown in red in this example. (See Figure 2) In the repair information, it states that "very high strength steel" has "very limited repairablity" which means it will be difficult to straighten damage. Chrysler also states that this steel should only be replaced at a factory seam using OE defined procedures.

As you can see, looking a little farther than just knowing a name can change the repair options that are available and change how a vehicle is repaired.

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