The effect of the regimes of pulsed laser treatment on the structure and properties of high-speed steels

Conclusions

• 1. With the pulse width τp decreasing from 8.0 to 1.5 msec, the microhardness of preliminarily hardened high-speed steels after laser hardening at temperatures close to the solidus temperature T_s first increases to the maximal value (H 1120-1150) at τp=3 msec, then it decreases. This is due to the occurrence of disperison hardening of different degrees and the formation of different amounts of residual austenite in the structure of the steels.

• 2. With τp=3 msec there is practically no residual austenite in steels whereas after laser hardening by pulses with τp=1.5 and 8.0 msec the structure contains about 15% γ-phase.

• 3. After laser hardening at temperatures close to T_S the structure of preliminarily hardened high-speed steels contains secondary carbides whose number per unit volume depends on τp. The maximal amount of secondary carbides (11.905–12.893)10¹³ mm⁻³ forms with τp=3

• 4. Secondary carbides segregate during the process of laser tempering occurring in laser heating to the temperature of the onset of α→γ transformation, and they do not have enough time to dissolve completely during the process of laser austenitization.

• 5. The maximal increase to tool life (3–5 times) is found after laser hardening at T_S with pulse width of 3 msec.