Hot-Formed Welded Steel Part With Coating Removal at Weld Edges
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for fabricating high-strength welded steel parts, particularly for automotive applications, face challenges in achieving sufficient mechanical strength and microstructural homogeneity in the weld metal zone due to aluminum content dilution and intermetallic compound formation during the welding process, leading to potential cracking and reduced hardenability.
Innovation Solution
The solution involves removing the metal alloy layer from the edges of steel sheets before welding, retaining the intermetallic alloy layer, and using a specific carbon content ratio in the weld metal zone to ensure a martensitic microstructure, thereby enhancing mechanical strength and preventing fracture in the weld zone under tensile stress.
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 invention extracts and removes the aluminum-based pre-coating from the edges of steel sheets before welding. This eliminates the source of aluminum that would otherwise dilute into the weld metal zone and form harmful intermetallic compounds, thereby preventing cracking while still allowing the welding process to proceed
Solution Approach 2:
The invention performs the removal of the aluminum pre-coating as a preliminary action before the welding operation. By removing the coating in advance, the subsequent welding process does not encounter aluminum that would dilute into the weld zone and create intermetallic compounds, thus preventing cracking before it can occur
2Reliability
If the aluminum content in the weld metal zone is low, then the pre-coating is not sufficiently diluted, but the aluminum prevents transformation into austenite and martensite or bainite cannot be obtained during cooling
Solution Approach 1:
The invention applies local quality by removing the aluminum pre-coating specifically from the edge regions that will become part of the weld metal zone, while retaining the pre-coating on the bulk of the steel sheets. This localized removal ensures proper austenite transformation and martensite formation in the weld zone without affecting the overall corrosion resistance of the steel sheets
3Strength
If the welded blank is heated to austenitization temperature and then hot-formed, then high mechanical strength can be obtained, but the weld metal zone exhibits hardness and mechanical strength less than the adjacent sheets
Solution Approach 1:
The invention extracts the aluminum pre-coating from the edge regions before welding, preventing aluminum dilution in the weld metal zone. This eliminates the formation of intermetallic compounds and ensures uniform austenite transformation during heating, resulting in homogeneous martensite formation and consistent mechanical properties throughout the welded structure after hot-forming
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 exceeding 1230 MPa, where fractures occur in the base metal rather than the weld zone, ensuring the part's suitability for automotive applications by maintaining high mechanical characteristics and preventing sudden fracture.
Implementation Method 1
heating the welded blank before performing a hot forming operation to impart to the steel part the shape required for its application
Implementation Method 2
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
Implementation Method 3
these welded blanks are heated to a temperature that makes possible the austenitization of the steel and are then hot-formed and rapidly cooled in the forming die
Data Source
AI summary
A welded steel part with a very high mechanical strength is provided. The welded steel part is 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. The at least one first and second sheets including, at least in part, a steel substrate and a pre-coating which includes an intermetallic alloy layer in contact with the steel substrate, topped by a metal alloy layer of aluminum or aluminum-based alloy. A method for the fabrication of a welded steel part and the fabrication of structural or safety parts for automotive vehicles are also provided.