Steel Wire Rod Spheroidizing Heat Treatment Properties
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Solution Overview
Problem
Existing steel wire rods, particularly those in the 800 MPa class boron steel, face limitations in hardenability and require spheroidizing heat treatment, which can be challenging due to the presence of ferrite and the need for additional alloying elements like Cr and Mn.
Innovation Solution
A steel wire rod composition with specific weight percentages of C, Si, Mn, Cr, B, Ti, P, S, Al, and N, along with a manufacturing process involving primary and secondary hot rolling, and controlled cooling to achieve a microstructure of ferrite+pearlite with a limited fraction of bainite or martensite, enhancing spheroidizing heat treatment properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If alloying elements such as Cr and Mn are added to improve hardenability for large-diameter materials and high-strength products, then hardenability and tensile strength are improved, but the steel wire rod requires spheroidizing heat treatment which increases process complexity and cost
Solution Approach 1:
The patent changes the chemical composition parameters by strictly limiting Cr content to 0.003% or less (excluding 0%) and Mn content to 0.5% or less, while optimizing C content to 0.40-0.50% and Si content to 0.02-0.40%. This parameter change allows achieving 1000 MPa or more tensile strength without requiring spheroidizing heat treatment, thus resolving the contradiction between strength improvement and process complexity
Solution Approach 2:
The patent extracts and removes the unnecessary spheroidizing heat treatment process from the manufacturing flow by achieving a microstructure with 5 area % or less of low-temperature structures (bainite and martensite) through controlled composition and hot rolling. This eliminates the need for additional alloying elements and complex heat treatment while maintaining high strength
2Productivity
If ferrite phase fraction is reduced to enable short heat treatment such as induction heat treatment, then heat treatment efficiency is improved, but the strength of the steel wire rod increases and workability is adversely affected
Solution Approach 1:
The patent changes the composition parameters by limiting Cr to 0.003% or less (excluding 0%) and Mn to 0.5% or less, while setting C to 0.40-0.50% and Si to 0.02-0.40%. This enables achieving a microstructure with 5 area % or less of low-temperature structures without requiring excessive ferrite reduction, thus maintaining both heat treatment efficiency and workability
Solution Approach 2:
The patent achieves local control of microstructure by ensuring that low-temperature structures (bainite and martensite) are distributed at 5 area % or less throughout the steel wire rod, while maintaining a ferrite+pearlite dominant structure. This local quality control allows efficient heat treatment while preserving adequate workability
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 proposed solution enables a steel wire rod with improved spheroidization rate of cementite during spheroidizing heat treatment, effectively addressing the limitations of hardenability and workability in existing boron steel wire rods.
Implementation Method 1
a steel wire rod having excellent spheroidizing heat treatment properties
Implementation Method 2
a microstructure is a complex structure having a main phase of ferrite+pearlite, with one or more of bainite or martensite accounting for 5 area % or less
Implementation Method 3
heating the billet, and then extracting the billet at 950 to 1050° C.
Implementation Method 4
cooling the steel wire rod to 2° C./sec or less
Data Source
AI summary
An embodiment of the present invention provides a wire rod and a method of manufacturing same. The wire rod comprises, by weight %, 0.3-0.5 wt % of C, 0.02-0.4 wt % of Si, 1.0-1.5 wt % of Mn, 0.3-0.7 wt % of Cr, 0.003 wt % or less (exclusive of 0 wt %) of B, less than 0.03 wt % (exclusive of 0 wt %) of Ti, 0.03 wt % or less (inclusive of 0 wt %) of P, 0.01 wt % or less (inclusive of 0 wt %) of S, 0.02-0.05 wt % of Al, 0.001-0.01 wt % of N, and the balance being Fe and inevitable impurities, wherein a microstructure is a complex structure having a main phase of ferrite+pearlite, with at least one of bainite or martensite accounting for 5 area % or less (inclusive of 0%), and has a cementite average aspect ratio of 35 or less in an area covering ⅖-⅗ of the diameter.