Orion Pulse 150i, pulse arc and resistance welder
A sharpened 1mm tungsten electrode is used to weld the high carbon steel springs. Weld spots can be placed quickly and easily in desired locations. The Orion Pulse 150i is set to 45ws energy to perform the welds on these samples. Higher energies can be used for increased weld penetration but more deformation along the edge of the spring will occur. Due to the high carbon content in the steel the welds are somewhat brittle and strength can be increased, as you suggested, by heating the springs after the weld process.
A capacitive discharge welder (CD1000DP) in conjunction with an opposed weld head (WH1125) would also be able to successfully weld these samples but with slightly less hold strength.
The Orion Pulse 150i is ideal for welding several different types of metals and combinations of metals. The touch screen user interface makes it easy for operators to quickly dial in settings and achieve desired results. The CD1000DP is also a viable solution.