High-Si Mn Steel Sheet Surface Treatment for Conversion Coating
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Solution Overview
Problem
High-strength cold-rolled steel sheets with high Si and Mn content face challenges in achieving excellent conversion treatability and corrosion resistance due to oxidation, which reduces the effectiveness of zinc phosphate coating and cationic electrodeposition coating.
Innovation Solution
A steel sheet with a specific chemical composition and surface treatment process, including Ni electrolytic plating, is used to remove silica and manganese silicate oxides, enhancing conversion treatability by covering porous silica with Ni, thereby improving corrosion resistance without compromising strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the content of Si and Mn is increased to obtain high ductility and good workability, then ductility and workability are improved, but conversion treatability and corrosion resistance deteriorate due to oxide formation on the surface
Solution Approach 1:
The patent applies preliminary action by performing pickling treatment before conversion treatment to remove oxide layers formed by Si and Mn oxidation. This preliminary removal of harmful oxides enables subsequent conversion treatment to proceed effectively, resolving the contradiction between maintaining high Si-Mn content for ductility and achieving good conversion treatability
Solution Approach 2:
The patent converts the harmful effect of Si and Mn oxidation into a beneficial process by utilizing the oxide layers as indicators for controlled pickling. The pickling treatment selectively removes these oxides while preserving the underlying metal, and the controlled oxidation during annealing actually creates a surface preparation that enhances subsequent conversion treatment adhesion when properly managed
2Reliability
If conventional techniques are used to improve conversion treatability, then conversion treatability is improved, but corrosion resistance and tensile strength are reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition ratios of Si and Mn within specific ranges (Si: 0.10-2.50%, Mn: 1.20-3.50%), and controlling the pickling treatment parameters to achieve optimal oxide layer removal. This controlled approach improves conversion treatability while maintaining the strength properties that would be lost with more aggressive conventional methods
Solution Approach 2:
The patent creates a composite surface structure consisting of a metal substrate with controlled oxide layers, followed by conversion treatment layers. This multi-layer composite structure achieves both good conversion treatability and maintained corrosion resistance, as each layer contributes specific functional properties while preserving the underlying metal's strength
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 approach allows for excellent conversion treatability and corrosion resistance without reducing tensile strength or fatigue strength, ensuring effective adhesion of zinc phosphate coatings and improved alkali resistance.
Implementation Method 1
Ni of 3 mg/m2 to 100 mg/m2 adheres to the surface
Implementation Method 2
exhibits an absorption peak at which a reflectance is not less than 50% nor more than 85% in a range of wave numbers of 1200 cm−1 to 1300 cm−1 by a Fourier transform-infrared spectroscopy analysis
Data Source
AI summary
A steel sheet has a predetermined chemical composition, and a surface exhibits an absorption peak at which a reflectance is not less than 50% nor more than 85% in a range of wave numbers of 1200 cm−1 to 1300 cm−1 by a Fourier transform-infrared spectroscopy analysis by a reflection absorption spectrometry method, and does not exhibit an absorption peak in a range of wave numbers of 1000 cm−1 to 1100 cm−1, or exhibits an absorption peak at which a reflectance is 85% or more in the range of wave numbers of 1000 cm−1 to 1100 cm−1, wherein Ni of 3 mg/m2 to 100 mg/m2 adheres to the surface.