Patent ID: 7014409

Claim:
A fastening element having a core ( 16 ) of a relatively hard, carbonized steel and a ferritic rim zone ( 15 ) of a less hard, low-carbon steel which circumferentially surrounds the core ( 16 ), said fastening element comprising: a stem ( 11 ); a head ( 14 ) provided at one end of the stem ( 11 ); a tip ( 13 ) provided at an opposite end of the stem ( 11 ); and a transition region ( 12 ) extending between the stem ( 11 ) and the tip ( 13 ); the ferritic rim zone ( 15 ) extending at a substantially constant thickness along the stem ( 11 ) from the head ( 14 ) to the transition region ( 12 ); and in the transition region, the thickness ( 18 , 19 , 20 ) of the ferritic rim zone ( 15 ) gradually diminishes from the stem ( 11 ) in a direction toward the tip ( 13 ) to a nill value ( 21 ), whereby the tip ( 13 ) is free from the ferritic rim zone ( 15 ).