Ferritic stainless steel with improved high temperature creep resistance and manufacturing method therefor
Disclosed is a ferritic stainless steel with improved high temperature creep resistance. The disclosed ferritic stainless steel comprises by weight %: 0.005 to 0.03% of C, 0.005 to 0.03% of N, 0.05 to 0.9% of Si, 0.05 to 0.9% of Mn, 14.0 to 19.0% of Cr, 0.1 to 0.6% of Ti, 0.1 to 0.6% of Nb, 0.1 to 0.6% of Cu, 0.01 to 0.04% of P, 0.01% or less (excluding 0) of S, and the balance of iron (Fe) and inevitable impurities, and is characterized by satisfying Expressions (1) and (2) below. 0.5≤Nb/Cu≤3 Expression (1) 20≤[2Nb+Ti]/[C+N] Expression (2) wherein Nb, Cu, Ti, C, and N denote contents (wt %) of each element.
1. A ferritic stainless steel with improved high temperature creep resistance comprising, in percent by weight (wt %), 0.005 to 0.03% of carbon (C), 0.005 to 0.03% of nitrogen (N), 0.05 to 0.9% of silicon (Si), 0.05 to 0.9% of manganese (Mn), 14.0 to 19.0% of chromium (Cr), 0.1 to 0.6% of titanium (Ti), 0.1 to 0.6% of niobium (Nb), 0.1 to 0.6% of copper (Cu), 0.01 to 0.04% of phosphorus (P), 0.01% or less of sulfur (S, except for 0), and the balance of iron (Fe) and inevitable impurities, and
satisfying Expressions (1) and (2) below,
wherein 7*10 5 /mm 2 or more of precipitates including Nb, Fe, and Cr are distributed in a region of the ferritic stainless steel from T/3 to T/5 based on thickness T:
0.5≤Nb/Cu≤3 Expression (1):
20≤[2Nb+Ti]/[C+N] Expression (2):
wherein Nb, Cu, Ti, C, and N denote contents (wt %) of the elements.
2. The ferritic stainless steel according to claim 1 , wherein the precipitates have sizes of 5 to 500 nm.
3. The ferritic stainless steel according to claim 1 , wherein a creep deformation rate is 50% or less under the conditions of 900° C. and 100 hours.
4. The ferritic stainless steel according to claim 1 , further comprising 0.001 to 0.1% of aluminum (Al) and 0.001 to 0.6% of nickel (Ni).
5. A method of manufacturing a ferritic stainless steel with improved high temperature creep resistance, the method comprising:
preparing a cold-rolled steel sheet comprising, in percent by weight (wt %), 0.005 to 0.03% of carbon (C), 0.005 to 0.03% of nitrogen (N), 0.05 to 0.9% of silicon (Si), 0.05 to 0.9% of manganese (Mn), 14.0 to 19.0% of chromium (Cr), 0.1 to 0.6% of titanium (Ti), 0.1 to 0.6% of niobium (Nb), 0.1 to 0.6% of copper (Cu), 0.01 to 0.04% of phosphorus (P), 0.01% or less of sulfur (S, except for 0), and the balance of iron (Fe) and inevitable impurities, and satisfying Expressions (1) and (2) below;
annealing the cold-rolled steel sheet;
cooling the cold-rolled, annealed steel sheet by quenching to a temperature of 650 to 750° C.; and
performing a cracking process for 5 minutes or more after the quenching:
0.5≤Nb/Cu≤3 Expression (1):
20≤[2Nb+Ti]/[C+N] Expression (2):
wherein Nb, Cu, Ti, C, and N denote contents (wt %) of the elements.
6. The method according to claim 5 , wherein a cooling rate is 10° C./sec or more in the cooling process.
7. The method according to claim 5 , wherein the cracking process is performed for 5 minutes to 20 minutes.
8. The method according to claim 5 , wherein 7*10 5 /mm 2 or more of precipitates including Nb, Fe, and Cr are distributed in fine structures after the cracking process.
9. The method according to claim 5 , wherein the ferritic stainless steel further comprises 0.001 to 0.1% of aluminum (Al) and 0.001 to 0.6% of nickel (Ni).