HK1032078B - Austenitic stainless steel including columbium - Google Patents

Description

Austenitic stainless steel containing niobium

Technical Field

The present invention relates generally to stainless steel alloys, and more particularly to T201LN stainless steel alloy, and more particularly to T201LN alloy strengthened by the addition of niobium (Nb).

Prior Art

Materials used at sub-zero low temperatures should have good ductility, toughness and strength, all of which are properties that are attainable with most austenitic stainless steels. The T201LN alloy is designed specifically for this type of use and is unique in that it is designed to be suitable for use in applications where high yield strength and ultimate tensile strength are specified. The T201LN alloy is disclosed in U.S. patent No. 4,568,987 to zieminski, the entire contents of which are incorporated herein by reference, and is an austenitic stainless steel having good low temperature austenite stability, elongation and strength properties. As described in U.S. Pat. No. 4,568,387, the compositionally balanced T201LN alloy consists essentially of up to 0.03 weight percent C, 6.4 to 7.5 weight percent Mn, up to 1.0 weight percent Si, 16 to 17.5 weight percent Cr, 4.0 to 5.0 weight percent Ni, up to 1.0 weight percent Cu, 0.13 to 0.20 weight percent N, and the balance Fe. The T201LN alloy is characterized by good austenite stability, high room temperature strength, minimal susceptibility to welding, high low temperature strength, and high ductility.

Although the T201LN alloy has been successfully used in low temperature applications, not all specifications for the T201LN alloy meet the strength requirements for certain low temperature applications. It is therefore desirable to develop methods for reliably increasing the strength of the T201LN alloy. Thereby more reliably exceeding the mechanical performance requirements specified for low temperature applications. In recent years, attention has focused on improving the strength of the T201LN alloy to expand its use in structural applications, where such uses may be in the production of truck frames and other uses where the T201LN alloy is substituted for carbon steel.

Industry efforts to produce high strength 201 series stainless steels have heretofore involved simply evaluating the alloy to determine how much, if any, of the alloy meets the strength requirements. Attempts have also been made to vary the amount of nitrogen during smelting. In either case, the alloy was rolled and then tested for strength characteristics. Alloys that do not meet the strength requirements are discarded. As can be expected from the prior production method, the yield strength is less than 2.622 multiplied by 10⁸The reject rate of Pa (38000Psi) rejects is extremely high. There is therefore a need for a reliable method for producing high strength 201 series stainless steels.

Brief description of the invention

The present invention relates to a method for reliably producing a high-strength 201-series stainless steel. The focus of this method is the effect of Nb (Cb) on the mechanical properties of the T201LN alloy. Molten steel of T201LN alloyed with nitrogen (-0.15%) to stabilize austenite was prepared in the laboratory with various amounts of Nb (as low as possible, up to about 0.20%) to determine the effect of Nb on the mechanical properties of the alloy. It has been found that when the Nb content is increased to 0.075%When the yield strength and the tensile strength are at least 3.450 x 10⁷An increase in Pa (5k.s.i) above about 6.901X 10 at a Nb content of greater than 0.15 percent⁷Pa (10 k.s.i). When the Nb content was increased from 0.003% to about 0.210%, the elongation (%) decreased from about 55% to 48%, the measured hardness increased from 89Rb to about 98Rb, and the grain size decreased from ASTM grade 6.5 to ASTM grade 10.

Experiments have shown that the impact energy (impactenergy) increases with increasing Nb content to about 0.10% for three test temperatures above the residual Nb content (0.003%). Above 0.10% Cb, the impact power decreases. Ductility remained fairly high at-45.6 ℃ (-50 ° F) to 21.1 ℃ (70 ° F). At the very low test temperature of-195.6 ℃ (-320 ° F), a reduction in ductility occurred, but did not completely disappear.

Accordingly, it is an object of the present invention to reliably increase the strength of the T201LN alloy so that it can exceed the mechanical performance requirements specified for low temperature applications. In this regard, it has been shown that the addition of 0.06% to 0.10% Nb slightly changes the morphology of the T201LN alloy under study. Thereby improving the mechanical properties of the alloy when used at temperatures as low as-195.6 ℃ (-320 ° F).

It is another object of the present invention to reliably improve the strength of the T201LN alloy at temperatures above-45.6 ℃ (-50 ° F). In this regard, the addition of 0.10-0.20% Nb demonstrated improved mechanical properties for the alloy when used at temperatures above-45.6 ℃ (-50 ° F).

From the above, the present invention is intended to provide a 201-series austenitic stainless steel containing 0.003% by weight or more of Nb. The present invention is also directed to a method of producing a high strength 201 series stainless steel, wherein the method comprises manufacturing a 201 series stainless steel molten steel and maintaining the Nb content in the molten steel at 0.003% or more.

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

Drawings

Fig. 1 shows a ferrite map made on a 0.0127 m (1/2') -thick section taken from the bottom of a laboratory-produced ingot, which was polished and etched before measurement (FN), and fig. 1 was obtained with Magne-Gage.

Figure 2 schematically illustrates tensile and small size (Subsize) Chargy specimens used to obtain experimental data for the mechanical properties of this study (all dimensions in inches, 1 inch being 0.0254 meters).

FIG. 3 is a graph of the yield strength (0.2% set) of tensile specimens of laboratory melt material from the T201LN alloy as a function of Nb.

FIG. 4 is a graph of ultimate strength of tensile specimens of laboratory melted material from the T201LN alloy as a function of Nb.

Fig. 5 is a graph of the ferrite content of laboratory test materials measured with Magne-Gage on a drawn billet.

FIG. 6 is a graph of the magnetic response of a tensile specimen after mechanical testing using a Magne-Gage test.

FIG. 7 is a plot of elongation (%) from tensile specimens of T201LN alloy laboratory melt material as a function of Nb.

FIG. 8 is a graph of hardness as a function of Nb for tensile specimens from the T201LN alloy laboratory melt material.

FIG. 9 is a grain size plot from a microscopic all-phase examination of T201LN alloy laboratory melt material as a function of Nb.

FIG. 10 is a plot of the work of impact as a function of Nb content at-195.6 ℃ (-320 ° F), -45.6 ℃ (-50 ° F), and 21.1 ℃ (70 ° F) for small size Chanpy specimens (-0.004572 meters (0.180 "), except for circled data.

FIG. 11 is a graph of the percent shear achieved by testing small size Chanpy specimens (0.004572 meters (0.180 "thick)) at-195.6 ℃ (-320 ° F), -45.6 ℃ (-50 ° F), and 21.1 ℃ (70 ° F) as a function of Nb content.

FIG. 12 is a plot of the lateral expansion values obtained by testing small size Chanpy specimens (-0.004572 meters (0.180 ") thick) at-195.6 ℃ (-320 ° F), -45.6 ℃ (-50 ° F), and 21.1 ℃ (70 ° F) as a function of Nb content.

Description of the preferred embodiments

Initial trials were conducted which included Nb addition to the T201LN material to provide 4 furnaces of molten steel containing the following additions of carbon, nitrogen and niobium.

Heat #	C	N	C+N	Nb	Average yield strength	Average tensile strength	Grain size	Plate with 6-grade grain size
																		Yield strength-tensile strength
2C152	.018	.176	.194	.011	48,000	96,100	6	48,000	96,200
										2C152	.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 test included providing 11 steel sheets (1Ft/Lbs 1.48816kg/m) with the 4 heats of molten steel as follows:

heat of furnace	Spindle No. No	Grade	Room temperature yield strength	Tensile strength at room temperature	Elongation percentage	Grain size	Ft/Lbs at-320 DEG F	Size of	-320 DEG F transverse expansion
										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
										2C153	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	58.9	6	75/76/72	3/4	35/37/33/5
	24010 original	.370	46,600	93,700	61	5	54/55/50	3/4	35.5/37/34.5
											24010Retest	.370	47,500	93,800	63	5
	24010 elongation 2%	.370	57,300	96,700	56.9	5	55/40.5/49.5	3/4	37/26/35/5

All the sheets from the 4 heats exhibited excellent impact and transverse expansion values at-195.6 ℃ (-320 ° F). This standard ingredient is sometimes not required and is relevant to the can manufacturer. Pressure vessel regulations require a minimum post-weld lateral expansion value of 3.81 x 10^-4Meter (15 mils). The mean transverse expansion of 201LN before this experiment was 7.874X 10^-4Meter (31 mil). This average value for high Nb steel is 35, while that for other heats is 39. This is a desirable improvement as this experiment produces more austenite component.

The triple furnace contains 0.17% to 0.18% nitrogen, while the Nb-free steel does not have a sufficiently high yield strength or tensile strength after being processed with an ingot. Some groups were marginal and one panel had a tensile strength of 6.466X 10⁸Pa (93700psi) less than minimum tensile strength 6.555X 10⁸Pa (95000psi) fail (see #24010, Heat No. 2C153, yield strength 3.216X 10⁸Pa(46600psi))。

The 4 th furnace molten steel (furnace No. 2C078) had acceptable strength because of the result of adding 0.05% Nb as will be described later. Finer grain sizes are also a result of the high Nb content. All plates exhibiting a grain strength of grade 6 were heated to distinguish the variable grains from the control.

During rolling, all plates were processed at temperatures below 871.1 ℃ (1600 ° F). Except for one plate of 21302, the plates of the first two furnaces were held at 815.6 ℃ (1500 ° F) in a reheating furnace with a compression ratio below 815.6 ℃ (1500 ° F) of 150% at final gauge. 21302 the plate was rolled directly without reheating the rear two furnace plates (2C152 and 2C 153). The panel was still processed below 815.6 ℃ (1500 ° F) and was comparable to a heavy hot plate.

The plates of the 2C078 furnace showed much higher yield and tensile strength than the plates made from the Nb-poor containing steel of the other heats. The impact and the transverse expansion values at-195.6 ℃ (-320 ° F) are also good. There is no limitation to adding Nb or adding other elements in the applicable specification. The 2C077 furnace molten steel (containing Nb 0.03%) containing a small amount of Nb showed an insufficient Nb content.

Early experiments on steel sheets containing more than 0.17% nitrogen found that porosity and porosity were a problem. Without any porosity or porosity in a plate made from said heat of molten steel. Product inspection found up to 0.198% nitrogen. If only nitrogen is used for the strength, it seems that 0.20% or more of nitrogen is used, but no attempt has been made in recent years. Nitrogen exceeding 0.16% is a limitation for continuous casting.

After seeing a rough surface due to severe scale, blobbing in an oxidizing atmosphere of 1204.4 ℃ (2200 ° F) was changed to a blobbing in a reducing atmosphere of 1176.7 ℃ (2150 ° F). No trace of grain boundary corrosion was seen after acid leaching. Hot rolling roughness is believed to have a detrimental effect on test performance. Polishing the room temperature tensile specimens did not improve performance. However, for the tensile test at-195.6 ℃ (-320 ° F), there was an increase in elongation when using small-sized round specimens compared to flat specimens with some cracks originating from hot-rolled surface roughness.

The tensile properties at-195.6 ℃ (-320 ° F) are not the lowest tensile properties, but earlier data show that some 201L sheets have low elongation at-195.6 ℃ (-320 ° F).

Shown below are the results for-195.6 ℃ (-320 ° F) and the equivalent room temperature (degrees fahrenheit in ° F to degrees celsius minus 32 times 5/9)1 ″ -0.0254 meters, degrees celsius (degrees fahrenheit F-32) x 5/9, 1PSI 6900.52557346Pa

Heat #	Plate number #	Size of sample	Type of sample	Test temperature (. degree.F)	Yield strength, PSI	Tensile strength, PSI	Elongation percentage%
								2C078	21302	.464＂×2＂	Flat plate	-320	100,400	134,400	4.5
″	21302	″	Flat plate	-320	115,900	134,500	5.0
								″	21302	.250×1.0	Round (T-shaped)	-320	106,100	218,400	25.0
″	21303	.350×1.4	Round (T-shaped)	-320	103,055	186,542	20.0
								″	21303	.350×1.4	Round (T-shaped)	-320	102,649	192,701	193
								2C077	91114	.350×1.4	Round (T-shaped)	-320	90,34	196,397	21.4
	91114	.350×1.4	Round (T-shaped)	-320	104,772	176,382	20.0
2C078	21302	.437×2.0	Flat plate	R.T.	53,450	103,800	58.3
								″	21303	.370×2.0	Flat plate	R.T.	52,000	101,000	57.7
								2C077	91114	.437×2.0	Flat plate	R.T.	49,700	97,300	59.1

The previous 201LN product was annealed at 1107.2 ℃ (2025 ° F) while the subsequent panels were annealed at 1065.6 ℃ (1950 ° F). Annealing studies on hot rolled samples taken from heat 2C078 showed that: 1065.6 deg.C (1950 deg.F) is the best choice. All of the panels in this study were annealed at 1065.6 deg.C (1950 deg.F).

No sheet started to be stretched and straightened due to fear of lowering the impact property.

Since 24010 plate failed in tensile strength, it was elongated by 2% to evaluate the effect. These results show that the first 2-furnace steel sheet produced a large yield strength after rolling, and the tensile strength was also dramatically improved. After stretching, the impact properties are still acceptable. It is clear that the performance is not significantly impaired (if not at all). Impact testing indicates that testing may be low due to testing variables. Having 54.911N.M (40.5ft. lbs) and 6.604X 10^-4The meter (26 mil) cross-direction expansion of the test specimens was still above acceptableThe value of (c).

These increases in strength due to stretching are expected to be lost at the weld seams of the cans and thus not contribute to the product strengthening as a result of changing composition. The specialized welding procedures used by the largest 201LN potential users in recent years are increasing the overall manufacturing costs due to the need to maintain the ultimate tensile properties of standard 201LN panels. This improvement in composition for achieving higher tensile strength is valuable.

As will be described in detail below, the secondary tests were performed. T201LN steel was laboratory smelted with varying amounts of Nb ranging from 0.063 to 0.210%. The batch was hot rolled to-3/16 "(4.76 mm) and then annealed at 1065.6 ℃ (1950 ° F). Tensile and small size Charpy specimens were taken from each plate to test mechanical properties. Measurements were made before and after the test to determine the ferrite content and austenite stability of the sheet. A microscopic sample was taken from the end of the tensile sample, which was then polished and acid etched to enable measurement of grain size.

When the Nb content is increased to more than 0.075 percent, the yield strength and the ultimate tensile strength are at least improved by 3.450 multiplied by 10⁷Pa (5k.s.i), and when the Nb content increases above 0.150%, the strength increases by about 6.901X 10⁷Pa (10 k.s.i). Elongation (%) decreased from about 55% to 48%, measured hardness increased from about 89Rb to 98Rb, and grain size decreased from about ASTM6.5 grade to ASTM10 grade when Nb content increased from 0.003% to 0.210%. Above the residual amount of Nb (0.003%), the impact power is slightly increased when the Nb content is up to 0.10% when tested at three temperatures. The ductility remained fairly high at-45.6 ℃ (-50 ° F) and 21.1 ℃ (70 ° F). Above 0.10% Nb, there is a reduction in ductility at the very low test temperature of-195.6 ℃ (-320 ° F), but not a complete loss. The addition of Nb improves the mechanical properties of the T201LN alloy.

Based on data obtained when laboratory melting and processing materials, adding about 0.075% Nb is sufficient to improve the mechanical strength properties of this alloy without significantly compromising any other mechanical properties.

The results of the specific protocol and the addition experiments are as follows. Three furnaces of 50 lbs of VIM laboratory molten steel were smelted. To reach the total chemical index of T201LN produced by the industry. Table 1 includes the chemical properties of the three laboratory-smelted steels, as well as the minimum, average and maximum chemical properties of the earlier-smelted 3-furnace commercial T201LN steel. The first furnace, RV #1184, was smelted to examine the effect of adding Nb in an amount of 0.01-0.10% by weight on the mechanical properties of T201 LN. However, the chemical properties of the first furnace molten steel slightly deviate from those of commercial T201 LN. Therefore, 2 nd furnace molten steel RV #1185 is smelted. In a later study, it was decided to examine the effect of a slightly higher Nb content (up to 0.20%) on the mechanical properties of this alloy, and the final third furnace steel, RV #1212, was also smelted. Once refined, each furnace was cast into 3 17 pound ingots, with the Nb content adjusted to different levels as the three individual ingots/heats were cast. The aim was to obtain 3 essentially identical alloys from which the effect of varying the Nb content on the mechanical properties of the alloy could be investigated.

A 0.0127 meter (half inch) slice was cut from the bottom of each ingot and then polished and acid leached to obtain a ferrite map on the as-cast material. Ferrite counts (FN) were obtained along a 0.0127 m (half inch) x 0.0127 m (half inch) grid on 0.00635-0.009525 m (2-3/8 ") inch square ingot slices per slice and the austenitic stability of the alloy was ascertained by Magne-Gage. Fig. 1 shows ferrite maps of three-furnace steels RV #184, RV #1185 and RV # 1212. The ingot was heated to 1176.7 deg.C (2150 deg.F) at the grinding angle (-1 hour TAT) for hot working. They were cross rolled to a width of 0.1778 meters (7 inches) and then hot rolled to target specifications of-0.0047625 meters (-0.1875 "). Each sheet was then annealed at 1065.6 ℃ (1950 ° F) for 6 minutes (TAT), then grit blasted and acid pickled. Tensile specimens were cut and then machined from each panel in the machine direction and the cross direction. A Charpy V-notch impact specimen was also cut and machined in the transverse direction. The tensile test specimens and the small size Charpy test specimens (0.01 meter (0.394 ") x sheet thickness) used to perform this study are shown in fig. 2.

After the mechanical property test was completed, a specimen was cut from the end of the tensile specimen to perform microscopic structure evaluation. These samples were ground, polished and electroetched at 6V in 10% oxalic acid for 20-30 seconds to reveal the general grain structure. The grain size of each sample was evaluated according to ASTM E112 using a comparative procedure with the following two exceptions. The first example is to take a micrograph at a magnification of 106 x instead of 100 x. The second exception is to compare the photograph with a standard from plate 1 instead of plate II, which is the recommended standard for austenitic stainless steels. Thus, the measured grain sizes in this report should be used only to characterize and compare the materials described in this report. It should be noted, however, that minor variations in the grain size measurement technique should not significantly alter the grain size and/or its tendency to change (grain size is a function of Nb content).

Table 2 includes results obtained or obtained from tensile specimen testing. Table 3 includes experimental results from Charpy samples. The results from these two samples were averaged to simplify the graphical representation of the data. In the detection of longitudinal and transverse samples, the whole sample was averaged. Examples of this are the yield limit (0.2% set) and ultimate tensile strength data plotted in figures 3 and 4, both as a function of Nb content. As can be seen, the two curves show that: when the Nb content was increased from-0.003% to 0.210%, the strength of T201LN was increased. When the Nb content is increased to more than 0.075 percent, the yield strength and the ultimate tensile strength are at least obviously improved by 3.450 multiplied by 10⁷Pa (5 k.s.i). When the Nb content is 0.15% or more, the strength is improved by about 6.901X 10⁷Pa (10 k.s.i). In FIG. 3 there is a low Nb content material (ingot RV # 1184-A) with an abnormally high yield strength, which is not consistent with the trend shown for the remainder. It should be noted, however, that prior to testing, the material was measured to have a relatively high ferrite content (-2.5%) on the drawn stock.

Fig. 5 is the ferrite content measured on the drawn stock before the test. Only 3 materials contained significant amounts of ferrite in this study. The first 2 materials were obtained from laboratory smelted molten steel RV #1184 (ingots A and B), which are not consistent with the chemical characteristics of the commercial product. Higher ferrite content is observed due to higher Cr and Mo, lower Ni and Mn content in the furnace steel. The reason for the unexpectedly high ferrite content in the material of the C ingot from laboratory smelted molten steel RV #1185 is not clear, but may be due to fluctuations in the heat treatment process which are intended to reduce the ferrite content in the as-cast material (see FIG. 1) to that in the final finished product.

After the test, the magnetic response was measured along the axial direction of the tensile specimen to determine the presence of martensite, which is a measure of austenite stability. For further reference, these data are shown in fig. 6. This measurement is an indication of the amount of martensite in the material. However, the relationship between this measurement and the actual amount of martensite is not known and is therefore used only for comparison between these samples.

Elongation and hardness measurements from tensile testing and grain size from full phase examination of microscopic specimens cut from tensile specimens (ends not deformed from testing) are shown in figures 7, 8 and 9, respectively. As the Nb content of the material increased, the elongation decreased (fig. 7) and the measured hardness increased (fig. 8).

The data from the impact test of small size Charpy specimens, < 0.01 meter (0.394 ") thick, include the impact energy (FIG. 10), shear rate (FIG. 11) and transverse expansion of the specimens at three temperatures (-195.6 deg.C (-320 deg.F), -45.6 deg.C (-50 deg.F) and 21.1 deg.C (70 deg.F)), all as a function of Nb content. It should be noted that the circled points in FIG. 10 are taken from RV #1212 heats, the material of the A ingot, which was accidentally rolled to a lesser thickness (0.0039878 meters (0.157 "), which is less than the remaining thickness rolled to-0.004572-0.004699 meters (0.180-0.185"). Due to the fact that the work of impact depends on the cross section of the samples tested, they will have at least 18% higher work of impact if the samples (from RV #1212 heat) have the correct thickness (-0.004572-0.004699 meters (0.180-0.185 ")). Therefore, these data are not considered when examining the work of impact, shear rate and tendency to lateral expansion as a function of Nb content.

As the Nb content increases, the impact power initially increases and then decreases. Little, if any, loss of toughness was seen when tested between 21.1 ℃ (70 ° F) and-45.6 ℃ (-50 ° F). However, tests conducted at-195.6 ℃ (-320 ° F) show that the toughness of the material decreases for Nb above 0.10%. It should be noted, however, that the impact properties at this temperature still exhibit a level of toughness which is worthy of reproduction.

The addition of Nb up to 0.10% was successful in increasing the strength of the alloy without significantly degrading either of the mechanical properties tested. Data examination showed that the desired mechanical properties were achieved with the addition of about 0.075% Nb.

Due to the fact that Nb is a strong stabilizer (i.e. hinders the formation of chromium carbides at the grain boundaries), the addition of Nb to the alloy makes the limitation of the maximum carbon content, which is still acceptable from a corrosion standpoint, no longer critical. With a slight increase in carbon content, the addition of Nb ensures the improved mechanical properties (additional strength and toughness due to improved austenite stability) required by the new market. Thus a change in the T201 grade steel (Nb 0.100%, C0.060% (max)) may produce a product that is acceptable under welding conditions.

Based on the results obtained in laboratory production materials, the addition of Nb acts as a grain refiner and improves the mechanical properties of the T201LN alloy. As a result, the yield strength and ultimate tensile strength increased by at least 3.450X 10 when the Nb content increased above about 0.075%⁷Pa (5k.s.i) when^NbAt contents greater than 0.150%, the strength is improved by about 6.901X 10⁷Pa (10 k.s.i). Further, elongation decreases from about 55% to 48% when the Nb content increases from 0.003% to 0.210%, the measured hardness increases from about 89Rb to 98Rb, and the grain size decreases from ASTM grade 6.5 to ASTM grade 10. Also, above the residual amount of Nb (-0.003%), the impact power increased by increasing the Nb content to about 0.10% at the three test temperatures. Ductility was quite high at-45.6 ℃ (-50 ° F) and 21.1 ℃ (70 ° F). With Nb greater than about 0.10%, ductility decreases, but ductility at the lower test temperature of-195.6 ℃ (-320 ° F) remains acceptable.

While certain preferred embodiments are shown and described, it will be understood that: the invention is not limited thereto but rather it has to be embodied within the scope of the following claims.

TABLE 1

Furnace number	Spindle number #	Cr	Mo	Si	Ni	Mn	C	N	Cu	Al	Ti	Co	Sn	W	V	P	S	Cb
																			**	Minimum size	16.78	0.20	0.35	4.23	6.41	0.021	0.151	0.42	0.003	0.001	0.057	0.008	0.011	0.066	0.027	0.010	0.006

	Average	16.95	0.25	0.40	4.24	6.48	0.023	0.157	0.43	0.003	0.001	0.061	0.008	0.012	0.075	0.029	0.010	0.012
																			Maximum of	17.19	0.35	0.49	4.26	6.63	0.027	0.160	0.43	0.003	0.002	0.063	0.009	0.013	0.093	0.030	0.011	0.021
	RV#1184	A	17.78	0.46	0.36	4.11	6.21	0.020	0.160	0.39	0.002	0.003	0.010	0.003	0.010	0.008	0.002	0.008																			0.003
B																			17.76	0.46	0.35	4.11	6.20	0.019	0.170	0.39	0.002	0.004	0.010	0.003	0.009	0.007	0.002	0.008	0.029
		C	17.74	0.46	0.35	4.12	6.19	0 027	0.160	0.39	0.002	0.004	0.010	0.003	0.009	0.007	0.002	0.008																		0.100
RV#1185																			A	16.91	0.20	0.35	4.22	6.76	0.021	0.168	0.42	0.002	0.003	0.010	0.003	0.008	0.007	0.003	0.0083		0.003
	B	16.92	0.20	0.35	4.23	6.78	0.020	0.170	0.42	0.002	0.004	0.010	0.003	0.011	0.007	0.003	0.0081	0.046
																			C	16.91	0.20	0.35	4.24	6.75	0.021	0.168	0.42	0.002	0.002	0.010	0.003	0.011	0.007	0.002	0.0091	0.120
	RV#1212	A	16.94	0.26	0.41	4.25	6.69	0.021	0.170	0.43	0.002	0.002	0.010	0.003	0.010	0.007	0.003	0.008																			0.078
B																			16.91	0.26	0.40	4.25	6.64	0.020	0.170	0.43	0.003	0.003	0.010	0.003	0.009	0.008	0.003	0.008	0.160
		C	16.93	0.26	0.40	4.24	6.60	0.022	0.170	0.43	0.002	0.004	0.010	0.003	0.010	0.007	0.003	0.009																		0.210

^**Chemical property ranges of three-furnace T201LN molten steel obtained from 1994 melting.

TABLE 2

Sample number i.d. #	Nb (wt%)	Initial dimensional specification/width		Sample orientation	Hardness (Rb)	Initial ferrite reading FN (1) FN (2)		Final ferrite reading 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	″		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
		0.178	0.500	″		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	0.499	″		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	″		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

TABLE 2 (continuation) (1psi 6900.52557346Pa)

Sample number #	Width specification of uniform deformation zone		Elongation (%)	Grain size of first annealing	Grain size of second annealing	Strain hardening exponent n (1) n (2)		Strength (p.s.i) yield-intensive (0.2%) ultimate strength
										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	0.152	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	109600
											0.418	0.130	51		8.0	0.24	0.41	54400	109200
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	58600	112100
											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

Table 3 (0.0254 meters for 1 inch (in); 1.35582N.M for 1ft

Sample number #	Nb (wt%)	Experiment temperature (F degree)	1950 ℃ annealing for 6 minutes (TAT) impact energy (ft ═ lbs) shear% transverse expansion (in)			Re-anneal at 1950 ℃ F. for 6 minutes (TAT) impact energy (ft-lbs) shear% lateral expansion (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	0.120	-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
									1184A	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

Table 3 (continuation)

Sample number #	Nb(wt％)	Experiment temperature (F degree)	Annealing at 1950 ℃ F. for 6 minutes (TAT) impact energy (ft-lbs) shear% lateral expansion (in)			Re-anneal at 1950 ℃ F. for 6 minutes (TAT) impact energy (ft-lbs) shear% lateral expansion (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

Claims (15)

1. An austenitic stainless steel comprising, by weight%, up to 0.06% C, 6.4-7.5% Mn, up to 1.0% Si, 16-17.5% Cr, 4.0-less than 5.0% Ni, less than 1.0% Cu, 0.13-0.20% N and greater than 0.003-1.0% Nb, with the balance being Fe.

2. The austenitic stainless steel of claim 1, wherein the content of C is at most 0.03%.

3. The austenitic stainless steel of claim 1, wherein the Nb content is at least 0.06%.

4. The austenitic stainless steel of claim 1, wherein the Nb content is at least 0.10%.

5. The austenitic stainless steel of claim 1, wherein the Nb content is no greater than 0.21%.

6. The austenitic stainless steel of claim 1, wherein the Cu content is 0.35-0.60%.

7. The austenitic stainless steel of claim 1, characterized by at least 6.901 x 10 at room temperature⁸Pa (100000psi) and a tensile strength of at least 3.450X 10⁸Pa (50000 psi).

8. The austenitic stainless steel of claim 1, wherein the ASTM grain size is grade 6 or greater.

9. The austenitic stainless steel of claim 1, consisting essentially of the following components (% by weight): up to 0.03% of C, 6.4-7.5% of Mn, up to 1.0% of Si, 16-17.5% of Cr, 4.0-less than 5.0% of Ni, less than 1.0% of Cu, 0.13-0.20% of N, more than 0.003-1.0% of Nb, unavoidable impurities and the balance of iron.

10. An article comprising, by weight, up to 0.06% C, 6.4-7.5% Mn, up to 1.0% Si, 16-17.5% Cr, 4.0-less than 5.0% Ni, less than 1.0% Cu, 0.13-0.20% N, greater than 0.003-1.0% Nb.

11. The article of claim 10, wherein said austenitic stainless steel comprises at least 0.06% Nb.

12. The article of claim 10, wherein the article is selected from the group consisting of a panel, a can, and a pressure vessel.

13. The article of claim 10, wherein the austenitic stainless steel is characterized by a room temperature yield strength of 3.450 x 10⁸Pa (50000psi), tensile strength 6.901X 10⁸Pa(100000psi)。

14. A method of providing a high strength stainless steel includes preparing a molten steel containing C up to 0.06%, Mn 6.4-7.5%, Si up to 1.0%, Cr 16-17.5%, Ni 4.0-less than 5.0%, Cu less than 1.0%, N0.13-0.20%, and Nb more than 0.003-1.0% by weight.

15. The method of claim 14, wherein the molten steel contains at least 0.06% Nb.