Vehicle manufacturers are once more asking us to become metallurgists. Without an understanding of the changes they’re incorporating into new vehicles, we in the collision business ultimately may compromise the safety of our customers and the integrity of their vehicles.
What’s the deal with steel? One consequence of strict government-mandated Corporate Average Fuel Economy (CAFE) standards will be a change in construction materials. As manufacturers strive to meet the 2016 requirement of 37.8 miles per gallon, structural integrity, safety and weight considerations will all come into play – which directly impact what the vehicle is made of.
Critical structural components will no longer be constructed of the mild steel that was once the norm. Ultra High Strength Steels (UHSS) with a yield strength or MPa of 800 or more will be one of the mainstays of vehicle design. Currently, repair of this material is not even considered.
Technicians, estimators and insurers need to understand that identification and reparability will be critical factors when a vehicle comes into the shop. Access to proper, up-to-date OE information will be
required before repair/replace decisions are made.
Decisions take time, and time cuts into productivity, profit and customer satisfaction. And what if you’re wrong? Can you really afford to do a job twice when you’re only getting paid once? Information is the name of the game in today’s world of complex vehicles.
There is no substitute for having manufacturers’ information readily available. OE information is the gold standard for material identification. Here are some manufacturers’ diagrams and information on vehicles that incorporate UHSS.
Always refer to ALLDATA Collision for safety procedures, identification of material types, recommended refinish materials, removal and installation procedures. Always refer to the manufacturer for questions relating to applicable or non-applicable warranty repair information.
The bodywork is made up of a number of different steels to improve fuel economy and provide optimal protection in the event of a collision. The types of steel in this section are High Strength Steel (HSS), which has a higher tensile strength and yield point than ordinary steel sheet. The yield point increases when it’s heat treated. HSS steel can be more difficult to align than ordinary steel plate.
When using an alignment bench, HSS components can cause problems if the counterhold is not fully tightened. Note how the bodywork reacts to tension, and ensure that only the deformed area moves.
NOTE: HSS steel must not be heat aligned.
Boron steel is in the same group as HSS steel. In Figures 1-3, the components marked in black are manufactured in boron steel, and the gray/dark gray sections are HSS with a yield point above 340 MPa and therefore must be treated with extra care during repair.
Boron steel is high tensile with a high breaking point. When replacing boron steel components, the welds cannot be drilled. Grind or plasma cut instead. It has good tolerance for welding, and it cannot be galvanized during manufacture. These components must be rust-proofed extra thoroughly.
NOTE: Boron steel must not be bent or heated.
NOTE: Boron steel can only be joined where indicated in the method. Mark carefully using a template. Use a cutting disc or plasma cutter.
Steel can be divided into further subgroups based on the yield point, or the force required to deform the steel. These groups are:
HS (High Strength Steel)
Steel with a yield point between 220 to 450 MPa (marked light gray in the illustration).
There are three main types of steel within this group:
1. Phosphorous-alloy steel
This steel has a higher strength due to the use of phosphorous alloy.
2. HSLA steel (High Strength Low Alloy)
This is a low alloy steel, where alloys such as vanadium, niobium or titanium are used to increase the yield strength.
3. DP steel (Dual Phase)
This steel is strengthened by heat treatment during manufacture. A two-phase structure of iron and carbon is formed. DP steel will lose its strength if it’s exposed to temperatures exceeding 300 °C.
EHS (Extra High Strength Steel)
EHS has a yield point between 450 and 800 MPa. It’s light gray in the illustration. Both HSLA and DP steel are within this group, although the strength has been increased through the addition of greater alloy substances.
UHS (Ultra High Strength Steel)
UHS has a yield point between 800 and 1400 MPa. UHS is dark gray in the illustration. There are two main types of steel within this group:
1. DP steel
The strength is even higher due to an advanced manufacturing process and the greater quantities of alloys.
2. Boron steel
The addition of boron gives this steel greater strength. Boron steel also contains relatively high quantities of carbon. The profiles of the sheets are formed between a press and pad while the metal is red hot. The material also hardens here. These sections must not be straightened because of their extremely high strength.
NOTE: These repair/service procedures are excerpted from information published by the vehicle manufacturer and are intended for the purpose of promoting OE collision repair information to trained, professional technicians with the knowledge, tools and equipment to do the job properly and safely. Before attempting any repairs described, refer to the complete article in ALLDATA Collision S3500. It’s recommended that these procedures not be performed by “do-it-yourselfers.”
Dan Espersen is ALLDATA’s senior collision program manager, holds an AA degree in automotive technology, and has 46 years of experience in the automotive industry, 19 in collision.