Multilayer Steel Decarburized Layer Mitigates Liquid Metal Embrittlement
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Solution Overview
Problem
Advanced high-strength steels, particularly TRIP steels, are susceptible to liquid metal embrittlement during welding due to factors like tensile stress and wetting by liquid zinc, which can lead to cracking and reduced weldability.
Innovation Solution
A multilayer steel composition and manufacturing process involving a core of transformation-induced plasticity (TRIP) steel with a decarburized layer and a zinc-based coating, where the decarburized layer is composed of at least 80% ferrite and has reduced carbon content, is developed to mitigate liquid metal embrittlement. This process includes cold-rolling, annealing, decarburizing, and applying a zinc-based coating to the TRIP steel core to form a coated blank that is less susceptible to embrittlement during welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a zinc-based coating is applied to TRIP steel for corrosion protection, then corrosion resistance is improved, but liquid metal embrittlement susceptibility increases during welding
Solution Approach 1:
The steel structure is segmented into multiple layers with different carbon contents: a high-carbon core region for strength and a low-carbon surface region for embrittlement resistance. This segmentation allows the material to simultaneously achieve corrosion protection from the zinc coating and resistance to liquid metal embrittlement during welding.
Solution Approach 2:
Different regions of the steel are given different local properties: the core maintains high carbon content (0.23-0.40 wt%) for strength, while the surface region has reduced carbon content (0.03-0.15 wt%) to prevent embrittlement. This local quality differentiation resolves the contradiction between needing zinc coating for corrosion protection and avoiding liquid metal embrittlement during welding.
2Ease of manufacture
If carbon content is reduced in the steel to improve weldability, then weldability is improved, but strength is reduced
Solution Approach 1:
The steel is divided into zones with different carbon contents: a high-carbon core (0.23-0.40 wt%) that provides strength and a low-carbon surface region (0.03-0.15 wt%) that enables weldability. This segmentation allows both strength and weldability to be achieved simultaneously in different regions of the same material.
Solution Approach 2:
The steel exhibits local quality variation where the core region has high carbon content for strength while the surface region has low carbon content for weldability. The carbon gradient transitions from the core to the surface, allowing the material to satisfy both conflicting requirements in their respective locations.
3Object-affected harmful factors
If a decarburized layer is created to reduce liquid metal embrittlement, then embrittlement resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The decarburized layer is formed preliminarily during the steelmaking and rolling processes before the steel is used for welding. By creating the low-carbon surface region during initial material production rather than during manufacturing or welding preparation, the process complexity is minimized while still achieving embrittlement resistance.
Solution Approach 2:
The carbon content parameter is changed during the steel production process to create a gradient from high carbon in the core to low carbon at the surface. This parameter change is achieved through controlled decarburization during rolling or heat treatment, creating the desired low-carbon surface layer without requiring complex post-processing steps.
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
The multilayer steel composition significantly reduces the likelihood of liquid metal embrittlement, enhancing weldability and maintaining strength by minimizing carbon content in surface regions, reducing grain boundary area, and altering the microstructure to withstand high temperatures during welding.
Implementation Method 1
a decarburized layer exterior to the core on at least one side. The decarburized layer has reduced carbon content relative to the core
Implementation Method 2
A method of creating a coated advanced high-strength steel component is also provided. The method includes cold-rolling a core from transformation-induced plasticity (TRIP) steel, and annealing the TRIP steel core
Implementation Method 3
applying a zinc-based coating to the decarburized layer to form a coated blank
Data Source
AI summary
A multilayer steel includes a core formed of transformation-induced plasticity (TRIP) steel. A decarburized layer is exterior to the core on at least one side thereof. The decarburized layer has reduced carbon content relative to the core. A zinc-based layer is exterior to the decarburized layer. The decarburized layer may have a composition of at least 80 percent ferrite, such that LME is reduced or mitigated. In some configurations, the decarburized layer is between 10-50 microns thick. A method of creating a coated advanced high-strength steel component is also provided. An apparatus for forming a coated advanced high-strength steel is also provided. The core of the multilayer steel may have a carbon weight-percent of less than or equal to 0.4. The decarburized layer of the multilayer steel may have a carbon weight-percent of less than or equal to 50 percent of the carbon weight-percent of the core.