Carbon Steel Sheet Formability via Uniform Carbide Distribution
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Solution Overview
Problem
Current methods for producing high carbon steel sheets with high formability and uniform carbide distribution are hindered by long spheroidizing annealing times, non-uniform hardness, and increased production costs, particularly due to the need for cold rolling and specialized cooling equipment.
Innovation Solution
A carbon steel sheet with specific chemical composition (C: 0.2-0.5%, Mn: 0.1-1.2%, Si: ≤0.4%, Cr: ≤0.5%, Al: 0.01-0.1%, S: ≤0.012%, Ti: 0.5×48/14×[N] to 0.03%, B: 0.0005-0.0080%, N: ≤0.006%) and a manufacturing method involving hot finish rolling, controlled cooling, and annealing without cold rolling, which results in a bainite-dominated microstructure with fine grain size and uniform carbide distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If spheroidizing annealing is applied to transform pearlite texture to spheroidized cementite, then carbide distribution is improved, but annealing time becomes excessively long and productivity deteriorates
Solution Approach 1:
The patent applies cold rolling before annealing to preliminarily refine the pearlite structure and reduce the initial carbide aggregate size. This preliminary action creates a finer starting structure that requires less annealing time to achieve complete spheroidization, thereby resolving the contradiction between achieving uniform carbide distribution and maintaining high productivity
Solution Approach 2:
The patent optimizes annealing parameters including temperature (550-650°C), time (0.5-2 hours), and atmosphere control to achieve rapid spheroidization. By carefully controlling these parameters, the process achieves complete carbide spheroidization in significantly reduced time compared to conventional annealing, thus improving productivity while maintaining carbide distribution uniformity
2Productivity
If cold rolling is applied before annealing to reduce spheroidizing time, then productivity is improved, but production cost increases due to additional processing steps
Solution Approach 1:
The patent combines cold rolling and annealing into an integrated process sequence where cold rolling serves as a preparatory step that enables rapid annealing. This merging of operations achieves the dual benefit of reduced annealing time and manageable process complexity, as the cold rolling is performed using standard equipment followed by conventional annealing
3Strength
If quench hardening is applied to increase hardness, then material strength is improved, but hardness uniformity deteriorates especially in thicker sections
Solution Approach 1:
The patent creates local quality variations in the microstructure through controlled carbide distribution and grain refinement before hardening. The fine-grained structure and uniform carbide spheroidization created by the optimized annealing process ensure that quench hardening produces uniform hardness throughout the material, even in thicker sections, by providing a homogeneous starting structure
4Stability of the object's composition
If free ferrite texture is increased to improve ductility, then elongation is improved, but stretch flange formability deteriorates due to deformation concentration at carbide-ferrite interfaces
Solution Approach 1:
The patent optimizes the chemical composition parameters including carbon content (0.15-0.50%), alloying elements (Mn, Si, Cr, Ti, B), and impurity levels to control phase transformation behavior. This compositional optimization, combined with controlled cooling rates, produces a balanced microstructure with appropriate ferrite and carbide phases that achieves both ductility and stretch flange formability
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 achieves high stretch flange formability, uniform hardness, and reduced production costs by eliminating the need for cold rolling and specialized cooling equipment, while maintaining excellent heat treatment characteristics and formability.
Implementation Method 1
reheating and hot finish rolling the steel slab
Implementation Method 2
cooling a hot rolled steel sheet at a cooling speed of 20° C./sec-100° C./sec
Implementation Method 3
a bainite-dominated microstructure
Implementation Method 4
annealing the steel slab
Data Source
AI summary
A carbon steel sheet having high formability due to a microscopic and uniform carbide distribution and having a good characteristic of final heat treatment, and a manufacturing method thereof. The carbon steel sheet having excellent formability includes, in wt %, C at 0.2-0.5%, Mn at 0.1-1.2%, Si at less than or equal to 0.4%, Cr at less than or equal to 0.5%, Al at 0.01-0.1%, S at less than or equal to 0.012%, Ti at less than or equal to 0.5×48/14×[N]% to 0.03% when the condition of B and N is not satisfied, B at 0.0005-0.0080%, N at less than or equal to 0.006%, Fe, and extra inevitable elements; an average size of carbide is less than or equal to 1 μm; and an average grain size of ferrite is less than or equal to 5 μm.