Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Structures and Tensile Properties of High Strength Ni-Cr-Mo-V Steels Containing 1-5% Nickel
Toru ARAKIRyuhei SAGAWAMinkyo SHIN
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JOURNAL FREE ACCESS

1975 Volume 61 Issue 2 Pages 214-228

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Abstract

Low carbon Ni-Cr-Mo-V steels containing 1-5% nickel were subjected to isothermal or continuous cooling transformations and tempering, which led to a variety of microstructure. Effects of nickel and carbon on the microstructures and on the tensile properties of these steels were examined by means of the tensile testing, dilatation measurement, X-ray measurement, and optical and electron microscopies.
An addition of nickel improved the tensile properties, particularly the ductility of the steels with the intermediate transformation products as well as the tempered martensitic structures. However, decrease of carbon content exhibited no appreciable contribution to a balanced improvement in the strength and ductility relationship. An increase of the nickel content was found to shift the transformation rariges of the ferrite and the intermediate products to a lower temperature and to a much longer time, and therefore, resulted in enhanced hardenability.
The intermediate transformation structure, which mainly consisted of bainite, had a considerably low yield strength ratio and low elongation and reduction of area values. The steels with this structure were in general inferior to those with the tempered martensite. When additional tempering at an appropriate temperature was applied to the steel, the intermediate structure of higher nickel steels had a trend of marked increase in yield strength (ratio) as well as an increase in ductility although the tensile strength was decreased. Most of the intermediate structures were composed of lathlike structure with high density of dislocations and precipitation of carbides, and the tempering caused both the rearrangement of dislocations and the secondary hardening, presumably associated with the molybdenum carbide precipitation which was enhanced by a higher nickel content; this seems to cause an optimum improvement in the conbination of strength and ductility.

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© The Iron and Steel Institute of Japan
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