Austenitic stainless steel product having excellent surface properties and manufacturing method of the same
An austenitic stainless steel product having excellent surface characteristics and a manufacturing method therefor are disclosed. The disclosed austenitic stainless steel product comprises an austenitic stainless steel comprising, by weight percent, 0.005 to 0.15% of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 6.0 to 8.0% of Ni, 16 to 18% of Cr, 0.1 to 4.0% of Cu, 0.005 to 0.2% of N, 0.01 to 0.2% of Mo, and the remainder comprising iron (Fe) and other unavoidable impurities, and a Ni surface negative segregation thereof defined by the following formula (1) is 0.6 to 0.9 and the martensite fraction thereof is 10 to 30%. (C Ni-Min )/(C Ni-Ave ) formula (1) Here, C Ni-min is the minimum concentration of Ni on the surface and C Ni-Ave is the average concentration of Ni on the surface.
1. An austenitic stainless steel product, the stainless steel comprising:
by weight percent, 0.005 to 0.15% of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 6.0 to 8.0% of Ni, 16 to 18% of Cr, 0.1 to 4.0% of Cu, 0.005 to 0.2% of N, 0.01 to 0.2% of Mo, and the remainder comprising iron (Fe) and other unavoidable impurities, and a surface degree of negative segregation of Ni defined by the following formula (1) is in the range of 0.6 to 0.9 and the martensite fraction thereof is 10 to 30%
(CNi-Min)/(CNi-Ave) Formula (1)
Where CNi-Min is the minimum concentration of Ni at the surface and CNi-Ave is the average concentration of Ni at the surface, and
wherein a surface hardness ratio defined by the following formula (2) is in the range of 1.1 to 1.6
A/B Formula (2)
where A is the average value of the upper 10% of the product surface hardness, and B is the average value of the lower 10% the product surface hardness.
2. The austenitic stainless steel product according to claim 1 , wherein cracks having a depth of 20 μm or more from the surface is 10 or less.
3. The austenitic stainless steel product according to claim 1 , wherein a Ni surface segregation portion is less than 60% in area fraction and a Ni surface negative segregation portion is more than 5%.
4. A method of manufacturing an austenitic stainless steel product, the method comprising:
processing the austenitic stainless steel product, comprising:
by weight percent, 0.005 to 0.15% of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 6.0 to 8.0% of Ni, 16 to 18% of Cr, 0.1 to 4.0% of Cu, 0.005 to 0.2% of N, 0.01 to 0.2% of Mo, and the remainder comprising iron (Fe) and other unavoidable impurities; and
heat treating the austenitic stainless steel product at a temperature of 900-1,150° C. for 10 minutes or less; and
cooling the heat-treated austenitic stainless steel to 500° C. within 30 minutes;
wherein the austenitic stainless steel product has a surface degree of negative segregation of Ni defined by the following formula (1) is in the range of 0.6 to 0.9 and the martensite fraction thereof is 10 to 30%
(CNi-Min)/(CNi-Ave) Formula (1)
Where CNi-Min is the minimum concentration of Ni at the surface and CNi-Ave is the average concentration of Ni at the surface, and
wherein a surface hardness ratio defined by the following formula (2) is in the range of 1.1 to 1.6
A/B Formula (2)
where A is the average value of the upper 10% of the product surface hardness, and B is the average value of the lower 10% the product surface hardness.
5. The method of claim 4 , wherein the martensite fraction of the austenitic stainless steel product before the heat treatment is 10 to 50%.
6. The method of claim 5 , wherein the martensite fraction of the austenitic stainless steel product after cooling is 10 to 30%.