High Strength Steel is becoming a standard in new vehicle frame and structural components and as an autobody technician you need to know how to identify and correctly repair these parts correctly or you can introduce problems which may lead to risk of injury in the case of an accident.
High Strength Steel comes in a variety of levels of hardness. The harder the steel the more difficult it is to repair and weld. The benefit of high strength steel is that it can replace standard steel of greater thickness.
The common tensile strength of steel you may find in the average automotive body includes 270 MPa, 440 MPa, 590 MPa, 980 MPa and 1,500 MPa. The higher the number the stronger or harder the steel.
The most common use for 1,500 MPa Steel is door pillars. Sometimes only the center pillar is made of this material but you may find the entire opening from the rocker panels to the roof rails are made of this extremely high strength steel.
The rest of the vehicle’s frame will normally be made of a lower grade steel.. normally 590 MPa but this material must also be cared for to manufacturers specs.
Performing Frame Repairs on High Strength Steel
When making repairs on high strength steel parts you must follow manufacturer guidelines to preserve the structural integrity of the steel components.
NEVER HEAT PARTS WITH A TORCH
Any high strength steel part that must be heated during frame pulling must be removed and replaced at its original spot welds. If you heat the part near adjoining parts you can damage those parts too so the main thing to do is NEVER HEAT HIGH STRENGTH STEEL WITH A TORCH TO REPAIR IT.
Never attempt to repair 1500 MPa Steel because it can crack or change the structure of the steel.
Welding can also cause excessive heat and when you are welding two parts of different tensile strengths you may find it difficult to complete the job with your average MIG welder. Many manufacturers suggest that you use a spot welder to complete all welds that are reachable and then spot weld with a pulse MIG welder for best results.
Sectioning and Welding High Strength Steel Frame Parts
It is normally not recommended that you section any part made of high strength steel. The preferred method is to remove the part back to its original spot welds and replace it completely.
If you are ordering a front or rear clip from your junkyard or making the section yourself from a donor car you should do so with care not to heat the part with a torch or grinder.
Drill out the spot welds to detach the parts and keep grinding to a minimum.
Depending on the part you may be required to place 2 spot welds close together to achieve the same attachment strength that the original factory welds had.
Again do not section 1,500 MPa Steel unless you know exactly what and why you are doing it.
Final Note about High Strength Steel Repair
This guide is only an overview of what you need to learn about High Strength Steel. To work with this material correctly you may need detailed training from a manufacturer’s representative or instructional materials that give the exact methods for the specific vehicle and part you are trying to repair.
Making repairs on these new materials can require new tools and training. If you do not feel you are up to the job farm the work out to a shop that has been certified by the OEM.