MXPA98002342A - Stainless steel alloy of high strength, ductile to hardware and hardening by precipitac - Google Patents

Abstract

A precipitation hardenable martensitic stainless alloy is present, consisting essentially of weight percent, approximately 0.03 max. of C, 1.0 max, 0.75 max. of Yes, 0.040 max. of P, 0.020 max. of S, 10-13 of Cr, 10.5-11.6 of Ni, 1.5-1.8 of Ti, 0.25-1.5 of Mo, 0.95 max. of Cu, 0.25 max. of Al, 0.3 max. of Nb, 0.10 max of B, 0.030 max. of N, the rest is essentially iron. The presented alloy provides a unique combination of resistance to stress corrosion cracking, mechanical strength and blade strength

Description

STAINLESS STEEL ALLOY OF HIGH STRENGTH, DUCTILE TO HARDWARE AND PRECIPITATION HARDNESS FIELD OF THE INVENTION The present invention relates to precipitation-hardened martensitic stainless steel alloys and, in particular, to a martensitic stainless steel alloy to Cr-Ni-Ti-Mo and to an article made therefrom having a unique combination of resistance to stress corrosion cracking, mechanical strength and tenacity to the notch.

BACKGROUND OF THE INVENTION Many industrial applications, including the aeronautical industry, require the use of manufactured parts from high strength alloys. An approach to the production of these high strength alloys has been to develop alloys with precipitation hardening. An alloy with precipitation hardening is an alloy where a precipitate forms inside the ductile matrix of the alloy. The particles of the precipitate inhibit the dislocations within the ductile matrix, thereby increasing the strength of the alloy. One of the stainless steel alloys for P11Ó5 / 98MX known aging hardening seek to provide high strength by adding titanium and columbium and controlling chromium, nickel and copper to ensure a martensitic structure. To provide optimum toughness, this alloy is annealed at a relatively low temperature. This low annealing temperature is required to form a Laves phase rich in Fe-Ti-Cb before aging. This action avoids the excessive formation of hardening precipitate and provides a greater availability of nickel for the reversion of austenite. However, at the low annealing temperatures used for this alloy, the microstructure of the alloy does not recrystallize completely. These conditions do not promote the effective use of additions of hardening elements and produce a material whose strength and tenacity are very sensitive to processing. In other known precipitation hardenable stainless steel, the elements chrome, nickel, aluminum, carbon and molybdenum are critically balanced in the alloy. In addition, manganese, silicon, phosphorus, sulfur and nitrogen are kept at low levels for the purpose. not to demerit the desired combination of properties provided by the alloy. While hardenable stainless steels P1165 / 98MX by precipitation known hitherto have provided acceptable properties, the need has arisen for an alloy which provides better strength together with at least the same level of tenacity to the notch and corrosion resistance provided by the hardenable stainless steels. known precipitation. An alloy that has superior strength while maintaining the same level of tenacity to the notch and corrosion resistance, particularly stress corrosion cracking resistance, would be particularly useful in the aeronautical industry because fabricated structural members from these alloys they could be of lighter weight than the same parts manufactured from the alloys currently available. A reduction in the weight of said structural members is desirable since improved fuel efficiency will result. Given the above, it would be highly desirable to have an alloy that provides an improved combination of stress corrosion resistance, mechanical strength and notch toughness while being easily and reliably processed.

SUMMARY OF THE INVENTION The limitations associated with alloys of ?:: O5 / 98M: -: martensitic stainless steel hardenable by known precipitation are largely resolved by the alloy according to the present invention. The alloy according to the present invention is a martensitic stainless steel alloy to Cr-Ni-Ti-Mo for precipitation hardening which provides a unique combination of stress corrosion cracking resistance, mechanical resistance and tenacity to the notch. The ranges of extended, intermediate and preferred composition of the martensitic stainless steel for precipitation hardening of the present invention are as follows, in percent by weight: Extended Preferred Intermediate C 0.03 ax. 0.02 max 0.015 max Mn 1.0 max 0.25 max 0.10 max Yes 0.75 max. 0.25 max 0.10 max P 0.040 max. 0.015 max 0.010 max S 0.020 max. 0.010 max 0.005 max Cr 10 - 13 10.5 - 12-5 11-0 - 12.0 Ni 10.5 - 11.6 10.75 - 11.25 10.85 - 11.25 Ti 1.5 - 1.8 1.5 - 1.7 1.5 - 1.7 Mo 0.25 - 1.5 0.75 - 1.25 0.9 - 1.1 Cu 0.95 max. 0.50 max 0.25 max At 0.25 max 0.050 max 0.025 max Nb 0.3 max 0.050 max 0.025 max B 0.010 max. 0.001 - 0.005 0.0015 - 0.0035 N 0.030 max. 0.015 max 0.010 max The rest of the alloy is essentially iron, with the exception of the usual impurities found in the commercial grades of these steels and smaller amounts of .Í5 / 98M additional elements that can vary from a few thousandths of a percent to larger quantities that do not objectively detract from the desired combination of properties provided by this alloy. The preceding tabulation is provided as a convenient summary and is not intended to restrict to it the lower and upper values of the ranges of the individual elements of the alloy of this invention that are used in combination with each other, nor to restrict the ranges of the elements that only some are used in combination with others. Thus, one or more of the ranges of the elements of the extended composition can be used with one or more of the other ranges for the rest of the elements in the preferred composition. In addition, a minimum or maximum for an element of a preferred embodiment may be used with the maximum or minimum for that element of another preferred embodiment. Throughout this application, unless otherwise indicated, the symbol of percent (%) means percent by weight.

DETAILED DESCRIPTION In the alloy according to the present invention, the unique combination of. mechanical strength, tenacity to the notch and resistance to cracking by corrosion under tension is achieved by balancing the = 1165/9? X elements chrome, nickel, titanium and molybdenum. At least about 10%, preferably at least about 10.5%, and more preferably at least about 11.0% of chromium is present in the alloy to provide a strength equal to that of conventional stainless steel under oxidizing conditions. At least about 10.5%, preferably at least about 10.75% and more preferably at least about 10.85% nickel is present in the alloy, because it benefits the tenacity to the notch of the alloy. At least about 1.5% of titanium is present in the alloy to benefit the mechanical strength of the alloy by means of the precipitation of the nickel-titanium-rich phase during aging. At least about 0.25%, preferably at least about 0.75%, and more preferably at least about 0.9% molybdenum is also present in the alloy, because it contributes to the tenacity to the notch of the alloy. Molybdenum also benefits the corrosion resistance of the alloy in a reducing medium and environments that promote corrosion attack by pitting and stress corrosion cracking. When chromium, nickel, titanium and / or molybdenum are not properly balanced, the P1I65 / 98MX ability of the alloy to completely transform into a martensitic structure using conventional processing techniques. In addition, the ability of the alloy to remain completely martensitic in substantial form when it receives a solution treatment and hardening by aging deteriorates. Under these conditions, the mechanical strength provided by the alloy is significantly reduced. Therefore, the chromium, nickel, titanium and molybdenum present in this alloy are restricted. More particularly, chromium is limited to no more than about 13%, even better, at no more than about 12.5% and, more preferably at no more than about 12.0% and, nickel is limited to no more than about 11.6% and, most preferably no more than about 11.25%. Titanium is restricted to no more than about 1.8% and, more preferably to no more than about 1.7% and, molybdenum is restricted to no more than about 1.5%, even better, to no more than about 1.25% and, with greater preference to no more than about 1.1%. Additional elements such as boron, aluminum, niobium, manganese and silicon may be present in controlled amounts to benefit other desirable properties provided by this invention. Plus ?: i55 / 98MX specifically, up to about 0.010% boron, even better, up to about 0.005%, and more preferably up to about 0.0035% boron can be present in the alloy to benefit the hot workability of the alloy. In order to provide the desired effect, at least about 0.001% and, more preferably at least about 0.0015% boron is present in the alloy. Aluminum and / or niobium may be present in the alloy to benefit the apparent limit of elasticity and tensile strength. More particularly, up to about 0.25%, better still, up to about 0.10%, still better, up to about 0.050% and, most preferably up to about 0.025% of aluminum may be present in the alloy. Also, up to about 0.3%, better still up to about 0.10%, still better up to about 0.050% and, most preferably up to about 0.025% of niobium may be present in the alloy. Although an apparent limit of elasticity and superior tensile strength is obtained when aluminum and / or niobium are present in this alloy, the increase in these resistances develops at the expense of the tenacity to the notch. Therefore, when you want a tenacity to the P11Ó5 / 98MX optimum notch, aluminum and niobium are restricted to the usual residual levels. Up to about 1.0%, better yet up to about 0.5%, still better up to about 0.25%, and more preferably up to about 0.10% manganese and / or up to about 0.75%, still better up to about 0.5%, even better up to about 0.25% and, more preferably up to about 0.10% of silicon may be present in the alloy as residues from scrap sources or from deoxidizing additions. These additions are beneficial when the alloy will not be vacuum melted. Manganese and / or silicon more preferably remain at low levels due to their detrimental effects on toughness, corrosion resistance and the balance of the austenite-martensite phases in the matrix material. The rest of the alloy is essentially iron in addition to the usual impurities found in the commercial grades of alloys that are intended for a similar service or use. The levels of these elements are controlled so that they do not adversely affect the desired properties. In particular, much carbon and / or nitrogen deteriorate the corrosion resistance and detrimentally affect the toughness provided by this alloy.

Pllóó / 96M In accordance with the foregoing, the alloy is not present more than about 0.03% better still, no more than about 0.02%, and more preferably no more than about 0.015% carbon. Also, more than about 0.030%, even better, no more than about 0.015% and, more preferably, no more than about 0.010% nitrogen is present in the alloy. When carbon and / or nitrogen are present in larger amounts, the carbon and / or nitrogen are bonded or bound to the titanium to form nonmetallic inclusions rich in titanium. This reaction inhibits the formation of the nickel-titanium-rich phase which is a primary factor in the high strength provided by this alloy. Phosphorus remains at a low level due to its detrimental effect on toughness and corrosion resistance. In accordance with the above, no more is present in the alloy. of about 0.040%, better yet, no more than about 0.015% and, most preferably no more than about 0.010% phosphorus. More than about 0.020%, better still, no more than about 0.010% and, more preferably, no more than about 0.005% sulfur is present in the alloy. Larger amounts of sulfur promote the formation of inclusions not ?: Metallic 5 / 98MX rich in titanium which, just like carbon and nitrogen, inhibit the desired effect of increasing the strength of titanium. Also, larger amounts of sulfur detrimentally affect the hot workability and corrosion resistance of this alloy and deteriorate its toughness, particularly in the transverse direction. Too much copper adversely affects the tenacity to the notch, the ductility and the strength of this alloy. Therefore, the alloy contains no more than about 0.095%, better still, no more than about 0.75%, even better, no more than about 0.50%, and most preferably no more than about 0.25% copper. No special techniques are required for melting, casting or working the alloy of the present invention. Vacuum induction melting or vacuum induction melting followed by vacuum arc remelting are the preferred methods for melting and refining, but other practices may be used. In addition, this alloy can be manufactured using powder metallurgy techniques, if desired. In addition, although the alloy of the present invention can be worked hot or cold, cold working improves the mechanical strength of the alloy.

P1165 / 98MX The precipitation hardening alloy of the present invention receives annealing in solution to develop the desired combination of properties. The annealing temperature in solution must be sufficiently high to dissolve essentially all the undesirable precipitates in the matrix material of the alloy. However, if the annealing temperature in solution is very high, the fracture toughness of the alloy will deteriorate due to the excessive promotion of grain growth. Normally, the alloy of the present invention receives annealing in solution at 927 ° C-1038 ° C (1700 ° F-1900 ° F) for 1 hour and then annealed. When desired, this alloy can also be subjected to a deep cooling treatment after it has been tempered, to further develop the high strength of the alloy. The deep cooling treatment cools the alloy to a temperature sufficiently below the martensite finishing temperature to ensure completion of the martensite transformation. Typically, a deep cooling treatment consists of cooling the alloy to below about -73 ° C (-100 ° F) for about 1 hour. However, the need for a deep cooling treatment will be affected, at least partially, by the finish temperature of p?: 5 / 9e > to; alloy martensite. If the martensite finishing temperature is sufficiently high, the transformation to a martensitic structure will proceed without the need for a deep cooling treatment. In addition, the need for a deep cooling treatment may also depend on the size of the part that will be manufactured. As the size of the piece increases, the segregation in the alloy becomes more significant and the use of a deep cooling treatment becomes more beneficial. In addition, the period of time in which the piece cools may need to be increased for large pieces, in order to complete or finish the transformation into martensite. The alloy of the present invention is hardened by aging in accordance with the techniques used for stainless steel alloys of known precipitation hardening. As those skilled in the art know. For example, the alloys are aged at a temperature between about 482 ° C (900 ° F) and about 621 ° C (1150 ° F) for about 4 hours. The specific aging conditions used are selected considering that: (1) the tensile strength of the alloy decreases as the aging temperature increases; and, (2) the time required P; io5 / 9oMX to age-harden the alloy to a desired resistance level increases as the aging temperature decreases. The alloy of the present invention can be shaped into a variety of product forms for a wide variety of uses and lends itself to the formation of billets, rods, rods, wires, strips, sheets or sheets using conventional practices. The alloy of the present invention is useful in a wide range of practical applications that require an alloy to have a good combination of stress corrosion cracking resistance, mechanical strength and notch tenacity. In particular, the alloy of the present invention can be used to produce structural members and fasteners for aeronautics and the alloy is also well suited for use in medical or dental instruments. ?: a35 / 96MX XW86 /? 9tTd SI EXAMPLES In order to demonstrate the unique combination of properties provided by the present invention, Examples 1-18 of the alloy of the present invention having the weight percent compositions shown in Table 1 were prepared. In comparison, comparative runs AD with compositions outside the range of the present invention were also prepared. Their compositions in percent by weight are also included in Table 1. The alloys A and B are representative of one of the alloys of stainless steel for hardening by known precipitation and the alloys C and D are representative of another alloy of stainless steel for hardening by known precipitation. Example 1 was prepared as a 7.7 kg (17 lb.) lab run which was vacuum melted and cast as a 6.98 cm (2.75 inch) square section conical ingot. The ingot was heated to 1038 ° C (1900 ° F) and forged in press to a square bar of 3.49 cm (1.375 inches). The bar received a forging finish to a square bar of 2.86 cm (1.125 inches) and cooled in air to room temperature. The forged bar was hot rolled at 1010 ° C (1850 ° F) to a round bar of 1.59 P1165 / 98MX cm (0.625 inches) and, then cooled to air to room temperature. Examples 2-4 and 12-18 and Comparative Runs A and C were prepared as 11.3 kg (25 lb.) lab runs, which were melted by vacuum induction under a partial pressure of gaseous argon and cast as conical ingots of square section of 8.9 cm (3.5 inches). The ingots were forged in press from an initial temperature of 1010 ° C (1850 ° F) to square bars of 4.76 cm (1875 inches) which were then cooled in air to room temperature. The square bars were reheated, forged in press from the temperature of 1010 ° C (1850 ° F) to square bars of 3.18 cm (1.25 inches), reheated, hot rolled from the temperature of 1010 ° C (1850 ° C) F) until rounded bars of 1.59 cm (0.625 inches) and, then cooled to air to room temperature. Examples 5, 6 and 8-10 were prepared as laboratory runs of 16.8 kg (37 lb.) which were melted by vacuum induction in a partial pressure of argon gas and cast as conical ingots of square section of 10.2 cm. (4 inches). The ingots were forged in press from an initial temperature of 1010 ° C (1850 ° F) to square bars of 5.1 cm (2 inches) and then ? :: Ó5 / 98M.-: cooled to air. A section of each 5.1 cm (2 inch) square forged bar was cut and forged from a temperature of 1010 ° C (1850 ° F) to a square bar of 3.33 cm (1.31 inches). The forged bars were hot rolled at 1010 ° C (1850 ° F) to round bars of 1.59 cm (0.625 inches) and cooled in air to room temperature. Examples 7 and 11 and the comparative runs B and D were prepared as 56.7 kg (125 lb.) lab runs which were melted by vacuum induction into a partial pressure of argon gas and cast as 4.5-inch square-section conical ingots. The ingots were forged in press from an initial temperature of 1010 ° C (1850 ° F) to square bars of 5.1 cm (2 inches) and then cooled in air to room temperature. The bars were reheated and then forged from a temperature of 1010 ° C (1850 ° F) to square bars of 3.33 cm (1.31 inches). The forged bars were hot rolled at 1010 ° C (1850 ° F) to round bars of 1.59 cm (0.625 inches) and, they were cooled in air to room temperature. The bars of each example and comparative run were turned into groups in annealed / cold-treated state to produce smooth specimens for tension, corrosion P11Ó5 / 98MX under tension and tension to the notch having the dimensions indicated in Table 2. Each specimen was cylindrical and the center of each specimen had a diameter reduction with a minimum radius connecting the central section with each end section of the specimen. specimen. The specimens for corrosion under tension were polished to a diameter of nominal caliber with a surface finish to grain 400.

TABLE 2 Central section Type of length Marretro length Emitter Radius rt Rough Dipore of specimen inch / an. inches / art. inches / ar inches / an. inches / cm. caliber inches (an) Smooth 3.5 / 8.9 0.5 / 1.27 1.0 / 2.54 0.25 / 0.64 0.1875 / 0.476 Corrosion under tension 5.5 / 14.0 0.436 / 1.11 1.0 / 2.54 0.25 / 0.64 0.25 / 0.64 0.225 / 0.57 Tension to the notch2 3.75 / 9.5 0.50 / 1.27 1.75 / 4.4 0.375 / 0.95 0.1875 / 0.4762'2 A notch was provided around the center of each specimen for tension to the notch. The diameter of the specimen was 0.64 cm (0.252 inches) at the base of the notch; the root radius of the notch was 0.0025 cm (0.0010 inches) to produce a merger concentration factor (kc) of 10. The test specimens for each Example / Run were traced thermally in accordance with Table 3 below. The conditions for the heat treatment used were selected for Plló5 / 9tJMX provide peak or maximum mechanical resistance.

TABLE 3 Treatment of Solution Treatment of Aging Examples 1-18 1800ßF (982 ßC) / l hour / WQ.1-2 900 ° F (428 ° C) / 4 hours / AC3 Run A and B 1700ßF (927 ° C) / l hour / WQ.4 950 ° F (510 ° C) / 4 hours / AC C runs C and D 1500 ,, F (816''C) / 1 hour / WQ 900e F (482 ° C) / 4 hours / AC Q = tempered in water Treated cold at -73 ° C (-100 ° F) for 1 hour and then heated in air AC = Chilled in air. 4 Treated cold at 0.6 ° C (33 ° F) for 1 hour and then warmed to air. The mechanical properties of Examples 1-18 were compared with the properties of the comparative runs A-D. The measured properties include the apparent yield strength with 0.2% residual strain (0.2% yield strenght or 0.2% YS), the tensile strength (ultimate tensile strenght or UTS), the elongation percentage in four diameters (% elongation or% elongation). The percentage of reduction of area (% Red.) And, the resistance to tension in the notch (notch tensile strength or NTS). All properties were measured along the longitudinal direction. The results of the measurements are given in Table 4.

FUÓ5 / 98MX o »TABLE 4 * No. of% of g ejepplo / .2% YS UTS Red. of the NTS run Cr Ni Mo Ti (Ksi / Mpa) (ksi / MPa)% alarg. Area (ksi / MPa) NTS / UTS) 1 11.54 11.13 1.00 1.61 253.7 / 1749 264.3 / 1822 12.0 * 50.0 309.0 / 2130 * 1.17 2 11.57 11.02 1.00 1.52 244.7 / 1687 256.2 / 1766 14.7 53.5 341.2 / 2352 * 1.33 3 11.61 11.03 1.00 1.68 246.8 / 1702 260.1 / 1793 12.6 49.4 324.9 / 2240 * 1.25 4 11.60 11.05 1.43 1-52 244.2 / 1684 256.7 / 1770 14 , 4 58.8 352.5 / 2430 * 1.37 11.58 10.46 1.00 1.58 248.5 / 1713 * 266.0 / 1834 * .11.5 * 49.6 * 288.3 / 1988 * 1.08 6 11.54 10.77 1.00 1.55 251.5 / 1734 * 268.3 / 1850 * 11.7 * 51.7 * 324.9 / 2240 * 1.21 7 11.62 11.05 0.99 1.58 240.5 / 1658 * 261.6 / 1804 * 11.5 * 51.1 * 344.5 / 2375 * 1.32 8 11.63 10.92 0.75 1.58 250.4 / 1726 * 267.9 / 1847 * 12.4 * 54.5 * 361.4 / 2492 * 1.35 9 11.49 10.84 0.50 1.58 251.4 / 1733 * 267.9 / 1847 * 11.3 * 50.6 339.3 / 2339 * 1.27 10 11.60 10.84 0.28 1.50 248.4 / 1713 * 264.5 / 1824 * 12.1 * 57.0 * 347.3 / 2395 * 1.31 11 11.62 10.99 1.49 1.67 227.6 / 1569 * 255.6 / 1762 * 11.6 * 47.9 * 332.8 / 2295 * 1.30 12 11.58 11.08 0.98 1.52 250.7 / 1728 262.4 / 1809 12.2 52.4 312.2 / 2153 * 1.19 13 11.56 10.98 1.00 1.70 255.8 / 1764 270.2 / 1863 13.2 50.2 281.6 / 1942 * 1.04 ro M 14 11.55 11.02 1.02 1.54 248.7 / 1714 262.9 / 1813 13.9 50.7 262.2 / 1808 * 1.00 15 11.62 11.03 1.03 1.54 247.8 / 1708 262.4 / 1809 12.4 48.3 289.3 / 1995 * 1.10 16 11.68 11.09 1.47 1.52 238.3 / 1643 251.2 / 1732 15.9 56.0 318.6 / 2197 * 1.27 17 11.56 10.98 1.00 1.49 239.2 / 1649 254.6 / 1755 12.7 39.6 289.0 / 1993 * 1.14 18 11.60 11.05 1.01 1.51 235.3 / 1622 250.0 / 1724 11.8 42.4 311.9 / 2150 * 1.25 A 12.63 8.17 2.13 0.01 210.1 / 1449 224.4 / 1547 14.4 59.4 346.9 / 2392 * 1.54 B 12.61 8.20 2.14 0.016 209.2 / 1442 230.1 / 1586 15.9 65.4 349.8 / 2412 1.52 C 11.66 8.61 0.11 1.10 250.5 / 1727 254.3 / 1753 12.2 52.0 319.6 / 2204 * 1.26 D 11.58 8.29 0.09 1.18 251.0 / 1731 259.3 / 1788 10.7 46.7 329.7 / 2273 1.27 * The reported value is an average of two measurements The data in Table 4 show that Examples 1-18 of the present invention provide superior apparent yield strength and tensile strength compared to runs A and B, while providing acceptable levels of notch toughness, as indicates by the NTS / UTS ratio and, the ductility. Thus, it is noted that Examples 1-18 provide a superior combination of strength and ductility with respect to runs A and B. In addition, the data in Table 4 also show that Examples 1-18 of the present invention provide a tensile strength that is at least as good as significantly better than runs C and D, while providing an acceptable yield strength and acceptable ductility, as well as an acceptable level of tenacity to the notch as indicated by the NTS / UTS ratio. The stress corrosion cracking properties of Examples 7-11 in a chloride-containing medium were compared with those of comparative runs B and D by a low speed strain test. For the stress corrosion cracking test, the specimens of Examples 7-11 received a solution treatment in a manner similar to tension specimens and then over-aged.

P1165 / 98MX at a selected temperature to provide a high level of resistance. The specimens from comparative runs B and D were subjected to a solution treatment in a manner similar to their respective tension specimens but, they were over-aged at a selected temperature to provide the level of resistance to stress corrosion cracking, usually specified in the aeronautical industry. More specifically, Examples 7-11 were cured by aging at 538 ° C (1000 ° F) for 4 hours and then cooled in air and comparative runs B and D hardened by aging at 566 ° C (1050 ° F) for 4 hours and then cooled in air. Resistance to stress corrosion cracking was tested or tested by subjecting sets of the specimens of each example / run to a tensile stress by means of a constant extension rate of 1 x 10 -5 cm / sec (4 x 10- 6 inches / sec). The tests were conducted in each of four different media: (i) boiling solution of acidified 10.0% NaCl at a pH of 1.5 with H3PO4; (2) a boiling solution of 3.5% NaCl at its natural pH (4.9-5.9); (3) a boiling solution of 3.5% acidified NaCl at pH 1.5 with H3PO4; and (4) air at 25 ° C (77 ° F) tests conducted in air were used as a reference against which P1165 / 98MX could compare the results obtained in the chloride-containing medium. The results of the stress corrosion tests are given in Table 5, including the time for the fracture of the test specimen (total test time) in hours, the percent elongation (% elongation), and the reduction in the cross-sectional area (% Red. Of area). TABLE 5 Mo. of Total Sample Time / of Test%% Red. Run Environment < hrs > Alarg. of area 7 Boiling 10.0% NaCl at a pH of 1.5 0.5 4.9 21.5 9.4 5.4 25.0 Boiling 3.5% NaCl at a pH of 1.5 13.5 11.3 53.7 13.6 11.1 58.6 12.6 11.5 53.9 Boiling 3.5% NaCl at a pH of 5.8 14.4 12.0 62.0 13.8 11.7 60.2 Air at 25 ° C (77 ° F) 14.4 12.6 60.4 12.6 10.6 58.6 14.2 12.8 56.1 8 Boiling 10.0% NaCl at a pH of 1.5 8.2 5.4 23.8 8.3 5.3 21.4 Boiling 3-5% NaCl at a pH of 1.5 13.0 11.0 54.4 13.3 11.0 53.4 Boiling 3.5% NaCl at a pH of 5.9 13.9 13.8 64.8 14.1 13.8 64.1 14.0 13.4 62.4 Air 25ßC (77 °F) 14.6 14.3 63.7 14.0 13.6 63.2 9 Boiling 10.0% NaCl at a pH of 1.5 10.0 6.6 20.6 10.3 6.2 20.7 Boiling 3.5% NaCl at a pH of 1.5 12.6 10.6 50.1 12.8 12.0 49.5 Boiling 3.5% NaCl at a pH of 4.9 13.6 12.2 55.8 13.6 12.0 54.4 Air 25 ° C (77 ° F) 13.8 12.6 59. or 14.0 12.8 58.5 10.0% NaCl boiling at a pH of 1.5 9.6 7.7 27.9 10.4 7.7 17.9 F :: Ó5 / 98M > : Boiling 3.5% NaCl at a pH of 1.5 13.7 11.8 58. 1 13.8 11.5 54.0 Boiling 3.5% NaCl at a pH of 5.9 13.5 13.3 61.8 14.3 14.6 61.7 14.0 11.9 50.0 Air 25 ° C (77 ° F) 14.4 13.1 63.8 14.4 12.7 63.9 11 Boiling 10.0% NaCl at a pH of 1.5 9.5 6.5 20.8 p 9.5 5. 0 00.3 11.3 7 .2 22.9 Boiling 3.5% NaCl at a pH of 1.5 13.5 10. 8 58.6 13.9 11. 0 56.5 13.0 11.6 53.2 Boiling 3.5% NaCl at a pH of 5.8 14.6 12.3 62.8 14. 1 12.7 61.6 Air 25 ° C (77 ° F) 14.4 12.7 61.5 •• or 14.4 11.5 58.5 i, ti) 13.6 11.3 53.8 Boiling 10.0% NaCl at a pH of 1.5 14.9 14.5 51.7 15.2 16.6 65.2 13.7 12.9 59.8 3.5% NaCl boiling at a pH of 1.5 14.2 13. 3 69. 9 13.5 14.0 69.9 13.8 14.5 68.4 Boiling 3"5% NaCl at a pH of 5.8 13.4 13.9 66. 1 13. 6 13.3 67.6 Air 25 ° C (77 ° F) 14.1 15.1 69.9 ?? (1) 15.1 15.7 69.7 (1) 15.4 15.4 69.3 Boiling 10.0% NaCl at a pH of 1.5 7. 4 3. 7 6. 9 9. 6 8.3 15.6 10.2 10.0 19.2 Boiling 3.5% NaCl at a pH of 1.5 13.4 11.3 49.6 13.2 10.1 46. 1 12.8 10.7 44.5 Boiling 3.5% NaCl at a pH of 5.8 13.4 11.5 51.3 13.4 11.9 52.0 Air 25 ° C (77 ° F) 14. 1 15.2 56.0 15. 1 14.4 54.4 15.8 15.4 59. 6 ^ 1) These measurements represent the reference values only for test conditions of boiling 10.0% NaCl. The resistance to cracking by corrosion under relative tension of the alloys tested can P1165 / 98MX better understood by referring to a proportion of the parameter measured in the corrosive medium with the parameter measured in the reference medium. Table 6 summarizes the data in Table 5 by presenting the data in a proportional format for ease of comparison. The values in the column named "TC / TR", are the proportions of the time for the average fracture under the corrosive condition, with the time for the average invoice under the reference condition. The values in the column labeled "EC / ER" are the proportions of the average elongation% under the corrosive condition indicated at the% elongation average under the reference condition. Likewise, the values in the column labeled "RC / RR" are the proportions of the% reduction of the average area under the corrosive condition indicated at the% reduction of the average area under the reference condition.

TABLE 6 Example No. / run TC / TR (1) EC / ER (2) RC / RR (3) (10.0% NaCl boiling at pH 1.5) 7. 67 44 41 8. 58 38 36 9. 73 fifty . 35 10. 69 57 36 11 175 155. 39 B. 96 94 85 D 159 149. 24 (3.5% NaCl boiling at pH 1.5) F1165 / 98MX 7 92 .90 .92 8 92 .79 .85 9 91 .89 .84 10 95 .90 .88 11 94 .88 .91 B 98 .92 .99 D 93 .70 .83 (3.5% NaCl in boiling at pH 4.9-5.9) 7 .98 .94 1.0 8 .98 .98 1.0 9 .98 .95 .93 10 .97 .1.0 .92 11 1.0 .98 1.0 B .96 .90 .96 D .95 177 .92 () tc / TR = Time for average fracture under corrosive conditions divided by time for average fracture under reference conditions. * 2) 'EC / ER = Average elongation under corrosive conditions divided by average elongation under reference conditions. (3 * '? RC / RR = Reduction of the average area to corrosive conditions divided by reduction of the average area under reference conditions.) The mechanical properties of Examples 7-11 and runs B and D were also determined and are presented in Table 7, including the apparent yield strength with 0.2% residual strain (0.2% YS) and the tensile rupture strength (UTS) in ksi (Mpa), the percent elongation in four diameters (% alarg. ), the reduction of the area (% Red. in area), and the tensile strength to the notch (NTS) in ksi (MPa).

P1165 / 98MX TABLE 7 No. of Exercise / Condition 0.2% YS UTS%% Network. NTS run or State (ksi / MPa) (ksi / KPa) alarg. in area (ksi / MPa) 7 H1000 216.8 / 1495 230.5 / 1589 15, .0 62,, 5 344, .6 / 2376 8 H1000 223.0 / 1538 233.6 / 1611 14, .5 64, .0 353, .0 / 2434 9 H1000 223.4 / 1540 234.8 / 1619 14. .8 64., 3 349. .6 / 2410 H1000 219.3 / 1512 230.0 / 1586 14. .4 65. .0 348, .6 / 2404 11 H1000 210.5 / 1451 230.9 / 1592 15, .0 63., 0 344, .2 / 2373 B H1050 184.1 / 1269 190.8 / 1316 17.9 72.3 303.4 / 2092 D H1050 182.9 / 1261 196.9 / 1358 17.6 62.1 296.3 / 2043 When taken together, the data presented in Tables 6 and 7 demonstrate the unique combination of mechanical strength and resistance to stress corrosion cracking provided by the according to the present invention, as represented by Examples 7-11. More particularly, the data in Tables 6 and 7 show that Examples 7-11 have the ability to provide significantly greater strength than comparative runs B and D, while providing a level of resistance to low corrosion cracking. tension that is comparable with those alloys. Additional specimens of Examples 7 and 11 were cured by aging at 538 ° C (1050 ° F) for 4 hours and then cooled in air. These specimens provided resistance to tensile rupture at room temperature of 214.3 ksi and 213.1 ksi, respectively, which are still significantly better than the resistance provided by runs B and D when they were aged P1165 / 98MX similarly. Although not tested, it would be expected that the resistance to stress corrosion cracking of Examples 7 and 11 would be at least the same or better when they are aged at higher temperature. In addition, it should be noted that boiling 10.0% NaCl conditions are more severe than the standards recognized by the aviation industry. The terms and expressions that have been used herein are used as terms of description and not limitation. There is no intent in the use of these terms and expressions to exclude any equivalents of the described features or any portion thereof. However, it is recognized that various modifications are possible within the scope of the claimed invention. = 1165 / 98MX

Claims (18)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS I 1 is claimed as property. A precipitation hardenable martensitic stainless steel alloy having a unique combination of strength to stress corrosion cracking, mechanical strength and tenacity to the notch which is approximately, in percent by weight, essentially C 0.03 max. Mn 1.0 max Yes 0.75 max. P 0.040 max. s 0.020 max. Cr 10 - 13 Ni 10.5 - 11.6 Ti 1.5 - 1.8 Mo 0.25 - 1.5 Cu 0.95 max. At 0.25 max Nb 0.3 max B 0.010 max. N 0.030 max. the rest is essentially iron. The alloy according to claim 1, which contains no more than about 0.75 weight percent copper. 3. The alloy according to claim 1, which contains no more than about 0.10 weight percent ? ll5 / 98M > : of aluminum. 4. The alloy according to claim 1, which contains no more than about 0.10 weight percent niobium. The alloy according to claim 1, which contains no more than about 11.25 weight percent nickel. The alloy according to claim 1, which contains at least about 10.75 weight percent nickel. The alloy according to claim 1, which contains at least about 10.5 weight percent chromium. The alloy according to claim 1, which contains no more than about 12.5 weight percent chromium. The alloy according to claim 1, which contains no more than about 1.7 weight percent titanium. The alloy according to claim 1, which contains no more than about 1.25 weight percent molybdenum. The alloy according to claim 1, which contains at least about 0.75 weight percent molybdenum. F :: Ó5 / 98MX 12. A precipitation-hardenable martensitic stainless steel alloy having a good combination of stress corrosion cracking resistance, mechanical strength and notch toughness consisting essentially of, in percent by weight, about C 0.02 max. Mn 0.25 max Yes 0.25 max. P 0.015 max. S 0.010 max. Cr 10.5 - 12.5 Ni 10.75 - 11.25 Ti 1.5 - 1.7 Mo 0.75 - 1.25 CU 0.50 max. At 0.050 max. Nb 0.050 max. B 0.001 - 0.005 N 0.015 max. the rest is essentially iron. The alloy according to claim 12, which contains no more than about 12.0 weight percent chromium. The alloy according to claim 12, which contains at least about 11.0 weight percent chromium. 15. The alloy according to claim 12, which contains at least about 10.85 percent by weight of nickel. 16. The alloy according to claim 12, which P1165 / 99MX does not contain more than about 1.1 weight percent molybdenum. The alloy according to claim 12, which contains at least about 0.9 weight percent molybdenum. 18. A precipitation-hardenable martensitic stainless steel alloy having a good combination of stress corrosion cracking resistance, mechanical strength and notch toughness consisting essentially of weight percent, of about C 0.015 max. Mn 0.10 max Yes 0.10 max. P 0.010 max. S 0.005 max. Cr 11-0 - 12.0 Ni 10.85 - 11.25 Ti 1.5 - 1.7 Mo 0.9 - 1.1 Cu 0.25 max. At 0.025 max. Nb 0.025 max. B 0.0015 - 0.0035 N 0.010 max. the rest is essentially iron. PU65 / 98MX