CN111996461A

CN111996461A - X70 pipeline coiled plate for microalloyed resistance welded pipe and production method thereof

Info

Publication number: CN111996461A
Application number: CN202010928531.2A
Authority: CN
Inventors: 张英慧; 黄国建; 孔祥磊; 黄明浩; 王杨
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2020-09-07
Filing date: 2020-09-07
Publication date: 2020-11-27

Abstract

The invention discloses an X70 pipeline coil plate for a microalloyed resistance welded tube and a production method thereof. The steel contains 0.05-0.09% of C, 0.15-0.35% of Si, 1.45-1.70% of Mn, less than or equal to 0.015% of P, less than or equal to 0.006% of S, 0.040-0.070% of Nb, 0.005-0.025% of Ti, and the balance of iron and inevitable impurities, and meets the requirements that Al/N is more than or equal to 4, Mn/C is more than or equal to 16, Ceq is less than or equal to 0.40, and Pcm is less than or equal to 0.20. Heating the casting blank at 1150-1250 ℃ for more than or equal to 150 min; the rough rolling starting temperature is more than or equal to 1000 ℃, and the cumulative reduction rate of the first three times is more than or equal to 50%; the rolling temperature of the finish rolling is 950-1050 ℃, the finishing temperature is 800-900 ℃, and the cumulative reduction rate of three times before the finish rolling reaches more than 65%; and the laminar flow cooling section adopts a collecting pipe for centralized cooling, the cooling speed is 15-25 ℃/s, the coiling temperature is 500-600 ℃, and then the laminar flow cooling section is air-cooled to the room temperature. Good low-temperature toughness at minus 40 ℃.

Description

X70 pipeline coiled plate for microalloyed resistance welded pipe and production method thereof

Technical Field

The invention belongs to the field of high-strength low-alloy steel, and particularly relates to an X70 pipeline steel hot-rolled coil for an ERW straight-seam resistance welded pipe with simple component design and good comprehensive mechanical properties and a production method thereof.

Background

The ERW welding process is one kind of straight seam welding process, has the advantages of low cost and high efficiency, and is suitable for oil and gas pipelines.

In the retrieved straight slit X70-grade patent, the alloy design contains at least 1 or more alloy elements in addition to Nb/Ti, which greatly increases the design cost and also brings certain difficulty and inconvenience to the actual production.

Patent No. ZL201010154675.3 entitled "steel sheet for straight welded pipe and method for manufacturing the same" discloses a rolled steel sheet of medium and wide plates, which is formed into a pipe by UOE or JCOE. Cu is added in the patent and is less than or equal to 0.20 percent; ni: 0.10 to 0.50 percent; mo is less than or equal to 0.30 percent; cr is less than or equal to 0.30 percent; v: 0.01 to 0.06 percent; ca: 0.0015% -0.0035%, and the like, and the tensile strength of the product of the patent only refers to one direction performance, the specific sampling direction is not determined, and meanwhile, the indexes of DWTT and HV10 mechanical properties are not given.

Patent No. ZL201110351541.5 entitled "steel for high-strength corrosion-resistant straight welded pipe and method for producing the same" discloses a steel for oil casing pipe used in acidic environment, which contains V: 0.02-0.04%, Cr: 0.050% -0.075%, Mo: 0.020-0.030%, Ni: 0.035% -0.050% alloy component, so that its production cost is raised.

Disclosure of Invention

The invention aims to solve the problems and develop an X70 pipeline coiled plate for a micro-alloyed ERW straight welded pipe, which is characterized by low alloy design cost, convenient production and feasible operation and excellent comprehensive mechanical property.

The specific technical scheme is as follows:

an X70 pipeline coiled plate for a micro-alloyed low-cost ERW straight welded pipe comprises the following chemical components in percentage by mass: 0.05 to 0.09 percent of C, 0.15 to 0.35 percent of Si, 1.45 to 1.70 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.006 percent of S, 0.040 to 0.070 percent of Nb, 0.005 to 0.025 percent of Ti, more than or equal to 4 percent of Al/N, more than or equal to 16 percent of Mn/C, less than or equal to 0.40 percent of Ceq, less than or equal to 0.20 percent of Pcm, and the balance of Fe and inevitable impurities, wherein Ceq is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15; pcm is C + Si/30+ (Cr + Mn + Cu)/20+ Ni/60+ Mo/15+ V/10.

The design principle of the main element content ratio is as follows:

c is the most basic economic strengthening element in steel, has obvious effect on improving the strength of the pipeline steel through solid solution strengthening and precipitation strengthening, but the toughness and the weldability are deteriorated due to the increase of the carbon content; the carbon content is reduced, the generation of niobium carbide can be prevented, more niobium content is dissolved into austenite when the plate blank is heated, high toughness, plasticity and excellent welding performance of the steel can be ensured, and segregation can be reduced due to low carbon. Therefore, the content of C is controlled to be 0.05-0.09%.

Si plays a role in solid solution strengthening and improving the tensile strength of the steel. The yield strength is greatly increased along with the increase of the Si content, so that the yield ratio is increased; the low-Si-content solid solution strengthening effect is not obvious enough, so that the Si content of the invention is controlled to be 0.15-0.35%.

Mn is added to the steel for line pipe to compensate for the loss of strength due to the reduced carbon content. High Mn can promote acicular ferrite nucleation, high Mn/C ratio (more than or equal to 16) can improve yield strength and impact toughness, reduce the size of precipitated carbide and promote precipitation strengthening effect; the low Mn content does not compensate for the loss of strength due to the reduced carbon content. The Mn content of the invention is controlled to be 1.45-1.70%.

Nb can increase austenite recrystallization temperature and realize high-temperature rolling, thereby reducing the load of a rolling mill and improving the production efficiency. By delaying the transformation from austenite to ferrite, the volume fraction of bainite is improved, and NbC in the ferrite is separated out to obtain an additional strengthening effect, and finally, the mechanical properties of high strength and high toughness are matched. Within the range of the design components of the invention, the Nb content exceeds 0.07 percent, the strengthening effect is saturated but not acted, and the strength loss caused by the low C content cannot be compensated by the Nb addition amount being less than 0.040 percent. Therefore, the Nb content of the invention is controlled to be 0.040-0.070%.

Ti is a strong nitrogen element, and in the process of slab continuous casting, the titanium is used for fixing nitrogen to form a fine TiN precipitated phase which is stable at high temperature, and the particles can effectively prevent austenite grains from growing to be large due to reheating of a casting blank. The strength of the steel can be improved to a certain extent due to the effect of Ti refined grains, but the beneficial effect of the refined grains on the impact toughness can be offset by the over-high Ti content, and the low-temperature impact toughness of the steel can be reduced, so that the Ti content is controlled to be 0.005-0.025 percent by adopting micro Ti treatment.

The Al/N ratio is more than or equal to 4, Ceq is less than or equal to 0.40, and Pcm is less than or equal to 0.20, and the aim is to ensure that the product has good weldability.

The production method adopts a thin slab continuous casting and rolling production process flow, and comprises the following specific steps: the method comprises the following steps of molten iron pretreatment, converter smelting, external refining, continuous casting, casting blank heating, controlled rolling, controlled cooling and coiling, wherein the level and the action of the process are controlled as follows.

The molten iron pretreatment in the invention mainly has the effects of improving the purity of the molten steel, reducing and reducing the content of impurities and impurities in the molten iron and preparing the final mechanical property of the subsequent pipeline steel hot-rolled coil.

The external refining process only needs an LF treatment process. During LF treatment, wire feeding Ca treatment is carried out, the wire feeding amount is more than or equal to 600m and is specifically determined according to the S content, and the process mainly aims to fully spheroidize inclusions in steel, so that the inclusions in finished products are not more than 2.0 grade.

In the continuous casting process, the center porosity and segregation can be reduced by putting the steel into soft reduction. The drawing speed of the continuous casting blank is controlled to be 1.0-2.0 m/min, and the thickness of the casting blank is 170-230 mm.

The casting blank adopts a stacking slow cooling and then cold charging process, and the stacking slow cooling is used for reducing the center porosity and segregation of the casting blank, improving the band-shaped defects of a finished steel plate and ensuring the metallurgical quality of the casting blank.

The heating temperature of the casting blank is controlled to 1150-1250 ℃, and the heat preservation time in the furnace is more than 150 minutes.

The heating temperature of the casting blank is 1150-1250 ℃. In order to fully precipitate alloy elements such as Nb and Ti and the like to play a role in fine grain strengthening, Nb and Ti alloys in the casting blank are dissolved back into steel as much as possible. At 1150 ℃, the precipitated particles of Nb in the billet already started to redissolve. At 1250 ℃, the resolubility degree of Nb precipitation particles in the steel is saturated, the heating temperature exceeds 1250 ℃, the original austenite grain size will grow rapidly, and therefore the heating temperature of the casting blank is determined to be 1150-1250 ℃.

The rolling process comprises rough rolling and finish rolling, the surface quality of the steel plate is ensured by removing phosphorus through high-pressure water before the rough rolling, the starting temperature of the rough rolling is controlled to be more than 1000 ℃, the rough rolling is carried out by adopting large reduction, and the accumulated reduction rate of the first three times is more than 50%; the rolling temperature of the beginning of finish rolling is 950-1050 ℃, the finishing temperature is 800-900 ℃, and the cumulative reduction rate of three times before finish rolling reaches more than 65%; and the laminar flow cooling section adopts a collecting pipe for centralized cooling, the cooling speed is 15-25 ℃/s, the coiling temperature is within the range of 500-600 ℃, and then the laminar flow cooling section is air-cooled to the room temperature.

The finish rolling initial rolling temperature is higher than 1050 ℃, the crystal grains of the finished product are not easy to refine, and the fine grain strengthening effect is not good. When the temperature is lower than 950 ℃, the load of a finish rolling machine frame is increased, and production accidents are easily caused; the finishing temperature is above 800 ℃, so that the condition that the rolling mill is overloaded during rolling in a double-phase region can be avoided, a deformation temperature region with difficult plate shape control is avoided, and the longitudinal and transverse performance difference of the steel plate can be reduced. But the finishing temperature is higher than 900 ℃, the grain refinement is insufficient, and the strengthening effect is influenced.

Has the advantages that:

compared with the prior art, the invention has the following beneficial effects:

(1) the X70 pipeline coiled plate for the microalloying resistance welded tube produced by the invention only adds Nb and Ti, and does not add other noble alloy elements such as Ni, Cr, Mo, Cu and the like, so that the alloy design cost is reduced, the smelting process is simple, and the production flow is easy to operate and execute;

(2) by adopting corresponding production and rolling process design, the produced product has excellent toughness and meets the API 5L standard requirement. The yield strength of the transverse tensile property reaches 520-598 MPa, the tensile strength reaches 621-670 MPa, the elongation reaches 31-37%, the yield ratio can reach 0.83-0.90, the single value of full-size impact toughness at-40 ℃ can reach 150-204J, the average value can reach 176-197J, the drop hammer shear area (DWTT SA) at 0 ℃ can reach 96-100%, and the HV10 can reach 186-235J; the yield strength of the longitudinal tensile property reaches 496-560 MPa, the tensile strength reaches 595-639 MPa, the elongation reaches 31.5-36%, the yield ratio can reach 0.80-0.88, the single value of the full-size impact toughness at minus 40 ℃ can reach 216-258J, and the average value can reach 228-248J; completely meeting the market demand.

Therefore, the successful development of the product brings certain economic and social benefits for enterprises, and also makes a contribution to the development of domestic high-grade ERW resistance welding pipeline steel.

Drawings

FIG. 1 is a metallographic microstructure of a hot rolled coil according to example 1, which structure is acicular ferrite + quasi-polygonal ferrite + a small amount of pearlite;

FIG. 2 is a microstructure of-40 ℃ impact fracture of the hot rolled coil in example 1, which is fully characterized by a dimple mechanism, and shows that the low temperature impact toughness is excellent.

Detailed Description

The above-mentioned embodiments are merely illustrative of the technical ideas and features of the present invention, and are not intended to limit the present invention, so as to enable those skilled in the art to understand the contents of the present invention and to implement the present invention accordingly. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

The chemical compositions of the example steels are listed in table 1; table 2 shows the parameters of the steel smelting and continuous casting process of the examples; table 3 lists the process performance of the example steels; the mechanical properties of the example steels are given in table 4.

Table 1 chemical composition of the example steels, wt.%

Serial number	C	Si	Mn	P	S	Nb	Ti	Mn/C	Al/N	Ceq	Pcm
												1	0.051	0.16	1.7	0.012	0.003	0.07	0.015	33	4.75	0.33	0.14
2	0.054	0.34	1.62	0.013	0.002	0.056	0.023	30	6.61	0.32	0.15
												3	0.062	0.31	1.44	0.015	0.002	0.064	0.012	23	8.79	0.30	0.14
4	0.088	0.32	1.53	0.011	0.002	0.057	0.022	17	4.07	0.34	0.18
												5	0.074	0.25	1.64	0.013	0.004	0.05	0.016	22	4.85	0.35	0.16
6	0.057	0.28	1.59	0.01	0.002	0.038	0.025	28	4.68	0.32	0.15
												7	0.077	0.23	1.58	0.008	0.003	0.047	0.018	21	7.29	0.34	0.16
8	0.089	0.15	1.47	0.011	0.004	0.051	0.014	17	7.45	0.33	0.17
												9	0.076	0.26	1.45	0.009	0.002	0.059	0.02	19	4.23	0.32	0.16
10	0.067	0.18	1.63	0.014	0.003	0.045	0.009	24	5.81	0.34	0.15
												11	0.053	0.21	1.55	0.015	0.005	0.068	0.024	29	6.3	0.31	0.14
12	0.078	0.19	1.52	0.012	0.006	0.054	0.01	19	4.37	0.33	0.16
												13	0.059	0.33	1.68	0.01	0.002	0.065	0.019	28	6.43	0.34	0.15
14	0.066	0.3	1.69	0.013	0.004	0.055	0.021	26	7	0.35	0.16
												15	0.071	0.35	1.56	0.009	0.002	0.062	0.011	22	4.79	0.33	0.16
16	0.083	0.27	1.48	0.013	0.003	0.04	0.013	18	10.47	0.33	0.17
												17	0.052	0.22	1.57	0.011	0.004	0.048	0.017	30	4.39	0.31	0.14
18	0.09	0.2	1.46	0.012	0.002	0.042	0.006	16	6.57	0.33	0.17
												19	0.081	0.17	1.6	0.013	0.003	0.053	0.007	20	8.79	0.35	0.17
20	0.075	0.24	1.65	0.014	0.005	0.058	0.008	22	5.26	0.35	0.17

In the table: ceq ═ C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15;

Pcm＝C+Si/30+(Cr+Mn+Cu)/20+Ni/60+Mo/15+V/10。

TABLE 2 example Steel smelting continuous casting process parameters

TABLE 3 examples steel rolling production process parameters

TABLE 4 mechanical properties of the steels of the examples

Note: in the table, half-size test specimens were used for the impact test of steel plates having a thickness of 6.25/7.7mm, dimensions (thickness width length) of 5 x 10 x 55mm, and standard test specimens were used for steel plates having a thickness of 12.5 mm.

Claims

1. An X70 pipeline coiled plate for a microalloyed resistance welded tube is characterized in that the steel comprises the following chemical components in percentage by mass: 0.05 to 0.09 percent of C, 0.15 to 0.35 percent of Si, 1.45 to 1.70 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.006 percent of S, 0.040 to 0.070 percent of Nb, 0.005 to 0.025 percent of Ti, and the balance of iron and inevitable impurities, wherein Al/N is more than or equal to 4, Ceq is less than or equal to 0.40, and Pcm is less than or equal to 0.20, and Ceq is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15; pcm is C + Si/30+ (Cr + Mn + Cu)/20+ Ni/60+ Mo/15+ V/10.

2. The coiled sheet of X70 pipeline for microalloyed resistance welded tube of claim 1, wherein Mn/C is 16 or more.

3. The X70 pipeline coil plate for the microalloyed resistance welded tube according to claim 1 or 2, wherein the single value of the full-size impact toughness of the finished coil plate at the transverse temperature of-40 ℃ can reach 150-204J, and the average value can reach 176-197J; the single value of the longitudinal-40 ℃ full-size impact toughness can reach 216-258J, and the average value can reach 228-248J.

4. A method for producing an X70 coil for a microalloyed electric resistance welded pipe as claimed in claim 1, 2 or 3, the steel sheet being produced by the process comprising: the method comprises the following steps of molten iron pretreatment, converter smelting, external refining, continuous casting, casting blank heating, controlled rolling, controlled cooling and coiling, and is characterized in that:

the casting blank adopts a stacking, slow cooling and then cold charging process, the heating temperature of the casting blank is controlled to be 1150-1250 ℃, and the heat preservation time in a furnace is more than 150 min; the rolling process comprises rough rolling and finish rolling, phosphorus is removed by high-pressure water before the rough rolling, the starting temperature of the rough rolling is controlled to be more than 1000 ℃, rolling with large reduction is adopted, and the accumulated reduction rate of the first three times is more than 50%; the rolling temperature of the beginning of finish rolling is 950-1050 ℃, the finishing temperature is 800-900 ℃, and the cumulative reduction rate of three times before finish rolling is more than 65%; and the laminar flow cooling section adopts a collecting pipe for centralized cooling, the cooling speed is 15-25 ℃/s, the coiling temperature is within the range of 500-600 ℃, and then the laminar flow cooling section is air-cooled to the room temperature.

5. The method for producing the X70 coiled sheet for the microalloyed resistance welded tube according to claim 4, wherein the external refining process only needs an LF treatment process, and during the LF treatment process, the wire feeding Ca treatment is carried out, wherein the wire feeding amount is more than or equal to 600m, so that the inclusions are not more than 2.0 grade; and (3) putting the continuous casting blank under light reduction in the continuous casting process, controlling the pulling speed of the continuous casting blank to be 1.0-2.0 m/min, and controlling the thickness of the casting blank to be 170-230 mm.