US2805942A - Alloy steel and articles thereof - Google Patents

Description

Sept- 10, 1957 P. PAYsoN 2,805,942

ALLOY STEEL AND ARTICLES THEREOF Filed NOV. 5, 1955 W2- IN VEN TOR.

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WLM/c1041@ United States ALLOY STEEL AND ARTICLES THERESE Peter Payson, New York, N. Y., assignor to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New Jersey Application November 5, 1953, Serial N 390,314

4 Claims. (Cl. 75-126) This invention pertains to alloy steels which are characterized in possessing a relatively high resistance to deformation under stress at high temperatures and a good resistance to oxidation at temperatures up t-o about 2100" F. Moreover, this invention relates to rider sheets made of alloy steels which are suitable for use in a normalizing furnace.

ln the processing of low carbon sheet steel which is made into automobile body parts, and the like, by deep drawing and forming operations, it is customary to normalize the steel before it is annealed. The normalizing is carried out in a furnace approximately 100 ft. long which may have as many as live zones each about 20 ft. long maintained at different temperatures, for example, 1725 F. at the intake end; and in succession l800 F.; l900 F.; l600 F.; and nally 1325o F., at the discharge end. The hearth of the furnace consists of a series rof rollers. Across the tops of the rollers are placed removable rider sheets made of heat resistant steel, and the sheets to be normalized are placed upon the rider sheets. In the normalizing operation, the sheets are moved by means of the rollers through the successive-zones of the furnace at a rate of about ft. per minute. The purpose -of the rider sheets is to provide a support for the sheets being normalized so that they will not bend or sag between the rollers, since the sheets being normalized are sometimes very light gauge, namely, 0.022 to 0.049 in. thick, and are suiciently weak at the high temperatures used in normalizing to sag under their own weight. The rider sheets themselves may sag somewhat in the hottest zones of the furnace, but being made of alloy heat resistant steel, and being somewhat thicker than many of the sizes of the sheets being normalized they provide sufficient support to the sheets being normalized to hold the distortion of the latter to a minimum. For ease of handling in subsequent operations it is desirable that the sheets after they have been normalized be as at as possible.

The rider sheets are used over and over again until they become perforated or warped to such a degree that they are no longer serviceable. They are placed across the rollers at the intake end of the furnace and are removed and placed on carts at the discharge end. They are then brought back on the carts to the intake end and again placed on the rollers for another trip through the furnace. Generally the rider sheets are used only in a position below the sheets being normalized, but when sheets made from cold rolled strip are normalized, the rider sheets may be used both below and above the sheets being normalized. The purpose of the top rider sheets is to protect the sheets being normalized against excessive scaling. In successive trips through the furnace, the rider sheets are used for either top or bottom sheets interchangeably.

In the past Vthe most satisfactory rider sheets were made from a 25% chromium-20% nickel, heat resistant steel generally designated as Type 310, Stainless. However, because of restrictions on the use yof nickel in steels rice for non-military applications, Type 310 steel is no longer available for rider sheets and the plain 25% chromium steel generally designated Type 446 Stainless has been used as a substitute. Because Type 446 has a structure consisting primarily of ferrite and carbides, in contrast tc the structure of austenite and carbides in Type 310, the sheets made from Type 446 are much weaker than those made from Type 310. As is well known, austenite is much stronger than ferrite at temperatures above about 1200o P. The rider sheets made from Type 446 stretch appreciably in service because of this weakness, and have to be sheared from time to time to get them back to their loriginal dimensions in length and width. They also perforate more rapidly than the Type 310 sheets because of this attenuation. Consequently, the lives of the Type 446sheets are only 35 to 50% as long as those of the Type 310 sheets, and the operators 4of these normalizing furnaces have demanded a steel for rider sheets which would be free of nickel but which would give much better performance than Type 446.

Now I have invented an alloy steel primarily for rider sheets, but which can be used for other heat treating furnace parts as well, either in wrought or cast form, which is free from nickel; which has excellent resistance to oxidation; and which has much better resistance to stretching under stress at elevated temperatures than Type 446.

Further objects, features and advantages rof the invention hereof will appear from the detailed description given below, taken in connection with the accompanying drawings which form a part of the specification and illustrate by way of example, preferred embodiments of the invention.

ln the drawings:

Fig. l is a longitudinal side elevation view of a normalizing furnace, partially broken away at one end showing the rider sheets and low-carbon steel sheets passing along the rollers thereof;

Fig. 2 is an enlarged transverse sectional elevation of the furnace, as taken at 2-2 of Fig. l;

Fig. 3 is an enlarged fragmentary perspective showing of a rider sheet supporting a low-carbon steel sheet on the rollers of the furnace; and

Fig. 4 is an enlarged fragmentary perspective showing of a low-carbon steel sheet, sandwiched between a pair of rider sheets.

Referring now in more detail to the drawings and particularly to Figs. l and 2 thereof, the normalizing furnace 10, is provided with burners 11 and a hearth l2. The Ahearth i2 consists of a plurality of longitudinally spaced, parallel shafts 13, rotatably supported above the floor of the furnace in bearings 14, mounted on upstanding supports 15. Each shaft 13 spans the Width of the furnace and is provided with a plurality `of transversely spaced rollers 16, keyed to the shaft. Suitable motor activated driving rneans 17, capable of rotating the shafts 13, are located exteriorly of the furnace i0, and thus a series of driven rollers is provided which extends from the inlet end to the exit of the normalizing furnace.

As has been described above, the low carbon steel sheets 18, which are to be normalized, are placed upon rider sheets 19 which in turn are laid upon rollers 16 at the inlet end 20 of the furnace. The driving means 17 iimparts rotation to the shafts T3 and rollers 16, whereby the rider sheets together with their associated low carbon steel sheets are then moved toward the exit end 21 of the furnace. As these low carbon steel sheets 1S are thus carried from inlet to exit of the funnace they successively pass through the various heating zones and are thus normalized in the manner that has been pointed out previously. When the sheets reach the exit end 21 of the furnace, they are removed and the low carbon steel sheets are carriedtothe nextprocessingstage where as tlerider sheets may be loaded upon a cart 22 and returned to the Iinlet-end of the furnace 10 for're-use.

As seen in Fig. 4, in some instances, and especially where the low carbon sheet is made from cold rolled strip,

i heated to 2l50 F. and air cooled. The samples were rated M'for strongly magnetic, SM for slightlymagnetic, and VSM for very slightly magnetic.

TABLE I it is desirable not only tosupport said sheet by ridersheet 5 V19,A interposed between 4the former and the furnace rollers Relative magnetic susceptibility and Rockwell C '16, but also to cover sald low carbon steel sheet 18 with hardness of C-Mn-Cr-N steels anadditional rider sheet 23 lwherebyscale formation on [Au Samples an. cooled from 2150, F 'the-top surface of sheet 18 1s minimized. V ,As-has been previously pointed out the Workiife of Mag. these rider sheets is dependent upon the type of Asteel Bar C Mn Gr v N lC-i-N nette Boekof which they are made, with steels of ferritic structure sctl Wen C vbeing far less advantageous than those of `austenitic maklings. In order to overcome the aforesaid difficulties .58 11.8 24A 15 73 M 2G which have beset rider sheets of present day steel com- .67 11.5 25.2 .09` .76 M 26 position I have developed a substantially austenitic alloy :g3 j jg :gg :gg 1% iste'el 'which nevertheless is substantially free of any nickel 7 14. 5 25.0 .43 .90 M 29 CGH-tent .59 12.2 27.6 .31 .9o M 31 l l .55 9.3 24.9 .35 .90 `SM 32 The composition vof the steel of my invention 1s as .56 11-5 24.4 38 94 VSM 32 follows. .59 11.8 21.8 .536 .95 VSM 32 .57 11.4 24.3 .39 .95 VSM 32 .69 9.1 24.8 .29 .es VSM 34 r .65 11.5 25.2 .34 .99 VSM 34 Broad Preferred .57 14.3. 24.6 .45 1.02 VSM 34 Range Range .72 14.3 25.1 .34 1.06 VSM l36 .66 13.5 24.7 .44 1.10 VSM V36 v .79 11.7 25.0 .40 1.19 VSM 3s Percent C .55/.80 .60/. 70 Percent:V Mm 9. 0,115.0 11. 0/12. 0 Percent S1 up to 2.5 20/1. 0 N ern-These steels also contained about 0.3% Siand up to about 0.4% Percent Cr.. 21. 0/27. 0 23. 0/25.,0 residual N1. Percent N .30/. 50 .35/. 40

It V1s clear from the above that the steel ofthe lnven- The balance of this steel is substantially all iron except for usual impurities within commercial tolerances, although the steel may include optional additions Of up to about 5% in the aggregate of theelements vanadium, tungsten and molybdenum, with none of these being over 2%.

It -is desirable to have `a minimum of 21% chromium in the steel of the invention to provide adequate resistance to oxidation in the steel at high temperatures. However, the chromium must be kept belowabout 27% in order to avoid diiculties in fabrication from ingots to sheets, and also to avoid the presence of-ferrite in the steel. Since chromium is a strong ferrite former, the more chromium there is in the-steel the more difficult it is to maintain the desired austenitc structure in the steel. As has already been mentioned above, steel is much stronger at temperatures over about 1200" F. when its structure is austenite than when its structure is ferrite.

For the reason given above, the other ingredients in the steel in addition to chromium are present primarily to maintain `an austenitic structure in the Steel. Nickel, as is well known, is very effective in forming and maintaining an austenitic structure in high chromium steels, but since the steel of this invention is designed to be substantially free of nickel, I depend upon additions of other strong austenite formers,'namely, carbon, nitrogen and manganese. Of these, carbon and nitrogen are about equally effective, and much more eective than manganese. However, it 'is necessary to use an appreciable amount of manganese due to the limited solubili- 'ties of carbon and nitrogen in the steel. It is desirable also, from the standpoint of fabrication, to limit the carbon and nitrogen contents to maxima of about 0.80% C and about 0.50% N. When the steel contains chromium at about 21% and carbon and nitrogen at about 0.55% and 0.30%, respectively, the steel can be maintained in an aust'enitic structure with manganese at about 9%. However, when the chromium is at the upper limit of the range, that is about 27%, it is necessary to increase the carbon, nitrogen and manganese contents of the steel.

A (quick indication' of the relative amount of ferrite in Vthe steel of the invention is obtained by applying a magnet to the steel and observing its relative magnetic sus- Iceptibility. The tabulation of Table I below shows a comparisonof a number of compositions based on magmetio-susceptibility. To put the steels in the most stably Vausten'itic condition, the Ysamples rwhich wereV tested were Sfretchfdara`at`1400 to 1800 F.

Test p. s. i. Amount-'0f Bar Type l.'Ielp., Stress Stretch 'Type 446 l 1, 400 8.000 5.0% in y hr.

This Invention 1, 400 15, 000 0.9% in 20 hrs. Type 446 l 1, 600 4. 000 5.0% in b hr. This Invention- 1, 600 8, 000 1.0%'in20 hrs Type 446 1 1, 800 1, 000 2.0% in 1 hr. This Invention.; 1, 800 1, 000 0.5%'in 20 hrs 1,800 1, 000 0.7% in 20'h`rs 1 0.29 C; 0.5 Mn; 24.4 Cr; 0.23 N. 2 See Table I for compositions.

Thus it is seen that thesteel of this invention is' vmuch more resistant than Type 446 to 'stretching-over'the'temperature range 1400 to 1800 F.

That the oxidation resistance of the steel of 'this invention is of high magnitude is'shown by'the-dataf'of the following Table III.

TABLE III Scale resistance of steels at 21'00" F.

Weight Loss Alter 200 Hrs.

Y At Temperature Bar Type With Intermittent- Cooling t0 VRoom Temperature, Grams'per Type 310 0.117-1118 Type 446..- 0. S7-0; 74 This Invent 0. 44-0. 48 do 0. 4,541. 52 do OAG-0.50 dn 0. 73-0. 82

v,blown-See Table I for composition.

What is claimed is:

1. A rider sheet for use in normalizing furnaces and the like made of a substantially austenitic and substantially nickel free alloy steel having a relatively high resistance to deformation under stress at high temperatures and high resistance to oxidation at temperatures up to about 2100 F., said steel containing about: 2l to 27% chromium; 9 to 15% manganese; 0.55 to 0.8% carbon and 0.3 to 0.5 nitrogen, the sum of carbon and nitrogen being not less than about 0.92%; up to about 2.5% silicon; up to about 5% in aggregate of at least one element selected from the group consisting of vanadium, tungsten, and molybdenum With no one of these being over 2%; and the balance substantially all iron.

2. A rider lsheet for use in a furnace for normalizing low carbon steel sheet, said rider sheet being made of substantially austenitic and substantially nickel free alloy steel having a relatively high resistance to deformation under stress at high temperatures and a high resistance to oxidation at temperatures up to about 2100 F., said steel containing about: 23 to 25% chromium; 11 to 12% manganese; 0.6 to 0.7% carbon and 0.35 to 0.4 nitrogen; up to about 2.5 silicon; up to about 5% in aggregate of at least one element selected from the group consisting of vanadium, tungsten, and molybdenum with no one of these being over 2%; and the balance substantially all iron.

3. A rider sheet for use in a furnace for normalizing low carbon steel sheet, said rider sheet being made of a substantially austenitic and substantially nickel free alloy steel having a good resistance to deformation under stress at high temperatures and a high resistance to oxidation at temperatures up to about 2l00 F., said steel containing about: 21 to 27% chromium; 9 to 15% manganese; 0.55 to 0.8% carbon and 0.3 to 0.5% nitrogen, thesum of carbon and nitrogen being not less than about 0.92%; up to about 2.5% silicon; and the balance iron.

4. A rider sheet for use in a furnace for normalizing low carbon steel sheet, said rider sheet being made of a substantially austenitic and substantially nickel free alloy steel having a good resistance to deformation under stress at high temperatures and good resistance to oxidation at temperatures up to about 2100 F., said steel containing 7 about: 23 to 25% chromium; l1 to 12% manganese; 0.6

to 0.7% carbon; 0.35 to 0.4% nitrogen, up to Iabout 2.5 silicon; and the balance iron.

References Cited in the tile of, this patent UNITED STATES PATENTS 2,212,495 De Vries Aug. 27, 1940 2,380,854 Lorig July 31, 1945 2,496,247 Jennings Jan. 31, 1950 2,698,785 Jennings Jan. 4, 1955 FOREGN PATENTS 152,291 Austria Ian.' 25, 1938

Claims (1)

1. A RIDER SHEET FOR USE IN NORMALIZING FURNACES AND THE LIKE MADE OF A SUBSTANTIALLY AUSTENITIC AND SUBSTANTIALLY NICKEL FREE ALLOY STEEL HAVING A RELATIVELY HIGH RESISTANCE TO DEFORMATION UNDER STRESS AT HIGH TEMPERATURES AND HIGH RESISTANCE TO OXIDATION AT TEMPERATURES UP TO ABOUT 2100*F., SAID STEEL CONTAINING ABOUT: 21 TO 27% CHROMIUM; 9 TO 15% MANGANESE; 0.55 TO 0.8% CARBON AND 0.3 TO 0.5% NITROGEN, THE SUM OF CARBON AND NITROGEN BEING NOT LESS THAN ABOUT 0.92%; UP TO ABOUT 2.5% SOLICON; UP TO ABOUT 5% IN AGGREGATE OF AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF VANADIUM, TUNGSTEN, AND MOLYBDENUM WITH NO ONE OF THESE BEING OVER 2%; AND THE BALANCE SUBSTANTIALLY ALL IRON.

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