Zinc-coated steel sheet with high resistance spot weldability
US11649522B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Jun 13, 2018 |
| Grant date | May 16, 2023 |
| Priority date | — |
| Expiry date | Jan 28, 2040 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC25D3/22
- WIPO fieldMaterials, metallurgy
- WIPO sectorChemistry
Abstract
A method for producing a zinc or zinc-alloy coated steel sheet with a tensile strength higher than 900 MPa, for the fabrication of resistance spot welds containing in average not more than two Liquid Metal Embrittlement cracks per weld having a depth of 100 μm or more, with steps of providing a cold-rolled steel sheet, heating cold-rolled steel sheet up to a temperature T1 between 550° C. and Ac1+50° C. in a furnace zone with an atmosphere (A1) containing from 2 to 15% hydrogen by volume, so that the iron is not oxidized, then adding in the furnace atmosphere, water steam or oxygen with an injection flow rate Q higher than (0.07%/h×α), α being equal to 1 if said element is water steam or equal to 0.52 if said element is oxygen, at a temperature T≥T1, so to obtain an atmosphere (A2) with a dew point DP2 between −15° C. and the temperature Te of the iron/iron oxide equilibrium dew point, then heating the sheet from temperature T1 up to a temperature T2 between 720° C. and 1000° C. in a furnace zone under an atmosphere (A2) of nitrogen containing from 2 to 15% hydrogen and more than 0.1% CO by volume, with an oxygen partial pressure higher than 10−21 atm., wherein the duration tD of h…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.