US2921849A - High strength alloy steels - Google Patents

Description

United States Patent" HIGH STRENGTH ALLOY STEEIS Clyde A. Furgason, Milwaukee, Wis., assignor to Ladish Co., Cudahy, Wis., a corporation of Wisconsin No Drawing. Application June 8, 1959 Serial No. 818,510

2 Claims. (Cl. 75-128) This invention relates to improvements in high strength alloy steels and more particularly to a steel suitable for .use where ultra high strength is desirable for weight saving, as well as where high strength must be maintained for prolonged periods of elevated temperatures, and is an improvement upon the alloy of my copending application Serial No. 800,663, filed March 20, 1959, in that with the present invention the stress rupture and elevated temperature properties are materially increased.

Heretofore low alloy steels, due to temper brittleness, have never been suitable for ultra-high strength applications, and in order to get a low alloy material in strength levels above 180,000-200,000 p.s.i. tensile it has heretofore been necessary to temper in a temper-brittle range where ductility was detrimentally affected.

A general object of theinvention is to provide an improved alloy steel which has only a nominal total alloy content whereby it uses only a minimum of strategic materials, making it economically desirable.

A further object of the invention is to provide an alloy steel asabove described which is capable of being heat treated to ultra high strength levels while maintaining adequate ductility, particularly transverse ductility.

A further object of the invention is to provide an alloy steel which is suitable for use where superior toughness, wear resistance, elevated temperature strength, and high impact load resistance are necessary, making it particularly suitable for elevated temperature structural applications.

A further object of the invention is to provide an alloy steel which exhibits superior properties at room temperature when heat treated to a predetermined high tensile strength range, the alloy retaining suflicient toughness so that it can be used for missile and aircraft structural applications and having excellent elevated temperature properties when heat treated to a predetermined tensile strength range.

A further object of the invention is to provide an alloy steel which maintains a high yield to ultimate ratio at all strength levels up to 280,000 p.s.i. ultimate.

Other objects are to provide an alloy steel which exhibits less distortion in quenching, and which is weldable in heavy sections while employing techniques and con- .rol normally used in welding medium carbon low alloy i naterials with high hardenability. 7 QMA further object of the invention is to provide im- "'jI'OVCmCHtS in the processing of an alloy steel of the class described.

In carrying out the invention it has been discovered thata relatively high carbon range can be used in the formula without causing brittleness while the product maintains ductility and good weldability.

2,921,849 Patented Jan. 19, 1060 The alloy of this invention has the following contents in percent:

Remainder iron with incidental impurities.

It is important to maintain the phosphorous and sulphur content relatively low.. The nickel content is always less than chromium content and is always less than the molybdenum content. In my copending application Serial No. 800,663, a small amount of vanadium has been used to control the grain size, this amount, however, being kept so low as not to affect the essential properties'of the alloy. In the invention of the present application it hasbeen found that the use of a substantially larger amount of vanadium as specified has a surprising efiect on the essential properties and appreciably increases the elevated temperature and stress rupture properties. I e

A desirable formula for many purposes is:

, approximate. Remainder iron with incidental impurities.

3 :The above formula may be modified by the addition of other elements and the present invention is not to be construed so as to preclude the use of small amounts of such additional elements as uranium 238, boron, or rare earth elements in the basic composition.

' It is apparent from the above total that the alloy content is very low'so that only a minimum of strategic materials need be employed to obtain properties heretofore obtained only by a much higher alloy content.

In manufacturing the improved alloy, alloying agents are added at the steel mill in accordance with the above formula, except that when there is tobe a vacuum arc consumable electrode remelt'the'amount of manganese is chemically adjusted at a higher level, for example, between -120 to allow for losses. While an air melt process produces a satisfactory alloy, transverse ductility and .other properties can be substantially improved by use of a vacuum arc consumable electrode remelt furnace process. When this process is used the alloy after being through an air melt process and in ingot formis 1 eliminated, so that the number and size of the impurities from the airmelt are greatly reduced. Those impurities which remain are smaller and better distributed. As a' result, the alloy is much cleaner and has improved transverse ductility and other properties.

The following tables indicate the improved properties of the alloy steel of the present invention:

Anaverage of the room temperature mechanical prep- 7 erties of the present alloy steel after normalizing at 1650 F., and oilquenching from 1550-.F., and tempering as shown are summarized in Table I. The maximum [ultimate and yield strength with adequate ductili'ty as measured by percent. elongation and. reduction ,of area is achievedi by vtempering -between 00. .F. and 700 F.

This temperi produces. an. ultimat.e. ..tens.ile strength of 255,000 tol- 28'5,000..p.s.i.,. a. yield. strength tofu 235,000 to 249,000 p.s.i., elongation .of..7.0. to. and anmlzod impact of.f20.0;'ft. lbs... The present alloy steelshows 'n'o blue brittle. range. when tempered fr.om 30 .F. to -1200. F.- and. tested. at room temperature. Ultimate strengths of over 300,000. p.s.i.. have. been .reaehed at some of the lower temperingtemperatures.

TABLE, I

M eehqnical properties at. room temperature,

r Percent Percent Rockwell Izod Temper 0.8., Y.S Elong.- Bed, of 0" Impact, Temp., F; p.s.i. p.s.i in two 'Area' Hardness it. s

inches 8.5 19.0 561 V 9.0 8. 9 25. 7 55. 5 14. 7 7. 5 26. 8 53. 5 20.0 8.1 30.0 54.0 8. 5 32. 3 51. 5 '9. 6 36. 8 50. 5 26. 7 10. 6 42. 4 50. 0 i 34. 7 13.0 45. 5 r 48.0 37. 1 '14. 2 49. 1 47. 5 52. 6 150, 120 18. 4 60. 8 39. 0 63. 4

marit me ETJEVATED TEMPERATURE-PROPERTIES Short timee t d. empr rmr rfi Pfithfi alloy steel of the present invention when tempered at 50 F.

- F. test temperature. With these high elevated temperatureproperties the present alloyris desirable for elevated temperature structural applications. 'T-his'data' is indicative of properties obtainable when designing to operating temperature-ranges.

ABLEII Short time elevated temperature properties {Normalize 1,650 F.; oil quench 1,550 F.; te1nper Fr abovethe test temperatureaverage of 5 tests] SHORT TIME ELEVATED TEMPERATURE PROPERTIES .AT STRENGTH LEVELS OF 180,000-200,000 2.8.1.;

200,000-220,000 P.S.I.; AND 220,000-240,000 P.S.I.

The data in Table III-A, B, and C shows additional elevated temperature properties for the above three strength levels. One inch diameter bars were normalized at 1650 F., oil quenched from 1550'F. and tempered at 950 F., 1050 F., and 1150 F. respectively. The ductility asmeasured by percent elongation increases uniformly 'asthe test temperature is increased. Since the yield strength is held well above 100,000 p.s.i. at 900 F. at all three strength levels, this makes the present alloy desirable for high temperature-structural applications.

TABLE HI(A) 180,000-200,000 p.s.i. strength level-tempered at 3 1150",,F.

v Ultimate Yield Percent Percent Test Temperature, F. Strength, Strength. Elouga- Red. of

p.s.i. p s.i. (0.2% tionintwo Area ofiset) inches g I 7 TABLE III(Bl I V 200,000-220,000 p.s.i. strength leveltemperedat 1 intimate Yield Percent Percent Test Temperature, F. Strength, Strength, Elonga- Bed. of

. p.s.i. p s i. (0.2% tionintwo Area offset) inches r TABLE 111 0 200,000-240,000 p.s.i. strength levellempered-at 950 F.

r 7 Ultimate Yield Percent Percent Test Temperature, F. Strength, Strength, Elonga- Bed. of

r p.s.i. p.s.i. (0.2% tionintwo Area offset) inches nL vATED TEMPERATURE 'IMPA'c'r PROPERTIES Charpy V-notch impact properties heat treated to 200,- 000 to 220,000'p.s.i. strength level and tested at elevated temperatures areshown in Table.

TABLE Test Temp., F. 1, foot 2, foot 3,foot Average,

. V pounds pounds pounds 'tt. lbs.

Low TEMPERATURE GHARPY V-NOTCH IMPACT TESTS The apparent need for information on low .temperature impacts at ultra-high strength levels and the possibility' of a transition temperature prompted the low temperature impact'testing from 70 F. down to 320v F. The date listed in Table V shows the results of these tests with no apparenttr'ansition down to 320 F. The fracture is completely tough and fibrous with an average impact value of 11.2 ft. lbs. at -'-210 F. A standard (.505'?) tensile washeated with the charpy V-notch specimens as follows: Normalize at 1650 F. oil quench from 5 r 1550 F., temper at 600 F. Results of the tensile were: Stress for 1000 hours rupture life at 900 F.-104,000 Ultimate strength 271,000 p.s.i.; 0.2% offset yield strength p.s.i. I

254,500 p.s.i.; elongation 9.5% in 2 inches; reduction of Stress for 1000 hours rupture life at 1000 F.-34,000

900 F. test temperature and stresses up to 100,000 p.s.i. The material may be used where applications of high temperature and stress are required for prolonged periods of time.

area 36.0%. p.s.i.

a TABLE v 10 Stress for 100 hours rupture life at 1000" F.'-66,000

. p.s.i. Low temperature Charpy impact properties (260,000-280,000 p.s.i. strength levels) TABLE VIII Av A I erage verage 1,000 F. 900 F. Test Temp.,F. 3'Tests. Test Temp.,F. 3'lests, Test Test ft. lbs. lbs. Stress, p.s.i. Temp., Stress, p.s.i. Temp.,

NOTCH TENSILE PROPERTIES Notch tensile heat treat response for the alloy of the present invention is shown on Table IX. Notch specimens were normalized at 1700 F., oil quenched from 1550 F. and tempered as shown. The tensiles had a Neuber stress concentration factor of 4.2. The results show a notch tensile strength of 50,000 to 70,000 p.s.i. higher than the un-notched properties of Table I.

ENDURANCE LIMIT The fatigue life comparing the alloy of the present invention and a known alloy AISI4340 is shown in Table VI. The specimens were heat treated to 260,000 p.s.i. strength level and show an endurance limit of 118,000 p.s.i. observed at 10,000,000 cycles.

TABLE VI TABLE IX AHOY t AISI 4340 presen Notch Notch Fatigue Lite 216r5v(%n)tiog,i 260i fgls 15.5.1. Temper Temp., F. Tensile Temper Temp., F. Tensile T, Strength Strength ELEVATED TEMPERATURE STABILITY The high temperature stability of the present alloy is summarized in Table VII. The ultimate strength ranges from 200,000to 220,000 p.s.i. with uniform ductility as 5 measured by percent elongation and reduction of area even after 100'hours of stabilizing at 1000' F.

NOTCH TOUGHNESS Additional notch tensile properties as compared to unnotched tensile are shown in Table X. The tensiles were normalized at 1650 F., oil quenched from 1550 F., and tempered as shown. A Neuber stress concentration factor of 4.2 was used on the notched tensiles.

TABLE VII 7 Procedure used in tensile stability tests TABLE X Normalize 1650 F. on quench 50 F. Smooth Bars (Ave) Notch o a Bars(Ave.) Temper 1050 F. V,

- Temper Avqage of 3 room P i tests after holding at Temp.,F. Ultimate Yield Percent Percent Notch time and temperature indicated. Strength, Strength, Elonga- Bed. of Tensile p.s.i. p.s.i. (0.2% tion in2 Area Strength,

offset) inches p.s.i. H time" F i ti at S gh E oursa en en v 011 a- Stabilize p.s.i. p.s.i.(0.2% t onin 2g Mrs) 211mm 159,320 162:570 16.3 53.6 2571170 '26 it: 7 10f): 205:0(1) 195:700 13:2 43: 3 N OTCH TENSILE PROPERTIES WHEN HEAT TREATE 1D0+10 hours at 1,050 F 201, 000 195, 000 14.0 50. 1 TO ULTRA-HIGH STRENGTH Notch tensile properties were studied by varying the specimen size, the strength level, and the stress concentration factor to determine the notch sensitivity as measured by the notched tensile tests at three strength levels.

Test specimen dimensions with stress concentration STRESS RUPTURE PROPERTIES The stress rupture properties of the improved alloy heat treated to 200,000 to 220,000 p.s.i strength level are shown in Table VIII. The properties are excellent up to 7 factors and corresponding notch radii are shown in the following-table: r

3 Major Di- Noth' Di- NotchRoot K-A' ameter, ameter, Radius, cording to Inches Inches Inches Neuber i .011 "K=3 .300 .2 12 82g 53 .500 .353 5 222- %;g

.0 ,aoo .sas moo K= The results obtainedwith the above specimen sizes are summarized in Table 'XI. The notch tensile test is a good measure of the notch sensitivity and is probably a better criterion than the V-notch impact test. The extremely high ultimate strengths exhibited by the notched bars is due to'the fact that the calculation is based upon the minor diameter of the notch, rather than the area of the major diameter. In contrast to this, anormal tensile calculation is. based on the original diameter rather than the reduced cross sectional area after the tensile tracture.

TABLE XI Tempera- Maior Diameter, Inches 7 ture, F.

I l Neuber stress concentration factor.

. EFFECT OF STRAIN AGING ALLOY OF PRESENT 1 I nvvmmrronv The mechanical properties as summarized in Table XII are the results of strain aginge Test results indicate that .strainagiug may offer a possibility of increase in tensile strength andyield strength above normal with an accompanying decrease in ductility. Subsequent stress relieve temperatures should be low (less than 600 F.) and prefstandard tensile results tested at various tempering temastures; Forexampleythe yield to ultimate ratio for the 'un's'trained alloy of-thepresent invention at 500" compared to .92'fo'r the'strained' tensilesa TABLE XII Initial Stress Ultimate Yield Percent Percent Tempen, Relieve, Strength; Strength Elongation Bed. of F. F. p.s.i.' p s.i. (0.2% in 2 inches Area 250 366. 000 1 352, 500 4. 5 23. 0 350 354, 000 L333, 800 5. 0 21.9 450 322, 000 298, 200 3. 0 15. 3 550 312, 000 290, 600 3. 8 15. 0 550 302.000 3. 5 550 279, 000 266, 800 2. 5 19. 4 550 256, 100 256. 100 4. 0 31. 6 550 241. 900 237, 900 6.0 42. 6 550 212,300 211. 900 8. 5 46.0 550 I56, 400 150, 400 a 9. 0 53,7

1 Fracture outside ga uge marks. I I V 7 It will be usae'stsbd that it is desired :6 comprehend within the invention and-the .scope offtheiclaimsthereof such equivalent materials and proportions as -may be,

iound necessary to adapt this invention'to the varying conditions met in actual practice and we do not limit ourselves to these specific materials and proportions.

* WhatIclaimisP I p 1. An improved alloy steel which contains about .40.50% carbon; about -.58.93%- manganese, about .13-.32% silicon, about .35.75% nickel, about .87-1.23% chromium,'about .881.l2 molybdenum, up to about .010% phosphorous, up to about .010% sulphur, and there being .20 to 1.00% vanadium, and the remainv der being iron with incidental impurities, and the metal being characterized by its ability to maintain high strength considering its low alloy content for prolonged periods of elevated temperatures with accompanying good ductility,

therebeing an'absence of temper brittleness when tempered at low tempering temperatures, and the metal being characterized by substantially increased elevated temperature andstress rupture properties.

- 2. An improved'alloy'steel wh'chcontains approximately .46% carbon, about .58.93% manganese, about .13'.32% silizon, about .35.75% nickel, about .87-l.23%

chromium, about .88- 1.-12% molybdenum, up to about '.0l0% phosphorous, upto about -'.010%- sulphur, and approximately .50,% vanadium, and the remainder being iron withfincidental impurities, and the metal being characterized by its, ability to maintain high-strength considering its low, alloy content-fojr prolonged periods of elevated temperatures with accompanying good ductility, there being an absence of temper brittleness when tempered at low tempering temperatures, and the metal being characterized by substantially increased elevated temperature and stress rupture properties.

References Cited in the file of this patent lished by John 'Wiley and Sons, Inc., New York,N.Y'.

Super-High Strength Steels for Aircraft Applications, March 1957. Pamphlet published by The International Nickel Co., Inc., New York, N.Y.

Ultra-StrengthSteels, 1957. Pamphlet published by Climax Molybdenum Co.,.New York, N.Y.-

Claims (1)

1. AN IMPROVED ALLOY STEEL WHICH CONTAINS ABOUT 40-50% CARBON, ABOUT .58-93% MANGANESE, ABOUT 13-32% SILICON, ABOUT 35-75% NICKEL, ABOUT 87-1.23% CHROMIUM, ABOUT .88-1.12% MOLYBDENUM, UP TO ABOUT .010% PHOSPHOROUS, UP TO ABOUT .010% SULPHUR, AND THERE BEING .20 TO 1.00% VANADIUM, AND THE REMAINDER BEING IRON WITH INCIDENTAL IMPURITIES, AND THE METAL BEING CHARACTERIZED BY ITS ABILITY TO MAINTAIN HIGH STRENGTH CONSIDERING ITS LOW ALLOY CONTENT FOR PROLONGED PERIODS OF ELVEATED TEMPERATURES WITH ACCOMPANYING GOOD DUCTILITY, THERE BEING AN ABSENCE OF TEMPER BRITTLENESS WHEN TEMPERED AT LOW TEMPERING TEMPERATURES, AND THE METAL BEING CHARACTERIZED BY SUBSTANTIALLY INCREASED ELEVEATED TEMPERATURE AND STRESS RUPTURE PROPERTIES.