EFFECT OF DEEP CRYOGENIC TREATMENT ON FRACTURE TOUGHNESS OF 300M STEEL USING CIRCUMFERENTIALLY NOTCHED KIC TEST SPECIMENS

Mr. Daniel Schuller , Universidade de São Paulo, São Carlos-SP, Brazil
Dr. Vojteh Leskovsek , Institute of Metals and Technology, Ljubljana, Slovenia
Dr. Lauralice Canale , Universidade de São Paulo, São Carlos-SP, Brazil
Deep cryogenic heat treatment (DC) has been performed in 300M aeronautic steel in order to assess its effects on fracture toughness using circumferentially notched KIc test.

Four groups of 13 specimens each have been austenitizing and tempered. Two groups were austenitizing at high austenitizing temperature (980 C) and other two with low austenitizing temperature (870 C). DC heat treatment was applied before tempering in one group with high austenitizing temperature and one with low austenitizing temperature.

Results shows a high influence of DC treatment on fracture toughness on specimens even with minimum influence on hardness. It is possible to see loss in order of 10 MPa √m and increase of 2 HRC for specimens that was submitted to DC treatment in comparison with specimens without DC.

Besides DC influence, austenitizing temperature has also a straight influence in fracture toughness. The higher is the austenitizing temperature, the higher is fracture toughness of 300M aeronautic steel.

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