GB2075550A - Abrasion Resistant Austenitic Stainless Steel - Google Patents

Abstract

An austenitic stainless steel exhibiting a very high work hardening rate, excellent abrasion resistance, high strength along with good ductility, and good hot workability, consists of, in weight percent, from 0.015% to 0.10% carbon, 5.5% to 10.0% manganese, 0.06% maximum phosphorus, 0.06% maximum sulfur, 2.0% maximum silicon, 12.5% to 20.0% chromium, 1.0% to 3.5% nickel, 0.85% maximum copper, 0.15% to 0.30% nitrogen, and balance iron, said steel having an instability factor ranging from 2.5 to 8.5 calculated by the equation: Instability factor=37.2-51.25(%C)- 2.59(%Ni)-1.02(%Mn)-0.47(%Cr)- 34.4(%N)-3(%Cu). The steel has particular utility for mining or material conveyors, automotive underbodies and similar products requiring high wear resistance and reasonable corrosion resistance.

Description

SPECIFICATION Abrasion Resistant Austenitic Stainless Steel This invention relates to an austenitic stainless steel of relatively low cost which exhibits a very high work hardening rate, excellent abrasion resistance, high strength in combination with good ductility, and good hot workability. Although not so limited, the steel of this invention has utility for mining or material conveyors, automotive underbody structures and similar applications requiring high resistance against wear and abrasion along with reasonable corrosion resistance.

The novel combination of properties in the steel of the invention is achieved by a critical balancing of the proportions of essential elements in order to obtain an austenite stability in hot rolled material which upon drastic cold reduction transforms to a controlled amount of deformation martensite with consequent high hardness, strength and abrasion resistance. Both the composition ranges of essential elements and austenite stability (as hereinafter defined) are critical in the steel of this invention.

United States Patent 3,940,266, to G. N. Goller and R. H. Espy, discloses an austenitic stainless steel having a high work hardening rate, good cryogenic toughness and good stress corrosion resistance, consisting essentially of from about 0.01% to about 0.06% carbon, about 11% to about 14% manganese, 0.06% maximum phosphorus, 0.04% maximum sulfur, 1% maximum silicon,15.5% to 20% chromium, 2.50% to 3.75% nickel, 0.20% to 0.38% nitrogen and balance iron except for incidental impurities. The steel of this patent has high austenite stability, thus resisting transformation to martensite during deformation.

United States Patent 3,989,474 a division of Patent No. 3,940,266, claims hot rolled stainless steel bar and rod, cold drawn wire and strand-like articles consisting essentially of from 0.06% to 0.12% carbon, 11% to 14% manganese, up to 0.06% phosphorus, up to 0.04% sulfur, up to 1% silicon, 1 5.5% to 20% chromium, 1.1% to 2.5% nickel, 0.20% to 0.38% nitrogen, and balance iron except for incidental impurities. Again these claimed products are substantially fully austenitic and have low magnetic permeability in the cold-reduced form.

United States Patent 2,778,731 to D. J. Carney, discloses an austenitic steel consisting of from 0.06% to 0.15% carbon, 14% to 20% manganese, 0.25% to 1.0% silicon, 17% to 18.5% chromium, 0.05% to 1.00% nickel, 0.25% to 1.0% nitrogen, and balance iron.

British Patent No. 995,068 discloses an austenitic stainless steel consisting of a trace to 0.12% carbon, 5% to 8.5% manganese, 2.0% maximum silicon,15.0% to 17.5% chromium, 3.0% to 6.5% nickel, 0.75% to 2.5% copper, a trace to 0.10% nitrogen, and remainder iron, with the constituents being controlled so that the martensite-forming characteristic is less than 10% according to a formula and the delta-ferrite forming characteristic is less than 10% according to a formula. The copper content is related to the manganese content. The steel of this patent is stated to have high austenite stability and a low work hardening rate, due to avoidance of transformation to martensite during cold working.

Allegheny Type 211 is an austenitic stainless steel having a low work-hardening rate, used for deep-drawing applications. Its nominal composition is 0.05% carbon, 6.0% manganese, 17.0% chromium, 5.5% nickel, 1.5% copper and remainder iron.

Allegheny Type 205 is an austenitic stainless steel containing from 0.12% to 0.25% carbon, 14.0% to 16.0% manganese, 0.2% to 0.7% silicon, 16% to 18% chromium, 1.1% to 2.0% nickel, 0.32% to 0.40% nitrogen, and remainder substantially iron.

Other disclosures of austenitic stainless steels having relatively low nickel levels include United States Patents 2,820,725,3,151,979, 3,192,041 and British Patent 882,893.

As will be evident from the above prior art, the desire to minimize the amount of nickel in austenitic stainless steels; with its attendant high cost, has led workers in the art to substitute relatively high amounts of manganese, copper, carbon and/or nitrogen. Although less expensive than nickel, manganese and copper are themselves, relatively high cost alloying elements, and excessive amounts thereof, particularly when used in combination, result in hot working problems. With the exception of United States Patents 3,940,266 and 3,989,470, the prior art steels mentioned above are in general of low strength and exhibit a low work hardening rate. In addition to cost, the main concern therein is with achieving austenite stability and maintaining corrosion resistance.

It is a principal object of the present invention to provide an austenitic steel having relatively low levels of expensive alloying ingredients, which at the same time exhibits high strength, excellent abrasion resistance, good ductility and good hot workability, together with adequate corrosion resistance.

It is a further object of the invention to provide a stainless steel having an austenitic structure at hot rolling temperature of such stability that very little, if any, (typically 1% maximum) transforms to martensite (thermal martensite) during cooling, but which upon cold reduction forms deformation martensite.

The above objects are obtained in the steel of the present invention by a critical balancing of the percentage ranges of the essential elements manganese, chromium, nickel, copper and nitrogen, and by controlling the austenite stability by an instability factor (IF) ranging between 2.5 and 8.5 in accordance with the equation: IF=37.2-51.25 (%C)2.59 (%Ni)1.02 (%Mn)0.47 (%Cr)34.4 (%N)--3 (%Cu).

Reference is made to the accompanying drawing wherein: Fig. 1 is a constitution diagram showing composition ranges in terms of nickel equivalent vs.

chromium equivalent; and Fig. 2 is a graphic representation of the relation of instability factor to percent ferrite and/or martensite.

In accordance with the invention there is provided an austenitic stainless steel having high strength, superior abrasion resistance, good hot workability, good ductility and a high work hardening rate, consisting essentially of, in weight percent, from 0.015% to 0.10% carbon, 5.5% to 10.0% manganese, 0.06% maximum phosphorus, 0.06% maximum sulfur, 2.0% maximum silicon, 12.5% to 20.0% chromium, 1.0% to 3.5% nickel, 0.85% maximum copper, 0.15% to 0.30% nitrogen, and balance essentially iron, said steel having an instability factor ranging from 2.5 to 8.5 calculated by the equation:: Instability factor=37.2-51 .25 (%C)2.59 (%Ni)-1 .02 (%Mn)0.47 (%Cr)34.4 (%N)--3 (%Cu).

The percentage ranges of and proportioning among the essential elements manganese, chromium, nickel, copper and nitrogen are critical in every respect, and departure therefrom results in loss of one or more of the desired properties.

Although less critical, the carbon and silicon ranges are nevertheless important in achieving the desired combination of properties.

Manganese is essential as a partial replacement for nickel as an austenite former and austenite stabilizer. A minimum of 5.5%, preferably 6.0% and more preferably 7.0%, is necessary for this purpose. A maximum of 10.0%, preferably 9.0% and more preferably 8.5% manganese, should be observed since higher levels reduce the work hardening rate and hence the strength levels. In addition high manganese in combination with relatively high copper levels result in hot working problems.

Chromium is essential for its usual function of imparting corrosion resistance, and a minimum of 12.5%, preferably 13.0% and more preferably 14.75% is essential for this purpose. A maximum of 20.0%, preferably 17.0% and more preferably 15.50%, must be observed in order to balance the ferrite-forming potential relative to the austenite-former potential of the elements carbon, manganese, nickel, copper and nitrogen. In addition, chromium in excess of the preferred maximum of 1 7.0% and certainly in excess of the broad maximum of 20.0%, lowers the work hardening rate and the strength levels attainable in the cold worked condition.

Nickel is essential as an austenite former, and a broad and preferred minimum of 1.0% and a more preferred minimum of 1.5% are necessary for this function. A maximum of 3.5%, preferably less than 3.0% and more preferably 2.5% should not be exceeded in view of the adverse effect of higher nickel levels on the work hardening rate and strength levels. It is further desired to maintain the maximum nickel content at the lowest possible level in view of its high cost.

Copper is essential as a partial replacement for nickel, and a preferred minimum of 0.5% and more preferably 0.6%, should be present. However, a maximum of 0.85% must be observed since copper has a strong effect in reducing the work hardening rate, and in combination with high manganese results in hot working problems. In addition, for fabricated products to be used in the dairy industry, there is a general belief that copper levels above about 0.85% would contaminate milk.

Nitrogen is essential for its strong austenite forming potential, and a broad and preferred minimum of 0.15%, and a more preferred minimum of 0.18%, are necessary for this purpose. In addition, a minimum of 0.15% nitrogen provides improved pitting corrosion resistance. A maximum of 0.30%, preferably 0.25% and more preferably 0.22%, should be observed in order to maintain the balance between the nickel equivalent and chromium equivalent elements with respect to austenite and ferrite forming tendencies.

Carbon is also a strong austenite former, and a minimum of 0.015%, and preferably and more preferably 0.02%, are desirable for this purpose. A maximum of 0.10%, preferably 0.06% and more preferably 0.05%, must be observed since carbon in excess of such levels adversely affects intergranular and pitting corrosion resistance.

Silicon is a strong ferrite former, and a broad maximum of 2.0%, preferably 1.0% and more preferably 0.75%, should be observed in order to avoid upsetting the austenite-ferrite balance.

Phosphorus and sulfur are present as normally occurring impurities, and a broad and preferred maximum of 0.06% of each, and a more preferred maximum of 0.04% of each, can be tolerated without adverse effects.

Accordingly, a preferred steel of the invention consists essentially of, in weight percent, from 0.02% to 0.06% carbon, 6.0% to 9.0% manganese, 0.06% maximum phosphorus, 0.06% maximum sulfur,1.0% maximum silicon,13.0% to 17.0% chromium, 1.0% to less than 3.0% nickel, 0.5% to 0.85% copper, O.15% to 0.25% nitrogen, and balance essentially iron, the steel having an instability factor ranging from 2.5 to 8.5 calculated by the instability factor equation set forth above.

A more preferred steel in accordance with the invention consists essentially of, in weight percent, from 0.02% to 0.05% carbon, 7.0% to 8.5% manganese, 0.04% maximum phosphorus, 0.04% maximum sulfur, 0.4% to 0.75% silicon, 14.75% to 15.50% chromium, 1.5% to 2.5% nickel, 0.6% to 0.75% copper, 0.18% to 0.22% nitrogen and balance essentially iron, the steel having an instability factor ranging from 2.5 to 8.5 calculated by the instability factor equation set forth above, having a nickel equivalent ranging from 12 to 1 5 calculated by the equation:: Nickel equivalent=0/oNi+30 (%C) 0.5 (%Mn)+30 (%N)+0.5 (%Cu), and a chromium equivalent ranging from 14 to 1 7 calculated by the equation: Chromium equivalent=%Cr+%Mo+1.5 (%Si)+0.5 (%Cb).

Instability factor is a quantitative calculation which indicates the tendency of austenitic microstructures to transform to deformation martensite with cold working. In this connection, it will be understood that a ferritic microstructure does not transform to martensite with cold working. As will be shown hereinafter by test data, the instability factor must be within the range of 2.5 to 8.5 in order to obtain a high work hardening rate. A correlation exists between the instability factor and the amount of ferrite and thermal martensite in the hot rolled and annealed condition, this being designated herein as "ferrite number" (FN). Austenite stability can also be quantified by means of a modified Schaeffler diagram wherein nickel equivalent is plotted against chromium equivalent, so as to predict the phases present at least qualitatively.

Fig. 1 is a constitution diagram which is a modified Schaeffler diagram. While the Schaeffier diagram was developed to predict weld microstructures, it has been found that good correlation exists in the steel of the present invention with respect to wrought and annealed microstructures. The preferred and more preferred compositions of the present steels fall within the area ABCD of Fig. 1, and hence are either a fully austenitic phase or mixed austenitic and martensitic phases.

Reference is next made to Fig. 2 which is a graphic representation of the relation between instability factor as calculated by the equation above and ferrite number (ferrite plus thermal martensite) in the wrought and annealed condition. It will be noted that the ferrite number increases sharply at an instability factor of about 8.2, thus indicating a duplex microstructure of austenite and martensite. It has been found that a relatively high level of thermal martensite does not result in substantially higher strength levels after drastic cold working with reductions greater than 50% and up to 60%. A higher ferrite number in the wrought and annealed condition does not cause the austenite to work harden at a faster rate, but the higher proportion of martensite in the annealed condition reduces the ductility of the steel thus causing difficulty in cold working.For this reason, a maximum instability factor of 8.5 must be observed. As would be expected, a higher ferrite number in the wrought and annealed condition exhibits a higher strength level, but this is achieved only at the expense of ductility.

For a best balance of strength and ductility in the wrought and annealed condition, the instability factor preferably is between 5.0 and 8.2, and the ferrite number between 1 and 2.

It has been found that increases in nickel, chromium, manganese plus nitrogen, or copper contents tend to lower the strength level and improve ductility. This is believed to be due to a lower instability factor (and hence ferrite number), with consequent reduction in the work hardening rate.

Nickel and manganese plus nitrogen exert the greatest effect in reducing strength. With respect to the work hardening rate, on a weight percent basis copper has the greatest effect in reducing the work hardening rate, followed in decreasing order by nickel, chromium and manganese. An addition of 0.5% copper is approximately as effective as 1.5% nickel, 3% chromium, or 4% manganese in reducing the strength levels and the degree of deformation martensite produced by cold working.

The above observations are confirmed by a series of heats which were prepared, processed and tested. The effect of variations in nickel, chromium, manganese plus nitrogen and copper was studied both within and outside the scope of the ranges of these elements in the steel of the present invention.

The compositions of these heats are set forth in Table I together with calculations of the instability factor, chromium equivalent and nickel equivalent by the equations set forth above. Properties of the heats of Table I in the cold rolled and annealed condition are summarised in Table II. For purposes of comparison, commercial samples of AISI Types 301 and 304 in the same condition were tested simultaneously.

The heats were melted and poured into ingots, hot rolled from 1 2600C to a thickness of 2.5 mm, and annealed at 1 0930C. Samples were cold reduced 50% to 1.3 mm and annealed at 1 093 OC. Test results in Table II are based on 1.3 mm thick annealed samples. Samples of the hot rolled and annealed 2.5 mm material were then subjected to varying degrees of cold reduction. More specifically one set was cold reduced 50% to 1.3 mm thickness, annealed at 1093 OC, descaled and further cold reduced 20% to 1.0 mm thickness. A further set of samples was cold reduced 30% to 1.7 mm thickness, annealed at 1 093 OC, descaled and further cold reduced 40% to 1.0 mm thickness. A final set of samples was cold reduced 60% in one reduction to 1.0 mm thickness.

Samples which were cold reduced 20%, 40% and 60% were subjected to work hardening tests, while annealed samples which were cold reduced 50% were subjected to tensile tests. Olsen cup formability trials, and GTA weld strength and formability evaluations. Samples of AISI Types 301 and 304 were also subjected to work hardening tests under the same conditions, for purposes of comparison. The work hardening tests are summarized in Table III, and the GTA weld mechanical properties are set forth in Table IV.

It is evident from the data of Table II that steels of the invention having a ferrite number of 1.0 exhibited higher strength than Types 301 and 304 and exhibited formability by the Olsen cup test substantially equivalent to Types 301 and 304. For ferrite numbers greater than 1 the strength increased while ductility and formability decreased.

The work hardening tests of Table III show that the work hardening rate of the steels of the invention is substantially greater than those of Types 301 and 304. In some instances Rockwell C hardnesses approaching 50 were exhibited by steels of the invention after about 60% cold reduction.

Steels of the invention which had a ferrite number of 1 in the cold reduced and annealed condition achieved strength levels far above those of conventional alloys, approaching the levels of heat treated precipitation-hardenable steels when subjected to greater than 50% cold reduction.

The autogenous GTA welds reported in Table IV had ferrite numbers quite comparable to those of the annealed base metal. Heats with high ferrite numbers exhibited high strength levels and low ductility and formability. Even some of the heats with low ferrite numbers showed ductility losses when the instability factor exceeded 8.0. With a low ferrite number and an instability factor less than 8, welds performed on steels of the invention were comparable in strength and formability to their base metai values.

Further heats of steels in accordance with the invention were prepared and subjected to abrasion resistance tests. For purposes of comparison samples of carbon steel, AISI Types 301 and 304, and a steel in accordance with the above mentioned United States Patent 3,940,266 (sold under the registered trademark "Nitronic 33") were subjected to the same tests. The compositions of these steels are set forth in Table V. Several series of abrasion tests were conducted, and the results are set forth in Tables VI through IX. In Table VI the steels of the invention were in the hot rolled condition, whereas in Tables VII through IX the steels of the invention were in the hot rolled and annealed condition.

The test in Table VI using pea gravel (Series 1 and 2) was a severely abrasive test with only slight corrosion effects. The tests in Table VI (Series 3) and Tables Vll and VEIL, using phosphate ore, combined abrasion and corrosion effects. The mixer test of Table IX, using a phosphate wet slurry, simulated dredge pipe service conditions due to the high slurry velocity and the open system.

In Table VI the relative wear life of the steels of the present invention ranged from 2.8 to 3.9 times that of carbon steel and were substantially superior to Nitronic 33, in the pea gravel tests. In the phosphate slurry test of Table VI the steels of the invention were at least four times better than carbon steel and 78% better than Nitronic 33.

In the annealed condition as reported in Table VII, there was a decrease in the relative wear life of the steels of the invention compared to carbon steel. Despite this, the steel of the invention had a relative wear life three times that of carbon steel and 60% better than Nitronic 33. It is possible that the new, annealed condition was going through a wear-in process during these tests which would have been higher than the steady state wear rate.

In Table VIII, direct comparative tests were made with stainless steels only. The steel of the present invention showed a slight superiority over Type 304 and Nitronic 33. In Table VIII a high nickel, high copper alloy was also tested for comparison and was used as the index at 1.0. At the conclusion of the test the steel of the present invention was 1 7% more abrasion resistant than the index alloy of high nickel and high copper content.

In the test of Table IX the conditions proved to be much more erosive to carbon steel in all the series, which were carried out under several conditions of mixing blade configurations, speeds and times. While the steel of the present invention was inferrior to Nitronic 33 and the high nickel and high copper alloy in a couple of series, the cummulative results of all five series indicated that the steel of the present invention was superior to Nitronic 33 and substantially equal to the high nickel and high copper alloy. The vast superiority of all three stainless steels over carbon steel in Table IX is quite evident.

It is evident that the steel of the present invention thus has a relative wear life both in the hot rolled and in the hot rolled and annealed conditions, at least 2.5 times that of carbon steel and exhibits overall superiority over all the steels which were tested.

For a given level of ductility (as measured in percent elongation) the steels of the present invention exhibit much higher hardness in the work hardened condition than standard steels of the 300 series.

The present invention thus provides a steel having high strength, superior abrasion resistance, good ductility and a high work hardening rate in the hot rolled and in the hot rolled and annealed conditions, and a 0.2% yield strength greater than 200 ksi (1379 MPa) when cold reduced more than 50%. While having utility for a wide range of applications, the steel has particular utility in the fabrication of dredge pipe by welding of a hot rolled band formed into a cylindrical shape, by reason of its greatly superior abrasion resistance as compared to carbon steel now used for the fabrication of dredge pipe.

Moreover, the steel of the invention can be provided in the form of bar, rod and wire, having both the broad and preferred compositions. The high strength and good ductility achieved in wire drawing provide a novel combination of properties not believed to be attainable in prior art steel, particularly with reductions in cross sectional area of greater than 50%.

Table I Compositions--Weight Percent Sample %C %Mn %P %S %Si %Cr %Ni %N %Cu IF CrE NiE 1 0.025 4.01 0.020 0.018 0.51 17.26 0.96 0.18 0.73 +12.8 18.2 9.5 2 0.025 3.95 0.020 0.018 0.48 17.21 1.75 0.18 0.71 +10.9 18.1 10.2 3 0.025 3.60 0.020 0.018 0.42 16.88 3.35 0.18 0.71 + 7.3 17.7 11.6 4 0.028 6.92 0.019 0.013 0.36 13.27 1.71 0.21 0.86 + 8.2 14.0 12.7 5* 0.028 6.38 0.018 0.013 0.30 16.23 1.68 0.21 0.85 + 7.5 16.9 12.4 6 0.043 4.70 0.020 0.015 0.39 15.35 1.71 0.20 0.76 + 9.7 16.2 11.7 7* 0.043 8.89 0.020 0.015 0.35 14.92 1.72 0.20 0.71 + 5.4 15.6 13.8 8 0.028 4.56 0.018 0.015 0.31 14.79 1.72 0.16 0.75 +12.0 15.5 10.0 9* 0.028 8.75 0.018 0.015 0.28 14.32 1.72 0.16 0.72 + 8.0 15.0 12.1 10 0.030 7.10 0.019 0.014 0.40 15.24 1.73 0.21 0.21 + 9.0 16.1 12.6 11 0.030 7.00 0.021 0.014 0.39 14.90 1.92 0.21 2.20 + 5.0 15.7 13.7 *Steels of the invention Table II H.R. and Annealed Properties .2% Y.S. U.T.S. % Elong. Hard. Olsen Cup Sample F.N. ksiRMPa) ksi(MPa) 2"{50.8mum) RB/C Ht-in. (mm) 1 28 64.5(444) 175.5(1210) 16.0 C27.5 0.210(5.4) 2 7.5 56.5(390) 164.0(1131) 20.0 C21.0 0.270(6.8) 3 1.0 51.0(352) 140.0(965) 34.0 B91.5 0.440(11.2) 4 2.5 47.9 (330) 137.0(945) 35.0 B94.5 0.345 (8.8) 5* 1.0 49.2(339) 130.0(896) 45.5 B92.O 0.465(11.8) 6 26 108.0(745) 188.5(1300) 14.0 C42.5 0.250(6.3) 7* 1.0 50.5(348) 119.5(824) 57.0 B93.5 0.485(12.3) 8 > 30 76.7(529) 186.5(1286) 10.0 C41.0 0.280(7.1) 9* 1.0 44.6(308) 127.0(876) 52.0 B88.5 0.485(12.3) 10 1.0 53.0(365) 152.5(1052) 49.5 B96.5 0.460(11.7) 11 1.0 50.0 (345) 108.0(745) 55.5 B89.5 0.460(11.7) T-301 - 40.0(276) 110.0(758) 60 B85 0.480(12.2) T-304 - 35.0(241) 85.0(586) 55 B80 0.475(12.1) *Steels of the invention Table III Cold Worked Mechanical Properties % .2% YS. U.T.S. %Elong. Hard Ferrite Sample C.W. ksi (MPa) ksi (MPa) 2" (50.8 mm) RB/C Number 1 0 64.5(444) 175.5(1210) 16.0 C27.5 28 19.2 172.5(1189) 210.5(1452) 9.5 C48.0 > 30 40.3 230.5(1589) 235.5(1624) 4.0 C49.0 > 30 56.9 253.5(1748) 256.0(1765) 3.0 C49.0 > 30 2 0 56.5(390) 164.0(1131) 20.0 C21.0 7.5 19.2 121.5(838) 204.0(1407) 12.0 C47.0 > 30 38.9 215.5(1486) 227.0(1565) 5.5 C49.5 > 30 56.6 247.0(1703) 249.5(1720) 2.5 C50.5 > 30 Table Ill (cont.).

Cold Worked Mechanical Properties % .2% Y.S. U.T.S. % Elong. Hard Ferrite Sample C. W. ksi (MPa) ksi (MPa) 2" (50.8 mm) RB/C Number 3 0 51.0(352) 140.0(965) 34.0 B91.5 1.0 17.6 107.0(738) 182.5(1258) 17.0 C43.0 16.5 39.7 180.0(1241) 204.5(1410) 13.5 C48.5 > 30 55.9 216.5(1492) 221.0(1524) 7.0 C50.5 > 30 4 0 47.9 (330) 137.0 (945) 35.0 B94.5 2.5 19.2 111.0(765) 179.0(1234) 18.0 C40.0 16 40.3 198.0(1365) 216.0(1489) 9.0 C47.O > 30 59.1 234.0(1613) 238.0(1641) 3.5 C48.5 > 30 5* 0 49.2 (339) 130.0 (896) 45.5 B92.O 1.0 18.8 110.0(758) 173.0(1192) 20.0 C39.5 11.5 40.6 185.5(1279) 198.5(1369) 14.0 C47.0 > 30 56.5 213 (1468) 229.0(1579) 4.0 C48.0 > 30 6 0 108.0(745) 188.5(1300) 14.0 C42.5 26 20.2 187.5(1290) 217.5(1500) 12.0 C49.5 > 30 40.0 244.5(1686) 248.0(1710) 5.0 C52.5 > 30 58.8 269.5(1858) 273.0(1882) 7.0 C53.0 > 30 7* 0 50.5 (348) 119.5(824) 57.0 B93.5 1.0 22.9 128.0(882) 172.5(1190) 23.0 C43.O 7.5 35.9 162.0(1116) 189.0(1303) 17.0 C47.5 12.5 58.4 221.0(1524) 229.0(1579) 4.0 C51.0 19.5 8 0 76.7(529) 186.5(1286) 10.0 C41.0 > 30 17.6 210.0(1448) 218.0(1503) 3,5 C45.0 > 30 39.8 230.5 (1590) 234.0 (1613) 3.0 C48.0 > 30 57.9 246.5(1700) 250.5(1727) 2.5 C48.O > 30 9* 0 44.6 (308) 127.0 (876) 52.0 B88.5 1.0 19.2 110.0(758) 164.5(1134) 22.0 C38.5 12.5 40.0 176.5(1217) 193.5(1334) 13.0 C46.0 29.5 56.6 210.5(1451) 221.0(1524) 3.5 C47.O > 30 10 0 53.0(365) 152.5(1052) 49.5 B96.5 1.0 16.3 112.0(772) 192.0(1324) 21.5 C44.5 12.5 39.5 209.0(1441) 221.5(1528) 13.0 C51.5 > 30 58.4 254.5(1754) 261.0(1800) 3.5 C53.5 > 30 11 0 50.0 (345) 108.0 (745) 55.5 B89.5 1.0 20.8 120.0(828) 153.5(1058) 25.0 C38.0 4.0 34.8 158.5(1092) 170.5(1176) 20.0 C44.0 8.0 56.8 194.5(1341) 203.5(1403) 5.0 C48.0 11.0 T-301 0 44.0 (303) 117.4(809) 63.0 B88.O 20 115.6(797) 165.4(1140) 30.0 C37.5 40 182.6(1259) 196.0(1351) 10.5 C45.0 60 203.1(1400) 4.5 C44.5 T-304 0 29.2 (201) 83.4 (575) 68.0 B70.0 18.5 91.0(627) 106.2(732) 32.0 C23.0 40.3 131.0(903) 145.2(1001) 9.0 C34.5 59.5 156.4(1078) 169.2(1167) 5.0 C38.0 *Steels of the invention.

Table IV G.T.A. Weld Mechanical Properties .2% YS. U.T.S. % Elong. Olsen Cup Ferrite IF Sample ksiRMPa) ksiRMPa) 2" (50.8 mm) Ht.-in. (mm) Number 12.8 1 65.0 (448) 108.0 (744) 4.0 0.135 (3.4) 26.5 10.9 2 58.5 (404) 107.0 (738) 8.5 0.175 (4.5) 6.5 7.3 3 52.5 (362) 125.0 (862) 21.0 0.390 (10.0) 1.0 8.2 4 47.2 (326) 66.0 (455) 7.0 0.290 (7.4) 1.5 7.5 5* 50.8 (350) 129.0 (890) 43.5 0.400 (10.2) 1.0 9.7 6 106.5 (734) 156.0 (1076) 7.0 0.160(4.0) > 30 5.4 .7* 50.5 (348) 120.0 (827) 54.5 0.470 (11.9) 1.0 12.0 8 773.(533) 158.0(1089) 3.0 0.170(4.4) > 30 8.0 9* 43.8 (302) 124.5 (858) 46.0 0.470(11.9) 1.0 9.0 10 54.0 (372) 147.5 (1017) 37.0 0.360 (9.2) 1.0 5.0 11 50.5 (348) 111.5(768) 53.0 0.475 (12.0) 1.0 *Steels of the invention.

Table V Compositions--Weight Percent Sample C Mn Si Cr Ni N Cu carbon steel (AISI 1030) 0.34 1.14 0.17 - - - - Nitronic 33 0.053 12.93 0.67 17.47 3.45 0.28 Type 304 0.068 1.66 0.48 18.45 8.9 0.01 12* 0.058 7.36 0.40 14.99 0.99 0.18 0.56 13* 0.059 7.34 0.38 14.95 1.50 0.18 0.55 14* 0.056 7.18 0.35 14.93 1.96 0.18 0.56 15(highNi,highCu) 0.035 1.76 0.45 17.05 4.56 0.14 248 *Steels of the invention.

Table Ball Mill Wet Slurry Abrasion Tests Conditions: 2000 ml water+200 ml pea gravel+100 ml SiO2, 42.38 m/min., one hour, duplicates, room temperature Relative Wear Life (carbon steel indexed at 1.0) Series 1 Period Carbon steel Sample 12 Sample 13 Sample 14 1 1.0 5.4 3.8 3.9 2 1.0 2.9 3.0 3.0 Cumulative 1.0 3.9 3.4 3.5 Series 2 Period Carbon Steel Nitronic 33 Sample 12 Sample 13 Sample 14 1 1.0 2.1 3.1 2.8 2.9 Series 3 1800 ml water+1000 ml phosphate ore-2 hours.

Period Carbon Steel Nitronic 33 Sample 12 Sample 13 Sample 14 1 1.0 2.4 4.8 4.8 4.7 2 1.0 2.1 4.0 3.6 3.5 Cumulative 1.0 2.3 4.3 4.1 4.0 Table VII Ball Mill Wet Slurry Abrasion Tests Conditions: 1800 ml water+1000 ml phosphate ore, 42.38 m/min., 2 hours, duplicates, room temperature Relative Wear Life (Carbon steel indexed at 1.0) Series 1 Period Carbon steel Nitronic 33 Sample 12 Sample 13 Sample 14 1 1.0 1.9 3.0 2.7 2.8 2 1.0 1.8 2.6 2.5 2.6 Cumulative 1.0 1.8 2.8 2.6 2.7 Series 2 Period Carbon steel Nitronic 33 Sample 12 Sample 13 Sample 14 1 1.0 2.2 3.7 3.5 3.4 2 1.0 1.8 3.1 3.0 3.2 3 1.0 1.6 2.5 2.5 2.5 Cumulative 1.0 1.86 3.00 2.93 2.91 Table VIII Ball Mill Wet Slurry Abrasion Test Conditions:: 1800 ml water+1000 ml phosphate ore, 42.38 m/min., 2 hours, duplicates, room temperature Relative Wear Life (Sample 1 5 indexed at 1.0) Series 1 Period Type 304 Nitronic 33 Sample 15 Sample 13 1 1.4 1.4 1.0 1.2 2 1.2 1.3 1.0 1.3 3 1.2 1.0 1.0 1.3 Cumulative 1.25 1.23 1.0 1.25 Series 2 New Slurry-6 hours Period 1 1.08 1.05 1.0 1.17 Table IX Mixer Test-Phosphate Wet Slurry Erosion Conditions: : 1000 ml phosphate ore diluted to 3000 ml solution, duplicates, room temperature Relative Wear Life (Carbon steel indexed at 1.0) Series 1-1 8 hours Carbon steel Nitronic 33 Sample 12 Sample 15 1.0 47.6 37.9 31.4 Series 2-2 hours-same slurry+300 ml SiO2 1.0 20.5 10.1 14.3 Series 3-23 hours 1.0 62.3 63.9 117.7 Series 4-5 hours-new slurry1500 ml phosphate ore, no SiO2 1.0 30.1 35.9 46.1 Series 5-20 hours1500 ml phosphate ore+300 ml SiO2 1.0 26.0 61.0 50.3 Cumulative 1.0 34.6 44.5 45.5

Claims (12)

Claims

1. An austenitic stainless steel having high strength, superior abrasion resistance, good hot workability, good ductility and a high work hardening rate, consisting essentially of, in weight percent, from 0.015% to 0.10% carbon, 5.5% to 10.0% manganese, 0.06% maximum phosphorus, 0.06% maximum sulfur, 2.0% maximum silicon, 12.5% to 20.0% chromium, 1.0% to 3.5% nickel, 0.85% maximum copper, 0.15% to 0.30% nitrogen, and balance essentially iron, said steel having an instability factor ranging from 2.5 to 8.5 calculated by the equation:: Instability factor=3 7.2-51.25 (%C)--2.59 (%Ni)-1 .02 (%Mn)--0.47 (%Cr)34.4 (%N)--3 (%Cu).

2. The steel according to claim 1, consisting essentially of, in weight percent, from 0.02% to 0.06% carbon, 6.0% to 9.0% manganese, 0.06% maximum phosphorus, 0.06% maximum sulfur, 1.0% maximum silicon,13.0% to 17.0% chromium, 1.0% to less than 3.0% nickel, 0.5% to 0.85% copper, 0.15% to 0.25% nitrogen, and balance essentially iron.

3. The steel according to claim 1, consisting essentially of, in weight percent, from 0.02% to 0.05% carbon, 7.0% to 8.5% manganese, 0.04% maximum phosphorus, 0.04% maximum sulfur, 0.4% to 0.75% silicon, 14.75% to 15.50% chromium, 1.5% to 2.5% nickel, 0.6% to 0,75% copper, 0.18% to 0.22% nitrogen, and balance essentially iron, said steel having a nickel equivalent ranging from 12 to 15 calculated by the equation: Nickel equivalent=%Ni+30 (%C)+0.5 (%Mn)+30 (%N)+0.5 (%Cu), and a chromium equivalent ranging from 14 to 17 calculated by the equation: Chromium equivalent=%Cr+%Mo+ 1.5 (%Si)+0.5 (%Cb).

4. The steel according to claim 2 or 3, having a relative wear life, in the hot rolled and hot rolled and annealed conditions, at least 2.5 times that of carbon steel by the tests described herein.

5. The steel according to claim 2 in the form of hot rolled and annealed band having an austenitic microstructure, high strength, superior abrasion resistance, good ductility and a high work hardening rate.

6. The steel according to claim 2 in the form of cold reduced and annealed sheet and strip having a 0.2% yield strength greater than 200 ksi when cold reduced more than 50%, and superior abrasion resistance.

7. The steel according to claim 1 in the form of a fabricated product having high strength, superior abrasion resistance and good ductility.

8. The steel according to claim 2 in the form of a fabricated product having high strength, superior abrasion resistance and good ductility.

9. Dredge pipe fabricated by welding of a hot rolled and formed austenitic stainless steel band according to claim 2, having abrasion resistance superior to that of carbon steel.

10. The steel according to claim 1 in the form of stainless steel bar, rod and wire having high strength, superior abrasion resistance and good ductility.

11. The steel according to claim 2 in the form of stainless steel bar, rod and wire having high strength, superior abrasion resistance and good ductility.

12. An austenitic stainless steel according to claim 1 and substantially as hereinbefore particularly described and illustrated.