Ferritic stainless steel sheet, method for the production thereof, and use of the same, especially in exhaust lines

1. A ferritic stainless steel sheet comprising a composition, expressed in weight percentages:

trace amounts≦C≦0.03%;

0. 2%≦Mn≦1%;

0. 2%≦Si≦1%;

trace amounts≦S≦0.01%;

trace amounts≦P≦0.04%;

15%≦Cr≦22%;

trace amounts≦Ni≦0.5%;

trace amounts≦Mo≦2%;

trace amounts≦Cu≦0.5%;

0.160%≦Ti≦1%;

0.02%≦Al≦1%;

0.2%≦Nb≦1%;

trace amounts≦V≦0.2%;

0.009%≦N≦0.03%;

trace amounts≦Co≦0.2%;

trace amounts≦Sn≦0.05%;

rare earths (REE)≦0.1%;

trace amounts≦Zr≦0.01%;

the remainder of the composition consists of iron and inevitable impurities resulting from the elaboration,

wherein the Al and rare earth (REE) contents satisfy the relationship:

Al+30×REE≧0.15%;

the Nb, C, N and Ti contents in % satisfy the relationship:

1/[Nb+(7/4)×Ti−7×(C+N)]≦3, and

said metal sheet comprises an entirely recrystallized structure and an average ferritic grain size is between 25 and 65 μm.

2. A method for manufacturing a ferritic stainless steel sheet comprising a composition, expressed in weight percentages:

trace amounts≦C≦0.03%;

0.2%≦Mn≦1%;

0.2%≦Si≦1%;

trace amounts≦S≦0.01%;

trace amounts≦P≦0.04%;

15%≦Cr≦22%;

trace amounts≦Ni≦0.5%;

trace amounts≦Mo≦2%;

trace amounts≦Cu≦0.5%;

0.160%≦Ti≦1%;

0.02%≦Al≦1%;

0.2%≦Nb≦1%;

trace amounts≦V≦0.2%;

0.009%≦N≦0.03%;

trace amounts≦Co≦0.2%;

trace amounts≦Sn≦0.05%;

rare earths (REE)≦0.1%;

trace amounts≦Zr≦0.01%;

the remainder of the composition consists of iron and inevitable impurities resulting from the elaboration,

wherein the Al and rare earth (REE) contents satisfy the relationship:

Al+30×REE≧0.15%;

the Nb, C, N and Ti contents in % satisfy the relationship:

1/[Nb+(7/4)×Ti−7×(C+N)]≦3, the method comprising:

casting a semi-finished product of the ferritic stainless steel sheet;

bringing the semi-finished product to a temperature above 1,000° C. and below 1,250° C.;

hot-rolling the semi-finished product in order to obtain a hot-rolled sheet with a thickness between 2.5 and 6 mm;

cold-rolling said hot-rolled sheet at a temperature between room temperature and 300° C., in a single step or in several steps separated by intermediate annealings;

final annealing the cold-rolled sheet performed at a temperature between 1,000 and 1,100° C. and for a period between 10 seconds and 3 minutes, in order to obtain a completely recrystallized structure with an average grain size between 25 and 65 μm.

3. A method for manufacturing a ferritic stainless steel sheet comprising a composition, expressed in weight percentages:

trace amounts≦C≦0.03%;

0.2%≦Mn≦1%;

0.2%≦Si≦1%;

trace amounts≦S≦0.01%;

trace amounts≦P≦0.04%;

15%≦Cr≦22%;

trace amounts≦Ni≦0.5%;

trace amounts≦Mo≦2%;

trace amounts≦Cu≦0.5%;

0.160%≦Ti≦1%;

0.02%≦Al≦1%;

0.2%≦Nb≦1%;

trace amounts≦V≦0.2%;

0.009%≦N≦0.03%;

trace amounts≦Co≦0.2%;

trace amounts≦Sn≦0.05%;

rare earths (REE)≦0.1%;

trace amounts≦Zr≦0.01%;

the remainder of the composition consists of iron and inevitable impurities resulting from the elaboration,

wherein the Al and rare earth (REE) contents satisfy the relationship:

Al+30×REE≧0.15%;

the Nb, C, N and Ti contents in % satisfy the relationship:

1/[Nb+(7/4)×Ti−7×(C+N)]≦3, the method comprising:

casting a semi-finished product of the ferritic stainless steel sheet;

bringing the semi-finished product to a temperature above 1,000° C. and below 1,250° C.;

hot-rolling the semi-finished product in order to obtain a hot-rolled metal sheet with a thickness comprised between 2.5 and 6 mm;

annealing the hot-rolled metal sheet at a temperature between 1,000 and 1,100° C. and for a period comprised between 30 seconds and 6 minutes;

cold-rolling said hot-rolled metal sheet at a temperature of less than 300 ° C., in a single step or in several steps separated by intermediate annealings;

final annealing the cold-rolled metal sheet performed at a temperature between 1,000 and 1,100° C. and for a period between 10 seconds and 3 minutes, in order to obtain a completely recrystallized structure having an average grain size between 25 and 65 micrometers.

4. The method according to claim 2 , wherein the hot-rolling temperature is from 1,180 to 1,200° C.

5. The method according to one of claims 2 , wherein the final annealing temperature is comprised between 1,050 and 1,090° C.

6. Parts involving shaping and welding and intended to be subject to a periodic use temperature between 150° C. and 700° C. and to projection of a mixture of water, urea and ammonia or to a projection of urea or of ammonia comprising the ferritic stainless steel sheet according to claim 1 .

7. The parts according to claim 6 , wherein said parts are parts of exhaust lines of internal combustion engines equipped with a catalytic system for reducing nitrogen oxides by injection of urea or ammonia.

8. The ferritic stainless steel sheet according to claim 1 , wherein the ferritic stainless steel sheet comprises 0.010%≦N≦0.020%.

9. The method for manufacturing a ferritic stainless steel sheet according to claim 2 , wherein the ferritic stainless steel sheet comprises 0.010%≦N≦0.020%.

10. The method for manufacturing a ferritic stainless steel sheet according to claim 3 , wherein the ferritic stainless steel sheet comprises 0.010%≦N≦0.020%.