Steel sheet provided with a coating providing sacrificial cathodic protection comprising lanthane
A steel sheet is provided with a coating providing sacrificial cathodic protection. The coating includes between 1 and 40% by weight zinc, between 0.01 and 0.4% by weight lanthanum, optionally up to 10% by weight magnesium, optionally up to 15% by weight silicon, and optionally up to 0.3% by weight, in cumulative amounts, of additional components, the remainder includes aluminum and unavoidable impurities or residual elements. A method of producing parts by hot or cold swaging and the parts which can be obtained in this way are also provided.
1. A process to manufacture a part in steel provided with a coating providing sacrificial cathodic protection comprising the steps of:
providing a steel sheet previously coated with a coating providing sacrificial cathodic protection, the coating consisting of:
more than 80 weight % aluminium,
from 1 to less than 19.99 weight % zinc,
from 0.01 to 0.4 weight % lanthanum,
up to 10 weight % magnesium,
up to 15 weight % silicon,
up to 5 weight % iron,
up to 0.3 weight %, in accumulated weight, of additional elements selected from among Sb, Pb, Ca, Mn, Cr, Ni, Zr, Hf and Bi, and
a remainder of the coating consisting of unavoidable impurities;
cutting the sheet to obtain a blank;
heating the blank in a non-protective atmosphere up to an austenitization temperature Tm of 840 to 950° C.;
holding the blank at the austenization temperature Tm for a time tm of 1 to 8 minutes;
hot drawing the blank to obtain a part that is cooled at a rate such that a microstructure of the steel comprises at least one constituent selected from among martensite and bainite to obtain a steel part provided with a coating providing sacrificial cathodic protection;
the temperature Tm, time tm, thickness of the prior coating and the lanthanum, zinc and optionally magnesium contents thereof being selected so that a final mean iron content in an upper portion of the coating of the steel part provided with a coating providing sacrificial cathodic protection is lower than 75 weight %.
2. A steel part provided with a coating providing sacrificial cathodic protection obtainable using the hot drawing process according to claim 1 .
3. A steel sheet provided with a coating providing sacrificial cathodic protection, the coating consisting of:
more than 80 weight % aluminium,
from 1 to less than 19.99 weight % zinc;
from 0.01 to 0.4 weight % lanthanum;
up to 10 weight % magnesium;
up to 15 weight % silicon;
up to 5 weight % iron;
up to 0.3 weight %, in accumulated weight, of additional elements selected from among Sb, Pb, Ca, Mn, Cr, Ni, Zr, Hf and Bi; and
a remainder of the coating consisting of unavoidable impurities.
4. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the unavoidable impurities are derived from pollution of hot dip galvanizing baths through a passing of steel strips or impurities derived from ingots feeding the galvanizing baths or from ingots feeding vacuum deposit processes.
5. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the coating comprises 2 to 20 weight % of zinc.
6. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the coating comprises 0.1 to 0.3 weight % of lanthanum.
7. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the coating comprises 0.2 to 0.3 weight % of lanthanum.
8. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the coating comprises from 0 to 5 weight % of magnesium.
9. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the coating comprises from 0.5 to 10 weight % of silicon.
10. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the steel includes a weight content of 0.15%<C<0.5%, 0.5%<Mn<3%, 0.1%<Si<0.5%, Cr<1%, Ni<0.1%, Cu<0.1%, Al<0.1%, P<0.1%, S<0.05%, 0.0005%<B<0.08%, the remainder being formed of iron and unavoidable impurities due to steel processing.
11. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the coating has a thickness of 10 to 50 μm.
12. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 11 , wherein the said coating has a thickness of 27 to 50 μm.
13. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 3 , wherein the coating is applied to the steel sheet by hot dip.
14. A steel part provided with a coating providing sacrificial cathodic protection obtainable by cold drawing a sheet according to claim 3 .
15. A steel sheet provided with a coating providing sacrificial cathodic protection, the coating comprising:
more than 80 weight % aluminium,
from 1 to less than 19.99 weight % zinc;
from 0.01 to 0.4 weight % lanthanum;
up to 10 weight % magnesium;
up to 15 weight % silicon;
up to 5 weight % iron;
up to 0.3 weight %, in accumulated weight, of additional elements selected from among Sb, Pb, Ca, Mn, Cr, Ni, Zr, Hf and Bi;
and unavoidable impurities;
wherein the coating providing sacrificial cathodic protection is free from Ti.
16. A steel sheet provided with a coating providing sacrificial cathodic protection, the coating consisting of:
from 1 to less than 19.99 weight % zinc;
from 0.01 to 0.4 weight % lanthanum;
up to 15 weight % silicon;
up to 5 weight % iron;
up to 0.3 weight %, in accumulated weight, of additional elements selected from among Sb, Pb, Ca, Mn, Cr, Ni, Zr, Hf and Bi; and
a remainder of the coating consisting of aluminium and unavoidable impurities.