US2735304A - toppfb haw - Google Patents

Description

Feb. 21, 1956 J. D. BERWICK, JR 27353O4 METHOD OF EVALUATING COPPER BASE ALLOYS Filed Feb. 27, 1952 OIX WW 3ZIS NIVH) INVENTOR United States Patent fice METHOD OF EVALUATING COPPER BASE ALLOYS John D. Berwick, Jr. North Haven, Conn., assignor to Olin Mathieson Chemieal Corporation, a corporation of Virginia Application February 27, 1952, Serial No. 273,758

4 Claims. (Cl. 73-432) This invention relates to a method of determining various properties of metals and alloys having definite polyhedral structure.

Various properties of metals having polyhedral structure and capable of deep drawing are related to each other and to the surface roughness of the metal. These properties include tensle strength p. s. i., elongation percentage in 2", and grain sze. Such metals include austenitic stainless steels, low alloy steels, deep drawing grades of aluminum, copper and copper base alloys. By way of description the followng specification will be directed to determining grain size of copper base alloys, but the invention is not limited to these alloys, and can also be employed for determining the other factors mentioned.

F abricators of brass, bronze and other copper base alloys desire to secure material from the rolling mills which will require the least amount of polishing to produce a high lustre on the finshed product. The ideal material is that having the smallest average grain size which can be drawn or otherwse formed without breakage. The smaller grain size results in the smoothest formed surface in the fabricated product. As some tolerances must be allowed for manufacturing varables, the specifications are generally establshed as the minimum grain size which the fabricator can use with an upper figure or spread to allow fl such manufacturing variables.

Grain size has heretofore been determined by one of several methods. When determined by estimate, the specimen is viewed in a microscope at a magnification of 75 diameters and compared with pictures of standard grain sizes published by the A. S. T. M. A second, and more accurate, method is to count the number of grains intersecting a line of known length. This is known as the Heyn intercept method. Both of these methods are open to the objection that they depend upon the skill of the operator. A more accurate method is the Jeffries modified pianimetric method. This requires counting of grains within an area and is, therefore, more cumbersome than either of the other methods.

My invention comprises a method of measuring grain size of these metals and alloys by mechanical means whereby more accurate results are obtained and in which the accuracy of the results does not depend upon the skill of the operator. I have discovered that upon stretching, the surface of a sample of a rolled alloy becomes roughened in proportion to the size of the grains it contains and that a curve of surface roughness plotted against grain size is a substantially straight line. 1, therefore, stretch a specimen of the material a predetermined amount, measure the roughness of the surface by apparatus available for that purpose, such a profilometer, and then convert the value obtained to grain size by means of charts or tables made available from experimental determinations.

In practicing the invention a specimen strip is first cut from the rolled sheet. The specimenis of a uniform wdth, and of a width that can be handled in the various apparatus. In actual practice I have employed specimens inch by 5 inches.

The specimen is marked with a one inch or two inch gauge length to facilitate determination of percentage of stretch. The specimen is then stretched to the desired percentage in any suitable stretching apparatus. It is then placed in a Profilometer, an apparatus manufactured by Physicists Research Corporation, to quantitatively measure surface roughness. This apparatus traces the surface and averages the roughness as the root means of the square of the distance from the valleys of the surface to the hilltops." It is indicated on the dial of the instrument as microinches R. M. S. (root means square). Any other apparatus capable of measuring the surface rough ness may be used in place of the Profilometer.

By means of previously prepared charts or tables, the value thus obtained may be converted to grain size. In the accompanying drawing I have shown a chart prepared from data I have determined in which surface roughness in microinches, R. M. S. is plotted against grain size.

Curve 1 represents the values of a copper base alloy that has been stretched 20 percent; and

Curve 2 the values of such an alloy that has been stretched 30 percent.

By way of example with 20 percent stretch, if the surface roughness reading is 82 microinches, as indicated by point 3, the grain size is 60 microns. Similarly with a 30 percent stretch, and a surface roughness of 68 microinches, as indicated by point 4, the grain size is 40 microns.

As a result of the experimental work performed, I have determined that the gauge of copper base alloys has little etcct on surface roughness-grain size relationship. The procedure herein described is best suited for grain sizes below 080 mm. but is satisfactory up to .140 mm. The relationship does not held good for very thn metal or relatively thn metal with very large grain size, but these consttute a very minor part of commercial production of copper base alloys. Separate curves or tables may be used to advantage for material over 100 in. thck and ander .006 in. thick. I have also found that small variations in the amount of stretch do not appreciably affect the results.

Experiments have been made in which the specimens were stretched 40 percent to secure maximum roughness. Many samples broke before being stretched to that point. A 30 percent stretch has been found to be satisfactory in most instances; The exceptions to this are the very large grained, relatively thn sheets referred to above. I have also found that for practical purposes a 20 percent stretch gives reliable results.

Instead of grain. size the usefulness of an alloy of the type discussd for fabricating is determined by its tensile strength p. s. i. or an elongation percentage in 2. These properties all indicate the ductilty of the metal, and the amount of polishing it will require after fabricating. By means of tables grain size may be translated into either of these values or these values may be translated into grain size. With copper base alloys diferences in composition of the alloy and difierences in gauge have little etect on the relation of surface roughness to grain size.

In determining properties other than grain size with metals or alloys other than copper base alloys, and of diflerent gauges, separate charts or tables must be used to convert the Profilorneter readings to the desired values.

Among the many advantages of the invention are its simplicty of operation, minimizing of variation When work is done by different operators, relatively large area of specimens covered as compared to micro examination,- and area traced not arbitrarily selected by the operator. I have also found that it makes substantially no 2,735,304 Patented Feb. 21, 1956 7 diiferenc whether the stretching is done in the directi0n of the grain or across the grain.

I claim:

1. The method of determining the grain size of a test sample of a rolled metal haviriga polyhedral structure whch comprises stretching the test sample by a predetermined amount ancl quantitatively measuring the surface roughness of the sample after subh stretching, whereby the grain size of such test sample may be determined by cunvertng the so measured surface roughness nto grain size by means of experimentally determined data on the relation between grain sizes and corrcsponding surface rouglmesses of rolled spcmens of such a metal whch have been stretched such predetermined amount.

2. The method according toelaim 1, in which the test sample is stretched substantially 20%.

-s. m method according claim 1, in which the u:

sample is strelched substantially 30% 4. The method aecording to claim 1, in which the metal is a copper base alloy.

Reference: Clted in the file of this patent UNITED. STATES PATENTS Cross Apr. 9 1946 UI'HER REFERENCES Grain sm, Symposium held during the Sixteenth Annual Conventon of the Society in New York city the

Claims (1)

1. THE METHOD OF DETERMINING THE GRAIN SIZE OF A TEST SAMPLE OF A ROLLED METAL HAVING A POLYHEDRAL STRUCTURE WHICH COMPRISES STRETCHING THE TEST SAMPLE BY A PREDETERMINED AMOUNT AND QUANTITATIVELY MEASURING THE SURFACE ROUGHNESS OF THE SAMPLE AFTER SUCH STRETCHING, WHEREBY THE GRAIN SIZE OF SUCH TEST SAMPLE MAY BE DETERMINED BY

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