Process for manufacturing stamped products, and stamped products prepared from the same
The invention relates to a process for making a hot stamped coated steel sheet product, comprising the steps of pre-coating a steel strip or sheet with aluminium- or aluminium alloy, cutting said pre-coated steel strip or sheet to obtain a pre-coated steel blank, heating the blank in a furnace preheated to a temperature and during a time defined by diagram according to thickness, at a heating rate V c between 20 and 700° C. comprised between 4 and 12° C./s and at a heating rate V c ′ between 500 and 700° C. comprised between 1.5 and 6° C./s, to obtain a heated blank; then transferring said heated blank to a die, hot stamping the heated blank in the die obtain a hot stamped steel sheet product, cooling at a mean rate V r between the exit of the heated blank from the furnace, down to 400° C., of at least 30° C./s.
1. A process for making a hot stamped coated steel product, comprising:
Heating a aluminum or aluminum alloy pre-coated steel blank, a thickness t p of the pre-coating being form 20 to 33 micrometers, in a furnace preheated to a temperature and time during a time defined by diagram ABCD of FIG. 1 if a thickness of said blank is greater than or equal to 0.7 mm and less than or equal to 1.5 mm, and by diagram EFGH of FIG. 1 if a thickness of said blank is greater than 1.5 mm and less than or equal to 3 mm, at a mean heating rate V c between 20 and 700° C. of 4-12° C./s, and a mean heating rate V c ′ between 500 and 700° C. of 1.5-6° C./s, to obtain a heated blank, wherein the mean heating rate V c is greater than the mean heating rate V c ′; and
Hot stamping said heated blank in a die.
2. The process according to claim 1 , further comprising:
hot stamping said heated blank in said die, to thereby obtain a hot stamped steel sheet product, and
cooling said hot stamped steel sheet product to 400° C. at a mean rate V r of at least 30° C./s.
3. The process according to claim 2 , wherein the pre-coated steel blank is formed by hot dipping a steel strip or sheet having a first side and a second side in an aluminium or aluminium alloy bath to provide a pre-coating having a thickness t p of the said pre-coating being from 20 to 33 micrometers at every location on said first and second sides of said strip or sheet.
4. The process according to claim 2 , wherein an elapsed time between when said heated blank exits said furnace and said stamping commences is not more than 10 seconds.
5. The process according to claim 1 , wherein a composition of the steel blank comprises iron and the following components by weight based on total weight:
0.15%<carbon<0.5%
0.5%<manganese<3%
0.1%<silicon<0.5%
0.01%<chromium<1%
nickel<0.1%
copper<0.1%
titanium<0.2%
aluminum<0.1%
phosphorus<0.1%
sulfur<0.05%
0.0005%<boron<0.08%.
6. The process according to claim 1 , wherein the composition of the steel blank comprises iron and the following components by weight based on total weight:
0.20%<carbon<0.5%
0.8%<manganese<1.5%
0.1%<silicon<0.35%
0.01%<chromium<1%
nickel<0.1%
copper<0.1%
titanium<0.1%
aluminum<0.1%
phosphorus<0.05%
sulfur<0.03%
0.0005%<boron<0.01%.
7. The process according to claim 1 , wherein the composition of the aluminum or aluminum alloy pre-coating comprises aluminum, from 8% to 11% silicon by weight, and from 2% to 4% iron by weight.