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 KNO3, KNO2, Ca(NO3)2, NaNO3 and NaNO2 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 (KNO3), potassium nitrite (KNO2), sodium nitrate (NaNO3), sodium nitrite (NaNO2), calcium nitrate (Ca(NO3)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.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a method for nitriding metal in a salt bath and nitrided metal manufactured using the same; and, more particularly, to a method for nitriding iron or steels by using non-cyanide salt bath, and nitrided iron or steels manufactured using the same.[0003]2. Background of the Related Art[0004]Steels have been widely used for machine parts because of their inherent properties. To be used for machine parts, steels are usually first heat-treated to impart thereto strength, toughness and durability, all of which are the qualities machine parts require. In addition, for machine parts that are often exposed to corrosive environment, surfaces thereof are further heat-treated to impart thereto corrosion resistance.[0005]Nitriding is one of the methods for processing the metal surface to impart thereto a corrosion resistance thereof. The nitriding methods include gas nitriding using NH3 gas, salt bath...

AI Technical Summary

Benefits of technology

[0012]It is yet another object of the present invention to provide a salt bath nitriding method for nitriding a metal, capable of increasing hardness and tensile strength of the metal to be treated, and a nitrided metal manufactured using the same.

[0013]It is still another object of the present invention to provide a salt bath nitriding method for nitriding a metal, capable of maximizing a nitriding depth, and a nitrided metal manufactured using the same.

[0020]The ultra-low carbon steel nitrided by the present invention has the surface hardness ranging from more than 120 Hv to equal to or less than 450 Hv. The low carbon steel has the surface hardness being more than 200 Hv to equal to or less than 410 Hv. The medium carbon steel has the surface hardness being more than 130 Hv to equal to or less than 420 Hv. The high carbon steel has the surface hardness being more than 150 Hv to equal to or less than 400 Hv. The alloy steel has the surface hardness being more than 200 Hv to equal to or less than 410 Hv. IF steel has the surface hardness being more than 165 Hv to equal to or less than 400 Hv. The surface hardness of the steels nitrided by the present invention can be improved to a maximum of 420 Hv. The surface hardness of the iron nitrided by the present invention is also improved.

[0021]The ultra-low carbon steel nitrided by the present invention has the tensile strength ranging from more than 35 kgf / mm2 to equal to or less than 110 kgf / mm2. The low carbon steel has the tensile strength ranging from more than 45 kgf / mm2 to equal to or less than 110 kgf / mm2. The medium carbon steel has the tensile strength ranging from more than 45 kgf / mm2 to equal to or less than 100 kgf / mm2. The high carbon steel has the tensile strength ranging from more than 60 kgf / mm2 to equal to or less than 95 kgf / mm2. The alloy steel has the tensile strength ranging from more than 55 kgf / mm2 to equal to or less than 110 kgf / mm2. The tensile strength of IF steel and iron can be improved by the nitriding method of the present invention.

Problems solved by technology

Since the cyanide ion is classified as a toxic chemical, it must be carefully and tightly controlled, and this can be an expensive proposition.

Also, there is a problem of a cost involved for processing waste water and gas.

The conventional salt bath nitriding method using a cyanide salt also has a problem that its applications are limited to molds or gears since the depth to which the material can be nitrided is limited.

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