US3710608A

US3710608A - Method for heating unfinished tellurium-containing steel articles before hot rolling

Info

Publication number: US3710608A
Application number: US00094282A
Authority: US
Inventors: R Hentz; G Henger
Original assignee: Inland Steel Co
Current assignee: Inland Steel Co
Priority date: 1970-12-02
Filing date: 1970-12-02
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16
Also published as: BE776027A; DE2157512A1; ES397586A1; BR7107898D0; IT943131B; CH545147A; DE2157512B2; FR2117249A5; AU3620771A; JPS523325B1; DE2157512C3; AR196484A1; LU64360A1; NO133938C; NL7116228A; ZA717939B; DK136256C; AT324387B; GB1365718A; NO133938B

Abstract

Heating tellurium-containing steel billets, before hot rolling, by moving the billets along a path in a furnace having an oxidizing atmosphere. Providing and maintaining a gas blanket around the billets to protect them from surface oxidation along the hotter portions of the path. Combusting the blanket gas at a cooler portion of the path before the gas is exhausted from the furnace.

Description

United States Patent 1 Hentz et al.

[54] METHOD FOR HEATING UNFINISHED TELLURIUM-CONTAINING STEEL ARTICLES BEFORE HOT ROLLING [75] Inventors: Ronald D. llentz, Crown Point, lnd.;

Gary W. llenger, Homewood, Ill.

[73] Assignee: Inland Steel Company, Chicago, Ill. 22 Filed: nec.2,1910

[21] Appl. No.: 94,282

[52] US. Cl. ..72/38, 72/364, 72/700 [51] Int. Cl. .132") 9/00, 821d 31/00 [58] Field of Search ..72/38, 200, 202, 342, 364, 72/365, 700; 263/6, 52

[.56] References Cited .UNITED STATES PATENTS l l 1966 Schrader et al. ..72/364 1 Jan. 16, 1973 3,345,846 10/1967 Hess ..72/364 3,365,922 l/l968 Conces'et a1... ..72/38 3,399,873 9/ I968 Dybal et a]. ..263/6 3,382,700 '5/1968 Heitmann et al.. .....72/364 3,503,240 3/1970 Lawler ..72/ 364 Primary Examiner-Charles W. Lanham Assistant Examiner-E. M. Combs Attorney-Merriam, Marshall, Shapiro & Klose 57 ABSTRACT Heating tellurium-containing steel billets, before hot rolling, by moving the billets along a path in a furnace having an oxidizing atmosphere. Providing and maintaining a gas blanket around the billets to protect them from surface oxidation along the hotter portions of the path. Combusting the blanket gas at a cooler portion of the path before the gas is exhausted from the furnace.

9 Claims, 1 Drawing Figure METHOD FOR HEATING UNFINISHED TELLURIUM-CONTAINING STEEL ARTICLES BEFORE HOT ROLLING BACKGROUND OF THE INVENTION The present invention relates generally to methods for heating unfinished tellurium containing steel articles, such as billets, prior to hot rolling, and more particularly to a method for heating these articles in a manner which deters surface tearing of the articles during hot rolling. As used herein, the term unfinished steel article includes not only billets, but also other intennediate steel shapes such as blooms.

The addition of tellurium to steel enhances the machinability of the steel, but steel containing tellurium undergoes a surface defect known as surface tearing, during hot rolling of the steel. Surface tearing is manifest by small cracks on the surface of the article undergoing hot rolling. These cracks occur during hot rolling and are concentrated at the corners of bars having polygonal cross sections and at sharp locations in ovals being hot rolled into rounds. Surface tearing renders the finished article commercially unacceptable.

Surface tearing is to be distinguished from other types of surface defects, such as those manifest by cracks in the unfinished steel article as it exits from the reheating furnace, before hot rolling.

Prior to the hot rolling of unfinished steel articles into finished articles such as rounds, hexagons, or other polygonal shapes, the unfinished articles are subjected to a reheating operation, which typically comprises moving the billets through an elongated furnace heated by burners. Surface tearing is influenced by this reheating operation which conventionally occurs in a furnace having an oxidizing interior atmosphere. An oxidizing atmosphere is generally desirable from a fuel efficiency standpoint, but an oxidizing atmosphere oxidizes a surface layer on the article, and this results in complications which contribute to surface tearing of telluriumcontaining steels.

The problem of surface tearing in tellurium-containing steels has previously been noted, and attempts to combat surface tearing include reheating the steel article without flame impingement on the surface of the article (U.S. Pat. No. 3,287,954, Schrader et al.), reducing the moisture content in the atmosphere of the reheating furnace (U.S. Pat. No. 3,365,922, Conces et al.) and removing the surface and first sub-layer of the unfinished article, e.g., by scarfing, after reheating (U.S. Pat. No. 3,382,700, Heitmann et al.).

Typical examples of tellurium-containing steel are disclosed in the above-noted U.S. patents and in Holowaty U.S. Pat. Nos. 3,152,889 and 3,152,890.

SUMMARY OF THE INVENTION Surface tearing during hot rolling, and surface oxidation or scaling during heating prior to hot rolling, are deterred by a method in accordance with the present invention.

The unfinished, tellurium-containing steel articles move along a path in an elongated reheating furnace extending from a relatively cool furnace entry to a relatively hot furnace exit. The steel articles are heated during this movement with several longitudinally spaced flames each originating at a respective burner located above the path.

A continuous blanket of gas (e.g., natural gas) is provided around the articles undergoing heating in the furnace, to protect the surface of the articles from oxidation. This blanket extends from the furnace exit toward the furnace entry. At least one of the article-heating flames originates near the furnace exit. The gas in the blanket is introduced into the furnace, also near the exit, beneath the flame there. The gas in the blanket moves upstream from the furnace exit toward the entry without substantial mixing of the blanket gas with other gas entering the furnace at the burner where the flame originates.

In the furnace, combusted gases are removed from the furnace at an exhaust opening located upstream of the exit; and the blanket gas is burned, in the furnace, before the blanket gas is exhausted. Burning of the blanket gas is conducted at a location in the furnace where the temperature is relatively low, compared to the temperature at the furnace exit, and where surface oxidation or scaling of the tellurium-containing steel article is not a significant problem.

The blanketgas is combusted by introducing oxygen into the furnace at a location between the exhaust opening of the furnace and the furnace exit (where the blanket gas is introduced). The furnace is provided with a flame originating at a burner located between the exhaust opening and the location where the oxygen is introduced, to assure combustion of the blanket gas before it is exhausted. This prevents flame in the exhaust conduit leading from the furnace, as would take place if the blanket gas were not combusted before it left the furnace.

Other features and advantages are inherent in the method claimed and disclosed or will become apparent to those skilled in the art from the following detailed description in conjunction with the accompanying diagrammatic drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view illustrating a furnace DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, there is illustrated generally, at 10, an elongated furnace in which tellurium-containing steel billets 11 are heated prior to hot rolling. Billets 11 are moved along a furnace path 12 extending from a furnace entry 13 to an exit 14.

The billets are heated, as they move along path 12, by flames originating at a number of burners longitudinally spaced along path l2. One flame l5 originates at a burner 25 located at the exit end 30 of furnace l0 and disposed above billets 11 on path 12. Also located above path 12 are flames l6, l7 originating at

respective burners

26, 27; and located below path 12 is flame l8 originating at burner 28. The direction and length of the flames are controlled so that they do not impinge upon the surface of billets ll.

The flames are generated by the combustion of conventional fuel (e.g., natural gas) and oxygen (using either commercially pure oxygen or air), and com-- busted gases are exhausted through an exhaust opening 20, in the top of furnace 10, between entry 13 and the burner 27, in this particular embodiment the burner located closest to entry 13. Gases exhausted through exhaust opening 20 are carried away through an exhaust conduit 21.

The atmosphere within furnace is generally slightly oxidizing. For example the fuel to oxygen ratio, on a stoichiometric basis, is generally about 0.95. This is desirable to assure combustion, in the furnace, of the maximum amount of combustible fuel. If all the fuel were not combusted within the furnace (e.g., some fuel being combusted in exhaust conduit 21) less than the full heating potential of the fuel would be realized in the furnace.

Although an oxidizing atmosphere in the furnace is desirable from a fuel efficiency standpoint, it contributes to the problem of surface tearing of telluriumcontaining steel billets during subsequent hot rolling.

In accordance with the present invention, a continuous blanket of gas is provided around billets 11, to protect the surface thereof from oxidation. The gas in this blanket is introduced into the furnace at nozzle 22; and the blanket extends from furnace exit end 30 toward entry 13. In this particular embodiment, the blanket terminates just before that part of path 12 under flame 17.

The blanket gas is typically natural gas, such as methane, although higher hydrocarbons such as butane, tetrane, ethane and pentane may be used. Carbon monoxide is permissible but not as desirable as the hydrocarbons. Hydrogen should not be used because it is too explosive.

There is a movement of all gases, in furnace 10, from exit end 30 toward exhaust port 20. This movement is essentially horizontal from exit end 30 to about wall 31 mounting burner 27. In addition, the blanket gas, injected at nozzle 22, is at a location below the elevation of

burners

25, 26, 27 where the combustion gases (fuel and oxygen) are introduced. These two factors prevent mixing of the oxygen from the burners with the blanket gas, thereby preventing the blanket gas from being burned off and maintaining the blanket for a substantial distance upstream of exit end 30. The blanket gas introduced at nozzle 22 does not rise to any substantial extent to intermingle with the gases introduced at burners 25-27 or nozzle 23 until the blanket gas is well upstream along path 12, adjacent burner 27 where the blanket gas is combusted with oxygen introduced at a nozzle 23, to be described subsequently.

The temperature of furnace 10 is hottest at exit end 30 and the temperature decreases gradually upstream along path 12 toward entry 13. For example, the furnace temperature at exit end 30 is typically in the range 2,2002,500F. and the billet temperature is typically in the range 2,l002,300F. At a location along path 12 just below burner 27, the furnace temperature is in the range l,8002,000F., and the billet temperature is in the range l,600-l ,700F.

The billets are subjected to maximum surface oxidation in the hottest parts of the furnace. As the furnace temperature decreases, there is a reduction in surface oxidation and its resultant adverse contribution to surface tearing during subsequent hot rolling. Therefore, it is important that the blanket of gas be maintained around billets 11 in the hottest part of the furnace, with the importance of blanket maintenance decreasing as the furnace temperature decreases.

The blanket gas is exhausted through exhaust opening 20 just as are the combusted gases resulting from the combustion of fuel and oxygen introduced at burners 25-28. Because of the heat in exhaust conduit 21, especially that portion adjacent exhaust opening 20, any unburned blanket gas exiting through exhaust opening 20 would combine with any excess oxygen or air exiting through exhaust opening 20 and would be burned in conduit 21, causing flames therein. This is undesirable, and, in accordance with the present invention, the blanket gas is combusted in furnace 10 before exiting through exhaust opening 20.

Combustion of the blanket gas is accomplished by introducing oxygen, at nozzle 23 located above path 12 between exit end 30 and exhaust opening 20. The oxygen from nozzle 23 is injected downwardly toward and mixes with the gas blanketing billets 11. Because flame 17 is located between oxygen injection nozzle 23 and exhaust opening 20, flame l7 assures substantially complete combustion of the blanket gas and the oxygen before they reach exhaust opening 20. By preventing uncombusted blanket gases from passing through exhaust opening 20, the likelihood of combustion occurring in exhaust conduit 20 is reduced.

Because surface oxidation of the tellurium-containing steel billets increases progressively as the temperature rises, it is desirable to burn off the blanket as far back in the furnace, i.e., as close to entry 13, as is possible. The closer to entry 13, the lower the temperature. Because the combustion of the blanket gas occurs at a location (adjacent burner 17) along billet path 12 where both the furnace temperature l ,8002,000F.) and the billet temperature (l,600l,700F.) are relatively low, the danger of surface oxidation where the blanket gas is combusted in minimal.

In a typical embodiment, the blanket gas is composed of 98 percent methane and about 2 percent higher hydrocarbons, such as ethane. The blanket gas is introduced at a rate in the range 40-80 cubic feet per minute. At burners 15-18, the fuel is introduced at a rate of 2,000 cubic feet per minute and the air at a rate of 20,000 cubic feet per minute, a volume ratio of air to fuel of 10 to 1. Oxygen introduced at nozzle 23 is introduced at a rate of about 500 cubic feet per minute.

Typical dimensions for furnace 10 are 45 feet wide and 100 feet long. The vertical dimension between path 12 and furnace roof 19 vary from 3 feet high at the low point 32 of the roof and 12 feet high at the high point 33 of the roof.

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 processing unfinished tellurium-containing steel articles so as to deter surface tearing during hot rolling, said method comprising the steps of:

moving said articles downstream along a path, in a furnace, extending from a relatively cool entry to a relatively hot exit;

heating said articles, as they move along said path,

with a flame originating above said path and without impinging said flame on said articles; providing a continuous, non-oxidizing blanket of combustible gas around said articles undergoing heating, to protect the surface thereof from oxidation, said blanket extending from said exit toward said entry;

and removing the heated articles from said furnace and hot rolling them.

2. A method as recited in claim 1 wherein:

said flame originates adjacent the exit of the furnace;

and the gas in said blanket moves upstream from said exit toward said entry end without substantial mixing of said blanket gas with other gas entering said furnace where said flame originates.

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

moving the gas in said blanket upstream toward said entry;

exhausting combusted gases from said furnace at an exhaust opening located upstream of said exit;

and burning said blanket gas in said furnace before the blanket gas is exhausted.

4. A method as recited in claim 3 wherein:

said burning is conducted at a location in the furnace where the temperature is relatively low compared to the temperature at said exit and where surface oxidation of the billets is not a significant problem.

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

moving the gas in said blanket upstream toward said entry;

exhausting gases from said furnace at an exhaust opening located upstream of said exit;

introducing oxygen into the furnace at a location between the exhaust opening and the exit;

and combusting said oxygen with said blanket gas before they are exhausted.

6. A method as recited in claim 5 wherein said last- 10 recited step comprises:

' 8. A method as recited in claim 7 and comprising:

providing said furnace with a flame originating adjacent said exit and extending upstream therefrom;

the gas for the blanket being introduced into said furnace at a location below said flame.

9. A method as recited in claim 1 wherein said combustible gas is a hydrocarbon.

Claims

2. A method as recited in claim 1 wherein: said flame originates adjacent the exit of the furnace; and the gas in said blanket moves upstream from said exit toward said entry end without substantial mixing of said blanket gas with other gas entering said furnace where said flame originates.
3. A method as recited in claim 1 and comprising: moving the gas in said blanket upstream toward said entry; exhausting combusted gases from said furnace at an exhaust opening located upstream of said exit; and burning said blanket gas in said furnace before the blanket gas is exhausted.
4. A method as recited in claim 3 wherein: said burning is conducted at a location in the furnace where the temperature is relatively low compared to the temperature at said exit and where surface oxidation of the billets is not a significant problem.
5. A method as recited in claim 1 and comprising: moving the gas in said blanket upstream toward said entry; exhausting gases from said furnace at an exhaust opening located upstream of said exit; introducing oxygen into the furnace at a location between the exhaust opening and the exit; and combusting said oxygen with said blanket gas before they are exhausted.
6. A method as recited in claim 5 wherein said last-recited step comprises: providing said furnace with a flame originating between the exhaust opening and the location where said oxygen is introduced.
7. A method as recited iN claim 1 and comprising: introducing said gas for said blanket into the furnace adjacent the exit thereof.
8. A method as recited in claim 7 and comprising: providing said furnace with a flame originating adjacent said exit and extending upstream therefrom; the gas for the blanket being introduced into said furnace at a location below said flame.
9. A method as recited in claim 1 wherein said combustible gas is a hydrocarbon.