ROŽNOVSKÁ Gabriela MATERIAL AND METALLURGICAL RESEARCH Ltd.

Spoluautoři KUBOŇ Zdeněk, Vodárek Vlastimil

Low carbon supermartensitic 13 % Cr steels with 4-6 % Ni and 0-2.5 % Mo additions have been developed from the type AISI 420 steel for applications in the oil industry. They offer significantly better weldability, improved general corrosion resistance and some grades exhibit improved resistance to sulphide stress corrosion cracking. The balance between strength and toughness of these steels can be controlled by heat treatment. Quality heat treatment of supermartensitic steels usually consists of quenching and single or double tempering above the Ac1 temperature. Such heat treatment results in stabilization of reverted austenite in the final microstructure. Tempering can also be accompanied by intensive precipitation processes in tempered martensite especially in grades with a high content of molybdenum. This paper deals with a detailed TEM characterisation of precipitation processes in a 13Cr – 6Ni – 2.4Mo supermartensitic steel during single tempering of martensite at temperatures of 600 °C and 690 °C. Results of experimental studies are compared with thermodynamic calculations of equilibrium phases in this grade of the supermartensitic steel.

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