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Influence of regenerative heat treatment on structure and properties of G20CrMo2-5 (L20HM) cast steel

Golanski G., Kupczyk J.

Archives of Foundry Engineering

2008

Vol. 8, iss. 1 spec.

109--114

The paper presents results of research on the influence of regenerative heat treatment on the structure and properties (hardness, impact energy)of L20HM cast steel. lnvestigated material was taken from outer frame of a turbinę which was serviced for 167 424 hours at the temperature of 535 °C and pressure of 12.75 MPa. In post-operating condition the investigated cast steel was characterized by low impact ,energy of 13J and hardness of 139HV30. Analysis of the influence of austenitization parameters (temperature and time) has revealed that at the temperature range of 895 ÷ 955 °C (i.e. Ac3 + 10 ÷ 70 °C), for both 3 and 5 hours of hold time, the obtained grain size amounts to 20 ÷ 25μm. I has been proved that tempered bainitic-ferritic and ferritic-bainitic-pearlitic structure of the investigated cast steel ensures high t energy, i.e. KV > 100J, as well as hardness, i.e. HV30, just at the temperature of 680 °C. Temperature of 700 °C causes further of impact energy along with a slight decrease of hardness. Moreover, it has been concluded that applying of under-annealing of tempering, after standardization, guarantees required impact energy of KV > 27J.