Cold-Heading Wire Rod Microstructure for Faster Spheroidizing
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Solution Overview
Problem
Current wire rods for cold heading require lengthy spheroidizing heat treatment, increasing manufacturing costs and reducing ductility, while non-normalized steel omits heat treatment, leading to decreased ductility and increased strength with continuous cold processing.
Innovation Solution
A wire rod composition with specific alloying elements (C, Si, Mn, Cr, Al, N, Nb, V, Mo, Ti) and microstructural features, allowing for reduced spheroidizing heat treatment time through controlled hot rolling and cooling processes, achieving high tensile strength and ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spheroidizing heat treatment is performed to increase rolling life, then rolling life is improved, but process time and manufacturing cost increase
Solution Approach 1:
The patent applies preliminary action by creating a spheroidized microstructure during the hot rolling process itself through controlled cooling rates (0.1-10°C/s) and specific finial rolling temperatures (700-950°C), rather than performing separate post-rolling spheroidizing heat treatment. This preliminary formation of spherical cementite particles during manufacturing eliminates the need for additional heat treatment steps, thereby reducing process time while ensuring adequate rolling life.
2Ease of manufacture
If heat treatment processes are omitted to reduce manufacturing cost, then manufacturing cost is reduced, but ductility decreases and strength increases excessively
Solution Approach 1:
The patent applies parameter changes by precisely controlling chemical composition parameters (C: 0.15-0.50%, Si: 0.10-0.40%, Mn: 0.30-1.50%, Cr: 0.10-1.50%, Al: 0.02-0.05%, N: 0.004-0.020%) and processing parameters (cooling rate: 0.1-10°C/s, finial rolling temperature: 700-950°C) to achieve the desired balance of strength and ductility without requiring additional heat treatment processes. The controlled cooling rate and composition parameters enable formation of a microstructure with spherical cementite particles that provide adequate strength while maintaining ductility.
3Productivity
If continuous cold processing is performed without heat treatment, then manufacturing efficiency is improved, but ductility continuously decreases
Solution Approach 1:
The patent applies preliminary action by pre-forming a microstructure with spherical cementite particles and refined grain structure during the hot rolling and cooling process, before cold heading operations begin. This preliminary microstructural preparation ensures that the material has adequate ductility to withstand continuous cold processing steps, and the controlled composition and cooling parameters maintain this ductility throughout subsequent cold forming operations without requiring intermediate heat treatments.
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 results in a wire rod with tensile strength of 1250 MPa or more and elongation of 30% or more, enabling efficient manufacturing of molded products for automotive and structural applications with improved economic efficiency.
Implementation Method 1
spheroidizing heat treatment must be performed after the wire rod is drawn in order to increase the rolling life
Implementation Method 2
a wire rod for cold heading having a tensile strength of 1200 MPa or more and a specific microstructure
Implementation Method 3
quenched and tempered steels that are reheated, quenched and tempered after hot processing to increase strength and toughness
Implementation Method 4
quenched and tempered after hot processing to increase strength and toughness
Data Source
Figure 1a
Figure 1b
Figure 2a
AI summary
The present disclosure provides a wire rod for cold heading that can shorten the spheroidizing heat treatment time, processed products using the same, and manufacturing method thereof. A wire rod for cold heading according to an embodiment of present disclosure includes, in percent (%) by weight of the entire composition, C: 0.15 to 0.5%, Si: 0.1 to 0.4%, Mn: 0.3 to 1.5%, Cr: 0.1 to 1.5%, Al: 0.02 to 0.05%, N: 0.004 to 0.02%, at least one selected from the group consisting of Nb: 0.001 to 0.03%, V: 0.01 to 0.3%, Mo: 0.01 to 0.5%, Ti: 0.001 to 0.03%, and the remainder of iron (Fe) and other inevitable impurities, and the microstructure has a long and short axis ratio of cementite present in pearlite colonies of 200: 1 or less.