Martensitic stainless steel for oil casing and manufacturing method thereof

Abstract

The invention relates to a martensitic stainless steel for an oil casing and a production method thereof. The artensitic stainless steel comprises the following chemical components in percentage by weight: at most 0.04% of C, 0.20-1% of Si, 0.30-1% of Mn, at most 0.02% of P, at most 0.010% of S, 14-17% of Cr, less than 5% and at most 7% of Ni, 1.5-2.3% of Mo, 0-0.16% of N, 0.05-2.5% of Cu, one or more of 0.01-0.10% of Nb, 0.01-0.10% of V and 0.01-0.10% of Ti, and the balance of iron and inevitable trace impurity elements. The manufacturing method of the steel comprises the following steps: heating the oil casing to 950-1100 DEG C, cooling to below 200 DEG C by air cooling, oil cooling or water cooling, and heating to 550-650 DEG C to implement tempering. The steel has a microstructure which uses a tempered martensite phase as a base phase, and contains high-temperature ferrite (delta-ferrite), austenite and other second phases of which the volume contents are respectively below 10% or the total content is below 15%. The steel provided by the invention has the characteristics of high strength (the yield strength is up to Grade 110-150ksi), strong carbon dioxide/chloride ion corrosion resistance and the like, and can partially substitute double-phase stainless steel to be used in deep wells, superdeep wells and other severe well conditions.

Description

technical field [0001] The invention relates to a super-martensitic stainless steel and a manufacturing method thereof, in particular to an ultra-low carbon martensitic stainless steel for oil casings with a yield strength of 110-150ksi steel grade and high resistance to carbon dioxide and chloride ion corrosion and a manufacturing method thereof. Background technique [0002] carbon dioxide (CO 2 ) and chloride ion coexistence environment is a long-term and ubiquitous corrosion type in the world petroleum industry. In recent years, the number of deep wells and ultra-deep wells in my country has continued to increase, and the environment at the bottom of the well has become increasingly harsh. High temperature and high pressure environment, the simultaneous presence of CO 2 , chloride ions and water have higher and higher requirements on the corrosion resistance, strength and toughness of oil casing materials. [0003] At high temperature and pressure, high CO content 2 ...

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Problems solved by technology

Although duplex stainless steel (22-25% Cr) can meet the requirements, but the cost is higher

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