N08810 high nickel alloy seamless steel pipe expanding and cold working process

Abstract

The present application relates to a kind of N08810 high nickel alloy seamless steel pipe extension continuous cold working process, belong to metal pipe forming technical field, solve the problem that N08810 high nickel alloy piercing blank pipe specification does not meet the requirement of cold rolling mill, solution is as follows: N08810 high nickel alloy seamless steel pipe extension continuous cold working process includes the following steps: blank pipe→cold expansion→first degreasing→cold rolling→second degreasing→heat treatment→straightening→flat head→pickling→finished product.The present application is by optimizing blank pipe and semi-finished product cold expansion deformation, reach the degree of control expansion hole cold deformation after steel pipe work hardening, while reasonable layout cold rolling deformation (elongation), after expansion hole steel pipe blank is directly transferred to cold rolling process after degreasing process, carries out cold rolling deformation, cold expansion continuous cold rolling belongs to cold deformation accumulation, need to consider simultaneously to cold expansion deformation and cold rolling deformation, and then ensure the quality of steel pipe after cold rolling and the physicochemical property after finished product heat treatment.

Description

Technical Field

[0001] This invention belongs to the field of metal tube forming technology, specifically relating to a cold working process for expanding and connecting N08810 high-nickel alloy seamless steel tubes. Background Technology

[0002] The chemical composition of N08810 high-nickel alloy is shown in Table 1 below. Due to the high nickel content in N08810 high-nickel alloy, it has good corrosion resistance and excellent resistance to stress corrosion cracking under water-based corrosion conditions. N08810 high-nickel alloy seamless pipes are used in polysilicon projects and petroleum cracking, with operating conditions ranging from 300℃ to 590℃ and from 1.5MPa.g to 3.5MPa.g.

[0003] Table 1 Chemical composition of N08810 high-nickel alloy

[0004]

[0005] During the production process, N08810 high-nickel alloy rough tubes are usually formed by hot extrusion. However, hot extrusion has high production costs and low yield, resulting in high production costs for N08810 high-nickel alloy seamless tubes.

[0006] The current immaturity of hot piercing technology has resulted in a mismatch between the specifications of the pierced rough tubes and those required by the rolling mill. This means that the pierced rough tubes cannot be directly rolled on the rolling mill. Furthermore, after the rolling mill rolls the semi-finished product, it is necessary to expand the hole before rolling. However, the deformation amount of the expanded hole is relatively small. In addition, the production process involves heat treatment, straightening, leveling, pickling, and other processes, which increases the production cost and lengthens the process flow, increasing the possibility of quality defects, especially some irreparable defects (such as over-acidification). Summary of the Invention

[0007] The main objective of this invention is to overcome the shortcomings of the prior art, solve the problem that the specifications of N08810 high-nickel alloy pierced rough tubes do not meet the requirements of cold rolling mills, and address the technical problems of long manufacturing cycles and high production costs of N08810 high-nickel alloy seamless steel pipes due to multiple heat treatments. This invention provides a cold working process for expanding the production of N08810 high-nickel alloy seamless steel pipes, which improves the yield, increases the material flow rate, and reduces the production cost of N08810 high-nickel alloy seamless steel pipes.

[0008] The design concept of this invention is as follows: During the production of N08810 high-nickel alloy seamless tubes, the specifications of the pierced rough tube do not match the specifications required by the rolling mill, necessitating hole expansion (cold expansion) after cold rolling. These two deformation processes work together: the cold rolling process reduces the wall thickness of the rough tube, while the cold expansion process increases the outer diameter of the rough tube or semi-finished product, ultimately achieving the required specifications for the finished product. This invention optimizes the cold expansion deformation of the rough tube and semi-finished product to control the degree of work hardening after hole expansion and cold deformation. Simultaneously, it rationally arranges the cold rolling deformation (elongation). The expanded steel tube billet is directly transferred to the cold rolling process after degreasing. Since cold expansion and cold rolling are cumulative cold deformations, both the cold expansion deformation and cold rolling deformation must be considered simultaneously to ensure the quality of the cold-rolled steel tube and the physical and chemical properties of the finished product after heat treatment.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: a cold working process for expanding and connecting N08810 high-nickel alloy seamless steel pipes, comprising the following steps:

[0010] Raw tube → Cold expansion → First degreasing → Cold rolling → Second degreasing → Heat treatment → Straightening → End finishing → Pickling → Finished product;

[0011] Cold expansion: Based on the actual specifications of the pierced rough tube and the specifications required by the rolling mill, the deformation amount of each cold expansion pass is controlled between 8.62% and 10.78%.

[0012] Cold rolling: The cold rolling deformation elongation rate is controlled to not exceed 2%, and the rolling force calculation formula is as follows:

[0013]

[0014] In the formula, K σ The coefficient is related to the hardening properties of metals, and is taken as 1.42 for steel and its alloys;

[0015] σ b50 The strength limit at 50% deformation;

[0016] D0 is the outer diameter of the pipe;

[0017] S0 is the pipe wall thickness;

[0018] D is the outer diameter of the rolled pipe;

[0019] S is the wall thickness of the rolled pipe;

[0020] μ is the overall elongation coefficient;

[0021] m is the rolling feed rate;

[0022] R' is the radius of the driving gear;

[0023] L g This refers to the length of the working section of the roll.

[0024] Furthermore, in the cold rolling process, the mandrel used in the rolling mill has a hardness of 55 HRC.

[0025] Furthermore, in the cold rolling process, the surface finish of the forming cavity inner wall and the mandrel surface is 0.4≤Ra≤0.8.

[0026] Furthermore, in the cold rolling process, the inner wall lubricating rolling oil has an anti-wear property of 98 kg, an extreme pressure property of 420 kg, and a viscosity of 149.8 mm. 2 / s, with a high-temperature stability of 330℃.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention provides a cold working process for expanding and connecting N08810 high-nickel alloy seamless steel pipes:

[0029] 1. Shorten the process flow by directly enlarging the hole after the rough pipe is perforated;

[0030] 2. Rationally determine the cold deformation amount of N08810 high-nickel alloy seamless steel pipe through hole expansion, so as to control the work hardening of the billet after diameter expansion, and the straightness of the steel pipe after hole expansion meets the requirements of cold rolling, which is beneficial to the rolling of the cold rolling mill and meets the rolling capacity requirements of the rolling mill.

[0031] 3. Improve the hardness of the mandrel used in the rolling mill, and ensure that the hardness of the mandrel meets the rolling requirements of cold-expanded N08810 high-nickel alloy seamless steel pipe;

[0032] 4. Ensure that the wear resistance, pressure resistance, and viscosity properties of the inner wall lubricating oil meet the production requirements of high-nickel N08810 expanded-hole tubes;

[0033] 5. It solved the problem of large deformation during cold rolling causing the rolling process to stall or the equipment to be insufficient. Attached Figure Description

[0034] Figure 1 This is a flow chart of the conventional production process for N08810 high-nickel alloy seamless steel pipes.

[0035] Figure 2 This is a flow chart of the production process of N08810 high-nickel alloy seamless steel pipe in this invention. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0037] like Figure 2 The cold working process for expanding and connecting N08810 high-nickel alloy seamless steel pipes, as shown, includes the following steps:

[0038] Raw tube → Cold expansion → First degreasing → Cold rolling → Second degreasing → Heat treatment → Straightening → End finishing → Pickling → Finished product;

[0039] Cold expansion: Based on the actual specifications of the pierced rough tube and the specifications required by the rolling mill, the deformation amount of each cold expansion pass is controlled between 8.62% and 10.78%.

[0040] The main components of the lubricant used in the cold expansion process of N08810 high-nickel alloy rough tubes are quicklime, calcium-based grease, and graphite. Normally, the expansion amount per pass is controlled between Φ5-Φ30mm, depending on the required outer diameter for cold rolling. After cold expansion, the tube is transferred to the cold rolling process according to the original procedure. However, with the improved process, since no heat treatment is performed after expansion before proceeding to the cold rolling process, the cold-state tube exhibits work hardening. Therefore, the amount of expansion deformation needs to be controlled according to the mill's rolling capacity to ensure successful cold rolling.

[0041] Table 2 Comparison of Deformation Amounts in Cold Expanding Process

[0042]

[0043] Within the deformation range of 8.62% to 10.78%, the cold expansion deformation can be maximized without affecting work hardening, meeting the actual specifications of piercing. The curvature after expansion can be guaranteed, and after slight completion, straightening can be performed without heat treatment before rolling. Within the deformation range of 8.62% to 10.78%, the yield strength of N08810 high-nickel alloy seamless tube increases by approximately 11%, not exceeding the yield strength of duplex steel.

[0044] Cold rolling: Combined with cold expansion deformation process, cold expansion and cold rolling are cumulative deformation processes. This requires that the cold rolling deformation elongation rate be controlled not to exceed 2%. When the elongation rate exceeds 2%, the rolling force changes greatly, which increases the load on the rolling mill capacity.

[0045] Rolling force calculation formula:

[0046]

[0047] In the formula, K σ The coefficient is related to the hardening properties of metals, and is taken as 1.42 for steel and its alloys;

[0048] σ b50 The strength limit at 50% deformation;

[0049] D0 is the outer diameter of the pipe;

[0050] S0 is the pipe wall thickness;

[0051] D is the outer diameter of the rolled pipe;

[0052] S is the wall thickness of the rolled pipe;

[0053] μ is the overall elongation coefficient;

[0054] m is the rolling feed rate;

[0055] R' is the radius of the driving gear;

[0056] L g The length of the working part of the roll;

[0057] Since the rolled billet is a cold-expanded tube, the steel pipe billet possesses work-hardening strength. When calculating the cold rolling force, it is essential to consider that the initial yield strength of the billet is not the same as the heat-treated yield strength, but rather the work-hardened strength.

[0058] When the cold rolling process remains unchanged, the tensile strength R of N08810 high-nickel alloy m (N / mm) is 2:450, yield strength R P0.2 With a yield strength of 2:180 (N / mm), the calculated rolling force reaches 710 tons. After cold expansion deformation, the yield strength increases by 11%, and the calculated rolling force reaches 810 tons, or even greater.

[0059] Furthermore, in the cold rolling process, the mandrel used in the rolling mill has a hardness of 55 HRC. This hardness is 5-10% higher than that used for rolling ordinary heat-treated steel pipes. This prevents the mandrel from sticking to the steel due to insufficient hardness, which could ultimately lead to spiral damage on the inner surface of the steel pipe and cause irreparable quality defects.

[0060] Furthermore, in the cold rolling process, the surface finish of the forming cavity inner wall and the mandrel surface is 0.4 ≤ Ra ≤ 0.8. Under normal conditions, the surface finish of the forming cavity inner wall and the mandrel surface in the cold rolling process is 0.8 ≤ Ra ≤ 1.6. In this invention, it is adjusted to 0.4 ≤ Ra ≤ 0.8 mainly because the surface of the perforated blank is relatively rough, and the friction generated on the surface is large, which easily causes steel to stick to the mandrel and the die surface, resulting in rolling defects on both the inner and outer surfaces. Improving the surface finish of the die is to reduce the friction between the die and the blank, and to increase the service life of the mandrel.

[0061] Furthermore, in the cold rolling process, the inner wall lubricating rolling oil has an anti-wear property (PB) of 98 kg, an extreme pressure property (PD) of 420 kg, and a viscosity of 149.8 mm. 2 / s, with a high-temperature stability of 330℃. The rolling process for cold-expanded billets places high demands on the anti-wear and extreme pressure properties of the lubricating oil to ensure effective internal wall lubrication and reduce the risk of the mandrel burning due to high temperatures.

[0062] This specific embodiment describes the processing of two specifications of N08810 high-nickel alloy seamless steel pipes:

[0063] I. Φ230*18mm (cold expanded) — Φ250*17.5mm (cold rolled) — Φ219*11.3mm;

[0064] The process flow is as follows: rough tube → cold expansion → primary degreasing → cold rolling → secondary degreasing → heat treatment → straightening → end flattening → pickling → finished product.

[0065] II. Φ240*25mm (cold expansion) — Φ250*25mm (cold rolling) — Φ219*18mm (secondary cold expansion) — Φ250*17.5 (secondary cold rolling) — Φ219*12.5mm;

[0066] The process flow is as follows: rough tube → first cold expansion → first degreasing → first cold rolling → second degreasing → heat treatment → pickling → second cold expansion → second degreasing → second cold rolling → third degreasing → heat treatment → straightening → end flattening → pickling → finished product.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A cold working process for expanding and connecting N08810 high-nickel alloy seamless steel pipes, characterized in that, Includes the following steps: Raw tube → Cold expansion → First degreasing → Cold rolling → Second degreasing → Heat treatment → Straightening → End finishing → Pickling → Finished product; Cold expansion: Based on the actual specifications of the pierced rough tube and the specifications required by the rolling mill, the deformation amount of each cold expansion pass is controlled within 8.62%~10.78%; Cold rolling: The mandrel used in the rolling mill has a hardness of 55 HRC; the surface finish of the forming cavity inner wall and mandrel is 0.4 ≤ Ra ≤ 0.8; the anti-wear property of the inner wall lubricating rolling oil is 98 kg, the extreme pressure property is 420 kg, and the viscosity is 149.8 mm. 2 / s, high temperature stability is 330℃, cold rolling deformation elongation is controlled not to exceed 2%, rolling force calculation formula: ； In the formula, K σ The coefficient is related to the hardening properties of metals, and is taken as 1.42 for steel and its alloys; σ b50 The strength limit at 50% deformation; D 0 The outer diameter of the pipe; S 0 For pipe wall thickness; D This refers to the outer diameter of the rolled pipe. S The wall thickness of the rolled pipe; μ The total elongation factor; m For the amount of material fed into the rolling mill; R' The radius of the driving gear; L g This refers to the length of the working section of the roll.

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