Surface hardening of steels with carbon by non-vacuum electron-beam processing

Surface layers containing ~ 1.57–2.55% (wt) carbon were produced by atmospheric electron-beam cladding of low carbon steel plates with an iron–graphite powder mixture. The main process parameter determining the thickness, structure, and mechanical properties of the hardened layer was the electron-beam current. As the beam current was increased from 20 to 26 mA, the thickness of the cladding layers increased from 1.2 to 2.6 mm and the hardness decreased from 5.7 to 4.5 GPa. In friction tests against fixed abrasive particles, the wear-resistance of the cladding layers was close to the wear resistance of pack-carburized specimens. In electron-beam cladding of steel plates 10 mm thick with the powder mixture with electron-beam scanning over the plate surface, the cooling rate of the surface layer was less than the critical value, which made it impossible to obtain a martensitic structure. The main structural components in the cladding layers were ledeburite, secondary Widmanstätten cementite, and pearlite. To produce a high-carbon martensitic structure directly during cladding by enhancing the heat transfer to the colder volume of the workpiece, it is necessary to increase the thickness and mass of the workpiece or reduce the thickness of the hardened layer. Saturation with carbon and quenching of the cladding layer can be performed successively using the same electron accelerator.