Thick Steel Plate Hot Forging for Center Toughness
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Solution Overview
Problem
Existing methods for producing thick steel plates with high tensile strength and toughness face challenges such as center porosity, insufficient elongation, and increased defect sensitivity due to the need for larger continuous casting lines and higher alloy additions, which can lead to higher manufacturing costs and longer construction times.
Innovation Solution
A high tensile strength thick steel plate with a plate thickness of 100 mm or more, composed of specific steel composition and processed using hot forging and hot rolling techniques, including heating to 1200° C to 1350° C, forging at 1000° C or more with controlled strain rates, and subsequent quenching and tempering to achieve a yield strength of 620 MPa or more and toughness of 70 J or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If ingot casting and blooming process is used to produce thick steel plates, then plate thickness can be achieved, but concentrated segregation areas and negative segregation areas must be discarded causing yield improvement to be hindered and manufacturing cost to increase
Solution Approach 1:
The patent applies parameter changes by controlling the heating temperature (1200-1350°C), forging temperature (1000°C or more), strain rate (3/s or less), and working reduction ratio during hot forging to transform the microstructure and eliminate segregation defects, enabling full utilization of the continuously-cast slab without discarding defective areas
Solution Approach 2:
The patent replaces the traditional ingot casting and blooming mechanical process with a continuously-cast slab direct hot forging process, substituting the complex multi-step mechanical system with a more efficient thermal-mechanical processing system that eliminates the need for discarding segregation areas
2Productivity
If continuously-cast slab is used as raw material, then discarded segregation areas do not exist, but working reduction to product thickness is low because slab thickness is smaller than ingot casting slab
Solution Approach 1:
The patent applies preliminary action by performing hot forging with controlled strain rate (3/s or less) and high heating temperature (1200-1350°C) before final rolling, which pre-compresses and redistributes the material to enable achieving thick plate dimensions from thinner continuously-cast slabs
Solution Approach 2:
The patent changes the processing parameters by maintaining high temperature (1000°C or more) during forging, controlling strain rate (3/s or less), and optimizing working reduction ratio to enable significant thickness increase from the continuously-cast slab without compromising material quality
3Strength
If alloying element addition is increased to ensure necessary properties in thicker steel plates, then strength can be improved, but center porosity from center segregation and inner quality degradation occur
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratios (C: 0.08-0.20%, Si: 0.40% or less, Mn: 0.5-5.0%, etc.) and controlling the equivalent carbon content (CeqIIW≥0.57%) to achieve high strength without excessive alloying, combined with thermal-mechanical processing parameters (heating temperature 1200-1350°C, strain rate 3/s or less) to eliminate center porosity and segregation
Solution Approach 2:
The patent replaces excessive alloying with a thermal-mechanical processing system that uses controlled hot forging (strain rate 3/s or less, temperature 1000°C or more) to achieve high strength and eliminate defects, substituting chemical strengthening with physical processing
4Loss of time
If hot forging with high strain rate is used to compress center porosity, then processing time can be reduced, but elongation and toughness of the center of plate thickness become insufficient
Solution Approach 1:
The patent applies parameter changes by inverting the conventional approach: instead of using high strain rate to reduce time, it uses low strain rate (3/s or less) combined with high temperature (1000°C or more) and adequate holding time to achieve both time efficiency and high toughness, transforming the parameter relationship to overcome the trade-off
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 the production of thick steel plates with excellent yield strength and toughness, suitable for larger steel structures, improving safety and reducing construction time without the need for larger continuous casting lines, while maintaining high properties even with a working reduction ratio from the raw material of 3 or less.
Implementation Method 1
heating to 1200° C to 1350° C
Implementation Method 2
subsequent quenching and tempering
Data Source
AI summary
A high toughness and high tensile strength thick steel plate has a plate thickness of 100 mm or more, wherein a reduction of area in a center of the plate thickness by tension in a plate thickness direction is 40% or more. Thus, a high tensile strength thick steel plate with excellent strength and toughness in a center of the plate thickness can be obtained with no need for a larger production line, even in the case of producing a high strength thick steel plate for which the addition amount of alloying element needs to be increased.