Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
  • C21D1/32—Soft annealing, e.g. spheroidising
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
  • C21D1/76—Adjusting the composition of the atmosphere
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling

Definitions

• ABSTRACT A process for making flat steel files wherein a highcar- [52] US Cl 72/203, 72/364, 72/365, bOn Steel is hot rolled on a wide strip mill and coiled. 75/24 R, 148/12 The coil is given a spheroidizing anneal and slit into [51] Int. Cl B2lb 3/02 bar and cut into flat bar stock. File blanks are cut [58] Field of Search 148/2, 12; 72/203, 204, from the flat bar stock and ground to remove a pure 72/364, 365; 76/24; 75/123 iron surface caused by the anneal. Thereafter, the file teeth or grooves are cut and the file hardened.
• An object of this invention is to provide a new and improved process for making flat steel files, and more particularly to an improved hot rolling procedure for making the flat bar stock from which files are made.
• the process utilizes a wide strip which not only simplifies and reduces the hot rolling costs, but further simplifies and reduces the costs encountered by the file 3O manufacturer.
• Another object of this invention is to provide a new process for hot rolling high-carbon steel flat stock as used for the manufacture of flat steel files.
• a further object of this invention is to provide a new process for manufacturing flat steel files.
• the steel is not hot rolled into billets and then hot rolled into flat bar stock on a merchant mill, but rather the steel is first hot rolled into slabs and then hot rolled on a wide strip mill to 0.080 to 0.160 inch and coiled while hot.
• l-lot rolling of the slab should be commenced at a sufficient temperature, usually about 2,l00 F, so that rolling should be completed at a temperature about l,600 F.
• the strip is coiled at a preferable temperature of 1,2001,300 F, but in no event should the strip be allowed to cool below l,000' F prior to coiling. After coiling, the strip may be allowed to cool to ambient temperatures.
• the cooled coil of hot rolled strip will be hard and brittle due to the pearlite microstructure containing carbides. In fact, the coil will be too brittle to open without cracking. Therefore, the strip is softened while coiled with a suitable spheroidizing anneal. Specifically, the coil is box annealed in a reducing atmosphere at a temperature just above the A, critical temperature, i.e., just above about l,330 F, to austenitize the pearlite. Specifically, I prefer to anneal within the range 1,350 to l,380 F for a period of at least 2 hours.
• the coil must be cooled slowly within the reducing atmosphere to a temperature well below the A, critical temperature to promote the precipitation of spheroidized carbides. Specifically, I first cool the coil at a rate of about 40 F per hour to the A, critical temperature of 1,330 F, and thereafter cool at a rate of about 20 F per hour through the critical temperature to about 1,250 F during which time the spheroidized carbides will precipi- 0 tate. After the carbides are precipitated, the cooling rate is of no great concern, but the coil should be retained in the reducing atmosphere for as long as necessary to prevent surface oxidation, i.e., to below 400 F.
• the annealing atmosphere must be reducing in nature in order to eliminate the mill scale formed athot rolling. That is, the mill scale, being primarily oxides of iron, will be reduced to a metallic iron film on the strip surface by the reducing atmosphere.
• the carbon content of the steel be retained and, therefore, decarburizing conditions during the anneal must be avoided.
• the annealing step should be effected as fast as possible to minimize decarburization and yet achieve a well spheroidized structure.
• the annealing atmosphere have a dewpoint of less than +15 F in order to minimize decarburization. Because of the presence of the mill scale, however, the dewpoint of less than +l5 F may be difficult to maintain because the mill scale reduced with hydrogen produces water. To eliminate this problem, 1 start the anneal without any dewpoint adjustments, heating the coil in a reducing atmosphere until a temperature of 1,100 F is reached. By the time l,l00 F is reached, all of the mill scale will be reduced to iron, while only a very slight surface decarburization will be effected, on the order of 0.001 to 0.002 inch at most.
• the strip is uncoiled and slit into the desired widths, and cut into lengths of flat bar stock. Prior to slitting, the strip may be given a light roll to eliminate coil set, if so desired.
• the process of this invention actually requires more steps to produce the cut lengths of flat bar stock than does the prior art process. Specifically, this process requires coiling, annealing and slitting steps not practiced by the prior art. These extra steps do of course mean added expense in producing the flat stock.
• the use of a conventional wide strip mill for hot rolling as compared to hot rolling the individual small bars on a merchant mill does provide a very substantial savings, far more than sufficient to offset the expenses of the added steps.
• the steel mill can supply annealed cut lengths of flat bar stock to a file manufacturer at a substantially lower cost than the unannealed flat bar stock produced by the prior art method.
• the file grooves or teeth are cut and the metal rehardened according to prior art practices, i.e., the individual files are immersed into a molten lead bath at l,450 F and held for about 3 or 4 minutes, and then quenched in a saturated brine solution until cold.
• the process of this invention would be particularly attractive to the file manufacturer because of the many forms of saving it would offer.
• the steel bars themselves would be cheaper because of the cost saving in hot rolling on a wide strip mill as opposed .to a merchant mill and, as previously noted, the file manufacturer would be able to eliminate the costly step of annealing the bars prior to grinding and cutting the teeth or grooves.
• this invention process would provide the file manufacturer with a greater opportunity to vary his practices in order to realize even more savings.
• the file manufacturer could, if he .wishes, purchase his steel in coil form and do his own annealing and/or slitting. That is to say, because of the complexities and extensive equipment necessary for hot rolling small bar sizes on merchant bar mills according to prior art practices, the hot rolled steel could only be made available in cut lengths of flat bar stock. In the practice of this invention, however, file steels could be shipped from the mill in coil form, annealed or unannealed. This would not only simplify handling of the steel stock, but by buying in coil form, the manufacturer would not have to stock a large variety of bar sizes. Specifically, file blanks of any desired width and length could be slit or cut from a single coil. In addition, the availability of annealed steel may even permit the file manufacturer to produce file shapes other than flat. For example, half round or half oval files could be produced from the annealed flat steel stock by a suitable cold forging procedure.
• Phosphorus Sulfur 0.34% Silicon 0.19% Nickel 0.01% Chromium 014% ingots were cut therefrom and subsequently rolled into four slabs 16% by 5% inches.
• the slabs were heated to 2,l00 F and hot rolled on a 43 inch hot strip mill to 17 inches by 0.116 inch and coiled.
• Hot rolling finishing temperature was 1,630 F and the strips were coiled at l,240 F.
• the strip coils exhibited a pearlitic microstructure containing carbides having a Rockwell C hardness of 26-27.
• the coils were heated to l,l00 F in a reducing atmosphere and the atmosphere then adjusted to a dewpoint of less than +15 F and then the coils annealed for 8 hours at 1,365 F. After annealing the coils were cooled at a rate of 40 F per hour to 1,330 and then cooled at 20 F per hour to 1,250. From 1,250 to 400 F, the coil was furance cooled in the protective atmosphere, and below 400 F the coil was air cooled. Examination of the annealed microstructure revealed that 100 percent of the carbides had been spheroidized, and that there was decarburization to a depth of 0.002 to 0.003 inch. The coils were slit at 200 F on a commercial slitting line without difficulty, and cut to lengths of 72 inches. The cut bar exhibited a Rockwell B hardness of -87.
• the bars produced as described above were shipped to a file manufacturer who proceeded to produce files therefrom in accordance with the above described procedure. That is, file blanks were cut therefrom, the surfaces ground to remove the iron down to the high car bon subsurface, grooves cut therein and finally hardened by a suitable lead heating and brine quenching. The file manufacturer reported that the files were most satisfactory.
• a method of making high-carbon steel flat bar stock comprising:
• a method of making steel files comprising:

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)

Priority Applications (9)

Applications Claiming Priority (1)

Related Child Applications (1)

Publications (1)

Family

ID=22785564

Family Applications (1)

Country Status (8)

Cited By (3)

• 0
  • BE BE793276D patent/BE793276A/fr unknown
• 1971
  • 1971-12-22 US US00211091A patent/US3820372A/en not_active Expired - Lifetime
• 1972
  • 1972-12-01 CA CA158,425A patent/CA971776A/en not_active Expired
  • 1972-12-04 GB GB5581172A patent/GB1412601A/en not_active Expired
  • 1972-12-06 AU AU49704/72A patent/AU460981B2/en not_active Expired
  • 1972-12-15 SE SE7216484A patent/SE381287B/xx unknown
  • 1972-12-18 DE DE19722261878 patent/DE2261878A1/de active Pending
  • 1972-12-22 JP JP47129200A patent/JPS4870615A/ja active Pending

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