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Testing the Hardness of Metals
This is from the 1924 edition of Machinery's Handbook, which I inherited from my granduncle Carl Granberg, a tool & die maker who came to the US from Sweden. He worked for Studebaker for 40 years and never missed a day. (He was late once, about ten minutes -- the snow was pretty deep that day; nobody else even tried.)
"Machinery", which I guess was a magazine, was published by The Industrial Press, New York; it was subtitled "The Open Window to the Machinery Industry".
The 1924 edition of Machinery's Handbook has 1592 pages. The copyright has expired.
DISCLAIMER: DON'T WRITE FOR ADVICE ON THIS STUFF. I DON'T HAVE ANY. -- I just had the book and figured that some of the material in it would be useful to a far wider audience than would see it on my bookshelf.
TESTING THE HARDNESS OF METALS
Different Methods of Hardness Testing. -- There are four typical methods for testing the hardness of metals. These are the sclerometer method introduced by Turner in 1896; the scleroscope method recently invented by Shore; the indentation test adopted by Brinell about 1900; and the drill test introduced by Keep a few years earlier. The principles underlying each of the four methods are briefly described in the following:
Turner's Sclerometer. -- In this form of test a weighted diamond point is drawn, once forward and once backward, over the smooth surface of the material to be tested. The hardness number is the weight in grams required to produce a standard scratch. The scratch selected is one which is just visible to the naked eye as a dark line on a bright reflecting surface. It is also the scratch which can just be felt with the edge of a quill when the latter is drawn over the smooth surface at right angles to a series of such scratches produced by regularly increasing weights.
Shore's Scleroscope. -- In this instrument, a small cylinder of steel, with a hardened point, is allowed to fall upon the smooth surface of the metal to be tested, and the height of the rebound of the hammer is taken as the measure of hardness. The hammer weighs about 40 grains, the height of the rebound of hardened steel is in the neighborhood of 100 on the scale, or about 6-1/4 inches, while the total fall is about 10 inches or 254 millimeters.
Brinell's Test. -- In this method, a hardened steel ball is pressed into the smooth surface of the metal so as to make an indentation of a size such as can be conveniently measured under the microscope. The spherical area of the indentation being calculated and the pressure being known, the stress per unit of area when the ball comes to rest is calculated, and the hardness number obtained. Within certain limits, the value obtained is independent of the size of the ball and of the amount of pressure.
Keep's Test. -- In this form of apparatus a standard steel drill is caused to make a definite number of revolutions while it is pressed with standard force against the specimen to be tested. The hardness is automatically recorded on a diagram on which a dead soft material gives a horizontal line, while a material as hard as the drill itself gives a vertical line, intermediate hardness being represented by the corresponding angle between 0 and 90 degrees.
Hardness Scales Compared Metal Sclerometer Scleroscope Brinell Method * Mohs's Scale for Minerals
Lead 1.0 1.0 1.0 Talc -- 1
Gypsum -- 2
Calcite -- 3
Fluor Spar -- 4
Apatite -- 5
Orthoclase -- 6
Quartz -- 7
Topaz -- 8
Sapphire
or
Corundum -- 9
Diamond -- 10
Tin 2.5 3.0 2.5
Zinc 6.0 7.0 7.5
Copper, soft 8.0 8.0 ...
Copper, hard ... 12.0 12.0
Softest Iron 15.0 ... 14.5
Mild steel 21.0 22.0 16 - 24
Soft cast iron 21 - 24 24.0 24.0
Rail steel 24.0 27.0 26 - 35
Hard cast iron 36.0 40.0 35.0
Hard white iron 72.0 70.0 75.0
Hardened steel ... 95.0 93.0
*Actual numerals have been divided by 6 for purposes of comparison.
Comparison between Testing Methods. -- Each form of test has its advantages and its limitations. The sclerometer is cheap, portable, and easily applied, but it is not applicable to materials which do not possess a fairly smooth reflecting surface and the standard scratch is only definitely recognized after some experience. The Short test is simple, rapid and definite for materials for which it is suited, but results obtained vary somewhat with the size and thickness of the sample. As a comparative measure of the hardness of material of the same quality and structure, however, it is quite accurate, but it is not reliable for comparing the hardness of two different metals. The Brinell test is especially useful for constructive materials. It is definite, and, with the new appliances recently brought out, easily applied. It cannot be applied, however, to very brittle materials, such as glass, nor is it satisfactory for use on hardened high-carbon steel. Keep's test is especially suited for castings of all kinds, as it records not only the surface hardness, but also the hardness of the whole thickness, and gives indications of blow-holes, hard streaks and spongy places. Obviously, it cannot be applied to materials too hard to be conveniently drilled by a hardened steel drill.
The accompanying table gives values obtained on the same materials by the scleroscope, sclerometer, and the Brinell test, the figures being reduced to a common unit, assumed as 1 as a starting point; thus the actual Brinell numerals have been divided by 6, thereby reducing the hardness values for purposes of comparison.
yada yada yada skipping down....
Application of the Brinell Method. -- The Brinell method, as mentioned, consist in partly forcing a hardened steel ball into the sample to be tested so as to effect a slight spherical impression. The diameter of the impression is measured and the surface of the spherical cavity calculated. The pressure required in kilograms for effecting the impression is divided by the area of the impression in square millimeters; the quotient is an expression of the hardness of the material tested, and is called the hardness numeral. The standard diameter of the ball is 10 millimeters (0.3937 inch) and the pressure, 3000 kilograms (6614 pounds) in the case of iron and steel, while in the case of softer metals, a pressure of 500 kilograms (1102 pounds) is used. The diameter of the impression in the original instrument is measured by means of a microscope, after which the hardness numeral may be obtained without calculation directly from the table of "Hardness Numerals -- Brinell System". Instruments have been constructed later so as to eliminate the need of the use of a microscope for measuring the diameter of the impression.
Relation between Hardness of Materials and Ultimate Strength. -- A constant relationship exists between the hardness numeral as determined by the Brinell test and the ultimate strength of the material tested. The coefficients by which the hardness numerals must be multiplied to obtain the ultimate strength in kilograms per square millimeter may be determined by tests, and are constant for each class and kind of material, but they differ slightly for different materials and for materials treated in a different manner. The following coefficients are given for different grades of steel:
Steels, extra soft K = 0.360
Steels, soft and semi-hard K = 0.355
Steels, semi-hard K = 0.353
Steels, hard K = 0.349
It will be seen that these coefficients differ by but a slight amount for steel of different composition, and, as a general rule, the factor 0.355 may be used for all grades of steel.
Example: -- Assume that a hardness test of structural steel (semi-hard) by the Brinell method gave an impression of 4.6 millimeters. The hardness numeral, from the table, would be 170, and the ultimate strength, 0.355 x 170 = 60 kilograms per square millimeter.
Accuracy of Brinell Hardness Test. -- When commercial apparatus, as ordinarily used for making the Brinell test, is employed, and the test is carried out with ordinary care and precaution, it is reliable within an error of five Brinell units above or below the actual hardness. In other words, if the hardness of two pieces of metal is tested, and the difference on the Brinell scale is more than ten hardness units, it is certain that there is an absolute difference in the hardness of the pieces tested. With regard to the conditions under which the tests should be made, it may be stated that the pressure should be gradually applied for two minutes or more, and the pressure should be kept on the test piece for a period of at least five minutes.
Relation between Hardness and Wear of Steel. -- There is no definite relation between hardness, as measured by the Brinell hardness testing method, and wear. While, in general, a high Brinell hardness number may be expected to indicate a metal which will give better wear, there are so many exceptions that this test for indication wearing properties would be unreliable. As an example, Hadfield's manganese steel,which has a low Brinell hardness number, is one of the best steels as far as wear is concerned. The relation of either Brinell tests of ordinary wear tests to wear in actual practice is a subject which requires further investigation. Wear tests should be made along different lines, according to the actual uses to which the metal is to be put.
Hardness Scales Compared
Scleroscope Hardness Scale * Name of Metal Annealed/ Hammered
Lead (cast) 2 - 5 3 - 7
Babbitt metal 4 - 9
Gold 5/ 8.5
Silver 6.5/ 20 - 30
Brass (cast) 7 - 35
Pure tin (cast) 8
Brass (drawn) 10 - 15 / 24 - 25
Bismuth (cast) 9
Platinum 10 / 17
Copper (cast) 6 / 14 - 20
Zinc (cast) 8/ 20
Iron, pure 18 / 25 - 30
Mild steel, 0.15 per cent carbon 22 / 30 - 45
Nickel anode (cast) 31/ 55
Iron, gray (cast) 30 - 45
Iron, gray (chilled)
50 - 90
Steel, tool, 1 per cent carbon 30 - 35/ 40 - 50
Steel, tool, 1.65 per cent carbon 35 - 40
Vanadium steel 35 - 45
Chrome - nickel steel 47
Chrome - nickel steel (hardened)
60 - 95
Steel, high - speed (hardened)
70 - 105
Steel, carbon tool (hardened)
70 - 105
* The figures given are subject to variation, owing to the differences in composition of the metals tested.
--------------------------------------------------------------------------------
Next section in the book: Principles of Iron and Steel Manufacture.
I don't have any immediate plans to put it up.
--------------------------------------------------------------------------------
Comments to: ebear@zianet.com (Eric Bear Albrecht)
My home page
Depends! Scroll down to the bottom scale. I bolded the comparisons, in case you don't want to read it all.
Testing the Hardness of Metals
This is from the 1924 edition of Machinery's Handbook, which I inherited from my granduncle Carl Granberg, a tool & die maker who came to the US from Sweden. He worked for Studebaker for 40 years and never missed a day. (He was late once, about ten minutes -- the snow was pretty deep that day; nobody else even tried.)
"Machinery", which I guess was a magazine, was published by The Industrial Press, New York; it was subtitled "The Open Window to the Machinery Industry".
The 1924 edition of Machinery's Handbook has 1592 pages. The copyright has expired.
DISCLAIMER: DON'T WRITE FOR ADVICE ON THIS STUFF. I DON'T HAVE ANY. -- I just had the book and figured that some of the material in it would be useful to a far wider audience than would see it on my bookshelf.
TESTING THE HARDNESS OF METALS
Different Methods of Hardness Testing. -- There are four typical methods for testing the hardness of metals. These are the sclerometer method introduced by Turner in 1896; the scleroscope method recently invented by Shore; the indentation test adopted by Brinell about 1900; and the drill test introduced by Keep a few years earlier. The principles underlying each of the four methods are briefly described in the following:
Turner's Sclerometer. -- In this form of test a weighted diamond point is drawn, once forward and once backward, over the smooth surface of the material to be tested. The hardness number is the weight in grams required to produce a standard scratch. The scratch selected is one which is just visible to the naked eye as a dark line on a bright reflecting surface. It is also the scratch which can just be felt with the edge of a quill when the latter is drawn over the smooth surface at right angles to a series of such scratches produced by regularly increasing weights.
Shore's Scleroscope. -- In this instrument, a small cylinder of steel, with a hardened point, is allowed to fall upon the smooth surface of the metal to be tested, and the height of the rebound of the hammer is taken as the measure of hardness. The hammer weighs about 40 grains, the height of the rebound of hardened steel is in the neighborhood of 100 on the scale, or about 6-1/4 inches, while the total fall is about 10 inches or 254 millimeters.
Brinell's Test. -- In this method, a hardened steel ball is pressed into the smooth surface of the metal so as to make an indentation of a size such as can be conveniently measured under the microscope. The spherical area of the indentation being calculated and the pressure being known, the stress per unit of area when the ball comes to rest is calculated, and the hardness number obtained. Within certain limits, the value obtained is independent of the size of the ball and of the amount of pressure.
Keep's Test. -- In this form of apparatus a standard steel drill is caused to make a definite number of revolutions while it is pressed with standard force against the specimen to be tested. The hardness is automatically recorded on a diagram on which a dead soft material gives a horizontal line, while a material as hard as the drill itself gives a vertical line, intermediate hardness being represented by the corresponding angle between 0 and 90 degrees.
Hardness Scales Compared Metal Sclerometer Scleroscope Brinell Method * Mohs's Scale for Minerals
Lead 1.0 1.0 1.0 Talc -- 1
Gypsum -- 2
Calcite -- 3
Fluor Spar -- 4
Apatite -- 5
Orthoclase -- 6
Quartz -- 7
Topaz -- 8
Sapphire
or
Corundum -- 9
Diamond -- 10
Tin 2.5 3.0 2.5
Zinc 6.0 7.0 7.5
Copper, soft 8.0 8.0 ...
Copper, hard ... 12.0 12.0
Softest Iron 15.0 ... 14.5
Mild steel 21.0 22.0 16 - 24
Soft cast iron 21 - 24 24.0 24.0
Rail steel 24.0 27.0 26 - 35
Hard cast iron 36.0 40.0 35.0
Hard white iron 72.0 70.0 75.0
Hardened steel ... 95.0 93.0
*Actual numerals have been divided by 6 for purposes of comparison.
Comparison between Testing Methods. -- Each form of test has its advantages and its limitations. The sclerometer is cheap, portable, and easily applied, but it is not applicable to materials which do not possess a fairly smooth reflecting surface and the standard scratch is only definitely recognized after some experience. The Short test is simple, rapid and definite for materials for which it is suited, but results obtained vary somewhat with the size and thickness of the sample. As a comparative measure of the hardness of material of the same quality and structure, however, it is quite accurate, but it is not reliable for comparing the hardness of two different metals. The Brinell test is especially useful for constructive materials. It is definite, and, with the new appliances recently brought out, easily applied. It cannot be applied, however, to very brittle materials, such as glass, nor is it satisfactory for use on hardened high-carbon steel. Keep's test is especially suited for castings of all kinds, as it records not only the surface hardness, but also the hardness of the whole thickness, and gives indications of blow-holes, hard streaks and spongy places. Obviously, it cannot be applied to materials too hard to be conveniently drilled by a hardened steel drill.
The accompanying table gives values obtained on the same materials by the scleroscope, sclerometer, and the Brinell test, the figures being reduced to a common unit, assumed as 1 as a starting point; thus the actual Brinell numerals have been divided by 6, thereby reducing the hardness values for purposes of comparison.
yada yada yada skipping down....
Application of the Brinell Method. -- The Brinell method, as mentioned, consist in partly forcing a hardened steel ball into the sample to be tested so as to effect a slight spherical impression. The diameter of the impression is measured and the surface of the spherical cavity calculated. The pressure required in kilograms for effecting the impression is divided by the area of the impression in square millimeters; the quotient is an expression of the hardness of the material tested, and is called the hardness numeral. The standard diameter of the ball is 10 millimeters (0.3937 inch) and the pressure, 3000 kilograms (6614 pounds) in the case of iron and steel, while in the case of softer metals, a pressure of 500 kilograms (1102 pounds) is used. The diameter of the impression in the original instrument is measured by means of a microscope, after which the hardness numeral may be obtained without calculation directly from the table of "Hardness Numerals -- Brinell System". Instruments have been constructed later so as to eliminate the need of the use of a microscope for measuring the diameter of the impression.
Relation between Hardness of Materials and Ultimate Strength. -- A constant relationship exists between the hardness numeral as determined by the Brinell test and the ultimate strength of the material tested. The coefficients by which the hardness numerals must be multiplied to obtain the ultimate strength in kilograms per square millimeter may be determined by tests, and are constant for each class and kind of material, but they differ slightly for different materials and for materials treated in a different manner. The following coefficients are given for different grades of steel:
Steels, extra soft K = 0.360
Steels, soft and semi-hard K = 0.355
Steels, semi-hard K = 0.353
Steels, hard K = 0.349
It will be seen that these coefficients differ by but a slight amount for steel of different composition, and, as a general rule, the factor 0.355 may be used for all grades of steel.
Example: -- Assume that a hardness test of structural steel (semi-hard) by the Brinell method gave an impression of 4.6 millimeters. The hardness numeral, from the table, would be 170, and the ultimate strength, 0.355 x 170 = 60 kilograms per square millimeter.
Accuracy of Brinell Hardness Test. -- When commercial apparatus, as ordinarily used for making the Brinell test, is employed, and the test is carried out with ordinary care and precaution, it is reliable within an error of five Brinell units above or below the actual hardness. In other words, if the hardness of two pieces of metal is tested, and the difference on the Brinell scale is more than ten hardness units, it is certain that there is an absolute difference in the hardness of the pieces tested. With regard to the conditions under which the tests should be made, it may be stated that the pressure should be gradually applied for two minutes or more, and the pressure should be kept on the test piece for a period of at least five minutes.
Relation between Hardness and Wear of Steel. -- There is no definite relation between hardness, as measured by the Brinell hardness testing method, and wear. While, in general, a high Brinell hardness number may be expected to indicate a metal which will give better wear, there are so many exceptions that this test for indication wearing properties would be unreliable. As an example, Hadfield's manganese steel,which has a low Brinell hardness number, is one of the best steels as far as wear is concerned. The relation of either Brinell tests of ordinary wear tests to wear in actual practice is a subject which requires further investigation. Wear tests should be made along different lines, according to the actual uses to which the metal is to be put.
Hardness Scales Compared
Scleroscope Hardness Scale * Name of Metal Annealed/ Hammered
Lead (cast) 2 - 5 3 - 7
Babbitt metal 4 - 9
Gold 5/ 8.5
Silver 6.5/ 20 - 30
Brass (cast) 7 - 35
Pure tin (cast) 8
Brass (drawn) 10 - 15 / 24 - 25
Bismuth (cast) 9
Platinum 10 / 17
Copper (cast) 6 / 14 - 20
Zinc (cast) 8/ 20
Iron, pure 18 / 25 - 30
Mild steel, 0.15 per cent carbon 22 / 30 - 45
Nickel anode (cast) 31/ 55
Iron, gray (cast) 30 - 45
Iron, gray (chilled)
50 - 90
Steel, tool, 1 per cent carbon 30 - 35/ 40 - 50
Steel, tool, 1.65 per cent carbon 35 - 40
Vanadium steel 35 - 45
Chrome - nickel steel 47
Chrome - nickel steel (hardened)
60 - 95
Steel, high - speed (hardened)
70 - 105
Steel, carbon tool (hardened)
70 - 105
* The figures given are subject to variation, owing to the differences in composition of the metals tested.
--------------------------------------------------------------------------------
Next section in the book: Principles of Iron and Steel Manufacture.
I don't have any immediate plans to put it up.
--------------------------------------------------------------------------------
Comments to: ebear@zianet.com (Eric Bear Albrecht)
My home page
Comment