Corrosion-Resistant Rebar Composition With Weldable Ferrite-Bainite Structure
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Solution Overview
Problem
Reinforced concrete structures in coastal environments face premature corrosion due to high chloride ion and sulfate content, leading to increased maintenance costs and waste, with existing corrosion-resistant steel bars having poor welding performance and high production costs, making them unsuitable for widespread use.
Innovation Solution
A 400 MPa corrosion-resistant steel bar with a chemical composition of 9.5-10.4% Cr, 1.0-1.2% Mo, 0.3-0.6% Mn, 0.01-1.00% Ni, 0.01-0.5% Cu, and a microstructure of ferrite and bainite, designed to provide excellent corrosion, mechanical, and welding performance while reducing material and production costs, suitable for ocean engineering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stainless-steel bars with high alloy elements (Cr, Ni, Mo) are used to improve corrosion resistance, then corrosion-resistant performance is greatly improved, but welding performance deteriorates and production cost increases exponentially
Solution Approach 1:
The patent precisely controls alloy element content within specific ranges (Cr: 1.50-3.00%, Ni: 0.50-1.00%, Mo: 0.10-0.50%) rather than using high concentrations, and controls carbon content at 0.01-0.05% to prevent excessive carbide precipitation that would harm weldability. This parameter optimization resolves the contradiction by achieving adequate corrosion resistance without sacrificing welding performance
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite and bainite phases through controlled cooling processes, where ferrite provides good weldability and ductility while bainite contributes to strength and corrosion resistance. This composite approach allows the steel to exhibit both excellent welding performance and corrosion resistance simultaneously
2Reliability
If stainless-steel bars with high alloy elements are used to improve corrosion resistance, then corrosion-resistant performance is greatly improved, but production cost increases exponentially
Solution Approach 1:
The patent optimizes alloy element concentrations to the minimum effective levels (Cr: 1.50-3.00%, Ni: 0.50-1.00%, Mo: 0.10-0.50%) required to achieve the desired corrosion resistance in marine environments, avoiding excessive alloying that would drive up costs. This cost-effective composition provides adequate protection without exponential cost increases
Solution Approach 2:
The patent uses conventional carbon steel as the base material rather than expensive stainless steel, and achieves corrosion resistance through controlled microstructure and moderate alloying rather than heavy reliance on expensive alloy elements, providing an economical alternative to traditional stainless-steel reinforcement bars
3Quantity of substance
If conventional steel bars are used in coastal environments, then production cost is low, but corrosion resistance is insufficient leading to premature failure
Solution Approach 1:
The patent develops a composite microstructure of ferrite and bainite phases, where ferrite provides corrosion resistance and ductility while bainite contributes to strength. This microstructural composite approach enables conventional carbon steel to achieve corrosion resistance comparable to stainless steel while maintaining low production costs
Solution Approach 2:
The patent optimizes chemical composition parameters (C: 0.01-0.05%, Si: 0.01-0.50%, Mn: 0.50-2.00%, Cr: 1.50-3.00%, Ni: 0.50-1.00%, Mo: 0.10-0.50%) and cooling rate parameters to transform the microstructure into a corrosion-resistant ferrite-bainite composite, enabling conventional steel to perform in harsh marine environments
4Reliability
If corrosion inhibitors and surface protection layers are applied to prolong service life, then corrosion resistance is improved, but structural complexity and maintenance requirements increase
Solution Approach 1:
The patent enables the steel bar itself to provide corrosion resistance through its inherent ferrite-bainite microstructure and optimized chemical composition, eliminating the need for external corrosion inhibitors, coating systems, or cathodic protection devices. The material self-provides the protection function that would otherwise require complex external systems
Solution Approach 2:
The patent extracts and eliminates the need for external protection systems (corrosion inhibitors, surface coatings, cathodic protection devices) by incorporating corrosion resistance directly into the base steel material through microstructural control, simplifying the overall structure by removing unnecessary protective layers
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 steel bar exhibits improved corrosion resistance by 45 times compared to HRB400, with enhanced mechanical properties and easy welding, meeting the requirements for ocean engineering while reducing costs and environmental impact.
Implementation Method 1
the surfaces of steel bars will be passivated to form a layer of stable metal oxide passivation film
Data Source
AI summary
The present invention discloses a 400 MPa corrosion-resistant steel bar and a production method thereof. The steel bar includes the following chemical ingredients: 9.5-10.4% of Cr, 1.0-1.2% of Mo, 0.3-0.6% of Mn, 0.01-1% of Ni, 0.01-0.5% of Cu, at most 0.014% of C, at most 0.004% of N, 0.01-0.05% of Nb, 0.2-0.6% of Si, and the balance of Fe, where Cr+Mo+0.5Mn+0.35Ni+0.25Cu is 11.1-12.2%, and C+N+0.3Si+Mn+1.8Nb is 0.4-0.8%.