High-Carbon Martensitic Stainless Steel and Production Method Therefor

Abstract

The present invention relates to a production method for high-carbon martensitic stainless steel as used in razorblades, knives and the like, which contains, as percentages by weight, 0.40 to 0.80% carbon and 11 to 16% chromium as main components. Provided is a production method for high-carbon martensitic stainless steel in a strip-casting device, wherein a stainless-steel thin sheet is cast by supplying a stainless molten steel containing, as percentages by weight, 0.40 to 0.80% carbon and from 11 to 16% chromium to a molten steel pool from a tundish via a nozzle, and the cast stainless-steel thin sheet is made into a hot-rolled annealed strip using in-line rollers to a rolling reduction of 5 to 40% immediately just after the casting so that the size of primary carbides within the microstructure of the hot-rolled annealed strip is 10 μm or less, and also provided is martensitic stainless steel produced by means of the production method. By reducing the size of the primary carbides formed in the cast structure and the hot-rolled sheet to 10 μm or less, the present invention produces high-carbon martensitic stainless steel having outstanding blade-end quality for use in cutting implements.

1 . A production method for a high-carbon martensitic stainless steel, wherein, in a strip-casting device comprising a pair of rolls rotating in opposite directions, edge dams respectively provided to both sides of the rolls so as to form a molten steel pool, and a meniscus shield for supplying inert nitrogen gas to the upper surface of the molten steel pool, a stainless-steel thin sheet is cast by supplying a stainless molten steel containing, as percentages by weight, 0.40 to 0.80% carbon and from 11 to 16% chromium to a molten steel pool from a tundish via a nozzle, and the cast stainless-steel thin sheet is made into a hot-rolled annealed strip using in-line rollers to a rolling reduction of 5 to 40% immediately just after the casting so that the size of primary carbides within the microstructure of the hot-rolled annealed strip is 10 μm or less. 
     
     
         2 . The production method of  claim 1 , wherein the martensitic stainless steel contains, as percentages by weight, 0.1 to 1.0% silicon (Si), 0.1 to 1.0% manganese (Mn), over 0 to 0.1% nickel (Ni), over 0 to 0.04 sulfur (S), and over 0 to 0.05 phosphorus (P), and Fe and other unavoidable impurities as remnants. 
     
     
         3 . The production method of  claim 1 , wherein a hot-rolled annealed sheet is produced by performing batch annealing on the hot-rolled annealed strip at a temperature of 700 to 950° C. under a reducing gas atmosphere. 
     
     
         4 . The production method of  claim 3 , wherein the batch annealing is performed in the range of once to three times. 
     
     
         5 . The production method of  claim 3 , wherein in the sectional microstructure of the hot-rolled annealed strip, the batch annealing is performed so that the number chromium carbides having a size of 0.1 μm or more is more than 50 EA/100 μm 2 . 
     
     
         6 . The production method of  claim 3 , wherein pickling treatment is performed on the hot-rolled annealed strip subjected to the batch annealing after shot blasting. 
     
     
         7 . The production method of  claim 6 , wherein in the hot-rolled annealed strip before the pickling treatment, the depth of a decarburized layer is 20 μm or less directly under a surface layer scale. 
     
     
         8 . The production method of  claim 1 , wherein cold rolling is performed on the hot-rolled annealed strip, and a one-time cold rolling rate is maximum 70%. 
     
     
         9 . The production method of  claim 8 , wherein annealing is performed on the cold-rolled strip five times or less under a reducing atmosphere. 
     
     
         10 . The production method of  claim 8 , wherein cold-rolled annealing is performed on the cold-rolled strip at a temperature of 650 to 800° C. 
     
     
         11 . A high-carbon martensitic stainless steel produced by means of a production method, wherein, in a strip-casting device comprising a pair of rolls rotating in opposite directions, edge dams respectively provided to both sides of the rolls so as to form a molten steel pool, and a meniscus shield for supplying inert nitrogen gas to the upper surface of the molten steel pool, a stainless-steel thin sheet is cast by supplying a stainless molten steel containing, as percentages by weight, 0.40 to 0.80% carbon and from 11 to 16% chromium to a molten steel pool from a tundish via a nozzle, and the cast stainless-steel thin sheet is made into a hot-rolled annealed strip using in-line rollers to a rolling reduction of 5 to 40% immediately just after the casting so that the size of primary carbides within the microstructure of the hot-rolled annealed strip is 10 μm or less. 
     
     
         12 . The high-carbon martensitic stainless steel of  claim 11 , wherein the martensitic stainless steel contains, as percentages by weight, 0.1 to 1.0% silicon (Si), 0.1 to 1.0% manganese (Mn), over 0 to 0.1% nickel (Ni), over 0 to 0.04 sulfur (S), and over 0 to 0.05 phosphorus (P), and Fe and other unavoidable impurities as remnants. 
     
     
         13 . The high-carbon martensitic stainless steel of  claim 11 , wherein a hot-rolled annealed sheet is produced by performing batch annealing on the hot-rolled annealed strip at a temperature of 700 to 950° C. under a reducing gas atmosphere. 
     
     
         14 . The high-carbon martensitic stainless steel of  claim 13 , wherein the batch annealing is performed in the range of once to three times. 
     
     
         15 . The high-carbon martensitic stainless steel of  claim 13 , wherein in the sectional microstructure of the hot-rolled annealed strip, the batch annealing is performed so that the number chromium carbides having a size of 0.1 μm or more is more than 50 EA/100 μm 2 . 
     
     
         16 . The high-carbon martensitic stainless steel of  claim 13 , wherein pickling treatment is performed on the hot-rolled annealed strip subjected to the batch annealing after shot blasting. 
     
     
         17 . The high-carbon martensitic stainless steel of  claim 16 , wherein in the hot-rolled annealed strip before the pickling treatment, the depth of a decarburized layer is 20 μm or less directly under a surface layer scale. 
     
     
         18 . The high-carbon martensitic stainless steel of  claim 11 , wherein cold rolling is performed on the hot-rolled annealed strip, and a one-time cold rolling rate is maximum 70%. 
     
     
         19 . The high-carbon martensitic stainless steel of  claim 18 , wherein annealing is performed on the cold-rolled strip five times or less under a reducing atmosphere. 
     
     
         20 . The high-carbon martensitic stainless steel of  claim 18 , wherein cold-rolled annealing is performed on the cold-rolled strip at a temperature of 650 to 800° C.