US2417760A - Making bimetallic products - Google Patents

Description

W. L. KEENE MAKING BIMETALLIC PRODUCTS Filed Aug. e, 1942 March 18, 1-947.

INVENTOR Walterll. Keene -15 20 Z5 T me at'emperture- Min uzes Patented Mar. 18k, 1947 MAKING BIMETALLIC PRODUCTS Walter L. Keene, Dormont, Pa., assigner to Superior Steel Corporation, Pittsburgh, Pa., a corporation of Virginia Application August 6, 1942, Serial No. 453,824

1 Claim. 1

This invention relates to making bimetallic products. It relates particularly to making bimetallic products having a steel component and a gilding metal component. The invention further relates to the annealing of worked or drawn metal of the type mentioned.

Merely by wayr of explanation and illustration the invention will be described in connection with the making of bimetallic bullet jacket cups. These cups consist of steel faced both internally and externally with a thin layer of gilding metal (about 90% copper and about 10% zinc). The cups are preferably drawn from bimetallic strip which in turn is made by rolling a bimetallic billet.

The backing member of the bimetallic billet is made of low carbon deep drawing type steel. The low carbon deep drawing type steel may be either killed steel, rimming steel or semi-killed steel (which lies between killed steel and rimming steel) and has the composition commonly recognized as the composition of low carbon deep drawing type steel. Typical compositions of deep drawing type killed steel and deep drawing type rimming steel are given at page 70 0f The Metallurgy of Deep Drawing and Pressing, by J. Dudley Jevons (1940) as follows:

l This applies to aluminiumdcilled steel. If silicon is used in place of aluminium, the percentage of residual silicon is usually 11.05 to 0.10. The term low carbon deep drawing type steel as used in the claim means a steel as above described.

The facing members of the bimetallic billet are made of gilding metal. vThe gilding metal facing members are applied to the steel backing member in known manner. For example, the backing member may be flanged and the facing members may be held in place with respect to the backing member by turning the flanges over and about the edges of the facing members. The billet is then hot rolled and cold rolled after which itis delivered to cuppng presses where it is blanked and cupped. The drawn cups are cleaned, annealed and pickled and are delivered (Cl. 14S-21.5)

1 should be annealed in such manner that desirable properties are developed in the steel. At the same time the annealing should not detrimentally affect the facing material.

The cups are formed from the bimetallie stripV by first blanking a disc and then forcing or drawing the disc through a die. The blanking and drawing operations maybe performed in rapid sequence, almost simultaneously. This cold works the metal to Varying degrees, vdifferent in different portions of the cup. For instance, there is very little cold work on the base of the cup, a slightly greater amount at the bottom of the side wall and various amounts in the side wall increasing toward the top of the cup.

In cold rolling steel,` for example, certain minimum reductions must be imposedv or else the grain size of the steel after sub-critical annealing will be coarse, resulting in the familiar orange peel surface when deformed. 'I'he most dangerous range of cold work (whether by elongation or compression) appears to be from 5 to 25%. In a cup drawn from a flat blank deformation in this range is found in areas both on the bottom and on theside wall near the bottom. The upper portion of the yside wall is ordinarily deformed in excess of 25%.

Consequentlyfthe annealing of the drawn cups is especially important and presents a perplexing problem. The annealing must be such as to avoid grain growth in certain regions of the cup. Areas of coarse grain will upon drawing out of the cup to a longer tube and subsequent pointing result in unsatisfactory jackets. The coarse grains become long and distinct and have a stringy appearance, the area near the point of the jacket having distinct high and low points. Upon firing 'the point of the jacket may separate from the remainder, causing jamming of the gun or inaccurate flight of the bullet.

The primary purpose of annealing bimetallic I bullet jacket cups is to remove the effects of the 3 let jacket. The annealing should both soften the cup uniformly, thereby developing best ductility, and also keep the grain size ne and uniform.

It is known to anneal drawn articles of steel by heating them to a temperature slightly above the upper critical point (which for low carbon steel is in the neighborhood of 1650 F.) and cooling in air. This is known as normalizing. If it be attempted to normalize bimetallic cups as above referred to the high temperature required results in a pronounced coarsening of the grain of the facing metal, which is undesirable, although the cold work later imposed upon the cup will refine the grain size to a certain extent. Normalizing is further disadvantageous because zinc is driven out of the gilding metal at temperatures around 1650 to 1'700J F.

Worked bimetallic products of the type above referred to whereby all the disadvantages of normalizing are overcome. By my annealing method I produce uniform softness of the cup and the absence of large coarse grains in the steel. I subject the cups or other products to a sub-critical anneal in a temperature range of from about 1175 to about l300 F. However, I have found that there is a highly important relationship between the annealing temperature and the time atwhich the products are subjected to the annealing temperature. I have discovered that for a certain annealing temperature the time at temperature should be controlled within substantially predetermined limits. 'I'he limits will be explained below in connection with the drawing.

, practicing the invention proceeds.

The accompanying drawing consists of a chart 'showing the relationship of annealing temperature and time at temperature in order to obtain the desired results in the annealing of bimetallicV products of the type above referred to.

1 VIn the drawing, as shown,` annealing temper- 4 which produce unsatisfactory results. Moreover, it is virtually impossible to obtain temperature readings more accurate than within a range of plus or minus 10 F. Therefore, it will be appreciated that the cross-hatched area on the chart is at best an approximation but denes as nearly exactly as is possible the vconditions necessary for successful results in the practice of my invention.

To explain the significance of the crosshatched area on the chart, the annealing temperature should be between about 1175 and about atures in degrees Fahrenheit'are plotted against time at temperature in minutes. On the graph thus .formed is a cross-hatched area which denes in a general way the conditions which should be obtainedin the annealing. vI have found that if bimetallic products as above referred to are annealed as indicated by the chart there will not be excessive or rapid grain growth in the steel, yet the material will be softened to adesired extent. Annealing conditions represented by any point plotted within the crosshatched area on the chart are satisfactory while those represented by any point out-side and substantiallyremoved from thecross-hatched area are unsatisfactory. Generally speaking, annealing conditions represented by points lying above 1300" F. vvhile the time at temperature should be betweenabout 1 minute and about 35 minutes. However, the time depends upon the temperature and the temperature depends upon the time. If the annealing temperature is 1300 F. the time 'at temperature should be not less than about 1 minute and not more than about 3 minutes. If the annealing temperature is 1250 F. the time should'be not less than about l2 minutes and not more than about 19 minutes. If the annealing temperature is 1200 F. thetime should be not less than about 25 minutes and not, more than about 35 minutes. i Conversely, if the time at temerature is the controlling factor an anneal for 5 minutes should be at a temperature between about 1275 and about 1290 F., while if the time at temperature is 10 minutes the temperature should be between about 1260 and about 1275 F. Experiments have shown that in order to obtain results which can be entirely relied on the annealing conditions should be represented by pointslying within the cross-hatched area on the chart or at least lying veryclose to, although outside, the borders of that area. I believe, and mytests show, that if the annealing conditions. in any particular instance are represented by a point lying within the cross-hatched area on the chart satisfactory results can be depended upon.4

`Subsequent to the heat treatment just described the-Work should be cooled to a temperature at least as low as in the neighborhood of 900 F. at a rate of the order of the rateof cool- 'ing in still air at atmospheric temperature. More rapid cooling results in undesirable increasein hardness.

` The annealing treatment above described effectively softens the cups so that they are in condition for further and severe cold work but does not allovvvthe formation of excessively coarse grains either in the steel or in the gilding metal such as would'upon further drawing and pointing of the cup to form a bullet jacket become long and stringy and cause a zone of weakness near the point of the jacket which in firing might cause the point to become separated from the balance of the jacket and cause jamming of the gun, rapid wear of the rifle or inaccurate travel of the bullet.

While I have described a present preferred method of practicing the invention it is to be distinctly understoodr that this invention is not limited thereto but may be otherwise variously practiced Within the scope of the following claim.

A method of annealing a 'shape of bimetal comprising a relatively thick layer of low carbon deep drawing type steel and a relatively thin layer of gilding metal bonded together and generally in the form of a cup having a side wall and a bottom and the thickness of the metal of which has been cold reduced in the range 5-25%'on the bottom and on the side Wall near the bottom and in excess of 25% at the upper portion of the side wall comprising subjecting the shape to a temperature and for a time indicated by the cross-hatched area on the accompanying chart and then cooling it to a temperature at least as low as about 999 F. at a rate about the rate of cooling of identical shapes in still air at atmospheric temperature to impart to the shape a uniform fine grained structure.

WALTER L. KEENE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,193,245 Buxton Mar. 12, 1940 6 Number Name Date 1,063,574 Monnet June 3, 1913 1,205,942 Buell Nov. 21, 1916 2,264,266 Jaco-bs Nov. 25, 1941 OTHER REFERENCES

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