Cleavage Initiation in Ti-V-N and V-N Microalloyed Forging Steels

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The effects of matrix microstructure and features of non-metallic inclusion (morphology, type, volume fraction and size) on cleavage initiation in medium-carbon Ti-V-N and V-N microalloyed resulphurized forging steels have been determined by examining fracture surfaces produced in room temperature Charpy impact tests. The steels were generally Al-deoxidised but one V-N steel was Si-deoxidised. It has been found that, in the Ti-treated steel, having a ferrite-pearlite microstructure, brittle fracture initiation occurred at cracked coarse (Ti,V)(C,N) single phase or [(Ti,V)(C,N)/Al2O3/MnS] multi-phase inclusions. In the Ti-free steels, cleavage initiation was dependent on matrix microstructure and non-metallic inclusions. In the low strength Ti-free steels, with a ferrite-pearlite microstructure, the absence of a continuous grain boundary ferrite layer led to initiation from interfacing pearlite colonies. For the bainitic microstructure, cleavage initiated close to the notch, but the microstructural feature responsible could not be identified. For the ferritepearlite microstructure in the Si-deoxidised V-N steel, cleavage initiated at cracked Mn-Al-(Ca) silicate inclusions. The higher matrix strength and more continuous nature of grain boundary allotriomorphic ferrite in the V-N steel deoxidised with Al was associated with cleavage initiation from V-rich (V,Ti)(C,N)-containing inclusions. These were generally of smaller size than those in the Ti-treated steels.

Info:

Periodical:

Materials Science Forum (Volumes 500-501)

Edited by:

J.M. Rodriguez-Ibabe, I. Gutiérrez, B. López and A. Iza-Mendia

Pages:

729-736

DOI:

10.4028/www.scientific.net/MSF.500-501.729

Citation:

M.J. Balart et al., "Cleavage Initiation in Ti-V-N and V-N Microalloyed Forging Steels", Materials Science Forum, Vols. 500-501, pp. 729-736, 2005

Online since:

November 2005

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Price:

$35.00

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