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

Claim 19:
20. A welded, hot press-formed and cooled steel part comprising:
a first coated steel part portion; and
a second coated steel part portion,
each coated steel part portion comprising a steel substrate having, on at least one of its main faces, a coating comprising at least iron and aluminum, the steel substrate being made of a press-hardenable steel,
the steel of the steel substrate of at least one among the first and the second coated steel part portions 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 first and second coated steel part portions 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 coated steel part portions, 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 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.