US3888659A

US3888659A - Free machining austenitic stainless steel

Info

Publication number: US3888659A
Application number: US834477A
Authority: US
Inventors: Jr Joseph A Ferree
Original assignee: Allegheny Ludlum Industries Inc
Current assignee: Allegheny Ludlum Corp; Pittsburgh National Bank
Priority date: 1968-05-29
Filing date: 1969-06-18
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10

Abstract

A free machining austenitic stainless steel consisting essentially of from a trace up to 0.15 percent carbon, from 2 to 10 percent manganese, from 4 to 13 percent nickel, from 10 to 20 percent chromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percent sulfur, 2 percent max. silicon, and 0.10 percent max. nitrogen, the balance essentially iron and residual impurities.

Description

atet 1 Ferree, J r.

FREE MACHINING AUSTENITIC STAINLESS STEEL Inventor: Joseph A. Ferree, Jr., Natrona Heights, Pa.

Allegheny Ludlum Industries, Inc., Pittsburgh, Pa.

The portion of the term of this patent subsequent to Aug. 12, 1986, has been disclaimed.

Filed: June 18, 1969 Appl. No.: 834,477

Related U.S. Application Data Division of Ser. No. 740,807, May 29, 1968, Pat. No. 3,460,939, which is a continuation-in-part of Ser. No. 418,991, Dec. 17, 1964, abandoned.

Assignee:

Notice:

References Cited UNITED STATES PATENTS 11/1940 Krivobok 75/128 A 3/1948 Lee 75/128 A LOG DRILL LIFE 1*June 10, 1975 2,495,731 l/l950 Jennings 75/128 A 2,697,035 12/1954 Clarke 75/125 2,775,519 12/1956 B]oom.. 75/125 2,802,755 8/1957 Bloom.. 75/128 2,848,323 8/1958 Harris 75/125 3,152,934 10/1964 Lula 75/125 3,401,035 9/1968 Moskowitz 75/125 3,401,036 9/1968 Dulis 75/125 3,437,478 4/1969 Moskowitz 75/128 3,460,939 8/1969 Ferree 75/125 FOREIGN PATENTS OR APPLICATIONS 1,458,042 9/1966 France 12/1967 United Kingdom Primary ExaminerL. Dewayne Rutledge Assistant ExaminerArthur J. Steiner Attorney, Agent, or FirmVincent G. Gioia; Robert F. Dropkin [57] ABSTRACT A free machining austenitic stainless steel consisting essentially of from a trace up to 0.15 percent carbon, from 2 to 10 percent manganese, from 4 to 13 percent nickel, from 10 to 20 percent chromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percent sulfur, 2 percent max. silicon, and 0.10 percent max. nitrogen, the balance essentially iron and residual impurities.

6 Claims, 6 Drawing Figures 8% MANGANESE 6 MANGANESE 4 MANGANESE PERCENT COPPER PATENTEDJUH 10 I915 8 8 5 5 9 SHEET 1 F /6. I0. I

8% MANGANESE 6 MANGANESE 4 MANGANESE LOG OR/LL LIFE [.5 I l I PERCENT COPPER I FIG. lb

LOG OP/LL LIFE /.a l l 1 1 I PERCENT COPPER INVENTOR. JOSEPH A. FERPEE, JR.

By /vWLA4iS-QW Attorney FREE MACHINING AUSTENITIC STAINLESS STEEL This Application is a division of previously copending application Ser. No. 740,807, filed May 29, 1968, now US. Pat. No. 3,460,939, issued Aug. 12, 1969, which in turn is a continuation-in-part of now abandoned, previously copending, application Ser. No. 418,991, filed Dec. 17, 1964.

This invention relates to ferrous base alloys, and more particularly to a free machining, austenitic stainless steel.

Of the many different grades of stainless steel, AISI Type 303 is the conventional, standard type free machining austenitic stainless steel. This type of stainless steel, which is a chromium-nickel type, contains, as principal alloying components, from about 17 to 19 percent chromium, from 8 to 10 percent nickel,'0.l5 maximum carbon, 2 percent maximum manganese and 1 percent maximum silicon, with up to about 0.20 percent phosphorus; up to 0.60 percent molybdenum and .60 percent zirconium may be added for some applications. It has been found, however, that an austenitic stainless steel with substantially improved free machining properties over those of AISI Type 303 is provided in a chromium-nickel-manganese-copper type austenitic stainless steel to which sulfur is added as a free machining element. Additionally, it has been found that the same chromium-manganese-copper system will provide a stainless steel of equivalent machinability to that of the Type 303 stainless steel with about half of the amount of sulfur that would be required in the Type 303 stainless steel. Since the sulfur content is lower the corrosion resistance is improved, as are the hot and cold working properties, inasmuch as the detrimental effects of sulfur on corrosion resistance and hot and cold working are well known.

It is therefore a principal object of this invention to provide an improved free machining austenitic stainless steel.

A more particular object of this invention is to provide an austenitic, free machining stainless steel which will have machinability comparable to that of the AISI Type 303 at reduced sulfur levels, and improved machinability at comparable sulfur levels.

A still further, more specific object is to provide an improved free machining austenitic stainless steel wherein the alloying elements are balanced to produce optimum corrosion resistance and free machining properties.

These and other objects, together with a fuller understanding of the invention, may be had from reference to the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 (a) is a graph showing the effect of copper at various manganese levels on the machinability of stainless steels of this invention;

FIG. I (b) is a composite of the lines of FIG. 1 (a)- showing this effect of copper at the average manganese content;

FIG. 2 (a) is a graph showing the effect of manganese at various copper levels on the machinability of stainless steels of this invention;

FIG. 2 (b) is a composite of the lines of FIG. 2 (a) showing this effect of manganese at the average copper content; I

FIG. 3 (a) is a graph showing the effect of nickel at various copper levels on the machinability of stainless steels of this invention, and

FIG. 3 (b) is a composite of the lines of FIG. 3 (a) showing the effect of nickel at the average copper content.

The free machining characteristics of any ferrous tain maximum free machining characteristics. 1 have found that by properly controllingthe alloying elements of chromium nickel, manganese, copper and sulfur, an austenitic stainless steel can be provided which will have materially improved machining characteristics over AISI Type 303 stainless steel at comparable sulfur levels, comparable machining characteristics at reduced sulfur levels, although the machining characteristics will not be as good as the free machining grades of ferritic stainless steels.

The alloy according to this invention will have from a trace up to about 0.15 percent maximum carbon,

from about 2 percent to about 10 percent manganese,

from about 4 percent to about 13 percent nickel, from 10 to 20 percent chromium, from 0.5 percent to about 3 percent copper, from 0.10 percent to about 0.40 percent sulfur, up to 2 percent silicon up to about 0.10 percent nitrogen, and optionally up to about 0.60 percent molybdenum and 0.60 percent zirconium; other elements may be added to obtain specific characteristics of stainless steel.

Table 1 below lists the composition and machinability, as measured by drill testing, of various types of free machining stainless steels, some within the scope of this invention and some not. The drill tests are performed in the following manner:

Slabs of material to be tested are provided which are three-fourths inch thick and have opposed flat machined faces. The slabs are chucked in a conventional drill press, and a series of holes is drilled in each slab with twist drills. The twist drills for such testing were manufactured by the Cleveland Twist Drill Company of Cleveland, Ohio, and are similar to conventional twist drills but are finished to the closest possible tolerances. In the present case the drills were 1 diameter drills manufactured from AISI Grade M-l high speed tool steel. The drill speed for the present tests was 3,050 R.P.M., and the feed was 0.005 inch per revolution. The feed was automatically accomplished by a screw drive incorporated in the drill press to maintain accuracy. Conventional sulfurized cutting oil was used .as a lubricant and maintained at a constant flow throughout the tests. Holes were drilled at least one-eighth inch apart to minimize the effect of work hardening radiating from the holes as they were drilled. The tests on the slabs of each heat continued until a wear land of 0.015 inch, as measured by a calibrated microscope, was worn on the cutting edge of the drill used for the test, and this was considered the end point of the test. The total inches drilled was then calculated by multiplying the number of holes drilled by three-fourths inch (the 3 4 thickness of the slabs), and this Inches of holes the purpose of determining the effect of each of these drilled the value l1sted 1n Table 1. elements on the machinab1lity. The machmabillty of TABLE I 1 11 111 1V V VI VII VIII Drill Log Drill Log Drill Life Heat No. %Cu %Mn %Ni %S Life (1) Life (2) Standardized(3) 1727 Res.(4) 1.00 8.97 .30 59 1.771 1.771 1462 do. 1.10 9.03 .34 53 1.724 1.552 1732 do. 1.99 7.07 .33 109 2.037 1.908 1672 do. 1.84 9.05 .33 79 1.898 1.769 1805 do. 1.99 9.15 .24 22 1.342 1.600 1731 do. 2.00 9.00 .33 107 2.029 1.900 1457 do. 2.09 9.10 .33 112 2.049 1.920 1459 do. 2.14 9.10 .32 87 1.940 1.854 1458 do. 2.16 9.09 .33 80 1.903 1.774 1750 do. 2.26 8.92 .35 110 2.041 1.826 1734 do. 1.98 10.84 .30 65 1.813 1.813 1735 do. 3.98 9.01 .34 21 1.322 1.160 1846* do. 4.12 6.18 .32 65 1.813 1.727 1847* do. 4.00 7.96 .30 25 1.398 1.398 1848* do. 5.92 8.02 .30 100 2.000 2.000 1743 do. 5.92 8.74 .33 58 1.763 1.634 1849* do. 6.06 6.34 .31 61 1.785 1.742 1761 do. 6.00 6.92 .32 1.477 1.391 1850* do. 7.90 6.24 .28 132 2.121 2.207 1851* do. 7.97 8.09 .28 109 2.037 2.123 1762 do. 8.00 7.07 .35 44 1.644 1.429 1764 do. 8.20 9.20 .31 74 1.869 1.826 1774 do. 10.08 5.08 .27 41 1.613 1.742 1778 do. 10.02 6.87 .25 30 1.477 1.692 1730 .98 2.03 8.99 .33 43 1.634 1.505 1852* 1.09 4.04 6.25 .35 161 2.207 1.992 1856* 1.14 4.12 7.83 .35 78 1.892 1.677 1740 1.04 5.73 6.93 .30 47 1.672 1.672 1860* 1.17 6.07 6.30 .31 1.978 1.935 1863* 1.23 6.00 8.10 .32 172 2.236 2.150 1865* 1.20 7.94 6.42 .29 163 2.212 2.255 1869* 1.07 8.04 7.84 .31 183 2.263 2.220 1469 1.50 2.20 6.65 .32 48 1.681 1.595 1467 1.45 2.13 6.85 .33 101 2.004 1.875 1677 1.55 5.25 4.80 .30 41 1.613 1.613 1679 1.56 5.47 5.02 .33 112 2.049 1.920 1857* 1.77 4.09 7.85 .35 2.130 1.915 1673 1.75 5.45 5.55 .30 178 2.250 2.250 1760 1.75 5.95 5.15 .30 97 1.987 1.987 1739 1.76 5.90 5.32 .25 75 1.875 2.090 1466 1.75 6.10 5.40 32 164 2.215 2.129 1474 1.70 6.40 5.65 32 231 2.364 2.278 1870* 1.73 7.97 8.00 29 143 2.155 2 198 1324 1.90 .49 7.00 33 41 1.613 1 484 1325 1.93 1.05 7.02 33 119 2.076 1 947 1473 2.06 1.12 7.15 34 184 2.265 2 093 1326 1.99 1.09 9.14 34 106 2.025 1 853 1728 1.92 1.01 11.15 30 59 1.771 1771 1729 1.95 1.94 7.32 33 82 1.914 1 785 1502 1.98 2.07 6.66 37 132 2.121 1 820 1472 1.98 2.20 6.73 34 145 2.161 1 989 1468 V 1.95 2.20 6.75 38 60 1.778 1 434 1470 l 1.98 2.20 7.15 34 186 2.270 2 098 1471 1.98 2.20 7.20 35 90 1.954 1 739 1737 1.88 2.13 9.10 31 80 1.903 1 860 1854* 1.94 4.00 6.25 32 129 2.11 1 2.025 1736 1.88 3.96 11.00 33 113 2.053 1.924 1759 2.05 6.00 4.82 30 11 1 2.045 2.045 1751 2.00 6.38 6.00 31 133 2.124 2.081 1861* 1.90 6.08 6.34 31 171 2.233 2.190 1864* 1.95 6.00 8.12 33 216 2.335 2.206 1765 1.96 8.30 9.25 29 113 2.053 2.096 1855* 2.54 4.08 6.05 33 2.176 2 047 1858* 2.49 4.19 7.90 35 236 2.373 2 158 1862* 2.65 6.08 6.32 31 154 2.188 2.145 1859* 2.54 6.00 7.93 .32 230 2.362 2.276 1868* 2.60 8.05 6.00 .30 234 2.369 2.369 1871* 2.46 7.99 8.03 .29 242 2.384 2.427

Note: All heats contained from 15 to 19% Cr; 15% Max. C; .10% Max. N; and normal residual impurities. (1) Inches of holes drilled. average of three tests.

(2) Logarithm of values in column V1. (3) Values in column Vll standardized to .30 sulfur level by the formula: Logarithm of Drill Life 4.30 (%S .30) =standardized logarithm of drill life. (4) Residual. i.e., about .196.

Of the ea listed in Table the 23 marked h an 65 each of these 23 heats, as well as various averages, is asterisk were melted as a group having controlled analtabulated in Table 11 below, and these values were used yses, particularly of manganese, copper and nickel, for to plot the graphs of FIGS. 1 to 3.

TABLE II Log Drill Life 23 Heats Adjusted to .30% Sulfur by the Formula Log D.L. 4.30(% S .30)

6% Ni 8% Ni Total 4% Mn 6% Mn 8%Mn Total 4%Mn 6%Mn 8%Mn Total 4%Mn 6%Mn 8%Mn Total (1846) (1849) (1850) (1874) (1848) (1851) Avg. 1.892 1.840 1.562 1.871 2.165 1.866 1% Cu 1.992 1.935 2.255 6.182 1.677 2.150 2.220 6.047 3.669 4.085 4.475 12.229

(1852) (1860) (1865) (1865) (1863) (1869) Avg. 2.061 2.016 1.834 2.042 2.238 2.038 2% Cu 2.025 2.190 4.215 1.915 2.206 2.198 6.319 3.940 4.396 2.198 10.534

(1854) (1861) (1857) (1864) (1870) Avg. 2.108 2.106 1.970 2.198 2.198 2.107 2.5% Cu 2.047 2.145 2.369 6.561 2.158 2.276 2.427 6.861 4.205 4.421 4.796 13.422

(1855) (1862) (1868) (1858) (1859) (1871) Avg. 2.187 2.287 2.102 2.210 2.398 2.237 Total 7.791 8.012 6.831 22.364 7.148 8.632 8.968 24.748 14.939 16.644 15.799 47.382 Avg. 1.948 2.003 2.277 2.058 1.787 2.158 2.242 2.062 1.867 2.080 2.257 2.060

Note: Heat Numbers in Parenlheses.

It should be noted that the machinability value used in Table II and in the figures is the logarithm of the drill life standardized to 0.30 percent sulfur. The logarithm of the drill life was chosen since this will tend to equalize variations at both high and low values. These logarithms were then corrected to a standarized sulfur content (0.30 percent sulfur was chosen since this is commercially the minimum required to obtain maximum machinability in austenitic alloys) to compensate for variation due to different sulfur contents, it being recognized that small variations in sulfur have large effects on the machinability. The correction factor for sulfur was determined empirically using the heats in Table I. The levels of the elements reported in Table II represent the nominal levels of each, although the actual average levels of copper are given in parentheses since they do deviate somewhat from the nominal values. Also, in the figures the various lines are labeled with the nominal values, and in fact the manganese and nickel values in FIGS. 2 and 3 are plotted at the nominal amounts since, in the case of these two elements, the nominal values are close to the actual; however, in FIG. 1 the copper values are plotted at the average because of the variation thereof from the nominal.

Referring now to FIG. 1(a), it can be seen that at all manganese levels when the copper is increased from zero to about 2.5 percent, a substantial increase in drill life occurs, which means the steel is more easily machined at the higher copper levels; also, the machinability is increased at higher manganese levels, as shown by the location of the lines for the various levels of manganese. The composite line shown in FIG. 1(b) shows also the effect of increasing copper as increasing the machinability at the average manganese content; FIG. 2(a) shows that at any given copper level, increasing the percentage of manganese in the steel substantially increases the drill life, thus indicating that at higher manganese levels the ease of machining is substantially increased; also, the location of the lines for the various levels of copper shows increased machinability at higher copper levels; FIG. 2(b) shows also the effect of increasing manganese as increasing the machinability at the average copper percentage; FIG. 3(a) shows that at any given copper level, increasing the nickel content does not have any significant effect on the machinability of the stainless steel, but that the machinability at any nickel level is higher with more copper, and FIG. 3(b) shows this lack of effect of nickel on machinability at average copper levels.

The results of the machinability tests on the various alloys listed in Table I, and particularly the controlled group also listed in Table II and plotted in the figures, indicate that the best machining composition is a composition wherein the manganese and copper are relatively high whereas the nickel content is relatively unimportant with respect to machinability. It has been found, however, that at this optimum high level of manganese and copper, the composition must be controlled so that the percentage of copper does not exceed 3.85 O.l8(% Mn 55/32% S); if the copper content exceeds this value, the alloy cannot be properly hot worked because of cracking and edge checking. In fact, the billets from heats 1868 and 1871, the composition of which approaches this limit, gave some indication of edge checking during processing which, if it had been any more severe, would have rendered the material unsuitable. It has further been found, and an examination of Table I will show, that when the manganese content exceeds about 6 percent there is a tendency for the alloy to retain less than 0.30 percent sulfur, which will materially reduce its free machining characteristics since sulfur is the major contributor to the free machining characteristics of the alloy. It is known that more sulfur can be retained in the final product if the melting temperature is raised; however, this introduces additional problems of increased erosion of furnace and ladle refractories which, in turn, may require costly changes in melting, tapping and teeming practices. Hence, when maximum free machining properties are desired, the sulfur should be in the range of 0.30 percent to 0.40 percent, which means the manganese content cannot exceed about 6 percent if conventional furnace and ladle practices are to be followed. However, the machinability of the alloys containing manganese and copper is so superior to that of AISI Type 303 which contains no copper and very little manganese, the sulfur content can actually be lowered to the range of about 0.15 percent and machinability comparable to that of AIS] 303 can be obtained. For example, heats 1859, 1868 and 1858, which are within the scopeof this invention, have a drill life about four times as great as heats 1727 and 1426, which are examples of conventional AISI Type 303 free machining stainless steel. Where increased hot and cold workability, as well as increased corrosion resistance, is desired, and where machinability merely comparable to Type 303 is desired, greater manganese contents can be used with a corresponding reduction in the amount of sulfur, it being understood that the lower the sulfur value, the greater the corrosion resistance and the greater the workability the alloy will have, but it will have decreased machining characteristics.

It is also known that the alloying elements of stainless steels containing manganese, nickel and copper must be properly balanced to prevent the formation of excessive delta ferrite during hot rolling. When excessive delta ferrite is formed during hot rolling, the ingot or bloom cannot be properly hot worked; the relationship of the alloying elements to the formation of delta ferrite must be such that the delta ferrite-forming characteristic or potential is less than 10 according to the formula:

delta ferrite potential Cr 1.5(% Si) .87[30(% C 7c N) With respect to the composition limits, the chromium content cannot be below about 10 percent in order to achieve proper corrosion resistance, and the chromium content should not exceed about percent since more than this would require excessive amounts of other elements to prevent the formation of delta ferrite, and higher amounts of the other elements could lead to hot shortness problems in the balance of copper and manganese and increased expense with respect to nickel. Hence, the broad limits for the chromium are about 10 to 20 percent. If there is less than about 4 nickel, the manganese and/or copper contents would have to be increased to obtain the stability with respect to the formation of excessive delta ferrite. This would tend to make the alloy hot short if enough manganese and/or copper were added to compensate for the reduced amount of nickel, and also would reduce the amount of sulfur retained if the manganese is increased. More than about 13 percent nickel adds needlessly and substantially to the cost of the alloyv There must be at least 2 percent manganese, since less than this would require excessive amounts of nickel for stability and corrosion resistance, adding to the cost of the alloy but not improving its machinability, or excessive copper which would tend to make the alloy hot short if the desired stability and-machinability are to be obtained; also, more than 2 percent manganese is required since it adds substantially to the machinability of the alloy. There cannot be more than about 10 percent manganese, since the amount of copper that could be used would be correspondingly reduced because of hot shortness problems, and also there is the problem of reduced sulfur retention. With less than about 0.50 percent copper, the machinability is greatly reduced, which would require excessive amounts of manganese to compensate for this which, in turn, reduces the amount of sulfur retained. With more than about 3 percent copper, the alloy tends to be hot short unless the manganese content is maintained low, and the copper has a lesser effect on the suppression of delta ferrite than manganese or nickel. When the carbon and nitrogen contents exceed about 0.15 percent and 0.10 percent respectively, they adversely affecting the corro- SlOn reslstance.

With an alloy falling within the broad limits described above and wherein the delta ferrite-forming potential is less than 10 percent and the copper does not exceed 3.85 0.18(% Mn 55/32%S), an austenitic stainless steel of superior machining characteristics is produced. As was indicated previously, the principal element relied on for ease of machining is sulfur. As can be seen from Table I, where the sulfur is in the range of 0.30 to 0.40 percent, an alloy having a machinability rating based on drill life three to four times as good as AlSl Type 303 is produced, and hence, for superior machinability sulfur contents of between 0.30 percent and 0.40 percent are desired. Where increased workability and corrosion resistance are desired, a sulfur content of between 0.10 percent and 0.30 percent is preferred It is easier to achieve an economic balance of elements within a substantially narrower melting range. This narrower or preferred range is as follows: about 0.08 percent maximum carbon, up to 1 percent silicon from about 4 to 6 percent manganese where sulfur in the range of 0.30 to 0.40 percent is required, and 6 to 8 percent manganese where sulfur in the range of 0.10 to 0.30 percent is required, from 5 to 7 percent nickel, from 14 to 18 percent chromium, and from 1.5 to 2.5 percent copper. Within this narrow range it is still necessary, though, to keep the delta ferrite-forming potential at less than 10, and the copper-manganese balance must be maintained according to the formulae given above for the alloy to be within the scope of this invention.

Although several embodiments of this invention have been shown and described, various adaptations and modofications may be made without departing from the scope of the appended claims.

I claim:

11. A free machining, austenitic stainless steel consisting essentially of from a trace up to 0.15 percent carbon, from 2 to 10 percent manganese, from 4 to 13 percent nickel, from 10 to 20% chromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percent sulfur, 2 percent maximum silicon, and 0.10 percent maximum nitrogen, balance essentially iron and residual impurities, the constituents being controlled so that the delta ferrite forming characteristic is less than 10 according to the formula:

delta ferrite potential Cr 1.5(% Si) .87 [30(% C N) and wherein the amount of copper is controlled so that it does not exceed 3.85 0.18 Mn- 55/32% S).

2. A free machining, austenitic stainless steel, according to claim 1, consisting essentially of from a trace up to 0.15 percent carbon, from 4 to 6 percent manganese, from 4 to 13 percent nickel, from 10 to 20 percent chromium, from 0.5 to 3 percent copper, from 0.30 to 0.40 percent sulfur, 2 percent maximum silicon,

0.10 percent maximum nitrogen, balance essentially iron and residual impurities.

3. A free machining, austenitic stainless steel according to claim 1 consisting essentially of from a trace up to 0.15 percent carbon, from 6 to 8 percent manganese, from 4 to 13 percent nickel, from to percent chromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percent sulfur, 2 percent maximum silicon, 0.10 percent maximum nitrogen, balance essentially iron and residual impurities.

4. A free machining, austenitic stainless steel according to claim 1 consisting essentially of from a trace up to 0.08 percent carbon, from 4 to 8 percent manganese, from 5 to 7 percent nickel, from 14 to 18 percent chromium, from 1.5 to 2.5 percent copper, from 0.10 to 0.40 percent sulfur, 1 percent maximum silicon, 0.10 percent maximum nitrogen, balance essentially iron and residual impurities.

5. A free machining, austenitic stainless steel according to claim 1 consisting essentially of from a trace up to 0.08 percent carbon, from 4 to 6 percent manganese, from 5 to 7 nickel, from 14 to 18 percent chromium, from 1.5 to 2.5 percent copper, from 0.30 to 0.40 percent sulfur, 1 percent maximum silicon, 0.10 percent maximum nitrogen, balance essentially iron and residual impurities.

6. A free machining, austenitic stainless steel according to claim 1 consisting essentially of from a trace up to 0.08 percent carbon, from 6 to 8 percent manganese, from 5 to 7 percent nickel, from 14 to 18 percent chromium, from 1.5 to 2.5 percent copper, from 0.10 to 0.30 percent sulfur, 1 percent maximum silicon, 0.10 percent maximum nitrogen, balance essentially iron and residual impurities.

Claims

1. A FREE MACHINING, AUSTENITIC STAINLESS STEEL CONSISTING ESSENTIALLY OF FROM A TRACE UP TO 0.15 PERCENT CARBON, FROM 2 TO 10 PERCENT MANGANESE, FROM 4 YO 13 PERCENT NICKEL, FROM 10 TO 20% CHROMIUM, FROM 0.5 TO 3 PERCENT COPPER, FROM 0.10 TO 0.40 PERCENT SULFUR, 2 PERCENT MAXIMUM SILICON, AND 0.10 PERCENT MAXIMUM NITROGEN, BALANCE ESSENTIALLY IRON AND RESIDUAL IMPURTIES, THE CONSTITUENTS BEING CONTROLLED SO THAT THE DELTA FERRITE FORMING CHARACTERISTIC IS LESS THAN 10 ACCORDING TO THE FORMULA:

2. A free machining, austenitic stainless steel, according to claim 1, consisting essentially of from a trace up to 0.15 percent carbon, from 4 to 6 percent manganese, from 4 to 13 percent nickel, from 10 to 20 percent chromium, from 0.5 to 3 percent copper, from 0.30 to 0.40 percent sulfur, 2 percent maximum silicon, 0.10 percent maximum nitrogen, balance essentially iron and residual impurities.

3. A free machining, austenitic stainless steel according to claim 1 consisting essentially of from a trace up to 0.15 percent carbon, from 6 to 8 percent manganese, from 4 to 13 percent nickel, from 10 to 20 percent chromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percent sulfur, 2 percent maximum silicon, 0.10 percent maximum nitrogen, balance essentially iron and residual impurities.