CN116875879A - 160 ksi-level economic non-standard oil casing and manufacturing method thereof - Google Patents

Abstract

The invention relates to a 160 ksi-level economical non-standard oil sleeve and a manufacturing method thereof, wherein the chemical components comprise the following components in percentage by weight: 0.10 to 0.40 percent of C, 0.05 to 0.35 percent of Si, 0.55 to 2.50 percent of Mn, 0.50 to 2.50 percent of Cr, 0.10 to 0.50 percent of Mo, 0.05 to 0.25 percent of V, less than or equal to 0.05 percent of Nb, 0.0005 to 0.002 percent of B, 0.01 to 0.05 percent of Ti, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and unavoidable impurity elements. The advantages are that: the high-temperature rolling is matched with direct on-line quenching, so that secondary heating is not needed, energy is saved, and the production efficiency is improved; the quenching end temperature is controlled to meet the requirements of tempering heat preservation temperature, so that the energy consumption of a tempering process is reduced.

Description

160 ksi-level economic non-standard oil casing and manufacturing method thereof

Technical Field

The invention belongs to the technical field of manufacturing of ultra-high strength structural steel, and particularly relates to an economic non-standard oil sleeve with yield strength not lower than 160ksi level and a manufacturing method thereof.

Background

The seamless pipe with the yield strength not lower than 160ksi level can meet the material selection requirement in the field of high-strength seamless pipes which are allowed to be supplied in a quenched and tempered state, and is suitable for producing seamless pipe products such as oil pipes, oil casings, pipe hoops and the like for deep wells and ultra-deep wells.

The oil well pipe is one of the necessary equipment in petroleum and natural gas development engineering and is a special material. Typically, 20% -30% of the cost of a well is the cost of an oil well pipe. In the total amount of steel for petroleum industry, the oil well pipe accounts for 40%, and the oil well pipe accounts for more than 90%.

At present, the easily-collected shallow oil and gas resources are gradually exhausted, so that the depth of an oil and gas well is gradually increased, and the well depth is accelerated year by year. After the well depth is increased, the pressure and the temperature in the well are continuously increased, the geological environment is more severe, and the stressed state of the oil casing is more complex and severe. The highest Q125 steel grade of the prior API oil casing can not meet the oil gas development requirements transferred to the western and ocean, and the safety operation of deep wells and ultra-deep wells is urgently required to be provided with the high-toughness oil gas exploitation steel with the grade of 160ksi or more.

With the increase of the strength, the existing seamless pipe with the strength exceeding the Q125 steel grade has various problems in composition or preparation process, and the technical proposal still has the defects of high content of added alloy elements, complex production process, poor toughness matching and the like although the yield strength of the existing product can reach 160 ksi.

The patent application number is CN201811165255.8, and discloses a 140ksi steel grade seamless steel pipe and a manufacturing method thereof, wherein the yield strength of the steel pipe is 980-1120MPa, and the full-size Charpy impact energy at 0 ℃ is not lower than 120J. In the composition design, 0.0005% -0.0040% of B element and 1.00% -3.00% of Ni element are added. In the production process, the hollow pipe blank is produced by adopting a centrifugal casting mode, and is rolled into a specified size by an MPM/PQF continuous rolling mill unit and then subjected to heat treatment. The patent application number is CN20090069758. X, a 150ksi steel grade high strength and toughness steel pipe for downhole operation of oil and gas well and a production method thereof are disclosed, the yield strength of the steel pipe is 1034-1148MPa, the transverse half-size Charpy impact energy at 0 ℃ is 46-53J, and the longitudinal 3/4 size Charpy impact energy is not lower than 87-101J. In the component design, B element is not added, and 0.70% -0.80% of Mo element is added. In the production process, the Si-Ca wire is used for changing the form of the inclusion, so that the toughness and the low-temperature-resistant toughness of the steel are improved essentially. The patent application number is CN201310409266.7, a petroleum casing pipe for ultra-deep well and a production process thereof are disclosed, and the yield strength of the steel pipe is 1158-1167MPa. In the component design, 0.02% -0.05% of Ce element is added. The patent application number is CN202111540297.7, and discloses a high-strength niobium-containing petroleum casing pipe based on controlled cooling and a manufacturing method thereof, wherein the yield strength of the steel pipe is 1180-1300MPa, and the transverse impact energy at 0 ℃ is 80-150J. In component design, ni is added, and B is selectively added; in the production process, the process methods of continuous cooling and sparse cooling are adopted, the average cooling speed of 20-60 ℃/s is used for obtaining a complex phase structure which mainly contains bainite and has ferrite and pearlite content of not more than 10%, and the complex phase structure is subjected to heat treatment to obtain a tempered sorbite structure so as to meet the requirement of toughness matching.

Disclosure of Invention

The invention aims to provide a 160ksi grade economic non-standard oil sleeve and a manufacturing method thereof, wherein the 160ksi grade seamless pipe is produced by adopting a traditional solid round billet through properly improving the Mn and Cr contents and strictly controlling the Mo and B element contents so as to obtain the ultra-high strength seamless pipe with yield strength not lower than 160ksi and excellent low-temperature toughness.

In order to achieve the above purpose, the present invention is realized by the following technical scheme:

160ksi grade economical non-standard oil casing pipe comprises the following chemical components in percentage by weight:

0.10 to 0.40 percent of C, 0.05 to 0.35 percent of Si, 0.55 to 2.50 percent of Mn, 0.50 to 2.50 percent of Cr, 0.10 to 0.50 percent of Mo, 0.05 to 0.25 percent of V, less than or equal to 0.05 percent of Nb, 0.0005 to 0.002 percent of B, 0.01 to 0.05 percent of Ti, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and unavoidable impurity elements.

In the oil sleeve, the size tp of a C precipitated phase containing Mo and V is not more than 200nm, the size tp of a C precipitated phase containing Mo and V with the volume fraction of more than 75 percent is not more than 50nm, the transverse Charpy impact Akv at 0 ℃ is not less than 120J, and the longitudinal Charpy impact Akv is not less than 150J.

A manufacturing method of 160 ksi-grade economic non-standard oil casing comprises the following steps:

1) Smelting and continuously casting steel billets: smelting molten iron by an electric furnace, feeding the molten iron into an LF furnace for refining, carrying out vacuum treatment by a VD furnace, and continuously casting into a round tube blank;

2) Rolling a steel pipe: heating the round tube blank to 1205-1255 ℃, wherein the temperature before perforation is 1160-1220 ℃, the temperature before oblique rolling is 950-1130 ℃, and the temperature before tension reducing is 850-920 ℃;

3) Quenching and tempering: the steel pipe is directly quenched on line after the tension reducing is finished, the quenching start temperature is 830-870 ℃, the quenching end temperature is 200-400 ℃, the steel pipe is directly tempered at the strip temperature after quenching, the tempering temperature is 200-400 ℃, and the air cooling is carried out after tempering.

The quenching medium in the step 3) is water or oil, and the average cooling speed of the quenching medium is more than 65 ℃/s.

The tempering heat preservation time t in the step 3) _T (unit: minutes) satisfies:

t _T ＝(4～6)t (1)

in the formula (1), t _T The heat preservation time of tempering is in min; t is the wall thickness of the steel pipe, and the unit is mm.

The main alloying elements of 160ksi grade economical non-standard oil casing are as follows:

carbon C: c is the main element next to Fe in steel, and directly affects the strength, plasticity, toughness and other properties of the steel. C has obvious effect on improving the strength of steel through solid solution strengthening and precipitation strengthening, but improving the content of C has negative effect on the plasticity and toughness of the steel. For this purpose, the C content range is set to 0.10% to 0.40%.

Silicon Si: si is an important reducing agent and deoxidizer in the steelmaking process, and can be dissolved in ferrite and austenite to improve the hardness and strength of steelDegree. Increasing Si content, and reducing Fe ₃ And C. The Si content is too high, which obviously reduces the plasticity and toughness of the steel. For this purpose, the Si content range is set to 0.05% to 0.35%.

Manganese Mn: mn can improve the hardenability of steel, and is beneficial to the strength of steel; can eliminate the influence of S (sulfur) and improve the hot workability of steel. Because Mn is relatively cheap and can be infinitely dissolved with Fe, the strength of the steel is improved, and meanwhile, the influence on plasticity is relatively small. Therefore, mn is widely used as a strengthening element in steel. The excessive Mn content can aggravate the segregation of the continuous casting billet, increase the band-shaped structure grade of the steel pipe, and deteriorate the structure uniformity, and is unfavorable for the plasticity and the low-temperature toughness of the steel pipe. For this purpose, the Mn content range is set to 0.55% to 2.50%.

Chromium Cr: cr can increase the hardenability of steel and has a secondary hardening effect, and can improve the strength, hardness and wear resistance of steel without embrittling the steel, but can reduce elongation and reduction of area. Cr has the main function of improving hardenability in a quenching and tempering structure, so that the steel has good comprehensive mechanical properties after quenching and tempering. If Cr is excessively added, cr-containing carbide is precipitated and aggregated at the prior austenite grain boundary in the tempering process to grow up, and the low-temperature toughness of the steel pipe is seriously damaged. For this purpose, cr content is selected to be 0.50% -2.50%.

Molybdenum Mo: mo has a similar effect to Cr, and is not excessively high in addition amount because of its high price. For this reason, the Mo content range is selected to be 0.10% -0.50%.

Vanadium V: v and C, N, O have a very strong affinity with which the corresponding stable compounds are formed. V exists mainly in the form of carbide in steel, and has the functions of refining structure and crystal grains, improving strength and toughness and reducing overheat sensitivity. Vanadium can increase the tempering stability of quenched steel and produce a secondary hardening effect; the main purpose of quenched and tempered steel is to improve the strength of the steel. For this purpose, the V content range is selected to be 0.05% -0.25%.

Titanium Ti: ti and C, N, O have extremely strong affinity, and form corresponding stable compounds with the Ti and C, N, O, and are one of the most main solid N elements. The precipitated phase containing Ti has strong binding force, is stable and not easy to decompose, can prevent the grain growth tendency of steel at high temperature and improve the welding performance of the steel. The N and the S are fixed by Ti, which is beneficial to improving the strength and the plasticity of the steel. Increasing the Ti content, the Ti-containing precipitate phase coarsens, adversely affecting performance. The Ti in the invention has the core function of fixing N, and avoiding the combination of N and V from affecting the cooperative precipitation of V and Mo. The Ti content range is selected to be 0.01% -0.05%.

Niobium Nb: nb is one of the most main microalloying elements, and is partially dissolved into solid solution to play a role in solid solution strengthening; when the carbide, nitride and oxide particles exist, the tempering stability of the steel can be improved, and the secondary hardening effect is realized. The trace Nb can improve the strength of the steel without affecting the plasticity or toughness of the steel. The impact toughness of the steel can be improved and the brittle transition temperature of the steel can be reduced due to the effect of grain refinement. In the rolling process, the solid solution Nb obviously improves the recrystallization temperature of the steel, and can finish the rolling process of the steel in a higher temperature range, thereby reducing the internal stress of the steel pipe. The Nb content is not higher than 0.05%.

Aluminum Al: al is added to steel as a deoxidizer or alloying element, and aluminum has a much stronger deoxidizing ability than silicon and manganese. The main function of aluminum in steel is to refine grains and fix nitrogen in the steel, so that the impact toughness of the steel is obviously improved, and the cold embrittlement tendency and the aging tendency are reduced; the aluminum can also improve the corrosion resistance of the steel, and particularly has better effect when being matched with elements such as molybdenum, copper, silicon, chromium and the like; the disadvantage of aluminum is that it affects the hot workability, weldability and machinability of the steel. The content range of Al is not higher than 0.05%.

Phosphorus P: p is carried into the steel by the ore and S is similarly one of the deleterious elements. P can increase the strength and hardness of steel, but causes a significant decrease in plasticity and impact toughness. Particularly, at low temperature, it makes the steel become significantly brittle, and the higher the P content, the greater the cold brittleness. Dep to a lower level can significantly increase steelmaking costs. The P content range is not higher than 0.015%.

Sulfur S: s is derived from ore and fuel coke in steelmaking, is one of the most common harmful elements in steel, and is unfavorable for ductility, toughness, weldability and corrosion resistance of the steel. If S is present in the steel in FeS form, it can also generate "hot shortness" during hot working. The S content range is not higher than 0.005%.

The reason for the control range of each parameter in the 160 ksi-grade economic non-standard oil casing manufacturing method is as follows:

the invention adopts the composite precipitation strengthening of Cr, mo, V, nb and other elements, controls the heating temperature of the continuous casting round tube blank at 1205-1255 ℃ for 2-4 hours in the total furnace time, ensures that the precipitation phases of alloy elements are fully dissolved back into austenite, fully plays the beneficial effects of inhibiting recrystallization, solid solution strengthening, precipitation strengthening, grain refinement and the like in the subsequent process, and prepares components and temperature for obtaining the final tissue structure. Below the selected temperature and time range, the solid solution will be insufficient, affecting the final steel pipe strength; above the selected time and temperature range, the original austenite grains of the continuous casting slab are easy to be too coarse, which is not beneficial to the control of the toughness of the steel pipe.

The steel pipe can be directly quenched on line after rolling, or quenched after offline reheating. The production process is properly controlled, so that the temperature of the reduced pipe meets the quenching requirement, the direct on-line quenching is easy to realize, the energy is saved, the production components are reduced, the reheating process is reduced, the production efficiency is improved, and the economic benefit is remarkable.

After the accelerated cooling of the steel pipe is finished, tempering heat treatment is carried out, the tempering heat preservation temperature is higher than 400 ℃, the strength of the steel pipe is obviously reduced, and the final toughness of the steel pipe is not matched; but below 200 ℃, the quenching structure is insufficiently tempered, and the low-temperature toughness is low. Tempering and heat preserving time is too long, and strength is poor; and the tempering and heat preserving time is too short, and the toughness is insufficient. Proper tempering temperature, tempering heat preservation time and control of the contents of Mo, V and Ti which are key alloying elements ensure that the beneficial precipitated phase is fully precipitated and has small size, and the size t of the precipitated phase (Mo, V) C is ^p A precipitated phase (Mo, V) C size t of not more than 200nm and a volume fraction of 75% ^p _75％ No more than 50nm. Therefore, the method achieves the characteristics of good toughness matching and good performance stability under a wider hardening and tempering process window.

Compared with the prior art, the invention has the beneficial effects that:

1) The rolling temperature and the deformation amount are not required to be controlled in the steel pipe rolling process, the quenching temperature is only required to be met before the tension reducing, and the high-temperature rolling is matched with the direct on-line quenching, so that secondary heating is not required, the energy is saved, and the production efficiency is improved; the quenching end temperature is controlled to meet the requirements of tempering heat preservation temperature, so that the energy consumption of a tempering process is reduced.

2) Mo is adopted instead of N element to promote effective precipitation of V element. Compared with V (C, N), the (Mo, V) C has higher thermal stability and more spherical shape, and can realize more stable obdurability matching effect in a wider heat treatment process parameter range.

3) The yield strength Rt0.7 is more than or equal to 1100MPa, the tensile strength Rm is more than or equal to 1200MPa, the elongation A is more than or equal to 15%, and the transverse and longitudinal Charpy impact Akv at 0 ℃ is not lower than 120J and 150J respectively.

Detailed Description

The present invention will be described in detail below, but it should be noted that the practice of the present invention is not limited to the following embodiments.

The chemical composition of 160ksi grade economic non-standard oil casing embodiments is shown in Table 1; the rolling and heat treatment process parameters of 160ksi grade economic non-standard oil sleeve embodiment steel are shown in Table 2; the mechanical properties of 160ksi grade economical non-standard oil casing example steels are shown in Table 3.

TABLE 1 chemical composition wt% of the steel pipes according to the examples of the present invention

Examples	C	Si	Mn	P	S	Cr	Mo	Nb	V	Ti	Al	B*
													1	0.11	0.34	0.56	0.01	0.005	0.55	0.20	0	0.24	0.02	0.04	12
2	0.23	0.24	0.76	0.01	0.003	1.05	0.11	0.05	0.06	0.01	0.02	18
													3	0.31	0.14	0.96	0.01	0.003	1.55	0.40	0.04	0.15	0.05	0	8
4	0.39	0.06	1.15	0.01	0.005	2.05	0.15	0.03	0.10	0.04	0.01	20
													5	0.15	0.19	1.45	0.01	0.005	2.45	0.17	0.02	0.25	0.01	0.03	10
6	0.28	0.29	1.75	0.01	0.003	2.35	0.25	0.01	0.19	0.02	0.02	6
													7	0.18	0.10	1.95	0.01	0.003	1.85	0.35	0.03	0.10	0.02	0.04	20
8	0.25	0.25	2.15	0.01	0.005	1.35	0.45	0	0.05	0.03	0.03	15
													9	0.25	0.25	2.45	0.01	0.004	0.75	0.49	0.03	0.15	0.02	0.01	15

Note that: * Representative levels are calculated in ppm.

TABLE 2 Rolling and Heat treatment Process parameters for example steels according to the invention

TABLE 3 mechanical Properties of the inventive example steels

As can be seen from the data in tables 1 to 3, the steel pipe prepared by the method has the yield strength of more than or equal to 1110MPa, the tensile strength of more than or equal to 1200MPa, the elongation rate of more than or equal to 15 percent, and the transverse and longitudinal Charpy impact energy at-0 ℃ of not less than 120J and 150J respectively, and has excellent toughness matching and low cost.

Claims (5)

1. A160 ksi grade economical non-standard oil sleeve is characterized by comprising the following chemical components in percentage by weight:

0.10 to 0.40 percent of C, 0.05 to 0.35 percent of Si, 0.55 to 2.50 percent of Mn, 0.50 to 2.50 percent of Cr, 0.10 to 0.50 percent of Mo, 0.05 to 0.25 percent of V, less than or equal to 0.05 percent of Nb, 0.0005 to 0.002 percent of B, 0.01 to 0.05 percent of Ti, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and unavoidable impurity elements.

2. The 160ksi grade economic non-standard oil casing according to claim 1, wherein the oil casing comprises a C precipitate phase size t of Mo and V ^p Not more than 200nm, and a volume fraction of C precipitated phase t containing Mo and V of 75% or more ^p _75％ Not more than 50nm, and the transverse Charpy impact Akv at 0 ℃ is not less than 120J, and the longitudinal Charpy impact Akv is not less than 150J.

3. The method for manufacturing a 160ksi grade economic non-standard oil casing according to claim 1 or 2, comprising the steps of:

1) Smelting and continuously casting steel billets: smelting molten iron by an electric furnace, feeding the molten iron into an LF furnace for refining, carrying out vacuum treatment by a VD furnace, and continuously casting into a round tube blank;

2) Rolling a steel pipe: heating the round tube blank to 1205-1255 ℃, wherein the temperature before perforation is 1160-1220 ℃, the temperature before oblique rolling is 950-1130 ℃, and the temperature before tension reducing is 850-920 ℃;

3) Quenching and tempering: the steel pipe is directly quenched on line after the tension reducing is finished, the quenching start temperature is 830-870 ℃, the quenching end temperature is 200-400 ℃, the steel pipe is directly tempered at the strip temperature after quenching, the tempering temperature is 200-400 ℃, and the air cooling is carried out after tempering.

4. The method for manufacturing 160ksi grade economic non-standard oil casing according to claim 3, wherein the quenching medium in the step 3) is water or oil, and the average cooling rate of the quenching medium is 65 ℃/s or more.

5. The method for manufacturing 160ksi grade economic non-standard oil casing according to claim 3, wherein the tempering heat preservation time t in step 3) is as follows _T (unit: minutes) satisfies:

t _T ＝(4～6)t (1)

in the formula (1), t _T The heat preservation time of tempering is in min; t is the wall thickness of the steel pipe, and the unit is mm.