A processing method to improve the chloride ion corrosion resistance of GH3625 bars

Abstract

This invention relates to a processing method for improving the chloride ion corrosion resistance of GH3625 bars, belonging to the field of bar production technology in the metallurgical industry. The technical solution is as follows: the bars are placed in a heating furnace and heated to 1195~1215℃ for a holding time T1=257.39*exp(D1 / 62.52)-26.45; then cooled after removal from the furnace at a rate greater than 100℃ / s; the GH3625 bars are then drawn with a deformation of 50%; the drawn GH3625 bars are then placed in a heating furnace and heated to 825~835℃ for a holding time T2=44.78*exp(D2 / 45.57)+70.47; finally cooled after removal from the furnace at a rate less than 5℃ / min. The beneficial effects of this invention are: it can improve the corrosion resistance of the material, eliminate deteriorating phases while ensuring the necessary mechanical properties of the material, and simultaneously solve the problem of mixed crystals.

Description

Technical Field

[0001] This invention relates to a processing method for improving the chloride ion corrosion resistance of GH3625 bars, belonging to the field of GH3625 bar production technology in the metallurgical industry. Background Technology

[0002] GH3625, as one of the most classic corrosion-resistant alloys, possesses excellent machinability and comprehensive performance, exhibiting superior corrosion resistance and high-temperature oxidation resistance. At temperatures of 980℃ or lower, Inconel 625 alloy demonstrates resistance to stress corrosion in fume atmospheres, good fatigue performance, and high-temperature mechanical stability. It can be used to manufacture bars, tubes, fasteners, welding wires, and other product materials, with wide applications in chemical, petroleum, and marine industries.

[0003] GH3625 bars can be used to manufacture fasteners such as bolts and gaskets, and can also be used to stamp flanges, making its applications very wide. This material's corrosion resistance is far superior to conventional iron-based stainless steel and iron-nickel-based corrosion-resistant alloys. However, this material mainly contains alloying elements such as nickel, chromium, molybdenum, and niobium, and its smelting requires a vacuum + electroslag or vacuum + consumable metallization process, resulting in extremely high production and raw material costs. The product's selling price is 5-8 times that of stainless steel. Improving product performance can reduce material costs and ensure safe use. Research has found that in chlorine-containing environments, chloride ion corrosion and stress corrosion are the main causes of GH3625 bar failure. After a certain period of use, pitting corrosion appears on the product surface. With prolonged use, the number of pits increases, and the pits gradually enlarge and deepen. In some rolled thin plates, even perforation occurs, posing a serious safety hazard in chemical pipeline transportation. Metallographic analysis revealed that the corrosion pits on the GH3625 bar were primarily caused by elemental enrichment near large precipitates at grain boundaries, while the surrounding area lacked corrosion-resistant elements, weakening its corrosion resistance and leading to corrosion. The deteriorating phases contributing to this effect were mainly carbides, Laves phase, and σ phase. The carbides were primarily niobium carbide and molybdenum carbide; the Laves phase was mainly (Ni,Cr,Fe)₂(Nb,Mo,Ti); and the σ phase was mainly Ni₃Nb. These deteriorating precipitates enriched corrosion-resistant elements such as Cr, Mo, and Nb, resulting in insufficient surrounding elements and areas with poor corrosion resistance. Simultaneously, mixed crystals leading to stress corrosion also caused corrosion pits. Therefore, to improve the material's corrosion resistance, it is necessary to eliminate the deteriorating phases and address the mixed crystal problem while ensuring the material's essential mechanical properties.

[0004] Experimental testing and verification revealed that niobium carbide and molybdenum carbide have precipitation temperatures of 900–950℃ and remelting temperatures of 1160–1800℃; the Laves phase has a remelting temperature of 1150℃; and the σ phase has a remelting temperature of 950℃. Therefore, to eliminate the deteriorating phases present in the material, phase elimination is necessary. While holding the material at high temperatures can remelt these deteriorating phases, this high-temperature holding can cause the original grains to grow, even leading to mixed crystals, resulting in reduced tensile strength and yield strength, and deteriorating mechanical properties. To ensure the material's high performance and high stability, it is necessary to improve grain size uniformity. Summary of the Invention

[0005] The purpose of this invention is to provide a processing method for improving the chloride ion corrosion resistance of GH3625 bars. This method can improve the corrosion resistance of the material, eliminate deteriorating phases while ensuring the necessary mechanical properties of the material, and solve the problem of mixed crystals, thus addressing the problems existing in the background art.

[0006] The technical solution of this invention is:

[0007] A processing method for improving the chloride ion corrosion resistance of GH3625 bars, comprising the following steps:

[0008] Step 1: Eliminate the deteriorating phase of the bar stock

[0009] The GH3625 bar was placed in a heating furnace and heated to a temperature of 1195~1215℃. The holding time was T1=257.39*exp(D1 / 62.52)-26.45, where T1 is the holding time for eliminating the deteriorating phase in min; D1 is the diameter of the bar entering the furnace in mm.

[0010] Step 2: After the GH3625 bar stock has finished heat preservation, it is taken out of the furnace and cooled. When the temperature is greater than 480℃, the cooling rate is greater than 100℃ / s, and then it is allowed to cool naturally to room temperature.

[0011] Step 3: The above-mentioned GH3625 bar is drawn with a drawing deformation of 50%, and the deformation range of a single pass is 10~20%;

[0012] Step 4: Uniform Structure and Properties

[0013] The drawn GH3625 bar is placed in a heating furnace and heated to a temperature of 825~835℃. The holding time is T2=44.78*exp(D2 / 45.57)+70.47, where T2 is the holding time for uniform microstructure and properties, in min; D2 is the diameter of the drawn GH3625 bar, in mm.

[0014] Step 5: After the GH3625 bar is heat-treated after drawing, it is taken out of the furnace for cooling. When the temperature is greater than 350℃, the cooling rate is less than 5℃ / min, and then it is allowed to cool naturally to room temperature.

[0015] The above-mentioned processing method for improving the chloride ion corrosion resistance of GH3625 bars, in step one: the diameter of the GH3625 bars is 5-80mm.

[0016] In the above-mentioned processing method for improving the chloride ion corrosion resistance of GH3625 bars, step five: the grain size of the GH3625 bars after natural cooling to room temperature after drawing is grade 7-8.

[0017] The beneficial effects of this invention are:

[0018] 1) This invention is applicable to improving the chloride ion corrosion resistance of GH3625 forged or rolled bars while ensuring mechanical properties, with corrosion resistance improved by more than 30% compared to conventional bars;

[0019] 2) This invention can improve the uniformity of the microstructure of GH3625 bars, and control the grain size to level 7-8;

[0020] 3) This invention can improve the elongation of GH3625 bar products to 55-65%. Attached Figure Description

[0021] Figure 1 The microstructure of Example 1;

[0022] Figure 2 This refers to the microstructure of Example 2;

[0023] Figure 3 The microstructure of Example 3; Detailed Implementation

[0024] The invention will be further described below with reference to the accompanying drawings and examples.

[0025] See attached document Figure 1-3 A processing method for improving the chloride ion corrosion resistance of GH3625 bars, comprising the following steps:

[0026] Step 1: Eliminate the deteriorating phase of the bar stock

[0027] The GH3625 bar was placed in a heating furnace and heated to a temperature of 1195~1215℃. The holding time was T1=257.39*exp(D1 / 62.52)-26.45, where T1 is the holding time for eliminating the deteriorating phase in min; D1 is the diameter of the bar entering the furnace in mm.

[0028] Step 2: After the GH3625 bar stock has finished heat preservation, it is taken out of the furnace and cooled. When the temperature is greater than 480℃, the cooling rate is greater than 100℃ / s, and then it is allowed to cool naturally to room temperature.

[0029] Step 3: The above-mentioned GH3625 bar is drawn with a drawing deformation of 50%, and the deformation range of a single pass is 10~20%;

[0030] Step 4: Uniform Structure and Properties

[0031] The drawn GH3625 bar is placed in a heating furnace and heated to a temperature of 825~835℃. The holding time is T2=44.78*exp(D2 / 45.57)+70.47, where T2 is the holding time for uniform microstructure and properties, in min; D2 is the diameter of the drawn GH3625 bar, in mm.

[0032] Step 5: After the GH3625 bar is heat-treated after drawing, it is taken out of the furnace for cooling. When the temperature is greater than 350℃, the cooling rate is less than 5℃ / min, and then it is allowed to cool naturally to room temperature.

[0033] Step 1: The diameter of the GH3625 bar is 5-80mm.

[0034] Step 5: After the drawn GH3625 bar is naturally cooled to room temperature, the grain size is grade 7-8.

[0035] Example 1

[0036] A 4000mm*φ10mm GH3625 hot-rolled bar was placed in a heating furnace and heated to 1195℃. The temperature was held for 211 minutes. After the holding period, the sample was removed from the furnace and cooled with water. When the temperature was greater than 480℃, the cooling rate was about 200℃ / s.

[0037] The drawing process was performed using a combined drawing machine. The deformation amounts are shown in the table below, with a drawing amount of 50%.

[0038] Deformation dimensions / mm 8.5 7.1 6.0 5.0 Deformation amount / % 15.0 16.5 15.5 16.7

[0039] Uniform structure and performance process: The drawn bar is placed in a heating furnace and heated to 825℃, held for 120 minutes. After holding, it is removed from the furnace and cooled. When the temperature is above 350℃, the cooling rate is 4℃ / min.

[0040] Example 2

[0041] A 3500mm*φ80mm forged bar was placed in a heating furnace and heated to 1215℃. The solution was held for 899 minutes. After the holding period, the sample was removed from the furnace and cooled with water. When the temperature was greater than 480℃, the cooling rate was about 210℃ / s.

[0042] The drawing process was performed using a combined drawing machine. The deformation amounts are shown in the table below, with a drawing amount of 50%.

[0043] Deformation dimensions / mm 66 55 49.5 40 Deformation amount / % 20.0 16.6 10.0 19.2

[0044] Uniform microstructure and performance process: The drawn bar is placed in a heating furnace and heated to 835℃, held for 178 minutes. After holding, it is removed from the furnace and cooled. When the temperature is above 350℃, the cooling rate is about 5℃ / min.

[0045] Example 3

[0046] A 3000mm*φ45mm rolled bar was placed in a heating furnace and heated to 1200℃. It was then solution-treated and held at this temperature for 502 minutes. After the treatment, the sample was removed from the furnace and water-cooled. When the temperature exceeded 480℃, the cooling rate was approximately 205℃. A combined drawing machine was then used for drawing. The deformation is shown in the table below, with a drawing amount of 50%.

[0047] Deformation dimensions / mm 38.3 32 26 22.5 Deformation amount / % 15.0 16.4 18.8 15.6

[0048] Uniform microstructure and performance process: The drawn bar is placed in a heating furnace and heated to 830℃, held for 144 minutes. After holding, it is removed from the furnace and cooled. When the temperature is above 350℃, the cooling rate is about 5℃ / min.

[0049] Corrosion resistance / g / m2*h Grain size Elongation / % Example 1 0.103 7 58 Example 2 0.105 7.5 64 Example 3 0.101 7.5 63 Comparative Example 1 0.142 10.5 25 Comparative Example 2 0.136 9.5 19

[0050] Among them, Comparative Example 1 is a φ5mm rolled bar and Comparative Example 2 is a φ40mm forged bar.

Claims

1. A method of improving the resistance of GH3625 bar to corrosion by chloride ions, characterized by: Follow these steps: Step 1: Eliminate the deteriorating phase of the bar stock The GH3625 bar was placed in a heating furnace and heated to a temperature of 1195~1215℃. The holding time was T1=257.39*exp(D1 / 62.52)-26.45, where T1 is the holding time for eliminating the deteriorating phase in min; D1 is the diameter of the bar entering the furnace in mm. Step 2: After the GH3625 bar stock has finished heat preservation, it is taken out of the furnace and cooled. When the temperature is greater than 480℃, the cooling rate is greater than 100℃ / s, and then it is allowed to cool naturally to room temperature. Step 3: The above-mentioned GH3625 bar is drawn with a drawing deformation of 50%, and the deformation range of a single pass is 10~20%; Step 4: Uniform Structure and Properties The drawn GH3625 bar is placed in a heating furnace and heated to a temperature of 825~835℃. The holding time is T2=44.78*exp(D2 / 45.57)+70.47, where T2 is the holding time for uniform microstructure and properties, in min; D2 is the diameter of the drawn GH3625 bar, in mm. Step 5: After the GH3625 bar is heat-treated after drawing, it is taken out of the furnace for cooling. When the temperature is greater than 350℃, the cooling rate is less than 5℃ / min, and then it is allowed to cool naturally to room temperature.

2. The processing method for improving the chloride ion corrosion resistance of GH3625 bars according to claim 1, characterized in that: Step 1: The diameter of the GH3625 bar is 5-80mm.

3. The processing method for improving the chloride ion corrosion resistance of GH3625 bars according to claim 1, characterized in that: Step 5: After the drawn GH3625 bar is naturally cooled to room temperature, the grain size is grade 7-8.

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