Composite Coating for Hot-Stamped Steel Sheet Lubricity
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Solution Overview
Problem
Existing technologies for hot stamping of steel sheets face issues such as oxidation, decarburization, and scale formation, leading to reduced surface strength, increased friction, and decreased mold service life. Additionally, current coatings like AlSi face challenges with Al-Fe alloy layer hardness causing surface damage and poor lubricity, resulting in defects and reduced production efficiency.
Innovation Solution
A coated steel sheet for hot stamping is developed with a composite coating layer formed by applying an aqueous surface treatment liquid containing anionic polymer resin, tungsten-containing compounds, zinc-containing compounds, boron-containing compounds, water-soluble thickeners, and surface improvement aids. This coating provides improved high-temperature lubricity, processability, and corrosion resistance, while reducing mold wear and improving weldability and adhesiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AlSi coating is applied to prevent oxidation and improve high temperature resistance, then corrosion resistance and oxidation resistance are improved, but Al-Fe alloy layer forms with extremely high hardness causing surface damage and poor lubricity
Solution Approach 1:
The patent introduces an intermediate coating layer between the AlSi coating and the steel substrate. This intermediate layer acts as a mediator that prevents direct contact and friction between the hard Al-Fe alloy layer and the mold surface, thereby eliminating surface damage and improving lubricity while maintaining the oxidation resistance of the AlSi coating
Solution Approach 2:
The patent creates a composite coating structure consisting of multiple layers with different functions. The outer AlSi layer provides oxidation resistance, while the inner intermediate layer provides lubricity and prevents surface damage. This composite structure resolves the contradiction by combining materials with complementary properties
2Reliability
If conventional coatings are used to prevent oxidation, then high temperature resistance is improved, but liquid-metal induced embrittlement occurs at heating temperatures above Zn melting point
Solution Approach 1:
The patent changes the chemical composition parameters of the coating by using AlSi-based coating instead of Zn-based coating. This parameter change shifts the melting point and chemical properties of the coating, allowing it to withstand hot stamping temperatures without causing liquid-metal induced embrittlement while maintaining high temperature resistance and oxidation protection
3Duration of action of stationary object
If scale is removed from mold surface during production, then friction is reduced and mold service life is improved, but production efficiency decreases due to additional processing steps
Solution Approach 1:
The patent applies a coating to the steel sheet before hot stamping that prevents scale formation in the first place. This preliminary action eliminates the need for subsequent scale removal operations, thereby maintaining mold service life without reducing production efficiency
Solution Approach 2:
The patent converts the harmful effect of scale formation into a benefit by using the hot stamping process itself to create a protective oxide layer on the coating surface. This layer actually protects the mold from damage while eliminating the need for separate scale removal 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 coated steel sheet achieves excellent high-temperature lubricity, improved processability, reduced mold wear, and enhanced production efficiency. It also exhibits good weldability, adhesiveness, chemical conversion treatability, and corrosion resistance after hot stamping.
Implementation Method 1
a composite coating layer formed by applying an aqueous surface treatment liquid on the coated steel sheet
Implementation Method 2
the element Fe from the steel sheet diffuses into the AlSi coating and generate a variety of Al—Fe—Si and Al—Fe alloy layers... the Al—Fe alloy layer has extremely high hardness, which can lead to surface damage and galling issues... poor lubricity
Data Source
AI summary
The present disclosure relates to a coated steel sheet for hot stamping and an aqueous surface treatment liquid applicable to the same. A composite coating layer is formed on the surface of a coated steel sheet by using an improved aqueous surface treatment liquid, such that the obtained coated steel sheet for hot stamping has good high-temperature lubricity during hot stamping process, the processability of the coated steel sheet for hot stamping is improved, the wear of the surface of a hot stamping mold is reduced, the frequency of mold repair decreased, and the production efficiency is improved.