Galvanized Hot Press-Formed Steel With Surface-Alloy Control for Microcracks
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Solution Overview
Problem
Hot press forming of high-strength steel sheets often results in microcracks due to severe friction and high temperatures, which can lead to reduced durability and corrosion resistance, especially in galvanized steel sheets with zinc-based plated layers.
Innovation Solution
A hot press-formed article is manufactured using a galvanized steel sheet with a zinc-based plated layer containing Sb, Sn, or Bi, where these elements are concentrated within 3 μm of the surface, and the sheet is heated at specific rates to prevent microcrack propagation by inhibiting internal oxide formation and improving corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If hot press forming is performed on galvanized steel sheets at high temperatures, then the steel sheet can be machined to complex shapes with high strength, but microcracks are formed in the plated layer and base steel sheet due to severe friction and high temperature
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the zinc-based plated layer. Specifically, it controls the content of Zn (55-85 wt%), Fe (10-40 wt%), and impurities (Al, Si, Pb, Sn, Ti, Mn, Mg, Ca, Nb, Mo, V, Cr, Cu, Ni, Co, B, P, C, S, O, N, H) within specific ranges. This compositional parameter optimization prevents excessive alloying between the plated layer and base steel sheet during hot press forming, thereby reducing microcrack formation while maintaining the ability to form complex shapes.
Solution Approach 2:
The patent creates a composite plated layer structure consisting of multiple phases (α-Zn, β-ZnFe, γ-ZnFe, δ-ZnFe) with controlled thickness ratios. The composite structure comprises an alloyed layer with specific phase distribution and an unalloyed layer, where the total thickness ratio of alloyed layer to unalloyed layer is controlled between 0.3-2.0. This composite material design provides both formability during hot press forming and resistance to microcrack propagation.
2Strength
If the zinc-based plated layer is alloyed during hot press forming, then the adhesion between the plated layer and base steel sheet is improved, but microcracks propagate to the base steel sheet due to stress from friction with the die
Solution Approach 1:
The patent applies local quality by creating a non-uniform alloying distribution within the plated layer. The alloyed layer has a specific phase composition (α-Zn, β-ZnFe, γ-ZnFe, δ-ZnFe) with controlled thickness, while the unalloyed layer remains primarily zinc. This localized differentiation allows the alloyed portion to provide strong adhesion to the base steel sheet while the unalloyed portion maintains ductility and resistance to stress-induced microcrack propagation during friction with the die.
Solution Approach 2:
The patent controls the thickness ratio parameter of the alloyed layer to unalloyed layer within 0.3-2.0, and specifies impurity element contents (Al: 0.01-5.0 wt%, Si: 0.01-3.0 wt%, Pb: 0.01-1.0 wt%, Sn: 0.01-2.0 wt%) to optimize the balance between adhesion strength and microcrack resistance. By adjusting these parameters, the alloying degree is controlled to prevent excessive stress concentration that would cause microcrack propagation.
3Stability of the object's composition
If Al-based plating is performed to suppress oxidation and increase corrosion resistance, then the plated layer maintains integrity during heating, but corrosion resistance is drastically lowered
Solution Approach 1:
The patent creates a composite plated layer system that combines zinc-based alloyed layer with controlled impurity phases. Rather than using pure Al-based plating, it utilizes a multi-phase zinc-iron alloy structure (α-Zn, β-ZnFe, γ-ZnFe, δ-ZnFe phases) with controlled impurity contents. This composite structure provides oxidation resistance during heating while maintaining corrosion resistance through the sacrificial protection mechanism of zinc, avoiding the corrosion resistance loss associated with Al-based plating.
Solution Approach 2:
The patent changes the plating material composition parameters from Al-based to Zn-based with controlled Fe content (10-40 wt%) and specific impurity levels. This parameter change transforms the protection mechanism from Al-oxide film formation to zinc-based sacrificial corrosion protection, thereby maintaining both oxidation resistance during hot press forming and corrosion resistance in the finished product.
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 effectively restrains microcrack propagation to the base steel sheet, enhancing the durability and corrosion resistance of the hot press-formed article by controlling the heating conditions and alloying process.
Implementation Method 1
an alloyed zinc-based plated layer, formed by alloying the zinc-based plated layer
Implementation Method 2
the steel sheet is machined and rapidly quenched simultaneously to transform the structure of the steel sheet into martensite
Implementation Method 3
an oxidation reaction on a surface of the steel sheet is suppressed
Data Source
AI summary
Disclosed are a hot press-formed article and a method for manufacturing the same. The article is manufactured by hot press forming a galvanized steel sheet comprising a base steel plate and a zinc-based coat layer formed on a surface of the base steel plate, wherein the zinc-based coat layer contains at least one element selected from the group consisting of Sb, Sn, and Bi in a total amount of 0.05% to 2.0% by weight, and a balanced amount of Zn and inevitable impurities, at least 70% by weight of the at least one element selected from the group consisting of Sb, Sn, Bi being concentrated in a region 3 μm or less distant from the surface of an alloyed zinc-based coat layer, formed by alloying the zinc-based coat layer, of the hot press-formed article.