CN111154963A - Welding heat influence region-resistant softened submarine pipeline steel and preparation method thereof - Google Patents
Welding heat influence region-resistant softened submarine pipeline steel and preparation method thereof Download PDFInfo
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D2211/005—Ferrite
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Abstract
The invention relates to softened submarine pipeline steel in a welding heat affected zone and a preparation method thereof, belongs to the technical field of rolling of submarine pipeline steel, and solves the technical problem that the performance of the submarine pipeline steel is affected due to the fact that the existing submarine pipeline steel is softened in different degrees in the welding heat affected zone. The invention comprises the following steps: step 1, putting a casting blank into a heating furnace for heating at 1180-1200 ℃ for 1-2 hours to ensure that the casting blank is completely austenitized, alloy elements are fully dissolved in a solid manner, carbides are dissolved, and austenite grains are not coarsened; step 2, rolling and cooling control process: controlling the rough rolling temperature to 1050-1000 ℃; the precision rolling temperature is controlled to be 830-800 ℃. The invention obviously improves the strength and hardness of the submarine pipeline steel and improves the softening phenomenon of a welding heat affected zone.
Description
Technical Field
The invention relates to the technical field of pipeline steel manufacturing, in particular to a welding heat influence resistant softened submarine pipeline steel and a preparation method thereof.
Background
According to the third petroleum resource evaluation result, the marine oil and gas resources in China are rich, the offshore petroleum resource amount is 151.5 hundred million tons, which accounts for 14 percent of the total amount of the petroleum resources in China, and the petroleum resource amount in the south of the south China sea is 201.5 hundred million tons. The ocean is an important strategic take-over area in the petroleum industry, and the development of the offshore, especially seabed oil and gas fields is urgent, so that the significance is great. The submarine pipeline, as a main form of ocean oil and gas storage and transportation, is an indispensable lifeline for the development and production of offshore oil and gas fields, and is also the safest, most economical and least environmentally damaging oil and gas transportation mode.
Because the submarine pipeline is difficult to construct and high in cost, particularly ocean pollution caused by oil leakage due to breakage, the maintenance cost and the environmental pollution compensation cost of the submarine pipeline are usually higher than the investment of pipeline engineering, and huge economic loss is caused. Therefore, the quality level of the pipe is one of the main factors for ensuring the safety and reliability of the pipeline and avoiding accidents. Unlike onshore pipelines, severe environments such as subsea high pressure, surge, vortex, etc. impose more stringent quality requirements on subsea pipelines.
Welding is an important process that must be performed for subsea pipeline steel applications, both hot rolled plate coiled pipeline steel and wide and thick plate pipeline steel are welded to form steel pipe.
The design requirements of the weld joint in actual production are required to be over-matched, but after the weld joint is subjected to welding heat circulation, the heat affected zone of the weld joint has coarsening grains and deterioration of structures, and softening phenomena of different degrees exist, so that the softened zone is generated. Especially, the softening phenomenon of the marine pipeline steel having the dual phase structure is more severe. The presence of the softened region creates a "barrel effect", i.e., the property of the heat affected zone is severely mismatched with the properties of the pipeline steel, resulting in the heat affected zone being the weakest part of the overall weld joint. At present, no report is found on the research of submarine pipeline steel developed by improving softening of a welding heat affected zone.
Disclosure of Invention
In view of the above analysis, the embodiment of the present invention aims to provide a welding heat affected zone softening submarine pipeline steel and a preparation method thereof, so as to solve the technical problem that the performance of the submarine pipeline steel is affected due to different softening phenomena occurring in the welding heat affected zone of the existing submarine pipeline steel.
The purpose of the invention is mainly realized by the following technical scheme:
on one hand, the invention discloses a preparation method of softened submarine pipeline steel in a welding heat influence resistant area, which is characterized by comprising the following steps:
step 1, smelting by using a vacuum induction furnace to obtain a continuous casting billet, and heating the continuous casting billet in a heating furnace at 1180-1200 ℃ for 1-2 hours to ensure that the casting billet is completely austenitized and alloy elements are fully dissolved in a solid solution;
step 2, carrying out hot rolling after heating the continuous casting billet, and carrying out controlled rolling and controlled cooling process:
controlling the rough rolling temperature to 1050-1000 ℃, and allowing austenite to deform in a crystallization area and to be recrystallized and refined; the precision rolling temperature is controlled to be 800-830 ℃.
Further, in step 2, air cooling is performed after the finish rolling, the open cooling temperature is controlled to be 780 ℃ to 820 ℃, polygonal ferrite is generated in the cooling process, and the crystal grains of the polygonal ferrite are not coarsened.
Further, in step 2, the final cooling temperature is controlled to be 460 ℃ to 520 ℃, and the acicular ferrite is transformed in the cooling process.
Further, in step 2, the air cooling rate after the finish rolling is 24 to 25 ℃/s.
Further, the type of the structure of the subsea pipeline steel is polygonal ferrite + acicular ferrite.
Further, in the structure type of the submarine pipeline steel, the content of polygonal ferrite is 30-50%.
Furthermore, the grain size of the polygonal ferrite is less than or equal to 6 μm.
Further, the pipeline steel grade is X70-X80 grade.
On the other hand, the invention also discloses a welding heat influence resistant zone softened submarine pipeline steel, which is characterized in that the preparation method of the submarine pipeline steel is adopted, and the submarine pipeline steel comprises the following chemical components in percentage by mass: c: 0.04-0.06 wt%, Si: 0.20-0.30 wt%, Mn: 1.60-1.80 wt%, V: 0.06-0.09 wt%, Nb: 0.02-0.04 wt%, Ti: 0.01-0.03 wt%, Mo: 0.05-0.15 wt%, Cr: 0.10-0.20 wt%, Ni: 0.20-0.30 wt%, P: < 0.015 wt%, S: < 0.005 wt%, Al: 0.0015-0.0035, and the balance of Fe and inevitable impurities.
Further, the mass percentage of V is 0.08-0.09 wt%.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
(1) by adopting a small amount of multi-element alloying principle and the interaction among different microalloy elements and the interaction among the microalloy elements, other alloys and other alloy elements, the pipeline steel can be endowed with more perfect performance, and the elements have a synergistic effect, so that the cost is saved.
(2) The ideal structure of the polygonal ferrite and acicular ferrite submarine pipeline steel is obtained by a reasonable rolling and cooling control process, the content of the polygonal ferrite is controlled within the range of 40-50%, the grain size is less than or equal to 6 mu m, and the submarine pipeline steel can obtain excellent comprehensive strength, toughness and plasticity.
(3) By utilizing V microalloying (the V microalloying means that a small amount of V element is added into steel to play a remarkable role), the microstructure, even the structure, the structure and the components are influenced through the solid solution of the elements and the solid reaction thereof, so that the metal obtains the required performance. The addition of V can help prevent the reheating austenite from coarsening and refine the ferrite grain size, thereby improving the toughness; the strength of the steel is improved through precipitation; solid solution of V also improves the hardenability of steel.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a metallographic photograph of a subsea pipeline steel, the microstructure type being polygonal ferrite + acicular ferrite;
FIG. 2 is a schematic representation of nano-scale second phase precipitated particles in the weld heat affected zone of subsea pipeline steel.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
The essence of the invention is further illustrated by the following examples.
Example 1
The embodiment provides a preparation method of softened submarine pipeline steel in a welding heat influence resistant area, which comprises the following steps:
step 1, smelting by using a vacuum induction furnace to obtain a continuous casting billet, and heating the continuous casting billet in a heating furnace at 1180-1200 ℃ for 1-2 hours.
By strictly controlling the heating temperature and the heating time, the casting blank can be completely austenitized, alloy elements are fully dissolved, carbides are dissolved, and austenite grains are not coarsened.
Step 2, rolling and cooling control process:
the rough rolling temperature is controlled to be 1050-1000 ℃, and the austenite recrystallization zone can be deformed by controlling the rough rolling temperature, so that the high-temperature austenite is recrystallized and refined;
and controlling the finish rolling temperature to be 800-830 ℃, and deforming an austenite non-recrystallization region to flatten austenite, increase interfaces in unit area, and provide more nucleation positions for the subsequent cooling phase transformation process, so that the crystal grains of the final structure are further refined.
Controlling the starting cooling temperature to be 780-820 ℃, and generating polygonal ferrite transformation in the cooling process to generate polygonal ferrite, wherein the crystal grains of the polygonal ferrite are not coarsened; after finish rolling, the air cooling rate is 24-25 ℃/s, the final cooling temperature is controlled to be 460-520 ℃, acicular ferrite is transformed in the cooling process, a polygonal acicular body is generated, and finally the polygonal ferrite and the acicular ferrite are obtained.
The design requirements of the weld joint in actual production are required to be over-matched, but after the weld joint is subjected to welding heat circulation, the heat affected zone of the weld joint has coarsening grains and deterioration of structures, and softening phenomena of different degrees exist, so that the softened zone is generated. According to the submarine pipeline steel, on one hand, the content of vanadium is adjusted, on the other hand, the strength and toughness of the submarine pipeline steel are guaranteed through a controlled rolling air cooling process, so that the submarine pipeline steel is prevented from softening and generating a softening zone in the welding process; thereby avoiding the property of the steel in the softened region from being mismatched with the properties of the other parts of the subsea pipeline steel and ultimately avoiding the creation of a softened region in the subsea pipeline steel that results in it being the weakest part of the overall weld joint.
The mass percentage of the vanadium element is 0.08-0.09 wt%. It is emphasized that the vanadium content affects the depth and width of the softened zone of the weld heat affected zone. When the V content is 0.025%, the width and depth of the softened region are large; when the vanadium content is increased to 0.08-0.09 wt%, the transverse and longitudinal distances of a softening zone are obviously reduced under the conditions of controlled rolling and air cooling (the rough rolling temperature is 1000-1050 ℃, the finish rolling temperature is 800-830 ℃, the open cooling temperature is 780-820 ℃, and the final cooling temperature is 460-520 ℃), so that nanoscale second-phase particles are separated out in a heat-affected zone in the welding process, the strength and the hardness are obviously improved, and the softening phenomenon of the welding heat-affected zone is improved.
In addition, in the present application, the V content affects the depth and width of the weld heat affected zone softened region. When the V content is 0.025%, the width and depth of the softening zone are large; when the V content is increased to 0.08 percent, the transverse and longitudinal distances of the softening zone are obviously reduced, so that nanoscale second-phase particles are separated out in the heat affected zone in the welding process, the strength and the hardness are obviously improved, and the softening phenomenon of the welding heat affected zone is improved.
In order to improve the deformation strengthening capacity and the overload capacity of the material, the structure type of the submarine pipeline steel is polygonal ferrite and acicular ferrite.
Compared with an acicular ferrite single-phase structure, the polygonal ferrite and acicular ferrite double-phase structure can reduce the yield strength and reduce the yield strength ratio of the pipeline steel due to the introduction of the polygonal ferrite, thereby increasing the deformation capacity of the material and improving the deformation strengthening capacity and overload capacity of the material.
Compared with a polygonal ferrite and bainite dual-phase structure, the effective grain size of the acicular ferrite in the polygonal ferrite and acicular ferrite dual-phase structure is small, so that the effective grain size of the whole microstructure is reduced, and the toughness of the material is obviously improved.
In order to improve the toughness of the submarine pipeline steel, the structure type of the submarine pipeline steel comprises 30-50% of polygonal ferrite, the grain size is less than or equal to 6 mu m, and the balance is acicular ferrite.
When the polygonal ferrite is in a certain range, the uniform elongation of the submarine pipeline steel is obviously increased along with the increase of the volume fraction of the ferrite; when the content of the polygonal ferrite is too large, the impact property of the material is reduced; because the number of the large-angle interfaces in a unit area is reduced along with the increase of the content of the polygonal ferrite, the large-angle interfaces can enable cracks to deflect greatly in the propagation process, consume more energy and improve the toughness, on one hand, the content of the polygonal ferrite is strictly controlled within the range of 30% -50%, on the other hand, the grain size of the polygonal ferrite is controlled while the content of the polygonal ferrite is controlled, the grain size is reduced, the toughness is improved, and for submarine pipeline steel, the grain size of the polygonal ferrite is controlled to be below 6 microns.
The pipeline steel grade prepared by the method is X70-X80 grade.
Example 2
The embodiment provides a welding heat influence resistant softened submarine pipeline steel, which comprises the following chemical components in percentage by mass: c: 0.04-0.06 wt%, Si: 0.20-0.30 wt%, Mn: 1.60-1.80 wt%, V: 0.06-0.09 wt%, Nb: 0.02-0.04 wt%, Ti: 0.01-0.03 wt%, Mo: 0.05-0.15 wt%, Cr: 0.10-0.20 wt%, Ni: 0.20-0.30 wt%, P: < 0.015 wt%, S: < 0.005 wt%, Al: 0.0015-0.0035, and the balance of Fe and inevitable impurities.
According to the method, the addition amount of vanadium is strictly controlled, so that the vanadium not only has a fine crystal strengthening effect, but also can be subjected to strain induction to separate out nanoscale second-phase particles during rolling, an obvious precipitation strengthening effect can be generated, the hardenability of steel is improved, and the dislocation density in a low-temperature phase change structure is increased, so that the microhardness is improved.
The effects of the elements of the invention are as follows:
carbon: forming carbides with vanadium, niobium and titanium to retard austenite recrystallization to refine grains; in the welding process, nano-scale carbide is precipitated with vanadium, so that the strength of a softening region is improved, and the softening is improved; the impact toughness is greatly influenced, and the welding performance is obviously damaged when the content is too high.
Silicon: the deoxidizer in the smelting process has a strong solid solution strengthening effect, but the toughness is damaged when the deoxidizer is too high.
Manganese: the steel has the solid solution strengthening effect, can make up for the reduction of yield strength caused by the reduction of carbon content, and simultaneously can improve the toughness of steel and reduce the ductile-brittle transition temperature; the phase transition temperature of the steel is reduced during cooling, and the grain size of ferrite is refined; too high manganese content increases the center segregation of the controlled rolling steel sheet, which is detrimental to the welding performance.
Phosphorus and sulfur: is a foreign element in steel, and can obviously reduce toughness and welding performance, particularly low-temperature toughness.
Vanadium: besides the fine-grain strengthening effect, the nano-scale second-phase particles are separated out by strain induction during rolling, so that the obvious precipitation strengthening effect can be generated; the hardenability of the steel is improved, and the dislocation density in a low-temperature phase transition structure is increased, so that the microhardness is improved.
Niobium: besides the fine-grain strengthening effect, the solid-solution niobium can reduce the phase transformation temperature, improve the hardenability and promote the generation of low-temperature phase transformation products (acicular ferrite, bainitic ferrite and the like); the dispersion precipitation in the controlled rolling and controlled cooling process produces precipitation strengthening effect, and the strength of the steel is improved.
Titanium: stable TiN is formed at high temperature, and austenite grains are inhibited from growing in the reheating process; too high a content may form large-sized precipitated phases, affecting the toughness of the steel.
Molybdenum: the formation of acicular ferrite is promoted, but the transformation of polygonal ferrite is inhibited, so that the addition amount is not easy to be excessive; is a carbide forming element and can be fused into the crystal lattice of the microalloy carbonitride during the welding heat cycle to reduce the mismatch energy, thereby promoting the precipitation of the microalloy carbonitride.
Nickel, chromium and copper: as a supplementary element of molybdenum, the influence on the phase change process is similar to that of molybdenum.
Example 3
In this example, the preparation method of the submarine pipeline steel provided in example 1 was adopted, and a vacuum induction furnace was used to obtain a continuous casting slab, whose chemical composition is shown in table 1.
Smelting a casting blank according to the components, heating the casting blank to 1200 ℃ for 2 hours, wherein the rough rolling temperature is 1050-1000 ℃, the finish rolling temperature is 830-800 ℃, the start cooling temperature is 780-820 ℃, and the final cooling temperature is 460-520 ℃.
The specific controlled rolling and cooling processes for the example steels are listed in table 2, and the longitudinal mechanical properties of the obtained example steels are shown in table 3.
TABLE 1 chemical composition (wt%) of softening submarine pipeline steel in weld heat affected zone
TABLE 2 controlled rolling and controlled cooling process for softening submarine pipeline steel in welding heat-affected zone
TABLE 3 longitudinal mechanical Properties of softened subsea pipeline steels in the weld Heat affected zone resistance
The micro-alloyed pipeline steel manufactured by adopting the controlled rolling and controlled cooling technology has the advantage that the increase of the yield strength is obviously larger than that of the tensile strength, so that the modern pipeline steel has higher yield strength ratio. When the yield strength ratio of the submarine pipeline steel is greater than 0.85, the excessively high yield strength ratio limits the ultimate plastic deformation capacity of the pipeline steel, thereby affecting the safety service of the pipeline structure. Under the patent, the yield strength ratios of the prepared pipeline steel are all less than 0.85, and the performance requirements of the submarine pipeline steel can be met.
Comparative example 1
The comparative example provides a preparation process of submarine pipeline steel and components of the submarine pipeline steel, and molten iron pretreatment → converter steelmaking → alloy fine-tuning station → LF external refining → RH external refining → continuous casting → casting blank slow cooling → heating → rolling → laminar cooling → coiling preparation is adopted. After LF external refining, the chemical components in the steel meet the following weight percentages (wt%): c: 0.020% to 0.060%, Si: less than or equal to 0.30 percent, Mn: 1.50% -1.70%, P: less than or equal to 0.015%, S: less than or equal to 0.0050%, Mo: 0.10% -0.35%, Nb: 0.040% -0.050%, V: 0.020 to 0.050%, Ti: 0.010-0.020%, Als: 0.020-0.035%; the balance of Fe and inevitable impurities. And carrying out protective casting in the whole continuous casting process.
This application compares with the comparative example, and this application mainly can avoid appearing the softening zone when to submarine pipeline steel welding, and the content of this application strict control vanadium is: 0.060-0.090 percent of the steel, and obtaining the ideal structure of the seabed pipeline steel of the polygonal ferrite and the acicular ferrite by a reasonable rolling and cooling control process, wherein the content of the polygonal ferrite is controlled within the range of 40-50 percent, and the grain size is less than or equal to 6 mu m, so that the seabed pipeline steel can obtain excellent comprehensive strength, toughness and plasticity.
The content of vanadium in the subsea pipeline steel provided in the comparative example is low, and after welding heat cycles, the weld heat affected zone has coarsened grains and deteriorated structure, so that softening phenomena of different degrees occur, and further the softening zone occurs.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A preparation method of softened submarine pipeline steel in a welding heat influence resistant area is characterized by comprising the following steps:
step 1, smelting by using a vacuum induction furnace to obtain a continuous casting billet, and heating the continuous casting billet in a heating furnace at 1180-1200 ℃ for 1-2 hours to ensure that the continuous casting billet is completely austenitized and alloy elements are fully dissolved in a solid solution;
step 2, carrying out hot rolling on the continuous casting billet heated in the step 1, wherein the controlled rolling and controlled cooling process comprises the following steps:
controlling the rough rolling temperature to 1050-1000 ℃, and allowing austenite to deform in a crystallization area and to be recrystallized and refined; the precision rolling temperature is controlled to be 800-830 ℃.
2. The method for manufacturing a soft subsea pipeline steel against welding heat influence according to claim 1, wherein in the step 2, air cooling is performed after finish rolling, the open cooling temperature is controlled to be 780 to 820 ℃, polygonal ferrite is generated during cooling, and crystal grains of the polygonal ferrite are not coarsened.
3. The method for preparing the welding heat affected zone softening submarine pipeline steel according to claim 2, wherein in step 2, the final cooling temperature is controlled to 460-520 ℃, and acicular ferrite is generated during cooling.
4. The method for manufacturing a soft subsea pipeline steel against weld heat influence according to claim 2, wherein the air cooling rate after finish rolling is 24-25 ℃/s in step 2.
5. The method for manufacturing a welding heat affected zone softening subsea pipeline steel according to claim 2, wherein the type of structure of the subsea pipeline steel is polygonal ferrite + acicular ferrite.
6. The method for manufacturing a welding heat affected zone softening subsea pipeline steel according to claim 1, wherein the polygonal ferrite is contained in an amount of 30-50% in the structure type of the subsea pipeline steel.
7. The welding heat affected zone softening subsea pipeline steel according to claim 6, wherein the grain size of the polygonal ferrite is 6 μm or less.
8. The weld heat affected zone resistant softened subsea pipeline steel according to claim 1, characterized in that the pipeline steel grade is X70-X80 grade.
9. The welding heat influence resistant softened submarine pipeline steel is characterized in that the preparation method of the claim 1 to 8 is adopted, and the submarine pipeline steel comprises the following chemical components in percentage by mass: c: 0.04-0.06 wt%, Si: 0.20-0.30 wt%, Mn: 1.60-1.80 wt%, V: 0.06-0.09 wt%, Nb: 0.02-0.04 wt%, Ti: 0.01-0.03 wt%, Mo: 0.05-0.15 wt%, Cr: 0.10-0.20 wt%, Ni: 0.20-0.30 wt%, P: < 0.015 wt%, S: < 0.005 wt%, Al: 0.0015-0.0035, and the balance of Fe and inevitable impurities.
10. The welding heat affected zone resistant softened submarine pipeline steel according to claim 9, wherein the V content is 0.08-0.09 wt%.
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| CN201911370411.9A CN111154963A (en) | 2019-12-26 | 2019-12-26 | Welding heat influence region-resistant softened submarine pipeline steel and preparation method thereof |
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| CN113106336A (en) * | 2021-03-17 | 2021-07-13 | 唐山钢铁集团有限责任公司 | Ultrahigh-strength dual-phase steel capable of reducing softening degree of laser welding head and production method thereof |
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