Low-temperature impact energy stabilization process for cylindrical forgings

Abstract

The invention provides a low-temperature impact energy stabilization process for a cylindrical forge piece, which enables the low-temperature impact energy of the manufactured cylindrical forge piece to be stable, enables the low-temperature impact value of the cylindrical forge piece to have a higher percent of pass, and ensures the quality of a pressure vessel. The method comprises the following steps that S1, element matching is conducted on a 20MnNiMo base metal raw material, and then smelting is conducted to obtain a steel ingot; s2, the steel ingot is forged, and a blank cylinder piece in a set shape is obtained through combination of a two-way forging method and a reversing forging method; and S3, performing post-forging heat treatment, rough turning exposure, UT flaw detection and cold saw cutting according to the length of the forge piece on the blank cylinder piece to obtain the cylinder forge piece.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical forging processing, and specifically to a process for stabilizing the low-temperature impact energy of cylindrical forgings. Background Art

[0002] Cylindrical forgings are defined in NB / T47008 as axisymmetric hollow parts with an axial length L greater than its outer diameter D. See Figure 1 , where t is the nominal thickness.

[0003] Cylindrical forgings are formed by hot forging and have advantages over cylinders obtained by other forming methods in terms of large diameter and large wall thickness. Single or multiple cylindrical forgings can be welded together to serve as the body or shell side of a pressure vessel, or as pipes for important projects, and are widely used in petrochemical, coal chemical, military scientific research projects, etc. The body of the cylindrical forging is welded with tube sheets, tube connectors are installed or welded, measuring instruments, safety and control valves, etc. are added, and a pressure vessel is formed, such as a reaction kettle, polymerization kettle, synthesis tower, conversion furnace, gas generator, heat exchanger, cooler, condenser, evaporator, etc.

[0004] The requirements for the low-temperature impact energy of the completed cylindrical forgings are as follows: The test is carried out at 0°C required by the standard or -20°C required by the user, and -20°C can cover 0°C. The low-temperature impact energy KV2 ≥ 47(33)J. Among the three impact values, one value is allowed to be lower than 47J, but not lower than 47J × 70% = 33J. In actual production, there will be a small number of cylindrical forgings with jumping low-temperature impact values, showing two highs and one low among the three impact values. When the low single value < 33J, the impact value will be judged as unqualified. If the re-sampling re-inspection is unqualified, the cylindrical forgings need to be heat-treated again.

[0005] For a small number of cylindrical forgings made by the prior art, the low-temperature impact energy shows jumps or is lower than the standard value. As the body components of a pressure vessel, it is necessary to improve their quality stability, which is an urgent technical problem to be solved in pressure vessel manufacturing. Summary of the Invention

[0006] In view of the above problems, the present invention provides a process for stabilizing the low-temperature impact energy of cylindrical forgings, which stabilizes the low-temperature impact energy of the completed cylindrical forgings, improves the qualification rate of the low-temperature impact values of cylindrical forgings, and ensures the quality of pressure vessels.

[0007] The process for stabilizing the low-temperature impact energy of cylindrical forgings is characterized by including the following steps:

[0008] S1. Perform element ratio on the 20MnNiMo base material raw material, and then smelt to obtain an ingot;

[0009] S2, forging the steel ingot by combining a bidirectional forging method and a reversing forging method to obtain a blank cylinder of a set shape;

[0010] S3. The blank cylinder is heat treated after forging, rough turned to light, UT tested, and cold sawed according to the length of the forging to obtain the cylinder forging.

[0011] It is further characterized by:

[0012] In step S1, the element composition content of the 20MnNiMo parent material is as follows:

[0013] Carbon C: 0.19% ~ 0.23%, Silicon Si: 0.15% ~ 0.30%, Manganese Mn: 1.10% ~ 1.30%, Chromium Cr: ≤ 0.30%, Nickel Ni: ≤ 0.30%, Molybdenum Mo: 0.20% ~ 0.35%, Copper Cu: ≤ 0.10%, Phosphorus P: ≤ 0.015%, Sulfur S: ≤ 0.028%, Arsenic As: ≤ 0.015%, Antimony Sb: ≤ 0.010%, Aluminum Al: 0.015% ~ 0.035%, Hydrogen H: ≤ 1.5ppm, Oxygen O: ≤ 20ppm, Nitrogen N: ≤ 80ppm, the rest is Fe;

[0014] In step S2, the forging process is performed using the following specific steps:

[0015] S201, ingot heating temperature 1230-1250℃;

[0016] S202, the first fire, according to the utilization rate of the ingot 83%, hot cut the head and tail, upset to 1 / 3 to 1 / 2 of the ingot height, and then draw four times, the drawing and forging ratio is 1.5-2.0, and the furnace is heated and the temperature is controlled at 1220-1230℃;

[0017] S203, after the second fire upsetting, the blank reaches the upper limit height of the punching, then punches the center hole, expands the hole, returns to the furnace, and the blank heating temperature is controlled at 1220-1230℃;

[0018] S204, the third fire is used to further expand the hole and reserve the thickness of the last fire, that is, at least ensure that the thickness of the last fire has a deformation amount of ≧30%, flatten the head, return to the furnace, and control the heating temperature of the billet to 1200-1220℃;

[0019] S205, the 4th fire, designed a bidirectional forging method and a reversing forging method. After coming out of the furnace, the cylinder is placed upright, one end is evenly flattened, and the other end is evenly flattened. The flattening pressure is controlled at 100-150mm. The core rod is put on, and the cylinder is evenly pressed down by a long anvil rolling. The pressure is ≧30% of the wall thickness. Finally, the cylinder is placed upright to level the end surface;

[0020] In step S3, the steps for post-forging heat treatment of the blank cylinder are to vertically install the blank cylinder according to the heat treatment process, quench it after holding at 920 ± 10 °C, with water as the medium, and then perform tempering treatment at 630 - 650 °C.

[0021] After adopting the present invention, the composition of the base material raw material is readjusted to make the mechanical properties of the 20MnMo steel ingot meet the standards. Then, through the two-way forging method and the reverse forging method, the sample position areas at both ends are fully thermally deformed uniformly, the grains are fully refined, and then the grains are further refined and the structure is homogenized through post-forging heat treatment. After that, rough turning is carried out until it is smooth, UT flaw detection is performed, and the cylinder forgings are obtained by cold sawing according to the length of the forgings; it makes the low-temperature impact work of the fabricated cylinder forgings stable, makes the low-temperature impact value of the cylinder forgings have a higher qualified rate, and ensures the quality of the pressure vessel. Description of the Drawings

[0022] Figure 1 It is a definition diagram of the cylinder forgings;

[0023] Figure 2 It is a schematic diagram of the size structure of the cylinder forgings fabricated by the present invention. Detailed Embodiment

[0024] The process for stabilizing the low-temperature impact work of cylinder forgings includes the following steps:

[0025] S1. Perform element ratio on the 20MnNiMo base material raw material and then smelt to obtain a steel ingot;

[0026] S2. Forge the steel ingot through a combination of the two-way forging method and the reverse forging method to obtain a blank cylinder with a set shape;

[0027] S3. Perform post-forging heat treatment on the blank cylinder, rough turn until it is smooth, perform UT flaw detection, and obtain cylinder forgings by cold sawing according to the length of the forgings.

[0028] Specifically, in step S1, the element composition content ratio of the 20MnNiMo base material raw material is as follows:

[0029] Carbon C: 0.19% - 0.23%, Silicon Si: 0.15% - 0.30%, Manganese Mn: 1.10% - 1.30%, Chromium Cr: ≤0.30%, Nickel Ni: ≤0.30%, Molybdenum Mo: 0.20% - 0.35%, Copper Cu: ≤0.10%, Phosphorus P: ≤0.015%, Sulfur S: ≤0.028%, Arsenic As: ≤0.015%, Antimony Sb: ≤0.010%, Aluminum Al: 0.015% - 0.035%, Hydrogen H: ≤1.5 ppm, Oxygen O: ≤20 ppm, Nitrogen N: ≤80 ppm, and the rest is Fe.

[0030] Specific embodiment, the production is as Figure 2The method comprises the following steps:

[0031] S1. The element composition ratio of the 20MnNiMo base material raw material is carried out, and then the steel ingot is obtained by smelting. The element composition ratio of the 20MnNiMo base material raw material is as follows:

[0032] Carbon C: 0.21%, Silicon Si: 0.25%, Manganese Mn: 1.20%, Chromium Cr: 0.20%, Nickel Ni: 0.20%, Molybdenum Mo: 0.30%, Copper Cu: 0.08%, Phosphorus P: 0.01%, Sulfur S: 0.025%, Arsenic As: 0.010%, Antimony Sb: 0.008%, Aluminum Al: 0.025%, Hydrogen H: 1ppm, Oxygen O: 15ppm, Nitrogen N: 60ppm, the rest is Fe;

[0033] The mechanical properties of the steel ingot meet the following conditions:

[0034]

[0035]

[0036] S2, forging the steel ingot by combining a bidirectional forging method and a reversing forging method to obtain a blank cylinder of a set shape;

[0037] S201, ingot heating temperature 1230-1250℃;

[0038] S202, the first fire, according to the utilization rate of the ingot 83%, hot cut the head and tail, upset to 1 / 3 to 1 / 2 of the ingot height, and then draw four times, the drawing and forging ratio is 1.5-2.0, and the furnace is heated and the temperature is controlled at 1220-1230℃;

[0039] S203, after the second fire upsetting, the blank reaches the upper limit height of the punching, then punches the center hole, expands the hole, returns to the furnace, and the blank heating temperature is controlled at 1220-1230℃;

[0040] S204, the third fire is used to further expand the hole and reserve the thickness of the last fire, that is, at least ensure that the thickness of the last fire has a deformation amount of ≧30%, flatten the head, return to the furnace, and control the heating temperature of the billet to 1200-1220℃;

[0041] S205, the 4th fire, designed the bidirectional forging method and the reversing forging method. After coming out of the furnace, the cylinder is placed upright, one end is evenly flattened, and the other end is evenly flattened. The flattening pressure is controlled at 100-150mm. The mandrel is put on, and the cylinder is evenly pressed down by rolling with a long anvil. The pressure is ≧30% of the wall thickness. Finally, the cylinder is placed upright to level the end surface. If necessary, the mandrel and the long anvil are further used to roll evenly for the final forming.

[0042] S3. Conduct post-forging heat treatment on the blank cylinder parts, rough turn until smooth, perform UT flaw detection, and cold saw cut according to the forging length to obtain cylinder forgings;

[0043] The steps for post-forging heat treatment of the blank cylinder parts are to vertically install the blank cylinder parts according to the heat treatment process, quench after holding at 920 ± 10 °C, with water as the medium, and then perform tempering treatment at 630 - 650 °C.

[0044] For the 30 cylinder forgings obtained by synchronously manufacturing according to the above steps, after performance heat treatment, take tangential test rings with dimensions of 30 * 30 * arc length L mm (L ≥ 200 mm) on both sides of the cylinder body. After simulating post-weld heat treatment on the test rings, make standard specimens and conduct tensile and impact tests. The first-pass rate is 100%, and the stability of the impact value is very good, achieving the expected goal of "stabilizing the low-temperature impact energy of 20MnMo cylinder forgings". The test values of 5 cylinders are listed as follows:

[0045]

[0046] This batch contains 30 pieces in total. According to the I-level ultrasonic flaw detection of NB / T47013.3 - 2023, the UT ultrasonic pass rate is 100%.

[0047] The principle is as follows: Re-adjust the composition of the base material raw materials to make the mechanical properties of the 20MnMo steel ingot meet the standards. Increase C to 0.19 - 0.23% to improve hardenability; reduce Si to 0.15 - 0.30% and Mn to 1.10 - 1.30% to improve the plasticity of the material; reduce Cu to ≤0.10% and P to ≤0.015% to reduce the impurity elements in the steel; add restrictions on As ≤ 0.015% and Sb ≤ 0.010% to reduce the impurity elements in the steel; add Al element at 0.015 - 0.035% to refine the grains; add restrictions on H ≤ 1.5 ppm, O ≤ 20 ppm, and N ≤ 80 ppm to reduce the harmful gas elements in the steel; then, through the two-way forging method and the reverse forging method, fully heat deform and homogenize the sample positions at both ends, fully refine the grains, and then further refine the grains and homogenize the structure through post-forging heat treatment. After that, rough turn until smooth, perform UT flaw detection, and cold saw cut according to the forging length to obtain cylinder forgings; this makes the low-temperature impact energy of the completed cylinder forgings stable, enables the low-temperature impact value of the cylinder forgings to have a higher pass rate, and ensures the quality of the pressure vessel.

[0048] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, in any aspect, 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, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0049] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner 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. The stabilization process of the low-temperature impact work of cylinder forgings is characterized in that It includes the following steps: S1. 20MnNiMo base material raw material is proportioned and then smelted to obtain a steel ingot; S2, forging the steel ingot by combining a bidirectional forging method and a reversing forging method to obtain a blank cylinder of a set shape; S3. The blank cylinder is heat treated after forging, rough turned to light, UT tested, and cold sawed according to the length of the forging to obtain the cylinder forging.

2. The low-temperature impact energy stabilization process for cylindrical forgings according to claim 1, characterized in that, In step S1, the element composition content of the 20MnNiMo parent material is as follows: Carbon C: 0.19% ~ 0.23%, silicon Si: 0.15% ~ 0.30%, manganese Mn: 1.10% ~ 1.30%, chromium Cr: ≤0.30%, nickel Ni: ≤0.30%, molybdenum Mo: 0.20% ~ 0.35%, copper Cu: ≤0.10%, phosphorus P: ≤0.015%, sulfur S: ≤0.028%, arsenic As: ≤0.015%, antimony Sb: ≤0.010%, aluminum Al: 0.015% ~ 0.035%, hydrogen H: ≤1.5ppm, oxygen O: ≤20ppm, nitrogen N: ≤80ppm, and the rest is Fe.

3. The low-temperature impact work stabilization process for cylindrical forgings according to claim 1, characterized in that, In step S2, the forging process is performed by the following specific steps: S201, ingot heating temperature 1230-1250℃; S202, the first fire, according to the utilization rate of the ingot 83%, hot cut the head and tail, upset to 1 / 3 to 1 / 2 of the ingot height, and then draw four times, the drawing and forging ratio is 1.5-2.0, and the furnace is heated and the temperature is controlled at 1220-1230℃; S203, after the second fire upsetting, the blank reaches the upper limit height of the punching, then punches the center hole, expands the hole, returns to the furnace, and the blank heating temperature is controlled at 1220-1230℃; S204, the third fire is used to further expand the hole and reserve the thickness of the last fire, that is, at least ensure that the thickness of the last fire has a deformation amount of ≧30%, flatten the head, return to the furnace, and control the heating temperature of the billet to 1200-1220℃; S205, the 4th fire, designed a bidirectional forging method and a reversing forging method. After coming out of the furnace, the cylinder is placed upright, one end is evenly flattened, and the other end is reversed up and down to evenly flatten the head. The flattening pressure is controlled at 100-150mm. The core rod is put on, and the cylinder is evenly pressed down by a long anvil. The pressure is ≧30% of the wall thickness. Finally, the cylinder is placed upright to level the end face.

4. The low-temperature impact work stabilization process for cylindrical forgings according to claim 1, characterized in that: In step S3, the step of heat treating the blank cylinder after forging is to vertically install the blank cylinder according to the heat treatment process, quench after keeping at 920±10℃, the medium is water, and then temper at 630-650℃.

Images