Machining process of forged pipe type connecting piece capable of preventing welding cracks

Abstract

The invention discloses a machining process of a forged pipe type connecting piece capable of preventing welding cracks, which enables the forged pipe type connecting piece to adapt to welding under the welding working condition of rapid cooling and rapid heating, reduces the phenomenon of cracks after welding, and ensures the reliability of a pressure container in a tool state. The method is suitable for manufacturing a forged pipe type connecting piece made of a 12Cr2Mo1 material, and comprises the following steps that S1, after component control is conducted, base metal matching is completed, then strengthening refining is conducted through double refining and rare earth adding, high-purity molten steel is obtained, and then pouring is conducted to obtain a continuous casting blank; s2, forging machining is conducted, specifically, forging machining is conducted according to the structural drawing of the product, and a blank piece is obtained; s3, heat treatment after forging; and S4, the obtained finished product is discharged after being subjected to NB / T47013.3 I-level detection flaw detection and qualified, and therefore the postwelding crack generation rate is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of processing forged pipe connectors, in particular to a processing technology of forged pipe connectors that are resistant to welding cracks. Background Art

[0002] The main pressure vessels related to petrochemical industry and coal chemical industry include reactors, polymerization reactors, synthesis towers, conversion furnaces, gas generators, heat exchangers, coolers, condensers, and evaporators; these pressure vessels generally include forged pipe connectors, among which forged pipe connectors are tubular forging products with thin wall thickness, which need to meet the welding conditions of rapid cooling and heating. There should be no cracks after welding, otherwise it will cause leakage. Therefore, it is necessary to check whether there are cracks in the connections of forged pipe connectors around the whole set of pressure vessels. Due to the relatively special installation position of forged pipe connectors, X-ray flaw detection is required, and the workload is very large, so it is necessary to avoid post-weld cracks as much as possible, so the weld resistance of forged pipe connectors becomes an extremely important requirement.

[0003] However, the structures of existing forged pipe connectors are diverse, including forged pipe connectors welded on the outer shell, forged pipe connectors used for butt welding of two similar pipe connectors, forged reducer pipe connectors (the welding ends are upper and lower ports), forged small-size pipe connectors (the welding ends are upper and lower ports), so how to prepare various types of forged pipe connectors as weld-resistant connectors so that after welding is completed, the forged pipe connectors are not prone to cracks.

[0004] However, according to historical data from 2023 and 2024, existing forged pipe connectors will crack after welding, and the number of scrapped connectors accounts for about 10‰. They need to be replaced and re-welded, and then PT and RT inspections are required to pass.

[0005] Therefore, it is urgent to develop a processing technology for improving the welding resistance of forged pipe connectors, so as to further reduce the proportion of cracks in forged pipe connectors after welding. Summary of the invention

[0006] In view of the above problems, the present invention provides a processing technology for forged pipe connectors that are resistant to welding cracks, which enables the forged pipe connectors to adapt to welding under rapid cooling and heating welding conditions and reduces the occurrence of cracks after welding, thereby ensuring the reliability of the pressure vessel in the tooling state.

[0007] The processing technology of the forged pipe connector for preventing welding cracks is characterized in that it is suitable for manufacturing the forged pipe connector made of 12Cr2Mo1 material, and comprises the following steps:

[0008] S1. After controlling the composition, the base metal ratio is completed, and then double refining and adding rare earth are carried out for enhanced refining to obtain high-purity molten steel, and then continuous casting billets are obtained by casting;

[0009] S2. Forging processing is carried out, and a blank is obtained by forging according to the structural drawing of the product;

[0010] S3. Post-forging heat treatment;

[0011] S4. The obtained finished parts pass the I-level inspection and flaw detection of NB / T47013.3 and then leave the factory, thereby reducing the crack rate after welding.

[0012] Its further features are as follows:

[0013] In step S1, the base metal composition of the forged pipe fittings is pre-designed, and its component content ratio is as follows:

[0014] Carbon C: 0.10% - 0.15%, Silicon Si: ≤0.12%, Manganese Mn: 0.30% - 0.60%, Chromium Cr: 2.10% - 2.50%, Nickel Ni: ≤0.30%, Molybdenum Mo: 0.90% - 1.10%, Copper Cu: ≤0.20%, Phosphorus P: ≤0.010%, Sulfur S: ≤0.010%, Arsenic As: ≤0.015%, Tin Sn: ≤0.015%, Antimony Sb: ≤0.010%, Lead Pb: ≤0.010%, Bismuth Bi: ≤0.010%, Calcium Ca: ≤0.010%, Hydrogen H: ≤2ppm, Oxygen O: ≤25ppm, Nitrogen N: ≤90ppm, and the rest is Fe;

[0015] Compared with the existing 12Cr2Mo1 material, it reduces the content of P and S, limits the content of harmful elements As, Sn, Sb, Pb, and Bi, and limits the content of gas elements H, O, and N in the steel;

[0016] The double refining and adding rare earth for enhanced refining in step S1 includes the first refining and the second refining; during the first refining, refining is carried out according to the base metal composition ratio of the pre-designed forged pipe fittings; during the second refining, 20 - 50% of the slag above the molten steel is removed, the bottom blowing Ar flow rate of the ladle is 130 - 380 ML / Min, enter the VD station for air extraction, start timing when the vacuum degree is ≤70 Mpa, keep the time for 20 - 30 Min, the ultimate vacuum degree is ≤25 Mpa, break the vacuum, add mixed rare earth metals according to 0.0005 - 0.0010% of the molten steel weight, the blowing Ar flow rate is 100 - 200 ML / Min, keep for 5 - 10 min to obtain purified molten steel, and then enter the casting process;

[0017] The designed composition of the added mixed rare earth metals: mainly composed of lanthanum, cerium, praseodymium, and neodymium, the total rare earth content is greater than 95%, and the light rare earth with cerium greater than 48%;

[0018] According to the alloy content of the material and the final quality requirements, electroslag remelting (ESR) is selected to further improve the weldability of the material.

[0019] After adopting the present invention, through composition control, the P and S contents of the base material are reduced compared with the existing 12Cr2Mo1 material, the contents of harmful elements such as As, Sn, Sb, Pb, and Bi are restricted, and the contents of gas elements H, O, and N in the steel are restricted, thereby improving the resistance to phase transformation stress and thermal stress of the material under the welding conditions of rapid cooling and heating, and improving the weldability of the material; and after double refining and adding rare earth for intensive refining to obtain purified molten steel and then pouring, a material with weldability is further obtained. Then the material is forged and processed to obtain a blank, and the blank is subjected to post-forging heat treatment to obtain a finished product. After the finished product passes the Class I inspection and flaw detection in accordance with NB / T47013.3, it is shipped out, thereby reducing the crack rate after welding. Description of the Drawings

[0020] Figure 1 It is the product processing drawing of the forged pipe fittings in the specific embodiment of the present invention. Detailed Embodiments

[0021] The processing technology of the forged pipe fittings for preventing welding cracks is applicable to the production of forged pipe fittings made of 12Cr2Mo1 material, and it includes the following steps:

[0022] S1. After completing the base material ratio through composition control, double refining and adding rare earth for intensive refining are carried out to obtain high-purity molten steel, and then continuous casting billets are obtained by pouring;

[0023] The base material composition of the forged pipe fittings is pre-designed, and its composition content ratio is as follows:

[0024] Carbon C: 0.10% - 0.15%, Silicon Si: ≤0.12%, Manganese Mn: 0.30% - 0.60%, Chromium Cr: 2.10% - 2.50%, Nickel Ni: ≤0.30%, Molybdenum Mo: 0.90% - 1.10%, Copper Cu: ≤0.20%, Phosphorus P: ≤0.010%, Sulfur S: ≤0.010%, Arsenic As: ≤0.015%, Tin Sn: ≤0.015%, Antimony Sb: ≤0.010%, Lead Pb: ≤0.010%, Bismuth Bi: ≤0.010%, Calcium Ca: ≤0.010%, Hydrogen H: ≤2ppm, Oxygen O: ≤25ppm, Nitrogen N: ≤90ppm, and the rest is Fe;

[0025] Compared with the existing 12Cr2Mo1 material, its P and S contents are reduced, the contents of harmful elements such as As, Sn, Sb, Pb, and Bi are restricted, and the contents of gas elements H, O, and N in the steel are restricted;

[0026] The double refining and adding rare earth for strengthening refining in step S1 includes the first refining and the second refining; during the first refining, refining is carried out according to the base metal composition ratio of the forged pipe fittings designed in advance; during the second refining, 20-50% of the slag above the molten steel is removed, the bottom blowing Ar flow rate of the ladle is 130-380 ML / Min, enter the VD station for air extraction, start timing when the vacuum degree is ≤70 Mpa, keep the time for 20-30 Min, the ultimate vacuum degree is ≤25 Mpa, break the vacuum, add mixed rare earth metals according to 0.0005-0.0010% of the weight of the molten steel, the blowing Ar flow rate is 100-200 ML / Min, keep for 5-10 min to obtain purified molten steel, and then enter the casting process;

[0027] The composition of the designed mixed rare earth metals: mainly composed of lanthanum, cerium, praseodymium, and neodymium, the total rare earth content is greater than 95%, and the light rare earth with cerium greater than 48%;

[0028] According to the alloy content of the material and the final quality requirements, select to increase electroslag remelting (ESR) to further improve the weldability of the material;

[0029] S2. Carry out forging processing, and obtain a blank part through forging processing according to the structural drawing of the product;

[0030] S3. Post-forging heat treatment;

[0031] The obtained finished parts pass the I-level inspection and flaw detection of NB / T47013.3 and then leave the factory, thereby reducing the crack rate after welding.

[0032] The tensile properties of the obtained finished parts after the heat treatment state are shown in Table 1

[0033]

[0034] Table 1

[0035] Specific embodiment: When manufacturing the corresponding forged pipe fittings as Figure 1 it includes the following steps:

[0036] S1. After controlling the composition to complete the base metal ratio, then carry out double refining and adding rare earth for strengthening refining to obtain high-purity molten steel, and then cast to obtain a continuous casting billet;

[0037] The base metal composition of the forged pipe fittings is designed in advance, and its composition content ratio is as follows:

[0038] Carbon C: 0.11% - 0.15%, Silicon Si: ≤0.09%, Manganese Mn: 0.30% - 0.60%, Chromium Cr: 2.20% - 2.50%, Nickel Ni: ≤0.30%, Molybdenum Mo: 0.90% - 1.10%, Copper Cu: ≤0.15%, Phosphorus P: ≤0.008%, Sulfur S: ≤0.008%, Arsenic As: ≤0.015%, Tin Sn: ≤0.015%, Antimony Sb: ≤0.003%, Lead Pb: ≤0.010%, Bismuth Bi: ≤0.010%, Calcium Ca: ≤0.010%, Hydrogen H: ≤1.8ppm, Oxygen O: ≤20ppm, Nitrogen N: ≤80ppm, the rest is Fe;

[0039] Compared with the existing 12Cr2Mo1 material, it reduces the contents of P and S, limits the contents of harmful elements As, Sn, Sb, Pb, and Bi, and limits the contents of gaseous elements H, O, and N in the steel;

[0040] The double refining and adding rare earth for strengthening refining in step S1 includes the first refining and the second refining; during the first refining, refining is carried out according to the base metal composition ratio of the forged pipe fittings designed in advance; during the second refining, 20 - 25% of the slag above the molten steel is removed, the bottom blowing Ar flow rate of the ladle is 200 - 230 ML / Min, enter the VD station for air extraction, start timing when the vacuum degree is ≤70 Mpa, keep the time for 22 Min, the ultimate vacuum degree is 17 Mpa, break the vacuum, add mixed rare earth metal according to 0.001% of the molten steel weight, the blowing Ar flow rate is 100 - 120 ML / Min, keep for 10 min to obtain purified molten steel, and then enter the casting process;

[0041] The designed composition of the added mixed rare earth metal: mainly composed of lanthanum, cerium, praseodymium, and neodymium, the total rare earth content is greater than 95%, and the light rare earth with cerium greater than 48%;

[0042] S2. Carry out forging processing, and obtain a blank part by forging processing according to the structure drawing of the product;

[0043] The continuous casting billet specification is 450 thick × 2000 wide × L mm in length, saw cut into 450 thick × 450 wide × L mm in length, the heating temperature is 1220 °C, the upsetting forging ratio is 2:1, the drawing forging ratio is 3 - 5, the reduction of the last pass is 20% - 35%, the final forging temperature ≥800 °C, multi-piece continuous forging, anneal at 660 °C after forging. UT rough inspection, cold saw cut according to the forging length, rough turning, and transfer to the heat treatment workshop;

[0044] S3. Post-forging heat treatment, heat the blank part at 920 °C for heat preservation and then quench, and then temper at 690 °C;

[0045] The obtained finished parts pass the level I inspection and flaw detection of NB / T47013.3 and then leave the factory, thus reducing the crack rate after welding.

[0046] For the detection of the mechanical properties of the samples of the specific embodiments, for the products in the same heat treatment furnace batch, 2 groups of specimens were randomly selected for detection. The tensile test and impact test met the standard requirements, as shown in Table 2.

[0047]

[0048] Table 2

[0049] There were a total of 3,200 pieces of this batch of products. According to the Class I ultrasonic flaw detection of NB / T 47013.3-2023, 3 pieces were unqualified in flaw detection and scrapped. The UT ultrasonic unqualified rate was 0.093‰, far better than the target of ≤3‰.

[0050] After welding the forged pipe connectors of the specific embodiments to the shells of multiple sets of pressure vessels, through manual visual inspection, PT penetrant testing, RT testing, pressure testing, and gas leakage testing, the reheat crack rate of this batch of pipe connectors was 0, far better than the target of ≤1‰.

[0051] Starting from the mechanism of material resistance to welding, it designed a chemical composition composition resistant to welding, adopted a new process of double refining and adding rare earths, and designed reasonable forging and heat treatment processes, achieving the goal that the reheat crack rate of the pipe connectors is ≤1‰ or 0 after being welded to the pressure vessel.

[0052] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims within the present invention.

[0053] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. Processing technology of forged pipe connectors for preventing welding cracks, characterized in that, It is applicable to the manufacture of forged pipe connectors made of 12Cr2Mo1 material, and it includes the following steps: S1. After controlling the composition, complete the base metal ratio, and then through double refining and adding rare earth for enhanced refining to obtain high-purity molten steel, and then pour to obtain continuous casting billets; S2. Conduct forging processing, and obtain blank parts through forging processing according to the structural drawings of the product; S3. Post-forging heat treatment; S4. The obtained finished parts pass the Class I inspection flaw detection of NB / T47013.3 and then leave the factory, thereby reducing the crack rate after welding.

2. The processing technology of the forged pipe connector for preventing welding cracks according to claim 1, characterized in that, In step S1, the base metal composition of the forged pipe connector is pre-designed, and its composition content ratio is as follows: Carbon C: 0.10% - 0.15%, Silicon Si: ≤0.12%, Manganese Mn: 0.30% - 0.60%, Chromium Cr: 2.10% - 2.50%, Nickel Ni: ≤0.30%, Molybdenum Mo: 0.90% - 1.10%, Copper Cu: ≤0.20%, Phosphorus P: ≤0.010%, Sulfur S: ≤0.010%, Arsenic As: ≤0.015%, Tin Sn: ≤0.015%, Antimony Sb: ≤0.010%, Lead Pb: ≤0.010%, Bismuth Bi: ≤0.010%, Calcium Ca: ≤0.010%, Hydrogen H: ≤2ppm, Oxygen O: ≤25ppm, Nitrogen N: ≤90ppm, and the rest is Fe.

3. The processing technology of the forged pipe connector for preventing welding cracks according to claim 2, characterized in that: The double refining and adding rare earth for enhanced refining in step S1 includes the first refining and the second refining; during the first refining, refine according to the base metal composition ratio of the pre-designed forged pipe connector; during the second refining, remove 20 - 50% of the slag above the molten steel, the bottom blowing Ar flow rate of the ladle is 130 - 380 ML / Min, enter the VD station for evacuation, start timing when the vacuum degree is ≤70 Mpa, keep the time for 20 - 30 Min, the ultimate vacuum degree is ≤25 Mpa, break the vacuum, add mixed rare earth metals according to 0.0005 - 0.0010% of the molten steel weight, the blowing Ar flow rate is 100 - 200 ML / Min, keep for 5 - 10 min to obtain purified molten steel, and then enter the pouring process.

4. The processing technology of the forged pipe connector for preventing welding cracks according to claim 3, characterized in that: Design the composition of the added mixed rare earth metals: mainly composed of lanthanum, cerium, praseodymium, and neodymium, the total rare earth content is greater than 95%, and the light rare earth with cerium greater than 48%.

5. The processing technology of the forged pipe connector for preventing welding cracks according to claim 4, characterized in that: According to the alloy content of the material and the final quality requirements, select to add electroslag remelting (ESR) to further improve the weldability of the material.

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