US2793969A

US2793969A - Method for scarfing steel

Info

Publication number: US2793969A
Application number: US580498A
Authority: US
Inventors: Werner Ephraim
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-04-25
Filing date: 1956-04-25
Publication date: 1957-05-28
Anticipated expiration: 1974-05-28

Description

E. WERNER METHOD FOR SCARFING STEEL May 28, 1957 Filed April 25 mvENToR 0MM/M Me/Vf@ ATTORNEY METHOD FOR SCARFING STEEL Ephraim Werner, Pittsburgh, Pa. Application April 2S, 1956, Serial No. 589,498

12 Claims. (Cl. 14S-9.5)

This invention relates to a method for simultaneously scarng all surfaces of a semi-finished steel shape, without using a blowpipe or a gang of blowpipes, thereby removing simultaneously all surface defects. The expression semi-linished steel shapes includes ingotst, billets, slabs, blooms, bars, plates and the like. By the expression surface defects or surface imperfections it is meant to include seams, cracks, laminations, scabs, snakes, slag inclusions, scale and the like.

Heretofore, the removal of surface imperfections or defects from semi-finished steel shape surfaces has been accomplished primarily with cutting blowpipes or torches, either manually operated or machine operated in gang formations. Attempts have been made to obviate the necessity for the use of blowpipes or torches by, exposing steel shapes at elevated temperatures to chemical reactants such as gaseous hydrogen sulfide or ammonium sulfide and to phosphorus containing reactants to form the corresponding iron compound layer which is then removed from the respective surfaces by chipping or by Sandblasting. However, with these compounds undesirable chemical reactions including carburizing or nitriding or phosphiding of the shape of steel, including its alloying elements, at its surfaces is obtained, and the handling of the aforesaid reactants at velevated temperatures is time consuming and diicult as compared to the handling of inert gases and oxygen gas. Further, in view of the fact that there is always present a certain amount of iron oxide on the semi-finished shape surfaces, it has heretofore been found necessary to subject the shape surfaces to a reducing media prior to treatment with the reactant in order to obtain good results. In the removal of surface defects with blowpipes or torches, it too has been heretofore found necessary to expose the shape surfaces to be treated to a reducing gas by projecting thereagainst reducing flames to break through the adherent oxide layer and then, after the reduction of the oxide to molten iron, to project immediately an oxygen stream thereagainst while the iron is in a molten state and the surface of the shape is at a kindling or ignition temperature.

I have discovered that surface defects or imperfections can be easily and economically removed from the surfaces of semi-finished steel shapes of the type hereinbefore described Without the use of blowpipes or torches and without the use of diicult-to-handle chemical reactants. l have accomplished this removal of surface defects or imperfections by exposing the shape to a substantially pure oxygen gas atmosphere or to an atmosphere containing substantially pure oxygen gas and an inert gas While the shape was at the critical ignition temperature of the steel at which temperature there Was formed a layer of iron oxide of such a composition, and including FeO, FezO3, and Fe304, that its thermal coeiiicient of United States Patent cubical expansion value is sufficiently less than the thermal "lce coeicient of cubical expansion of the steel to cause the steel upon cooling to separate cleanly from the oxide upon cooling.

ln carrying out my method, a semi-finished shape of steel is placed inside a high temperature reactor furnace, is heated to the critical ignition temperature of the steel, and is then exposed simultaneously at all surfaces to a substantially pure oxygen gas atmosphere While it is maintained at the critical ignition temperature of the steel within the furnace, which is at all times vented to the atmosphere. The oxygen gasV atmosphere is preferably maintained by continuously flowing the oxygen gas into the furnace, and the shape is so exposed for a predetermined time. In this way, all the surfaces of the shape are simultaneously exposed to, or blanketed with, the oxygen gas, and there is formed at the surfaces of the shape a non-adherent substantially continuous and contiguous layer of oxide which, upon the simultaneous cooling of the shape and of the layer, is loose with respect to the shape and falls from the surfaces of the shape, leaving the surfaces substantially free from all imperfections therein. In my process, the entire shape, and not only the surfaces of the shape, is heated to the critical ignition temperature of the steel, and the shape is exposed to the substantially pure oxygen gas atmosphere at all points of the surfaces thereof simultaneously rather than to a single jet or plurality of jets of oxygen gas While it is held at that critical ignition temperature, thus preventing the formation of molten metal at any time during the carrying out of my process of removal of the surface imperfections. When the steel is heated to its critical ignition temperature and exposed to the oxygen gas While at that temperature, it combines with the oxygen so rapidly that it actually burns forming an inner oxide composition which has an average molecular heat of formation ranging from approximately 269,000 to 271,000 gram calories which causes an increase in the temperature of the shape at the surfaces thereof. Because the shape, in my process, is heated to the critical ignition temperature of the steel throughout its entire mass andI the shape is blanketed with the oxygen gas, no moltenmetal is formed at the surfaces of the shape and 'the temperature is almost immediately equalized throughout the entire mass of the shape. The critical ignition temperature values of the various types of steels range from approximately 1900 F. to approximately 2400 F., and, my method accomplishes the removal of surface defects from or scarring' of semi-nished shapes of steel alloys including carbon steels, chromium-nickel steels, nickel-containing steels, and the like.

l have also found that, in the removal of surface defects from the surfaces of a semi-finished steel shape having an unusually large number of imperfections therein or imperfections therein of unusually large sizes in accordance With my process, it is preferable to expose the semi-finished steel shape to an inert gas atmosphere While heating it to the required temperature prior to exposure to the pure oxygen gas atmosphere. The semi-linished steel shape is placed inside the high temperature reactor. While', the steel shape is being brought to the preferred temperature, inert gas is continuously owed into the furnace to form an inert gas atmosphere. The steel shape is maintained Iat this temperature, and the pure oxygen gas is continuously ilowed into the furnace to replace the inert gas and to form an atmosphere of substantially pure oxygen gas. Where the semi-finished shape is rst exposed to an yinert gas atmosphere prior to being exposed to thev pure oxygen gas atmosphere, the surfaces of the. shape are exposed actually to an atmosphere of pure oxygen gas and inert gas until the inowing oxygen gas completely replaces the inert gas being vented from the furnace to the atmosphere.

Upon the removal of the treated steel shape, in all instances, from the furnace and upon the cooling thereof, an oxide layer of substantially constant thickness fell from the steel shape at all l'points on all surfaces thereof, and the surface defects formerly present had been corn- Vpletely removed from the surfaces of the steel shape.

The thermal coefficient of cubical expansion of a substance is the change of volume of a unit volume of the substance per degree rise in temperature of said substance.

By the expression inert gas it is meant to include such gases as helium, argon, krypton, and the like and .simultaneously scarfing all surfaces of a semi-finished steel shape without the use of blowpipes or torches.

Other objects and features will become apparent from the following description.

Figure l is a view partially in cross-section of the apparatus, including the high temperature reactor furnace, used for scarring the surfaces of the semi-finished steel shape.

More specifically, the high temperature reactor furnace 1 is an electrical type furnace and comprises an outer steel casing 2 having a high temperature refractory lining 3 forming an open top cylindrical heating chamber or hearth 4 in which are mounted silicon carbide glow-bar heating elements 5, 5, 5, 5. In the furnace wall is opening 6 to receive a refractory plug 7 in which is mounted a thermocouple 8 for recording the hearth temperatures and thus the surface temperatures of the semi-finished steel shape 9. On the hearth bottom 10 are positioned refractory support members 11, 11 for the steel shape 9. In the furnace wall adjacent the hearth bottom 10 is a passage opening 12 into the hearth 4 at the bottom thereof for receiving a gas inlet member 13 for connection to .the inert gas source and to the oxygen gas source. The gas inlet member 13 is in the shape of a T and head of the T has therein valves 14 and 15 at the opposite ends thereof for connection to the inert gas source and to the oxygen gas source, respectively. The flow of the respective gases into the reactor furnace is controlled by the opening and closing of said valves 14 and 15 depending on the gas to be passed thereinto. By opening valve 14 and closing valve 15, the inert gas will p'ass into the lreactor furnace, and by closing valve 14 and opening valve 15 the oxygen gas will pass into the reactor furnace. The .rate of ow of each of the respective gases was measured by flow gauges (not shown) positioned in the respective lines and calibrated in liters per minute. Positioned in the open end of the reactor is the refractory lined cover 16 having the vent passage 17 therethrough. The furnace temperature is raised or lowered, as the case may be, by controlling the line voltage with a powerstat 18.

I have determined that the amount of surface metal including the surface defects therein removed from the surfaces of the semi-finished steel shape is dependent upon the amount of pure oxygen gas introduced into the furnace to react with the steel at the critical ignition temperature of the steel and that the thickness of the oxide layer formed at the surfaces of the steel shape depends both upon the amount of pure oxygen gas introduced into the furnace to react with the steel at the said temperature and on the length of time to which the steel shape is exposed to the gas atmosphere. The partial pressure of the oxygen gas is maintained at the highest possible level at all times within the reactor preferably by constantly feeding` the oxygen gas thereinto at a con-4 EXAMPLE l A billet sample having a substantially square crosssection and substantially rectangular sides, weighing 1.855 pounds and having a surface area of 177 -square centimeters was positioned in the high temperature reactor furnace on the support blocks therein. The billet sample had several slight cracks approximately 0.012 to 0.014 inch deep on the surfaces thereof. The cover, having the venting means, was then positioned in the open end of the furnace, and the billet sample was vheated to a temperature of approximately 2000 F.

Upon the billet sample and the furnace reaching the temperature of approximately 2000 F., commercially pure oxygen gas was continuously flowed into the furnace at the rate of l0 liters per minute for 45 minutes, thereby maintaining the oxygen pressure at the highest possible level at all times within the furnace, and the temperature of the billet sample was maintained constant at approximately 2000 F. during this time period. The oxygen gas flow was then stopped, the billet sample was removed from the furnace and allowed to cool. Upon cooling, an oxide layer of uniform thickness loosened and fell from the surfaces of the so-treated billet sample, and the surfaces previously having the cracks therein were now entirely free from said cracks. The sample was allowed to cool on supports mounted on the plate of a scale. The weight of the treated sample including the voxide formed was 1.895 pounds; the weigh-t of the oxide formed was 0.175 pound; the weight of the scarfed billet sample was 1.72 pounds; the average thickness, determined by averaging ten thickness values of the oxide thickness, was 0.0410 inch; and weight of the oxide in pounds per square centimeter of area was 0.000989 pound per square centimeter.

EXAMPLES 2 AND 3 A second billet sample and a third billet sample were each exposed to an atmosphere of commercially pure oxygen gas and scarfed according to the process described in Example 1. The surfaces of each billet sample, prior to treatment, had several slight cracks approximately 0.012 to 0.014 inch deep on the surfaces thereof. The second billet sample was exposed to the oxygen atmosphere for minutes, and the third billet sample was exposed to the oxygen atmosphere for 45 minutes. Table I sets forth Examples 2 and 3 in tabular form. The second and third billet samples also had a substantially square cross-section and substantially rectangular sides. The surfaces of the treated billet samples were free of cracks.

T able l Example 2 3 Temperature, F. app. 2,000 app. 2.000 Rate of oxygen how, liters/min. at S. T. 10 1U Initial Weight of Sample, ll s 1.885 5. 7l Final Weight of Sample, lbs 1. 940 'In Weight of oxide layer formed, lbs... O. 220 r). 2U Weight of sample less, oxide layer, lbs l. 72 40 Weight of oxide por unit 0l surfe sample, lbs/em.2 0. 001220 0. 000933 Thickness of oxide, inches. U. 0576 0. 040B Surface atea of sample, om! 180 295 Time of exposure of sample to oxygen, m1nutes 90 45 5 EXAMPLES 4, s, AND. isY

A fourth billet sample, having several cracks at its surfaces, and having a substantially square cross-.section and substantially rectangular sides was positioned in the furnace on the support blocks therein, and the cover was then positioned in the open end of the furnace. Argon gas was then flowed thereinto at a rate of 5 liters per minute, and the heating of the furnace, and the billet sample therein, was commenced immediately upon the flowing of the argon thereinto. The rate of flow of the argon was kept constant throughout the heating of the billet sample. Upon the billet sample reaching the temperature of approximately 2000 F., the ow of argon was stopped, and commercially pure oxygen was flowed into the furnace at a constant rate of flow to replace the inert gas and to form an oxygen gas atmosphere therein. By passing the oxygen gas into the furnace at a constant rate of ow the oxygen partial pressure was maintained at the highest possible level at all times within the reactor. The treated billet was removed after exposure to the oxygen gas atmosphere, and the formed oxide layer fell from the billet upon the cooling of said layer and said billet, leaving the surfaces free of cracks. A fifth billet sample and a sixth billet sample were each treated in accordance with the treating process of the fourth billet sample to obtain surfaces free from defects. However, in the desurfacing of the surfaces of said fifth and sixth billet samples, the Vrates of flow of the oxygen gas in'to the furnace were lowered and increased, respectively. Table II sets forth Examples' 4, 5 and 6 'in tabular form. Y

Table Il Example 4 5 6 Temperature, "F app. 2,000 app. 2,000 app. 2,000 Rate of oxygen flow, litcrs/ n.

at; S. T. P 10 5 15 Initial Weight of Sample, lbs. 5. 93 7. 69 8.50 Final Weight of Sample, lbs 6.00 7. 73 8. 56 Weight of oxide layer formed, lbs. 29 0. 30 0.32 Weight of sample less oxide layer,

lbs 5. 71 7. 43 8. 24 W eight of oxide per unit of surface area ei sample, lbs./em.2. 000983 0.000865 0. 000869 Thickness of oxide, inches. 0. 0459 0.0339 0. 0380 Siu-ffice area of sample, cm.2 295 370 3&5 Time of exposure of sample to Oxygen, minutes 45 45 45 EXAMPLES 7, 8, 9 and l0 A seventh billet sample, an eighth billet sample, and a ninth billet sample, were each exposed to a commercially pure oxygen gas atmosphere in accordance with the process of Examples 4, and 6 used to treat the fourth, iifth, and sixth billet samples, respectively. Here, however, each of the samples was heated to approximately 1800" F. Each of the billet samples had slight cracks approximately 0.012 to 0.014 inch deep on the surfaces thereof. Upon removal of each of the billet samples from the furnace and upon cooling there was observed an adherent oxide layer which was removed by chipping. Each of the respective surfaces was free from cracks.

A tenth billet sample having slight cracks approximately 0.012 to 0.014 inch deep on the surfaces thereof was exposed to a commercially pure oxygen gas atmos phere in accordance with the process of Examples l, 2 and 3 used to treat the iirst, second, and third billet samples. However, this tenth sample was heated to approximately 1800" F. Upon removal of this billet sample from the furnace and upon cooling there was observed an adherent oxide scale which was removed by chipping. Each of the surfaces was free from icracks.

Table III setsforth Examples 7, 8, 9, and 10 in tabular form.

Table III Example 7 8 9 k10 Temperature, F-. app.f1,'800 app. 1,800 app. 1,800 app. 1, 800 Rate of oxygen flow,

liters/mm. at B. T.

P ..v 10 -5 15 10 Initial Weight V01! Sample, lbs 3. 59 10. 78 2. 295 3. 53 Final Weight of A Y Y Sample, lbs 3. 61 10. 82 2. 31 3. 50 Weight of oxide layer formed, 1bs 0. 09 0.016 0.08 0. 10 Weight of Sample less oxide layer,

lbs 3. 52 10. 66 2. 23 3. 40 Weight of oxide per unit of surface area of sample, lbs./

cm.2 0. 000409 0. 000363 0. 000457 0. 000454 Thickness of oxide,

inches 0.0192 0. 0142 0. 0189 0. 0180 Surface area of sample, 0111.2 220 440 220 Time of exposure of sample to oxygen,

minutes 45 45 45 45 EXAMPLES 11, 12, 13 AND 14 An eleventh billet sample, a twelfth rbillet sample, and a thirteenth billet sample, each having slight cracks approximately 0.012 to 0.014 inch deep, were exposed to a commercially pure oxygen gas atmosphere in accordance with the process of Examples 4, 5 and 6 used to treat the fourth, fth, and sixth billet samples, respectively. Here, however, each of the samples was heated to approximately 1500 F. Upon removal of each ofthe billet samples from the furnace and upon cooling there was observed a tightly adherent oxide layer which was removed by chipping. Each of the surfacesrstill had therein slight cracks which, however, were shallower than they were prior to exposure to the oxygen gas atmosphere.

A fourteenth billet sample having slight cracks approximately 0.012 to 0.014 inch deep on the surfaces thereof was exposed to a commercially pure oxygen gas atmosphere in accordance with the process of Examples l, 2, and 3 followed in the treatment of the first, second, and third billet samples. This sample was heated to approximately l500 F. Upon removal of this billet sample from the furnace and upon cooling there was observed a tightly adherent oxide layer which was removed by chipping. Each of the surfaces still had therein slight cracks which, however, were shallower than they were prior to exposure to the oxygen gas atmosphere.

Table IV sets forth Examples l1, l2, 13, and 14 in tabular form.

Table IV Example 11 12 13 14 Temperature, F app. l, 500 app. 1,500 app. 1, 500 app. 1, 500 Rate of oxygen iiow,

liters/min. at S. T.

P: 5 10 15 10 nitial Weight o Sample, lbs 5.49 10.67 8.25 7. 50 Final Weight of Sample, bs 5. 50 10.69 8.26 7. 51 Weight of oxide layer formed, lbs 0. 01 0.02 0.01 0.01 Weight of sample less oxide layer, lbs. 5. 49 10. 67 8. 25 7. 50 Weight of oxide per unit of surface area oisample, lbs/cmi 0.0000340 0.0000454 0. 0000270 0. 0000290 Thickness of oxide,

inches 0.005 0.005 0.005 0. 005 Surface area of sample, om.2 295 440 370 345 Time of exposure of sample to oxygen,

minutes 45 45 45 45 In all cases, the oxide layer Was uniform in appearance.

The heat analysis of the steel of each of the fourteen Ybillet samples was as follows:

The scarfng of each of the billet samples here was lcarried out under conditions approximating actual mill conditions rather than under exacting laboratory conditions.

My process here set forth is capable of being carried out for the scarfing of any size semi-finished steel shape, and the determination of the period of exposure of the billet to be scarfed to the oxygen gas atmosphere is readily and easily determinable by any worker of ordinary skill in the art who Will become aware of my proc- 'ess set forth herein.

In instances where the surface defects will be comparatively deep, it may be necessary to carry out my process several successive times.

For scarfing only one surface of a semi-finished steel shape, a furnace similar to that of Figure 1 having an opening in the wall thereof to receive the surface of the shape can be used.

Many alterations and changes may be made without departing from the spirit and the scope of my invention here described and set forth in the appended claims which are to be construed as broadly as possible in view of the prior art.

I claim:

l. A method of removing surface imperfections simultaneously from all surfaces of a semi-finished shape of steel comprising heating said shape to the critical ignition temperature of the steel, simultaneously subjecting all of the surfaces of said shape at said critical ignition temperature to substantially pure oxygen gas for a predetermined time thereby forming on all of said surfaces a contiguous layer of oxide having a thermal coefficient of cubical expansion smaller than the thermal coefficient of cubical expansion of the steel, and cooling the semi- Vfinished shape of steel, thereby causing the so-formed layer of oxide to separate from the shape of steel at the surfaces thereof, to remove a predetermined quantity of steel from all surfaces including the imperfections.

e u l r 2. A method of removing surface imperfections simultaneously from all surfaces of a semi-nished shape of steel comprising heating said shape to the critical ignition temperature of the steel, blanketing said shape at said critical ignition temperature with substantially pure oxygen gas for a predetermined time thereby forming on all of said surfaces a contiguous layer of oxide having a thermal coeicient of cubical expansion smaller than the thermal coeicieiit of cubical expansion of the steel, and cooling the semi-finished shapeof steel, thereby causing the so-formed layer of oxide to separate from the shape of steel at the surfaces thereof, to remove a predetermined quantity of steel from all surfaces including the imperfections.

3. A method of removing surface imperfections simultaneously from all surfaces of a ysemi-finished shape of steel comprising heating said shape to the critical ignition temperature of the steel in :an inert gas atmosphere, simultaneously subjecting all of the surfaces of said shape at said critical ignition temperature to substantially pure oxygen gas for a predetermined time thereby forming on all of said surfaces a contiguous layer of oxide having a thermal coeicient of cubical expansion smaller than the thermal coeicient of cubical expansion ofthe steel, thereby causing the so-formed layer of oxide to separate from the shape of steel at the surfaces thereof, to remove a predetermined quantityof steel ing the imperfections.

4. Amethod of removing surface imperfections simultaneously/from all surfaces of a semi-finished shape of steel comprising heating said shape to the critical ignition temperature of the steel in an inert -gas atmosphere, blanketing said shape at said critical ignition temperature with substantially pure oxygen gas for a predetermined time thereby forming on all of said -surfaces a contiguous layer of oxide having a thermal coefficient of cubical expansion smaller than the thermal coeflicient of cubical expansion of the steel, and cooling the semi-finished shape of steel, thereby causing the so-formed layer of oxide to separate from the shape of steel at the surfaces thereof, to remove. 'a predetermined quantity of -steel from all surfaces including the imperfections.

5. A method of removing surface imperfections simultaneously from all surfaces of a semi-finished shape of steel comprising heating said shape to a predetermined temperature and subjecting lsimultaneously all of said surfaces of said shape at said predetermined temperature to substantially pure oxygen gas for a predetermined time, thereby forming a contiguous layer of oxide on all of said surfaces, said temperature being of such value that the thermal coeflcient of cubical expansion of said steel at said predetermined temperature is sufficiently greater than the thermal coefficient of cubical expansion of said oxide in the form of the layer so as to enable the steel upon cooling to separate from the so-formed oxide upon cooling, thereby allowing the so-formed oxide to separate from the steel shape at the lsurfaces thereof to remove a predetermined quantity of steel from all surfaces including the imperfections.

6. A method of removing surface imperfections simultaneously from all surfaces of a semi-finished shape of steel comprising heating said shape to the critical ignition temperature of the steel and simultaneously subjecting all of the surfaces of said shape at said critical ignition temperature to substantially pure oxygen gas for a predetermined time thereby forming a layer of oxide having a thermal coefficient of cubical expansion value at said temperature suiciently less than the thermal coefficient of cubical expansion value of said steel so as to enable the steel upon cooling to separate from the so-formed oxide upon cooling to allow the so-formed layer of oxide to separate from the shape at the surfaces thereof to remove a predetermined quantity of steel from all surface-s including the imperfections.

7. A method of removing surface imperfections simultaneously from all surfaces of a semi-finished shape of steel comprising simultaneously exposing all surfaces of said shape held at the critical -ignition temperature of the steel to substantially pure oxygen gas for a predetermined time thereby forming on all of said surfaces a contiguous layer of oxide having a thermal coefficient of cubical expansion value sufficiently less than the thermal coeicient of cubical expansion value of said steel so as to enable the steel upon cooling to separate from the so-formed oxide upon cooling to :allow the so-formed layer of oxide to separate from the shape at the surfaces thereof to remove a predetermined quantity of steel from all surfaces including the imperfections.

8. A method of removing surface imperfections simultaneously from all surfaces of a semi-finished shape of steel comprising placing said Vshape in a high temperature reactor furnace, bring-ing said shape to the critical ignition temperature of the steel of said shape Within said furnace, and flowing substantially pure oxygen gas into said furnace While said shape is held at said critical ignition temperature of said steel of said shape, thereby forming on all of said surfaces a contiguous layer of oxide having a thermal coeicient of cubical expansion value sufficiently less than the thermal coefficient of cubical expansion value of said steel Aso as to enable the steel upon cooling to separate from the so-formed oxide upon cooling from all surfaces includto allow the so-formed layer of oxide to separate from the shape at the surfaces thereof to remove a predetermined quantity of steel from all surfaces including the imperfections therein.

9. A method of simultaneously scaring all surfaces of a semi-finished shape of steel comprising placing said shape in a high temperature reactor furnace, simultaneously bringing said shape to the critical ignition temperature within said furnace and continuously flowing an inert gas into said furnace, and owing substantially pure oxygen gas into said furnace while Isaid shape is held at the said critical ignition temperature of said steel, thereby replacing said inert gas, and thereby forming on all of said surfaces a contiguous layer of oxide having a thermal coeicient of cubical expansion value suiciently less than the thermal coeicient of cubical expansion value of said steel so as to enable the steel upon cooling to separate from the so-formed oxide upon cooling to allow the so-formed layer of oxide to separate from the shape at the surfaces thereof to remove :a predetermined quantity of steel from all surfaces including the imperfections therein.

10. A method of -simultaneously scarting all surfaces of a semi-finished shape of steel comprising heating said steel shape to the critical ignition temperature of the steel in -an inert gas atmosphere within a high temperature reactor furnace and exposing said steel to a substantially pure oxygen gas atmosphere while said shape is at said critical ignition temperature of said steel within said high temperature reactor furnace, thereby removing a predeter- CTI mined quantity of steel from all surfaces of said shape including the imperfections therein.

11. A method of simultaneously scarting all surfaces of a semi-finished yshape of steel comprising placing said shape in a high temperature reactor furnace, bringing said shape to the critical ignition temperature of the steel within the furnace, and flowing substantially pure oxygen gas into said furnace while said shape is held at the said critical ignition temperature of the steel, thereby forming a non-adherent oxide layer on all of the surfaces of said shape and thereby removing a predetermined quantity of steel from :all surfaces of said shape including the imperfections therein.

12. A method of simultaneously scarling all surfaces of a semi-finished shape of steel comprising subjecting an inert gas preconditioned semi-iin-ished shape of steel to substantially pure oxygen gas While said shape is at the critical ignition temperature of the steel, thereby forming a non-adherent layer of oxide on the surfaces of said shape and thereby removing a predetermined quantity of steel from said surfaces of said shape including the imperfections therein.

References Cited in the tile of this patent UNITED STATES PATENTS 1,090,469 Friedrich Mar. 17, 1914 2,282,163 Burgwin May 5, 1942 2,389,838 Bromberg Nov. 27, 1945 2,494,791 Arnoldy Ian. 17, 1950

Claims

1. A METHOD OF REMOVING SURFACE IMPERFECTIONS SIMULTANEOUSLY FROM ALL SURFACES OF A SEMI-FINISHED SHAPE OF STEEL COMPRISING HEATING SAID SHAPE TO THE CRITICAL IGNITION TEMPERATURE OF THE STEEL, SIMULTANEOUSLY SUBJECTING ALL OF THE SURFACES OF SAID SHAPE AT SAID CRITICAL IGNITION TEMPERATURE TO SUBSTANTIALLY PURE OXYGEN GAS FOR A PREDETERMINED TIME THEREBY FORMING ON ALL OF SAID SURFACES A CONTIGUOUS LAYER OF OXIDE HAVING A THERMAL COEFFICIENT OF CUBICAL EXPANSION SMALLER THAN THE THERMAL COEFFICIENT OF CUBICAL EXPANSION OF THE STEEL, AND COOLING THE SEMIFINISHED SHAPE OF STEEL, THEREBY CAUSING THE SO-FORMED LAYER OF OXIDE TO SEPARATE FROM THE SHAPE OF STEEL AT THE SURFACES THEREOF, TO REMOVE A PREDETERMINED QUAMTITY OF STEEL FROM ALL SURFACES INCLUDING THE IMPERFECTIONS.