US2751291A - Alloy steel - Google Patents

Description

ALLGY STEEL John N. Carter and Donald N. Rosenblatt, Salt Lake City, Utah, assignors to The Eimco Corporation, Salt Lake City, Utah, a corporation of Utah No Drawing. Application May 20, 1955, Serial No. 510,036

Claims. (Cl. 75-128) This invention relates to steels. it relates more particularly to austenitic steels which have a high resistance to erosive wear and a high sensitivity to work hardening.

A principal object of this invention is to provide an alloy steel which may be used for producing wrought and cast articles having a high capacity for work hardening.

Another object of this invention is to provide an alloy steel used for producing articles having a high sensitivity to work hardening which possesses a high degree of resistance to erosive and abrasive wear.

A further object of this invention is to provide a Work hardenable alloy steel product having great strength and toughness.

Still another object of this invention is to provide a strong, tough, work-hardenable alloy steel product possessing a high degree of resistance to erosive and abrasive wear.

Other objects and advantages of this invention will become apparent from the following description and drawing.

We have found that a fine dispersion of vanadium or other alloy carbides in an austenitic matrix provides a structure much superior in work-hardening properties to the ordinary carbide-free austenitic structure of austenitic 11 to 15% manganese steel. Our alloy retains the high toughness characteristics of austenitic manganese steel and still overcomes certain undesirable characteristics found in austenitic manganese steel.

Those features generally considered undesirable in the commercial application of articles made from austenitic manganese steel are:

(1) Relatively poor resistance to abrasion and erosion in the absence of heavy impact or high stress.

(2) Excessive flow under impact.

(3) Embrittlement caused by reheating the toughened steel above 500 F.

(4) Poor response to heat treatment in heat treating sections exceeding 6 inches in thickness.

Our alloy has overcome each of the above undesirable features commonly found in austenitic manganese steel to a remarkable degree.

The composition range in which the specified advantages are found is as follows: Carbon .85 to 1.3%, manganese .5 to 2.5%, copper 1.5 to 4.5%, nickel 5 to chromium traces to 3%, molybdenum traces to 3%, at least one metal of the group consisting of vanadium, titanium, columbium and tungsten, the total of chromium molybdenum and metals of said group being at least 2% and not exceeding about 5%, the remainder being iron, together with the usual amounts of silicon, sulphur, phosphorus, and aluminum normally in steel. From traces up to .15% phosphorus, from traces up to .10% sulphur, and from traces up to 1.5% silicon may be present in the steel.

A particularly useful range of compositions is: carbon .95 to 1.05%, nickel 6 to 7%, copper 2.5 to 3.5%, chromium .5 to 1.5%, manganese 1 to 1.5%, molybdenum .25 to .5%, vanadium .75 to 1%, prosphorus traces to 2,751,291 Patented June 19, 1956 .15 sulphur traces to .1%, silicon traces to 1.5%, the balance being substantially all iron.

We have discovered the combining of nickel, copper, and carbon in the proportions indicated makes steel very sluggish to allotropic changes, so that after rapid cooling from an austenitizing treatment it remains in the austenitic condition. Such an alloy will have substantially the same physical properties as austenitic manganese steel. However, a steel made austenitic by nickel and copper has certain advantages over a steel made austenitic by the addition of large quantities of manganese, either with or without copper and/or nickel. The advantages are in heat treatment and in casting, and are the result of the nature of the basic austenitizer. Manganese, while it is a strong austenitizer, is also a carbide former, and under favorable conditions of time and temperature will form iron manganese carbides which favor the grain boundaries and embrittle the austenite by their continuity. Where copper and nickel are used, this difiiculty is overcome because these elements are not carbide formers.

We have further discovered that by adding suitable proportions of certain carbide forming elements to the above, such as chromium, molybdenum, vanadium, or tungsten, columbium, or titanium, and arresting the cooling from the austenitizing treatment for a short time at a high temperature and then rapidly cooling to room temperature, an austenitic structure containing a fine dispersion of alloy carbides within the austenite grains may be obtained.

The additions of manganese, chromium, and molybdenum also serve to augment the carbon, nickel, and copper in retaining austenite. This is accomplished by retarding the transformation rate of gamma to alpha iron. This applies in retarding reactions, including the pearlite and bainite reactions and also the suppression of martensite.

Water, oil, or salt quenched specimens of steel within the range of composition previously specified have a Brinell hardness in the range of. to 225, whether or not cooling has been arrested to cause carbide precipitation. Repeated heavy impacts will harden the alloy to a maximum value of about 620 Brinell hardness. In the range of composition centering around .95 to 1.05% carbon, 6 to 7% nickel, 2.5 to 3.5% copper, .5 to 1.5% chromium, 1 to 1.5% manganese, .25 to .5% molybdenum, .75 to 1% vanadium, which is one preferred composition range, the desired structure for articles which are to have a high toughness and a high sensitivity to work hardening may be obtained by heating the articles to 1900 to 2100 F., holding at temperature 4 to 8 hours, furnace cooling to 1650 to 1750 F., and holding 1 to 3 hours at this temperature, and then rapidly cooling by salt, oil, or water quenching.

The length of time at which the articles are subjected to the 1700 F. temperature largely determines (together with the amount and kind of carbide forming element present) the amount of dispersed carbide present in the quenched materials micro-structure. Suflicient carbide to considerably enhance wear resistance is normally obtained in relatively short periods of time, one hour representing good commercial practice. Larger amounts of carbide occasioned by prolonged holding in the precipitation temperature range lower the stability of the matrix austenite and result in articles having less impact strength. The treatment may be adjusted in accordance with the particular service in which the article is to be used. When an article is to be used in a service requiring extremely high resistance to shock, the heat treatment should be designed so as to allow the minimum time (approximately 4 hour) to be held in the precipitation temperature (1700 F.) range. It should be'noted that in cooling articles having heavy sections, it is possible that the necessary amount of time in the precipitation temperature range is attained through the natural cooling process without any intentional arrest of cooling from the austenitizing temperature.

We have found that the precipitation of carbide should, whenever possible, be controlled in the heat treatment of the alloy steel. If the steel is held for long periods of time below the correct (l7S0-1650 F.) precipitation range, that is, from 1650 to 1450 F., carbide precipitation will occur at the grain boundary rather than as spheroids within the grains. When grain boundary carbide is precipitated wear resistance is not enhanced and a very severge loss of toughness takes place. If the steel is held for long periods of time above the correct precipitation temperature range, very little carbide precipitation will take place.

An important advantage of our alloy steel over austenitic manganese steel is that in the preferred composition range of our alloy steel grain boundary carbide is formed in a narrower temperature range and at a lower rate in said temperature range. This means that whereas austenitic manganese steel cannot be successfully heat treated in sections exceeding 6 inches, our alloy steel can be heat treated in sections up to about 10 inches in thickness.

In the ascast condition the alloy steel contains some spheroidal carbide, some grain boundary carbide, and some large primary carbides, in an austenitic matrix. The ascast alloy, does not contain appreciable quantities of pearlite, bainite, or martensite, regardless of section size, except where decarburization has occurred. An important advantage of the alloy steel of the invention over austenitic manganese steel is that our steel is not extremely brittle in the ascast condition and is thus more easily handled in the foundry and the steel mill, prior to heat treatment.

Still another advantage of our alloy steel over austenitic manganese steel is that our alloy is easily manufactured by either the acid or basic steel making processes, Whereas austenitic manganese steel is not easily produced by an acid steel making process.

Carbon is an important element in our steel and must be controlled within a narrow range. In our preferred composition range (.95 to 1.05% carbon), if the carbon is lower than .95% it is necessary to reduce the amount of carbide forming elements, particularly vanadium. The reason for this is that about .80% carbon must remain in the solution as an austenite stabilizer, leaving only the excess over .80% carbon to form alloy carbides. With lower amounts of carbide forming elements, the wear resistance of the steel is reduced. When the carbon content exceeds 105%, there is a strong tendency for the steel in its initial cooling from solidification to form a cellular network of primary alloy carbide which embrittles the steel and is extremely difficult to redissolve by heat treating. This is particularly true in heavy sections having slow initial cooling rates from the solidification temperature. The same thing happens when there is an excess carbide forming elements present, so that we prefer to hold the total of all carbide forming elements present, including manganese, to a maximum of Mechanical properties of the steel in the preferred range of composition are of sufficiently high level to make the steel suitable for services in which conditions include severe shock. The alloy steel of the invention, properly heat treated, will have a V notch charpy impact value in excess of 20 foot pounds. This value is not appreciably lowered when impact testing is conducted at sub-zero temperatures. The steel is suitable, by virtue of its high toughness, for the manufacture of articles, such as jaw crusher plates, scoop lips, dipper teeth, ball mill liners, railroad frogs and switch work, caterpillar shoes, roll shells, breaker bars for crushers, etc.

Our alloy steel can be machined by using carbide tools, slow speeds, and heavy feeds.

The alloy is nonmagnetic as heat treated but becomes noticeably magnetic after cold-work. The magnetic effect appears to be the result of phase changes at the carbide spheroid-matrix interface. Magnetism in our alloy is not caused by the formation of martensite in the worked metal except in the presence of decarburization. We have found that the formation of martensite in-the decarburized zone of our alloy does not contribute to wear resistance, but rather severely embrittles the steel in the areas where martensite forms. However, the. skin embrittlement is not a serious problem because of the relatively shallow depth of a decarburized skin. Surface cracks forming in the decarburized skin will not progress into the tough underlying true austenitic structure of the steel.

When the steel is used for articles as described above, the usual advantages of austenitic manganese steel in toughness are retained, and the added advantage of high erosion resistance normally found only in much more brittle materials (less than 1 foot pound notched impact strength), such as martensitic alloy white irons, is also attained. In addition, when our steel is used in such articles they can be field welded without causing embrittlement in the heat affected zone. Further, when our steel is used in such articles it will not cause buckling, binding, .and distortion in such articles as is experienced with austenitic manganese steel which flows excessively under repeated impact.

Table I is a comparative study of the alloy of this invention in wear resistance under conditions of high and low stress wear against several commercial wear resisting materials tested under identical conditions.

Erosion Wear Post: An 8" dia. canvas covered redwood disc 15 I0- tated at 36 R. P. M. through aslurry of 52% 200 mesh aluminum oxide, 26% 2G() mesh silica flour, 22% bcntorute and water to 65 Baum. A dia. x 1 long specimen of the material being tested is held against the disc with a 3 pound pressure. Weight loss is measured alter a hr. run-in over a test period of 5 hrs. The wear test values are reported in grns. lost per 100 gms. of standard material lost under identical testing conditions. Figures represent average of 3 or more tests. The wear test for erosion has a reproducibility of plus or minus 3.5%.

2 Gouging \Vcar Test: An 8 dia. grinding wheel (Norton A36P5l3) is rotated at 36 R. I. M. in a water cooling trough. A it dia. x 1" long specimen of the material being tested is held against the rlndwheel under a compressive load of 250 p. i. Weight loss is measured after a. 10 minute run-in over a test period of minutes. The wear test values are reported in gins. lost per 100 grins. of standard material lost under identical testing conditions. Figures represent average of 3 or more tests. The Wear test for gouging has a reproducibility of plus or minus 5.0%.

3 Composition:

0 MN P Si Or Mo Ni Cu V l. 0]. 1. l2 0. 32 .0-i3 58 I. 5O 6. 3. 20 83 Heat treated in a 4-ton batch load; heated to 1975" F.; held 4 hours; furnace cooled to 1700 F.; held 1 hour; water quenched from 1700 F.

resist low stress erosive wear are quite hard and also brittle. Table I shows that the erosion wear resistance is poor for the softer materials, particularly austenitic manganese steel, except that the alloy of this invention has a high resistance to erosion wear at a low hardness level. This is due to the eifect in our alloy steel of the finely dispersed, extremely hard alloy carbide particles.

The high stress or gouging wear resistance of ferrous materials is of a nature that softer materials exhibit good wear resistance if they are work-hardenable. Table I shows that the austenitic nature of the alloy steel of this invention permits of sufiicient work-hardening to confer excellent resistance to gouging wear. This property of our alloy steel is not dependent on the carbides but rather on the austenitic matrix of the steel.

The beneficial effects of the dispersed carbide in our steel become effective as the wear stress is reduced. As the compressive load is decreased our alloy steel shows increased wear resistance over austenitic manganese steel, until at a load of 15 pounds per square inch for every 100 grams of austenitic manganese steel lost by wear, our alloy loses only 30 grams or about three times less.

Thus, a remarkable property of our alloy steel is in its ability to resist low stress wear without appreciable work hardening. This makes the steel suitable for use in articles where austenitic manganese steel is known to give poor performance. At the same time, our alloy steel possesses suflicient work hardening properties to equal the performance of austenitic manganese steel where that steel is used under conditions most favorable for its successful performance.

It is well known that austenitic manganese steel workhardens only where there is plastic deformation or flow. Articles made from austenitic manganese steel when subjected to repeated impacts show considerable flow while work hardening. Often the flow accompanying work hardening is an undesirable characteristic of the steel. Our alloy steel, while it also must be deformed somewhat during work hardening, needs do so to a much lesser extent than austenitic manganese steel.

Under identical conditions, after about 1000 foot pounds of cumulative impact, our alloy steel exhibits only slightly more than half the flow of austenitic manganese steel. Another advantage of our steel over austenitic manganese steel is that up to 100 foot pounds of total impact our alloy steel shows no flow whatsoever.

in addition to the benefits previously noted, which are conferred by a dispersed carbide phase, the presence of these alloy carbides also accelerates the rate of work hardening. For example, our alloy steel exceeds a 300 Brinell hardness level after about 1500 foot pounds of total impact. In order for austenitic manganese steel to exceed a 300 Brinell hardness level, under identical testing conditions, about 4000 foot pounds of total impact are required.

One of the chief difficulties in the manufacture and use of articles made from work hardenable austenitic manganese steel is the tendency towards embrittlement of this steel when it is reheated after the initial toughening heat treatment. This is particularly troublesome when the article must be field welded and the heat affected zone being subcritically heated becomes severely damaged and embrittled. Thus, an important and identifying characteristic of our alloy austenitic steel over manganese austenitic steel is the ability of the alloy to withstand subcritical reheating.

We claim:

1. An alloy steel consisting of .85 to 1.3% carbon, .5 to 2.5% manganese, 1.5 to 4.5% copper, 5 to 10% nickel, up to 3% chromium, up to 3% molybdenum and up to 1.5% of at least one metal selected from the group consisting of vanadium, titanium, columbium and tungsten, the total of chromium, molybdenum and metals of said group being at least 2% and not exceeding about 5%, traces to .15% phosphorous traces to .1% sulphur and traces to 1.5% silicon, the balance substantially all iron.

2. An alloy steel consisting of .85 to 1.3% carbon, .5 to 2.5% manganese, 1.5 to 4.5% copper, 5 to 10% nickel, up to 3% chromium, up to 3% molybdenum and up to 1.5% vanadium in amounts totaling at least 2% and not exceeding about 5%, traces to .15 phosphorous, traces to .1% sulphur, and traces to 1.5% silicon, the balance substantially all iron.

3. An alloy steel consisting of .95 to 1.05% carbon, 6 to 7% nickel, 2.5 to 3.5 copper, 1 to 1.5% manganese, .5 to 1.5% chromium, .25 to .5 molybdenum, .75 to 1% vanadium, the total chromium, molybdenum and vanadium being at least 2%, traces to .15% phosphorous, traces to .1% sulphur, traces to 1.5% silicon, the balance substantially all iron.

4. A method of heat treating an alloy steel consisting of .85 to 1.3% carbon, .5 to 2.5% manganese, 1.5 to 4.5% copper, 5 to 10% nickel, up to 3% chromium, up to 3% molybdenum and up to 1.5% at least one metal selected from the group consisting of vanadium, titanium, columbium and tungsten, the total of chromium, molybdenum and metals of said group being at least 2% and not exceeding about 5%, traces to .15% phosphorous traces to .1% sulphur, and traces to 1.5% silicon, the balance substantially all iron which comprises heating the alloy to a temperature of at least 1900" F. for several hours, cooling to a temperature of about 1700 F., holding at about 1700 F. for several hours, and then rapidly quenching the alloy.

5. A method of heat treating an alloy steel consisting of .95 to 1.05% carbon, 6 to 7% nickel, 2.5 to 3.5% copper, 1 to 1.5% manganese, .5 to 1.5% chromium, .25 to .5 molybdenum, .75 to 1% vanadium, the total chromium, molybdenum and vanadium being at least 2%, traces to .15% phosphorus, traces to .1% sulphur, traces to 1.5% silicon, the balance substantially all iron which comprises heating the alloy to a temperature of from 1900% F. to 2100 F. for 4 to 8 hours, furnace cooling to from 1650 to 1750 F., holding at from 1650 to 1750 F. for 1 to 3 hours and then rapidly quenching the alloy.

No references cited.

Claims (1)

1. AN ALLOY STEEL CONSISTING OF .85 TO 1.3% CARBON, .5 TO 2.5% MANGANESE, 1.5 TO 4.5% COPPER, 5 TO 10% NICKEL, UP TO 3% CHROMIUM, UP TO 3% MOLYBDENUM AND UP TO 1.5% OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF VANADIUM, TITANIUM, COLUMBIUM AND TUNGSTEN, THE TOTAL OF CHROMIUM, MOLYBDENUM AND METALS OF SAID GROUP BEING AT LEAST 2% AND NOT EXCEEDING ABOUT 5%, TRACES TO .15% PHOSPHOROUS TRACES TO .1% SULPHUR AND TRACES TO 1.5% SILICON, THE BALANCE SUBSTANTIALLY ALL IRON.