Nickel Interlayer Zinc Coating for LME-Resistant Steel Sheet
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Solution Overview
Problem
Zinc-based coated steel sheets experience liquid metal embrittlement (LME) during heating processes like hot press hardening and welding, leading to cracks and reduced mechanical properties, particularly in high-strength steels with alloying elements like Mn, Al, and Si, due to the interaction between zinc and the steel substrate.
Innovation Solution
A method involving coating the steel sheet with a nickel layer of specific thickness (750-950 nm) followed by recrystallization annealing in a hydrogen atmosphere, and then applying a zinc coating, forming a diffused alloy layer that acts as a barrier against LME, while optimizing the nickel thickness and annealing conditions to prevent zinc penetration and enhance weldability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a zinc coating is applied to steel sheet for corrosion protection, then corrosion resistance is improved, but liquid metal embrittlement susceptibility increases during heating processes
Solution Approach 1:
A nickel intermediate layer is introduced between the zinc coating and the steel substrate. This nickel layer acts as a barrier that prevents zinc from penetrating into the steel substrate during heating processes, thereby eliminating LME susceptibility while preserving the zinc coating's corrosion protection function. The nickel layer thickness is controlled at 750-950 nm to achieve optimal protection.
Solution Approach 2:
The invention creates a composite coating structure consisting of multiple layers: the base steel substrate, the nickel intermediate layer, and the zinc outer coating. This composite structure combines the advantages of both materials - the nickel provides LME resistance by blocking zinc diffusion, while the zinc provides corrosion protection, achieving both functions simultaneously without compromising either.
2Object-affected harmful factors
If nickel coating thickness is increased to improve LME resistance, then LME susceptibility decreases, but coating cost and processing complexity increase
Solution Approach 1:
The invention optimizes the nickel layer thickness to a specific range (750-950 nm) where the LME protection effect is maximized. Below this range, insufficient protection is provided; above this range, unnecessary cost and processing complexity increase. This precise parameter control achieves the best balance between protection effectiveness and manufacturing efficiency.
Solution Approach 2:
The nickel layer is applied to the steel substrate before the zinc coating process. This preliminary action ensures that the nickel barrier is already in place to prevent LME, while also serving as a base layer that facilitates subsequent zinc coating application. The pre-coated steel sheet is then annealed to diffuse the nickel slightly into the substrate for enhanced protection.
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 method significantly reduces LME susceptibility, resulting in fewer cracks during welding and improved mechanical properties, with optimal nickel thickness between 600-1400 nm, and further enhanced by a decarburized layer, achieving excellent resistance to liquid metal embrittlement and maintaining mechanical integrity.
Implementation Method 1
forming a diffused alloy layer that acts as a barrier against LME
Implementation Method 2
followed by recrystallization annealing in a hydrogen atmosphere
Data Source
AI summary
The present invention relates a Method for the manufacture of a coated steel sheet comprising the following successive steps: A. the coating of the steel sheet with a first coating consisting of nickel and having a thickness between 600 nm and 1400nm, the steel sheet having the following composition in weight: 0.10 < C < 0.40%, 1.5 < Mn < 3.0%, 0.7 < Si < 3.0%, 0.05 < Al < 1.0%, 0.75 < (Si+Al) < 3.0 %, and on a purely optional basis, one or more elements such as Nb ≤ 0.5 %, B ≤ 0.010%, Cr ≤ 1.0%, Mo ≤ 0.50%, Ni ≤ 1.0%, Ti ≤ 0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, B. the recrystallization annealing at a temperature between 820 to 1200°C, C. the coating with a second coating based on zinc not comprising nickel.