Method of making flat steel files

Abstract

A process for making flat steel files wherein a highcarbon steel is hot rolled on a wide strip mill and coiled. The coil is given a spheroidizing anneal and slit into bar and cut into flat bar stock. File blanks are cut from the flat bar stock and ground to remove a pure iron surface caused by the anneal. Thereafter, the file teeth or grooves are cut and the file hardened.

I claim: 
     
       1. A method of making high-carbon steel flat bar stock, the steps comprising: a. hot rolling a high-carbon steel slab at a temperature within the range 1,600° to 2,200°F on a strip mill to form a strip having a thickness as desired for the final flat bar stock,   b. coiling said strip at a temperature above 1,000° F,   c. annealing said coiled strip in a reducing atmosphere at a temperature above the A 1  critical temperature for at least 2 hours to austenitize the steel microstructure,   d. maintaining the reducing annealing atmosphere at a dewpoint of less than +15° F at least at temperatures above about 1,100° F,   e. furnace cooling the annealed coiled strip at a rate of about 20° to 40° F per hour to a temperature of about 1,250° F while maintaining the reducing atmosphere at a dewpoint of less than +15° F to form spheroidized carbide precipitates, and then furnace cooling the coiled strip to a temperature below about 400° F while maintaining the reducing atmosphere to avoid surface oxidation, and   f. uncoiling .[. and slitting.]. the strip .[.into bars of the desired width.]. .Iadd.and cutting bars of the desired size therefrom..Iaddend.   
     
     
       2. The method of claim 1 in which strip is hot rolled to a thickness of 0.080 to 0.160 inch. 
     
     
       3. The method of claim 1 in which said coiled strip is annealed at a temperature within the range 1,350° to 1,380°F. 
     
     
       4. The method of claim 1 in which said coiled strip is box annealed by heating the coiled strip in a reducing atmosphere to a temperature of about 1,100°F and then adjusting the dewpoint of the reducing atmosphere to less than +15°F and thereafter continue heating to a temperature within the range 1,350° to 1,380° F and maintaining said temperature for about 5 hours, thereafter furnace cooling said coiled strip at a rate of about 40°F per hour to a temperature of about 1,330°F, and then at a rate of about 20°F per hour to a temperature of about 1,250°F. 
     
     
       5. A method of making steel files, the steps comprising: a. hot rolling a high-carbon steel slab at a temperature within the range 1,600° to 2,200°F on a strip mill to form a strip having a thickness as desired for the final flat bar stock.   b. coiling said strip at a temperature above 1,000°F.   c. annealing said coiled strip in a reducing atmosphere at a temperature above the A 1  critical temperature for at least 2 hours to austenitize the steel microstructure,   d. maintaining the reducing annealing atmosphere at a dewpoint of less than +15°F at least at temperatures above about 1,100°F,   e. furnace cooling the annealed coiled strip at a rate of about 20° to 40°F per hour to a temperature of about 1,250°F while maintaining the reducing atmosphere at a dewpoint of less than +15°F to form spheroidized carbide precipitates, and then furnace cooling the coiled strip to a temperature below about 400°F while maintaining the reducing atmosphere to avoid surface oxidation,   f. uncoiling and slitting the strip into bars of the desired width,   g. cutting the bars to the desired length, and cutting the bar lengths into file blanks,   h. grinding the surface of the file blanks to remove a pure iron surface layer caused by the anneal and expose a high-carbon subsurface,   i. cutting file grooves into the file blanks, and   j. hardening the file blanks.