Abstract:

The cast martensitic stainless steel CA6NM is used in the construction and repair of rotors and its choice occurs due to the cost of manufacture and the performance in operation. Both in the construction and in the repair of these, a similar welding metal is used in the welding process, containing 13% chromium, 4% nickel and 0.4% molybdenum, with carbon contents below 0.04%. Through the use of double-stage tempering heat treatment, it is possible to obtain improvements in toughness, mainly due to the formation of austenite retained in the microstructure. The aim of this study was to evaluate the effect of temperature and time of this treatment on the microstructure and toughness of the weld metal. Five different conditions were analyzed (580 °C/2h, 620 °C/2h, 650 °C/2h, 620 °C/2h+580 °C/4h and 650 °C/2h+580 °C/4h), in addition to of as a soldier. In all conditions analyzed, retained austenite was formed, however, the highest levels were found in double-stage heat treatments. The toughness was evaluated using the V-notch Charpy test and the absorbed energy values ​​obtained for the weld metal showed a relationship directly proportional to the percentage of retained austenite found and, for Vickers hardness, this relationship was inverse. Heat treatments with the use of more energy (650 °C/2h+580 °C/4h) led to a higher formation of retained austenite, while for the lesser energy (580 °C/2h) less retained austenite content was obtained and lowest tenacity value.

Key-words:
Martensitic stainless steel; Heat treatment; Retained austenite; Toughness