US3164495A - Ultra high strength alloy steels - Google Patents

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United States Patent O 3,164,495 ULTRA HIGH STRENGTH ALLOY STEELS Clyde A. Furgason, Milwaukee, Wis., assignor to Ladish Co., Cudahy, Wis., a corporation of Wisconsin N Drawing. Filed Sept. 26, 1961, Ser. No. 140,67

1 Claim. (Cl. 148-36) A This application is a continuation-impart of my application Serial No. 82,969, filed January 16, 1961, now

abandoned. e t

This invention relates to improvements in ultra high strength alloy steels and particularly to a steel that con tains a minimum of strategic alloying elements while possessing high yield and ultimate strength when tempered at high temperatures and the 'ability to maintain high strength at elevated temperatures.

Users and manufacturers of hot work tool and die steels are constantly looking for improved steels which are stronger, tougher, have higher impact resistance, and can withstand higher temperatures. Most hot work die steels possess a secondary hardening characteristic which provides higher temperature resistance because high hot hardnesses can be obtained and'retained whentempering at high temperatures. At the same time, these steels must be capable of being hardened deeply. j

. Prior to the present invention, the lowest alloy analysis which would impart secondary hardening was generally considered to be an alloy containing no less than 7% total alloying elements.

It is therefore an object of this invention to provide an alloy steel analysis containing only approximately 4% total alloying elements, that is deep hardening and possesses a secondary hardening characteristic plus good ductility. The alloy steel of this invention is applicable to critical hot work tool and die applications as wellas to ultra high strength structural applications subject to elevated temperatures and both dynamic and static loading.

Aircraft, and more recently missile, manufacturers have been constantly seeking newer and better materials for utilization on critical parts where high strengths and strength/ weight ratios could bring about substantial weight savings on the vehicles. Coupled with this trend toward lighter weight, higher strength is the increase in speed with an accompanying aerodynamic heating problem. This has necessitated high strength materials which are capable of withstanding sustained elevated temperatures without losing strength and ductility. v

The abilities of aircraft and missilestructural materials to perform under these conditions has necessitated a shift from the A131 4340 type material and its modifications to the more highly alloyed materials (for example SAE H- 11) (0.40% C, 5.0% Cr, 130% Mo,0.50% V).

The reason for this shift is the need for a steel which 1 essary, making it particularly suitable for elevated "temcan be heat treated to tensile strengths of 220,000 to 280,000 psi and retain suflicient toughness for landing gear, engine mounts, hot work tools and dies, and other structural applications. A greater problem was to provide an alloy steel capable of being. heat treated to these high strengths and .at the same time maintain its strength:

3,164,495 Patented Jan. 5, 1965 works which adversely affect the hear treat response if cooling from the hot working temperature is not precisely controlled or executed properly. It has heretofore been generally believed that H-ll is the lowest alloy analysis that will impart secondary hardening.

It is therefore an object of the present invention to provide an improved alloy steel that possesses an extremely low alloying element content, thereby using a minimum of strategic materials, while possessing secondary hardening characteristics with good ductility especially at room temperature.

It is a further object of the invention to provide an alloy composition that posesses secondary hardening characteristics while only containing approximately 4% total alloy content, said alloy also possessing excellent high strength and toughness properties.

Many of the so-called ultra high strength steels rely on high Silicon contents to reduce temper brittleness while producing high strength levels when tempering between 400 F. and 700 F. It is therefore an object of the invention to provide an alloy steel which exhibits high strength with adequate ductility when tempered in excess of 1000 F., thereby providing maximum stress relief of quenching stresses as well as permitting distortion correction at high temperatures where correction is much simplier.

It is a further object of the invention to provide an alloy steel which restricts the amount of the alloying element silicon to less than 0.5 thereby maintaining high stress rupture properties. Silicon contents in excess of 0.5% results in degradation of said stress rupture properties.

A still further object of the invention is to provide alloy steel which maintains higher elevated temperature stability than other secondary hardening alloys.

In the alloys of my prior patents Nos. 2,919,188, dated December 29, 1959, and 2,921,849, dated January 19, 1960, if it were attempted to heat treat to ultra high strength levels, the tempering temperature would have to be substantially lower than with the present invention as there would be considerably less relief of quenching stresses .duringtempering at the low temperature. The results of the present invention are obtained principally by substantially increasing the amount of molybdenum over that contained in the alloys of my. prior patents, whereas to obtain the results of the present invention it would be conventional practice to substantially increase the amount of chrome to a level substantially affecting the cost of the alloy, as. compared to the cost when molybdenum is moderately increased as in the present invention.- i

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, stress rupture strength and high impact load resistance are necperature structural, die and tool steel applications.

A further objectof 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 high strength at elevated temperatures so that it can be used for applications where high strength at both room temperatures and elevated temperatures is required.

A further object 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.

A further object is to provide an alloy steel of low creep rate' at elevated temperatures so that the material may be used where applications at high temperature stress are required for prolonged periods of time.

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 controls normally used in welding medium carbon low 4 v materials need be employed to obtain prop'ertiesiheretm fore obtained by a much higher alloy content.

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

An average of the room temperature' mechanical prop-: erties of the present alloy steel afterf normalizing at 1900 F., air quenching from 1850 F., as shown, are summarized in Table I.

strength of 265,000v to 275,000 p.s.i. a yield strength of 235,000 to 255,000 p.s;i. elongation of 910%, and a reduction of area of -45%.

TABLE I Mechanical Properties at Room Temperature, Air

Quenched From 1850 F. and Tempered as Shown Percent Percent Rockwell Oharpy Temper U.S., Y.S., Elong. Red. 0 V-Notch Temp., F. p.s.i p.s.i. m2" of Area Hardness Inpacts,

' ft. lbs

formula without causing brittleness while the product maintains ductility and good weldability. It has also been discovered that a moderate increase in the amount of molybdenum over that of my prior patents, heretofore referred to, will permit 'heat treatment to ultra high strength levels While tempering at a high temperature to provide less likelihood of distortion from stresses.

The alloy of this invention 'has the following contents in percent:

Mn e. 57-.93.

P .010-maximum. S -2 .010 maximum. V Q. .49.61.

Remainder iron with residual impurities.

It is important to maintain a relatively low phosphoru and sulfur content. 7

A desirable formula for many purposes is:

C e .48 approximately. Mn --i .75 approximately. Si -35 approximately. Ni .55 approximately. Cr 1.00 approximately. Mo 2.00 approximately. P .010 maximum.

S .OIOmaximum.

V .50 approximately.

Remainder iron with incidental impurities. v

The above formula may be modified by the addition of other elements andthe present invention is not to be construed so as to preclude the use of small amounts of such elements as uranium-23 8, tungsten, columbium, or rare earth elements in the basic composition.

It is apparent from the above total that the alloy con tent is very low so that only a minimum of strategic The short time elevated temperature properties of the alloy steel of the present invention when austenized at 1850 F. and tempered at 1050 F. to produce the maximum strength in the secondary hardening tempering range are summarized in Table II. The test temperatures are below the corresponding'temper temperature to simulate treatment necessary to be compatible with operating temperatures, i.e., the tempering-temperature must be higher than the operating-temperature to prevent tempering the material while in operation.

'The elevated temperature data shows the yield and ultimate strengths to be well above 170,000 p.s.i. at 900 F. test temperature, and at 1000 F. test temperature the ultimate strength is 185,000 p.s.i. andthe yield strength is 162,720 p.s.i. With these high elevated temperature propertiesflhe present alloy is desirable for elevated temperature structural application. This data is "indicative of properties obtainable when designing to operating temperature ranges. i

TABLE II Short Time Elevated Temperature Mechanical Properties [Heat treatmenti Normalized, 1,900 F.; air quenched, 1,850 F.; temperedas shown] Temper. Test Temp., Ult. Stu, Yield Elong. Red. of. 'Iemp., F. p.s.i. p.s.i. Percent Area,

7 Str. p.s.i. Percent Charpy V-Notch impact properties, heat treated to 260,000 p.s.i. to 280,000 p.s.i. strength level and tested at elevated temperatures are shown in Table III.

Th' maximum ultimate and yield strength with adequate ductility, as measured by the percent elongation and reduction of area, is achieved by tempering between 1000 F. 1100 F. This temper produces an ultimate tensile? "TABLE I11 Elevated Temperature Impact Properties [Normalized, 1,000 E; air quenched, 1,850 F4 tempered, 1,050 El ELEVATED TEMPERATURE STAR'ILITY The elevated temperature stability of the present alloy is summarized in Table VII. The ultimate and yield strength remain unchanged, for all practical purposes,

5 with uniform ductility, as measured by the percent elon- 1 3 a 1 1 t' r ft 100 h 1 Test Temp.,F. Ft. Lbs. ga n an re ucion 0 area, evena er ours 0 Ft. Lbs. Ft. Lbs. Ft. Lbs. stabilizing at 1000 F,

19 ,18 18 p 18.3 TABLE VII -22 1 23 22 22.5 ;22 23 23 0 22.7

23 20 21.2 Elevated Temperature Stability T elzszle Properties 20 23 27 25.6 1 1 g2 [Heat treatment: Normalized, 1-,900 F.; Air quenched, 1,850 F.;te1nv 27 I 26 0 pered at 1,050 F. Specimens held at 1,100 F. for time indicated and L testedat room temperature] 1 25 25 25.5

Ultimate Yield Elong. Red. of TABLE IV Timeat1,000 F.Hrs Str.,p.s.i. Str.,p.s.i. percent Area, per- 08D Modulus of Elasticity 20388 a: 12- Mdul IE1 t- .5 TestTemp F) f 5 1 203, 200 247,900 9.0 30.3

80 3m RooM TEMPERATURE MECHANICAL PROPERTIES AT Am 214 STRENGTH LEVELS OF 180,000-200,000 p.s.i., AND 200,000- m 2 0 220,000 p.s.i. 000 26.7 700 27.1 25 The data m Table VIII shows additional room temperafi 321g ture mechanical properties for the above two strength 1,000 24.9 levels. The data further exhibits the higher strength levels obtainable with the steel of the present invention.

TABLE VIII Room Temperature Mechanical Properties at 200,000 220,000 p.s.i. Strength Level V-Notch Charpy Norm. Quench Temper Ult.Str., Yield Elong, Bed. of Impact Temp, Temp.,1*. Temp, p.s.i. Str.p.s.i. percent Area, (Avg.6 F. F. percent Tests),

Ft.Lbs.

Angle of bend, 180 for each of the above heat treatments.

TABLE v sTREss RUPTURE PROPERTIES 10min}, End Quench Hardenability The stress rupture propertles of the improved alloy h dE d Ext th are shown in Table 1X. The propertles are excellent up [Dmme mm the Queue e n em 8)] to 1000" F. test temperature and stresses up to 100,000

.s.i. Quench 'I;emp. 1 2 3 4 5 0 8 10 12 14 16 20 24 28 32 p TABLE 1X 58 57 57 57 57 50 50 55 54 53 52 50 56 55 50 55 50 50 55 55 55 54 54 Stress Rupture Properties 55 55 55 54 54 54 54 54 53 53 53 53 55 [Normalized, 1700 F.; tempered, 1050 F.]

cREEP RUPTURE PROPERTIES The creep rupture properties of the improved alloy Test -N ggl r s t g heat treated to 260,000 to 280,000 p.s.i. strength level are shown in Table VI. The properties show a very low 1006007 98 9 creep rate at temperatures of 950 F. and 1000" F. This 901000 14813 material may be used where applications of high tem- $8 383 22 2-: perature and stress are required for prolonged periods of time.

TABLE VI Creep Rupture Properties [Normalized, 1,850" F.; double tempered, 1,050 11. All tests terminated after 500 hours] It will be understood that it is desired to comprehend within the invention and the scope of the claim thereof such equivalent materials and proportions as may be found necesary to adapt this invention to the varying conditions met in actual practice and we do not limit ourselves to these specific materials and proportions.

60,000 What I claim is:

7 -0074 An improved alloy steel consisting essentially of about .40.55% carbon, about .57 to .93% manganese, about Stress, p.s.i. Creep, per- Test Tem F.

p centin50hrs.

7 .23-.45% hsilicon, about 351.70% tnickel about .87- cl.23 Chromium, up to 1,0 10% pho sphor-ugup'vto about .Q l,0%. ulflur, about 1 .88 2.27 molybdenum in. combinationwith about -.49. ,.61%;vanadiurn to produce a sec- :ondary -hardening characteristic,v and the remainder being ironyvith incidental impurities, and the metal having the ability to maintain high strength considering itsi low alloy content for prolonged periods of elevated temperatures with accompanying good ductility, there being an absence of temper brittleness when tempered at 10W;10 temperingtempqratures, said talloy .steellhavinglbeennheat treated by austenitizing at 1800 F.1900 F. followed by quenching, and sub sequenttempering between 1000 F.

to 1100 F. I

References,(l'itedpbytthe Examiner UNI-TEDSTATES-PATENTS 2,327,490 "8/43 iBagSar 75 128.85 5 "2,919,188 "'12/59 -Furgason f75"128;85 2,921,849 1/ 60 Furgason 75128.85

-OTHER-REFERENCES Archer ,et al.: Molybdenum-Steels, Irons, Alloys, jClimax Molybdenum Company; New York, September 12, 1949,-page 10, FIG.'"7 relied' upon. 1 {DAVID L.: RECK, 'Primm y iExaminer.

RAY K. WINDHAM, Examiner.