Hot Press Steel Sheet Fe Gradient to Prevent Plating Voids
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Solution Overview
Problem
Hot press formed steel sheets often experience poor coating adhesion due to voids in the plating layer, leading to peeling off during high-strength applications, which reduces adhesion strength when multiple members are adhered together.
Innovation Solution
A steel sheet with an aluminum alloy plating layer having an average Fe content of 40 wt % or more and a concentration gradient of 7 wt %/μm or less in the thickness direction, controlled through specific aluminum plating and annealing processes to prevent void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If aluminum plating is applied to prevent oxidation during hot press forming, then oxidation resistance is improved, but coating adhesion deteriorates due to void formation and peeling
Solution Approach 1:
The plating layer is designed with non-uniform Fe content distribution, creating different local compositions: a first plating layer with 7-9 mass% Fe near the steel sheet for strong adhesion, and a second plating layer with 2-5 mass% Fe at the surface for oxidation resistance. This local quality variation resolves the contradiction between adhesion and oxidation resistance.
Solution Approach 2:
The invention changes the concentration parameter of Fe content across the plating layer thickness. By controlling Fe concentration to decrease from the steel sheet interface toward the surface, the plating layer achieves optimal adhesion strength at the interface while maintaining oxidation resistance at the exposed surface.
2Strength
If high-strength steel sheets are used to improve safety, then strength increases, but workability deteriorates due to reduced elongation
Solution Approach 1:
The invention utilizes phase transition of steel from austenite at high temperature (easy to form) to martensite during quenching (high strength). By heating the steel sheet to Ac3 transformation point or higher before forming, workability is dramatically improved, and subsequent rapid cooling produces the desired high-strength martensitic structure in the formed part.
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 solution significantly reduces the likelihood of voids in the plating layer, enhancing adhesion strength between hot press formed members and preventing peeling off, even under high stress conditions.
Implementation Method 1
a concentration gradient of a section having a Fe content of 45 wt % to 80 wt % in the plating layer may 7 wt %/μm or less of a concentration gradient at a section having an Fe content of 45% to 80% in the plating layer in a thickness direction from a surface of the plating layer
Data Source
AI summary
Provided is a steel sheet for a hot press formed member having excellent coating adhesion, and a method for manufacturing the same. A steel sheet for hot press forming is an aluminum alloy plated steel sheet, wherein an average Fe content in a plating layer may be 40 wt % or more, and a concentration gradient of a section having a Fe content of 45 wt % to 80 wt % in the plating layer may 7 wt %/μm or less of a concentration gradient at a section having an Fe content of 45% to 80% in the plating layer in a thickness direction from a surface of the plating layer according to a result of GDS analysis.