Seamless OCTG Stainless Steel Composition for Hot Workability
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Solution Overview
Problem
Current seamless stainless steel pipes for Oil Country Tubular Goods lack stable manufacturing methods that achieve high strength, toughness, and corrosion resistance, especially in high-temperature environments with CO2 and Cl- presence, due to inadequate control over quenching and tempering processes.
Innovation Solution
The method involves optimizing the composition of seamless stainless steel pipes by adjusting the content of Mo, C, Si, Mn, Cr, Ni, and other elements to suppress intermetallic compound precipitation, ensuring a parameter P(Mo, t) ≤ 2100 and a density of intermetallic compounds ≤ 2×10^4/mm², while improving hot workability through controlled quenching and tempering processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two-phase stainless steel is used to achieve corrosion resistance in high-temperature environments, then corrosion resistance is improved, but raw material cost increases and hot workability deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the stainless steel by precisely controlling the content ranges of Cr (15-18%), Mo (2-4%), Ni (3-5%), and other alloying elements. This parameter optimization enables the steel to achieve excellent corrosion resistance in high-temperature CO2 and Cl- environments while maintaining good hot workability for seamless pipe manufacturing
Solution Approach 2:
The invention creates a composite microstructure consisting of ferrite phase and martensite phase in a dual-phase stainless steel. This composite structure combines the corrosion resistance of ferrite with the strength of martensite, achieving both high corrosion resistance and good manufacturability through controlled phase distribution
2Strength
If martensitic stainless steel with 13Cr is used to achieve strength and toughness, then mechanical properties are improved, but corrosion resistance in high-temperature corrosive environments deteriorates
Solution Approach 1:
The invention increases the chromium content from 13% to 15-18% and adds specific amounts of molybdenum (2-4%) and nickel (3-5%), creating a new compositional parameter set that simultaneously enhances both mechanical properties and corrosion resistance in high-temperature CO2 and Cl- environments
Solution Approach 2:
The invention develops a dual-phase composite structure with ferrite and martensite phases, where the ferrite phase provides excellent corrosion resistance and the martensite phase provides high strength and toughness, achieving synergistic performance
3Device complexity
If cooling stop temperature in quenching is not controlled to simplify the process, then manufacturing complexity is reduced, but strength becomes unstable
Solution Approach 1:
The invention specifies a precise cooling stop temperature range (Ms-50℃ to Ms-20℃) during quenching that controls the transformation of austenite to martensite. This parameter control ensures stable and reproducible strength properties in the seamless pipes while maintaining a relatively simple manufacturing 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
This approach stabilizes the production of seamless stainless steel pipes with yield strength ≥ 758 MPa, toughness ≥ 40J at -10°C, and excellent corrosion resistance up to 230°C, enhancing both industrial productivity and pipe performance.
Implementation Method 1
quenching and tempering are applied to the seamless steel pipe thus acquiring a seamless stainless steel pipe
Implementation Method 2
quenching and tempering are applied to the seamless steel pipe thus acquiring a seamless stainless steel pipe
Implementation Method 3
intermetallic compounds are precipitated in a martensite phase
Data Source
Figure 1
AI summary
Provided are a method of manufacturing a seamless stainless steel pipe for Oil Country Tubular Goods with excellent hot workability, by which a seamless stainless steel pipe for Oil Country Tubular Goods having high strength of 110ksi (=758MPa) or more in terms of yield strength, high toughness of 40J or more in terms of absorption energy vE-10 in a Charpy impact test at a test temperature of -10°C and excellent corrosion resistance can be acquired, and a seamless stainless steel pipe for Oil Country Tubular Goods acquired by the method. A billet which has the composition containing predetermined components and in which the contents of C, Si, Mn, Cr, Mo, Ni, N, W, Cu satisfy the predetermined relationship is heated, hot working is applied to the billet thus forming a seamless steel pipe, the seamless steel pipe is cooled to a room temperature at a cooling rate of air cooling or more, thereafter, quenching is performed by heating the seamless steel pipe to a temperature of 850°C or above and, subsequently, by cooling the seamless steel pipe to a temperature of 100 °C or below at a cooling rate of air cooling or more and, subsequently, tempering is applied to the seamless steel pipe at a temperature of 700°C or below for a predetermined holding time.