Method for nitriding metal in salt bath and metal manufactured using the same

Abstract

Provided is a method for nitriding a metal in a salt bath by using a non-cyanide salt and a nitrided metal manufactured using the same. The method includes the steps of: immerging at least one salt selected from the group consisting of KNO 3 , KNO 2 , Ca(NO 3 ) 2 , NaNO 3 and NaNO 2 into the salt bath; melting the salt by heating and maintaining the molten salt at a predetermined temperature; and submerging the metal in the salt bath. Nitriding in non-cyanide salts, such as potassium nitrate (KNO 3 ), potassium nitrite (KNO 2 ), sodium nitrate (NaNO 3 ), sodium nitrite (NaNO 2 ), calcium nitrate (Ca(NO 3 ) 2 ) and their mixtures, is capable of solving an environmental pollution problem and reducing a cost. Also, the method is capable of increasing nitrided depth of the metal two to six times compared to conventional nitriding methods. As a result, the method can be carried out in various application fields.

1 . A method for nitriding a metal in a salt bath, comprising the steps of:
 a) immersing at least one salt selected from a group consisting of KNO 3 , KNO 2 , Ca(NO 3 ) 2 , NaNO 3  and NaNO 2  into the salt bath;   b) melting the salt by heating and maintaining the molten salt at a predetermined temperature; and   c) submerging the metal in the salt bath.   
   
   
       2 . The method as recited in  claim 1 , wherein the predetermined temperature is within a range of 400° C. to 700° C. 
   
   
       3 . The method as recited in  claim 1 , wherein, in the step c), a submerging time is within a range of 1 minute to 24 hours. 
   
   
       4 . The method as recited in  claim 2 , wherein the metal is one of iron and steels. 
   
   
       5 . The method as recited in  claim 3 , wherein the metal is one of iron and steels. 
   
   
       6 . A metal nitrided in a salt bath including at least one selected from a group consisting of KNO 3 , KNO 2 , Ca(NO 3 ) 2 , NaNO 3  and NaNO 2 , wherein the metal is iron and the iron is nitrided to a depth of 0.1 mm to 3.0 mm from the surface. 
   
   
       7 . A metal nitrided in a salt bath including at least one selected from a group consisting of KNO 3 , KNO 2 , Ca(NO 3 ) 2 , NaNO 3  and NaNO 2 , wherein the metal is steel and the steel is nitrided to a depth of 0.1 mm to 3.0 mm from the surface. 
   
   
       8 . The metal as recited in  claim 7 , wherein the steel is at least one selected from a group consisting of ultra low carbon steel, low carbon steel, medium carbon steel, high carbon steel, alloy steel and IF steel. 
   
   
       9 . The metal as recited in  claim 8 , wherein the ultra low carbon steel has a surface hardness being more than 120 Hv to equal to or less than 450 Hv. 
   
   
       10 . The metal as recited in  claim 8 , wherein the low carbon steel has a surface hardness being more than 200 Hv to equal to or less than 410 Hv. 
   
   
       11 . The metal as recited in  claim 8 , wherein the medium carbon steel has a surface hardness being more than 130 Hv to equal to or less than 420 Hv. 
   
   
       12 . The metal as recited in  claim 8 , wherein the high carbon steel has a surface hardness being more than 150 Hv to equal to or less than 400 Hv. 
   
   
       13 . The metal as recited in  claim 8 , wherein the alloy steel has a surface hardness being more than 200 Hv to equal to or less than 410 Hv. 
   
   
       14 . The metal as recited in  claim 8 , wherein the IF steel has a surface hardness being more than 165 Hv to equal to or less than 400 Hv. 
   
   
       15 . The metal as recited in  claim 9 , wherein the ultra-low carbon steel has a tensile strength being more than 35 kgf/mm 2  to equal to or less than 110 kgf/mm 2 . 
   
   
       16 . The metal as recited in  claim 10 , wherein the low carbon steel has a tensile strength being more than 45 kgf/mm 2  to equal to or less than 110 kgf/mm 2 . 
   
   
       17 . The metal as recited in  claim 11 , wherein the medium carbon steel has a tensile strength being more than 45 kgf/mm 2  to equal to or less than 100 kgf/mm 2 . 
   
   
       18 . The metal as recited in  claim 12 , wherein the high carbon steel has a tensile strength being more than 60 kgf/mm 2  to equal to or less than 95 kgf/mm 2 . 
   
   
       19 . The metal as recited in  claim 13 , wherein the alloy steel has a tensile strength being more than 55 kgf/mm 2  to equal to or less than 110 kgf/mm 2 . 
   
   
       20 . The metal as recited in  claim 14 , wherein a chromium content of the steel ranges from 0.1 wt % to 1.5 wt %. 
   
   
       21 . The metal as recited in  claim 15 , wherein a chromium content of the steel ranges from 0.1 wt % to 1.5 wt %. 
   
   
       22 . The metal as recited in  claim 16 , wherein a chromium content of the steel ranges from 0.1 wt % to 1.5 wt %. 
   
   
       23 . The metal as recited in  claim 17 , wherein a chromium content of the steel ranges from 0.1 wt % to 1.5 wt %. 
   
   
       24 . The metal as recited in  claim 18 , wherein a chromium content of the steel ranges from 0.1 wt % to 1.5 wt %. 
   
   
       25 . The metal as recited in  claim 19 , wherein a chromium content of the steel ranges from 0.1 wt % to 1.5 wt %. 
   
   
       26 . The metal as recited in  claim 14 , wherein a molybdenum content of the steel ranges from 0.05 wt % to 0.5 wt %. 
   
   
       27 . The metal as recited in  claim 15 , wherein a molybdenum content of the steel ranges from 0.05 wt % to 0.5 wt %. 
   
   
       28 . The metal as recited in  claim 16 , wherein a molybdenum content of the steel ranges from 0.05 wt % to 0.5 wt %. 
   
   
       29 . The metal as recited in  claim 17 , wherein a molybdenum content of the steel ranges from 0.05 wt % to 0.5 wt %. 
   
   
       30 . The metal as recited in  claim 18 , wherein a molybdenum content of the steel ranges from 0.05 wt % to 0.5 wt %. 
   
   
       31 . The metal as recited in  claim 19 , wherein a molybdenum content of the steel ranges from 0.05 wt % to 0.5 wt %. 
   
   
       32 . The metal as recited in  claim 14 , wherein a nickel content of the steel ranges from 0.1 wt % to 10 wt %. 
   
   
       33 . The metal as recited in  claim 15 , wherein a nickel content of the steel ranges from 0.1 wt % to 10 wt %. 
   
   
       34 . The metal as recited in  claim 16 , wherein a nickel content of the steel ranges from 0.1 wt % to 10 wt %. 
   
   
       35 . The metal as recited in  claim 17 , wherein a nickel content of the steel ranges from 0.1 wt % to 10 wt %. 
   
   
       36 . The metal as recited in  claim 18 , wherein a nickel content of the steel ranges from 0.1 wt % to 10 wt %. 
   
   
       37 . The metal as recited in  claim 19 , wherein a nickel content of the steel ranges from 0.1 wt % to 10 wt %. 
   
   
       38 . The metal as recited in  claim 14 , wherein a manganese content of the steel ranges from 0.1 wt % to 2.0 wt %. 
   
   
       39 . The metal as recited in  claim 15 , wherein a manganese content of the steel ranges from 0.1 wt % to 2.0 wt %. 
   
   
       40 . The metal as recited in  claim 16 , wherein a manganese content of the steel ranges from 0.1 wt % to 2.0 wt %. 
   
   
       41 . The metal as recited in  claim 17 , wherein a manganese content of the steel ranges from 0.1 wt % to 2.0 wt %. 
   
   
       42 . The metal as recited in  claim 18 , wherein a manganese content of the steel ranges from 0.1 wt % to 2.0 wt %. 
   
   
       43 . The metal as recited in  claim 19 , wherein a manganese content of the steel ranges from 0.1 wt % to 2.0 wt %. 
   
   
       44 . The metal as recited in  claim 14 , wherein a boron content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       45 . The metal as recited in  claim 15 , wherein a boron content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       46 . The metal as recited in  claim 16 , wherein a boron content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       47 . The metal as recited in  claim 17 , wherein a boron content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       48 . The metal as recited in  claim 18 , wherein a boron content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       49 . The metal as recited in  claim 19 , wherein a boron content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       50 . The metal as recited in  claim 14 , wherein a titanium content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       51 . The metal as recited in  claim 15 , wherein a titanium content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       52 . The metal as recited in  claim 16 , wherein a titanium content of the steel ranges from 0.1 wt % to 0.1 wt %. 
   
   
       53 . The metal as recited in  claim 17 , wherein a titanium content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       54 . The metal as recited in  claim 18 , wherein a titanium content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       55 . The metal as recited in  claim 19 , wherein a titanium content of the steel ranges from 0.001 wt % to 0.1 wt %. 
   
   
       56 . The metal as recited in  claim 14 , wherein a vanadium content of the steel ranges from 0.05 wt % to 0.15 wt %. 
   
   
       57 . The metal as recited in  claim 15 , wherein a vanadium content of the steel ranges from 0.05 wt % to 0.15 wt %. 
   
   
       58 . The metal as recited in  claim 16 , wherein a vanadium content of the steel ranges from 0.05 wt % to 0.15 wt %. 
   
   
       59 . The metal as recited in  claim 17 , wherein a vanadium content of the steel ranges from 0.05 wt % to 0.15 wt %. 
   
   
       60 . The metal as recited in  claim 18 , wherein a vanadium content of the steel ranges from 0.05 wt % to 0.15 wt %. 
   
   
       61 . The metal as recited in  claim 19 , wherein a vanadium content of the steel ranges from 0.05 wt % to 0.15 wt %. 
   
   
       62 . The metal as recited in  claim 14 , wherein a niobium content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       63 . The metal as recited in  claim 15 , wherein a niobium content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       64 . The metal as recited in  claim 16 , wherein a niobium content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       65 . The metal as recited in  claim 17 , wherein a niobium content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       66 . The metal as recited in  claim 18 , wherein a niobium content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       67 . The metal as recited in  claim 19 , wherein a niobium content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       68 . The metal as recited in  claim 14 , wherein an aluminum content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       69 . The metal as recited in  claim 15 , wherein an aluminum content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       70 . The metal as recited in  claim 16 , wherein an aluminum content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       71 . The metal as recited in  claim 17 , wherein an aluminum content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       72 . The metal as recited in  claim 18 , wherein an aluminum content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       73 . The metal as recited in  claim 19 , wherein an aluminum content of the steel ranges from 0.005 wt % to 0.1 wt %. 
   
   
       74 . The metal as recited in  claim 15 , wherein the ultra-low carbon steel has a carbon content ranging from at least 0.0001 wt % to less than 0.13 wt %. 
   
   
       75 . The metal as recited in  claim 16 , wherein the low carbon steel has a carbon content ranging from at least 0.13 wt % to less than 0.2 wt %. 
   
   
       76 . The metal as recited in  claim 17 , wherein the medium carbon steel has a carbon content ranging from at least 0.21 wt % to less than 0.51 wt %. 
   
   
       77 . The metal as recited in  claim 18 , wherein the high carbon steel has a carbon content ranging from at least 0.51 wt % to less than 2.0 wt %.