US1550489A - Heat-treated zirconium steel and process of making same - Google Patents

Description

creased hardness,

Patented Aug. 18, 1925.

UNITED STATES PATENT OFFICE.

FREDERICK M. BECKETAND ALEXANDER L. FEILD, NEW YORK, -Y., ASSIGNOCES TO ELECTED METALLURGICAL COMP- NY. A CORPORATION OF WEST VIRGINIA.

I HEAT-TREATED ZIRCONIUM STEEL AND PROCESS OF MAKING- SAME.

1% Drawing.

To all whom it may concern:

Be it known that we, FREDERICK M. BECKET and ALEXANDER L. FEILD, citizens of the United States of America, residing at 565 Park Ave, and 52 East 41st Street, respectively, New York, in the county of New York and State of New York, have invented.- certain new and useful Improvements in Heat-Treated Zirconium Steel and Processes of. Making Same, of which the following is a specification.

This invention relates manufacture and comprises a process for heat-treating steel containing zirconium whereby is obtained a product possessing mechanical properties of a superior order of.merit. The invention comprises also, as a novel product, a heat-treated steel, sin1i lar in composition to an ordinary carbon steel except for the presence therein'of a small percentage-of zirconium, (with or without small percentages of certain other alloying elements as hereinafter more fully described) yet which possesses properties hitherto obtainable only in the so-called alloy steels containing in customary amount (that is to say, the sum of the alloying elements usually upward-of one per cent) one,

or more of the well known alloying elements such as chromium, nickel, vanadium, and molybdenum. These results are attained, in accordance with the present invention, by

the heat-treatment of a steel having a zir-' conium content, said zirconium being incorporated in the molten steel bath during the rocess of manufacture. Optimum treating conditions in so far as now known are hereinafter set forth.

As is Well known, it is possible by the heat-treatment of steels of the grades known as forging, tool, or spring steels to obtain products possessing a wide range of properties. Generally speaking, the higher the temperature employed I to dl aw or temper a given quenched steel, the greater is the ex tent to which the initial properties of the quenched steel are altered in the direction of increased ductility and toughness, de-

and lowered tensile strength. In the manufacture of heat- .treated forgingsand rolled products a temporing or drawing temperature is commonly employed whichresults in'such balancing of the various mechanical properties as appears, from practical experience and theto the art of steel Application filed January 25, 1923. Serial No. 615,438.

oretical considerations, to be most desirable and advantageous from the standpoint of serviceability or engineering design, or both. In the automobile and air-craft industries, in particular, the properties obtainable by the employment of the various commercial alloy steels in the heat-treated state have been especially desirable, due among other things, to the obvious advantages of decreased weight and the ability of such steels to Withstand severe service conditions.

We have found it possible, in accordance with the present invention, so to improve the properties of an ordinary carbon steel by the incorporation therein of a small percentage of zirconium followed by suitable heat-treatment that the resulting heattreated product has properties much more nearlycomparable to those of the more 8X pensive heat-treated alloy steels to which reference has'already been made.

The effect of zirconium, employed under conditions as specified below, is exhibited in a tendency to maintain the ductility of the steels, as indicated by per cent reduction '350450 C. The desired effect is brought about in marked degree by the presence in the steel, for instance, of about 0.15 per cent zirconium in the case of a steel of about 0.70 per cent carbon content. As a preferred range of zirconium content we would specify from 0.04 to 0.40 per cent zirconium, although we do not consider the present invention to be restricted to any particular range ofcontained zirconium.

There exist -a multiplicity of methods, familiarto those skilled in-the art, bywhich the zirconium may be incorporated in the molten steel. It is preferably added to the steel (for example in the furnace or ladle), in the form of an alloy with silicon, or in the form of an alloy or aggregate containing zirconium and silicon. But our invention is not limited to the use of zirconium in conjunction with silicon, or to its introduction in the form of an alloy.

The table which follows contains under columns I and II the results of tests con ducted on two steels tapped from the same electric furnace heat. The steels analyzed 0.70 per cent carbon, 0.62 per cent manganese, 0.026 per cent phosphorus, and 0.03 per cent 5 sulphur. They were identical in com sition and manner of treatment except that the steel described under column I contained 0.15% zirconium, incorporated in the molten steel in the form of an alloy of iron, silicon 1 and zirconium, (ferrosilicon-zirconium).

Columns I and II contain the results obtained' b drawing, at five different tem era tures, t e steels previously quenche in water from 825 C. The zirconium-treated 1 and the untreated steels were, for each temerature of draw, heat-treated simultaneousiy and with every precaution to secure uniformity of pract ce to the end that the test data might be strictly comparable. M

TABLE 0.70% carbon without zirconlum Drawing temperature Per cent elongation $0 Per cent reduction claret..- Yield point, lbs. sq. in Ultimate strength, lbs. sq. in-

Izod number, lt.-1bs. Brinell hardness Drawing temperature", Per cent elongation Per cent reduction of area. Yield point, lbs. sq. in Ultimate strength lbs. sq. in- Izod number, tt.-lbs v Brinell hardness Drawing temperature....

Per cent elongation Brinell hardness Drawing temperature Per cent elongation Per cent reduction 0! area.. Yield point, lbs. sq. in Ultimate strength, lbs. sq. in Izod number, it.-lbs Brlnell number Drawing tem tnre.....

Per cent elongation.

The Izod numbers given under columns I and-II were obtained by tests conductedwith 5 a 120 ft-lb. Izod machine, using a testpiece of 10 b 10 mm cross-section, a 2-mm. 45 notch with 0.01 inch radius at' the bot: tom, and a'striking distance of 0.866 inches.

The notch was out after the test pieces were heat-treated." .Itiwill bea arent to those familiar with this art that t e properties-of the zirconiumtreated steel, as given in column I, closely approach those 0 certain alloy steels. For convenience of comparison we have given in ,quenched steels during the temperingiproc- The Izod numbers for the steel of column III are not available. It is, however, certainly true that the'zirconium-treatedsteel above described has a value for notch-toughness (Izod number) which falls not far below that of a nickel-vanadium or chromevanadium steel tempered to produce approximately the same ultimate strength and duetility 1 We have also conducted comparative experiments onheat-treated carbon steels containing both more and' less than 0.7 0 per cent of carbon, with and without a zirconium content, and have found beneficial effects due to zirconium similar to those above de scribed. We conclude therefore that our discovery is applicable broadly to the heattreatment of carbon steels containing zirconium.

The most notable improvement brought about by zi'rconiumoccurs, as can be seen,

in that range of drawing temperatures associatedwith the formation of troostite in the finished product, 350450 C.

. An advantageous manner of practicing the invention is to draw (ltemper) the steel in a furnace, for examp e of the electric 0 muiile type, in such manner thatthe heattreated parts are'brought u to the temperature of the furnace by re. iation from the walls, and thereafter allowed to remain at this temperature for an appreciable period,

say 15 minutes for a standard testpiece;

then remove and allow to cool in air. Suchtreatment has given decidedly better results both in the zirconium-treated and themtreated (control) steel than a 15-minute draw in a lead bath at corresponding temperatures. Evidently the rate of heating during the draw, or the time of draw, or both, have an important efl'ect upon the transformations occurring in the steel. Just what is the exact optimum procedure, however, is a'question which must be determined for each kind and grade of steel b means of a simple series of tests ofthe c aracter usually applied for this purpose.

, The structural changes occurring in ess are not yet fully understood. the

'- present state of knowledge relating. to this narrower range of temperature than is possible in steel not contalning zirconium, and

probably before the appearance of an appreciable amount of sorbite.

There are a large number of chemical elements which if present in steels in sufficient quantity, either singly or in combination, give rise to compositions which are technically known as alloy steels. It will be understood that steels as produced industrially are rarely if ever entirely free from all these elements. Certain of the alloying elements, for example silicon and manganese, are normal constituents of carbon steels as now made, but the quantities present in such carbon steels are insufiicient to produce the characteristic alloy steels of these elements. Most or all of the other alloying elements are at times present in small quantities in steels which are nevertheless universally designated as carbon steels. In many cases such elements are introduced fortuitously, it being impracticable to exclude them completely from the raw materials, including steel scrap, which make up the furnace charge.

VVeregarcl as within the scope of our invention all heat-treated steels containing zirconium and containing other alloying elements in less than their normal alloying proportions when such steels are characterized by substantially higher ductility than is characteristic of zirconium-free steels of comparable composition, strength, and hardness; and we make no exception to. the foregoing when the alloying element or elements (other than zirconium) are intentionally added to produce a special efiect.

We claim:

1. A heat-treated carbon steel containing zirconium and characterized by substantially higher ductility as indicated by percent reduction of area than is characteristic of zirconium-free steels of comparable strength and hardness.

2. A heat-treated carbon steel containing 0.0i..to' 0.40 per cent zirconium and characterized by substantially higher ductility as indicated by per cent reduction of area than is characteristic of zirconium-free steels of comparable strength and hardness.

3. Heat-treated steel containing zirconium in association with an alloying element or elements, the latter in less than normal alloying proportion.

4. Heat-treated steel containing 0.04 to 0. .0 per cent zirconium in association with an alloying element or elements, the latter in less than normal alloying proportion.

5. The herein described process comprising introducing zirconium into a carbon steel, and heat-treating the product, whereby it acquires a substantially higher duc tility as indicated by per cent reduction of area than is characteristic of zirconiumfree carbon steels of comparable strength and hardness.

6. The herein described process comprising introducing 0.04 to 0.40 per cent zirconium into a carbon steel, and heat-treating the product, whereby it acquires a substantially higher ductility as indicated by per cent reduction of area than is characteristic of zirconiunrfree carbon steels of comparable strength and hardness.

7 The herein described process comprising introducing into a steel zirconium and an alloying element or elements, the latter in less than normal alloying proportion, and

-heat-treating the product.

8. The herein described process comprising introducing into a steel 0.04. to 0.40 per cent zirconium and an alloying element or elements, the latter in less than normal alloying proportion, and heat-treating the product.

In testimony whereof, we aiiix our signatures.

FREDERICK M. BECKET. ALEXANDER L. FEILD.