Bainite Drilling Pipe Composition for Air-Cooled Strength and Toughness
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Solution Overview
Problem
Traditional geological drilling pipes face issues of deformation, fracture, and wear failure due to high tensile, pressure, bending, and torsional forces, with high production costs and environmental constraints from quenching and tempering heat treatments, leading to inefficient and costly operations.
Innovation Solution
A bainite geological drilling pipe with a specific chemical composition (C, Si, Mn, Nb, Al, B) and a two-stage air cooling process, eliminating the need for quenching and tempering heat treatment, resulting in high strength and toughness, and improved structural refinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If quenching and tempering heat treatment is adopted to improve strength, then tensile strength and hardness are improved, but production cost increases and environmental protection requirements are violated
Solution Approach 1:
The patent changes the chemical composition parameters by eliminating Cr and Mo elements and adjusting C, Mn, Si, Nb, Al, and B content ranges. This compositional parameter change enables the steel to achieve high strength through air cooling instead of expensive quenching and tempering heat treatment, thereby reducing production costs while maintaining tensile strength ≥1100 MPa
Solution Approach 2:
The patent extracts and removes the expensive alloying elements Cr and Mo from the steel composition. By taking out these noble metal elements and replacing them with more economical elements like Mn and Nb in optimized proportions, the patent achieves the same hardenability and strength effects at lower cost without requiring complex heat treatment processes
2Strength
If quenching and tempering heat treatment is adopted to improve strength, then tensile strength is improved, but deformation and cracking occur after treatment
Solution Approach 1:
The patent changes the hardenability parameters through optimized chemical composition (C: 0.14-0.22%, Mn: 2.1-2.9%, Si: 0.20-0.55%, Nb: 0.01-0.04%, Al: 0.015-0.04%, B: 0.001-0.005%). This composition enables the steel to achieve uniform hardening during air cooling without the thermal shocks and phase transformation stresses that cause deformation and cracking in conventional quenching processes
Solution Approach 2:
The patent converts the naturally slow air cooling process, which would normally produce insufficient hardening, into a beneficial process by optimizing the chemical composition. The enhanced hardenability from optimized Mn, B, and Nb content transforms the gentle air cooling into an effective heat treatment that achieves high strength without the harmful effects of rapid quenching
3Ease of manufacture
If traditional steel composition is used to maintain low cost, then alloy cost is reduced, but strength and toughness are insufficient
Solution Approach 1:
The patent creates a composite alloy system combining multiple elements in optimized proportions: C (0.14-0.22%) for strength, Mn (2.1-2.9%) for hardenability, Si (0.20-0.55%) for deoxidation and strength, Nb (0.01-0.04%) for grain refinement and precipitation hardening, Al (0.015-0.04%) for deoxidation, and B (0.001-0.005%) for hardenability enhancement. This composite composition achieves high strength and toughness at lower cost by eliminating Cr and Mo
Solution Approach 2:
The patent optimizes the concentration parameters of each alloying element to achieve the desired balance between cost and performance. By precisely controlling the content ranges of C, Mn, Si, Nb, Al, and B, the patent achieves maximum hardenability and mechanical properties without expensive Cr and Mo, resulting in cost-effective high-strength steel
4Productivity
If drilling pipe operates under complex stresses, then drilling depth increases, but deformation, fracture and wear failure occur
Solution Approach 1:
The patent employs a composite alloy composition with synergistic elements: C and Mn for strength and hardenability, Si for deoxidation and solid solution strengthening, Nb for grain refinement and precipitation hardening, Al for deoxidation, and B for hardenability. This composite material structure provides comprehensive resistance to tensile, compressive, bending, torsional, and wear stresses encountered during deep geological drilling
Solution Approach 2:
The patent optimizes the mechanical property parameters by controlling the chemical composition and heat treatment process. The optimized composition achieves yield strength ≥750 MPa, tensile strength ≥1100 MPa, hardness 35-45 HRC, and elongation ≥12%, enabling the drilling pipe to withstand complex stresses at greater depths with improved reliability
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 bainite pipe achieves yield strength ≥750 MPa, tensile strength ≥1100 MPa, hardness ≥35 HRC, toughness ≥60 J, and low residual stress ≤40 MPa, reducing production costs and enhancing drilling efficiency and safety.
Implementation Method 1
a phase transformation point of bainite is obviously reduced through a dragging effect of the element Mn on element diffusion at a phase transformation interface
Implementation Method 2
a dragging effect of the element Mn on element diffusion at a phase transformation interface
Implementation Method 3
a main body of a microstructure of the bainite geological drilling pipe is granular bainite
Implementation Method 4
performing two-stage air cooling on the pipe body after sizing
Implementation Method 5
0.01-0.04% of Nb
Implementation Method 6
the element B may further strengthen grain boundaries, prevent excessive precipitation of MA island, and improve the toughness of materials
Data Source
AI summary
The present disclosure provides a bainite geological drilling pipe, comprising the following chemical elements in percentage by mass: 0.14-0.22% of C, 0.2-0.55% of Si, 2.1-2.9% of Mn, 0.01-0.04% of Nb, 0.015-0.04% of Al, 0.001-0.005% of B, 0<N≤0.007%, with the balance being Fe and inevitable impurities, wherein a content ratio of Al to N is Al/N≥3. In addition, the present disclosure further provides a manufacturing method for the bainite geological drilling pipe, comprising the following steps: (1) performing smelting and casting on molten steel to obtain a pipe blank; (2) performing heating, piercing, continuous rolling and sizing on the pipe blank to obtain a pipe body; and (3) performing two-stage air cooling on the pipe body; in first-stage air cooling, performing air circular blowing cooling on the outer surface of the pipe body, the temperature before cooling is greater than or equal to Ar/3+50° C., the cooling rate is 5-15° C./s, and cooling to a temperature range from Bs-100° C. to Bs-50° C.; in second-stage air cooling, performing natural air cooling on the pipe body, the cooling rate is 0.5-4° C./s.