Notch Toughness of the Synthetic Heat-Affected-Zone Microstructures of High Strength Steels

Abstract

Following the previous paper, the notch toughness of the weld HAZ microstructures of high strength steels was evaluated by means of the synthetic apparatus. Summalizing the whole results, including previous tests, the effects of steel composition, microstructure and other factors on the notch toughness of weld HAZ specimens have been clarified. From these discussions, the following conclusions were summalized ;
(1) The notch toughness of coarsened HAZ microstructures in high strength steels was generally decreased compared that of their unaffected base metals, especially in quenched and tempered steels.
(2) The toughness of HAZ microstructures was decreased in accordance with the order of decreasing hardness, namely, martensite, mixed structure (martensite and bainite), coarse bainite and pearlite or ferrite.
(3) The critical carbon content at which the martensite toughness in weld HAZ was markedly declined, may be about 0.18%.
(4) The superiority of the test steels, when compared to the toughness of reproduced HAZ microstructures, was convinced by the test to agree with that of the tensile ductility which obtained by synthetic HAZ ductility tests in previous studies.