Silicon Steel Sheet Pickling for Conversion Treatment
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Solution Overview
Problem
High-strength cold rolled steel sheets containing silicon face challenges in maintaining conversion treatment properties and post-painting corrosion resistance due to silicon oxide formation, which inhibits the formation of conversion crystals and leads to non-covered areas and poor corrosion resistance.
Innovation Solution
A process involving thermal annealing in a non-oxidizing atmosphere, followed by pickling to remove surface oxides, and electroplating with zinc to form a dense and uniform conversion layer, along with a P-containing aqueous solution contact step to enhance conversion treatment properties and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If silicon is added to increase strength, then strength increases, but conversion treatment properties deteriorate due to SiO2 formation on the surface
Solution Approach 1:
The patent applies preliminary action by performing pickling treatment before conversion treatment to remove the SiO2 layer that forms during annealing. This preliminary removal of the harmful oxide layer enables the subsequent conversion treatment to proceed effectively, forming conversion crystals that provide both strength and corrosion resistance. The pickling step prepares the surface in advance to accept the conversion treatment coating.
2Strength
If annealing temperature is increased to achieve desired strength and ductility, then strength and ductility improve, but SiO2 formation on the surface increases, making the steel sheet unacceptable
Solution Approach 1:
The patent converts the harmful effect of SiO2 formation into a beneficial process by using the SiO2 layer as a target for pickling treatment. The high-temperature annealing that creates SiO2 is followed by controlled pickling that removes the oxide to a specific depth (0.3-0.7 μm), transforming the surface condition from unacceptable to optimal for conversion treatment. The SiO2 formation and subsequent removal creates a controlled surface state that enhances conversion crystal formation.
3Weight of moving object
If the thickness of steel sheets is reduced to save weight, then weight decreases, but stiffness decreases and safety is compromised
Solution Approach 1:
The patent creates a composite surface structure consisting of the base steel sheet combined with a conversion crystal layer. This composite structure provides both the weight reduction benefits of thin steel sheets and the enhanced strength and stiffness provided by the conversion treatment coating. The conversion crystals form a protective layer that compensates for the reduced thickness, maintaining safety while achieving weight savings.
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 process effectively forms a dense and uniform conversion layer on high-Si cold rolled steel sheets, improving their strength, workability, and corrosion resistance after painting, making them suitable for automobile body applications.
Implementation Method 1
thermal annealing in a non-oxidizing atmosphere
Implementation Method 2
pickling to remove surface oxides
Implementation Method 3
electroplating with zinc to form a dense and uniform conversion layer
Data Source
AI summary
The invention provides a process for manufacturing cold rolled steel sheets containing silicon as a strengthening element so as to obtain excellent conversion treatment properties and post-painting corrosion resistance. For the production of high-strength cold rolled steel sheets containing 0.5 to 2.0 mass% silicon, a process for manufacturing high-strength cold rolled steel sheets is adopted which includes a pickling step of thermally annealing a steel sheet in a non-oxidizing atmosphere and thereafter pickling the steel sheet to dissolve away 0.5 g/m2 to less than 2.0 g/m2 of the steel sheet, and an electroplating step of electroplating the surface of the steel sheet after pickling with zinc under such conditions that a coating mass of 100 to 5000 mg/m2 is obtained.