Observations of Factors Which Influence the Spot Weldability of High-Strength Steels 810353
Spot weldability of sheet steel has been related to the current range over which welds with acceptable size and/or mechanical properties are obtained. There are many factors which affect the size of the current range, the location of this range, and the type and location of spot weld failure. Some of these factors include (a) chemistry, (b) surface conditions (including coatings, rust, etc.), (c) subsurface oxides and steel cleanliness, and (d) mill production procedures.
Some observations on the effects of these factors upon the spot weldability of high-strength, low-alloy steels have been made. Sheet chemistries containing excessive levels of phosphorus or oxygen have been observed to cause brittle nuggets because of weld center-line hot cracking. Materials with excessive subsurface oxides likewise have been noted to promote centerline failures. High resistance surfaces tend to move the location of the current ranges. Finally, steel processing techniques can affect the nugget tear location.
Examples of each of these observations will be given, together with examples of how specific weld problems were solved.