WO2023103514A1 - Pipeline steel having excellent acid resistance property, and manufacturing method therefor - Google Patents

Abstract

The present invention provides acid-resistant pipeline steel and a manufacturing method therefor. The manufacturing method comprises: performing a pre-desulfurization treatment on molten iron by means of a mechanical stirring method, so that the mass percentage of S in the molten iron is less than or equal to 0.0020%; adding, according to design of compositions, corresponding metals to the molten iron for converter smelting, and controlling the mass percentage of S in molten steel to be less than or equal to 0.0020% and the mass percentage of P to be less than or equal to 0.018%; in a tapping process, adding silicon-manganese, aluminum ingot, micro-carbon ferrochromium, ferro-molybdenum alloy, and lime, so that the mass percentage of Mn in the molten steel is less than or equal to 0.90%, the mass percentage of C is less than or equal to 0.06%, and the sum of the mass percentages of Cr and Mo is greater than or equal to 0.40%; performing ladle refining and RH vacuum treatments, so that the mass percentage of Nb in the molten steel to be greater than or equal to 0.060%, the mass percentage of Ti is greater than or equal to 0.010%, and the sum of the mass percentages of Nb and Ti is greater than or equal to 0.085%; feeding a Ca wire to the molten steel for soft stirring, a superheating degree of casting being no lower than 30°C; and forming a steel plate. The manufacturing method is economical in compositions and facilitates smelting and production.

Description

Pipeline steel with excellent acid resistance and manufacturing method thereof technical field

The invention relates to the field of metallurgy, in particular to a pipeline steel with excellent acid resistance and a manufacturing method thereof.

Background technique

With the continuous increase of people's demand for natural gas, natural gas resource exploration and gathering and transportation pipeline materials are facing major challenges. Natural gas resources contain a large proportion of hydrogen sulfide components, and the probability of hydrogen-induced cracking (HIC) and sulfur stress corrosion cracking (SSC) Therefore, special alloy and smelting process design must be adopted for such exploration and gathering pipelines. Existing research or production practices have shown that in order to avoid hardening structures such as large inclusions, MnS precipitation, composition segregation of elements such as C and Mn, and coarse MA islands formed by incomplete phase transformation, composition design and clean steel smelting process, rolling The manufacturing process has special requirements, such as harmful elements such as S and P in steel must be as low as possible. Based on these research results, how to effectively match manufacturing engineering with composition design and reduce manufacturing costs while ensuring excellent HIC and SSC resistance performance is the key core technology for steel manufacturing enterprises. For the high-grade acid-resistant pipeline steel delivered by TMCP process, segregated banded structure, coarse MA islands and large inclusions formed by incomplete phase transformation are the key problems that cause the deterioration of its acid-resistant performance.

Existing studies have shown (Nie Wenjin, Lin Taozhu, etc., the development of low C, low Mn, high Nb, H2S resistant pipeline steel X65MS, welded pipe, 2015 Supplement 1, pp: 20-27), the use of low C, low Mn, high Nb and Cr, Ni, Cu, etc. are alloyed to produce pipeline steel with excellent acid resistance. Ferrite phase transformation will occur when rolling deformation at a low temperature below 850°C, which requires high temperature rolling and rapid cooling after rolling (finish rolling temperature is about 850°C, rolling The final cooling rate is about 30°C/s, and the final cooling temperature is about 500°C), in order to suppress the transformation of pearlite structure, form acicular ferrite or low-carbon bainite structure, and meet the strength, toughness and acid resistance requirements of X65 pipeline steel , the process requirements are more stringent.

Contents of the invention

In view of the above problems, the present invention aims to provide a pipeline steel with excellent acid resistance and a manufacturing method thereof designed with a wider process window for finishing rolling temperature and cooling rate, and adopting low C, low Mn, and high Nb components, so as to achieve high-strength grades The large-scale production, popularization and application of pipeline steel with excellent acid resistance.

The embodiments of the present invention provide a pipeline steel with excellent acid resistance. The mass percentage of elements in the pipeline steel is: C≤0.06%, Si≤0.25%, Mn≤0.90%, Al≤0.050%, Nb≥ 0.050%, 0<Ti≤0.060%, 0<Cr≤0.50%, 0<Mo≤0.50%, Ni≤0.35%, Cu≤0.35%, P≤0.020%, S≤0.002%, N≤0.004%.

Further, the yield strength Rt0.5 is not lower than 415MPa, the tensile strength Rm is not lower than 525MPa, and Cr+Mo≥0.40%.

The embodiment of the present invention also provides a method for manufacturing pipeline steel with excellent acid resistance, including:

In the first step, the molten iron is pre-desulfurized by a mechanical stirring method, so that the mass percentage of S in the molten iron is ≤0.0015%;

The second step is to add corresponding metals into the molten iron according to the composition design for converter smelting, and control the mass percentage of S in molten steel to be ≤0.0020%, and the mass percentage of P to be ≤0.018%; Ingot, micro-carbon ferrochrome alloy, ferromolybdenum and lime, so that the mass percentage of Mn in molten steel is ≤0.90%, the mass percentage of C is not higher than 0.06%, and the sum of the mass percentages of Cr and Mo is ≥0.40%;

In the third step, the molten steel is refined through a ladle refining furnace, and ferroniobium is added to the molten steel so that the mass percentage of Nb in the molten steel is not less than 0.060%;

In the fourth step, RH vacuum-treats the molten steel, and adds ferro-titanium for alloying, so that the mass percentage of Ti in the molten steel is not less than 0.010%, and Nb+Ti≥0.065%;

Step 5, feeding Ca wire to molten steel and performing soft stirring; and

In the sixth step, the steel plate is formed.

Further, steel plate forming includes the slab continuous casting stage. The slab continuous casting stage adopts non-oxidation protection pouring, high superheat casting, tundish superheat 35±5℃, slab stacking and slow cooling, and slab unstacking Temperature≤150℃.

Further, in the sixth step, steel plate forming also includes slab reheating, rough rolling, intermediate billet cooling, finish rolling, steel plate cooling, steel plate straightening, off-line stack cooling out of the stack, and ultrasonic flaw detection.

Further, the reheating temperature of the slab is controlled at 1150-1250° C., and the heating rate is 1.1-1.5 min/mm.

Further, the starting temperature of rough rolling is not lower than 1050°C, the thickness of the intermediate slab after rough rolling is greater than 2.0 times the thickness of the steel plate, the starting temperature of the finishing rolling stage is controlled below 960°C, and the finishing rolling temperature is not lower than 780°C. Stage total compression ratio ≥ 40%.

Further, after finishing rolling, the steel plate start-cooling temperature is not lower than 720°C, the accelerated cooling rate is not lower than 15°C/s, the reddening temperature of the steel plate is not higher than 500°C, and the steel plate is air-cooled to room temperature on a cooling bed after heat straightening.

Beneficial effects: the pipeline steel with excellent acid resistance and its manufacturing method of the present invention are designed by adopting low C, low Mn, high Nb and Cr and Mo alloys, the segregation of the central component of the continuous casting slab is basically eliminated, and the harmful P elements that are easy to segregate can be further improved. To relax the control range, the tempering embrittlement of P (such as the heat-affected zone in the welding process) can be suppressed by adding Mo element. The mass percentage of P is designed to be no higher than 0.020%, thus liberating the difficulty of removing P in the converter. The tapping temperature can be further increased, which is beneficial to the deoxidation, desulfurization and alloying of molten steel, and reduces the problems of large inclusions such as N increase and slag entrainment caused by refining temperature rise; further, this composition design can realize the use of high superheat casting process (Superheating degree 30-40°C), which is beneficial to the effective removal of inclusions in the soft stirring and casting process (tundish, crystallizer), the cleanliness of molten steel is significantly improved, the inclusions are controlled at no higher than 0.5, and acid resistance is achieved. improvement.

For the high-grade acid-resistant pipeline steel of TMCP process, in order to obtain uniform acicular ferrite structure with excellent acid resistance, rolling process, cooling process and corresponding alloy design are required to achieve. In the present invention, under the premise of adopting the low-C and low-Mn standard composition system, Ni and Cu elements can be selectively added according to needs (but the addition amount of each element is not more than 0.35%). By adding Cr, Mo alloy and Nb, Ti microalloy , control the N content not to exceed 40ppm, increase the heating temperature to 1150-1250°C, ensure the full re-dissolution of alloying elements, and help to further eliminate the microsegregation of components in the continuous casting process; compared with Cu and Ni, the same amount Cr and Mo can effectively improve the stability of supercooled austenite and inhibit the transformation of pearlite, so as to realize the process conditions of lower rolling temperature and lower post-rolling cooling rate (final rolling temperature ≥ 780 ° C, post-rolling cooling rate ≥ 15°C/s) to obtain a uniform acicular ferrite structure, and further increase the wall thickness specification of pipeline steel with excellent acid resistance, and the highest strength level can reach X70 level.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute improper limitations to the present invention. In the attached picture:

Fig. 1 is the metallographic structure of the acid-resistant pipeline steel plate in Example 1 of the present invention, which is an acicular ferrite structure.

Fig. 2 is the metallographic structure of the acid-resistant pipeline steel plate in Example 2 of the present invention, which is an acicular ferrite structure.

Fig. 3 is the metallographic structure of the acid-resistant pipeline steel plate in Comparative Example 1 of the present invention, which is ferrite structure + pearlite structure.

Fig. 4 shows the metallographic structure of the acid-resistant pipeline steel in Comparative Example 2 of the present invention, which is an acicular ferrite structure with structure hardening bands with segregated components.

Fig. 5 shows the detection of inclusions in acid-resistant pipeline steel in Comparative Example 2 of the present invention, category B, large inclusions.

Fig. 6 shows the hydrogen-induced cracks formed on the B-type inclusions at 1/4 of the thickness of the acid-resistant pipeline steel HIC experimental steel plate in Comparative Example 1 of the present invention.

Fig. 7 shows the hydrogen-induced cracks formed on the composition segregation hardened structure zone at the center 1/2 of the thickness center of the acid-resistant pipeline steel HIC experimental steel plate in Comparative Example 2 of the present invention.

Fig. 8 is the (NbTi)(CN) nano-precipitated phase in the acid-resistant pipeline steel plate matrix of Example 1 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings and examples. It should be noted that, in the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

It should be noted that the terms "first" and "second" in the description and claims of the present invention and the above drawings are used to distinguish similar objects, but not necessarily used to describe a specific sequence or sequence.

The embodiments of the present invention provide a pipeline steel with excellent acid resistance. The mass percentage of elements in the pipeline steel is: C≤0.06%, Si≤0.25%, Mn≤0.90%, Al≤0.050%, Nb≥ 0.050%, 0<Ti≤0.060%, 0<Cr≤0.50%, 0<Mo≤0.50%, Ni≤0.35%, Cu≤0.35%, P≤0.020%, S≤0.002%, N≤0.004%.

Further, the yield strength Rt0.5 of the pipeline steel is not lower than 415MPa, the tensile strength Rm is not lower than 525MPa, and Cr+Mo≥0.40%.

The embodiment of the present invention also provides a method for manufacturing pipeline steel with excellent acid resistance, including:

In the first step, the molten iron is pre-desulfurized by a mechanical stirring method, so that the mass percentage of S in the molten iron is ≤0.0015%;

The second step is to add corresponding metals into the molten iron according to the composition design for converter smelting, control the mass percentage of S in molten steel to be ≤0.0020%, and the mass percentage of P to be ≤0.018%; Ingot, micro-carbon ferrochrome alloy, ferromolybdenum and lime, so that the mass percentage of Mn in molten steel is ≤0.90%, the mass percentage of C is not higher than 0.06%, and the sum of the mass percentages of Cr and Mo is ≥0.40%;

In this step, copper blocks, ferronickel, ferromolybdenum, etc. are added according to the composition design and alloy yield according to the preset steel composition for smelting. In this step, the top-bottom combined blowing converter is used for smelting.

In this step, the tapping temperature after the converter smelting is ≥1630° C., and argon gas is blown from the bottom during the tapping process to melt the alloy completely. Avoid nitrogen inhalation during operation.

Since the method requires that the mass percentage of P is ≤0.018%, which is far higher than the upper limit of the P content in the existing method, it can adopt converter single slag operation and direct tapping without downturning the furnace, and the increase of tapping temperature can be guaranteed.

An increase in the tapping temperature is beneficial to desulfurization of the converter, and is conducive to the dissolution and slagging of auxiliary materials such as alloys and lime during the tapping process. The subsequent step of refining the ladle refining furnace will reduce the temperature rise pressure, and avoid the slag curling caused by the strong stirring of the ladle refining furnace. Cleanliness has deteriorated.

Place the desulphurization operation in the KR and converter processes to ensure that S is not higher than 0.002%, which releases the desulfurization burden of ladle refining furnace refining, avoids the deterioration of the cleanliness of molten steel caused by slag rolling caused by strong refining in ladle refining furnace, and avoids the absorption of N by molten steel And the addition of N also further improves the refining rhythm of the ladle refining furnace and saves smelting time.

In the third step, the molten steel is refined through a ladle refining furnace, and ferroniobium is added to the molten steel so that the mass percentage of Nb in the molten steel is not less than 0.060%;

In this step, ferroniobium is added to the ladle refining furnace for fine adjustment of composition and slag adjustment operation. The basicity of the slag is controlled at about 4.0, and the S content is ≤0.0020%.

In the fourth step, RH vacuum-treats the molten steel, and adds ferro-titanium for alloying, so that the mass percentage of Ti in the molten steel is not less than 0.010%, and Nb+Ti≥0.065%;

In this step, the net circulation is performed for 12 minutes after the alloying is completed, so that the H content in the steel is less than 2 ppm.

Step 5, feeding Ca wire to molten steel and performing soft stirring; and

In this step, 150-400m of Ca wire is fed, and soft stirring is performed, and the soft stirring time is not less than 12min.

In the sixth step, the steel plate is formed.

Further, the steel plate forming includes the slab continuous casting stage, the slab continuous casting stage adopts non-oxidation protection pouring, high superheat casting, the tundish superheat is 35±5°C, and the slow cooling time of slab stacking is not less than 3 days , The temperature of the slab during unstacking is ≤150°C.

Since this method is designed with low C and low Mn components, the superheat of the tundish can be further increased to realize high-temperature soft stirring and casting. During the soft stirring and casting process, the inclusions will be effectively removed by floating in the ladle, tundish, and crystallizer. The cleanliness of molten steel is significantly improved.

Further, steel plate forming also includes slab reheating, rough rolling, intermediate slab cooling, finish rolling, steel plate cooling, steel plate straightening, off-line stack cooling, and ultrasonic flaw detection.

Further, the reheating temperature of the slab is controlled at 1150-1250° C., and the heating rate is 1.1-1.5 min/mm.

Further, the starting temperature of rough rolling is not lower than 1050°C, the thickness of the intermediate slab after rough rolling is greater than 2.0 times the thickness of the steel plate, the starting temperature of the finishing rolling stage is controlled below 960°C, and the finishing rolling temperature is not lower than 780°C. Stage total compression ratio ≥ 40%.

Further, after finishing rolling, the steel plate start-cooling temperature is not lower than 720°C, the accelerated cooling rate is not lower than 15°C/s, the reddening temperature of the steel plate is not higher than 500°C, and the steel plate is air-cooled to room temperature on a cooling bed after heat straightening.

Referring to Fig. 1 to Fig. 8, the present invention is described below with some specific embodiments:

The process routes of the following embodiments 1 and 2 are: hot metal KR pre-desulfurization, converter smelting and direct tapping, LF refining, RH vacuum treatment, continuous casting of slabs, reheating of slabs, rough rolling, intermediate slabs for cooling, Finish rolling, MULPIC rapid water cooling after steel rolling, steel hot straightening, cooling bed cooling, ultrasonic flaw detection, shearing, storage. Please refer to Table 1 to Table 3 for the specific process parameters of Examples 1 and 2. The process route of the comparison case is: hot metal KR pre-desulfurization, converter double slag smelting deep desulfurization, LF refining, RH vacuum treatment, slab continuous casting, slab reheating, rough rolling, intermediate slab cooling, finish rolling, steel plate After rolling, MULPIC rapid water cooling, steel plate hot straightening, cooling bed cooling, ultrasonic flaw detection, shearing, storage. In both examples 1 and 2, the element Mo is added, and Mo+Cr is greater than 0.40, the tapping temperature of the converter is greater than 1630°C, the degree of superheat is greater than 30°C, the heating temperature and starting rolling temperature are high, and the final rolling temperature is between 780-820°C ℃, the cooling rate after rolling is greater than 15℃ (≤30℃) to obtain acicular ferrite structure. Comparative example 1 adopts the design of low C, low Mn, high Nb, low P, and Cu, Ni, and Cr components. When the cooling rate of the steel plate after rolling is lower than 30°C, ferrite and pearlite structures are obtained, and the strength level only meets the requirements of X65, and because Controlling P leads to low tapping temperature and low superheat, which affects the cleanliness. In the HIC test, the inclusions cause hydrogen-induced cracks. Comparative example 2 is designed with low C, high Mn, micro Nb and low P composition. The converter tapping temperature and superheating degree are both low, and the cleanliness is poor. The high Mn causes composition segregation in the core, and finally the result in the HIC experiment is not ideal. Cracking is the worst.

Table 1 Embodiment 1, 2 and the first part of the rolling process control parameters of the comparative ratio

Table 2 Embodiment 1, 2 and the second part of the rolling process control parameters of the comparative ratio

Table 3 Embodiment 1, 2 and comparative example element content (wt%)

The steel plate that embodiment 1, 2 and comparative example are made detects, and test result sees table 4 (Rt0.5 is yield strength, and Rm is tensile strength, and Y/R is yield ratio, and A ₅₀ is elongation , DWTT is the ferrite drop weight tearing test), the steel plates of Examples 1 and 2 all reached the X70 strength level, the comparative example 1 reached the X65 strength level, and the comparative example 2 reached the X70 strength level.

The mechanical property of the steel plate that table 4 embodiment 1, 2 and comparative example make

In Table 5, AF is acicular ferrite, F is ferrite, P is pearlite, and in the inclusion grade, A is sulfide inclusion, B is alumina inclusion, C is silicate inclusion, and D is spherical oxide Inclusions, DS is single particle large inclusions. The cleanliness of the steel plates in Examples 1 and 2 is high, and neither Class B nor Class Ds is greater than Class 0.5.

The metallographic examination result of the steel plate that table 5 embodiment 1, 2 and comparative example make

Test the anti-HIC performance of the steel plates of Examples 1 and 2 and the comparative example: test standard NACE TM0284-1996, use A solution, time 96h, sample size: 100×20×t mm, test result: no hydrogen bubbling on the surface, golden cross section Phase observation shows no HIC cracks. In Table 6, CLR is the percentage of crack length, CSR is the percentage of crack sensitivity, and CTR is the percentage of crack thickness. Using low C, low Mn and high Nb composition system, the HIC test results are satisfactory, but using low C, high Mn and micro Nb composition system, the HIC test results are not satisfactory, and hydrogen-induced cracks are formed on the segregation zone and inclusions.

Table 6 Example 1, 2 and the steel plate anti-HIC property that comparative example makes

The anti-SSC performance test of the steel plates of Examples 1 and 2: test standard NACE TM0177-2005, A solution, 720h, four-point bending, test result: no cracks on the sample surface.

Table 7 The steel plate anti-SSC performance of embodiment 1, 2 and comparative example

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. A pipeline steel with excellent acid resistance, characterized in that the mass percentage of elements in the pipeline steel is: C≤0.06%, Si≤0.25%, Mn≤0.90%, Al≤0.050%, Nb≥0.050 %, 0<Ti≤0.060%, 0<Cr≤0.50%, 0<Mo≤0.50%, Ni≤0.35%, Cu≤0.35%, P≤0.020%, S≤0.002%, N≤0.004%.
2. A pipeline steel with excellent acid resistance according to claim 1, characterized in that the yield strength Rt0.5 of the pipeline steel is not less than 415MPa, the tensile strength Rm is not less than 525MPa, and Cr+Mo≥0.40% .
3. A method for manufacturing a pipeline steel with excellent acid resistance based on claim 1 is characterized in that it comprises:

   In the first step, the molten iron is pre-desulfurized by a mechanical stirring method, so that the mass percentage of S in the molten iron is ≤0.0015%;

   The second step is to add corresponding metals into the molten iron according to the composition design for converter smelting, and control the mass percentage of S in molten steel to be ≤0.0020%, and the mass percentage of P to be ≤0.018%; Ingot, micro-carbon ferrochrome alloy, ferromolybdenum and lime, so that the mass percentage of Mn in molten steel is ≤0.90%, the mass percentage of C is not higher than 0.06%, and the sum of the mass percentages of Cr and Mo is ≥0.40%;

   In the third step, the molten steel is refined through a ladle refining furnace, and ferroniobium is added to the molten steel so that the mass percentage of Nb in the molten steel is not less than 0.060%;

   In the fourth step, RH vacuum-treats the molten steel, and adds ferro-titanium for alloying, so that the mass percentage of Ti in the molten steel is not less than 0.010%, and Nb+Ti≥0.065%;

   Step 5, feeding Ca wire to molten steel and performing soft stirring; and

   In the sixth step, the steel plate is formed.
4. A method for manufacturing pipeline steel with excellent acid resistance as claimed in claim 3, characterized in that: steel plate forming includes a slab continuous casting stage, and the slab continuous casting stage adopts non-oxidation protection pouring and high superheat casting, The superheating degree of the tundish is 35±5°C, the slabs are stacked and cooled slowly, and the slab temperature is ≤150°C when unstacking.
5. A method for manufacturing pipeline steel with excellent acid resistance as claimed in claim 1, characterized in that: in the sixth step, the forming of the steel plate also includes reheating the slab, rough rolling, cooling the intermediate slab, finish rolling, and steel plate forming. Cooling, steel plate straightening, off-line stack cooling out of the stack and ultrasonic flaw detection.
6. A method for manufacturing pipeline steel with excellent acid resistance as claimed in claim 5, characterized in that: the reheating temperature of the slab is controlled at 1150-1250°C, and the heating rate is 1.1-1.5min/mm.
7. A method for manufacturing pipeline steel with excellent acid resistance as claimed in claim 5, characterized in that: the starting temperature of rough rolling is not lower than 1050°C, the thickness of the intermediate slab after rough rolling is greater than 2.0 times the thickness of the steel plate, and the finishing rolling The stage rolling temperature is controlled below 960°C, the finish rolling temperature is not lower than 780°C, and the total compression ratio in the finish rolling stage is ≥40%.
8. A method for manufacturing pipeline steel with excellent acid resistance as claimed in claim 5, characterized in that: after finish rolling, the steel plate start-cooling temperature is not lower than 720°C, the accelerated cooling rate is not lower than 15°C/s, and the steel plate returns The red temperature is not higher than 500°C. After the steel plate is straightened by heat, it is air-cooled to room temperature on a cooling bed.

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