CN114737110B

CN114737110B - Steel for X52 straight welded pipe for HIC-resistant oil and gas pipeline and manufacturing method thereof

Info

Publication number: CN114737110B
Application number: CN202210192706.7A
Authority: CN
Inventors: 徐海健; 沙孝春; 康超; 闵承鑫; 乔馨; 杨雨泽
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2022-02-28
Filing date: 2022-02-28
Publication date: 2023-03-03
Anticipated expiration: 2042-02-28
Also published as: CN114737110A

Abstract

The steel for the X52 straight welded pipe for the HIC-resistant oil and gas pipeline comprises the following chemical components in percentage by weight: 0.035 to 0.05 percent of C, 0.10 to 0.25 percent of Si, 0.45 to 0.65 percent of Mn, 0.02 to 0.04 percent of Zr, 0.12 to 0.2 percent of Cu, less than or equal to 0.010 percent of P, less than or equal to 0.005 percent of S, 0.045 to 0.065 percent of Nb, 0.015 to 0.025 percent of Ti, 0.015 to 0.045 percent of Al, 0.004 to 0.006 percent of N, and the balance of Fe and inevitable impurities. The steel plate has high strength, high toughness, 2-10nm Cu-rich and Nb-and Zr-rich nanometer precipitated phases dispersed in the structure, excellent flaw detection qualification rate and good comprehensive performance, and can ensure the service safety of HIC-resistant oil and gas pipelines.

Description

Steel for X52 straight welded pipe for HIC-resistant oil and gas pipeline and manufacturing method thereof

Technical Field

The invention relates to the technical field of low-carbon microalloyed steel production, in particular to steel for an X52 straight welded pipe for an HIC (hydrogen induced cracking) resistant oil and gas pipeline and a manufacturing method thereof.

Background

Pipeline transportation is the most economical, convenient and dominant transportation mode for transporting natural gas over long distances. In order to reduce the construction investment and the operation maintenance cost of the long-distance oil and gas transmission pipeline and improve the transmission efficiency, the long-distance oil and gas transmission pipeline develops towards the direction of large pipe diameter and high pressure; meanwhile, the service economy and safety of the steel pipe are ensured, the thickness of steel pipes of some branch line projects is gradually reduced, and the corresponding pipeline steel plate needs to meet the requirements of the wall thickness (10-20 mm), the pipe diameter below phi 1016mm and the steel grade below X52; due to the diversity of energy transmission media, part of petroleum and natural gas contain a small amount of corrosive media such as hydrogen sulfide, and the corrosive media have certain corrosivity on pipelines, so that the safety of the transmission pipelines is seriously influenced. In order to prevent cracking caused by hydrogen sulfide corrosion, various HIC (hydrogen induced cracking) and SSC (sulfide stress cracking) resistant pipeline steel plates are developed in the industry, for the traditional natural gas X52 steel-grade pipeline steel, a low-carbon component design with the carbon content of 0.04-0.09% is adopted, the manganese content is higher in a range of 1-1.45%, and alloy elements such as niobium, vanadium, titanium and the like are added to ensure the performance. However, in the case of the HIC-resistant oil and gas pipeline steel, the HIC sensitivity of the steel pipe increases when the content of carbon, which is a main solid solution strengthening element of the pipeline steel, increases. This is because the increase in carbon content in the steel causes the steel to have a martensite structure which is most sensitive to HIC in a hot rolled state. Manganese and phosphorus are easily segregated elements, and the hot rolled plate is easily segregated in the center of the steel plate to generate a low-temperature transformation hardening microstructure band sensitive to HIC. The sulfur content has a great influence on the HIC performance, and hydrogen atoms permeating into the material from the environment are easily accumulated at the tip of a long-strip sulfide inclusion (such as manganese sulfide), so that a large hydrogen internal pressure is formed, and further microcracks are induced. In addition, with the change of the alloy composition design system of the X52 steel plate, the steel-making, continuous casting and rolling processes of the steel plate are obviously changed, and then the performance of the steel plate, the flaw detection qualification rate, the control of strip-shaped, mn and P segregation elements, the control of key process parameters in the production processes of smelting, rolling and the like are obviously changed. Therefore, how to solve the problems of the X52 steel grade HIC-resistant pipeline steel with the pipe diameter of less than phi 1016mm is the key for developing the X52 steel grade HIC-resistant oil-gas pipeline steel.

Compared with the prior art:

so far, few reports are made on X52 steel grade pipeline steel for producing HIC-resistant oil and gas pipelines at home and abroad. Before the invention, the patent with the application number of CN 201010243258.6 discloses a method for manufacturing X52 steel grade pipeline steel, which comprises the following chemical components of, by mass, 0.070-0.090% of C, 0.15-0.30% of Si, 1.10-1.30% of Mn, less than or equal to 0.006% of S, less than or equal to 0.020% of P, 0.020-0.040% of Nb, 0.010-0.020% of Ti, less than or equal to 0.008% of N and 0.010-0.040% of Als, and in order to enable the steel plate to be provided with the pipeline steel with high strength and excellent low-temperature toughness, the scheme needs to add higher Mn and Nb metal elements in component design, but the production process aims at a coil plate for natural gas, and the thickness and the width of the steel plate are not clear.

The patent with the application number of CN 201910949817.6 discloses an ultra-thick X52 pipeline steel hot-rolled coil and a production method thereof, wherein the chemical components of the coil are as follows by mass percent: 0.060-0.070% of C, 0.15-0.25% of Si, 1.40-1.50% of Mn, 0.034-0.050% of Nb, 0.008-0.022% of Ti, 0.11-0.17% of Cr, 0.015-0.045% of Al, less than or equal to 0.02% of P, less than or equal to 0.008% of S, less than or equal to 0.008% of N and less than or equal to 0.17% of Pcm, and more metal elements such as Mn, nb and Cr need to be added in the component design in order to enable the steel plate to be an X52 pipeline steel with high strength, high toughness and the like, and the thickness specification only aims at natural gas coiled plates with the thickness of more than 20mm.

The medium-carbon L360 low-cost production process mentioned in journal paper 'development of medium-carbon low-cost L360 pipeline steel' (metallurgy management 2019) adopts medium-carbon component design: 0.14-0.19% of C, 0.14-0.19% of Mn, less than or equal to 0.03% of V, less than or equal to 0.03% of Ti and low alloy cost, but the alloy mainly aims at the pipeline steel plate for natural gas, and the production thickness and width are not clear.

Although the steels disclosed in the above patent documents have high toughness, they are either coil formed or used as steel for natural gas pipelines, and therefore, they are not suitable for producing low-cost, thin-gauge, HIC-resistant steel sheets for oil and gas pipelines.

Disclosure of Invention

The invention aims to provide steel for an X52 straight welded pipe for an anti-HIC oil and gas pipeline and a manufacturing method thereof, and the steel is used for manufacturing an X52 steel grade straight welded pipe for an anti-HIC oil and gas pipeline with the diameter of phi 1016mm or less and the manufacturing method thereof. The technical requirements of the ultra-wide HIC-resistant X52 steel plate for the oil and gas pipeline can be met without subsequent off-line heat treatment, the technical problems of rolling resistance, steel plate performance uniformity, HIC-resistant oil and gas pipeline component design, rolling process and the like are solved by optimizing components and processes, the steel plate has high strength and high toughness, cu-rich and Nb-and Zr-rich nanometer precipitated phases which are distributed in a 2-10nm dispersion manner in the structure, excellent flaw detection qualification rate and good comprehensive performance, and the service safety of the HIC-resistant oil and gas pipeline can be ensured.

In order to achieve the purpose, the invention adopts the following technical scheme:

the steel for the X52 straight welded pipe for the HIC-resistant oil and gas pipeline comprises the following chemical components in percentage by weight: 0.035 to 0.05 percent of C, 0.10 to 0.25 percent of Si, 0.45 to 0.65 percent of Mn, 0.02 to 0.04 percent of Zr, 0.12 to 0.2 percent of Cu, less than or equal to 0.010 percent of P, less than or equal to 0.005 percent of S, 0.045 to 0.065 percent of Nb, 0.015 to 0.025 percent of Ti, 0.015 to 0.045 percent of Al, 0.004 to 0.006 percent of N, the balance of Fe and inevitable impurities, less than or equal to 0.0020 percent of H, less than or equal to 0.0050 percent of O, and the total amount of other impurity elements is less than 0.05 percent.

The target thickness of the steel for the X52 straight welded pipe is 10-20mm.

The steel for the X52 straight welded pipe is used for manufacturing an HIC-resistant oil and gas pipeline with the pipe diameter of phi 1016mm or less.

The steel plate provided by the invention has the following main elements in chemical components:

c: the most economical and basic strengthening elements in the steel have obvious effect on improving the strength of the steel through solid solution strengthening and precipitation strengthening, but the improvement of the content of C has negative influence on the plasticity, the toughness and the weldability of the steel. Therefore, the content range of C is set to be 0.035-0.05%.

Mn: the strength of steel is improved by solid solution strengthening, and the loss of strength of the steel sheet due to the decrease of the C content is compensated. In addition, the gamma-alpha phase transformation temperature can be reduced, so that ferrite grains are refined, a fine low-temperature phase transformation product is obtained, and the toughness of the product is improved. However, the increase of the Mn content can aggravate the center segregation and the structure deterioration of the continuous casting billet, generate a low-temperature transformation hardening microstructure band sensitive to HIC, be not beneficial to the improvement of the low-temperature toughness of the steel plate, and also can not ensure the uniformity of the cross section structure of the steel plate, so the Mn content range of the invention is designed to be 0.45-0.65%.

Si: has the functions of steelmaking deoxidization and matrix strength improvement. But excessive Si can reduce the toughness of a welding heat affected zone of the base material, improve the content of Si, purify ferrite, reduce the content of pearlite and facilitate the reduction of the Bauschinger effect of the base material. Therefore, the Si content is set to 0.10% to 0.25% in the present invention.

Nb: is one of common elements in modern microalloyed pipeline steel, and has good fine grain strengthening and precipitation strengthening effects; austenite recrystallization is also delayed, but excess Nb increases production costs and difficulties in controlling the continuous casting process. The invention selects the Nb content range of 0.045-0.065%, and can obtain a uniform composite phase which mainly takes acicular ferrite or a formation structure of an M-A island by matching with a reasonable TMCP process, so that the composite phase has good toughness.

N: the N element in the steel has no other obvious effect except that fine TiN grains are formed to refine austenite grains, so that the content of the N element needs to be kept at a lower content level, and the content of the N element is selected to be in a range of 0.004-0.006%.

Ti: is a strong solid N element and exists in the form of TiN in the continuous casting billet. The fine TiN particles can effectively inhibit the growth of austenite grains when reheating a continuous casting slab, and contribute to the improvement of the solid solubility of Nb in austenite and the improvement of the impact toughness of a welding heat affected zone. When the addition amount of Ti exceeds a certain value, the TiN particles will be coarsened, and the stress concentration level of the particle interface and the matrix is improved. Therefore, the content range of Ti is 0.015-0.025%.

Cu: the strength of the steel can be improved through solid solution strengthening and precipitation strengthening, and the corrosion resistance can also be improved, but too high Cu causes hot brittleness and is not favorable for toughness, so the Cu content is selected to be 0.12-0.2%.

Zr: zr is a strong carbide and a strong hardenability forming element, crystal grains can be obviously refined by adding a small amount of Zr, the low-temperature toughness of the steel is improved, the hardenability of the steel is improved, the strength and the structural uniformity of the steel are further improved, and meanwhile, the hot brittleness of the steel is improved by Zr, so that the Zr content is selected to be 0.02-0.04 percent.

Al: in general, alN also has a function of refining the structure when it is formed as a deoxidizer in steel. When the content of Al exceeds 0.045%, excessive alumina inclusions may degrade the cleanliness of the steel. The lower limit of the Al content is set to 0.015% because deoxidation is insufficient when the Al content is too low and an easily oxidizable element such as Ti forms an oxide.

P, S: the alloy is an inevitable impurity element in steel, phosphorus is an easily segregated element, and a hot rolled plate is easily segregated in the center of a steel plate to generate a low-temperature transformation hardening microstructure band sensitive to HIC. The sulfur content has a great influence on the performance of the HIC, and hydrogen atoms penetrating into the material from the environment are easy to accumulate at the tip of a long-strip sulfide inclusion (such as manganese sulfide) to form a larger hydrogen internal pressure so as to induce micro-cracks, so that the lower the P, S is, the better the HIC performance is. But cannot be lowered without limit due to smelting cost and process. Therefore, the present invention sets the upper limit of the P, S content to 0.010% and 0.005%.

The manufacturing method of the steel for the X52 straight welded pipe for the HIC-resistant oil and gas pipeline uses a continuous casting billet with the thickness of 200-250mm to produce on a medium-thick plate reciprocating mill, and the cooling medium is water. The process route comprises the steps of molten steel smelting → external refining, degassing → continuous casting + slow cooling → slab reheating → controlled rolling → controlled cooling → steel plate slow cooling, and specifically comprises the following steps:

1) Steel making and continuous casting: pretreating the raw material by KR molten iron, controlling the content of S to be lower than 0.015 percent, and feeding the raw material into a converter after slagging off; the double-slag method is adopted to remove P in the converter smelting, the content of P is controlled to be less than or equal to 0.01 percent, the content of C is controlled to be 0.035-0.05 percent at the smelting end point of the converter, and argon is blown for 15-20 min during tapping; then LF refining and RH vacuum degassing are carried out, and RH vacuum is kept for more than 30min (hydrogen in liquid molten iron is accelerated to rapidly overflow in a molecular form); then carrying out continuous slab casting, wherein the continuous casting superheat degree is 15-25 ℃, and the continuous casting blank drawing speed is 1.5-1.8 m/min; stacking and slow cooling are carried out on a horizontal sector section, namely the solidification tail end, under heavy reduction, the continuous casting blank reduction is 12-15 mm, after the continuous casting blank is off line, the number of the stacked continuous casting blank blocks is not less than 10, meanwhile, high-temperature asbestos is used for heat preservation, the slow cooling time is not less than 32H, (the central loose grade and segregation of the casting blank are reduced, the H molecule diffusion is accelerated, and the flaw detection qualification rate of the finished casting blank and a steel plate is improved);

2) Heating a casting blank: feeding a casting blank (with the thickness of 200-250 mm) into a stepping heating furnace for heating, and discharging the casting blank after the casting blank sequentially passes through a preheating section, a heating section and a soaking section; the temperature range of the preheating section is 980-1150 ℃ (carbide and nitride of Nb and Zr are promoted to be rapidly and fully dissolved in a matrix and fully diffused), the temperature range of the heating section is 1220-1240 ℃, the temperature range of the soaking section is 1210-1220 ℃, and the furnace time is 4.5-5.5 hours (elements such as C, N are further uniformly distributed, further diffusion and overflow of H molecules are promoted, the furnace time is controlled, and excessive growth of crystal grains is inhibited);

3) Descaling by high-pressure water, controlled rolling and slow cooling: before rolling, descaling the discharged casting blank for 1.5-2 min by using high-pressure water, wherein the pressure of a descaling machine is 20-25 MPa; rolling in two stages: the first stage is that the initial rolling temperature of recrystallization rolling (rough rolling) is more than or equal to 1100 ℃, the temperature interval of rough rolling and final rolling is 1000-1050 ℃, the rough rolling is not more than six times, the pass reduction system is that the first two passes ensure that the reduction rate is more than 15 percent, one pass of the last three passes is not less than 10 percent, and the thickness of the obtained intermediate blank is 3.5-4.5 times of the thickness of the finished product; the intermediate billet is heated for 1 to 1.5min (promoting the dispersion and precipitation of Cu, zr and Nb-rich nanophase), the second stage is that the initial rolling temperature interval of non-crystallization rolling (finish rolling) is 900 to 930 ℃, the final rolling temperature interval is 780 to 840 ℃, the finish rolling is not more than eight times, the pass reduction system is that the first four passes have two passes to ensure that the reduction rate is more than 20 percent, and the second pass ensures that one pass is not less than 15 percent, the (the grain structure of different stages is refined by the two-stage rolling and the dynamic crystallization occurs in the intermediate billet temperature waiting process, so that the grains are uniformly distributed, and the dispersion and precipitation of 2 to 10nm nanophase are promoted), the accelerated rolling (after the head of the intermediate billet is bitten with low speed, the speed of a roller table is rapidly increased from 20r/min to 40 to 60r/min, the final rolling temperature is prevented from being lower than the required temperature interval), the slow steel throwing is adopted after the rolling, the speed of the steel is 1.5 to 2.5m/s (the nanophase phase and precipitation of Cu, zr and Nb-rich nanophase is further promoted to be precipitated in the dispersion and the steel plate is put into a pre-straightening plate (the control head in the process of the dispersion and the rolling process, the water cooling performance is prevented, and the uniformity is subsequently influenced in the surface of the steel plate is subsequently stored; and simultaneously, the thermal stress generated in the steel plate rolling process is favorably released), then laminar cooling is adopted, the open cooling temperature range is 760-820 ℃, the temperature range of the red returning is 550-580 ℃, the cooling speed is 20-30 ℃/s (the final cooling temperature is increased, the generation of banded structures is further inhibited), the steel plates after controlled cooling are stacked and slowly cooled, the stacked steel plates are isolated by battens, and the slowly cooling temperature is not lower than 300 ℃ (further accelerating the diffusion of H molecules).

The adoption of the components and the rolling and cooling control scheme overcomes the defects in the prior art, realizes the production and application of the steel plate for manufacturing the X52 steel-grade straight welded pipe for the HIC-resistant oil and gas pipeline with the thickness specification of 10-20mm and the pipe diameter of phi below 1016mm, the steel plate has a complex phase structure with ferrite and pearlite as main structures, and 2-10nm of Cu-rich and Nb, zr and Ti-rich nanometer precipitated phases are dispersedly distributed in the structure.

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

1) The KR molten iron is pretreated for deep desulfurization and then is completely drossed, a converter adopts a double-slag method for dephosphorization, so that the P, S content of a casting blank is lower, and the argon blowing time and the RH vacuum degassing time are controlled, thereby overcoming the defects of casting blank center segregation, inclusion, H, O content standard exceeding and the like caused by higher Mn content, and being beneficial to improving the ductility and toughness of HIC-resistant oil-gas pipeline steel. The superheat degree and the withdrawal rate of the continuous casting billet are reasonably controlled, heavy reduction is added, steel billet segregation is favorably reduced, austenite grains are refined, internal structure defects are reduced, the casting billet after being off-line is stacked and slowly cooled, enriched alloy elements in the center of the steel billet are gradually diffused, H molecules are further diffused, the center porosity level and segregation of the casting billet are reduced, the content of H is overhigh, and the flaw detection qualification rate of a finished steel plate is improved.

2) The invention has reasonable components, reduces the contents of C, mn, P and S, and adds a small amount of microalloy elements Cu, zr and Nb in a matching way, so that Cu-rich and Nb-rich and Zr-rich nanometer precipitated phases with the sizes of 2-10nm are dispersed and distributed in the structure, and high-temperature rolling is adopted to reduce the high-temperature deformation resistance in the rough rolling and finish rolling stages, thereby being beneficial to improving the rolling reduction of each pass and ensuring the comprehensive performance of the thin X52 steel plate.

3) The rolling process is controlled in two stages, the rolling reduction of rough rolling and finish rolling passes is controlled, the temperature waiting time of an intermediate billet is ensured, the thickness of the intermediate billet is optimized, the finish rolling initial rolling temperature is improved, relaxation waiting is not needed after rolling, the temperature of the steel plate is controlled to be 550-580 ℃ through slow steel throwing, pre-straightening investment, laminar cooling and the like after rolling, the generation of a steel plate banded structure is inhibited, the dispersion distribution of Cu-rich and Nb-rich nanometer precipitated phases of 2-10nm in the steel plate is further promoted, and the technical index of the steel plate is ensured to meet the requirement of an anti-HIC oil-gas pipeline.

4) According to the invention, through optimizing the composition design, the steel plate of the X52 straight welded pipe for the HIC-resistant oil and gas pipeline with the thin specification (10-20 mm) and the pipe diameter of less than phi 1016mm is obtained through regulating and controlling the processes of steel making, continuous casting and controlled rolling and controlled cooling, the structure takes ferrite and pearlite as main materials, and 2-10nm of Cu-rich and Nb-and Zr-rich nano precipitated phases are dispersedly distributed in the structure, so that the steel plate has good low-temperature toughness control. The concrete properties are as follows: the yield strength performance of transverse stretching is between 400 and 450MPa, the tensile strength is between 500 and 540MPa, the strength interval range is narrow, the elongation is more than or equal to 30 percent, the transverse summer specific impact energy at minus 20 ℃ is more than or equal to 250J, the hardness value is less than or equal to 210HV10, the DWTT shearing area (%) at minus 15 ℃ is more than or equal to 85 percent, the Crack Length Rate (CLR) is less than or equal to 15 percent, the Crack Thickness Rate (CTR) is less than or equal to 5 percent, and the Crack Sensitivity Rate (CSR) is less than or equal to 1.5 percent according to NACE TM0284-2011 (A solution) standard. The flaw detection qualified rate of the steel plate is more than 99.5 percent. The steel sheet has high strength and excellent low-temperature toughness.

Detailed Description

The following examples are intended to illustrate the present disclosure in detail, and are intended to be a general description of the present disclosure, and not to limit the present disclosure.

Wherein, table 1 shows the chemical components of the steel of the embodiment, table 2 shows the smelting process system of the steel of the embodiment, and Table 3 shows the heating system of the casting blank of the steel of the embodiment and the high-pressure water descaling process before the continuous casting blank is rolled; table 4 shows the rolling reduction of each pass in different rolling stages of the example steels; table 5 shows the main process parameters for controlled cooling of example steels; table 6 shows the transverse mechanical properties of the steel sheets of the examples.

TABLE 1 chemical composition of inventive examples (wt%)

Examples	C	Si	Mn	Ti	Zr	Cu	Nb	N	Al
										1	0.038	0.12	0.55	0.015	0.021	0.12	0.046	0.0042	0.015
2	0.042	0.15	0.65	0.018	0.032	0.15	0.058	0.0051	0.026
										3	0.037	0.23	0.46	0.022	0.038	0.18	0.062	0.0047	0.044
4	0.048	0.18	0.62	0.025	0.022	0.2	0.048	0.0058	0.036
										5	0.049	0.22	0.57	0.023	0.025	0.17	0.049	0.0045	0.045
6	0.039	0.12	0.49	0.019	0.035	0.16	0.064	0.0059	0.031

Note: the impurity element P in the steel is less than or equal to 0.01 percent; s is less than or equal to 0.005 percent; h is less than or equal to 0.0020 percent, 0 is less than or equal to 0.0050 percent, and the total amount of other impurity elements is less than 0.05 percent.

TABLE 2 smelting process system of steel in examples

TABLE 3 heating system of casting blank of steel and high-pressure water descaling process before rolling of the casting blank

TABLE 4 heating, rolling and controlled Cooling parameters of the steels of the examples

TABLE 5 reduction of each pass in different rolling stages of the example steels

Table 6 shows the transverse mechanical properties of the steel sheets of the examples

Table 7 shows HIC resistance of the steel sheets of examples

Therefore, compared with the prior art, the X52 steel grade HIC-resistant pipeline steel adopts a design system of low C, mn, P and S and Nb, cu and Zr composite addition components, can meet the technical requirements of the X52 steel plate for the ultra-wide HIC-resistant oil and gas pipeline without subsequent off-line heat treatment, has high strength, high toughness, cu-rich and Nb-and Zr-rich nanometer precipitated phases which are dispersed and distributed in the structure by 2-10nm, has excellent flaw detection qualification rate and good comprehensive performance, and can be used for manufacturing the X52 steel grade HIC-resistant pipeline steel pipe with the pipe diameter of 10-20mm being less than phi 1016 mm.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered in the protection scope of the present invention.

Claims

1. The steel for the X52 straight welded pipe for the HIC-resistant oil and gas pipeline is characterized by comprising the following chemical components in percentage by weight: 0.035 to 0.05 percent of C, 0.10 to 0.25 percent of Si, 0.45 to 0.65 percent of Mn, 0.02 to 0.04 percent of Zr, 0.12 to 0.2 percent of Cu, less than or equal to 0.010 percent of P, less than or equal to 0.005 percent of S, 0.045 to 0.065 percent of Nb, 0.015 to 0.025 percent of Ti, 0.015 to 0.045 percent of Al, 0.004 to 0.006 percent of N, the balance of Fe and inevitable impurities, less than or equal to 0.0020 percent of H, less than or equal to 0.0050 percent of O, and the total amount of other impurity elements is less than 0.05 percent;

the manufacturing method of the steel for the X52 straight welded pipe for the HIC-resistant oil and gas pipeline comprises the following steps:

1) Steel making and continuous casting: pretreating raw materials by KR molten iron, removing P by a double-slag method in converter smelting, and blowing argon for 15-20 min during tapping; then LF refining and RH vacuum degassing are carried out, RH vacuum is kept for more than 30min, the continuous casting superheat degree is 15-25 ℃, and the continuous casting and billet drawing speed is 1.5-1.8 m/min; the rolling reduction of the continuous casting billet is 12-15 mm, stacking and slow cooling are carried out after the continuous casting billet is off line, the number of stacked continuous casting billet blocks is not less than 10, and the slow cooling time is not less than 32h;

2) Heating a casting blank: sending the casting blank into a heating furnace for heating, wherein the temperature interval of a preheating section is 980-1150 ℃, the temperature interval of a heating section is 1220-1240 ℃, the temperature interval of a soaking section is 1210-1220 ℃, and the furnace time is 4.5-5.5 hours;

3) Descaling by high-pressure water, rolling control and slow cooling: descaling the cast blank discharged from the furnace for 1.5-2 min by using high-pressure water before rolling; rolling in two stages: the initial rolling temperature of rough rolling is more than or equal to 1100 ℃, the final rolling temperature interval of rough rolling is 1000-1050 ℃, the rough rolling is not more than six times, the pass reduction system is that the first two passes ensure that the reduction rate is more than 15%, the last three passes have one pass not less than 10%, and the thickness of the obtained intermediate blank is 3.5-4.5 times of the thickness of the finished product; the intermediate billet is heated to 1-1.5 min for finish rolling, the initial rolling temperature range is 900-930 ℃, the final rolling temperature range is 780-840 ℃, the finish rolling is not more than eight times, the pass reduction system is that the first four passes have two passes to ensure that the reduction rate is more than 20 percent, the second pass ensures that one pass is not less than 15 percent, the steel throwing speed is 1.5-2.5 m/s, then laminar cooling is adopted, the initial cooling temperature range is 760-820 ℃, the red returning temperature range is 550-580 ℃, the cooling speed is 20-30 ℃/s, the steel plate after controlled cooling is stacked and slowly cooled, and the slow cooling temperature is not lower than 300 ℃.

2. The steel for an X52 straight welded pipe for an HIC-resistant oil and gas pipeline according to claim 1, wherein the steel for an X52 straight welded pipe has a target thickness of 10-20mm.

3. The steel for the X52 straight welded pipe for the HIC-resistant oil and gas pipeline according to claim 1, wherein the steel for the X52 straight welded pipe is used for manufacturing the HIC-resistant oil and gas pipeline with the pipe diameter of phi 1016mm or less.

4. The steel for X52 straight welded pipes for HIC-resistant oil and gas pipelines according to claim 1, wherein the slab thickness is 200-250mm.

5. The steel for X52 straight welded pipes for HIC-resistant oil and gas pipelines according to claim 1, wherein the pressure of the high-pressure descaling water descaler before rolling in step 3) is 20 to 25MPa.