US 3395528 A
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United States Patent 3,395,528 STAINLESS STEEL WIRE PRODUCTS AND METHOD OF MAKING THE SAME Wilbert A. Lucht, Orange, -Conn., assignor to United States Steel Corporation, a corporation of Delaware No Drawing. Filed Feb. 11, 1966, Ser. No. 533,116 6 Claims. (Cl. 57-145) ABSTRACT OF THE DISCLOSURE A method of making stainless steel wire in which a hot rolled rod of astenitic stainless steel having a specific composition is cold drawn to reduce its area between 30 and 75% after which it is stress relieved at a temperature between 850 and 1200 F. A second cold drawing step reduces its cross sectional area at least 40% with the total reduction being at least 85% of the cross sectional area of the hot rolled rod. The product may then be stress relieved at a temperature between 850 and 1200 F. The stainless steel wire so produced has a minimum tensile strength of 300,000 lbs. per sq. in. and is capable of withstanding at least 25 twists in a length of wire 100 times its diameter.
This invention relates to stainless steel wire products and to a method of making the same, and particularly relates to austenitic stainless steels containing 17 to 20% chromium, 7 to 10% nickel, and .03 to .70% carbon. Stainless Steel Types 302 and 304 are in this category. Such steels are made into wire which in many cases is used to make wire rope. Wire of this type, produced in the normal manner is very poor in torsion. Wire rope should also have high tensile strength and good ductility, which properties are not particularly good when the steels of the above type are processed in the usual manner.
Therefore it is an object of my invention to provide a method of making stainless steel wire which has better ductility, higher torsional properties and higher tensile strength than normally processed wire.
Another object is to provide a method of making a stainless steel wire rope with wire having high torsional properties and high tensile strength.
A still further object is to provide a stainless steel wire product having good ductility, high torsional properties and high tensile strength.
These and other objects will be more apparent after referring to the following specification.
According to my invention, I start with an elongated austenitic stainless steel member having the composition disclosed above and which has been processed in the usual manner. This member may be a hot rolled rod which has been cooled after hot rolling in such a manner that it is essentially in an annealed state, or it may be processed wire which has been annealed in the usual manner. I first subject this member to a cold drawing step in which its cross-sectional area is reduced between 30 and 75%. I find it necessary to have a minimum reduction of 30% in order that the product will not be too brittle for the further drawing operation discussed below. On the other hand, if the reduction is above 75%, costs will increase due to drawing difiiculties and heat treating without obtaining any further improvement. The drawn member is then stress relieved at a temperature between 850 and 1200 F. Subsequently, it is subjected to a second cold drawing step in which its crosssectional area is reduced at least 40%. The total reduction in the two drawing steps must be at least 85 of the cross sectional area of the starting member.
When using my improved wire in the manufacture of wire rope, I find it desirable to make the wire rope in 'ice the usual manner and then to stress relieve it at a temperature of between 850 and 1200 F. For some other uses of the wire it is also desirable to stress relieve the wire in this manner after the second reduction.
One particular rope has been made as follows:
A Type 304 annealed wire of .135" diameter was given a reduction to .068" and was then stress relieved for 6 hours at 925 F. This wire was then given a 75% reduction to a diameter of .034" so that there was an overall reduction in area of approximately 93.7%. The wire so produced had a tensile strength of 344,000 pounds per square inch and 76 twists in 8". This Wire was then' processed in the usual manner to make a Regular Lay 6 x 36 wire rope with an independent wire rope core, and the wire rope so formed was then stress relieved by heating it to a temperature of 1000 F. This wire rope had a breaking strength of 67,000 pounds. A similar wire rope, without the final stress relieving step, had a breaking strength of 55,000 pounds. This compares with a breaking strength of 44,000 pounds for a similar rope processed in a conventional manner.
The wire produced above, when given a final stress relief at 1000 F., had a tensile strength of 358,000 p.s.i. and 93 twists in 8". A wire of the same size and composition produced in a conventional manner had a tensile strength of 290,000 pounds per square inch and between 14 and 40 turns in 8".
I have found that wire reduced by drawing according to my invention will have a minimum tensile strength of 300,000 pounds per square inch and can be given a minimum of 25 twists in a length of wire times the wire diameter, before breaking. The tensile strength will increase as the amount of total reduction increases. In all cases the torsion properties will be at least as good as the minimum stated above. Other examples of Type 304 stainless wires made according to my invention, without a final stress relieving are as follows:
While one embodiment of my invention has been shown and described it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.
1. The method of making stainless steel wire having high torsional properties, good ductility and high tensile strength which comprises providing an elongated austenitic stainless steel member containing 17 to 20% chromium, 7 to 10% nickel and .03 to .70% carbon, cold drawing said member to reduce its cross sectional area between 30 and 75%, then stress relieving said drawn member at a temperature of between 850 and 1200 F., then cold drawing said member to reduce its cross sectional area at least 40% with the total reduction being at least 85% of the cross sectional area of the starting member.
2. The method of making stainless steel wire accord ing to claim 1 including the step of stress relieving the member after the second drawing at a temperature between 859 and 1200 F.
3. The method of claim 1 including the step of stranding wires together after the second drawing step to produce a wire rope.
4. The method of claim 3 including the step of stress relieving the wire rope at a temperature between 850 and 1200 F.
3 4 5. Stainless steel Wire containing 17 to 20% chromium, 3,035,403 5/1962 Grimes et al. 57l45 7 to 10% nickel and .03 to .70% carbon, said wire 3,070,871 1/1963 Ryckebosch. having a minimum tensile strength of 300,000 lbs. per 3,217,833 11/1965 Peterson 6t 57-466 XR sq. in. and capable of withstanding at least 25 twists in OTHER REFERENCES 21 length of Wire 100 times the wire diameter.
6. A fatigue resistant wire rope made of stainless steel Publication: Edwards How Edwards Wire Rope Is Made, published June 1955. Original in group wires of claim 5.
References Cited 366 class; 57/145 UNITED STATES PATENT FRANK J. COHEN, Primary Examiner. 2.40 6 /194 Kr n 7 R w. H. SCHROEDER, Assistant Examiner.
2,767,836 10/1956 Nachtmann 72286 XR