Duplex stainless steel and formed object thereof
The present disclosure relates to a corrosion resistant duplex stainless steel (ferritic austenitic alloy), which is suitable for use in a plant for the production of urea and uses thereof. The disclosure also relates to objects made of the duplex stainless steel. Furthermore, the present disclosure relates to a method for the production of urea and to a plant for the production of urea having one or more parts made from the duplex stainless steel, and to a method of modifying an existing plant for the production of urea.
1. A duplex stainless steel comprising in weight % (wt %):
C
0.012 to 0.030;
Si
max 0.8;
Mn
0.5-1.5;
Cr
29.0 to 31.0;
Ni
5.5 to 8.5;
Mo
3.0 to 4.0;
W
≤2.55;
N
0.28 to 0.40;
Cu
max 0.8;
S
max 0.02;
P
max 0.03;
balance Fe and unavoidable occurring impurities,
wherein the content of Mo+W is greater than 3.0 but less than 4.0,
wherein the duplex stainless steel has a corrosion rate of 0.186 to 0.191 mm/year,
wherein the corrosion rate is evaluated on a sample of the duplex stainless steel in an oxygen-free carbamate solution at a temperature of 210° C. for 14 days, and
wherein the sample is in the form of a coupon having dimensions of 20×10×3 mm obtained from a 5 mm strip produced by hot warming to 1200° C. and cold rolling at room temperature with intermediate annealing at 1100° C. and final annealing at 1070° C., and surfaces of the sample were machined and finished by wet grinding.
2. The duplex stainless steel according to claim 1 , comprising in weight % (wt %)
C
0.012 to 0.020;
Si
0.08 to 0.23;
Mn
1.0 to 1.05;
Cr
29.07 to 29.92;
Ni
5.76 to 7.17;
Mo
3.0 to 4.0;
W
≤2.55;
N
0.3 to 0.35;
Cu
max 0.01;
S
max 0.008;
P
max 0.008.
3. A formed object, comprising the duplex stainless steel according to claim 1 .
4. The formed object according to claim 3 , wherein said formed object is a tube.
5. The duplex stainless steel according to claim 1 , wherein sigma phase is substantially zero.
6. The duplex stainless steel according to claim 1 , wherein sigma phase is max 0.05 wt. %.
7. The duplex stainless steel according to claim 2 , wherein the content of Mo+W is 3.01 to 3.03.
8. The duplex stainless steel according to claim 2 , wherein sigma phase is substantially zero.
9. The duplex stainless steel according to claim 2 , wherein sigma phase is max 0.05 wt. %.
10. A formed object, comprising the duplex stainless steel according to claim 2 .
11. The formed object according to claim 10 , wherein said formed object is a tube.
12. The duplex stainless steel according to claim 1 , wherein Ni is present in an amount of 5.5 to 7.5 wt. %.
13. The duplex stainless steel according to claim 1 , wherein the duplex stainless steel is substantially free of intermetallic phase.