A method for manufacturing S32760 super duplex stainless steel seamless pipe

Abstract

The invention discloses a manufacturing method of S32760 super duplex stainless steel seamless pipe, which comprises the following steps: (i) peeling, cutting and core setting corresponding round steel, and punching the round steel by a puncher; the punching temperature is 1150-1200°C, the heating time is 4-6 hours, and the insulation time is 10-15 minutes; (ii) the rough pipe obtained in step (i) is pickled to remove the oxide scale; (iii) the steel pipe obtained in step (ii) is cold rolled in two passes of a deformation process, and then heat-treated to the finished product specification; (iv) the finished pipe obtained in step (iii) is visually inspected, penetrated, dimensionally inspected, cleaned, sprayed and finished, and finally packaged and stored; the method solves the problems of poor quality of finished products and low yield rate caused by poor hot processing plasticity and large cold processing deformation resistance of S32760 by strictly limiting process optimization; the products produced by the method have high dimensional accuracy, good surface quality, stable organizational properties, strong practicality, and are conducive to batch production.

Description

Technical Field

[0001] The invention relates to the manufacture of a stainless steel seamless pipe, in particular to a method for manufacturing an S32760 super duplex stainless steel seamless pipe, and belongs to the technical field of material processing. Background Art

[0002] S32760 is a super duplex stainless steel in the American standard. From the composition point of view, its Cr, Mo and N content are higher than ordinary duplex steel, and a small amount of W and Cu elements are added on the basis of ordinary duplex steel, so its pitting corrosion equivalent PREN is also higher, generally 40-45. Compared with ordinary duplex steel, S32760 super duplex steel has better resistance to pitting corrosion, crevice corrosion and intergranular corrosion, and is mainly used in fields with severe corrosive environments such as petroleum, natural gas, chemical processing, and nuclear energy.

[0003] Compared with austenitic stainless steel, UNS S32760 super duplex steel seamless pipe has poor hot working plasticity and high cold working deformation resistance. Based on this, developing a production process for S32760 super duplex steel seamless pipe that can overcome the above defects and developing S32760 finished pipe that can meet the technical requirements in terms of chemical composition, mechanical properties, metallographic structure, corrosion resistance, etc. has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for manufacturing an S32760 super duplex stainless steel seamless pipe. The method solves the problems of poor finished product quality and low yield rate caused by poor hot processing plasticity and high cold processing deformation resistance of S32760 by strictly limiting process optimization. The products produced by the method have high dimensional accuracy, good surface quality, stable organizational properties, strong practicality, and are conducive to batch production.

[0005] In order to solve the above technical problems, the present invention provides a method for manufacturing a S32760 super duplex stainless steel seamless pipe, which specifically comprises the following steps:

[0006] (1) peeling, cutting and core setting the corresponding round steel, and punching the round steel with a punching machine;

[0007] The perforation temperature is 1150-1200℃, the heating time is 4-6 hours, and the insulation time is 10-15min;

[0008] (ii) pickling the capillary tube obtained in step (i) to remove the oxide scale;

[0009] (iii) cold rolling the steel tube obtained in step (ii) by a deformation process, and then heat treating it to the finished product specifications, specifically:

[0010] The steel pipe is cold rolled twice on the cold rolling unit. After each cold rolling, it is degreased, heat treated, straightened, cut, pickled, and polished. Then, it is ultrasonically, hydraulically, sampled, physically and chemically tested, and finally cut to obtain the finished pipe.

[0011] During rolling, the cold rolling deformation is 40-50%, the elongation coefficient is less than 2, the rolling speed is controlled at 60-110 times / min, the feed amount is 1-3mm / time, and the Q value is greater than 1.2;

[0012] After the first cold rolling, the outer diameter deviation is controlled within ±0.25mm, and the wall thickness deviation is controlled within ±0.25mm;

[0013] After the second cold rolling, the outer diameter deviation is controlled within ±0.55mm, and the wall thickness deviation is controlled within ±0.30mm;

[0014] During heat treatment, the heat treatment temperature is controlled to be 1080-1120°C, and the insulation time is wall thickness × 1-3min;

[0015] (iv) subjecting the finished pipes obtained in step (iii) to visual inspection, penetration, dimensional inspection, cleaning, spray marking and finishing processes, and finally packaging and warehousing.

[0016] The technical solution further defined in the present invention is:

[0017] Furthermore, in the manufacturing method of the aforementioned S32760 super duplex stainless steel seamless pipe, in step (i), the corresponding round steel is peeled, and the single-side peeling is greater than 1.5 mm. The steel billet after peeling is cut into rods, and a stepped centering hole of φ (24 ± 2) mm is drilled at one end of the rod. The rod after centering is then sent to an inclined bottom furnace for heating and perforation. After the perforation is completed, the pipe is rolled into a cooling pool for cooling, and then inspected on an inspection table.

[0018] In the aforementioned method for manufacturing the S32760 super duplex stainless steel seamless pipe, molybdenum plug perforation is used for perforation.

[0019] In the aforementioned method for manufacturing S32760 super duplex stainless steel seamless pipe, during the heat treatment in step (iii), the steel pipes are placed in a roller hearth furnace, and the atmosphere in the furnace is oxidizing.

[0020] In the manufacturing method of the aforementioned S32760 super duplex stainless steel seamless pipe, the room temperature tensile properties of the seamless pipe are: the yield strength is controlled at 621-724 MPa, the tensile strength is ≥793 MPa, the elongation after fracture is ≥20%, and the HRC hardness is ≤30.

[0021] In the aforementioned method for manufacturing the S32760 super duplex stainless steel seamless pipe, the austenite-ferrite structure of the manufactured seamless pipe is controlled to have a ferrite content of 35-55%.

[0022] The beneficial effects of the present invention are:

[0023] The method of the present invention regulates the punching machine parameters, punching temperature, intermediate product deformation process, steel pipe process heat treatment, finished product deformation process, and finished product heat treatment; and solves the problems of poor finished product quality and low yield rate caused by poor hot processing plasticity and high cold processing deformation resistance of S32760.

[0024] The room temperature tensile properties of the seamless pipe prepared by the method of the present invention are as follows: the yield strength is controlled at 621-724 MPa, the tensile strength is ≥793 MPa, the elongation after fracture is ≥20%, and the HRC hardness is ≤30. The product produced by the method has high dimensional accuracy, good surface quality, stable organizational properties, strong practicality, and is conducive to batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a cold working flow chart of the manufacturing method of S32760 super duplex stainless steel seamless pipe of the present invention;

[0026] Figure 2 This is a harmful phase precipitation diagram after sampling and analysis of the capillary tube after perforation;

[0027] Figure 3 This is the ferrite content diagram after sampling and analysis of the perforated wool pipe;

[0028] Figure 4 The microstructure morphology of dual-phase steel material after cold rolling with different deformation amounts;

[0029] Figure 5 This is a 100-fold metallographic structure diagram of a finished S32760 tube manufactured using the manufacturing method of the S32760 super duplex stainless steel seamless tube of the present invention. DETAILED DESCRIPTION

[0030] Example 1

[0031] The present embodiment provides a method for manufacturing a S32760 super duplex stainless steel seamless pipe, which specifically includes the following steps:

[0032] (I) Peel, cut and core the Φ130mm round steel and pierce the round steel with a punching machine, specifically:

[0033] The Φ130mm round steel is peeled, with a single-side peeling of 2mm. The peeled billet is cut into bars, and a φ(24±2)mm stepped centering hole is drilled at one end of the bar. The bar after centering is then sent to an inclined bottom furnace for heating and perforation. The perforation temperature is 1170℃, the heating time is 4 hours, and the insulation time is 10-15min. After the perforation is completed, the pipe is rolled into a cooling pool for cooling, and then inspected on the inspection table;

[0034] The whole process of perforation is performed by using a molybdenum plug. The perforator adopts different setting parameters according to the specifications of the round steel and the finished product. The setting parameters of the perforator in this embodiment are shown in Table 1 below:

[0035] Table 1 Punching machine setting parameters

[0036]

[0037] When the perforation temperature in this embodiment is 1170°C, the inner and outer surfaces of a batch of S32760 raw tubes are good, without obvious crack defects, slight guide plate marks on the outer surface, local steel adhesion, and slight head marks on the inner wall;

[0038] After perforation, the capillary tubes were sampled and analyzed. Figure 2-3 As shown, Figure 2 For the harmful phase precipitation, Figure 3 The content of ferrite. It can be seen from the figure that there is no obvious inclusion and precipitation in the metallographic structure. The mass fraction of ferrite is 50%, and the average hardness of the capillary tube is about 28HRC.

[0039] (ii) pickling the capillary tube obtained in step (i) to remove the oxide scale;

[0040] (iii) cold rolling the steel tube obtained in step (ii) by a specific deformation process and heat treating it under a specific system to the finished product specifications, the process is as follows: Figure 1 As shown, specifically:

[0041] After perforation, the qualified S32760 rough pipe with a size of φ128×14mm is rolled in two passes on the LG110 cold rolling unit. The sizes of the two rolls are φ108×9mm and φ88.9×5.49mm respectively. After each cold rolling pass, degreasing, heat treatment, straightening, pipe cutting, pickling, grinding are carried out, and then ultrasonic, water pressure, sampling, physical and chemical inspection, and final cutting are carried out to obtain the finished pipe;

[0042] The yield strength of S32760 material after cold working is higher than that of ordinary austenitic stainless steel, and its resistance to cold working deformation is large, and its elongation coefficient is also smaller than that of ordinary austenitic steel; therefore, we need to reasonably distribute the deformation when using two passes of cold rolling. This embodiment strictly selects cold rolling process parameters with an elongation coefficient of less than 2 and a deformation of 40-50%, and selects a reasonable rolling speed of 60-110 times / min and a relatively small feed amount of 1-3mm / time to ensure the quality of its inner and outer surfaces. The uniformity of the structure in the wall thickness direction is ensured by Q value>1.2, thereby improving the dimensional accuracy and improving the inner wall quality. The specific cold rolling parameters are shown in Table 2 below, and the technical requirements for dimensional accuracy and actual dimensions are shown in Table 3. The actual measured dimensions meet the technical requirements.

[0043] Table 2 Cold rolling parameters

[0044]

[0045] Table 3 Technical requirements dimensional accuracy and actual measured dimensions

[0046]

[0047] The heat treatment of S32760φ108×9mm intermediate quality pipe and φ88.9×5.49mm finished pipe are both carried out in a roller hearth furnace, and the atmosphere in the furnace is oxidizing (there are three types of steel pipe heat treatment, namely reducing atmosphere, oxidizing atmosphere and vacuum atmosphere. The present invention adopts oxidizing atmosphere heat treatment, and oxide scale will be generated on the surface. After pickling, a passivation film will be formed on the surface to avoid surface corrosion). The heating temperature of the φ108×9mm intermediate quality pipe is 1100℃, the holding time is 20min, and it is quickly cooled. The heating temperature of the φ88.9×5.49mm finished pipe is 1080℃, the holding time is 8min, and it is quickly cooled.

[0048] Figure 4 The transmission electron microscope (TEM) photos of the dual-phase steel tube after cold rolling with different deformation amounts (5%, 10%, 15%, 20%, 30%, 40%, 60%, 80%) are shown. It can be seen that with the increase of deformation amount, when the deformation amount reaches more than 15%, obvious slip bands and twin bands appear inside the deformed grains, and have a certain directionality; when the deformation amount exceeds 40%, the grains are fully "crushed", and high-density dislocations appear near the grain boundaries, and as the deformation increases further, the dislocation density increases further. The formation of these high-density dislocations causes serious lattice distortion of the grains, which not only accumulates a large amount of internal energy inside the grains, but also sharply increases the strength and hardness of the material, that is, the so-called "cold work hardening" is produced; it can be seen that the deformation amount of 40-50% of the present invention can not only fully crush the grains, but also prevent the steel pipe from being too cold-work hardened, resulting in poor processing plasticity.

[0049] On the basis of the deformation process, heat treatment is the main factor that determines the material structure and performance. The selection of S32760 heat treatment process must be based on ensuring its metallographic two-phase ratio and mechanical properties. In this embodiment, the heat treatment temperature of the φ88.9×5.49mm finished pipe is strictly controlled to be 1080~1120℃, and the holding time is the wall thickness multiplied by 1~3 (min). The room temperature performance, high temperature performance, corrosion performance, two-phase structure ratio, etc. of the obtained seamless pipe all meet the technical requirements, as shown in Table 4-5 below;

[0050] Test method: ASTM A370-20:

[0051] Table 4 Tensile test results

[0052]

[0053] Test method: ASTM E18-20:

[0054] Table 5 Hardness test results

[0055]

[0056] Test method: ASTM E407-07(2015)εl ASTM E562-19εl;

[0057] Test process: After grinding and photocorrosion, the sample was tested for ferrite area percentage in 10 viewing fields under a metallographic microscope at 400x according to ASTM E562-19εl. The original results and statistical analysis results of ferrite content are shown in 6-7 below, and the ferrite morphology is shown in Figure 3 As shown;

[0058] Table 6 Original results of ferrite content

[0059]

[0060] Table 7 Statistical analysis results of ferrite content Statistical analysis results of ferrite content

[0061]

[0062] Test method: ASTM E407-07(2015) εl

[0063] Test process: After grinding and polishing, the sample was examined for nitrides and carbonitrides under a metallographic microscope. After re-polishing and corrosion, the intergranular precipitation phase, intermetallic phase and σ phase were examined. The test results are shown in Table 8 below, and the metallographic photos are shown in Figure 5 ;

[0064] Table 8 Metallographic inspection results

[0065]

[0066] (iv) subjecting the finished pipes obtained in step (iii) to visual inspection, penetration, dimensional inspection, cleaning, spray marking and finishing processes, and finally packaging and warehousing.

[0067] In this embodiment, the room temperature tensile properties of the seamless pipe are as follows: the yield strength is controlled at 645 MPa, the tensile strength is controlled at 840 MPa, the elongation after fracture is 34%, and the average HRC hardness is 22.2.

[0068] The microstructure of the manufactured S32760 sample tube is an austenite-ferrite two-phase structure. The ferrite mass fraction measured by the ferrite meter is 50%, which meets the technical condition requirement of ferrite content of 35% to 55%. The harmful phase σ phase precipitation is 0.2%, which meets the technical condition requirement of ≤0.5%. The method of the present invention specifies the parameters of the piercing machine, the piercing temperature, the deformation process of the intermediate product, the heat treatment of the steel pipe process, the deformation process of the finished product, and the heat treatment of the finished product;

[0069] The method solves the problems of poor finished product quality and low yield rate caused by poor hot processing plasticity of S32760 and high cold processing deformation resistance. The products produced by this method have high dimensional accuracy, good surface quality, stable organizational properties, strong practicality, and are conducive to mass production.

[0070] The elongation of the finished product in mechanical properties reaches more than 30%, and the average HRC hardness is only 22.2, which proves that the S32760 seamless steel pipe produced by this process improves hot processing plasticity and reduces cold processing deformation resistance.

[0071] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for manufacturing a S32760 super duplex stainless steel seamless pipe, characterized in that: The specific steps include: (1) peeling, cutting and core setting of the corresponding round steel, and punching the round steel with a punching machine; The perforation temperature is 1150~1200℃, the heating time is 4-6 hours, and the insulation time is 10~15min; In the step (i), the corresponding round steel is peeled, and the single-side peeling is greater than 1.5 mm. The steel billet after peeling is cut into bars, and a stepped centering hole of φ (24±2) mm is drilled at one end of the bar. The bar after centering is then sent to an inclined bottom furnace for heating and perforation. After the perforation is completed, the pipe is rolled into a cooling pool for cooling, and then inspected on an inspection table; (ii) pickling the capillary tube obtained in step (i) to remove the oxide scale; (iii) cold rolling the steel tube obtained in step (ii) by deformation process, and then heat treating it to the finished product specifications, specifically: The steel pipe is cold rolled twice on the cold rolling unit. After each cold rolling, it is degreased, heat treated, straightened, cut, pickled, and polished. Then, it is ultrasonically, hydraulically, sampled, physically and chemically tested, and finally cut to obtain the finished pipe. During rolling, the cold rolling deformation is 40-50%, the elongation coefficient is less than 2, the rolling speed is controlled at 60-110 times / min, the feed amount is 1-3mm / time, and the Q value is greater than 1.2; After the first cold rolling, the outer diameter deviation is controlled within ±0.25mm, and the wall thickness deviation is controlled within ±0.25mm; After the second cold rolling, the outer diameter deviation is controlled within ±0.55mm, and the wall thickness deviation is controlled within ±0.30mm; During heat treatment, the heat treatment temperature is controlled to be 1080~1120℃, and the insulation time is wall thickness × 1~3min; (iv) The finished tubes obtained in step (iii) are subjected to visual inspection, penetration inspection, dimensional inspection, cleaning, labeling and finishing processes, and finally packaged and stored.

2. The method for manufacturing the S32760 super duplex stainless steel seamless pipe according to claim 1, characterized in that: The holes are punched with molybdenum punches.

3. The method for manufacturing the S32760 super duplex stainless steel seamless pipe according to claim 1, characterized in that: During the heat treatment in step (iii), the steel pipes are placed in a roller hearth furnace, and the atmosphere in the furnace is oxidizing.

4. The method for manufacturing the S32760 super duplex stainless steel seamless pipe according to claim 1, characterized in that: The room temperature tensile properties of the seamless pipe are: yield strength controlled at 621-724Mpa, tensile strength ≥793MPa, elongation after fracture ≥20%, and HRC hardness ≤30.

5. The method for manufacturing the S32760 super duplex stainless steel seamless pipe according to claim 1, characterized in that: The austenite-ferrite structure of the manufactured seamless pipe is controlled as follows: the ferrite content accounts for 35-55%.

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