US2724647A - Steel and article for high temperature uses - Google Patents

Description

United States Patent 2,724,647 STEEL AND ARTICLE FggsHIGH TEMPERATURE Martin Fleischmann, Canton, Ohio, assignor to The Timken Roller Bearing Company, Canton, Ohio, a corporation of Ohio 1 No Drawing. Application March 26, 1953, Serial No. 344,901

Claims. (Cl. 75-428) carbon, and nickel in an amount such as to render the alloy austenitic, suitably about 14 to 35 per cent, with the remainder essentially iron. Those alloying elements are, r

in accordance with the invention of that patent, balanced with relation to one another so that the. alloys. are free from delta iron when quenched from about 2150 F. Manganese may be present within the amounts normal to such steels but because it assists in the production of'austenite the preferred embodiment contains from about 1 to 2 per cent of manganese. Silicon may likewise be present in normal amounts and although somewhat largeramounts may be present to increase oxidation resistance silicon should not exceed about 2 per cent. Preferably, those steels contain also from about 0.05 to about 0.25 per cent of nitrogen.

The preferred embodiment of that patent contains 1 about 16 per cent of chromium, per cent of nickel,

and 6 per cent of molybdenum, in consequence of which the steels of the patent arecornmonly referred to as 16-25-6. Because of their outstanding creep and rupture strengths at high temperatures, many millions of pounds of the l6-256 steels have been used during the past ten years in the production of turbine wheels for jet engines, either to constitute the entire wheel or, more recently, as rims for welding to hubs of more lightly.

alloyed steels, and in the production of aircraft supercharger wheels and such other high temperature parts as gas turbine elements. The 16-25-=6 steels have performed admirably for such purposes as indicated by the extent of use just stated. However, the large amount of nickel contained in them coupled with the increasing demand forl6-25-6 steels constitutes a serious drain of nickel which is presently a critical metal in short supply. It would be desirable and advantageous,.therefore, to provide comparable room and high temperature properties by the use of lower amounts of nickeL.

It is among the objects of .thisinvention toprovide. articles for use at high temperatures which possess a combination of desirable mechanical properties atroom temperature, coupled with creep and rupture strengths at elevated temperatures at. least comparable to those of 16-256 steels.

Another object is to provide austenitic steels for the production of such articles. and which require the use of substantially lower amounts of nickel than are requisite in 16-25 6 steels. j

Yet another object is to proyide articles and steels in accordance with the foregoing objects and which possess 2,724,647 Patented Nov. 22, 1955 ductility at high temperatures greatly superior to that of 16-25-6 steels- Other objects will appear from the following specification.

This invention is predicated upon my discovery that its stated objects are attained by greatly lowering the nickel content and greatly increasing the manganese content in comparison with 16-25-6 steels. Further in accordance with the present invention, the maximum carbon content is decreased likewise, the maximum being 0.1 per cent. In the practice of this invention the new alloys comprise about 10 to 20 per cent of chromium and 4 to 8 per cent of molybdenum. In contradistinction to the 16-25-6 alloys, however, the alloys of this invention contain only about 10 to 20 percent of nickel, while the manganese ranges from 5 to 10 per cent. These essential elements are balanced, as exemplified by. the preferred composition described hereinafter, to be austenitic and to be free from delta iron when quenched from 2150 F. In general, to this end, the nickel content is increased with increase in the content of chromium and molybdenum, and vice versa.

The remainder of the new steels consists of iron, together with impurities and elements in amounts which do not essentially alter the characteristics of the steels as just described. Silicon may be present in amounts normal to such steels, and although somewhat larger amounts may be present, the silicon should not exceed about 2 per cent, and preferably not over about 1 per cent.

The alloys may, and with advantage will, contain nitrogen also because it tends to produce a fine primary grain structure which is beneficial to the forging properties. Also, it is productive of precipitation hardening properties, which improves the high temperature strength, and of particular importance, nitrogen tends to stabilize the austenite. The amount of nitrogen present is largely a function of the chromium content, with which it combines to form a nitride. Although exact limits can not be fixed which are applicable to all purposes, I now believe that for, all practical purposes these steels may contain from about 0.1 to 0.2 per cent of nitrogen. This element may be introduced readily in the production of these alloys by the use of high nitrogen ferrochrome.

In the preferred embodiment of the invention the steels contain not over about 0.08 per cent of carbon, about 15 to 17 per cent of chromium, about 7 to 8 per cent of manganese, about 5 to 7 per cent of molybdenum, about 14 to 16 per cent of nickel, and about 0.1 to 0.2 per cent of nitrogen. Preferably the silicon content is 1 per cent, or less. t

The alloys are preferably produced in an electric furnace.

Experience has shown that these alloys are exceedingly stiff under the forging hammer, and that at temperatures above about 2200 F. they tend to break up under the hammer. However, they may be forged satisfactorily at a temperature of about 2100 F. t t

In the as-forged or as-rolled condition these alloys contain an appreciable amount of a complex carbide phase which is distributed Widely throughout the entire strucalso, there is no evidence of the presence of the Sigma 1 phase. Likewise, the microstructures are similar to those of the 1625-6 steels. However, the hot roller strength proximately the same results.

V at room temperatures of the new steels is greater than mately those of 16-25-6. Hot-rolled steels of this invention undergo recrystallization beginning at about 1900 F.', while maximum ductility at room temperatures is developed by solution treatment at 2150 F. followed by quenching; for example, material in accordance with thepreferred embodiment when treated in that manner showed 50 per cent elongation in 2 inches and reduction of area of 68 per cent.

These alloys being austenitic, it is necessary to subject them to cold work for the development of maximum room temperature properties and optimum creep resistance and rupture strength at elevated temperatures. This may be accomplished by giving the hot wrought articles an equalizing treatment involving heating at about l900 to 2100 F. to effect recrystallization, followed by quenching. They arethen cold worked, suitably at an elevated temperature but below the recrystallization temperature, i. e., not over about 1700 F.

. Cold worked articles made from these new steels forge more easily. than the 16-256 steels in the sense that they are subject to less cracking during forging although the power requirements are about the same. Likewise, 'theyshow less tendency to crack under high stresses at high temperatures. Presumably these results are attributable to the fact that the new steels show ductility at elevated temperatures much superior to that of the 16-25-6 alloys at a given stress and time exposure. Additionally, after being solution quenched, as described above, the new steels possess mechanical properties at room temperature closely comparable to those of 16-25-6 steels; the same thing is true of creep resistance.

The outstanding characteristic of my new steels is their excellent ductility both at room and at high temperatures. As evidencing this reference will be made to tests of an electric furnace heat in accordance with the preferred embodiment of the invention. The analysis of the steel was as follows:

Per cent 0.07 "Cr 16.16 Mn 7.10 MO 6.10 Ni 15.60 'N 0.168 Si I 0.42 P v 0.016 s 0.009

' in steps to 4-inch squares, to 2%-.inch squares, and finished to l A-inch by'% -inch bars.

Test specimens were cut from the finished bars and subjected to cold stretching, after being given a solution treatment at 2150 F. followed by quenching. As

-quenched the room temperature tensile strength was about 107,000 p. s. i. and the elongation was about 45 percent. Stretching of the bars up to 30 per cent elongation followed by tempering 4 hours at 1300 P. re-

sulted in progressive increase in tensile strength to about 135,000 p. s. i., with the elongation decreasing to about 24 percent; tempering hours at 1300'? F. produced ap- The yield strength (0.2% offset) increased from about 57,000 p. .s. i. .in theasquenched condition to 103,000 ,p. s. i. at 3 per cent elon- .gation by 'cold stretching. The results demonstrate the exc'ellent'room temperature ductility of these new steels.

Standard specimens for rupture strength tests were prepared also from the hot rolled bars, solution treated at 2150 F. and quenched. The following table shows these alloys to possess excellent rupture strength under stress at high temperatures.

. 6 Stress, Time, Elongation, Red. Area, Temp" p. s. 1. Hrs. percent percent As evidencing the fact that the ductility of these steels at high temperature reference is made to the following data comparing the foregoing tests results with those obtained with 16-25-6 at the same temperatures and stresses:

I Time to Elonga- Red. Steel 3 Rupture, tion,pcr- Area,

Hrs. cent percent 1, 60,000 21 17. 0 21. I 1,100 00, 000 64 21. 5 60. 5 l, 100 50, 000 226. 5 9. 0 16. 7 1,100 50. 000 549. 0 13. 5 15. 0 1,300 25,000 203 10.0 18.5) This invention.... l, 300 25, 000 d 781. 5 6%. 1 16-2 1,400 20,000 106 15.5 24 1 This invention... 1, 400 20,000 92 63. 0 62. 5

These data show that the ductllity of these new steels is greatly superior at any given stress and temperature to that of 16-25-6.

In addition to this outstanding and important improvement in ductility, amajor feature of the invention is that it reduces by about 40 per cent the amount of nickel needed in the 16-25-.6 steel.

According to the provisions of the patent statutes, 1 have explained the principle and mode of practicing my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A wrought steel article formed from an iron alloy comprising about 10 to 20 per cent of chromium, about 5 to 10 per cent of manganese, about 4 to 8 percent of molybdenum, about 10 to 20 per cent of nickel, not over about 0.1 per cent of carbon, and the remainder iron together with impurities and elements in amounts which do not essentially change the character .of the alloy, and characterized by being austenitic and free from delta iron when quenched from about 2150" F. and by high creep and rupture strengths and ductility under stress at a temperature of 13.00 .F.

.2. An article according to claim 1, the alloy containing also not'over about :2 per cent of silicon.

3. An article according'to claim 1, the alloy containing also about 0.1 to 0.2 per cent of nitrogen.

4. A wrought steel article formed from an iron alloy comprising about '15 to "17 percent of chromium, about 7 to '8 per cent of manganese, about 5 to 7 per cent of molybdenum, about 14 to 16 per cent of nickel, not over about 0.08 per cent of carbon, and the remainder iron together with impurities'and elements in amounts which do not essentially change the character ,of the all y, and characterizedby being austenitic and freefromdelta iron when quenched ,from about 2150 F. and by high creep and rupture strengthsand ductility understress at a temperature 0151300" F.

5. An article according to claim 4, the alloy also containing not over about I per cent of silicon, and about 0.1 to 0.2 per cent of nitrogen.

6. An iron alloy comprising about 10 to 20 per cent of chromium, about 5 to 10 per cent of manganese, about 4 to 8 per cent of molybdenum, about 10 to 20 per cent of nickel, not over about 0.1 per cent of carbon, and the remainder iron together withimpurities and elements in amounts which do not essentially change the character of the alloy, and characterized by being austenitic and free from delta iron when quenched from about 2150 F. and by high creep and rupture strengths and ductility under stress at a temperature of 1300 F.

7. Alloy according to claim 6, the alloy containing also not over about 2 per cent of silicon.

8. Alloy according to claim 6, the alloy containing also about 0.1 to 0.2 per cent of nitrogen.

9. An iron alloy comprising about 15 to 17 per cent of chromium, about 7 to 8 per cent of manganese, about 5 to 7 per cent of molybdenum, about 14 to 16 per cent of nickel, up to about 0.08 per cent of carbon, and the remainder iron together with impurities and elements in amounts which do not essentially change the character of the alloy, and characterized by being austenitic and free from delta iron when quenched from about 2150 F. and by high creep and rupture strengths and ductility under stress at a temperature of 1300 F.

10. Alloy according to claim 9 containing also not over about 1 per cent of silicon, and about 0.1 to 0.2 per cent of nitrogen.

References Cited in the file of this patent UNITED STATES PATENTS 2,159,725 Franks May 23, 1939 2,398,702 Fleischmann Apr. 16, 1946 2,602,738 Jennings July 8, 1952

Claims (1)

1. A WROUGHT STEEL ARTICLE FORMED FROM AN IRON ALLOY COMPRISING ABOUT 10 TO 20 PER CENT OF CHROMIUM, ABOUT 5 TO 10 PER CENT OF MANGANESE, ABOUT 4 TO 8 PER CENT OF MOLYBDENUM, ABOUT 10 TO 20 PER CENT OF NICKEL, NOT OVER ABOUT 0.1 PER CENT OF CARBON, AND THE REMAINDER IRON TOGETHER WITH IMPURITIES AND ELEMENTS IN AMOUNTS WHICH DO NOT ESSENTIALLY CHANGE THE CHARACTER OF THE ALLOY, AND CHARACTERIZED BY BEING AUSTENTIC AND FREE FROM DELTA IRON WHEN QUENCHED FROM ABOUT 2150*F. AND BY HIGH CREEP AND RUPTURE STRENGTHS AND DUCTILITY UNDER STRESS AT A TEMPERATURE OF 1300*F.