In this study an effect of intercritical annealing was observed on an PK993/1CH13N3 martensitic stainless steel. Current heat treatment for PK993/1CH13N3 steel consists of quenching from 1000 °C and tempering at 530 °C. With this heat treatment all required mechanical properties are achieved, with an exception of impact toughness. Additional intercritical annealing was purposed to achieve better combination of all mechanical properties. To test that, two series of heat treatments were performed on samples taken from a rolled bar diameter 70 mm. In first series all samples were water quenched and tempered at different low temperatures. In second series an additional intercritical annealing above AC1 temperature was performed in between two previously mentioned steps of heat treatment. The study focuses on how this additional intercritical annealing effects microstructure and mechanical properties of PK993/1CH13N3 steel. Microstructure was observed using light and scanning electron microscope, while mechanical tests were performed to determine yield point, tensile strength, impact toughness, elongation, contraction and hardness. In addition to that, dilatometry tests were performed to determine AC1, AC3, Ms and Mf temperatures for PK993/1CH13N3 steel. For additional research Thermo-calc simulations and XRD analysis were performed. It has been concluded that a thin carbide film forms around austenitic grain bounders during austeitization. After only tempering at low temperatures this film stays stable. With intercritical annealing bigger spherical carbides form and the film is no longer present on the grain boundaries. Because more carbides form, Ms temperature raises after intercitical annealing. In addition to that, new and fresh martensite forms after cooling form an annealing temperature higher than AC1 point. Changes in microstructure lower all mechanical properties except impact toughness and provide a better combination of all mechanical properties. It also lowers standard deviations of all mechanical properties within a given heat treated series.
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