Cold-Rolled High-Strength Steel Surface Control for Phosphating
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Solution Overview
Problem
Existing methods for producing cold-rolled high-strength steel with excellent phosphating performance face challenges due to the external oxidation of alloying elements like Si and Mn, which affect the nucleation and growth of the phosphating film, thereby impacting coating quality.
Innovation Solution
Control the mass percentage peak values and depth positions of Mn and Si elements on the steel surface using a unique continuous annealing process, forming a ferrite surface layer to prevent enrichment and using specific atmospheric conditions to manage oxidation, ensuring Mn ≤ 10.0% and Si ≤ 4.0% with depths of 50-500 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If alloying elements (Si and Mn) are added to achieve high strength, then tensile strength is improved, but external oxidation occurs on the surface affecting phosphating performance
Solution Approach 1:
The patent changes the chemical composition parameters by strictly limiting Si content to 0.01-3.00% and Mn content to 0.05-5.00%, and controls the depth distribution parameters of these elements (peak values ≤10.0% for Mn and ≤4.0% for Si at depth ≥50nm). This parameter control prevents external oxidation while maintaining high tensile strength (≥780 MPa) through optimized alloying levels.
2Object-affected harmful factors
If alloying element content is limited to prevent oxidation, then phosphating performance is improved, but material strength is reduced
Solution Approach 1:
The patent optimizes the parameter range of alloying elements (Si: 0.01-3.00%, Mn: 0.05-5.00%) and their depth distribution (peak values and positions at ≥50nm depth) to achieve the best balance. This allows sufficient alloying for strength (tensile strength ≥780 MPa) while preventing surface oxidation that would harm phosphating performance, resolving the contradiction between strength and phosphating quality.
3Object-affected harmful factors
If annealing atmosphere dew point is controlled at high level to prevent oxidation, then phosphating performance is improved, but decarburization occurs on the surface
Solution Approach 1:
The patent controls the annealing atmosphere dew point within -40°C to 0°C and oxygen content at 5-50 ppm. This parameter optimization prevents both excessive oxidation (which would harm phosphating) and decarburization (which would occur at higher dew points), while achieving excellent phosphating performance with uniform film coverage and high tensile strength (≥780 MPa).
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
Achieves excellent phosphating performance by ensuring sufficient Fe reacts with the phosphating solution, resulting in a uniform and dense phosphating film, enhancing coating quality and mechanical strength.
Implementation Method 1
alloying elements such as Si and Mn in the steel can form external oxidation on a surface of a strip steel after annealing
Implementation Method 2
a mass percentage peak value of Mn element Mn p and a mass percentage peak value of Si element Si p are detected by glow discharge optical emission spectroscopy (GDOES)
Implementation Method 3
By immersing a steel plate or a part made of a steel plate in phosphating solution, a layer of insoluble phosphating film is formed on the surface of the steel plate or the part
Data Source
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AI summary
Disclosed in the present invention is a cold-rolled high-strength steel plate with excellent phosphating performance. On the element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate, the Mn mass percentage peak Mnp is less than or equal to 10.0%, the Si mass percentage peak Sip is less than or equal to 4.0%, and the Mn mass percentage peak Mnp and the Si mass percentage peak Sip are both located at a depth position greater than or equal to 50 nm from the surface of the steel plate. Correspondingly, further disclosed in the present invention is a manufacturing method for the cold-rolled high-strength steel plate, and a unique continuous annealing process is used in the manufacturing method.