Welded Hot-Stamped Steel Blank With Coating Removal at Weld Edges
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Solution Overview
Problem
Existing methods for fabricating welded steel parts with high mechanical strength, such as those used in the automotive industry, face challenges in achieving sufficient hardness and microstructure in the weld metal zone due to aluminum content dilution and intermetallic compound formation during the welding process, leading to potential cracking and decreased mechanical properties.
Innovation Solution
The solution involves removing the metal alloy layer from the edges of steel sheets before welding, while retaining the intermetallic alloy layer, and using a specific carbon content ratio between the weld metal zone and the substrate, along with controlled laser welding and filler metal addition, to achieve a martensitic microstructure and enhanced mechanical strength in the weld metal zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the aluminum-based pre-coating is diluted with the steel substrate during welding, then the weld metal zone forms, but intermetallic compounds are formed resulting in sites where incipient cracking is most likely to occur
Solution Approach 1:
The patent applies preliminary action by removing the aluminum-based metal alloy layer from the steel sheets before welding. This pre-removal prevents the formation of harmful intermetallic compounds during the welding process, eliminating the root cause of cracking while still allowing the welding operation to proceed effectively.
Solution Approach 2:
The patent extracts the harmful component (aluminum-based metal alloy layer) from the steel sheets prior to welding. By selectively removing this layer, the patent eliminates the source of intermetallic compound formation and cracking susceptibility, while preserving the beneficial intermetallic alloy layer for corrosion protection.
2Reliability
If the aluminum content in the weld metal zone is lower, then the pre-coating provides corrosion resistance, but the aluminum prevents transformation into austenite, making it no longer possible to obtain martensite or bainite during cooling
Solution Approach 1:
The patent applies local quality by creating different aluminum content zones: the weld metal zone has low aluminum content (≤0.1%) to enable martensitic transformation and high strength, while the intermetallic alloy layer is preserved at the interface for corrosion resistance. This spatial differentiation of composition allows both contradictory requirements to be satisfied in different locations.
Solution Approach 2:
The patent performs preliminary removal of the aluminum-based metal alloy layer before welding to ensure the weld metal zone has sufficiently low aluminum content for martensitic transformation, while the underlying intermetallic alloy layer remains intact to provide corrosion resistance during service.
3Strength
If the carbon content of the weld metal zone is increased to achieve high strength, then mechanical strength improves, but the risk of sudden fracture increases
Solution Approach 1:
The patent optimizes the carbon content parameter in the weld metal zone to a specific range (0.20-0.35%) that balances mechanical strength and fracture resistance. This precise parameter control ensures the weld metal achieves sufficient strength (≥1230 MPa) while maintaining adequate toughness and resistance to sudden fracture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a welded steel part with mechanical strength greater than 1230 MPa, where fractures occur in the base metal rather than the weld metal zone under tensile stress, ensuring the weld joint meets the required strength and toughness for automotive applications.
Implementation Method 1
a welding step consisting of melting, by means of a laser beam, the peripheral edges to be welded of the first and second steel sheets, together with the filler wire
Implementation Method 2
One known welding technology is laser beam welding
Implementation Method 3
heating the welded blank before performing a hot forming operation, for example by hot stamping
Implementation Method 4
The subsequent heat treatment applied during a hot-forming process or after the forming and cooling carried out after this heat treatment makes it possible to obtain a martensitic microstructure
Data Source
AI summary
The invention relates principally to a welded steel part with a very high mechanical strength characteristics obtained by heating followed by hot forming, then cooling of at least one welded blank obtained by butt welding of at least one first and one second sheet consisting at least in part of a steel substrate and a pre-coating which is constituted by an intermetallic alloy layer in contact with the steel substrate, topped by a metal alloy layer of aluminum or aluminum-based alloy.This welded steel part claimed by the invention is essentially characterized in that the metal alloy layer (19, 20) has been removed from the edges (36) in direct proximity to the weld metal zone (35), while the intermetallic alloy layer (17, 18) has been left in place, and in that over at least a portion of the length of the weld metal zone (35), the ratio between the carbon content of the weld metal zone (35) and the carbon content of the substrate (25, 26) of either the first or the second sheet (11, 12) having the higher carbon content (Cmax) is between 1.27 and 1.59.The invention likewise relates to a method for the fabrication of a welded steel part as well as the use of this welded steel part for the fabrication of structural or safety parts for automotive vehicles.