A production method of low-hardness acid-resistant submarine pipeline steel X65MOS

Abstract

The invention discloses a production method of low-hardness acid-resistant submarine pipeline steel X65MOS. The chemical components of the steel are as follows: C=0.02%-0.05%, Si=0.10%-0.20%, Mn=0.80%-0.90%, P≤0.012%, S≤0.0015%, Nb=0.075%-0.085%, Ti=0.015%-0.025%, Cr=0.25-0.30%, Ni=0.13-0.16%, Cu=0.20-0.25%, B≤0.0005%, and the balance is Fe and unavoidable impurities. The adoption of a micro-alloy composition system of low carbon + low manganese + high niobium breaks through the micro-alloy composition design of low carbon + medium manganese + low niobium of conventional acid-resistant pipeline steel, solves the problem of high surface hardness of the steel plate under TMCP conditions, and combines with the unique controlled rolling and controlled cooling process of "high starting rolling + high cooling rate + high final cooling" to obtain the high-strength, low-hardness, strong-toughness-matched acid-resistant submarine pipeline steel X65MOS.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline steel manufacturing and relates to a production method of low-hardness acid-resistant submarine pipeline steel X65MOS. Background Art

[0002] With the rapid development of the offshore oil industry, long-distance submarine pipelines have become a continuous, fast, and large-volume fluid transportation medium. Their construction is showing an increasingly strong momentum and demand is also increasing day by day. The development of high-strength, high-toughness, corrosion-resistant, and low-temperature-resistant submarine pipelines has become the mainstream direction of pipe manufacturing companies. Among offshore oil pipes, X65 steel grade pipelines are the largest in use. In view of the current production status of submarine oil pipelines, the quality problems of existing products need to be solved urgently. Due to the influence of waves, ocean currents, surrounding soil, corrosion and other factors, the working environment of submarine pipelines has become more and more harsh, and the failure probability has also increased significantly. Strict requirements are put forward for materials to resist corrosion caused by seawater, working environment, hydrogen sulfide and other factors. The bimetallic composite pipe of stainless steel + X65MOS has gradually replaced the ordinary submarine pipeline steel X65MOS, and there are currently two common manufacturing methods for bimetallic composite plates, namely explosive composite and rolling composite. Due to the limitation of rolling reduction ratio, it is difficult to produce thick composite plates by symmetrical rolling composite. However, explosive composite can avoid the limitation of reduction ratio, and the thickness of composite plates is not limited. It is a relatively conventional manufacturing method for high-grade thick bimetallic composite plates. However, due to the increase of hardness and stress in explosive composite, the original performance index of the material is directly affected. It is urgent to produce low-hardness X65MOS substrate (hardness ≤ 200HV10) to promote the development of explosive composite bimetallic composite plates. Therefore, the demand for the development of submarine pipelines with high strength, corrosion resistance and low hardness is increasing, and it is of great significance to study low-hardness thick-walled submarine acid-resistant pipeline steel X65MOS.

[0003] CN117165870A discloses a hot-rolled steel plate for thick-walled submarine pipelines. The hardness values ​​of the upper and lower surfaces of the steel plate application examples are both over 200HV10, with the highest reaching 216HV10, which cannot meet the requirements of X65MOS for explosive composite.

[0004] CN116463552A discloses a method for producing a thick-gauge economical high-performance hot-rolled steel coil for submarine pipelines. The hardness values ​​of the steel plate application examples all exceed 200HV10, with the highest reaching 234HV10, which cannot meet the requirements of X65MOS for explosive composite.

[0005] CN113278880A discloses "a low yield strength ratio and low hardness submarine pipeline steel L485MO, the hardness of the steel plate is between 210 and 220 HV10, all exceeding 200 HV10, which cannot meet the requirements of X65MOS for explosive composite.

[0006] Similar patents such as CN111979497A, CN111534741A, and CN117966049A do not mention the hardness of the steel plate, and all of them belong to the composition and cooling process of conventional pipeline steel. The hardness of the upper and lower surfaces of the steel plate will almost exceed 200HV10. Summary of the invention

[0007] The present invention aims to provide a production method of low-hardness acid-resistant submarine pipeline steel X65MOS, so as to obtain high-strength, low-hardness, strong-toughness-matched acid-resistant submarine pipeline steel X65MOS to solve the problem of manufacturing low-hardness substrates for explosive composite plates.

[0008] The technical solution of the present invention:

[0009] A production method of low-hardness acid-resistant submarine pipeline steel X65MOS, the chemical composition of the steel is C=0.02%~0.05%, Si=0.10%~0.20%, Mn=0.80%~0.90%, P≤0.012%, S≤0.0015%, Nb=0.075%~0.085%, Ti=0.015%-0.025%, Cr=0.25-0.30%, Ni=0.13~0.16%, Cu=0.20-0.25%, B≤0.0005%, and the balance is Fe and unavoidable impurities. Key process steps:

[0010] (1) Heating: Steel burning temperature 1160~1200℃, furnace time 240~280min;

[0011] (2) Rolling: rough rolling final rolling temperature ≥ 1020℃, the reduction ratio of the last three passes ≥ 30%, the starting rolling temperature at the finishing rolling entrance is 960~980℃, the starting cooling temperature is 780~820℃, the final cooling temperature is 540~570℃, and the cooling rate is 20~25℃ / s;

[0012] (3) Online electric induction heating tempering, tempering temperature 590℃, heating time 3~5min; the acid-resistant submarine pipeline steel plate is obtained, the structure is ferrite + tempered troostite, yield strength 460~560MPa, tensile strength 590~650MPa, yield strength ratio ≤0.88, -60℃ impact value 400~500J, -30℃ drop hammer 90%~98%, hardness HV10≤195; HIC test NACE solution immersion 96 hours, CLR, CTR, CSR are all 0; SSC test four-point bending constant load nominal yield 90% immersion 720 hours, no cracks appear on the surface of the sample; the crack tip opening displacement CTOD value of the material at -30℃ is ≥0.6mm.

[0013] The invention has the following beneficial effects: it adopts a microalloy component system of low carbon + low manganese + high niobium, breaking through the microalloy component design of low carbon + medium manganese + low niobium of conventional acid-resistant pipeline steel, and cooperates with the cooling process of "high opening rolling + high cooling rate + high final cooling" to obtain ferrite + bainite structure at a higher final cooling temperature, so that the strength and toughness of the material are well matched. It adopts online electric induction heating tempering to eliminate the residual stress of the steel plate after cooling, improve the plate shape, change the organizational characteristics, and transform from "ferrite + bainite" after cooling to "ferrite + tempered troostite", reduce the surface hardness of the steel plate, and at the same time, the process shortens the delivery cycle of the steel plate, saves energy and is environmentally friendly. The acid-resistant submarine pipeline steel X65MOS with high strength, low hardness and matched toughness was obtained, with a microstructure of ferrite + tempered troostite, yield strength of 460~560MPa, tensile strength of 590~650MPa, yield strength ratio ≤0.88, -60℃ impact value of 400~500J, -30℃ drop hammer 90%~98%, hardness HV10≤195; HIC test NACE solution immersion for 96 hours, CLR, CTR, CSR are all 0; SSC test four-point bending constant load nominal yield 90% immersion for 720 hours, no cracks appeared on the surface of the sample; the crack tip opening displacement CTOD value at -30℃ is ≥0.6mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The steel plate and metallographic structure diagram produced in Example 1. DETAILED DESCRIPTION

[0015] The present invention is further described below with reference to the embodiments. Example 1

[0016] A production method of low-hardness acid-resistant submarine pipeline steel X65MOS, the thickness of the steel pipe is 28mm. The chemical composition of the steel is C=0.04%, Si=0.15%, Mn=0.86%, P=0.010%, S=0.0012%, Nb=0.082%, Ti=0.018%, Cr=0.27%, Ni=0.14%, Cu=0.23%, B=0.0003%, and the balance is Fe and unavoidable impurities. Key process steps:

[0017] (1) Heating: Steel burning temperature 1180℃, furnace time 245min;

[0018] (2) Rolling: The final rolling temperature of rough rolling is 1025°C, the reduction ratios of the last three passes are 33.1%, 33.6%, and 34.2% respectively, the starting rolling temperature of finishing rolling is 972°C, the starting cooling temperature is 790~815°C, the final cooling temperature is 545~565°C, and the cooling rate is 23.6°C / s;

[0019] (3 Online electric induction heating tempering, tempering temperature 590℃, heating time 3.6min.

[0020] The structure of the steel is ferrite + tempered troostite. The mechanical properties test results of the steel are shown in Table 1. Example 2

[0021] A production method of low-hardness acid-resistant submarine pipeline steel X65MOS, with a steel pipe thickness of 36 mm. The chemical composition of the steel is C=0.035%, Si=0.18%, Mn=0.87%, P=0.009%, S=0.0010%, Nb=0.081%, Ti=0.018%, Cr=0.28%, Ni=0.15%, Cu=0.24%, B=0.0005%, and the balance is Fe and unavoidable impurities. Key process steps:

[0022] (1) Heating: Steel burning temperature 1170℃, furnace time 272min;

[0023] (2) Rolling: The final rolling temperature of rough rolling is 1026°C, the reduction ratios of the last three passes are 32.5%, 32.6%, and 33.8% respectively, the starting rolling temperature of finishing rolling is 971°C, the starting cooling temperature is 782~812°C, the final cooling temperature is 542~561°C, and the cooling rate is 21.6°C / s;

[0024] (3) Online electric induction heating tempering, tempering temperature 590℃, heating time 3.8min.

[0025] The structure of the steel is ferrite + tempered troostite. The mechanical properties test results of the steel are shown in Table 1.

[0026] Table 1 Mechanical properties test results of X65MOS steel pipe produced in Example

[0027] .

Claims

1. A method for producing low-hardness acid-resistant submarine pipeline steel X65MOS, characterized in that: The chemical composition of steel is as follows: C = 0.02% ~ 0.05%, Si = 0.10% ~ 0.20%, Mn = 0.80% ~ 0.90%, P ≤ 0.012%, S ≤ 0.0015%, Nb = 0.075% ~ 0.085%, Ti = 0.015% - 0.025%, Cr = 0.25-0.30%, Ni = 0.13 ~ 0.16%, Cu = 0.20-0.25%, B ≤ 0.0005%, the balance is Fe and unavoidable impurities; The key process steps include: (1) Heating: Steel burning temperature 1160~1200℃, furnace time 240~280min; (2) Rolling: rough rolling final rolling temperature ≥ 1020℃, the reduction ratio of the last three passes ≥ 30%, the starting rolling temperature at the finishing rolling entrance is 960~980℃, the starting cooling temperature is 780~820℃, the final cooling temperature is 540~570℃, and the cooling rate is 20~25℃ / s; (3) Online electric induction heating tempering, tempering temperature 590℃, heating time 3~5min; the acid-resistant submarine pipeline steel plate is obtained, the structure is ferrite + tempered troostite, yield strength 460~560MPa, tensile strength 590~650MPa, yield strength ratio ≤0.88, -60℃ impact value 400~500J, -30℃ drop hammer 90%~98%, hardness HV10≤195; HIC test NACE solution immersion 96 hours, CLR, CTR, CSR are all 0; SSC test four-point bending constant load nominal yield 90% immersion 720 hours, no cracks appear on the surface of the sample; the crack tip opening displacement CTOD value at -30℃ is ≥0.6mm.

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