Hot rolling method for producing low-cost low-temperature pipeline steel L360M

Abstract

The invention discloses a hot rolling method for producing low-cost low-temperature pipeline steel L360M, which comprises the following steps: 1) selecting the pipeline steel L360M, smelting and pouring to prepare a plate blank, heating to 1190-1220 DEG C, carrying out cold charging in-furnace time of 165-270 min, carrying out hot charging in-furnace time of 160-270 min, carrying out soaking temperature of 1170-1210 DEG C, carrying out cold charging soaking time of 25-50 min, carrying out hot charging for 20-45 min, and then carrying out rough rolling at 980 + / -10 DEG C; (2) the finish rolling temperature ranges from 835 DEG C to 865 DEG C, and the accumulated rolling reduction of finish rolling ranges from 80% to 85%; and (3) the plate blank obtained after finish rolling is cooled to the coiling temperature, coiling is conducted, and the coiling temperature is 600 + / -15 DEG C. The invention aims to stably produce the low-cost and low-temperature service pipeline steel L360M and improve the quality and competitiveness of the product.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a hot rolling method for producing low-cost low-temperature pipeline steel L360M. Background Art

[0002] At present, many oil and gas fields have been discovered in remote areas and areas with harsh geographical conditions in the world, and refineries are also built far away from central cities. As a result, the length of oil and gas pipelines is getting longer and longer, and the construction sites are mostly in various harsh environments. At the same time, affected by global production capacity and the development of marine and extremely low oil and gas fields, higher requirements are placed on pipeline construction. Only low-cost and high-quality products can maintain profitability in the market. Therefore, under the premise of meeting standard performance, all companies have begun to take the path of green, low-carbon and low-cost.

[0003] The drop weight tear test (DWTT) is a key indicator for testing the low-temperature dynamic tear resistance of pipeline steel. Meeting this indicator is an important technical difficulty in manufacturing low-temperature service pipeline steel pipes. Due to the uneven distribution of oil and natural gas in the world, a considerable portion of oil and gas resources are distributed in high-altitude cold areas, where the climate is cold and the environment is harsh, and some are covered with permafrost and ice and snow all year round, such as Siberia in Russia and northern my country. For the service conditions of pipeline steel in this environment, the stability of the low-temperature performance of pipeline steel will be the key means to solve this problem.

[0004] After searching, a document with Chinese patent application number CN 103952638 B discloses a "Pipeline Steel with Excellent Low-Toughness", which is applicable to: C: 0.03-0.06%, Si: 0.15-0.25%, Mn: 0.55-0.72%, Ni: 0.55-0.80%, Cr: 0.15-0.30%, Cu: 0.05-0.12%, Mg: 0.02-0.05%, Ti: 0.02-0.05%, Ca: 0.001-0.003%, Mo: 0.005-0.02%, Al s: 0.025-0.055%, N≤0.02%, P≤0.012%, S≤0.005%, and the balance is Fe and unavoidable impurities; and wherein: Mg+Ni / 10+5Mo-Cr / 5-C-2N≥0.02. The pipeline steel contains appropriate amounts of Mg, Ni and Mo, which not only ensures high tensile strength, but also good low-temperature toughness. By controlling the contents of C, N and Cr within an appropriate range, the pipeline steel can be ensured to have excellent cold quenching resistance. The disadvantage of this document is that although the performance is good, the Mo element exists, and its market price is high, increasing the cost by 500-1000 yuan per ton, so the relative cost is higher than that of the present invention.

[0005] After searching, the document with Chinese patent application number CN 108467993 B, "An ultra-wide high-toughness hot-rolled thick plate for low-temperature pipelines and its production method", is suitable for C: 0.030% ~ 0.055%, Si: 0.16% ~ 0.30%, Mn: 1.45% ~

[0006] 1.70%, Nb: 0.04% ~ 0.07%, Ti: 0.012% ~ 0.025%, Cr: 0.20% ~ 0.40%, Mo≤0.14%, Ni≤0.20%, Cu≤0.15%, Al≤0.030%, P≤0.010%, S≤0.0015%, O: 0.0005% ~ 0.0020%, N: 0.001% ~ 0.004%, Ca: 0.0010% ~ 0.0045%, Ca / S ≥ 1.8, (Mo + Ni + Cr + Cu): 0.30% ~ 0.60%, the rest is Fe and unavoidable impurities. The shortcomings of this document are that the transverse yield strength is 485-540MPa, the transverse tensile strength is 610-680MPa, the transverse elongation A 50mm≥43%, and the -20℃ transverse DWTT shear area is ≥85%. The overall performance is excellent, but its low-temperature drop hammer temperature only reaches -20℃. The present invention meets the standards in terms of overall performance with a large margin, and the low-temperature drop hammer temperature is -35℃.

[0007] After searching: the document with Chinese patent application number CN 110616383 B discloses a "Pipeline Steel with Excellent Toughness for Extremely Low Temperature Environment of -45℃ and Its Manufacturing Method", which is applicable to C: 0.030~0.060%, Si: 0.10~0.30%, Mn: 1.30~1.60%, P≤0.0100%, S≤0.0015%, Ni: 0.40~0.55%, Cr: 0.05~0.20%, Nb: 0.050~0.075%, T i: 0.008-0.020%, Ca: 0.0010-0.0040%, Al: 0.010-0.050%, B≤0.0005%, N: 0.0010-0.0060%, O≤0.0050%, the rest is Fe and unavoidable impurities; the yield strength of pipeline steel is ≥450MPa, the tensile strength is ≥535MPa, and the elongation is ≥18%; the Charpy impact energy AKV at -45℃ is ≥250J; the shear area rate of DWTT fracture at -45℃ is ≥85%. The shortcoming of this document is that although the comprehensive performance is excellent and the low-temperature drop hammer performance is good, the relative manufacturing cost is increased, which is not conducive to long-term development. Summary of the invention

[0008] The purpose of the present invention is to provide a hot rolling method for producing low-cost low-temperature pipeline steel L360M, so as to meet the -30°C impact performance and -35°C ultra-low temperature drop hammer performance while improving the comprehensive performance and service performance of the finished strip steel.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] The present invention provides a hot rolling method for producing low-cost low-temperature pipeline steel L360M, comprising the following steps:

[0011] 1) Select pipeline steel L360M, smelt and cast it into slab, heat it to 1190-1220℃, cold charging in the furnace for 165-270min, hot charging in the furnace for 160-270min, soaking temperature is 1170-1210℃, cold charging soaking time is 25-50min, hot charging is 20-45min, and then rough rolling is carried out at 980±10℃;

[0012] 2) The finishing rolling temperature range is 835-865℃, the cumulative reduction of finishing rolling is 80-85%; the final rolling temperature of finishing rolling is guaranteed to be 850±15℃

[0013] 3) After finish rolling, the slab is cooled to the coiling temperature for coiling, and the coiling temperature is 600±15℃.

[0014] Furthermore, the composition of the adopted pipeline steel L360M is as follows by weight percentage: C: 0.06-0.08%, Si: 0.10-0.20%, Mn: 1.20-1.35%, Nb: 0.020-0.030%, Ti 0.010-0.020%, the balance being Fe and other inevitable impurities, wherein P≤0.013%, S≤0.005%, and O≤0.005%.

[0015] Furthermore, the finishing rolling start temperature is 1160-1200°C.

[0016] Furthermore, the coiling temperature is 600°C.

[0017] Furthermore, the intermediate billet thickness is 40-45 mm, and the finished product thickness is 7.9 mm.

[0018] Furthermore, the temperature is lowered to the coiling temperature by laminar cooling.

[0019] Furthermore, the method improves the comprehensive performance and service performance of the finished strip steel while meeting the -30°C impact performance and -35°C ultra-low temperature drop hammer performance.

[0020] Furthermore, the continuous casting billet drawing speed is 1.0-1.2 m / min, and the continuous casting slab with a billet thickness of 230 mm is obtained.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are:

[0022] Based on the continuous casting and rolling process, the present invention creatively adjusts the alloy composition of pipeline steel L360M at a microscopic level, and utilizes Nb and Ti elements to inhibit the growth of austenite grains and promote nucleation during austenite transformation to refine grains, control the thickness core structure, and improve the uniformity of the structure. According to the distribution of structures at different positions in the steel, the consistency and stability of the granular bainite structure and performance of low-temperature pipeline steel are evaluated, and the pipeline steel L360M for low-temperature service can be stably produced, thereby improving the quality and competitiveness of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 This is the metallographic microstructure diagram of the slab at 1 / 2.

[0025] Figure 2 This is the metallographic microstructure diagram of the slab at 1 / 4. DETAILED DESCRIPTION

[0026] The present invention is described in more detail below with reference to examples. These examples are merely descriptions of the best mode for carrying out the present invention and are not intended to limit the scope of the present invention in any way.

[0027] The following example 1 hot rolled ingot has a thickness of 230 mm, after R1 rough rolling and R2 rough rolling, the thickness is 38-50 mm, and after finishing rolling F1-F7, the thickness is 7.9 mm. The microstructure metallographic diagram of the finished product at 7.9 mm1 / 2 is as follows Figure 1 As shown, the microstructure metallographic diagram at 1 / 4 is as follows Figure 2 As shown, the metallographic structure diagram shows that the granular bainite structure at different positions is uniform and fine, with good uniformity and consistency. The actual production performance is shown in Table 1, and the results show that the performance is relatively stable.

[0028] Example 1

[0029] The composition of L360M used in the embodiment of the present invention is C: 0.06-0.08%, Si: 0.10-0.20%, Mn: 1.20-1.35%, Nb: 0.020-0.030%, Ti 0.010-0.020%, and the balance is Fe and other inevitable impurities, wherein P≤0.013%, S≤0.005%, and O≤0.005%.

[0030] In the embodiment of the present invention, the heating temperature is 1190-1220°C, the cold charging time in the furnace is 165-270min, and the hot charging time in the furnace is 160-270min. The soaking temperature is 1170-1210°C, the cold charging soaking time is 25-50min, and the hot charging time is 20-45min.

[0031] The starting rolling temperature in the embodiment of the present invention is 1160-1200° C., and the cumulative reduction of the rough rolling is 80-85%.

[0032] In the embodiment of the present invention, the cumulative reduction of the finishing rolling is 80-85%, and the final rolling temperature of the finishing rolling is ensured to be 850±15°C.

[0033] The coiling temperature in the embodiment of the present invention is 600±15°C.

[0034] In the embodiment of the present invention, the thickness of the intermediate blank is 40-45 mm, and the thickness of the finished product is 7.9 mm.

[0035] In the embodiment of the present invention, the laminar cooling method is used to cool the temperature to the coiling temperature.

[0036] The performance results in the embodiments of the present invention fully meet the standard requirements, and the drop hammer performance at -35°C is stable.

[0037] Table 1L360M performance distribution

[0038]

[0039] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A hot rolling method for producing low-cost low-temperature pipeline steel L360M, characterized in that: The following steps are involved: 1) Select pipeline steel L360M, smelt and cast it into slab, heat it to 1190-1220℃, cold charging in the furnace for 165-270min, hot charging in the furnace for 160-270min, soaking temperature is 1170-1210℃, cold charging soaking time is 25-50min, hot charging is 20-45min, and then rough rolling is carried out at 980±10℃; 2) The finishing rolling temperature range is 835-865℃, the cumulative reduction of finishing rolling is 80-85%; the final rolling temperature of finishing rolling is guaranteed to be 850±15℃ 3) After finish rolling, the slab is cooled to the coiling temperature for coiling, and the coiling temperature is 600±15℃.

2. The hot rolling method for producing low-cost low-temperature pipeline steel L360M according to claim 1, characterized in that: The composition of the pipeline steel L360M used is as follows by weight: C: 0.06-0.08%, Si: 0.10-0.20%, Mn: 1.20-1.35%, Nb: 0.020-0.030%, Ti 0.010-0.020%, and the balance is Fe and other inevitable impurities, among which P≤0.013%, S≤0.005%, and O≤0.005%.

3. The hot rolling method for producing low-cost low-temperature pipeline steel L360M according to claim 1, characterized in that: The finishing rolling start temperature is 1160-1200℃.

4. The hot rolling method for producing low-cost low-temperature pipeline steel L360M according to claim 1, characterized in that: The coiling temperature is 600°C.

5. The hot rolling method for producing low-cost low-temperature pipeline steel L360M according to claim 1, characterized in that: The intermediate billet thickness is 40-45mm and the finished product thickness is 7.9mm.

6. The hot rolling method for producing low-cost low-temperature pipeline steel L360M according to claim 1, characterized in that: The laminar cooling method is used to cool down to the coiling temperature.

7. The hot rolling method for producing low-cost low-temperature pipeline steel L360M according to claim 1, characterized in that: This method not only meets the -30°C impact performance and -35°C ultra-low temperature drop hammer performance, but also improves the comprehensive performance and service performance of the finished strip steel.

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