US2933424A - Method of making cold headed wire - Google Patents

Description

hilf l 2,933,424 METHOD OF MAKING COLD BEADED WIRE Charles G. Canney, Holden, and Francis P. Whalen, Shrewsbury, Mass, assignors to United States Steel Corporation, a corporation of New Jersey N 8- Applicatlon May 8, 1957 Serial No. 657,729 u 1 Claim. 01. 148-212} This invention relates to a method of making cold heading wire. Cold heading wireis used in the production of screws, bolts, rivets and the like and is normally formed from low carbon steel rods, the steel normally containing .11 to .16% carbon, .50 to .80% manganese, .04% maximum phosphorus, and .05% maximum sulphur. In the manufacture, of the wire a hot rolled round rod which may vary in size from .207 to 1.125 in. in diameter was first sealed at about 1400 F. for about four hous for the purpose of improving surface quality. The rod was then given one or more drawing drafts to reduce its diameter to between .08 and 1.00 in. depending upon the size of the starting rod. The drafted wire was then spheroidized by heating it in coil form, preferably in a gas atmosphere under the inner cover of a batch type annealing furnace at approximately 1280 F. for about four hours. In the spheroidizing operation the wire was gradually heated for about one hour until it reached a temperature of 1280 R, where it was held for about four hours. The wire was then cooled to room temperature under the inner cover for about six hours. The gas atmosphere may be cracked ammonia gas containing about 75% nitrogen and 25% hydrogen. The spheroidized wire was then given a light drawing draft of between approximately 5 and 15% down to a diameter of between .075 and .975 in. depending upon the size of the starting rod. The wire drawing lubricant was of a type that remained on the wire as it was sent to the customer and acted as an aid during cold forming operations. A suitable lubricant was aluminum stearate or calcium stearate. For several reasons it is desirable to use higher carbon steels such as AISI No. C-1018 which has between .15 and 20% carbon, between .60 and .90% manganese, .04 maximum phosphorus and .05% maximum sulphur. It was found that this particular steel when made into wire according to the procedure outlined above had a tensile strength of 75,000 lbs. per square inch, a yield point of 64,000 lbs. per square inch and an elongation of 1%. However, it was found in many instances that the wire was not acceptable when subjected to severe cold working operations such as when making special head screws. In this operation ruptures appeared in the recesses of the heads of the screws and caused them to be rejected. This was especially true when using the higher carbon steels mentioned above.

It is therefore an object of our invention to provide a method of making cold heading steel wire which will be suitable for severe drawing or forming operations.

This and other objects will be more apparent after referring to the following specification.

In the practice of our invention carbon steels of the grades of (3-1005 to 0-1038 and certain alloy steels may be subjected to the same surfacing treatment as in the previous practice. These carbon steels contain .05 to .42% carbon, 1.50% maximum manganese, .05% maximum sulphur, .04% maximum phosphorus and the re- 2 maining substantially all iron with the usual impurities. The alloy steels in addition to the above may have 2.00% maximum nickel, 2.00% maximum chromium and 50% maximum molybdenum. The rod is preferably of the same starting sizes as in the former practice. The starting rod is given one or more drafts to reduce its crosssectional area between approximately and 90%. It will he understood that the larger percent reductions will be made on the smaller size rods and the smaller percent reductions on the larger size rods, as is usual in wire V drawing operations. The drafted wire is then spheroidized.

This may be done by subcritical spheroidizing in the manner described above or by spheroidizing by heating to or over the lower critical temperature and controlling the cooling rate through the spheroidizing range in the usual manner. The spheroidizing is preferably, but not necessarily, performed in a non-oxidizing atmosphere. The spheroidized wire is then given a drawing draft to reduce its cross-sectional area between approximately 5 and 15%. The wire drawing lubricant is the same as that described above so as to eliminate the need of subsequent coating. The wire is then given a further heat treatment. This treatment consists of heating the steel wire in coil form to a temperature between approximately 950 and 1150 F. in a gas atmosphere similar to the atmosphere used in spheroidizing. if the neutral or reducing atmosphere is not used subsequent cleaning and coating steps would be necessary to prepare the wire for many of the desired uses to which it is put. The wire is brought up to temperature as rapidly as possible under the inner cover of a batch type annealing furnace and is held at that temperature for about eight hours after which the wire is cooled to room temperature as rapidly as possible while still under the inner cover in the gas atmosphere. The wire may also be heat treated by passing it continuously through a molten lead bath to heat it to a temperature of between approximately 950 and 1150 F. and then cooling. In other words, it is only necessary that all parts of the wire be brought to a term perature of between 950 and 1150 F. without remaining at that temperature for any particular length of time. The cooling rate is not critical. The wire drawing iubricant will remain on the wire during this heat treatment.

It will be seen that the heat treatment is carried out at least below the lower critical Ac, of the steel. The wire treated in this manner has a tensile strength of between 50,000 and 100,000 lbs. per square inch, a yield point of at least approximately 60% of the tensile strength and an elongation of at least 7% in 10 inches. The relationship between the tensile strength and yield point will vary greatly depending upon the carbon content of the steel and the amount of cold working during the drawing operations, particularly dur ing the final draw. With the same amount of cold work the yield point will be a much smaller percentage of the tensile strength for low carbon steels than for the higher carbon steels and increased cold working will cause this percentage to increase. Normally low carbon steels will have a greater elongation than the higher carbons. Typical examples of the physical characteristics of various steels are as follows. C-1 005 steel has a tensile strength of 58,000 lbs. per square inch, 21 yield point of 35,000 lbs. per square inch and an elongation in 10 inches of 16%;(3-4018 steel has a tensile strength of 72,000 lbs. per square inch, a yield point of 58,000 lbs. per square inch and an elongation in 10 inches of 14%; -C-1038 steel has a tensile strength of 88,000 lbs. per square inch, a yield point of 70,000 lbs. per square inch and an elongation in 10 inches of 10%; and 4037 steel has a tensile strength of 85,000 lbs. per square inch, a yield point of 68,000 lbs. per square inch and an elongation in 10 inches of 10%. Thus, it will be seen that the C- ll8 wire, for

example, produced according to our invention has a much greater elongation and only a siightiy lower tensile strength and yield point than the wire prior to the final treatment. This isftrue in each case. It has been found that the cold headed wire so treated may be formed into the screws without the formation of ruptures.

While one embodiment of our 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 claim.

We claim: The method of making cold heading wire which comprises providing a hot rolledround rod made from steel containing .05 to .42% carbon, 1.50% maximum manganese, .05% maximum sulphur, 04% maximum phosphorus, 200% maximum nickel, 2.00% maximum chromium and .50% maximum molybdenum," and the remaining substantially all iron, drawing said rod to reduce its area between approximately and90%, then sphe'roidizing said wire, drawing said 'spheroidized wire to reduce'its area between-approximately" Sand 15% to finished size, then heating said wire throughout to a temperature of between approximately 950 and 1150 1955 Book of ASTM Standards "part 1 (Ferrous Metals), pages 721-723. a

Steel and Its Heat Treatment, volume 1, by .Bullens; v

1948; John. Wiley & Sons; page 464.

Metals Handbook, 1948' edition, pages 7-360.