High-Mn Steel for Expandable Oil-Well Pipes
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Solution Overview
Problem
Existing steel materials for oil well casings lack sufficient uniform elongation and sulfide stress cracking (SSC) resistance, making them inadequate for expanded applications in hydrogen sulfide environments, where high expandability and corrosion resistance are required.
Innovation Solution
A steel material with a specific chemical composition, including C, Mn, Cu, and V, that stabilizes an austenitic structure, ensuring high uniform elongation and SSC resistance, while managing C content to prevent carbide formation and maintain austenite stability, and incorporating Cu to enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high Mn content is added to improve uniform elongation and expandability, then uniform elongation increases, but corrosion resistance deteriorates
Solution Approach 1:
The patent optimizes the Mn content parameter to a specific range (25-45%) rather than using excessive amounts, and combines it with controlled amounts of Cu (0.5-3.0%) and other alloying elements to achieve the desired balance between uniform elongation and corrosion resistance in wet H2S environments
Solution Approach 2:
The patent creates a composite alloy system by combining Mn with Cu, Cr, Mo, and other elements in specific proportions. This multi-element composition works synergistically to provide both high uniform elongation (40% or more) and adequate corrosion resistance, resolving the contradiction between these two properties
2Strength
If C content is increased to improve strength, then yield strength increases, but austenite stability decreases and carbide formation occurs
Solution Approach 1:
The patent precisely controls the C content parameter within a narrow range (0.6-1.8%) and combines it with high Mn content (25-45%) which acts as an austenite stabilizer. This parameter optimization ensures adequate yield strength (241 MPa or higher) while maintaining austenite single-phase structure and preventing carbide formation
3Ease of operation
If cold working is performed to achieve expansion, then expandability is achieved, but SSC resistance may be compromised without proper material selection
Solution Approach 1:
The patent performs preliminary alloying with high Mn content and controlled C content before cold working to ensure the material has adequate SSC resistance from the outset. The austenite single-phase structure created by this preliminary composition design maintains both expandability during cold working and SSC resistance after expansion, eliminating the need for post-expansion heat treatment
Data Source
Figure 1~2
AI summary
There is provided a steel material having a chemical composition consisting, by mass percent, of C: 0.6-1.8%, Si: 0.05-1.00%, Mn: >25.0-45.0%, Al: 0.003-0.06%, P: ≤0.03%, S: ≤0.03%, Cu: 0.5-3.0%, N: ≤0.10%, V: 0-2.0%, Cr: 0-3.0%, Mo: 0-3.0%, Ni: 0-1.5%, Nb: 0-0.5%, Ta: 0-0.5%, Ti: 0-0.5%, Zr: 0-0.5%, Ca: 0-0.005%, Mg: 0-0.005%, REM: 0-0.01%, B: 0-0.015%, the balance: Fe and impurities, and satisfying [0.6 < C - 0.18V < 1.44], wherein a metal micro-structure is consisting of an austenite single phase, a yield strength is 241 MPa or higher, and a uniform elongation is 40% or higher.