Bainite Seamless Steel Tube Cooling Without Alloying or Heat Treatment
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Solution Overview
Problem
The existing methods for manufacturing seamless steel tubes face challenges in achieving high strength and toughness while controlling the matrix structure, often requiring expensive alloying elements and off-line heat treatments, which increase costs and risk cracking due to complex internal stress states.
Innovation Solution
A method for manufacturing bainite high-strength seamless steel tubes through on-line controlled cooling, where the quenching starting temperature is set above the Ar3 temperature, and the finish cooling temperature is controlled within specific ranges to achieve a bainite matrix structure, without additional alloying elements or off-line heat treatments, utilizing water cooling and appropriate chemical compositions to ensure strength and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If expensive alloying elements are added to improve strength, then the strength of the steel tube is improved, but the manufacturing cost increases
Solution Approach 1:
The patent changes the processing parameters (cooling rate, finishing temperature) to obtain bainite matrix structure instead of relying on expensive alloying elements. By controlling the cooling process parameters, the steel achieves high strength through microstructure control rather than chemical composition modification.
Solution Approach 2:
The patent replaces expensive alloying elements with a controlled cooling process that uses water or air as cooling media. This substitutes costly materials with inexpensive processing methods to achieve the same strengthening effect.
2Strength
If off-line heat treatment is carried out to improve strength and toughness, then the performance of the steel tube is improved, but the manufacturing cost increases and the process complexity increases
Solution Approach 1:
The patent merges the cooling process with the rolling process by implementing on-line controlled cooling directly after rolling. This combines two previously separate operations (rolling and heat treatment) into a continuous process, eliminating the need for separate off-line heat treatment facilities and operations.
Solution Approach 2:
The patent implements continuous on-line controlled cooling immediately after rolling while the steel tube is still hot. This continuous process eliminates interruptions and separate handling steps required by off-line heat treatment, maintaining the useful thermal action throughout the processing sequence.
3Strength
If on-line quenching is used to control matrix structure, then the strength is improved, but the complex internal stress state causes cracking
Solution Approach 1:
The patent changes the cooling parameters (cooling rate, finishing temperature range) to achieve bainite transformation instead of martensite. By controlling the cooling rate to be within specific ranges and maintaining finishing temperature above Ms point, the steel develops bainite matrix structure that provides both strength and crack resistance.
Solution Approach 2:
The patent utilizes the phase transition from austenite to bainite during controlled cooling. By controlling the cooling process to achieve bainitic transformation rather than martensitic transformation, the steel obtains a microstructure that balances strength and toughness while reducing internal stresses and cracking tendency.
4Ease of manufacture
If air cooling on cooling bed is used, then the process is simple, but the residual heat is wasted and the matrix structure cannot be controlled
Solution Approach 1:
The patent changes the cooling parameters from passive air cooling to active controlled cooling with specific cooling rates and finishing temperatures. By implementing on-line controlled cooling with measurable and adjustable parameters, the process maintains simplicity while achieving precise control over the matrix structure transformation.
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 method produces seamless steel tubes with yield strength ≥555 MPa and impact energy >50 J at 0°C, achieving high strength and toughness while preventing cracking, thus enabling low-cost, high-performance production without expensive alloying elements.
Implementation Method 1
spray water on the inner wall of the high-temperature steel tube along the extending direction of the high-temperature steel tube... spray water along the tangent line of the outer wall of the high-temperature steel tube... the high-temperature steel tube is submerged in 10-12 seconds
Implementation Method 2
control the quenching starting temperature to meet the following formula: the quenching starting temperature≥the Ar3 temperature of the steel grade +20° C.; the finish cooling temperature is controlled to be within a range between T1 and T2... so that a bainite seamless steel tube with high strength and toughness is obtained
Data Source
AI summary
A method for manufacturing a bainite high-strength seamless steel tube, comprising the following steps: smelting, manufacturing a billet, heating, perforating, rolling, stretch reducing or sizing to obtain tube, and cooling. In the cooling step, the quenching starting temperature is controlled to be at least 20° C. higher than the Ar3 temperature of the steel grade; the finish cooling temperature is controlled to be within a range between T1 and T2, where T1=519-423 C-30.4Mn, T2=780-270 C-90Mn, and the units of the T1 and the T2 are ° C.; in the formulas, C and Mn respectively represent the mass percents of element C and element Mn of the steel grade, the content of the element C is 0.06-0.2%, and the content of the element Mn is 1-2.5%; the cooling rate is controlled to be 15-80° C./s; and the finished product of the bainite high-strength seamless steel tube is directly obtained after the cooling step. The manufacturing of a bainite high-strength seamless steel tube using the method requires neither the addition of precious alloying elements nor the subsequent heat treatment. Therefore the production costs are low.