High-Strength Steel Pipe Aging Resistance
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Solution Overview
Problem
Conventional techniques for manufacturing high-strength steel pipes for steam injection methods fail to maintain tensile strength of 620 MPa or more after long-term exposure to mid-temperature ranges, and often require excessive alloy chemical elements, leading to increased costs and decreased strength over time.
Innovation Solution
A manufacturing process involving controlled rolling, accelerated cooling, and reheating of Nb-containing or Nb-V-containing steel, with specific chemical compositions and heating rates to inhibit dislocation recovery and promote fine precipitate formation, thereby maintaining strength and reducing alloy element usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional techniques are used to manufacture high-strength steel pipes for steam injection, then the pipes can be manufactured with initial strength, but the tensile strength decreases significantly after long-term exposure to mid-temperature ranges
Solution Approach 1:
The patent applies parameter changes by precisely controlling chemical composition parameters (C: 0.10-0.25%, Si: 0.05-0.30%, Mn: 1.50-2.50%, Mo: 0.20-0.60%, Nb: 0.020-0.070%, Ti: 0.020% or less, V: 0.080% or less) and processing parameters (heating rate, rolling temperature, cooling rate) to achieve a microstructure that maintains strength after long-term aging. The controlled composition and processing create fine precipitates that inhibit dislocation recovery during aging, resolving the contradiction between initial strength and long-term strength retention.
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (bainite, untransformed austenite, and fine precipitates of Nb carbides and V carbides) within the steel matrix. This composite structure provides both initial high strength through the mixed microstructure and long-term strength retention through the dispersed precipitates that prevent dislocation recovery during aging exposure.
2Strength
If large amounts of alloy chemical elements are used to achieve high strength in the mid-temperature range, then strength is improved, but manufacturing cost increases and long-term strength is decreased
Solution Approach 1:
The patent optimizes alloying parameters by limiting total alloy content while achieving high strength through precise composition control. Specifically, it uses moderate amounts of strong carbide-forming elements (Nb: 0.020-0.070%, V: 0.080% or less, Mo: 0.20-0.60%) combined with controlled carbon content (0.10-0.25%) to generate sufficient fine precipitates for strengthening without excessive alloy addition. This resolves the contradiction by achieving mid-temperature strength with minimized alloy quantity.
Solution Approach 2:
The patent replaces expensive long-term strengthening mechanisms (large amounts of alloy elements) with a more efficient, shorter-duration strengthening mechanism: controlled precipitation during manufacturing. The fine precipitates formed during controlled cooling and reheating provide both initial strength and long-term aging resistance, eliminating the need for excessive alloy content and reducing manufacturing costs.
3Strength
If Nb and V are used to form solid solutions for strength, then strength is improved, but fine precipitate formation during reheating is inhibited when TiN is present
Solution Approach 1:
The patent controls the Ti content parameter (0.020% or less) and the Ti/N ratio (2.0 to 4.0) to prevent excessive TiN formation that would interfere with Nb and V carbide precipitation. By maintaining Ti at low levels and controlling the Ti/N ratio, sufficient Nb and V carbides can form as fine precipitates during reheating, providing the desired precipitation strengthening without the harmful interference of excess TiN.
Solution Approach 2:
The patent creates local quality differences in the microstructure by controlling where and how precipitates form. The controlled composition and processing create regions with fine Nb and V carbide precipitates that provide strengthening, while limiting TiN formation to levels that do not interfere with this local precipitation process. This selective control of precipitate formation resolves the contradiction between strength improvement and TiN interference.
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 process achieves and maintains a tensile strength of 620 MPa or more in high-strength steel pipes even after long-term exposure to mid-temperature ranges, while reducing the amount of alloy chemical elements used, thus lowering manufacturing costs and ensuring durability.
Implementation Method 1
Nb forms a solid solution, or Nb—V-containing steel, in which Nb and V form solid solutions
Implementation Method 2
precipitation strengthening due to fine precipitates which are precipitated from bainite and untransformed austenite when reheating is performed
Implementation Method 3
bainite transformation when accelerated cooling is performed
Data Source
AI summary
A high-strength steel having a specified chemical composition, wherein parameter Peff is 0.050% or more, the relationship (TS0−TS)/TS0≤0.050 is satisfied, wherein TS is defined as tensile strength determined at a temperature of 350° C. after aging has been performed under the condition of a Larson-Miller Parameter (LMP) of 15700, and wherein TS0 is defined as tensile strength determined at a temperature of 350° C. before the aging is performed, and having a toughness represented by a vE−20 of 100 J or more in a weld heat-affected zone, which is formed when welding is performed.