Wire Rod Microstructure Control to Omit Softening Heat Treatment
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Solution Overview
Problem
Existing methods for manufacturing wire rods require lengthy softening heat treatments, which can decrease productivity and necessitate specialized cooling facilities.
Innovation Solution
A wire rod composition with specific alloying elements (C, Si, Mn, Cr, Al, Mo, N) and a manufacturing process involving two-step hot rolling, controlled cooling rates, and a spheroidizing heat treatment to omit the softening heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a slow cooling rate (0.02 to 0.3°C/sec) is used after hot-rolling to refine grains and omit softening heat treatment, then the softening heat treatment can be omitted, but productivity decreases and separate slow cooling facilities and slow cooling yards are necessary
Solution Approach 1:
The patent changes the cooling rate parameter from the conventional slow cooling rate (0.02 to 0.3°C/sec) to a controlled cooling rate (1 to 5°C/sec). This parameter change allows the steel to achieve the desired microstructure (ferrite grain size of 11 or more, segmented cementite phase) without requiring extremely slow cooling, thereby eliminating the need for separate slow cooling facilities and improving productivity while still omitting the softening heat treatment step
Solution Approach 2:
The patent applies preliminary grain refinement during the hot-rolling process by controlling the cooling rate in the finishing stage. By pre-establishing the appropriate microstructure (ferrite grain size and segmented cementite distribution) during hot-rolling with controlled cooling, the material is prepared in advance to eliminate the need for subsequent softening heat treatment, thus improving productivity without sacrificing microstructure quality
2Ease of operation
If a lengthy heat treatment (10 to 20 hours or more) at high temperature (600 to 800°C) is used for softening, then the material can be softened for cold processing, but productivity decreases due to the lengthy treatment time
Solution Approach 1:
The patent performs preliminary microstructure control during hot-rolling by implementing a controlled cooling rate (1 to 5°C/sec) to create a specific microstructure (ferrite grain size of 11 or more with segmented cementite). This preliminary action prepares the material in advance to have adequate softness for cold processing, eliminating the need for subsequent lengthy softening heat treatment (10 to 20 hours), thereby maintaining ease of operation while dramatically improving productivity
Solution Approach 2:
The patent extracts and eliminates the softening heat treatment step from the conventional manufacturing process. By taking out this lengthy (10 to 20 hours) high-temperature treatment step and replacing it with controlled cooling during hot-rolling, the patent achieves the same softening effect for cold processing while significantly reducing treatment time and improving productivity
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 allows for the omission of softening heat treatment in wire rod manufacturing, enhancing productivity and reducing the need for specialized cooling facilities while maintaining adequate tensile strength.
Implementation Method 1
heating a billet at a temperature within a range of 950 to 1050° C.
Implementation Method 2
cooling the coiled rod wire to 600° C. at a cooling rate of 2° C./sec, and then cooling the cooled rod wire at a cooling rate of 3° C./sec
Implementation Method 3
the wire rod has a microstructure consisting of, by area %, 40% or more of proeutectoid ferrite based on an equilibrium phase, 40% or more of regenerated pearlite and bainite, and 20% or less of martensite
Data Source
AI summary
The present invention relates to a wire rod of which softening heat treatment can be omitted, and a manufacturing method therefor. One embodiment of the present invention provides a wire rod of which softening heat treatment can be omitted, and a manufacturing method therefor, the wire rod comprising, by wt %, 0.2-0.45% of C, 0.02-0.4% of Si, 0.3-1.5% of Mn, 0.3-1.5% of Cr, 0.02-0.05% of Al, 0.01-0.5% of Mo, 0.01% or less of N, and the balance of Fe and other inevitable impurities, and having a microstructure consisting of, by area %, 40% or more of proeutectoid ferrite based on an equilibrium phase, 40% or more of regenerated pearlite and bainite, and 20% or less of martensite, and wherein the colony average size of the pearlite in the region amounting to ⅖ to ⅗ of the diameter is 5 μm or less.