Hypereutectoid Wire Rod Microstructure for Drawability Without Spheroidizing
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Solution Overview
Problem
The high heat treatment costs and prolonged production time associated with spheroidization softening heat treatment for hypereutectoid steel wire rods used in mechanical structural parts, such as bearings, make it challenging to achieve excellent drawability and strength while minimizing energy consumption and manufacturing costs.
Innovation Solution
A wire rod composition with specific alloying elements (C: 0.8-1.2%, Si: 0.01-0.6%, Mn: 0.1-0.6%, Cr: 0.8-2.0%, Al: 0.01-0.06%, N: 0.02% or less, with a microstructure of pearlite and proeutectoid cementite, and an average AlN particle diameter of 30 nm or less, is developed, along with a manufacturing method involving heating, rolling, and controlled cooling to achieve fine austenite grain size and deformation, thereby omitting or shortening the spheroidization softening heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If spheroidization softening heat treatment is performed to improve cold workability and drawability, then drawing characteristics are improved, but heat treatment costs increase and production time is prolonged
Solution Approach 1:
The invention applies preliminary action by controlling the microstructure during the rolling process itself. Specifically, it creates a microstructure with spheroidized cementite and refined austenite grains (10-20 μm) through controlled rolling at 750-950°C with 80-150% total reduction and 20-50% finish rolling reduction, eliminating the need for subsequent spheroidization heat treatment. This preliminary microstructure control during manufacturing replaces the need for later heat treatment operations.
Solution Approach 2:
The invention applies parameter changes by optimizing specific process parameters: heating temperature (750-950°C), total reduction ratio (80-150%), finish rolling reduction ratio (20-50%), and cooling rate (10-50°C/s). These parameter changes transform the microstructure in-situ during rolling, creating the desired spheroidized cementite morphology and fine austenite grain structure without requiring additional heat treatment time.
2Ease of operation
If spheroidization softening heat treatment is performed to reduce hardness and improve drawability, then drawing characteristics are improved, but manufacturing costs increase
Solution Approach 1:
The invention performs the microstructure modification action during the rolling process itself by controlling temperature (750-950°C), reduction ratios (80-150% total, 20-50% finish), and cooling rate (10-50°C/s). This creates spheroidized cementite and fine austenite grains (10-20 μm) preliminarily, eliminating the need for separate heat treatment operations and associated manufacturing costs.
Solution Approach 2:
The rolling process itself serves the dual function of shaping the wire rod and creating the desired microstructure. The controlled rolling parameters cause cementite spheroidization and austenite grain refinement automatically during the forming process, making the material self-prepare its own microstructure without requiring external heat treatment services.
3Reliability
If spheroidization softening heat treatment is performed to prevent disconnection during wire drawing, then drawing characteristics are improved, but energy consumption increases
Solution Approach 1:
The invention creates the reliable microstructure preliminarily during rolling by controlling temperature (750-950°C), reduction (80-150% total), and cooling rate (10-50°C/s). This produces spheroidized cementite and fine austenite grains (10-20 μm) that prevent disconnection during drawing, eliminating the need for energy-intensive subsequent heat treatment.
Solution Approach 2:
The rolling process continuously performs both forming and microstructure creation functions in one operation. The controlled continuous deformation at 750-950°C with specific cooling rate creates the reliable microstructure throughout the entire wire rod cross-section during the forming process itself, maintaining drawing reliability without additional energy-consuming heat treatment steps.
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 enables wire rods with excellent drawability and strength, reducing manufacturing costs and carbon emissions by eliminating or shortening the spheroidization softening heat treatment process without compromising the material's properties, allowing for increased drawing capacity and reduced defect occurrence.
Implementation Method 1
at least 20 AlN particles with an average particle diameter of 30 nm or less per unit area (μm2) are included
Implementation Method 2
a microstructure includes a pearlite main structure and proeutectoid cementite
Implementation Method 3
cooling the wire rod at an average cooling rate of 3°C/sec or more to a temperature of 550 to 650°C
Data Source
AI summary
The present invention relates to a machine structure wire rod, which is applicable to vehicles, construction components and the like, and a manufacturing method therefor, and to a wire rod having excellent drawability, and a method for manufacturing same.