Results of studies on impact tested gas and plasma nitrided or nitrocarburized blunt notch die steel samples with varying notch root radii are presented. A detailed fracture mechanism sequence is proposed encompassing, (i) multiple mode-I radial cracks formation at the root of the notch within the N-diffusion zone; (ii) development of a cylindrical stress-free zone effectively creating a notch with a radius larger than the previous one; (iii) concurrent mode-II fractures running along logarithmic spirals of the slip line field forming at the new larger notch; (iv) race restricting to two of them, with one hitting the notched sample centerline before the other and further propagating into the region of minimum thickness with a mode-I fracture. Suggestions for improved steel compositions are given after developing relationships among impact absorbed energies and geometrical features of the fracture surfaces of plasma nitrided Charpy-U specimens.

Fracture of nitrided and nitrocarburized blunt notch three-point bending die steel specimens / Firrao, Donato; Ugues, Daniele. - In: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING. - ISSN 0921-5093. - 409:(2005), pp. 309-316. [10.1016/j.msea.2005.07.059]

Fracture of nitrided and nitrocarburized blunt notch three-point bending die steel specimens

FIRRAO, Donato;UGUES, Daniele
2005

Abstract

Results of studies on impact tested gas and plasma nitrided or nitrocarburized blunt notch die steel samples with varying notch root radii are presented. A detailed fracture mechanism sequence is proposed encompassing, (i) multiple mode-I radial cracks formation at the root of the notch within the N-diffusion zone; (ii) development of a cylindrical stress-free zone effectively creating a notch with a radius larger than the previous one; (iii) concurrent mode-II fractures running along logarithmic spirals of the slip line field forming at the new larger notch; (iv) race restricting to two of them, with one hitting the notched sample centerline before the other and further propagating into the region of minimum thickness with a mode-I fracture. Suggestions for improved steel compositions are given after developing relationships among impact absorbed energies and geometrical features of the fracture surfaces of plasma nitrided Charpy-U specimens.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/1612052
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