Spheroidized Steel Hot Rolling Microstructure Control
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Solution Overview
Problem
Conventional methods for producing high-strength hot rolled steel with a spheroid microstructure are costly and time-consuming, often requiring prolonged isothermal treatment or complex heat treatment steps, which are not economical for mass production.
Innovation Solution
A method involving hot rolling steel slabs at a temperature range of Ae3 to Ae3+100°C, followed by controlled cooling and coiling, with retention at ambient temperature for 1-24 hours to achieve a high-strength hot rolled steel comprising 75-95% spheroid microstructure and 5-25% pearlite microstructure, utilizing specific alloy compositions and processing parameters to optimize microstructure and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional heat treatment methods (prolonged isothermal treatment or quench and temper) are used to produce spheroidized microstructure, then the microstructure quality (spheroidization) is improved, but the production time and cost increase significantly
Solution Approach 1:
The patent applies preliminary action by controlling the hot rolling process to pre-form the microstructure in a favorable state before final cooling. By optimizing rolling temperature (Ae3 to Ae3+100°C), rolling reduction (40-80%), and cooling rate (1-50°C/s), the austenite grains are prepared in advance to transform into spheroidized microstructure during controlled cooling, eliminating the need for subsequent prolonged heat treatment
Solution Approach 2:
The patent utilizes parameter changes by systematically varying hot rolling parameters (temperature range Ae3 to Ae3+100°C, reduction 40-80%), cooling parameters (rate 1-50°C/s, final temperature 500-700°C), and alloy composition (C: 0.2-1.0%, Mn: 0.5-2.0%, Si: 0.1-0.5%, P: 0.01-0.05%, S: 0.01-0.05%, Nb: 0.01-0.05%) to achieve spheroidized microstructure directly during the hot rolling process, replacing conventional multi-step heat treatment
2Manufacturing precision
If conventional heat treatment methods are used to achieve spheroidized microstructure, then the microstructure quality is improved, but the manufacturing cost increases due to additional heat treatment steps
Solution Approach 1:
The patent merges the microstructure control function into the hot rolling process itself. By integrating temperature control, deformation control, and cooling control into a single hot rolling operation, the patent eliminates separate heat treatment steps, thereby reducing manufacturing cost while achieving the desired spheroidized microstructure
Solution Approach 2:
The patent achieves cost reduction through parameter changes by optimizing hot rolling parameters (temperature Ae3 to Ae3+100°C, reduction 40-80%), cooling parameters (rate 1-50°C/s, final temperature 500-700°C), and alloy composition (C: 0.2-1.0%, Mn: 0.5-2.0%, Si: 0.1-0.5%, P: 0.01-0.05%, S: 0.01-0.05%, Nb: 0.01-0.05%) to produce spheroidized microstructure directly during hot rolling, eliminating expensive prolonged heat treatment steps
3Strength
If steel with pearlite microstructure is produced, then the strength is improved, but the machinability and ductility deteriorate
Solution Approach 1:
The patent applies parameter changes by controlling hot rolling temperature (Ae3 to Ae3+100°C), rolling reduction (40-80%), and cooling rate (1-50°C/s) to transform the microstructure from lamellar pearlite to spheroidized form. This parameter optimization achieves a balance where the steel maintains high strength (ultimate tensile strength ≥950 MPa) while improving machinability and ductility (total elongation ≥15%)
Solution Approach 2:
The patent creates a composite microstructure consisting of spheroidized cementite particles distributed in a ferrite matrix, with controlled amounts of pearlite (5-30%). This composite structure combines the strength benefits of cementite with the ductility and machinability benefits of ferrite, achieving ultimate tensile strength ≥950 MPa while improving total elongation to ≥15%
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 method results in high-strength hot rolled steel with improved machinability, toughness, ductility, and tensile strength, achieving ultimate tensile strength greater than 950 MPa and total elongation greater than 15%, while reducing production time and costs.
Implementation Method 1
hot rolling the steel slab at a temperature ranging from Ae3 to Ae3+100°C, where Ae3 is the temperature at which transformation of austenite to ferrite starts at equilibrium
Data Source
AI summary
The present disclosure discloses a method for producing high strength hot rolled steel. The method includes casting a steel slab of a composition, comprising in weight %: carbon (C) of about 0.45 wt. %-1.2 wt. %, manganese (Mn) of about 0.0-1.0 wt. %, silicon (Si) of about 0.0-0.5 wt. %, niobium (Nb) up-to 0.03 wt. %, sulphur (S) up-to 0.05 wt. % of S, phosphorous (P) up-to 0.05 wt. %, nitrogen (N) 0.002 wt. %-0.012 wt. % and balance being Iron (Fe) optionally along with incidental elements. The method also involves, heating, hot rolling, cooling, coiling the steel and retaining the steel at an ambient temperature to produce high strength hot rolled steel with 75-95% spheroid microstructure and 5-25% pearlite microstructure.