Cr-Mo-Cu Stainless Steel Seamless Pipe for Sour-Service Toughness
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Solution Overview
Problem
Existing stainless steel seamless pipes for oil country tubular goods lack sufficient high strength, low-temperature toughness, and sulfide stress cracking resistance in severe corrosive environments containing CO2, Cl-, and H2S, with existing technologies failing to meet the required standards for yield strength, low-temperature absorption energy, and ductile-brittle transition temperature.
Innovation Solution
A stainless steel seamless pipe composition with specific ranges of Cr, Mo, Cu, and controlled microstructure to achieve high strength, excellent corrosion resistance, and low-temperature toughness, including a microstructure of at least 40% martensitic phase, at most 60% ferrite phase, and at most 30% retained austenite phase, with Mo content above 3.80% and Cu above 1.03% to enhance pitting corrosion resistance and hydrogen entry prevention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high Cr, Mo, and Cu content is used to improve corrosion resistance, then pitting corrosion resistance and hydrogen entry prevention are enhanced, but manufacturing cost and alloy complexity increase
Solution Approach 1:
The patent applies parameter changes by precisely controlling the content ranges of Cr (13-17%), Mo (3.80-6.0%), and Cu (1.03-3.5%) to achieve optimal corrosion resistance. This quantitative parameter optimization resolves the contradiction by finding the balance point where sufficient protection is achieved without excessive alloy complexity
Solution Approach 2:
The patent creates a composite microstructure consisting of martensitic phase (40-60%), ferrite phase (10-40%), and retained austenite phase (5-30%). This multi-phase composite structure synergistically provides both corrosion resistance and mechanical properties, resolving the contradiction between reliability and material complexity
2Strength
If high strength is achieved through martensitic phase, then yield strength reaches 862 MPa or more, but low-temperature toughness deteriorates with ductile-brittle transition temperature above -40°C
Solution Approach 1:
The patent employs a composite microstructure with multiple phases (martensitic, ferrite, and retained austenite) where each phase contributes different properties. The martensitic phase provides high strength while the ferrite and retained austenite phases maintain low-temperature toughness, resolving the contradiction between strength and toughness
Solution Approach 2:
The patent applies local quality by distributing different phases in specific proportions throughout the microstructure. The controlled distribution of ductile ferrite and retained austenite phases within the martensitic matrix provides localized toughness enhancement at low temperatures while maintaining overall high strength
3Reliability
If ferrite phase content is increased to improve low-temperature toughness, then absorption energy at -10°C reaches 300 J or more, but strength decreases below 862 MPa
Solution Approach 1:
The patent uses a multi-phase composite microstructure where ferrite phase (10-40%) provides low-temperature toughness and martensitic phase (40-60%) provides high strength. The synergistic combination of these phases resolves the contradiction by allowing both properties to coexist through their complementary contributions
Solution Approach 2:
The patent applies parameter changes by precisely controlling the ferrite phase content within 10-40% and adjusting the overall microstructure composition. This quantitative control optimizes the balance between toughness and strength, resolving the contradiction through parameter optimization
4Reliability
If Mo content is increased above 3.80% to improve sulfide stress cracking resistance, then corrosion resistance in CO2 and H2S environments is enhanced, but manufacturing cost increases
Solution Approach 1:
The patent applies parameter changes by setting the Mo content within the specific range of 3.80-6.0%, which is sufficient to achieve the required sulfide stress cracking resistance and corrosion protection while avoiding excessive Mo addition that would unnecessarily increase material cost and complexity
Data Source
AI summary
Provided herein is a stainless steel seamless pipe having high strength and excellent low-temperature toughness and corrosion resistance. The stainless steel seamless pipe has a composition comprising, in mass%, C: 0.06% or less, Si: 1.0% or less, Mn: 0.01% or more and 1.0% or less, P: 0.05% or less, S: 0.005% or less, Cr: 14.0% or more and 17.0% or less, Mo: more than 3.80% and 6.0% or less, Cu: more than 1.03% and 3.5% or less, Ni: 3.5% or more and 6.0% or less, Al: 0.10% or less, N: 0.10% or less, and O: 0.010% or less, in which C, Si, Mn, Cr, Ni, Mo, Cu, and N satisfy a predetermined relationship, and the balance is Fe and incidental impurities, the stainless steel seamless pipe having a microstructure that contains at least 40% martensitic phase, at most 60% ferrite phase, and at most 30% retained austenite phase by volume, the stainless steel seamless pipe having a yield strength of 862 MPa or more.