Duplex Seamless Steel Pipe Cooling for Crack-Free Hot Working
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Solution Overview
Problem
Existing methods for manufacturing duplex stainless steel pipes with high strength and low-temperature toughness require expensive facilities, complex heat treatments, and can lead to cracks due to strain concentration in ferrite phases with low deformation resistance.
Innovation Solution
A manufacturing apparatus line that includes a heating apparatus, piercing apparatus, rolling apparatus, cooling apparatus, and heat retention apparatus, where the steel is heated to a specific temperature range, subjected to hot working, and cooled at a controlled speed to refine the microstructure, primarily forming an austenitic phase with ferrite as a nucleation site for strain, thereby enhancing strength and toughness without requiring strong cold working or complex heat treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If duplex stainless steel is subjected to hot working at ordinary temperature regions, then the material can be processed, but embrittlement phase precipitates causing deteriorated hot workability and lowered mechanical properties and corrosion resistance
Solution Approach 1:
The patent applies temperature parameter changes by heating the steel to austenite region temperatures (above the embrittlement phase precipitation temperature) before hot working, then controlling cooling to achieve desired microstructure. This parameter change prevents embrittlement phase formation during processing while maintaining material integrity and properties.
2Ease of manufacture
If duplex stainless steel with multi-phase microstructure is hot worked, then the material can be processed, but strain concentrates in ferrite phase causing cracks
Solution Approach 1:
The patent changes the temperature parameter to austenite region before hot working, where the material has more uniform deformation characteristics. This prevents strain concentration in ferrite phase that occurs at lower temperatures, thereby avoiding crack formation while maintaining workability.
3Reliability
If hot working is finished at high temperature to suppress defects, then crack occurrence is reduced, but strain generated by hot working cannot be stored and crystal grain refinement becomes difficult
Solution Approach 1:
The patent implements continuous useful action by maintaining the steel in austenite region during hot working to enable defect-free processing, then immediately controlling the cooling process to trap strain and promote crystal grain refinement. This continuous process from heating through working to controlled cooling achieves both defect suppression and property enhancement.
Solution Approach 2:
The patent utilizes phase transitions by heating to austenite region, performing hot working, then controlling cooling to achieve desired phase transformation. The phase transition during cooling allows strain storage and crystal grain refinement, improving low-temperature toughness and yield strength while maintaining defect-free structure.
4Reliability
If solution heat treatment is performed to melt embrittlement phase, then alloy element distribution is improved, but additional processing steps and energy consumption increase
Solution Approach 1:
The patent merges the solution heat treatment step with the hot working process by heating to austenite region temperatures that simultaneously dissolve embrittlement phase and enable hot working. This consolidation eliminates separate solution treatment steps, reducing process complexity and energy consumption while achieving uniform alloy element distribution.
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
This approach allows for the stable production of duplex seamless stainless steel pipes with high strength and toughness, achieving yield strength of 588 MPa or more and absorbed energy of 50 J or more at -10°C without cracks, while reducing the amount of working and energy consumption.
Implementation Method 1
a heating apparatus for heating a steel raw material
Implementation Method 2
a cooling apparatus... where the steel is heated to a specific temperature range, subjected to hot working, and cooled at a controlled speed to refine the microstructure
Implementation Method 3
cooled at a controlled speed to refine the microstructure, primarily forming an austenitic phase with ferrite as a nucleation site for strain
Data Source
AI summary
An apparatus line for manufacturing seamless steel pipes and tubes includes: a heating apparatus for heating a steel raw material; a piercing apparatus for piercing the heated steel raw material thus forming a hollow material; and a rolling apparatus for applying working to the hollow material to form a seamless steel pipe having a predetermined shape. A cooling apparatus is arranged on an exit side of the rolling apparatus. A heated steel raw material is worked by the rolling apparatus after being pierced by the piercing apparatus, and thereafter, using a surface temperature of a hollow piece before being cooled by the cooling apparatus as a cooling start temperature, the hollow piece is cooled to a cooling stop temperature differing by 50° C. or more from the cooling start temperature and being equal to or above 600° C. at an average cooling speed of 1.0° C./s or more in terms of an outer surface temperature.