US2442944A - Perrous alloy - Google Patents

Description

June 8, 1948. N, A, zlEGLER 2,442,944

FERROUS ALLOY Filed May l5, 1944 2 Sheets-Sheet 1 vJwi.

l l I N07 AFFECTED WELD AFFECT@ [V07- wi' AFI-'6759 WEI-D ZONE PKOPER ZOO V/ CKERS HARD/V555 NUMBERS June 8, 1948. N, A, ZIEGLER 2,442,944

FERROUS nALLOY Filed May l5, 1944 2 Sheets-Sheet 2 /var Aff-'cran wf/ Q' AFFECTED /var AFFEL' ZONE P/YO PE1? Z ONE NFFFC LOCA 7"/0N 0F HARD/V555 READ/N65 LOCATION OF HARDNESS fDM/t Patented June 8, 1948 UNITED sierras:

`PATENT QfFFICE Crane Co., Chicago, Illinois Ill.' a corporation of Application -May15`, 1944, Serial Nor 535,704

2 Claims.

invention relates to ferrous alloys and more particularly to; chromium-.molybdenum steels with low carbon :content:

Steels of this type are commonly used for the construction of pressure-containing vessels and parts, such as valve bodies, bonnets, discs and the like. Such structures are frequently fabrie cated and installed inservice by Welding and thus new problems arise with respect tothe physical. properties of the steel alloysemployed;` NotfonlyL must the castmembers exhibit acceptable strength properties before fabrication, hutrthennalas: sembly.- after fabrication must be. structurally strong, free from porosity, internal strains, and capable of withstanding: the stresses resulting from high operatingI pressures.

Previousy investigations; and studies of chromiumemolybdenum vsteelsin the range of 2.5.9% Cr, -'2% Mo and 0-0.3% C have indicated that, generally' speaking, a reduction in the-carboni content will give better: thermal4 properties; that is-,r lessssusceptibility to thermal cracks-when the material cools-down in the mold fromtheliquid sta-te, as; well .as when `it .is subjected Ytovarious heattreating operations, involving rapid cooling, such as normalizing or quenching. Reduced sus.- cepti'bility t0. thermal crackingi is particularly important. during welding, when rapid alternate heating. and-cooling is yapart of the operation. It is-therefore desirable to reduce the `carbon contenti to asV Iowa gureas possible-without im7 pairing; the] strength properties. It has been found thatzvvhen the carbon content of these steels is. decreased. to values belowv 0.10%,.the strength ofthe resultant steel decreases-very rapidly, This decreaseis serious in commercialsteels which must meet the: following requirements-setup by various. engineering bodies-suchas, for example, the 4American Society for-Testing Materials:

Oneeof 'thelimportant lobjectsfot -this invention is .to provide a chrominrn-molybdern-im:Y steel 4of low` Carbon content and. suitableas-a material for the cast members of pressure vessels, such as valves or the like, the complete structures of which are fabricated by welding the individual cast members into an assembled unit.

Another object of this invention is the provisionl of anal'loy steel of such favorable thermal properties and welding-characteristics as to permit the fabrication o-f cast members into pressure-containinbodies characterized by freedom from porosity, internal strains and high resistance to stresses. resulting. from operating pressure.

A further obectof this invention is the provision of farwelding'steel'adapted to the construction ofiwel'dedpressure vessels which will have therecluired-tightness,A strength and freedom from linternalastrains Without the necessity of stress-relievingthe welded portions.

With' the foregoing Y"objects in vieW;I"have dis,-v coveredthat the addition of' nickel i in small amounts to low-carbon chromiumamolybd'enum' steels of va denite compositional' range' will have physical. properties, Without making them unduly thermallysluggisnair hardenable, susceptible 'to internal strains, thermal cracks or diilcult to Weld. While the addition of nickel to steels' o-f this type is known to have abenecial effect upon' the physical properties, noone, to my .knowledge, has. discoveredftheeffect of the addition of den; nite amounts of nickel upon` the Welding qualities content.

To investigate the effect of nickel on the weldingfqualitiesuof this. type of steel, some direct Welding, experimentswere performed-` Parts of 4o castingsmade vof.eight'experimental` steels were Minimum y g Maximum i Tensileeduction.A mpact ar ess Yield Polnt Elongation Strengthn of Area Resistance, Number .15s/sani. 21M/Sq m" Percent Per cent mais;

a. marked strengthening` e'ct on'.v the 'resulting' of chromium-molybdenum. steelsofflovv carbon.

sectioned and then arc-welded together in their original shapes, using chromium-molybdenum electrodes of the following specied composition:

The compositions of the eight experimental steels tested are shown in Table 1 below.

TABLE 1 Composition Serial No.

Si Mn S I C Ni Cr Mo 0. 56 0. 67 0. 026 0.020 0. 09 0 4. 39 0. 51 0.77 0. 69 0.021 0.022 0. 09 1.30 4. 68 0. 48 0.65 0.64 0.020 0.024 `0.10.j-0.63 7.22 Y 1.08 0. 56 0. 60 0. 026 0. 028 0.10 l.' 17 7. ll 1.10 0. 74 0.59 0.023 0. 034 0.12 0. 02 8. 94. 1. 45 0. Gl 0. 59 0. 023I 0. 030 0. 07 1.29 9. 0l 1.78

It may be noted that the prime object of adding molybdenum to these types of Steels is to develop a desired high temperature creep resistbon steels.

Arepresents a nickel-free steel and the solid-line Vickers hardness tester and taking readings at about 1A; inch intervals across the Weld and affected zone. (Vickers readings for these types of steels are directly comparable to Brinell numbers.) Figs. 1-4 of the drawings accompanying this specification are graphic representations of these hardness distribution studies, in which Fig. l represents steels containing 5% Cr, 0.5% Mo and 0.2% C;

Fig. 2 represents steels containing 5% Cr, 0.5% Mo and 0.1% C;

Fig, 3 represents steels containing 7% Cr, 1% Mo and 0.1% C, and

Fig. 4 represents steels containing 9% Cr, approximately 2 Mo and 0.1% C. v

Generally speaking, Fig. 1 represents high-carbon steels and Figs. 2, 3 and 4 represent low-car- In each case, the dotted-line curve curve represents a steel containing 1% nickel. The numbers along the vertical axes of these curves represent Vickers hardness units. T-'he numbers 1-10 along the horizontal axes designate the location ofmthe points in the various zones of the welded section at which Vickers hardness readings were taken.

In order to demonstrate that the steels treated according to this invention were improved in physical properties, the results of physical tests are presented in Table 2 below.

TABLE 2 Tensile properties Chrpytlmpact Tensile Yield Elonga- Reduction e515 ance Serial No. Strength, Point, :Eilormnl tion, of Area, BHrd' p. s. i. p. s. i. p" Per Cent Per Cent Ft Lbs R. T. 25 F.

100, 000 75, 000 40, 000 23. 5 00. 5 23. 0 14. 0 0 0 27 C 101, 000 76, 000 59, 000 v 24. 0 01. 0 19. 0 8. 0 308 o 000 52, 000 37, 000 32. 5 67. 5 26. 5 24. 5 215 o 17 C 101, 000 78, 000 00, 000 22. 0 64. 0 26. 0 17. 0 202 o (The analyses of these steels are given in Table 1.)

ance. When the amount of chromium exceeds about 2 per cent, molybdenum in amounts up to about 2 per cent has relatively small effect on the room temperature physical properties and thermal characteristics.

While the experimental data presented relate speciiically to compositions including chromium `contents up to about 9%, I have found that the favorable results to be gained by the practice of this invention will applyv to steels of this type containing chromium contents of up to 12%, since this represents the known upper limit of chromium for heat treatability with low carbon. The eight experimental steels were heat treated by (1) normalizing from 1750 F., (2) air quenching from l550 F. and (3) drawing at 1250- 1300F. Y In summary, the range of analysis (in percent) of my improved weldable cast steel is chro- Referring now to Tables 1 and 2, it may be noted that steels l and 2 are standard 4-6% Cr, 0.5% Mo steels containing 0.2% C. No. I contains no nickel and No. 2 contains 1.0% nickel.

u Both meet the A S. T. M. specifications given above, except that No. 2 is slightly hard. Al-l the rest of the steels contain 0.1% C, i. e. half of the carbon contents of Nos. I and 2. Nos. 3 and 4 contain 46% Cr, 0.5% Mo; Nos. Sand S contain 7% Cr and 1% Mo, and Nos. 1 and 8 contain 9% Cr and 1.5% Mo. In each of these three pairs the first steel is nickel-freeor low 4in nickel and the second contains 1% Ni. 'Ihe point of interest is the fact thatV the tensile` 'i strength of the three nickel-free steels is below.

mium from 2 to 10%, molybdenum .5 to 2% with A transverse section was cut from each of the welds (without stress-relieving them) and the sections roughly polished. A hardness A,survey was made over each of these test pieces usina .f

90,000 pounds persquare inch (A. S. T.V M. speciiication) and the tensile strength of the threenickel-bearing steels is about 100,000 pounds per square inch. Likewise, the yield pointof two of the three nickel-free steels is below th A. S. T. specification of 65,000 pounds per square inch and the yield point of the three nickel-bearing steels is aboveV 7:0,000 pounds per square inch. At the same time. the elongation, reduction of area and impact resistance, at4 room temperature, of all these steels are well above ,1 8%, 3,0% 15 foot-pounds, respectively, that is, the A. S. T, M. specifications.

Likewise, the hardness of all these steels is below the A. S. T. M. maximum of 235. Thus, the addition of nickel in amounts of about 1% improves the physical properties of chromium-molybdenum steels of low carbon content.

From the above data it will be evident that I have made an important contribution to the art of metallurgy by the provision of a steel of superior weldability and with physical properties in excess of the requirements for steels of this type in commercial practice.

It should .be understood that the invention is not limited to the particular examples which have been given for purposes of illustration, but may be otherwise embodied within the scope of the following claims:

I claim:

1. A cast steel article composed of: 2 to 10 per cent chromium, 0.5 to 2.0 per cent molybdenum, usual amounts of silicon, manganese, sulphur and phosphorus, containing at least 0.75 per cent but not over 1.5 per cent nickel, not over 0.10 per cent carbon, and the balance iron and incidental impurities characterized by improved strength and welding characteristics.

2. A welded construction made of cast steel of the following composition: 2 to 10 per cent chromium, 0.5 to 2.0 per cent molybdenum, usual amounts of silicon, manganese, sulphur and phosphorus, containing at least 0.75 per cent but not over 1.5 per cent nickel, not over 0.10 per cent carbon, and the balance iron and incidental impurities.

NICHOLAS A. ZIEGLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 882,112 Illingworth Mar. 17, 1908 2,059,746 Ritterhausen Nov. 3, 1936 2,227,891 Rose Jan. 7, 1941 2,281,219 Ziegler Apr. 28, 1942 OTHER REFERENCES Alloys of Iron and Chromium, vol. I, Low Chromium, page 467, published in 1937 by the McGraw-Hill Book Co., New York.

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