Method of thermomechanical shaping a final product with very high strength and a product produced thereby
A method of thermomechanical shaping a final product with very high strength including the steps of: providing a coated hot-rolled and/or cold-rolled steel strip or sheet including (all percentages in wt. %): 0.04%<carbon<0.5%, 0.5%<manganese<3.5%, silicon<1.0%, 0.01%<chromium<1%, titanium<0.2%, aluminum<0.2%, phosphorus<0.1%, nitrogen<0.015% N, sulphur<0.05%, boron<0.015%, unavoidable impurities, balance iron, the steel being coated with a zinc alloy coating layer, wherein the zinc alloy consists of 0.3-4.0% Mg and 0.05-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc; cutting the steel sheet to obtain a steel sheet blank; thermomechanical shaping of the steel sheet blank to a final product with its final properties.
1. Method of thermomechanical shaping a final product with very high strength comprising the steps of:
providing a coated hot-rolled and/or cold-rolled steel strip or sheet comprising (all percentages in wt. %):
0.04%<carbon<0.5%
0.5%<manganese<3.5%
silicon<1.0%
0.01%<chromium<1%
titanium<0.2%
aluminium<2.0%
phosphorus<0.1%
nitrogen<0.015%
sulphur<0.05%
boron<0.015%
unavoidable impurities,
balance iron,
the steel being coated with a zinc alloy coating layer, wherein the zinc alloy consists of 1.6-2.3% Mg and 1.6-2.3% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc;
cutting the coated steel strip or sheet to obtain a steel sheet blank;
thermomechanical shaping of the steel sheet blank to a final product with its final properties;
wherein the thermomechanical shaping comprises
heating the blank to a temperature above Ac1 to at least partially austenitise the blank, shaping the blank into a product at elevated temperature and rapid cooling the product to obtain the final product with its final properties.
2. Method according to claim 1 , wherein the steel comprises:
0.15%<carbon<0.5%
0.5%<manganese<3%
0.1%<silicon<0.5%
0.01%<chromium<1%
titanium<0.2%
aluminium<0.1%
phosphorus<0.1%
nitrogen 0-0.01%
sulphur<0.05%
0.0005%<boron<0.015%
unavoidable impurities,
balance iron.
3. Method according to claim 1 , wherein the coated hot-rolled and/or cold-rolled steel strip or sheet consists of (all percentages in wt. %):
0.15%<carbon<0.5%
0.5%<manganese<3.5%
silicon<1.0%
0.01%<chromium<1%
titanium<0.2%
aluminium<2.0%
phosphorus<0.1%
nitrogen<0.015%
sulphur<0.05%
boron<0.015%
Nb<0.05%
unavoidable impurities,
balance iron,
the steel being coated with a zinc alloy coating layer, wherein the zinc alloy consists of 1.6-2.3% Mg and 1.6-2.3% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc.
4. Method according to claim 1 , wherein the steel comprises:
0.15%<carbon<0.40%
0.8%<manganese<1.5%
0.1%<silicon<0.35%
0.01%<chromium<1%
nitrogen 0-0.01%
titanium<0.1
aluminium<0.1%
phosphorus<0.05%
sulphur<0.03%
0.0005%<boron<0.01%,
unavoidable impurities,
balance iron,
wherein Ti>3.4N.
5. Method according to claim 1 , wherein the steel comprises:
0.15-0.25% C
1.0-1.5% Mn
0.1-0.35% Si
max 0.8% Cr
max 0.1% Al
0-0.05% Nb
0-0.01% N
0.01-0.07% Ti
phosphorus<0.05%
sulphur<0.03%
0.0005%<boron<0.008%
unavoidable impurities,
balance iron.
6. Method according to claim 1 , wherein the steel comprises at least 0.0015% B.
7. Method according to claim 1 , wherein the steel comprises:
0.15-0.25% C
1.0-1.5% Mn
0.1-0.35% Si
max 0.8% Cr
max 0.1% Al
0-0.05% Nb
0-0.01% N
0.0015-0.008% B
0.01-0.07% Ti wherein Ti>3.4N
unavoidable impurities
balance iron.
8. Method according to claim 1 , wherein the steel comprises Ti-3.4N<0.05%.
9. Method according to claim 1 , wherein the final product is an automotive part.
10. Structural and/or anti-intrusion or substructure parts for a land motor vehicle selected from the group consisting of a bumper beam of a car, a door reinforcement or a B-pillar reinforcement produced according to claim 1 .
11. Method according to claim 1 , wherein the steel comprises Ti-3.4N<0.02%.
12. Method according to claim 1 , wherein the steel includes nitrogen 0.005-0.015%.
13. Method according to claim 1 , wherein the amount of aluminum in wt. % is the same as the amount of magnesium in wt. % plus or minus a maximum of 0.3 wt. %.
14. Method according to claim 1 , further comprising galvannealing the zinc alloy coating prior to said shaping to achieve an iron content in the zinc alloy coating of between 7 and 15 wt. %.
15. The method of claim 1 , wherein the coated hot-rolled and/or cold-rolled steel strip or sheet comprises (all percentages in wt. %):
0.15%<carbon<0.5%
0.5%<manganese<3.5%
silicon<1.0%
0.01%<chromium<1%
titanium 0.01-0.2%, wherein Ti>3.4N
aluminium<2.0%
phosphorus<0.1%
nitrogen 0.005-0.015%
sulphur<0.05%
boron 0.0005%-0.015%
Nb<0.05%
unavoidable impurities,
balance iron.
16. Method according to claim 15 , wherein the steel comprises 0.0015%<boron<0.015% and 0.01-0.07% Ti and 0.012-<0.1% P, wherein the steel comprises Ti-3.4N<0.05%.
17. Method according to claim 16 , wherein the steel comprises Ti-3.4N<0.02%.