Patent ID: 11945503
Assignee: ARCELORMITTAL
Field: Machine tools (Mechanical engineering)
Classification: CPC B  C | IPC B  C

Claim 15:
16. A welded steel blank comprising:
two precoated sheets, each precoated sheet comprising a steel substrate having a precoating on at least one of its main faces, the precoating comprising an intermetallic alloy layer comprising at least iron and aluminum, the steel substrate being made of a press-hardenable steel,
for at least one of the precoated sheets, the steel of the steel substrate comprising, by weight:
0.10%≤C≤0.5%
0.5%≤Mn≤3%
0.1%≤Si≤1%
0.01%≤Cr≤1%
Ti≤0.2%
Al≤0.1%
S≤0.05%
P≤0.1%
B≤0.010%
a rest being iron and impurities resulting from manufacturing,
and the precoated sheets being joined by a weld joint, the weld joint being characterized by:
(a) a quenching factor FTWJ of the weld joint such that FTWJ−0.9FTBM≥0, where:
FTBM is the quenching factor of a least hardenable steel substrate among the steel substrates of the two precoated sheets, and
the quenching factors FTWJ and FTBM are determined using the following formula: FT=128+1553×C+55×Mn+267×Si+49×Ni+5×Cr−79×Al−2×Ni2−1532×C2−5×Mn2−127×Si2−40×C×Ni−4×Ni×Mn, where Al, Cr, Ni, C, Mn and Si are, respectively, a mean aluminum, chromium, nickel, carbon, manganese and silicon content, expressed in weight percent, of an area whose quenching factor is to be determined, this area being the weld joint in the case of FTWJ and the least hardenable steel substrate in the case of FTBM, and

(b) a carbon content CWJ of the weld joint strictly smaller than 0.15 wt. % or, if the carbon content CWJ of the weld joint is greater than or equal to 0.15 wt. %, a softening factor FAWJ of the weld joint such that FAWJ>5000, where the softening factor FAWJ of the weld joint is calculated as a function of a mean aluminum, chromium, nickel, molybdenum, carbon, manganese and silicon content of the weld joint, expressed in weight percent, using the following formula:

FA=10291+4384.1×Mo+3676.9Si−522.64×Al−2221.2×Cr−118.11×Ni−1565.1×C−246.67×Mn,

and the weld joint is such that, after hot press-forming and cooling, a maximum hardness variation ΔHV(WJ) across the weld joint is smaller than or equal to 20% of a mean hardness HVmean (WJ) of the weld joint.