Method for hot dip galvanizing of AHSS or UHSS strip material, and such material
A method for hot dip galvanizing of advanced high strength or ultra high strength steel strip material, such as dual phase steel, transformation induced plasticity steel, transformation induced plasticity assisted dual phase steel and twinning induced plasticity steel strip material. The strip material is pickled and thereafter heated to a temperature below the continuous annealing temperature before the strip material is hot dip galvanized.
1. Method for hot dip galvanizing of dual phase steel, transformation induced plasticity steel, transformation induced plasticity assisted dual phase steel or twinning induced plasticity steel strip material comprising,
pickling the strip material and thereafter heating the pickled strip material to a temperature below a continuous annealing temperature of the strip material, between 400 and 600° C., before the strip material is hot dip galvanized;
wherein Fe in the strip material is reduced during or after the heating to a temperature below the continuous annealing temperature and before the hot dip galvanizing;
hot dip galvanizing the strip material after said heating, wherein the reduction is performed using H 2 N 2 in the reducing atmosphere.
2. Method according to claim 1 , wherein an excess amount of O 2 is provided in the atmosphere during or after the heating of the strip material and before the reduction of the strip material.
3. Method according to claim 2 , wherein the excess amount of O 2 is provided in an amount of 0.05-5% O 2 .
4. Method according to claim 1 , wherein the steel strip material is hot rolled before galvanizing to form a hot rolled strip material and the steel strip material is hot dip galvanized as the hot roiled strip material.
5. Method according to claim 4 , wherein the hot rolled strip material is hot dip galvanized without a continuous annealing step between the hot rolling and the hot dip galvanizing of the strip material.
6. Method according to claim 1 , wherein the steel strip material is cold rolled before galvanizing and hot dip galvanized as a cold rolled product, which has been annealed after cold roiling and before pickling.
7. Method according to claim 6 , wherein the steel strip material has been pickled before the cold rolling.
8. Method according to claim 1 , wherein the cold rolled strip material is produced from a hot rolled strip material or a belt cast strip material.
9. Method according to claim 1 , wherein the steel strip material comprises 0.04-0.30% C, 1.0-3.5% Mn, 0-1.0% Si, 0-2.0% Al and 0-1.0% Cr, the remainder being Fe and inevitable impurities.
10. Method according to claim 9 , wherein the steel strip material is a transformation induced plasticity steel strip material, comprising 0.15-0.30% C, 1.5-3.5% Mn, 0.2-0.8% Si and 0.5-2.0% Al, the remainder being Fe and inevitable impurities.
11. Method according to claim 9 , wherein the steel strip material is a transformation induced plasticity steel strip material, comprising 0.15-0.24% C, 1.5-2.0% Mn, 0.2-0.6% Si and 0.5-1.5% Al, the remainder being Fe and inevitable impurities.
12. Method according to claim 1 , wherein the steel strip material is a twinning induced plasticity steel strip material comprising between 10 and 40% manganese, and up to 10 aluminium.
13. Method according to claim 1 , wherein the steel strip material is a twinning induced plasticity steel strip material comprising between 12 and 25% manganese, and up to 10% aluminium.
14. Method for hot dip galvanizing of dual phase steel, transformation induced plasticity steel, transformation induced plasticity assisted dual phase steel or twinning induced plasticity steel strip material comprising,
pickling the strip material and thereafter heating the pickled strip material to a temperature below a continuous annealing temperature of the strip material, between 400 and 600° C., before the strip material is hot dip galvanized;
wherein Fe in the strip material is reduced during or after the heating to a temperature below the continuous annealing temperature and before the hot dip galvanizing;
hot dip galvanizing the strip material after said heating, wherein the reduction is performed using 5-30% H 2 N 2 in the reducing atmosphere.
15. Method according to claim 14 , wherein an excess amount of O 2 is provided in the atmosphere during or after the heating of the strip material and before the reduction of the strip material.
16. Method according to claim 15 , wherein the excess amount of O 2 is provided in an amount of 0.05-5% O 2 .
17. Method according to claim 14 , wherein the steel strip material is cold rolled before galvanizing and hot dip galvanized as a cold rolled product, which has been annealed after cold rolling and before pickling.
18. Method according to claim 14 , wherein the steel strip material comprises 0.04-0.30% C, 1.0-3.5% Mn, 0-1.0% Si, 0-2.0% Al and 0-1.0% Cr, the remainder being Fe and inevitable impurities.
19. Method according to claim 14 , wherein the steel strip material is a twinning induced plasticity steel strip material comprising between 10 and 40% manganese, and up to 10 aluminium.
20. Method according to claim 14 , wherein the steel strip material is a transformation induced plasticity steel strip material, comprising 0.15-0.30% C, 1.5-3.5% Mn, 0.2-0.8% Si and 0.5-2.0% Al, the remainder being Fe and inevitable impurities.