As you may already know, the modern motor vehicle has many more types of steel to make the body shell, compared to 15 years ago.
Instead of using Mild and HSS steels, manufacturers have moved on to AHSS (Advanced High Strength Steels)and UHSS Steels (Ultra High Strength Steels).
These new materials are alloys, and as such, they have unique properties such as work hardening and malleability. They are ideal for vehicle body panels and chassis frames and are extensively used in the modern vehicle bodyshell.
The use of these "alloys" has created problems when spot welding and more noticeably dent pulling when welding.