The invention may be used to produce {HEAD ~ hardened springs} with uniform mechanical and physical characteristics, fine grain microstructures, and {TAIL ~ high fatigue resistance} 
The invention may be used to produce { HEAD ~ hardened springs } with uniform mechanical and physical characteristics , fine grain microstructures , and { TAIL ~ high fatigue resistance }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL