Oriented Martensitic Steel Wire for High Strength and Ductility
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Solution Overview
Problem
Existing high-tensile steel wires face a trade-off between mechanical strength and ductility, making them inadequate for applications requiring both high tensile strength and acceptable flexibility, such as spring wires and rope production.
Innovation Solution
A high-tensile elongated steel element with a non-round cross-section and a work-hardened state, featuring a steel composition with specific carbon, silicon, manganese, and chromium content, and a manufacturing process involving austenitizing, quenching, tempering, and work hardening to achieve an oriented martensitic microstructure, which enhances both tensile strength and ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the carbon content is increased to improve tensile strength, then the tensile strength increases, but the ductility deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the carbon content within a narrow range (0.20-1.00 wt%) rather than simply increasing it. This controlled parameter adjustment, combined with specific silicon (0.05-2.0 wt%) and manganese (0.40-1.0 wt%) content ranges, creates an optimized composition that achieves high tensile strength (≥1200 MPa) while maintaining acceptable ductility (≥3% elongation).
Solution Approach 2:
The patent creates a composite microstructure consisting of martensitic grains with specific orientation characteristics. The microstructure is engineered to contain a fraction of at least 10 volume percent oriented martensitic grains, which provides both high strength and improved ductility compared to conventional random-oriented martensitic structures. This microstructural composite approach resolves the strength-ductility trade-off.
2Strength
If conventional heat treatment is applied to increase tensile strength, then the tensile strength improves, but the elongation at fracture deteriorates
Solution Approach 1:
The patent applies preliminary action by implementing a specific sequence of heat treatment operations: austenitizing above Ac3 temperature for less than 120 seconds, followed by quenching below 100°C for less than 60 seconds, and tempering between 320-700°C for 10-600 seconds. This pre-planned thermal sequence creates the oriented martensitic microstructure before final work hardening, ensuring both high strength and acceptable ductility are achieved in advance of service conditions.
3Strength
If work hardening is increased to improve tensile strength, then the tensile strength increases, but the ductility decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the work hardening parameters within specific ranges rather than maximizing them. The work hardening is performed on steel with precisely controlled composition (carbon 0.20-1.00 wt%, silicon 0.05-2.0 wt%, manganese 0.40-1.0 wt%) and specific microstructure (oriented martensitic grains ≥10 vol%). This controlled approach achieves high tensile strength (≥1200 MPa) while maintaining ductility (≥3% elongation), resolving the strength-ductility contradiction.
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 resulting steel wire achieves exceptionally high tensile strength of at least 1200 MPa and elongation at fracture of at least 3%, with a yield to tensile ratio of 80-96%, suitable for use as spring wire or rope production, and can be further tuned with heat treatment for specific applications.
Implementation Method 1
austenitizing a steel ingot, a steel wire rod or a steel (drawn or rolled) wire above Ac3 temperature
Implementation Method 2
quenching said austenitized steel ingot, steel wire rod or steel wire below 100° C.
Implementation Method 3
tempering said quenched steel ingot, steel wire rod or steel wire between 320° C. and 700° C.
Data Source
AI summary
An elongated steel element having a non-round cross-section and being in a work-hardened state, said elongated steel element having as steel composition: a carbon content ranging from 0.20 weight percent to 1.00 weight percent, a silicon content ranging from 0.05 weight percent to 2.0 weight percent, a manganese content ranging from 0.40 weight percent to 1.0 weight percent, a chromium content ranging from 0.0 weight percent to 1.0 weight percent, a sulfur and phosphor content being individually limited to 0.025 weight percent, contents of nickel, vanadium, aluminium, molybdenum or cobalt all being individually limited to 0.5 weight percent, the remainder being iron and unavoidable impurities, said steel having martensitic structure that comprises martensitic grains, wherein a fraction of at least 10 volume percent of martensitic grains is oriented.