Alloys or metallic compositions – Ferrous – Chromium containing – but less than 9 percent
Patent
1998-10-15
2000-11-14
Yee, Deborah
Alloys or metallic compositions
Ferrous
Chromium containing, but less than 9 percent
148335, C22C 3846
Patent
active
061465836
DESCRIPTION:
BRIEF SUMMARY
This invention relates to steel alloys and to chain links and associated products fabricated of such alloys.
Chain links are formed by taking a portion of steel alloy rod as feedstock, subjecting the portion to a bending operation to bend the portion into a chain link shape with ends of the portion abutting a central part of a limb of the chain link shape and electric arc welding together the said ends to form the chain link. During the bending process, the portions are either interlinked together, or to alternate links forged into shape previously, in sequence, and the welding, in turn, is effected sequentially to form a continuous chain length of interlinked links. The continuous chain length is then heat treated to develop a requisite strength and toughness in the chain links.
To produce high performance chain lengths it is conventional to utilise a low alloy steel feedstock with a typical analysis of:
______________________________________ Nickel 0.75%
Chromium
0.5%
Molybdenum
0.5%
Carbon 0.23%
Iron balance
______________________________________
The alloy material content increases the hardenability of the steel and enables the temperature at which the chain is tempered to be raised in comparison with a mild steel whilst retaining strength. The strength is largely governed by the carbon content, but both alloy content and carbon content must be kept low in order to maintain good, reliable, weldability of the feedstock.
It is known in the general field of alloy steel that vanadium may be used as a substitute for, or in addition to, molybdenum to improve the hardenability and temper resistance of alloy steel. Thus the molybdenum content may be replaced or augmented by a somewhat smaller content of vanadium to form an alloy having similar properties to the alloy containing molybdenum alone.
According to the present invention there is provided a steel alloy for fabricating into chain links having a composition including nickel in the range of 0.3 to 1.5%, chromium in the range of 0.2 to 1.0%, molybdenum in the range of 0.1 to 1.0%, carbon in the range of 0.15 to 0.28% and vanadium in the range of 0.05 to 0.2%.
Preferably the steel alloy has a molybdenum content in the range of 0.2 to 0.8% and a vanadium content in the range of 0.05 to 0.15%.
Desirably the steel alloy has a composition including nickel 1.0%, chromium 0.5%, molybdenum 0.75%, carbon 0.23% and vanadium 0.1%.
Steel alloys as set out having a vanadium content in addition to a molybdenum content have a weldability only marginally inferior to that of the corresponding steel alloy not containing a vanadium content but have an increased temper resistance.
In one example, by increasing the tempering temperature from 480.degree. C. to 600.degree. C. of a typical high strength chain, such as grade 80 industrial chain or DIN grade 2 mining chain, by the addition of vanadium to the steel alloy, a very high resistance to stress corrosion cracking is found as measured by K.sub.1.sbsb.scc to the extent that the chain strength was effectively immune from the effect of the working environment. The steel alloy has a better than normal toughness and stress corrosion resistance at higher than normal hardness, that is, higher than normal strength.
Chain links and associated products are frequently required to operate in specific, adverse, environments such as in marine applications, mining operations involving adverse geo-chemical conditions, particularly those involving mildly acidified chlorides and sulphides, or in particular chemical environments. Hitherto, requirements of toughness and resistance to stress corrosion have necessitated the utilisation of a steel alloy of lesser strength than that utilised for conventional chain.
Utilising the steel alloy of the present invention enables the fabrication of mining chain having an acceptable stress corrosion resistance to aggressive conditions likely to be encountered in mining without sacrificing hardness and strength in comparison with a conventional composition steel chain.
In compari
REFERENCES:
PCT International Search Report, Application No. PCT/GB96/03117, pp. 1-4.
Ann. Chim., vol. 6, No. 3, 1981, pp. 225-236, XP000653543.
Association Technique De Traitement Thermique (ATTT) XP000653532, copyright 1994, PYC Edition 5, Ivry-Sur-Seine ISBN 2 85330-133-8, pp. 111-119.
Zvaranie, vol. 22, copyright 1973, pp. 301-307, XP002029918.
Excerpt from Database Registry in Host STN XP002029919, 1981.
Thyssen Edelstahl Tech. Ber., vol. 6, No. 2, 1980, pp. 104-110, XP000653333.
Derwent Abstract, 76210B, 1979.
Derwent Abstract, 47872R, 1970.
Burdon Christopher
Price Geoffrey David Smyth
Parsons Chain Company Limited
Yee Deborah
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