Ultra-High Strength Casing Steel Tempered Sorbite Microstructure
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Solution Overview
Problem
Current steel materials for deep well casings face a challenge in achieving both high strength and high toughness, as increasing strength typically reduces toughness, and existing methods struggle to develop steel pipes with impact toughness exceeding 10% of their yield strength value, especially at 155 ksi or more.
Innovation Solution
The development of ultra-high strength and ultra-high toughness casing steel with a microstructure of tempered sorbite, optimized chemical element composition including C, Si, Mn, Cr, Mo, Nb, V, Al, and Ca, which forms fine precipitates to enhance strength while maintaining toughness, and a manufacturing process involving smelting, casting, piercing, rolling, and heat treatment to achieve the desired properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strength of the steel is increased, then the load-bearing capacity improves, but the toughness decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.20-0.40%, Si: 0.10-0.40%, Mn: 0.45-0.60%, Cr: 0.95-1.10%, Mo: 0.70-0.80%, Al: 0.015-0.040%, Ni: 0.001-0.005%, P: ≤0.015%, S: ≤0.003%) and heat treatment parameters (heating temperature: 750-950°C, rolling temperature: 700-850°C, deformation amount: ≥20%) to achieve the optimal balance between strength and toughness, producing steel with yield strength ≥950 MPa and impact toughness ≥100 J
Solution Approach 2:
The patent creates a composite microstructure consisting of tempered sorbite and residual austenite through controlled alloying and heat treatment. The combination of multiple alloying elements (C, Si, Mn, Cr, Mo, Al, Ni) works synergistically to form a composite material structure that simultaneously provides high strength and high toughness, resolving the contradiction between these two properties
2Ease of manufacture
If the heating temperature is increased to improve austenite formation, then the rolling process becomes easier, but excessive austenite leads to reduced toughness
Solution Approach 1:
The patent precisely controls the heating temperature parameter within 750-950°C and rolling temperature within 700-850°C to achieve optimal austenite formation without excessive transformation. This controlled parameter change ensures sufficient austenite for easy rolling while limiting residual austenite to 5-20% to maintain toughness
Solution Approach 2:
The patent applies partial action by controlling the austenite transformation to achieve only the necessary amount (5-20% residual austenite) required for improved rollability, rather than allowing excessive austenite formation. This partial transformation approach maintains toughness while providing sufficient ductility for the rolling process
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 solution achieves a strength of 155 ksi or more with impact toughness exceeding 10% of the yield strength, specifically yielding 130 J or more for 155 ksi steel grade and 120 J or more for 170 ksi steel grade, along with improved ductile-brittle transition temperatures, ensuring safety and performance in high-temperature, high-pressure environments.
Implementation Method 1
the content by mass percent of chemical elements thereof being as follows: C: 0.1-0.22%, Si: 0.1-0.4%, Mn: 0.5-1.5%, Cr: 1-1.5%, Mo: 1-1.5%, Nb: 0.01-0.04%, V: 0.2-0.3%, Al: 0.01-0.05%, Ca: 0.0005-0.005%
Implementation Method 2
having a microstructure of tempered sorbite
Implementation Method 3
the precipitates on the tempered sorbite include at least one of a carbonitride of Nb and a carbonitride of V
Data Source
AI summary
The present invention discloses an ultra-high strength and ultra-high toughness casing steel, having a microstructure of tempered sorbite, and the content of chemical elements by mass percent thereof being as follows: C: 0.1-0.22%, Si: 0.1-0.4%, Mn: 0.5-1.5%, Cr: 1-1.5%, Mo: 1-1.5%, Nb: 0.01-0.04%, V: 0.2-0.3%, Al: 0.01-0.05%, Ca: 0.0005-0.005%, the balance being Fe and unavoidable impurities. Correspondingly, the invention also discloses a casing obtained by processing the ultra-high strength and ultra-high toughness casing steel and a manufacturing method thereof. The ultra-high strength and ultra-toughness casing steel and the casing of the present invention have a strength of 155 ksi or more and an impact toughness greater than 10% of its yield strength value, thereby realizing a combination of ultra-high strength and ultra-high toughness.