To realize a fastening element which has a high resistance to hydrogen embrittlement and can be manufactured at a low cost.
The fastening element has a core zone 14 made of a relatively hard carbon steel 14 and a peripheral zone 17 which is located outside the core zone 14 and is made of a first low-carbon austenitic steel alloyed with a first alloying metal. At least one first intermediate zone (15a, 15b) made of a second low-carbon steel having a smaller hardness than the steel forming the core zone 14 is provided between the core zone (14) and the peripheral zone 17. The second low-carbon steel of the first intermediate zone (15a) is an austenitic or ferritic steel alloyed with a second alloying metal. A second intermediate zone (16) made of a relatively hard carbon steel is provided between the first intermediate zone (15b) made of a ferritic steel and the peripheral zone (17).
THEILER CARMEN
Shiro Fujitani
Tatsuya Sawada