Production method of heat treatment type thick anti-acid pipe fitting steel X65MS

Abstract

The invention discloses a production method of heat treatment type thick-specification acid-resistant pipe fitting steel X65MS, aims to solve the bottleneck of difficult drop hammer performance of thick-wall pipe fitting steel and the difficult problem of softening after heat treatment of a pipe fitting, adopts a low-carbon, low-manganese and high-chromium microalloy component system, and is matched with a production process of large-section ultralow-temperature steel burning, temperature gradient rolling and subcritical quenching, so that the heat treatment type thick-specification acid-resistant pipe fitting steel X65MS is obtained. The high-strength thick-wall anti-acid pipe fitting steel capable of keeping the drop hammer performance is obtained, the heat treatment performance after a steel plate pipe is manufactured can reach the yield strength of 470-570 MPa, the tensile strength of 600-660 MPa, the yield ratio of less than or equal to 0.85, the impact value of minus 40 DEG C of 400-500 J and the drop hammer of minus 40 DEG C of 85-92%, and an HIC test is that CLR, CTR and CSR are all 0 after the steel plate pipe is soaked in an NACE solution for 96 hours; when four-point bending constant load nominal yield is 90% and soaking is performed for 720 hours, no crack appears on the surface of the sample.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline steel manufacturing, and relates to a production method of heat-treated thick-specification acid-resistant pipe fitting steel X65MS. Background Art

[0002] Since the initial development of industrial pipelines to date, the construction of oil and gas pipelines has experienced more than two centuries of development. With the continuous increase in global energy demand, the construction of oil and gas pipelines has entered a new historical development stage. Currently, most newly discovered oil fields are in remote areas and regions with harsh geographical and climatic conditions, such as the Algerian gas field supplying gas to the Western European market, the East and West Siberian gas fields supplying gas to the Far East market, the North Alaska gas field supplying gas to the US market, and the oil and gas fields in Northeast and Northwest China. It can be seen that the challenges faced by the oil and gas pipeline industry are: building long-distance, high-pressure, large-capacity pipelines in harsh environments such as high-cold, deep-sea, desert, and areas prone to geological disasters, which puts higher requirements on the performance of steel pipes for pipelines.

[0003] At the same time, the development conditions of oil and gas in various countries have changed significantly. Although natural gas is currently purified before transportation, the corrosion of pipelines caused by the presence of H2S and water is still inevitable. There are also corrosion phenomena in pipeline steel in some special oil and gas transportation areas. Internal hydrogen sulfide corrosion of pipelines is one of the main forms of pipeline corrosion, and this corrosion damage is mainly caused by three ways: hydrogen-induced cracking, sulfur-induced stress corrosion cracking, and electrochemical corrosion.

[0004] To ensure the safety of oil and gas transportation, in recent years, pipeline steel has increasingly higher requirements for corrosion resistance, especially resistance to hydrogen-induced cracking and sulfide stress corrosion. There are many studies and reports on acid-resistant pipeline steel abroad, but very few studies on thick-walled acid-resistant pipe fitting steel. Therefore, it is of great significance to develop high-strength, corrosion-resistant thick-walled acid-resistant pipe fitting steel. Generally speaking, domestic pipe fitting steel does not require the low-temperature drop-weight performance of steel plates, but for exports to Middle Eastern countries such as the UAE and Abu Dhabi, requirements for drop weight are put forward for acid-resistant pipe fitting steel.

[0005] Chinese Patent CN106591718A published "Yield 420MPa Grade High-Toughness Acid-Resistant Quenched and Tempered Pipe Fitting Steel Plate and Production Method". The strength level of the steel plate only reaches 420 grade, and this invention patent does not mention drop weight and cannot meet the requirements of the DWTT performance of overseas acid-resistant pipeline steel.

[0006] Chinese Patent CN114807751A published "An A516 Gr.70(HIC) Acid-Resistant Pipe Fitting Steel with Excellent Welding and Low-Temperature Performance and Its Manufacturing Method". The strength level of the steel plate is even lower, only reaching 245 grade, and the maximum wall thickness is only 50mm. This invention also does not involve the study of drop weight performance.

[0007] Chinese Patent CN118996275A discloses "A Steel for Thick-Walled High Acid-Resistant Pipeline and Its Production Method". Although the drop hammer performance is mentioned, a large amount of precious alloys are added in this invention patent, and the manufacturing cost is quite high, which is not suitable for industrial production. For example, Ni: 0.50% - 0.60%, Cu: 0.10 - 0.30%, etc.

[0008] In addition, Chinese Patents CN118086780A, CN117987732A, CN118028582A, etc. all belong to the category of acid-resistant pipeline line pipes and are not suitable for making acid-resistant pipe fittings steel. After the steel plate for acid-resistant pipe fittings is made into a pipe, heat treatment is still required, and these patents do not mention the heat treatment process for pipe fittings. Summary of the Invention

[0009] The present invention aims to provide a production method for heat treatment type thick specification acid-resistant pipe fitting steel X65MS to solve the bottleneck of difficult drop hammer performance of thick-walled pipe fitting steel and the problem of softening after heat treatment of pipe fittings, and obtain high-strength thick-walled acid-resistant pipe fitting steel with guaranteed drop hammer performance. After the steel plate is made into a pipe, the heat treatment performance can reach a yield strength of 470 - 570 MPa, a tensile strength of 600 - 660 MPa, a yield ratio ≤ 0.85, an impact value of 400 - 500 J at -40 °C, a drop hammer of 85 - 92% at -40 °C; HIC test: soaked in NACE solution for 96 hours, with CLR, CTR, and CSR all being 0; under a constant load of 90% of the nominal yield in four-point bending and soaked for 720 hours, no cracks appear on the surface of the specimen.

[0010] The implementation solution of the present invention: The mass percentage of the chemical composition of the steel is C = 0.04% - 0.05%, Si = 0.05% - 0.10%, Mn = 1.10% - 1.25%, P ≤ 0.012%, S ≤ 0.0008%, Nb = 0.025% - 0.035%, Ti = 0.010% - 0.020%, Cr = 0.45 - 0.50%, Ni = 0.13 - 0.16%, Cu = 0.20 - 0.25%, Mo = 0.05 - 0.08%, B ≤ 0.0005%, and the balance is Fe and inevitable impurities; the key process steps include: (1) Continuous casting billet: The continuous casting billet specification is 420 - 450 × 2400 - 2500 mm, and the hot pickling macrostructure meets Grade 1.0 of the Mansfield standard; (2) Heating: The furnace temperature is controlled at 1000 - 1120 °C, the holding time of the steel billet in the furnace is 400 - 450 min, and the tapping core temperature is 1020 - 1100 °C; (3) Rolling: Three-stage controlled rolling, with a reduction of 40 - 50 mm in the last three passes of rough rolling; the intermediate billet is 150 - 180 mm, and after rolling the intermediate billet, it is rapidly water-cooled for 100 - 120 s, and the temperature difference in the thickness direction of the intermediate billet is ≥120 °C; the starting rolling temperature of finish rolling is 780 - 800 °C, the starting cooling temperature is 700 - 730 °C, and the final cooling temperature is 350 - 420 °C; (4) Heat treatment: Subcritical quenching at 820 - 830 °C, with a holding time of 180 - 220 min, and low-temperature tempering at 400 - 420 °C, with a holding time of 200 - 250 min.

[0011] After the steel plate produced by the above technical solution is made into a pipe, its heat treatment performance can reach a yield strength of 470 - 570 MPa, a tensile strength of 600 - 660 MPa, a yield ratio of ≤0.85, an impact value of 400 - 500 J at -40 °C, and a drop weight of 85 - 92% at -40 °C; HIC test: Immersed in NACE solution for 96 hours, with CLR, CTR, and CSR all being 0; Four-point bending with a constant load of 90% of the nominal yield for 720 hours, and no cracks appear on the surface of the specimen.

[0012] The beneficial effects of the present invention are as follows: 1) Adopting a microalloy composition system of low carbon + low manganese + high chromium, combined with a production process of "ultra-low temperature burning of large-section steel + temperature gradient rolling + subcritical quenching", it breaks through the conventional steel burning process of acid-resistant pipeline steel, avoids the growth of the original austenite grains in the continuous casting billet, and the large-section continuous casting billet ensures that the reduction per pass in rough rolling reaches 40 mm, which can effectively increase the reduction ratio and further refine the grains. At the same time, the intermediate billet is water-cooled to form a temperature difference in the thickness direction, increasing the deformation of the wall thickness and the core during finish rolling, improving the grain size of the core, and being very beneficial to improving the low-temperature drop weight performance of thick-walled pipe fittings. 2) Adopting subcritical quenching + low-temperature tempering to make up for the tissue difference in the thickness direction caused by temperature gradient rolling. At the same time, subcritical quenching can promote the formation of ferrite, and ferrite belongs to a soft-phase tissue, further improving the low-temperature drop weight performance of the steel plate. Low-temperature tempering can promote the decomposition of M / A and eliminate residual stress, facilitating subsequent steel plate forming and pipe making. Description of the Drawings

[0013] Figure 1 It is the metallographic structure diagram of the steel produced in Example 1. Detailed Embodiments

[0014] The following further illustrates the content of the present invention in combination with embodiments.

[0015] Example 1: Production of 56mm X65MS Steel The chemical composition of the steel in weight percentage is C = 0.04%, Si = 0.06%, Mn = 1.15%, P = 0.008%, S = 0.0006%, Nb = 0.030%, Ti = 0.012%, Cr = 0.46%, Ni = 0.15%, Cu = 0.22%, Mo = 0.06%, B = 0.0003%, and the balance is Fe and inevitable impurities; the key production process steps: (1) Continuous casting billet: 420×2400mm, hot pickling, macrostructure grade 1.0 according to the Mansfield standard; (2) Heating: The furnace temperature is controlled at 1080°C, the residence time of the steel billet in the furnace is 420 min, and the temperature at the center of the steel billet when discharged is 1090°C; (3) Rolling: Three-stage controlled rolling, the reduction in the last three passes of rough rolling is 42 mm; the intermediate billet is 160 mm, and the intermediate billet is rapidly water-cooled for 108 s after rolling, with a temperature difference of 125°C in the thickness direction of the intermediate billet; the starting rolling temperature of finish rolling is 790°C, the starting cooling temperature is 715°C, and the final cooling temperature is 380°C; (4) Heat treatment: Subcritical quenching at 822°C, holding time of 192 min, low-temperature tempering at 410°C, holding time of 230 min.

[0016] The mechanical properties of the steel plate are shown in Table 1.

[0017] Example 2: Production of 60mm X65MS steel The chemical composition of the steel in mass percentage is C = 0.04%, Si = 0.08%, Mn = 1.12%, P = 0.008%, S = 0.0006%, Nb = 0.032%, Ti = 0.018%, Cr = 0.48%, Ni = 0.15%, Cu = 0.23%, Mo = 0.07%, B = 0.0004%, and the balance is Fe and inevitable impurities. The key process steps: (1) Continuous casting billet: 450×2500mm, hot pickling, macrostructure grade 1.0 according to the Mansfield standard; (2) Heating: The furnace temperature is controlled at 1050°C, the residence time of the steel billet in the furnace is 446 min, and the temperature at the center of the steel billet when discharged is 1060°C; (3) Rolling: Three-stage controlled rolling, the reduction in the last three passes of rough rolling is 46 mm; the intermediate billet is 170 mm, and the intermediate billet is rapidly water-cooled for 118 s after rolling, with a temperature difference of 125°C in the thickness direction of the intermediate billet; the starting rolling temperature of finish rolling is 782°C, the starting cooling temperature is 712°C, and the final cooling temperature is 366°C; (4) Heat treatment: Subcritical quenching at 822°C, holding time of 195 min, low-temperature tempering at 418°C, holding time of 236 min.

[0018] Table 1 Mechanical property results of X65MS steel pipe in Example .

Claims

1. A production method of heat-treatment type thick-specification acid-resistant pipe fitting steel X65MS, characterized in that: The chemical composition of the steel is by mass percentage: C = 0.04% - 0.05%, Si = 0.05% - 0.10%, Mn = 1.10% - 1.25%, P ≤ 0.012%, S ≤ 0.0008%, Nb = 0.025% - 0.035%, Ti = 0.010% - 0.020%, Cr = 0.45 - 0.50%, Ni = 0.13 - 0.16%, Cu = 0.20 - 0.25%, Mo = 0.05 - 0.08%, B ≤ 0.0005%, and the balance is Fe and unavoidable impurities; The key process steps include: (1) Continuous casting billet: The continuous casting billet has a specification of 420 - 450 × 2400 - 2500 mm, and the hot pickling macrostructure is Grade 1.0 according to the Mansfield standard; (2) Heating: The furnace temperature is controlled at 1000 - 1120 °C, the residence time of the steel billet in the furnace is 400 - 450 min, and the tapping core temperature is 1020 - 1100 °C; (3) Rolling: Three-stage controlled rolling, the reduction in the last three passes of rough rolling is 40 - 50 mm; the intermediate billet is 150 - 180 mm, and the intermediate billet is rapidly water-cooled for 100 - 120 s after rolling, and the temperature difference in the thickness direction of the intermediate billet is ≥ 120 °C; the finishing rolling start temperature is 780 - 800 °C, the start cooling temperature is 700 - 730 °C, and the final cooling temperature is 350 - 420 °C; (4) Heat treatment: Subcritical quenching at 820 - 830 °C, holding time of 180 - 220 min, low-temperature tempering at 400 - 420 °C, holding time of 200 - 250 min; After the steel plate is made into a pipe and heat-treated, the yield strength is 470 - 570 MPa, the tensile strength is 600 - 660 MPa, the yield ratio is ≤ 0.85, the impact value at -40 °C is 400 - 500 J, and the drop weight at -40 °C is 85 - 92%; for the HIC test, it is soaked in the NACE solution for 96 hours, and the CLR, CTR, and CSR are all 0; for the four-point bending constant load nominal yield of 90% soaked for 720 hours, no cracks appear on the surface of the specimen.

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