Seamless Steel Pipe Rolling With Rapid Cooling for Grain Refinement
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Solution Overview
Problem
Existing methods for producing seamless steel pipes struggle to refine crystal grains in piercing mills, leading to coarsening issues, which compromises both strength and sulfide stress cracking resistance.
Innovation Solution
A production method involving an Nb-containing steel material with specific chemical composition, heated to 800-1030°C, undergoes piercing-rolling or elongation-rolling in a piercing mill with skewed rolls, followed by rapid cooling using a cooling liquid to reduce the outer surface temperature to 700-1000°C within 15 seconds, effectively suppressing crystal grain coarsening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strength of a seamless steel pipe is increased, then SSC resistance of the seamless steel pipe decreases
Solution Approach 1:
The invention changes the chemical composition parameters by adding specific amounts of Ti (0.002-0.050%), Nb (0.010-0.050%), V (0.010-0.300%), and B (0.0005-0.0050%) to the steel material. These compositional parameter changes enable the formation of fine precipitates that refine crystal grains while maintaining high strength, thus resolving the contradiction between strength and SSC resistance
Solution Approach 2:
The invention creates a composite microstructure by forming multiple types of precipitates (Ti carbides, Nb carbides, V carbides, and borides) within the steel matrix. This composite structure at the micro level provides both strength through precipitation hardening and SSC resistance through refined grain structure, eliminating the trade-off between these properties
2Manufacturing precision
If quenching is carried out a plurality of times to refine crystal grains, then crystal grain size is reduced, but production time and process complexity increase
Solution Approach 1:
The invention performs preliminary action by adding Ti, Nb, V, and B elements to the steel composition before manufacturing. These elements form fine precipitates during controlled cooling after a single quenching process, achieving crystal grain refinement without needing multiple quenching cycles. This preliminary compositional preparation enables grain refinement to occur naturally during the standard heat treatment process
Solution Approach 2:
The invention replaces the mechanical approach of multiple repeated quenching operations with a chemical approach using microalloying elements. The Ti, Nb, V, and B elements chemically interact with the steel matrix during cooling to form precipitates that refine grains, substituting the need for repeated mechanical quenching cycles and thereby reducing production time and process complexity
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 effectively refines crystal grains, enhancing the seamless steel pipe's strength and sulfide stress cracking resistance while maintaining the pinning effect of Nb carbides, thereby improving the pipe's overall performance.
Implementation Method 1
heating an Nb-containing steel material to 800 to 1030°C
Implementation Method 2
carrying out cooling by using a cooling liquid on a hollow shell portion that passes between rear ends of the plurality of skewed rolls, in the hollow shell, so as to reduce an outer surface temperature of the hollow shell portion to 700 to 1000°C within 15.0 seconds
Data Source
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AI summary
A production method of a seamless steel pipe capable of suppressing coarsening of crystal grains in a piercing mill is provided. The production method of a seamless steel pipe according to the present embodiment includes a heating step of heating an Nb-containing steel material to 800 to 1030°C, a pipe-making step of producing a hollow shell by performing piercing-rolling or elongation-rolling on the Nb-containing steel material, by using a piercing mill including a plurality of skewed rolls disposed around a pass line on which the Nb-containing steel material passes, a plug disposed between the plurality of skewed rolls and on the pass line, and a mandrel bar extending rearward of the plug along the pass line from a rear end of the plug, and a cooling step immediately after rolling, of carrying out cooling using a cooling liquid on a hollow shell portion that passes between rear ends of the plurality of skewed rolls, in the hollow shell, so as to reduce an outer surface temperature of the hollow shell portion to 700 to 1000°C within 15.0 seconds after the hollow shell portion passes between the rear ends of the plurality of skewed rolls.