AUSTENITIC STAINLESS STEEL HAVING IMPROVED STRENGTH

1 . An austenitic stainless steel with improved strength comprising, in percent (%) by weight of the entire composition, C: 0.02 to 0.14%, Si: 0.2 to 0.6%, S: less than 0.01%, Mn: 2.0 to 4.5%, Ni: 2.5 to 5.0%, Cr: 19.0 to 22.0%, Cu: 1.0 to 3.0%, Mo: less than 1.0%, N: 0.25 to 0.40%, the remainder of iron (Fe) and other inevitable impurities, and

wherein the Solubility of Nitrogen in Liquid (SNL) value represented by the following equation (1) is equal to or greater than the content of N,

SNL=−0.188−0.0423×C−0.0517×Si+0.012×Mn+0.0048×Ni+

0.0252×Cr−0.00906×Cu+0.00021×Mo  Equation (1)

(Here, C, Si, Mn, Ni, Cr, Cu, and Mo mean the content (% by weight) of each element.)

2 . The austenitic stainless steel of claim 1 , wherein the C+N is 0.5% or less (excluding 0).

3 . The austenitic stainless steel of claim 1 , further comprising: one or more of B: 0.001 to 0.005% and Ca: 0.001 to 0.003%.

4 . The austenitic stainless steel of claim 1 , wherein the Md 30 value represented by the following equation (2) satisfies −50 or less,

Md 30 =551−462×(C+N)−9.2×Si−8.1×Mn−13.7×Cr−29×(Ni+

Cu)−8.5×Mo  Equation (2)

(Here, C, N, Si, Mn, Cr, Ni, Cu, and Mo mean the content (% by weight) of each element.)

5 . The austenitic stainless steel of claim 1 , wherein the austenitic stainless steel satisfies the following equation (3),

Creq/Nieq≤1.8  Equation (3)

(Here, Creq=Cr+Mo+1.5×Si, Nieq=Ni+0.5×Mn+30×(C+N)+0.5×Cu.)

6 . The austenitic stainless steel of claim 1 , wherein the Pitting Resistance Equivalent Number (PREN) represented by the following equation (4) satisfies 22 or more,

PREN=16+3.3Mo+16N−0.5Mn  Equation (4)

(Here, Mo, N, and Mn mean the content (% by weight) of each element.)

7 . The austenitic stainless steel of claim 1 , wherein the yield strength (0.2 off-set) is 400 to 450 MPa and the tensile strength is 700 to 850 MPa.

8 . The austenitic stainless steel of claim 1 , wherein the elongation is 35% or more.