Seamless Steel Pipe Toughness via Controlled Cooling and Tempering
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Solution Overview
Problem
Existing methods for manufacturing seamless steel pipes for line pipes do not adequately improve toughness, and previous methods are not specifically suited for seamless steel pipes, leading to a need for enhanced techniques to refine crystal grains and enhance toughness.
Innovation Solution
The method involves accelerated cooling of seamless steel pipes followed by quenching and tempering, with a specific water cooling stop temperature of at most 450°C to produce a bainitic structure, which is then quenched and tempered to refine crystal grains, thereby improving toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the wall thickness of seamless steel pipe is increased to achieve high strength, then strength is improved, but toughness decreases and brittle fracture becomes more likely
Solution Approach 1:
The patent applies parameter changes by precisely controlling cooling rates (5-50°C/sec) and tempering temperatures (200-500°C) to transform the microstructure and mechanical properties of the steel pipe, achieving both high strength and high toughness simultaneously
Solution Approach 2:
The patent utilizes phase transitions during cooling and tempering processes to transform austenite into martensite and then temper the martensite, achieving a microstructure that provides both high strength and high toughness
2Ease of manufacture
If conventional cooling methods are used after piercing-rolling, then manufacturing simplicity is maintained, but crystal grain refinement and toughness improvement are insufficient
Solution Approach 1:
The patent applies dynamics by implementing a two-stage cooling process with variable cooling rates - rapid cooling (5-50°C/sec) followed by controlled tempering - to dynamically adjust the microstructure for optimal toughness
Solution Approach 2:
The patent changes thermal parameters by controlling cooling rates and tempering temperatures to achieve crystal grain refinement and improved toughness while maintaining manufacturing feasibility
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 significantly enhances the toughness of seamless steel pipes for line pipes, as demonstrated by the decrease in energy transition temperature and achievement of desired strength grades according to API standards.
Implementation Method 1
water cooling the produced seamless steel pipe at a cooling rate of at least 10°C/sec and stopping water cooling when the temperature of the seamless steel pipe reaches at most 450°C
Implementation Method 2
quenching the water-cooled seamless steel pipe, and tempering the quenched seamless steel pipe
Implementation Method 3
quenching the water-cooled seamless steel pipe, and tempering the quenched seamless steel pipe
Data Source
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AI summary
There is provided a method for manufacturing a seamless steel pipe for line pipe, capable of improving the toughness of the seamless steel pipe for line pipe. A round billet having a chemical composition, by mass percent, of C: 0.02 to 0.15%, Si: at most 0.5%, and Mn: 0.5 to 2.5%, the balance being Fe and impurities, is heated (S1). The heated round billet is piercing-rolled to produce a hollow shell (S2). The hollow shell is elongated and rolled and sized to produce a seamless steel pipe (S3). The seamless steel pipe is water cooled, and the water cooling is stopped when the temperature of the seamless steel pipe reaches at most 450°C (S5). The water-cooled seamless steel pipe is quenched (S6), and the quenched seamless steel pipe is tempered (S7).