There are eight main columns in this matrix. The first three columns are used to explain the type of steel that is being referenced. The first column identifies the steel ID stamping symbol or International Organization for Standardization (ISO) symbol for the steel. The second column identifies the grade of steel, such as mild, laminated, dual phase, or boron steel. The third column is used by the steel companies to identify the GM specification for the type of steel.
Column four identifies whether or not certain types of welding are recommended including GMA (MIG) welding, squeeze-type resistance spot welding (RSW), and MIG brazing. It is stated in footnote number one that when MIG brazing is recommended, slotted holes 8 x 16 mm should be used. For some steels, like DP>800, UHSS, martensitic, boron, and TRIP, it is noted that GMA (MIG) plug welds are the only type of GMA (MIG) welding that is recommended. The footnote stresses that these steels should not be stitch welded during repairs, nor used as a backer for stitch welding. It is noted that “Deviation from this chart is only allowed if there has been a crash analysis completed by the Design Engineer and a service procedure has been written.”
The last four columns address straightening and the use of heat. The fifth column addresses if a steel part may be repaired without the use of heat. If cold repairs are allowed, footnote number two states that it should only be done if the damaged area is not kinked. The sixth column identifies if heat may be used for repairs. When heat is allowed, the last two columns show a maximum temperature of 1200F (650C) with heat being applied for no more than 90 seconds and no more than two heat applications.̊̊
Additional information in the footnotes includes number three which references sectioning being allowed on DP<800 using a sleeve or backer plate. It is also noted that GM does not endorse door impact beam repairs.
Descriptions of GM Steel, found on the second page of the matrix, include information on the steel grades, alloy content, heat treatment process that are used when making the steel, typical applications of the types of steel, and additional comments.
The Recommended GM Steel Reparability Matrix is a good source for general information on repairing the steels that are found on GM vehicles. Keep in mind that vehicle-specific repair procedures may vary from the general recommendations listed in the matrix based on specific application and design intent. Always reference the repair procedures for the specific vehicle model and year during repairs. The second page of this GM document gives additional information on GM steels including a column that gives typical applications for the types of steel to help make the technician aware of areas where they may encounter these types of steels.
A discussion of different grades of steels is featured in the I-CAR Live Steel Unitized Structure Technologies And Repair (SPS07) program, premiering at this year’s NACE. Advanced high-strength steels are discussed in the Advanced High-Strength Steel Overview (AHS01) online training program. To review this program, please go to www.i-caronlinetraining.com.
This Advantage Online article first appeared in the I-CAR e-newsletter, which is published and distributed free of charge. I-CAR, the Inter-Industry Conference on Auto Collision Repair, is a not-for-profit international training organization that researches and develops quality technical education programs related to collision repair. To learn more about I-CAR, and to subscribe to the free e-newsletter, visit http://www.i-car.com or contact I-CAR Supervisor of Marketing Communications Brandon Eckenrode at Brandon.Eckenrode@i-car.com.