CA2316332C - Austenitic stainless steel including columbium - Google Patents

Abstract

An austenitic stainless steel of the 201 series includes, in weight percent, greater than 0.003 % Cb. Also disclosed is a method for providing a high strength 201 series stainless steel wherein the method includes preparing a heat of a 201 series stainless steel and maintaining the Cb in the heat at a level, in weight percent, greater than 0.003 %.

Description

TITLE
Austenitic Stainless Steel Including Columbium BACKGROUND OF THE INVENTION
Field of the Invention This invention relates generally to stainless steel alloys and more particularly to the T201 LN stainless steel alloy, and still more particularly to strengthening the T201 LN
alloy through the addition of columbium (Cb).

Description of the Prior Art Materials which are used at sub-zero temperatures should have good ductility, toughness and strength, which are all properties that are achievable with most of the austenitic stainless steels. The T201LN alloy was specifically designed for such applications and is unique in that it is designated as an acceptable material for applications in which high yield and ultimate strengths are specified. The T201LN alloy, which is disclosed in United States Patent No. 4,568,387 to Ziemianski, is an austenitic stainless steel having good low temperature properties of austenitic stability, elongation and strength. As described in the '387 patent, the compositionally-balanced T201LN alloy consists essentially of, in weight percent, 0.03% carbon max., 6.4 to 7.5% manganese, up to 1.0% silicon, 16 to 17.5%
chromium, 4.0 to 5.0% nickel, up to 1.0% copper, 0.13 to 0.20% nitrogen, and the balance iron. The T201LN alloy is characterized by austenitic stability, high room temperature strength, minimized sensitization to welding, and high strength and ductility at low temperatures.

Although the T201LN alloy has been successfully used in sub-zero applications, the strength requirements cannot always be achieved in all gages to satisfy the specifications of some cryogenic applications. Therefore, it would be desirable to develop methods to reliably increase the strength of the T201 LN alloy so that it may more reliably exceed the mechanical requirements of material specified for cryogenic applications. Recent interest has also surfaced in increasing the strength of the T201LN alloy to expand its use in structural applications where it may possible be used to replace carbon steel in the production of truck frames and other applications.

Industry attempts to produce high strength 201 series stainless steel have until now involved simply evaluating the alloy to determine how much, if any, of the alloy meets the strength requirements. Modifying the amount of nitrogen during melt has also been attempted. In any event, alloys are milled and the strength characteristics are tested. Alloys which do not meet the strength requirement would be scrapped. Extremely high scrap rates were anticipated based on prior production, to a lower 38,000 psi yield strength. Therefore, a more reliable means of producing higher strength 201 series stainless steel is needed.
SUMMARY OF THE INVENTION

The present invention relates to methods for reliably producing high strength series stainless steel. As defined in The Making, Shaping. and Treating of Steel (10' ed., AISI, 1985), p. 1334, an AISI 201 series stainless steel includes: 0.15%
carbon max.; 5.5-7.5% manganese max.; 1.00% silicon max.; 0.060% phosphorus max.; 0.030% sulfur max.;
16.00-18.00% chromium; 3.50-5.0% nickel; and 0.25% nitrogen max. The method of the present invention focuses on the influence of Cb on the mechanical properties of the T20ILN
alloy. Laboratory heats of T201 LN alloy, which were significantly alloyed with nitrogen (-0.15%) to stabilize the austenite, were made with varying amounts of Cb (as low as possible up to approximately 0.20%) to determine the influence the Cb would have on the mechanical properties of the alloy. It was found that a significant increase of at least 5 k.s.i.

is obtained in both the yield and ultimate strengths as the Cb level is increased above 0.0%5%, and approximately 10 k.s.i. at Cb levels above 0.150%. The percent elongation is decreased from about 55% to 48%, measured hardness is increased from about 89 Rb to about 98 Rb, and grain size is decreased from about ASTM 6.5 to about ASTM 10 as Cb content is increased from about 0.003% to about 0.210%.

Testing has shown that above a residual level of Cb (0.003%), impact energy increases as Cb content increases to about .10% at the three temperatures tested. Impact energy decreases at above about .10% Cb. Ductility remains relatively high at -50 F and 70 F. A decrease, but not a complete loss, of ductility occurs at a very low test temperature of -320 F.

Accordingly, an object of the present invention is to reliably increase the strength of the T201 LN alloy so that it may exceed the mechanical requirements of material specified for cryogenic applications. In this regard, a .06% to .10%
addition of Cb to a slightly modified version of studied T201LN alloy has been shown to improve the mechanical characteristics of the alloy for applications in temperature down to -320 F.

It is a further object of the present invention to reliably increase the strength of the T201 LN alloy for temperatures above -50 F. In this regard, a .10% to .20%
addition of Cb has been shown to improve the mechanical characteristics of the alloy for application in temperatures above -50 F.

In light of the foregoing, the present invention is directed to an austenitic stainless steel of the 201 series that includes, in weight percent, greater than 0.003%
Cb. The present invention also is directed to a method for providing a high strength 201 series stainless steel where in the method includes preparing a heat of a 201 series stainless steel and maintaining the Cb in the heat at a level, in weight percent, greater than 0.003%.

In a more preferred aspect, columbium is present in an amount selected greater than 0.003% up to 0.25% by weight, and preferably greater than 0.03% up to 0.21%
by weight.

In another aspect, the present invention provides a stainless steel which consists essentially of, in weight percent 0.02% to 0.027% carbon, 6.4 to 7.5%
manganese, up to 1.0% silicon, 16.78 to 17.74% chromium, 4.0 to less than 5.0%
nickel, copper in an amount up to 0.43%, 0.13 to 0.17% nitrogen, greater than 0.075 up to 0.20% columbium, inevitable impurities, and a balance iron.

Other objects and advantages of the invention will become apparent from the following description of certain presently preferred embodiments thereof.

4a BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows ferrite maps made on 1/2" thick slices, taken from the bottom of the laboratory produced ingots, which were then polished and etched before measurements (FN) were obtained with the Magne-Gage TM;
FIG. 2 is a schematic illustration of the tensile and subsize Charpy specimens which were used to obtain the mechanical data for this study (with all dimensions in inches);

FIG. 3 is a plot of the yield strength (0.2% offset), obtained from tensile specimens of the laboratory melted material of T201 LN alloy, as a function of Cb;

FIG. 4 is a plot of the ultimate strength, obtained from tensile specimens of the laboratory melted material of T201 LN alloy, as a function of Cb;

5 FIG. 5 is a plot of the ferrite content, as measured with the Magne-Gage, of the as-tested laboratory material, on the tensile blanks;

FIG. 6 is a plot of the magnetic response as measured with the Magne-Gage on the tensile samples after mechanical testing;

FIG. 7 is a plot of the % elongation, obtained from tensile specimens of the laboratory melted material of T201LN alloy, as a function of Cb;

FIG. 8 is a plot of the hardness, obtained from tensile specimens of the laboratory melted material of T20I LN alloy, as a function of Cb;

FIG. 9 is a plot of the grain size as a function of Cb obtained by metallographic examination of micros taken from laboratory melted material of T20ILN alloy;

FIG. 10 is a plot of the impact energies as a function of Cb content for the testing of subsize Charpy samples (0.180" except the data which are circled) at -320, -50 and 70 F;
FIG. 11 is a plot of the percent shear as a function of Cb content for the testing of subsize Charpy samples (0.180" thick) at -320, -50 and 70 F; and FIG. 12 is a plot of the lateral expansion as a function of Cb content for the testing of subsize Charpy samples (0.180" thick) at -320, -50 and 70 F.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Initial testing was conducted which involved making Cb additions to T201 LN
material to provide four heats comprising the following additions of carbon, nitrogen, and Cb.
Heat # C N C+N Cb Avg. Avg. Grain Plates with #6 Yield Tensile Sizes Grain Size Yield - Tensile 2C 152 .018 .176 .194 .011 48,000 96,100 6 48,000 96,200 2C153 .014 .175 .199 .013 48,950 95,600 5-6 50,450 96,850 2C077 .022 .170 .192 .030 48,333 96,533 5-7 49,700 97,300 2C078 .025 .180 .205 .050 52.550 101,867 6-8 53,450 103,800 The initial testing involved providing eleven groups of plates from the four heats as follows:

Heat I.D. No. Gage R.T. R.T. Elong. G.S. Ft/Lbs. - Size Lateral No. Yield Tensile 320F Expan. -2C077 21301 .370 46,700 95,400 59.7 5 55.5/52/59.5 3/4 30/30/30 91114 .437 49,700 97,300 59.1 6 44.5/47/55.5 3/4 37/44/38.5 24006 .437 48,600 96,900 61.8 7 68/53/64 3/4 44/36/43 2C078 21303 .370 52,000 101,000 57.5 8 42/43/42 3/4 33/36.5/32 21302 .437 53,450 103,800 58.3 6 60/60/60 Full 28/26/31 24005 .437 52,200 100,800 61 7 66/50/63 3/4 40/31/41 2C152 24007 .370 48,000 96,200 60.3 6 60/66/51 3/4 41/45/33 2C 153 24008 .370 49,100 96,800 59.2 6 63/59/63 3/4 43/39.5/43 24009 .370 48,300 95,000 61.2 5 67/67/79 3/4 42/44/50 91242 .370 51,800 96,900 P5695 6 75/76/72 3/4 35/37/33/5 24010 .370 46,600 93,700 5 54/55/50 3/4 35.5/37/34.5 Original 24010 .370 47,500 93,800 5 Retest 240102% .370 57,300 96,700 55/40.5/49.5 3/4 37/26/35/5 Stretch All plates from all four heats showed excellent impact and lateral expansion values at 320 F. The standard composition had been marginal at times and was of concern to the intended cryogenic tank fabricators. The pressure vessel code requires a minimum of 15 mils lateral expansion after welding. The average lateral expansion values of 201 LN prior to this trial were 31 mils. The average of the high Cb heat was 35 and the other heats averaged 39.
This is the expected improvement due to the more austenitic compositions of this trial.

The three heats of .17% to .18% nitrogen without Cb did not have sufficiently high enough yield or tensile strength after processing from ingots. Several groups were marginal and one plate failed with a 93,700 psi tensile versus 95,000 psi minimum.
(Slip # 24010, Heat 2C153, yield strength was 46,600 psi).

The fourth heat (Heat 2C078) as shown has acceptable strength, which appears to result from the .05% Cb addition, as is discussed later. Finer grain size also results from the high Cb content. All plates with #6 grain size were shown by heat to separate that variable from the comparison.

During rolling, all plates had work below 1600 F. The first two heats had more reduction below 1500 F via a 1500 F hold in the reheat furnace at 150% of the final gage except for one plate of 21302. This plate was direct rolled without reheat like the second two heats (2C152 and 2C153). This plate still had work below 1500 F and compares favorably with the reheated plates.

Heat 2C078 shows considerably higher yield and tensile strength than the other heats without as much Cb. Impact and lateral expansion values at -320 were also very good.
There is no restriction in the applicable specifications against the addition of Cb or other elements. The lower Cb (.03%) heat 2C077 does show that level of Cb to be insufficient.
Earlier 201LN sheet experience over .17% nitrogen found blistering and porosity to be a problem. None of the plates from the above heats showed any blistering or porosity.
Product checks found up to .198% nitrogen. If only nitrogen was used for strength, it would appear that more than .20 % nitrogen would be needed, but this has not been tried recently.
There is reluctance to continuous cast over .16% nitrogen.

The initial rolling of 2200 F oxidizing atmosphere was changed to 2150 F
reducing atmosphere after seeing a rough surface due to heavy scale. No evidence of intergranular attack was seen after dip pickling. It was thought that the hot rolling roughness may have had a deleterious effect on the test properties. Room temperature tensile samples were polished without improving the properties. However, for the -320 F tensile test, improvement was seen in the elongations when a subsize round was used versus the flat sample which had several cracks starting at the hot rolled surface roughness.

There is no minimum tensile properties at -320 F currently, but earlier data show low elongations in certain 201L plates at -320 F.

Shown below are the -320 F and corresponding room temperature (R.T.) results:

Heat # I.D.# Sample Sample Test Yield PSI Tensile PSI Elong. %
Size Type Temp. ( F) 2C078 21302 .464"x 2" Flat -320 100,400 134,400 4.5 21302 Flat -320 115,900 134,500 5.0 21302 .250x 1.0 Round -320 106,100 218,400 25.0 21303 .350x1.4 Round -320 103,055 186,542 20.0 21303 .350x 1.4 Round -320 102,649 192.701 19.3 2C077 91114 .350x 1.4 Round -320 90,314 196,397 21.4 91114 .350x 1.4 Round -320 104,772 176,382 20.0 2C078 21302 .437x2.0 Flat R.T. 53,450 103,800 58.3 21303 .370x2.0 Flat R.T. 52,000 101,000 57.7 2C077 91114 .437x2.0 Flat R.T. 49,700 97,300 59.1 Previous 201LN product was annealed at 2025 F with later plates using 1950 F. An anneal study done on hot rolled samples from heat 2C078 showed 1950 F to be the best choice. All plates in this study were annealed at 1950 F.

Due to concerns about diminishing the impact properties, none of the plates were stretcher leveled initially.

After plate 24010 failed the tensile strength, it was given a 2% stretch to evaluate the effects. The results shown after the first two roller levelled results show a large yield and notable tensile increase. The impact properties were still acceptable after stretching. It is clear that they were not greatly diminished, if at all. Impact testing recognizes that a test may be low due to testing variance. This one sample with 40.5 ft. lbs. and 26 mils lateral expansion is still above acceptable values.

These increases in strength from stretching can be expected to be lost in the welded joints of the tank and do not contribute to the true strengthening of the product as does a compositional change. Special weld procedures currently used by the largest potential customer are adding to the total fabrication cost due to the need to preserve the marginal tensile properties of the standard 201 LN plate. These improvements in the composition for higher tensile strength would be of value.

As is described in greater detail below, additional testing was performed.
Three laboratory heats of T201 LN were melted with various additions of Cb in the range of 0.003-0.210%. The material was hot rolled to -.3/16" (4.76 mm) and annealed at 1950 F. Tensile and subsize Charpy specimens were obtained from each of the plates for mechanical testing.
Measurements were made on the tensile specimens before and after testing to determine the ferrite content of the plate and the stability of the austenite. Micros were also obtained from the ends of the tensile specimens which were then polished and etched so that the grain size could be measured.

A significant increase of at least 5 k.s.i. is obtained in both the yield and ultimate strengths as the Cb level is increased above 0.075%, and approximately 10 k.s.i at Cb levels above 0. 150%. The percent elongation is decreased from about 55% to 48%, measured hardness is increased from about 89 Rb to 98 Rb, and grain size is decreased from about ASTM 6.5 to ASTM 10 as Cb content is increased from 0.003% to 0.2 10%. Above a residual level of Cb (0.003%), impact energy is increased slightly as Cb content increased at the three 5 temperatures tested up to .10% Cb. Ductility remains relatively high at -50 and 70 F. A
decrease, but not complete loss, of ductility occurs at a very low test temperature of -320 F
above.10% Cb. The addition of Cb enhances the mechanical properties of the T201 LN alloy.

Based on the data obtained on laboratory melted and processed material, an addition of approximately .075% Cb is sufficient to enhance the strength mechanical properties of this 10 alloy without significantly degrading any of the other mechanical properties.

The specific procedure and results of the additional testing were as follows.
Three fifty pound VIM laboratory heats were melted to the general chemistry aims of the T201 LN
alloy which is commercially produced. Table 1 contains the chemistries of the three laboratory heats that were melted for this study along with the minimum, average and maximum of the three commercial heats of T201 LN which were previously melted.
The first heat. RV # 1184, was melted to examine the influence of Cb additions in the range 0.01-0.10% by weight on the mechanical properties of T201 LN. However, the final chemistry of this first heat was slightly off the commercial chemistry of T201 LN.
Therefore a second heat, RV #1185, was melted. Later in the investigation, it was decided to examine the influence of slightly higher Cb contents (up to 0.20%) on the mechanical properties of this alloy, so a third and final heat, RV #1212, was melted. Once each heat was melted, it was cast into three seventeen pound ingots with the Cb content adjusted to various levels in between the pouring of the three individual ingots/heat. The purpose of this was to have essentially three identical alloys from which the influence of the varying Cb content on the mechanical properties of the alloy could be studied.

A half-inch slice was cut from the bottom of each ingot which was then polished and etched so that ferrite maps could be obtained on the as-cast material. The Ferrite Number (FN) measurements were obtained along a half-inch by half-inch grid on each of the 2-3/8"
square ingot slices with the Magne-Gage to ascertain the stability, with respect to austenite, of these alloys. These ferrite maps are shown in Figure 1 for heats RV #184, RV
#1185 and RV
#1212 respectively. The ingots were ground and heated to 2150 F (-1 hr TAT) for hot working. They were cross rolled to obtain a width of seven inches and then hot rolled to an aim gage of - 0.1875". Each panel was then annealed at 1950 F for six minutes (TAT) followed by grit blasting and pickling. Tensile specimens were cut and machined from each of the plate samples in both the longitudinal and transverse directions.
Charpy v-notch impact specimens were also cut and machined from each of the plate samples from the transverse direction. A schematic of the tensile and subsize Charpy specimens (0.394" x thickness of the plate material) used in this study are shown in Figure 2.

Samples were cut from the ends of the tensile specimens for microstructure evaluation after the mechanical tests were completed. These were mounted, polished and electrolytically etched in 10% oxalic acid at 6V for 20 - 30 seconds to reveal the general grain structure. The grain size of each sample was estimated per ASTM E 112 using the comparison procedure with the following two exceptions. The first is that the photomicrographs were taken at a magnification of 106X instead of 100X. The second is that the photomicrographs were compared to standards from Plate I and not Plate II, which is the recommended standard for austenitic stainless steels. Therefore, the grain sizes measured in this report should be used only to characterize and compare the material which is described within this report.

However, it should be noted that these minor variations in the grain size measuring technique should not significantly alter the grain size and/or the trend (grain size as a function of Cb content).

Table 2 contains the results which were obtained on or from the testing of the tensile specimens. Table 3 contains the results obtained from testing of the Charpy specimens. The results obtained from duplicate test specimens were averaged to simplify the graphical representation of the data. Where both longitudinal and transverse specimens were tested, an average of all the samples is also given. An example of this is the data which are plotted in Figures 3 and 4 of the yield (0.2% offset) and ultimate strengths, respectively, as a function of Cb content. As can be seen, both plots show an increase in the strength of T201LN as the Cb content is increased from -0.003 to 0.210%. A significant increase of at least 5 k.s.i. is seen in both the yield and ultimate strengths as the Cb level is increased above 0.075%. The increase is approximately 10 k.s.i. at Cb levels above 0.150%. In Figure 3, there is an abnormally high yield strength associated with a low Cb level material (RV
#1184 - Ingot A) which does not conform to the trend shown by the rest of the data. However, it should be noted that this material had the highest ferrite level (-2.5%) as measured on the tensile blanks, before testing.

Figure 5 is a plot of the ferrite content measured on the tensile blanks before testing.
Only three of the materials examined in this study had a significant amount of ferrite. The first two of these are from the laboratory heat RV #1 1 84 (ingots A & B) which did not match the commercially produced chemistry. The higher ferrite levels observed in this heat are due to the higher chromium and molybdenum and lower nickel and manganese contents.
The cause of the higher-than-expected ferrite level in the material from ingot C
of laboratory heat RV #1185 is unknown but may be due to fluctuations in the heat treating process which reduces the ferrite level from that which is found in the as-cast material (shown in Figure 1) to that in the final product.

The magnetic response (FN) was also measured along the shaft of the tensile specimens after testing to determine the presence of martensite which is a measure of the austenite stability. These data are shown in Figure 6 for future reference.
This measurement is an indication of the amount of martensite in the material. However, the relationship between this measurement and actual amount of martensite is not known and therefore should only be used for comparison between these samples.

The elongation and hardness measurements obtained from the tensile testing and the grain size obtained from the metallographic examination of micros cut from the tensile specimens (from the ends which were not deformed during testing) are shown in Figures 7, 8 and 9, respectively. The percent elongation decreases (Figure 7) and the measured hardness (Figure 8) of the material increases as the Cb content of the material increases.

The data that were obtained from impact testing of the subsize Charpy specimens (i.e.
< 0.394" thick) included the impact energies (Figure 10), percent shear (Figure 11) and the lateral expansion of the samples (Figure 12) as a function of Cb for three different temperatures (320 F, -50 F and 70 F). It should be noted that the data points in Figure 10 which are circled were obtained from the material of Heat RV # 1212, ingot A, which was accidentally rolled to a lighter gage (0.157") than that of the rest of the material which was rolled to a gage of 0.180 - 0.185". Due to the fact that the impact energy is dependent upon the cross-section of the sample being tested, these samples (from Heat RV#1212) would have had at least 18% higher impact energy if they were the correct thickness (0.180 - 0.185").
Therefore, these data were not considered when examining the impact energy, %
shear and lateral expansion trends as a function of Cb content.

The impact energies initially increase and then decrease as the Cb content increases.
Very little, if any, loss of toughness was observed between the testing at 70 and -50 F.
However, the tests that were completed at -320 F showed a decrease in the toughness of the material above .10% Cb. However, it should be noted that the impact properties at this temperature still show a respectable level of toughness.

The Cb addition up to .10% was successful in increasing the strength of this alloy without significantly degrading any of the other mechanical properties tested.
Examination of the data suggests that about .075% Cb is an appropriate addition to achieve the desired mechanical properties.

Due to the fact that Cb is a strong stabilizer (i.e., retards the formation chromium carbides at grain boundaries), the addition of Cb to this alloy may allow the maximum carbon content to be relaxed and still be acceptable from a corrosion standpoint.
This addition of Cb along with a slight increase in the carbon content may insure the enhanced mechanical properties needed for these new markets (additional strength and toughness due to the increased austenite stability). Therefore, a variation of the T201 grade (Cb 0.100% & C
0.060% max.) may produce an acceptable product in the as-welded condition.

Based upon the results obtained on laboratory produced material, the addition of Cb acts as a grain refiner and enhances the mechanical properties of the T201 LN
alloy. It was concluded that a significant increase of at least 5 k.s.i. is obtained in both the yield and ultimate strengths as the Cb level is increased above about 0.075%, and an approximately 10 k.s.i. increase is obtained at Cb levels above 0.150%. Further, the percent elongation is decreased from about 55% to 48%, measured hardness is increased from about 89 Rb to 98 Rb and grain size is decreased from ASTM 6.5 to ASTM 10 as Cb content is increased from 0.003% to 0.210%. In addition, above the residual level of Cb (-Ø003%), the impact energy is increased as Cb content is increased up to about .10% at the three temperatures tested.
Ductility remains relatively high at -50 and 70 F. At above about .10% Cb. a decrease, but still acceptable ductility occurs at the low test temperature of -320 F.

While certain presently prefered embodiments have been shown and described, it is distinctly understood that the invention is not limited thereto but may be otherwise embodied within the scope of the following claims.

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:tt SUBSTITUTE SHEET (RULE 26) Table 2 Sample Cb Initial Dimensions Sample Hard- Initial Ferrite Final Femte I.D. # (Wt %) Gage Width Orienta- ness Reading Reading Lion (Rb) FN(1) FN(2) FN(1) FN(2) 1184A 0.003 0.180 0.501 L 86.5 2.3 2.3 18.2 18.5 0.179 0.501 11 2.3 2.3 20.5 19.5 0.176 0.501 T 90.4 1.5 3.9 19.8 16.4 0.172 0.502 " 1.8 3.9 19.5 17.5 1184B 0.029 0.186 0.501 L 90.3 1.5 1.3 13.6 15.7 0.186 0.500 1.0 1.8 11.3 12.3 0.188 0.501 T 92.5 1.8 2.6 17.5 16.7 0.189 0.501 2.8 1.5 18.2 15.1 1184C 0.100 0.183 0.499 L 90.5 0.0 0.0 9.8 7.4 0.183 0.498 0.0 0.0 8.7 7.4 0.188 0.500 T 95.3 0.0 0.0 8.7 8.5 0.187 0.500 11 0.0 0.0 8.5 8.5 1185A 0.003 0.186 0.498 L 95.3 0.0 0.0 11.0 10.5 0.185 0.499 " 0.0 0.0 15.1 13.4 0.183 0.499 T 90.0 0.5 0.0 11.6 12.6 0.181 0499 0.0 0.3 14.1 13.1 1185B 0.046 0.186 0.501 L 88.0 0.0 0.0 10.8 9.5 0.187 0.501 0.0 0.0 10.0 8.5 0.181 0.501 T 94.0 0.0 0.0 11.3 11.3 0.182 0.501 11 0.0 0.0 11.0 10.5 1185C 0.120 0.185 0.498 L 94.2 1.3 1.3 14.1 11.3 0.186 0.498 1.3 1.3 15.4 11.6 0.186 0.498 T 96.3 0.8 0.8 15.1 15.4 0.187 0.497 1.0 1.0 13.4 15.4 1212A 0.078 0.156 0.499 L 94.3 0.0 0.0 12.8 10.5 0.157 0.500 0.0 0.2 13.9 12.3 0.158 0.499 T 0.0 0.0 10.8 11.3 0.158 0.500 0.0 0.0 12.6 11.5 1212B 0.160 0.180 0.499 L 97.6 0.0 0.0 10.8 10.3 0.181 0.499 0.0 0.0 13.6 11.5 0.186 0.499 T 0.0 0.0 12.1 13.3 0.186 0.499 0.0 0.0 12.3 13.1 1212C 0.210 0.181 0.500 L 97.8 0.0 0.2 16.9 17.2 0.178 0.499 0.0 0.0 12.3 14.6 0.180 0.500 T 0.0 0.0 12.8 10.3 0.181 0.499 0.0 0.0 12.6 13.9 SUBSTITUTE SHEET (RULE 26) ................ .

Table 2 (continued) Sample Uniform Elongat Grain Grain Strain Strength (p.s.i.) I.D. # Deformed Region ion (%) Size IU Size Hardening Yield Ultimate Width Gage Anneal Ind Exp. (0.2%) Anneal n(1) n(2) 1184A 0.421 0.148 55 7.5 0.23 0.43 57100 105200 0.420 0.148 53 0.23 0.43 57500 103900 0.417 0.146 53 7.5 7.0 0.24 0.44 51100 104500 0.423 0.143 54 7.5 0.24 0.44 48500 103800 1184B 0.423 0.155 54 6.5 0.24 0.44 49400 103200 0.423 0.153 54 0.24 0.42 49900 102000 0.420 0.154 54 7.0 6.5 0.24 0.40 48800 103800 0.417 0.155 54 7.0 0.24 0.38 48200 102700 1184C 0.422 0.154 50 10.0 0.23 0.39 58500 108200 0.428 0.153 51 0.24 0.39 56400 108200 0.422 0.158 50 9.5 9.5 0.23 0.39 53600 109400 0.424 0.158 50 9.5 0.23 0.39 55000 109300 1185A 0.415 0.153 57 6.5 0.26 0.45 49100 101300 0.415 0.154 57 0.26 0.46 47900 103000 0.417 0.153 55 6.5 6.0 0.26 0.46 46100 103300 0.415 0.152 55 6.0 0.25 0.46 47500 102800 1185B 0.422 0.151 54 6.5 0.26 0.46 45700 98600 0.418 0.150 54 0.26 0.44 44900 96500 0.418 0152 55 6.0 6.5 0.26 0.45 47800 103900 0.420 0.152 55 6.5 0.26 0.44 48600 103300 1185C 0.423 0.151 51 9.0 0.23 0.38 54700 104500 0.424 0.153 52 0.24 0.39 55100 105700 0.423 0.156 50 8.5 10.0 0.24 0.40 50800 108600 0.420 0.154 52 9.5 0.23 0.40 56100 109200 1212A 0.425 0.133 52 8.5 0.24 0.41 55200 108400 0.420 0.133 52 0.24 0.43 54700 108400 0.417. 0.130 52 8.0 8.5 0.25 0.42 54200 109200 0.418 0.130 51 8.0 0.24 0.41 54400 109600 L 1212B 0.420 0.153 51 10.0 0.23 0.38 57900 110300 0.417 0.148 51 0.23 0.39 58600 112100 0.415 0.153 50 10.0 9.5 0.23 0.39 57900 113400 0.422 0.157 49 10.0 0.23 0.39 58700 113100 1212C 0.420 0.152 50 10.0 0.23 0.41 58500 113400 0.420 0.148 50 0.24 0.38 57300 112600 0.425 0.150 46 10.0 10.0 0.24 0.39 56400 112000 0.421 0.151 47 10.0 0.24 0.39 57100 112400 SUBSTITUTE SHEET (RULE 26) Table 3 Sample Cb Testing Annealed @ 1950 F for 6 min. Reannealed @ 1950 F for 6 min.
I.D. # (wt %) Temp (TAT) (TAT) ( F) Impact Lateral Impact Lateral Energy Expansion Energy Expansion (ft-lbs) % Shear (in) (ft-lbs) % Shear (in) 1184A 0.003 -320 21.0 10 0.023 28.5 10 0.026 1184A 0.003 -320 18.5 10 0.018 23.0 10 0.034 1184A 0.003 -320 24.0 15 0.021 16.0 5 0.021 1184B 0.029 -320 42.0 20 0.025 27.5 10 0.038 1184B 0.029 -320 22.5 15 0.024 26.0 10 0.037 1184B 0.029 -320 40.0 15 0.033 27.0 10 0.041 1184C 0.100 -320 24.0 10 0.018 13.5 5 0.020 1184C 0.100 -320 20.0 5 0.020 13.0 5 0.013 1184C 0.100 -320 19.0 5 0.021 13.0 5 0.016 1185A 0.003 -320 24.0 10 0.014 26.0 5 0.035 1185A 0.003 -320 30.0 10 0.021 25.0 5 0.041 1185A 0.003 -320 24.0 15 0.016 25.0 5 0.028 1185B 0.046 -320 30.0 10 0.034 32.0 10 0.035 1185B 0.046 -320 28.5 10 0.032 27.0 10 0.024-1185B 0.046 -320 26.0 10 0.023 24.0 5 0.029 1185C 0.120 -320 17.0 5 0.013 17.5 5 0.019 1185C 0.120 -320 15.0 5 0.018 14.0 5 0.019 1185C 0.120 -320 16.0 5 0.016 14.0 5 0.018 1212A 0.078 -320 14.0 5 0.013 19.0 5 0.020 1212A 0.078 -320 19.0 5 0.011 14.0 5 0.020 1212A 0.078 -320 25.0 5 0.022 1212B 0.160 -320 11.5 5 0.016 13.0 5 0.020 1212B 0.160 -320 15.0 5 0.017 12.0 5 0.019 1212B 0.160 -320 13.0 5 0.015 1212C 0.210 -320 11.5 5 0.011 11.0 5 0.012 1212C 0.210 -320 14.0 5 0.010 11.5 5 0.015 1212C 0.210 -320 11.0 5 0.013 11 84A 0.003 -50 38.0 80 0.044 46.0 60 0.051 1184A 0.003 -50 42.5 75 0.059 44.0 55 0.044 1184A 0.003 -50 1184B 0.029 -50 47.5 85 0.057 45.0 60 0.055 1184B 0.029 -50 51.5 90 0.058 53.0 50 0.054 1184B 0.029 -50 1184C 0.100 -50 38.0 60 0.043 42.0 45 0.048 1184C 0.100 -50 38.5 65 0.032 42.0 55 0.059 1184C 0.100 -50 1185A 0.003 -50 41.0 60 0.040 46.0 35 0.041 1185A 0.003 -50 38.5 65 0.055 46.0 35 0.054 1185A 0.003 -50 1185B 0.046 -50 43.0 65 0.051 50.0 50 0.054 1185B 0.046 -50 44.0 75 0.038 52.0 50 0.049 SUBSTITUTE SHEET (RULE 26) Table 3 (continued) Sample Cb Testing Annealed Lu 1950 F for 6 min. Reannealed @ 1950 F for 6 min.
I. D. (wt %) Temp (TAT) (TAT) ( F) Impact Lateral Impact Lateral Energy Expansion Energy Expansion (ft-lbs) % Shear (in) (ft-lbs) Shear (in) 1185B 0.046 -50 1185C 0.120 -50 36.5 70 0.039 39.5 55 0.051 1185C 0.120 -50 39.0 80 0.044 40.0 45 0.043 1212A 0.078 -50 33.5 75 0.025 32.0 60 0.047 1212A 0.078 -50 31.5 70 0.026 33.5 65 0.049 1212A 0.078 -50 1212B 0.160 -50 36.5 70 0.037 36.0 50 0.040 1212B 0.160 -50 34.0 80 0.040 37.0 50 0.047 1212B 0.160 -50 1212C 0.210 -50 34.0 50 0.025 34.0 40 0.044 1212C 0.210 -50 30.5 50 0.025 32.0 40 0.046 1212C 0.210 -50 1184A 0.003 70 42.5 90 0.053 41.0 70 0.052 1184A 0.003 70 42.0 95 0.056 42.0 75 1184A 0.003 70 40.0 60 0.055 1184B 0.029 70 48.0 95 0.064 51.0 85 0.059 1184B 0.029 70 48.5 90 0.058 46.0 75 1184B 0.029 70 50.0 75 0.059 1184C 0.100 70 39.5 80 0.055 42.5 55 0.047 1184C 0.100 70 40.0 85 0.053 44.0 65 1184C 0.100 70 41.5 55 0.044 1185A 0.003 70 41.0 90 0.047 45.0 50 0.058 1185A 0.003 70 41.5 90 0.061 44.5 55 1185A 0.003 70 44.0 50 0.049 1185B 0.046 70 45.5 95 0.051 50.0 60 0.054 1185B 0.046 70 45.0 90 0.056 51.0 60 1185B 0.046 70 49.5 50 0.053 1185C 0.120 70 45.0 95 0.056 42.5 55 0.060 1185C 0.120 70 41.5 85 0.059 45.0 60 1185C 0.120 70 42.0 50 0.051 1212A 0.078 70 29.5 95 0.052 34.0 65 0.047 1212A 0.078 70 28.0 90 0.050 34.0 65 1212A 0.078 70 31.5 65 0.051 1212B 0.160 70 32.0 90 0.044 39.0 50 0.047 1212B 0.160 70 32.0 90 0.046 37.0 50 1212B 0.160 70 36.0 60 0.042 1212C 0.210 70 30.0 80 0.043 34.0 50 0.046 1212C 0.210 70 30.0 85 0.047 34.0 45 1212C 0.210 70 32.0 55 0.036 SUBSTITUTE SHEET (RULE 26)

Claims (29)

We Claim:

1. An austenitic stainless steel comprising, in weight percent, 0.06% carbon max., 6.4 to 7.5% manganese, 0 to 1.0% silicon, 16 to 17.5% chromium, 4.0 to less than 5.0%
nickel, copper in an amount greater than 0% and less than 1%, 0.13 to 0.20%
nitrogen, and greater than 0.003 up to 0.21% columbium, inevitable impurities, and a balance iron.

2. The austenitic stainless steel of claim 1, wherein said carbon is present in an amount up to 0.03% max in weight percent.

3. The austenitic stainless steel of claim 1, wherein said columbium is present in an amount of at least 0.06% in weight percent.

4. The austenitic stainless steel of claim 1, wherein said columbium is present in an amount of at least 0.10% in weight percent.

5. The austenitic stainless steel of claim 3, wherein columbium is present in an amount of at least 0.075% in weight percent.

6. The austenitic stainless steel of claim 1, or claim 4, or claim 5, wherein said copper is present in an amount of 0.35 to 0.60% in weight percent.

7. The austenitic stainless steel of any one of claims 1 to 6, characterized by at least 100,000 psi tensile strength and at least 50,000 psi yield strength at room temperature.

8. The austenitic stainless steel of claim 7, further characterized by an ASTM
grain size of 6 or higher.

9. The austenitic stainless steel of claim 1, consisting essentially of, in weight percent 0.02% to 0.027% carbon, 6.4 to 7.5% manganese, 0 to 1.0% silicon, 16.78 to 17.5% chromium, 4.0 to less than 5.0% nickel, copper in an amount up to 0.43%, 0.13 to 0.17% nitrogen, greater than 0.075 up to 0.20% columbium, inevitable impurities, and a balance iron.

10. An article of manufacture comprising, in weight percent, 0.06% carbon max., 6.4 to 7.5% manganese, 0 to 1.0% silicon, 16 to 17.5% chromium, 4.0 to less than 5.0%
nickel, copper in an amount greater than 0% and less than 1.0%, 0.13 to 0.20%
nitrogen, and greater than 0.003 up to 0.21% columbium, inevitable impurities, and a balance iron.

11. The article of manufacture of claim 10, wherein said austenitic stainless steel comprises columbium in an amount of at least 0.06% in weight percent.

12. The article of manufacture of claim 10, wherein the article of manufacture is selected from the group consisting of a plate, a tank, and a pressure vessel.

13. The article of manufacture of claim 10, wherein said austenitic stainless steel is characterized by at least 100,000 psi tensile strength and at least 50,000 psi yield strength at room temperature.

14. A method for providing a high strength stainless steel, the method comprising preparing a heat comprising, in weight percent, 0.06% carbon max., 6.4 to 7.5%

manganese, 0 to 1.0% silicon, 16 to 17.5% chromium, 4.0 to less than 5.0%
nickel, copper in an amount greater than 0% and less than 1.0%, 0.13 to 0.20%
nitrogen, and greater than 0.003 up to 0.21% columbium, inevitable impurities, and a balance iron.

15. The method of claim 14, wherein the alloy includes columbium in an amount of at least 0.06% in weight percent.

16. A method for providing an article of manufacture comprising a high strength stainless steel, the method comprising processing at least a portion of an alloy comprising, in weight percent, 0.06% carbon max., 6.4 to 7.5% manganese, 0 to 1.0%
silicon, 16 to 17.5% chromium, 4.0 to less than 5.0% nickel, copper in an amount greater than 0% and less than 1.0%, 0.13 to 0.20% nitrogen, and greater than 0.003 up to 0.21%
columbium, inevitable impurities, and a balance iron.

17. The method of claim 16, wherein the alloy includes columbium in an amount of at least 0.06% in weight percent.

18. The method of claim 16, wherein the act of processing comprises hot rolling at least a portion of the alloy at less than 2200°F in a reducing atmosphere.

19. The method of claim 16, wherein the act of processing comprises hot rolling at least a portion of the alloy at approximately 2150°F in a reducing atmosphere.

20. The method of claim 18, further comprising annealing at least a portion of the alloy at approximately 1950°F.

21. The method of claim 16, wherein the article of manufacture is a plate.

22. The austenitic stainless steel of claim 1 or claim 2, wherein said columbium is present in an amount of at least 0.03% up to 0.20% in weight percent.

23. The article of manufacture of any one of claims 10, 12 and 13, wherein said columbium is present in an amount of at least 0.03% in weight percent.

24. The method of any one of claims 14, 16 and 18 to 21, wherein said columbium is present in an amount of at least 0.03% in weight percent.

25. The method of any one claims 14, 16 and 18 to 21 wherein said columbium is present in an amount of at least 0.03 up to 0.2% in weight percent.

26. The article of manufacture of any one of claims 10, 12 and 13, wherein said columbium is present in an amount greater than 0.003 up to 0.2% in weight percent.

27. The method of any one of claims 14, 16 and 18 to 21, wherein said columbium is present in an amount greater than 0.003 up to 0.2% in weight percent.

28. The method of any one of claims 24, 25 or 26, wherein said columbium is present in an amount greater than 0.075% in weight percent.

29. The stainless steel of any one of claims 1 to 8 wherein said columbium is present in an amount up to 0.2% in weight percent.