Titanium Intermediate Layers for Hot-Formed Steel Corrosion Protection
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Solution Overview
Problem
Existing anticorrosion coatings and intermediate layers for steel components, particularly in press-hardened steel sheets, suffer from iron diffusion into the coating, leading to reduced cathodic protection and crack formation due to liquid metal embrittlement during hot forming, with known solutions like tungsten-based barriers being brittle and prone to rupture.
Innovation Solution
A component comprising a steel substrate with a titanium-based metallic intermediate layer and an anticorrosion coating, where the coating differs in material from the intermediate layer, effectively preventing iron and zinc diffusion while maintaining structural integrity during hot forming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an Al-Si coating is applied to prevent scale formation during hot forming, then scale protection is improved, but corrosion protection is reduced because the coating only protects passively through barrier action
Solution Approach 1:
The patent applies a composite coating system consisting of an Al-Si scale protection layer combined with a Zn-Mn anticorrosion layer. The Al-Si layer (5-15 μm) provides passive barrier protection against scale formation during hot forming, while the Zn-Mn layer (15-30 μm) provides active cathodic corrosion protection. This composite structure resolves the contradiction by combining materials with complementary functions rather than relying on a single coating to provide both protections.
2Reliability
If a Zn coating is used for active corrosion protection, then corrosion protection is improved, but liquid metal embrittlement and crack formation occur during hot forming due to liquid zinc penetration into the base material
Solution Approach 1:
The patent segments the coating system into two distinct functional layers: an upper Al-Si layer that remains solid during hot forming and prevents liquid zinc penetration, and a lower Zn-Mn layer that provides corrosion protection. This segmentation resolves the contradiction by separating the scale protection function from the corrosion protection function, allowing each layer to perform its specific role without interfering negatively with the other.
Solution Approach 2:
The Al-Si coating acts as an intermediary barrier between the steel substrate and the Zn-Mn anticorrosion layer during hot forming. It prevents liquid zinc from directly contacting and penetrating the steel substrate, thereby eliminating liquid metal embrittlement while still allowing the Zn-Mn layer to provide cathodic corrosion protection to the steel.
3Strength
If the proportion of Mn in the anticorrosion layer is increased to raise the melting point, then liquid metal embrittlement is reduced, but the sacrificial corrosion protection effect is diminished
Solution Approach 1:
The patent optimizes the Mn content in the Zn-Mn anticorrosion layer to be between 5-25% by weight. This parameter range is carefully selected to raise the melting point of the coating above the hot forming temperature, preventing liquid metal embrittlement, while maintaining sufficient Zn content (75-95% by weight) to preserve the cathodic sacrificial corrosion protection effect. The Al-Si layer compensates for any reduced corrosion protection by providing additional barrier protection.
4Ease of manufacture
If iron diffusion into the coating is allowed during heating, then the heating process is simplified, but cathodic protection is reduced and crack formation occurs
Solution Approach 1:
The Al-Si layer serves as a diffusion barrier intermediary between the steel substrate and the Zn-Mn coating during hot forming. It prevents excessive iron diffusion into the anticorrosion layer while allowing the heating process to proceed at typical hot forming temperatures (850-950°C). This maintains cathodic protection by preserving the coating's metallic structure and prevents crack formation by avoiding excessive interdiffusion that would embrittle the interface.
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 titanium intermediate layer significantly reduces iron and zinc diffusion, preventing crack formation and enhancing the anticorrosion properties of the coating, even after hot forming, resulting in a hardened component with improved durability.
Implementation Method 1
the metallic intermediate layer, whose main constituent is titanium... significantly reduces iron and zinc diffusion
Implementation Method 2
heating the steel sheet to above the austenitizing temperature and obtaining an essentially purely martensitic structure by cooling during pressing
Data Source
AI summary
A component including a steel substrate having a structure that can be transformed into a martensitic structure, a metallic intermediate layer which covers the steel substrate and has a main constituent of titanium and an anticorrosion coating covering the intermediate layer, wherein the anticorrosion coating includes one or more layers and at least the layer of the anticorrosion coating adjoining the metallic intermediate layer is metallic and differs in terms of material from the intermediate layer.