Cold-Workable Steel via Dislocation Density Control
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Solution Overview
Problem
Current methods for shortening spheroidizing annealing time in mechanical structural steel production compromise cold workability and spheroidization degree, failing to meet the demand for even shorter processing times while maintaining steel softness and strength.
Innovation Solution
A cold-workable mechanical structural steel with specific chemical composition (C: 0.30-0.45%, Si: 0.10-0.40%, Mn: 0.50-1.00%, P: 0.050% or less, S: 0.050% or less, Cr: 0.80-1.30%, Al: 0.01-0.10%, and additional elements) is developed, combined with a thermomechanical treatment process involving hot-working, controlled cooling rates, and holding times to achieve a dislocation density of 3.5×10^14 m^-2 or larger, ensuring sufficient softening at lower temperatures and shorter annealing times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If spheroidizing annealing time is shortened to reduce energy consumption and CO2 emission, then energy efficiency improves, but cold workability deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the steel (specific C: 0.30-0.45%, Si: 0.10-0.40%, Mn: 0.50-1.00%, Cr: 0.80-1.30%, Al: 0.01-0.10%) to achieve a unique metallographic structure that enables both shortened annealing time and maintained cold workability. This compositional parameter change fundamentally alters the material's response to heat treatment, allowing rapid softening while preserving formability.
Solution Approach 2:
The patent creates a composite metallographic structure containing multiple phases (pro-eutectoid ferrite, bainite, martensite, and pearlite) with specific characteristics. This multi-phase composite structure provides both the softness needed for cold working and the strength required for structural applications, resolving the contradiction between energy efficiency and workability.
2Productivity
If spheroidizing annealing time is shortened, then productivity improves, but spheroidization degree deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters to create a steel that achieves high spheroidization degree (70% or more) in significantly reduced time. The specific ranges of C, Si, Mn, Cr, and Al content create favorable conditions for rapid cementite spheroidization during brief annealing cycles, enabling high productivity without sacrificing microstructural quality.
Solution Approach 2:
The patent performs preliminary chemical composition design and controlled cooling from austenite region before the actual spheroidizing annealing. This preliminary preparation of the steel's chemical and microstructural state enables the subsequent annealing to achieve high spheroidization degree much faster than conventional steels, thus improving productivity while maintaining precision.
3Loss of time
If spheroidizing annealing time is shortened, then operation time decreases, but steel softness deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters (particularly C: 0.30-0.45%, Si: 0.10-0.40%, Mn: 0.50-1.00%) to enable rapid softening kinetics. This compositional modification allows the steel to achieve the required softness (HV 180 or less) in dramatically reduced annealing time compared to conventional steels, directly resolving the time-softness contradiction.
Solution Approach 2:
The patent creates a composite metallographic structure with pro-eutectoid ferrite, bainite, martensite, and pearlite phases that provides both softness and strength. This multi-phase composite achieves steel softness of HV 180 or less while maintaining structural integrity, enabling short annealing times without compromising the required material softness.
4Ease of operation
If pro-eutectoid ferrite area percentage is increased to improve cold workability, then formability improves, but strength may deteriorate
Solution Approach 1:
The patent creates a composite metallographic structure containing pro-eutectoid ferrite (10-70% area percentage) combined with bainite, martensite, and pearlite. This multi-phase composite provides both the formability from ferrite and the strength from the other phases, resolving the contradiction between cold workability and strength through synergistic phase combination.
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 approach allows for the production of steel that is sufficiently softened at a relatively low spheroidizing annealing temperature and for a significantly shorter duration than previous methods, enhancing cold workability and maintaining strength, while reducing energy consumption and CO2 emissions.
Implementation Method 1
Manufacture of various parts such as automotive parts and construction machine parts often employs spheroidizing annealing, for the purpose of enhancing cold workability of a hot-rolled material such as carbon steel or alloy steel
Implementation Method 2
The rolled material whose cold workability was improved by spheroidizing annealing is cold worked, optionally followed by mechanical working such as cutting, and is then formed into a predetermined shape, quenched-and-tempered, to finally adjust the strength
Data Source
AI summary
A cold-workable mechanical structural steel may include: C: 0.30 to 0.45 mass %; Si: 0.10 to 0.40 mass %; Mn: 0.50 to 1.00 mass %; P: 0.050 mass % or less; S: 0.050 mass % or less; Cr: 0.80 to 1.30 mass %; Al: 0.01 to 0.10 mass %; and a balance of iron and inevitable impurity, the steel having an area percentage of pro-eutectoid ferrite of 10% or larger and 70% or smaller; containing at least one selected from the group consisting of bainite, martensite, and pearlite; and having a dislocation density of 3.5×1014 m−2 or larger.