Hot-Rolled Steel Composition for Adherent Corrosion-Resistant Scale
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Solution Overview
Problem
Hot rolled steel products for industrial machinery face challenges in achieving a balance between corrosion resistance, mechanical properties, and environmental standards, particularly in harsh environments, with existing solutions either compromising on scale adhesiveness or being energy-intensive and economically inefficient.
Innovation Solution
A hot rolled steel product with a specific composition and tertiary scale structure, comprising 0.06-0.18% C, 0.01-0.6% Ni, 0.001-2% Cu, 0.001-2% Cr, 0.001-0.8% Si, and controlled amounts of other elements, forming a scale with >50% magnetite and ferrite, and up to 10% wustite, which enhances adhesiveness, corrosion resistance, and weldability while maintaining economic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hot rolled steel is developed with high corrosion resistance for harsh industrial environments, then corrosion resistance is improved, but scale adhesiveness deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.06-0.18%, Si: 0.01-0.6%, Mn: 1.50-3.00%, P: 0.020% or less, S: 0.020% or less, Cr: 0.01-1.00%, Ni: 0.01-0.60%, Cu: 0.01-1.00%, Mo: 0.01-0.50%, Ti: 0.01-0.10%, Al: 0.01-0.10%, Nb: 0.01-0.10%, V: 0.01-0.50%, B: 0.0005-0.0050%) and processing parameters (finishing rolling temperature: 800-950°C, cooling rate: 5-30°C/s) to achieve a balance between corrosion resistance and scale adhesiveness. The controlled composition and processing parameters enable the formation of a tertiary scale with appropriate magnetite content that provides both corrosion protection and good adhesion.
Solution Approach 2:
The patent creates a composite scale structure on the steel surface consisting of multiple oxide phases (primarily magnetite Fe3O4 with controlled hematite Fe2O3 content). This composite scale layer, formed through controlled oxidation during cooling, provides enhanced corrosion resistance while maintaining scale adhesiveness. The specific composition ratios of different oxide phases in the scale create a protective barrier that resists corrosion in harsh environments without compromising adhesion to the base steel.
2Object-generated harmful factors
If holding time between 400°C and 450°C for 90 minutes or more is applied to improve scale adhesion, then scale adhesiveness is improved, but energy consumption increases
Solution Approach 1:
The patent applies preliminary action by pre-establishing the appropriate chemical composition and microstructure during the hot rolling and cooling processes. The steel composition is designed with specific ranges of alloying elements that predispose the material to form an adherent tertiary scale during normal cooling, eliminating the need for subsequent prolonged holding treatments. The finishing rolling temperature and cooling rate are controlled to initiate and complete scale formation in-situ, avoiding energy-intensive post-processing holding steps.
Solution Approach 2:
The patent skips the conventional energy-intensive prolonged holding step (90 minutes or more at 400-450°C) by optimizing the cooling rate (5-30°C/s) and finishing rolling temperature (800-950°C) to achieve rapid formation of adherent tertiary scale during the cooling process itself. This approach rushes through the scale formation phase efficiently, achieving the same or better scale adhesion results without the extended time and energy expenditure of traditional holding treatments.
3Quantity of substance
If high amount of Hematite is present in the scale, then scale formation is enhanced, but scale adhesion deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the oxidation conditions during cooling (cooling rate: 5-30°C/s) and the chemical composition (particularly C: 0.06-0.18%, Si: 0.01-0.6%, Mn: 1.50-3.00%, Cr: 0.01-1.00%, Ni: 0.01-0.60%, Cu: 0.01-1.00%) to regulate the phase transformation and oxide formation. These controlled parameters ensure that magnetite (Fe3O4) becomes the dominant scale phase with limited hematite (Fe2O3), achieving sufficient scale formation while maintaining excellent adhesion. The specific composition ranges promote magnetite formation kinetics over hematite, resolving the contradiction between scale quantity and adhesion.
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 product exhibits excellent scale adhesiveness (>60% reflectivity), corrosion resistance (<20% red dust), and surface cleanliness (>65% reflectivity), along with improved mechanical properties and weldability, while being compatible with conventional industrial processes and less sensitive to manufacturing parameter variations.
Implementation Method 1
Scale formed during the heating of steel to rolling temperatures in the reheating furnace is known as primary scale
Implementation Method 2
a scale with >50% magnetite and ferrite, and up to 10% wustite
Data Source
AI summary
A hot rolled steel product having a composition comprising in percentage by weight:0.06%≤C≤0.18 %,0.01%≤Ni≤0.6 %, 0.001%≤Cu≤2%,0.001%≤Cr≤2%,0.001%≤Si≤0.8 %, 0%≤N≤0.008%, 0%≤P≤0.03%, 0%≤S≤0.03%,0.001%≤Mo≤0.5%,0.001%≤Nb≤0.1%, 0.001%≤V≤0.5%,0.001%≤Ti≤0.1% and one or more following optional elements 0.2 % ≤Mn ≤ 2%, 0 005% ≤ Al ≤ 0.1 %,0 % ≤ B ≤ 0.003%,0% ≤ Ca≤ 0.01%,0 % ≤ Mg ≦ 0.010% the remainder composition being composed of iron and unavoidable impurities caused by processing, such product having a tertiary scale layer comprising, in area fraction, a total amount of at least 50% of magnetite and ferrite wherein ferrite is at least 25%, 0% to 50 % of wustite, and 0% to 10% of hematite, such scale layer having a thickness between 5 microns and 40 microns.