Hot Rolled Steel Plate Microstructure Control for Strength and Workability
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Solution Overview
Problem
High-strength steel plates with superior workability and anti-delayed fracture properties are challenging to achieve due to the trade-off between strength and ductility, with existing methods either compromising on workability or requiring excessive alloy addition, and existing hot rolling processes leading to reduced efficiency and increased manufacturing costs.
Innovation Solution
A high-strength hot rolled steel plate with a bainite phase containing finely dispersed retained austenite particles, manufactured through specific rolling conditions and composition, including carbon, silicon, chromium, manganese, nickel, molybdenum, phosphorus, sulfur, and nitrogen, to achieve a balance of strength, ductility, and workability, while minimizing alloy usage and reducing anisotropy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strength of the steel plate is increased, then the tensile strength is improved, but the workability and ductility are degraded
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.15-0.35%, Si: 0.50-2.50%, Mn: 1.50-3.00%, Cr: 0.50-2.00%, Mo: 0.10-0.50%, B: 0.0005-0.0050%) and processing parameters (finishing temperature 850-950°C, coiling temperature 500-650°C, finishing roll diameter 600-1200mm) to achieve a balanced microstructure that provides both high strength and good workability
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (ferrite, bainite, martensite, and retained austenite) within the steel plate. This composite structure at the micro level allows the material to exhibit both high strength from the hard phases and good ductility from the softer ferrite matrix, resolving the contradiction between strength and workability
2Strength
If hot pressing is used to enhance strength, then the tensile strength is improved, but the manufacturing efficiency is deteriorated due to heating and reduction steps
Solution Approach 1:
The patent performs preliminary action by achieving the desired microstructure and strength properties during the hot rolling process itself, rather than requiring subsequent hot pressing. The controlled cooling and coiling during rolling preliminarily establishes the microstructure, eliminating the need for separate heating and reduction steps that would reduce manufacturing efficiency
3Strength
If hot pressing is used to enhance strength, then the tensile strength is improved, but the manufacturing cost is increased due to mold wear
Solution Approach 1:
The patent achieves the desired strength properties during the hot rolling process through controlled microstructure formation, eliminating the need for subsequent hot pressing operations that would cause mold wear and increase manufacturing costs
4Strength
If the steel plate is subjected to hot press working, then the tensile strength is improved, but the elongation and impact absorbing ability are reduced
Solution Approach 1:
The patent creates a composite microstructure with multiple phases (ferrite, bainite, martensite, and retained austenite) that work together to provide both high strength and good elongation. The softer ferrite matrix provides ductility and impact absorption, while the harder bainite and martensite phases provide strength, eliminating the need for hot press working that would compromise elongation
5Strength
If reinforcement by solid solution treatment or precipitation is used, then the tensile strength is improved, but the alloy addition amount is increased
Solution Approach 1:
The patent optimizes the parameters of solid solution treatment by controlling the finishing temperature (850-950°C) and coiling temperature (500-650°C) during hot rolling, along with precise alloy composition parameters. This optimized parameter control achieves the desired strength through controlled microstructure formation during rolling, reducing the need for excessive alloy additions compared to conventional solid solution treatment methods
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 solution provides a steel plate with tensile strength of 1200MPa or greater and elongation of 13% or more, enhancing both strength and workability while ensuring secure anti-delayed fracture properties, suitable for critical automotive and industrial applications.
Implementation Method 1
a bainite phase, in which a martensite phase and a retained austenite phase are dispersed
Implementation Method 2
cooling the steel material and coiling the steel material at a coiling temperature of 550 to 650°C
Data Source
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AI summary
The present invention provides a new high-strength and Si-Cr containing hot rolled steel plate provided with higher strength as well as excellent workability and a method for manufacturing the steel plate. The high-strength steel plate can be obtained by controlling the particle size of prior austenite to be 10µm or less, and properly selecting the coiling temperature. The steel plate obtained includes a retained austenite phase in a volume fraction of 5% to 20%; a martensite phase in a volume fraction equal to or less than 10%; and a bainite phase in the remaining volume fraction. The particle size of the retained austenite particle is 1µm or less and the retained austenite particles are dispersed uniformly.