US3365922A - Method for producing hot-worked tellurium-containing steel article - Google Patents

Description

United States Patent 3,365,922 METHUD FOR PRGDUCENG HUT-WORKED TEL- LURlUM-CQNTAlNlNG STEEL ARTICLE Robert A. (lenses, Highland, and Louis Molnar, Hammond, Ind, assignors to Inland Steel Company, Chicago, llll., a corporation of Delaware No Drawing. Filed Feb. 1, 1965, fier. No. 429,612

13 Claims. (Cl, 72-38) ABSTRACT @F THE DESCLGSURE The diminution of surface checking in tellurium-containing steel during hot-working thereof by heating an unfinished form of the steel, before hot-working, in an atmosphere in which oxidizing gases, and especially water vapor, are minimized.

The present invention relates generally to methods for producing hot-worked steel articles, and more particularly to a method for producing a hot-worked, tellurium-containing steel article under conditions which minimize surface checking of the steel article.

A steel article normally undergoes a series of hotworking operations between the as-cast stage of the steel and the final marketable stage in which the steel is in the form of a bar, for example. Before each hot-working operation, the steel normally undergoes a heating operation to render the steel more susceptible to deformation. For example, assuming the steel to be initially cast into ingot form, the ingot is generally heated in what is known as a soaking pit prior to deformation of the ingot into an intermediate stage, such as a bloom; the bloom is typically subjected to a preheating operation before it is deformed by hot-rolling into a further intermediate stage, such as a billet; and the billet is typically subjected to a preheating operation before the billet is deformed by hotrolling into a bar. The ingot, the bloom and the billet are all unfinished forms of steel.

Tellurium is added to steel to increase the steels machinability. A problem associated with tellurium-containing steels is that these steels are susceptible to a hotworking-caused defect reflected in checking or cracking at the surface of the steel article undergoing hot-working.

Incident to the present invention, it has been determined that this hot-Working-caused defect in tellurium-containing steels is aggravated when the tellurium-containing steel is heated (prior to hot-working) in an oxidizing atmosphere, and that this is especially so when the atmosphere contains water vapor. In accordance with the present invention, hot-working-caused surface defects in telluriumcontaining steels are minimized by performing the heating operation, to which the telluriurn-containing steel is subjected prior to hot-working, in an atmosphere in which oxidizing gases are maintained at a minimum, and especially in which water vapor (other than the immediate product of combustion of fuels containing hydrocarbons) is minimized to less than three percent and preferably less than two percent, by volume.

The method of the present invention applies to tellurium-containing carbon and alloy steels, and the carbon or alloy steel may contain either or both of sulphur and lead as additional machinabilitydncreasing ingredients. Some typical examples of tellurium-containing steels, to which the present invention would apply, are described in Holowaty U.S. Letters Patent No. 3,152,889. Typical carbon steels to which tellurium may be added are disclosed on pages 817-18 of The Making, Shaping and Treating of Steel, United States Steel Corporation, Pittsburgh, Pa., 1957; and typical examples of alloy steels to which tellurium may be added are disclosed on pages ICC 827-9 of the same publication. More specifically the invention is applicable to tellurium-containing steels having a base composition (i.e., Without tellurium) identified by AISI Nos. 1018, 1040, 1045, 1117, 1213, 12L14, 1215, 4140, 4142 and 8620.

A typical sequence of hot-working operations for reducing tellurium-containing plain carbon steel from ingot form to bar form includes heating the ingot, in a soaking pit of conventional construction, until the steel is at a temperature in the range 2350-2400" F. and then subjecting the heated steel ingot to a hot-working operation to reduce the ingot to a bloom, with the steel undergoing hot-Working until the steel is typically at a temperature in the range 2080-2120" F.

Oftentimes, before the bloom can be further reduced in cross-section, it undergoes a decrease in temperature to a temperature level below that at which subsequent hot-working can be performed, so that the bloom must be subjected to further heating before it can be subjected to further hot-deformation. Accordingly, blooms are typically subjected to a reheating operation, in a reheating furnace of conventional construction, until the temperature of the bloom is in the range 19002200 F., following which the bloom is subjected to hot-working with the temperature of the bloom at the time hot-working thereof is finished being in excess of 1800 F.

The typical product of a hot-working operation having a bloom as its starting product is a billet. Before the billet is subjected to a hot-working operation, it is usually preheated, in a furnace of conventional construction, until the billet has a temperature in the range 1900-2200 F.; and the billet is then subjected to a hot-working operation which produces a bar, for example, and the temperature of the bar at the finish of the hot-Working operation is in the range 1750-2000" F.

The above-described heating and hot-working operations are typical for many tellurium-containing plain carbon steels, e.g., a plain carbon steel containing up to 0.13 wt. percent carbon, 0.80-1.20 wt. percent manganese, 0.04-0.09 Wt. percent phosphorus, 0.25-0.35 wt. percent sulphur, 0.15-0.35 wt. percent lead and 0.04-0.06 Wt. percent tellurium. Variations in heating and hot-working conditions may be necessary for particular compositions of steels.

As previously indicated, surface defects, resulting from hot-Working operations of tellurium-containing steels, are aggravated by the presence of an oxidizing gas, such as water vapor, in the atmosphere to which the steel is subjected during any of the above-described heating operations. Therefore, a method in accordance with the present invention comprises minimizing or eliminating the oxidizing gases in the heating atmosphere.

The optimum conditions would be to heat the tellurium-containing steel ingot or bloom or billet, or Whatever the shape may be, in an inert gas atmosphere (e.g., nit-rogen or a rare gas such as argon) or in an atmosphere consisting of endothermic gases (e.g., carbon monoxide or hydrogen) and utilize electricity as the heating medium (e.g., electric radiant heating coils). The use of radiant heating coils as the source of heat energy eliminates one source of the oxidizing gases, H 0 and CO both of which are the product of combustion of hydrocarboncontaining fuels such as natural gas, blast furnace gas, coke oven gas, or oil, all of which are typically used to fire furnaces normally utilized in the heating of steel articles preparatory to a hot-Working operation.

In situations Where the furnaces utilized for preheating are of a conventional construction and use natural gas, oil, blast furnace gas, etc., as fuel, the presence, in the furnace atmosphere, of some 11 0 resulting from combustion cannot be avoided. The H 0 content from a; combustion may be as high as 15%. Therefore, precautions should especially be taken to minimize other sources of water content within the furnace in which the heating operation is conducted.

More specifically, in a soaking pit in which the ingot is heated, water of condensation sometimes accumulates in the cooled-off soaking pit, between heating operations; and this water should be drained from the soaking pit prior to the heating of the ingot. In soaking pits of the regenerative type (typical embodiments of which are illustrated at pages 401-6 of The making, Shaping and Treating of Steel, supra) water will seep into the checkerboard lines through which air is passed for preheating prior to combustion with the fuel; and steps should be taken to minimize this seepage and/or to remove seepage water from the air fiues. Water may also accumulate in the fuel line leading to the soaking it, so that the fuel line should 'be drained periodically.

The same precautions described above with respect to ingot soaking pits should also be taken with respect to reheating furnaces for the blooms and billets. Typical embodiments of conventional reheating furnaces are disclosed on pages 406-11 of The Making, Shaping and Treating of Steel, supra. In billet-reheating furnaces having water-cooled skids, leaks in the skids can be a source of water vapor in the furnace atmosphere; and maintenance precautions should be exercised to prevent this.

Another precaution is to provide billets or blooms which are dry at the time they are placed in the reheating furnace. Often times, the billets or blooms are stored in outside locations where they are exposed to rain or snow, and the surface of the steel is wet at the time the reheating furnace is ready to receive the steel. To prevent the introduction of water vapor into the furnace through this medium, the billet or bloom surfaces should be dry and this can be accomplished by storing the billets or blooms indoors, or by subjecting the billets or blooms to a drying operation before putting them in the reheating furnaces.

Another factor to be considered in minimizing the water content within the reheating furnaces, is the use of wet blast furnace gas as a fuel in soaking pits or reheating furnaces. Blast furnace gas is conventionally subjected to a wetting operation following the withdrawal of the gas from the blast furnace. The purpose of the wetting operation is to remove certain impurities, and this operation leaves the gas supersaturated with water vapor. There fore, the blast furnace gas should be dried or dehumidified before utilizing it as a fuel in a soaking pit or reheating furnace. This can be accomplished, for example, by cooling the gas to condense the water vapor and reduce the H content of the gas.

Thus, extraneous H O (i.e., H O other than that which is the immediate product of combustion) should be prevented from becoming a part of the furnace atmosphere.

An optimum condition for a furnace atmosphere in which tellurium-containing steels are heated prior to hotworking is an atmosphere devoid of water, both extraneous and the product of combustion. If this optimum situation cannot be obtained, the extraneous water vapor should be kept out of the furnace atmosphere; and if this is not entirely possible, then the extraneous water vapor content should preferably be less than 2%, by volume, or, at the very most, less than 3%, by volume.

Therefore, by minimizing or eliminating the water vapor and/ or other oxidizing gases in the atmosphere of a furnace in which tellurium-containing steel articles are reheated before hot-working, surface defects on telluriumcontaining steels will be minimized.

The present invention is also applicable to minimize similar defects in selenium-containing steels or in steels containing both tellurium and selenium, these two elements being used interchangeably in steels for the same purpose.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. A method for producing a hot-worked steel article containing at least one ingredient selected from the group consisting of tellurium and selenium, said method comprising the steps of:

heating of an unfinished form of tellurium-containing steel, before hot-working, within a furnace, and to a hot-working temperature;

controlling the atmosphere in said furnace to minimize oxidizing gases in the furnace;

and then removing said unfinished form of telluriumcontaining steel from said furnace and subjecting said unfinished form of steel in a hot-working operation.

2. A method as recited in claim 1 wherein the atmosphere in said furnace in a gas selected from the group consisting essentially of inert gases and endothermic gases.

3. A method as recited in claim 2 wherein said heating is performed with radiant electric coils.

4. A method as recited in claim 1 and comprising:

heating said furnace with a combustible gas and air which produce water vapor as a product of combustion;

said atmosphere-controlling step comprising excluding extraneous water vapor from the furnace atmosphere.

5. A method as recited in claim 4 wherein the total water vapor content of the furnace atmosphere is no greater than 15% by volume.

6. A method as recited in claim 1 and comprising:

heating said furnace with a combustible gas and air which produce water vapor as a product of combustion;

carrying said combustible gas to the furnace through a gas line;

said atmosphere-controlling step comprising removing,

before said heating step, water which has accumulated in said gas line.

7. A method as recited in claim it and comprising:

heating said furnace with a combustible gas and air which produce water vapor as a product of combustion;

passing said air through a preheating flue in a regenerative checkerwork, on the way to said furnace;

said atmosphere-controlling step comprising removing water which has seeped into said preheating flues.

8. A method as recited in claim it and comprising:

heating said furnace with a combustible gas and air which produce water vapor as a product of combustion;

said atmosphere-controlling step comprising removing,

before said heating step, water which has condensed within said furnace.

9. A method for producing a hot-worked steel article containing at least one ingredient selected from the group consisting of tellurium and selenium, said method comprising the steps of:

heating an unfinished form of tellurium-containing steel, before hot-working, within a furnace, and to a hot-working temperature;

excluding extraneous water vapor from the atmosphere of said furnace;

and then removing said unfinished form of telluriumcontaining steel from said furnace and subjecting said unfinished form of steel to a hot-working operation;

whereby surface checking of the steel during hot-workis diminished.

10. A method for producing a hot-worked steel article containing at least one ingredient selected from the group consisting of tellurium and selenium, said method comprising the steps of:

heating an unfinished form of telluriumcontaining steel, before hot-Working, within a furnace, and to a hot'working temperature;

excluding water vapor from the atmosphere of said furnacep' and then removing said unfinished form of telluriumcontaining steel from said furnace and subjecting said unfinished form of steel to a hot-working operation;

whereby surface checking of the steel during hot-workis diminished.

11. A method as recited in claim ll wherein said atmosphere-controlling step comprises:

controlling the extraneoun water vapor content of the furnace atmosphere to less than 3%, by volume.

12. A method as recited in claim 1 wherein said at- 5 References Cited UNITED STATES PATENTS 2,914,434 11/1959 Snavely 266-2 3,098,776 7/1963 Elarde 148-16 3,169,857 2/1965 Rathke 75123 3,257,835 6/1966 Cofe-r et a1 7238 3,303,064 2/4967 Bernick et. a1. 14812.1

OTHER REFERENCES The Making, Shaping and Treating of Steel, US. Steel, 1957, p. 414.

0 RICHARD J. HERBST, Primary Examiner.

E. M. COMBS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,365,922 January 30, 1968 Robert A. Conces et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 11, for "making" read Making line 12, for "will" read may same line 12, for "checkerboard" read checkerwork column 4, line 15, for "in" read to column 5, line 13, for "extraneoun" read extraneous Signed and sealed this 18th day of March 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents