US2021214816A1PendingUtilityA1
Method for fabricating steel sheet for press hardening, and parts obtained by this method
Est. expiryJul 30, 2034(~8 yrs left)· nominal 20-yr term from priority
C21D 8/00C22C 38/18C21D 9/0068B21B 3/02C23C 2/12C22C 38/40C22C 38/38C21D 9/46C21D 8/02C22C 38/32C22C 38/04C22C 38/54C21D 8/0278C22C 38/48B21D 22/022C21D 8/0263C22C 38/08C22C 38/14C22C 38/12C22C 38/02C22C 38/06C21D 1/18C22C 38/44C21D 2211/009C22C 38/001C22C 38/002C21D 2211/008C22C 38/50C21D 1/673C21D 8/0236C23F 17/00C23C 2/40C22C 38/58C21D 1/06C21D 8/0226C21D 2211/002C21D 2211/005C21D 8/0273C23C 2/06C21D 8/005C23C 2/28C23C 2/29C23C 2/261
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Claims
Abstract
The present invention provides fabrication methods for cold rolled, precoated and press hardened steel sheets, for which the chemical composition includes, with contents expressed by weight, 0.24%≤C≤0.38%, 0.40%≤Mn≤3%, 0.10%≤Si≤0.70%, 0.015%≤Al≤0.070%, 0%≤Cr≤2%, 0.25%≤Ni≤2%, 0.015%≤Ti≤0.10%, 0%≤Nb≤0.060%, 0.0005%≤B≤0.0040%, 0.003%≤N≤0.010%, 0.0001%≤S≤0.005%, 0.0001%≤P≤0.025%, it being understood that the titanium and nitrogen content satisfy: Ti/N>3.42, and that the carbon, manganese, chromium and silicon content satisfy: 2.6C+Mn/5.3+Cr/13+Si/15≥1.1%, with the chemical composition optionally including one or more of the following elements: 0.05%≤Mo≤0.65%, 0.001%≤W≤0.30%, 0.0005%≤Ca≤0.005%, with the remainder made up of iron and inevitable impurities coming from preparation.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A fabrication method for a cold rolled and annealed sheet, comprising the steps of:
supplying a hot rolled sheet, coiled and pickled, and fabricated by:
casting an intermediate product with a chemical composition including, with contents being expressed by weight:
0.24%≤C≤0.38%;
0.40%≤Mn≤3%;
0.10%≤Si≤0.70%;
0.015%≤Al≤0.070%;
0%≤Cr≤2%;
0.25%≤Ni≤2%;
0.015%≤Ti≤0.10%;
0%≤Nb≤0.060%;
0.0005%≤B≤0.0040%;
0.003%≤N≤0.010%;
0.0001%≤S≤0.005%; and
0.0001%≤P≤0.025%;
the titanium and nitrogen contents satisfying Ti/N>3.42;
the carbon, manganese, chromium and silicon contents satisfying:
2
.
6
C
+
Mn
5
.
3
+
Cr
1
3
+
Si
1
5
≥
1
.1
%
;
a remainder of the chemical composition being made up of iron and inevitable impurities resulting from processing;
reheating the intermediate product to a temperature between 1250° C. and 1300° C. for a hold time between 20 and 45 minutes;
hot rolling the intermediate product until an end of rolling temperature, ERT, between 825° C. and 950° C. to obtain a heat rolled sheet;
coiling the hot rolled sheet at a temperature between 500° C. and 750° C. to obtain a hot rolled and coiled sheet; and
pickling an oxide layer formed during the preceding steps;
cold rolling the hot rolled, coiled and pickled sheet to obtain a cold rolled sheet; and
annealing the cold rolled sheet at a temperature between 740° C. and 820° to obtain a cold rolled and annealed sheet.
2 . A fabrication method for a precoated sheet, comprising the steps of:
supplying a rolled sheet and fabricated by:
casting an intermediate product with a chemical composition including, with contents being expressed by weight:
0.24%≤C≤0.38%;
0.40%≤Mn≤3%;
0.10%≤Si≤0.70%;
0.015%≤Al≤0.070%;
0%≤Cr≤2%;
0.25%≤Ni≤2%;
0.015%≤Ti≤0.10%;
0%≤Nb≤0.060%;
0.0005%≤B≤0.0040%;
0.003%≤N≤0.010%;
0.0001%≤S≤0.005%; and
0.0001%≤P≤0.025%;
the titanium and nitrogen contents satisfying Ti/N>3.42;
the carbon, manganese, chromium and silicon contents satisfying:
2
.
6
C
+
Mn
5
.
3
+
Cr
1
3
+
Si
1
5
≥
1
.1
%
;
and
a remainder of the chemical composition being made up of iron and inevitable impurities resulting from processing;
reheating the intermediate product to a temperature between 1250° C. and 1300° C. for a hold time between 20 and 45 minutes;
hot rolling the intermediate product until an end of rolling temperature, ERT, between 825° C. and 950° C. to obtain a heat rolled sheet;
coiling the hot rolled sheet at a temperature between 500° C. and 750° C. to obtain a hot rolled and coiled sheet; and
pickling an oxide layer formed during the preceding steps; and
performing a continuous hot-dip pre-coating, the precoating being aluminum or an aluminum or aluminum-based alloy, or zinc or a zinc or zinc-based alloy.
3 . The fabrication method as recited in claim 2 wherein the performing step is with the aluminum or aluminum-based alloy; and further comprising performing a thermal pretreatment of the precoated sheet at a temperature θ1 between 620° C. and 680° C. for a holding time t1 between 6 and 15 hours, such that the pre-coating no longer contains free aluminum of phase τ 5 of type Fe 3 Si 2 Al 2 , and τ 6 of type Fe 2 Si 2 Al 9 , and such that an austenitic transformation does not occur in the steel substrate, the pretreatment being done in a furnace under hydrogen and nitrogen atmosphere.
4 . A fabrication method for a press hardened part comprising the steps of:
supplying a sheet fabricated by:
casting an intermediate product with a chemical composition including, with contents being expressed by weight:
0.24%≤C≤0.38%;
0.40%≤Mn≤3%;
0.10%≤Si≤0.70%;
0.015%≤Al≤0.070%;
0%≤Cr≤2%;
0.25%≤Ni≤2%;
0.015%≤Ti≤0.10%;
0%≤Nb≤0.060%;
0.0005%≤B≤0.0040%;
0.003%≤N≤0.010%;
0.0001%≤S≤0.005%; and
0.0001%≤P≤0.025%;
the titanium and nitrogen contents satisfying Ti/N>3.42;
the carbon, manganese, chromium and silicon contents satisfying:
2
.
6
C
+
Mn
5
.
3
+
Cr
1
3
+
Si
1
5
≥
1
.1
%
;
and
a remainder of the chemical composition being made up of iron and inevitable impurities resulting from processing;
reheating the intermediate product to a temperature between 1250° C. and 1300° C. for a hold time between 20 and 45 minutes;
hot rolling the intermediate product until an end of rolling temperature, ERT, between 825° C. and 950° C. to obtain a heat rolled sheet;
coiling the hot rolled sheet at a temperature between 500° C. and 750° C. to obtain a hot rolled and coiled sheet; and
pickling an oxide layer formed during the preceding steps;
cutting the sheet to obtain a blank;
heating the blank to a temperature between 810° C. and 950° C. to obtain a fully austenitic structure in the steel;
transferring the blank inside a press;
hot stamping the blank to obtain a part; and
holding the part inside the press to obtain a hardening by martensitic transformation of the austenitic structure.
5 . The fabrication method as recited in claim 4 wherein the steps are performed successively.
6 . The fabrication method as recited in claim 4 further comprising the step of deforming the blank by cold stamping after the step of cutting the sheet.
7 . The fabrication method as recited in claim 4 wherein the chemical composition includes at least one of the following elements, by weight:
0.05%≤Mo≤0.65%;
0.001%≤W≤0.30%; and
0.0005%≤Ca≤0.005%.
8 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.32%≤C≤0.36%;
0.40%≤Mn≤0.80%; and
0.05%≤Cr≤1.20%.
9 . The fabrication method as recited in claim 4 wherein the chemical composition thereof includes, by weight:
0.24%≤C≤0.28%; and
1.50%≤Mn≤3%.
10 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.50%≤Si≤0.60%.
11 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.30%≤Cr≤0.50%.
12 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.30%≤Ni≤1.20%.
13 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.30%≤Ni≤0.50%.
14 . The fabrication method as recited in claim 4 wherein the chemical composition thereof comprises, by weight:
0.020%≤Ti.
15 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.020%≤Ti≤0.040%.
16 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.15%≤Mo≤0.25%.
17 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.010%≤Nb≤0.060%.
18 . The fabrication method as recited in claim 4 wherein the chemical composition includes, by weight:
0.030%≤Nb≤0.050%.
19 . The fabrication method as recited in claim 4 wherein a diffusible hydrogen content below 0.16 ppm is obtained in the sheet.Join the waitlist — get patent alerts
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