Low Temperature Oil Casing Steel Composition and Heat Treatment
Solution Overview
Problem
Existing oil casings for low-temperature environments face challenges in maintaining high strength and toughness while minimizing ductile-brittle transition temperatures and reducing longitudinal cracking, with prior solutions either being costly or compromising on mechanical strength.
Innovation Solution
A low-temperature resistant oil casing with a specific chemical composition (C: 0.08-0.14%, Si: 0.1-0.4%, Mn: 0.6-1.3%, Cr: 1-1.4%, Mo: 0.2-0.5%, Ni: 0.2-0.5%, Nb: 0.02-0.05%, Al: 0.01-0.05%, and controlled impurities) and manufacturing process, including smelting, continuous casting, rolling, heat treatment, and hot sizing, to achieve a fine tempered sorbite microstructure and optimal austenite distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If medium-carbon system with high C content is used, then strength is improved, but ductile-brittle transition temperature increases and toughness deteriorates at low temperature
Solution Approach 1:
The patent changes the chemical composition parameters by reducing C content to 0.08-0.14% (lower than conventional medium-carbon steel) while precisely controlling alloying elements (Mn: 0.6-1.3%, Cr: 1-1.4%, Mo: 0.2-0.5%, Ni: 0.2-0.5%, Nb: 0.02-0.05%) to achieve both high strength and low ductile-brittle transition temperature at -60°C to -100°C
Solution Approach 2:
The patent creates a composite microstructure consisting of tempered sorbite as the main phase with dispersed carbides and controlled alloying elements, achieving a synergistic effect where the composite structure provides both high strength (≥1034 MPa) and excellent low-temperature toughness (impact energy ≥100 J at -60°C to -100°C)
2Reliability
If high Ni content is added to improve low-temperature toughness, then toughness is improved, but cost increases significantly
Solution Approach 1:
The patent optimizes the Ni content parameter to 0.2-0.5% (significantly lower than conventional high-Ni alloys) while compensating with coordinated additions of Mn (0.6-1.3%), Cr (1-1.4%), and Mo (0.2-0.5%) to achieve the required toughness at -60°C to -100°C without incurring high material costs
Solution Approach 2:
The patent develops a cost-effective composite alloy system where Ni (0.2-0.5%) works synergistically with Mn, Cr, and Mo to create a microstructure with excellent low-temperature impact toughness (≥100 J) while maintaining high strength (≥1034 MPa) and reasonable manufacturing cost
3Strength
If C content is increased to improve strength, then strength is improved, but segregation worsens and low temperature toughness deteriorates
Solution Approach 1:
The patent reduces C content to 0.08-0.14% (lower than conventional medium-carbon steel) to prevent segregation and maintain composition uniformity, while compensating for strength through optimized alloying elements (Mn: 0.6-1.3%, Cr: 1-1.4%, Mo: 0.2-0.5%, Nb: 0.02-0.05%) that provide strengthening without causing segregation
Solution Approach 2:
The patent creates a homogeneous composite microstructure with fine dispersed carbides and tempered sorbite phases, where the low C content (0.08-0.14%) prevents excessive segregation while the alloying elements provide uniform distribution of strengthening phases, achieving both high strength (≥1034 MPa) and composition stability
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 provides an oil casing with yield strength ≥965 MPa, tensile strength ≥1034 MPa, ductile-brittle transition temperature between −60° C. and −100° C., transverse and longitudinal impact energies ≥100 J and ≥120 J respectively, and a fracture shear ratio ≥75%, while being cost-effective and suitable for mass production.
Implementation Method 1
heat treatment, wherein an austenitizing temperature is controlled in the range of 900-930° C., and held for 30-60 minutes, followed by quenching, subsequently, tempering at temperature of 480-600° C.
Implementation Method 2
tempering at temperature of 480-600° C., holding the temperature for 50-80 minutes
Implementation Method 3
The solid solution of Si in ferrite can improve the yield strength of the steel
Implementation Method 4
C is a carbide forming element, which can improve the strength of steel
Data Source
AI summary
The present disclosure provides a low temperature resistant oil casing having high strength and high toughness, and the manufacturing method thereof, the chemical composition of the oil casing by mass of: C: 0.08-0.14%, Si: 0.1-0.4%, Mn: 0.6-1.3%, Cr: 0.5-1.5%, Mo: 0.2-0.5%, Ni: 0.2-0.5%, Nb: 0.02-0.05%, V: 0-0.1%, Al: 0.01-0.05%, Ca: 0.0005-0.005%, and the balance being Fe and unavoidable impurities. The method of manufacturing the oil casing includes: (1) smelting and continuous casting; (2) perforating and continuous rolling; (3) heat treatment, wherein an austenitizing temperature is controlled in the range of 900-930° C., and held for 30-60 min, followed by quenching, subsequently, tempering at temperature of 480-600° C., holding the temperature for 50-80 min; (4) hot sizing.