Welded Coated Steel Blanks With Uniform Microstructure at the Joint
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Solution Overview
Problem
The formation of intermetallic areas during welding of coated steel blanks leads to reduced deformability and increased corrosion risk due to the presence of segregated metal elements, which can cause rupture under mechanical loading and corrosion when exposed.
Innovation Solution
A steel plate with a precoat consisting of an intermetallic alloy layer topped by a metal alloy layer, where the metal alloy layer is selectively removed from the periphery to prevent its introduction into the molten weld area, allowing for the formation of an intermetallic alloy compound that provides corrosion protection and decarburization resistance during heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the metal alloy layer is not removed from the periphery, then the coating provides corrosion protection, but the alloy layer is transferred into the molten weld area forming intermetallic areas that reduce deformability
Solution Approach 1:
The metal alloy layer is selectively removed from the periphery of the steel plate before welding. This extraction prevents the alloy layer from being transferred into the molten weld area, eliminating the formation of harmful intermetallic areas that would reduce deformability, while the intermetallic alloy layer remaining on the plate continues to provide corrosion protection.
Solution Approach 2:
The coating structure is modified locally: the periphery has the metal alloy layer removed to prevent weld contamination, while the central areas retain the full coating structure (intermetallic alloy layer plus metal alloy layer) to provide corrosion protection. This local differentiation resolves the contradiction between corrosion resistance and weldability.
2Strength
If the metal alloy layer is removed from the periphery, then intermetallic areas are eliminated improving deformability, but the coating structure is modified requiring additional processing
Solution Approach 1:
The metal alloy layer is removed from the periphery in advance, before the welding operation. This preliminary action prevents the formation of intermetallic areas during welding, ensuring high deformability of the welded joint without requiring post-weld removal of intermetallic areas, thus simplifying the overall manufacturing process.
3Adaptability or versatility
If welding is performed on coated steel blanks, then assembly is achieved, but segregated metal elements form intermetallic areas that cause rupture under mechanical loading
Solution Approach 1:
The harmful metal alloy layer is extracted from the periphery before welding, eliminating the source of segregated metal elements that would form intermetallic areas. This allows welding to proceed while preventing the formation of weak points that would cause rupture under mechanical loading, thus maintaining both welding capability and mechanical strength.
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 eliminates intermetallic areas, enhancing the deformability and corrosion resistance of welded steel parts, ensuring a ductility of at least 4% across the welded joint and maintaining mechanical strength while preventing oxidation and decarburization.
Implementation Method 1
the precoat is converted throughout its thickness by the heat treatment into an intermetallic alloy compound providing protection against corrosion and decarburization of the steel substrate
Implementation Method 2
butt welding the first and second steel plates at a weld so as to melt material from at least the first base, the first intermetallic alloy layer, the second base and the second intermetallic layer to form a molten weld material
Implementation Method 3
austenizing the welded steel plates at a temperature between Ac1 and Ac3+100 degrees C. for a time greater than or equal to 20 seconds
Implementation Method 4
cooling the welded steel plates so as to render a uniform microstructure to the weld
Data Source
AI summary
A method for creating a welded steel part includes providing a first steel plate having a first base, a first intermetallic alloy layer on the first base and a first metal alloy layer on the first intermetallic alloy layer; providing a second steel plate having a second base, a second intermetallic alloy layer on the second base and a second metal alloy layer on the second intermetallic alloy layer; butt welding the first and second steel plates at a weld so as to melt material from at least the first base, the first intermetallic alloy layer, the second base and the second intermetallic layer to form a molten weld material; austenizing the welded steel plates at a temperature between Ac1 and Ac3+100 degrees C. for a time greater than or equal to 20 seconds; and cooling the welded steel plates so as to render a uniform microstructure to the weld.