Heat treatment process for improving grain size of ultra-large-diameter TP347H seamless steel pipe

Abstract

The invention discloses a heat treatment process for improving the grain size of a TP347H seamless steel tube with an ultra-large diameter, which is suitable for improving the grain size of the TP347H seamless steel tube with the outer diameter of more than or equal to 650 mm, the wall thickness of 80-100 mm and the length of more than 6000 mm, so as to improve the quality of the TP347H seamless steel tube. Stepped solid solution, variable-speed cooling and composite stabilization processes are effectively combined, raw NbC is sufficiently dissolved in a low-temperature stage, grain boundary migration and growth are inhibited in a high-temperature stage, an anaphylaxis interval can be quickly exceeded through variable-speed cooling, sigma phase precipitation is avoided, residual stress is relieved and reduced, multi-temperature-zone stabilization treatment can promote uniform precipitation of nanoscale NbC, pinning of grain boundaries and grain refinement, and the stability of NbC is improved. According to the TP347H seamless steel pipe produced by the method, the phenomena of mixed crystals and coarse crystals are improved, the quality is improved, and the market demand is met.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for metallic materials, and specifically relates to a heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipes with an outer diameter ≥650mm, wall thickness 80mm-100mm, and length ≥6000mm. Background Technology

[0002] TP347H material is a niobium-containing high-nickel austenitic stainless steel, widely used in industries such as boilers, power generation, petroleum, chemical, synthetic fiber, food, and papermaking. However, improper heat treatment during production can easily lead to grain coarsening, affecting product quality and ultimately causing product scrap. Currently, the largest specifications of TP347H products used in coal chemical hydrogen pipelines are 711mm outer diameter, 70mm wall thickness, and 6000mm length. Due to market demand, when producing TP347H seamless steel pipes with an outer diameter of 914mm, a wall thickness of 100mm, and a length of 6100mm using conventional heat treatment processes (1140℃ solution treatment + 900℃ stabilization), significant mixed grain and coarse grain phenomena occur. To study the ultra-large diameter heat treatment process for this material and solve the grain mixing and coarse grain problems, it is urgent to develop a heat treatment process that can effectively improve the grain size of high-nickel austenitic stainless steel.

[0003] Purpose of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a heat treatment process for controlling the grain size of ultra-large diameter TP347H seamless steel pipes, effectively solving the problem of mixed grains and coarse grains in ultra-large diameter TP347H seamless steel pipes. Summary of the Invention

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipes, the process steps of which are as follows:

[0006] Step 1) Stepped solution treatment: The furnace temperature is ≤350℃. The temperature is increased to 400℃~500℃ at a rate of 50~100℃ / h and held for 1~3h. Then the temperature is increased to 600℃~700℃ at a rate of 50~100℃ / h and held for 1~3h. Then the temperature is increased to 950℃~1000℃ at a rate of 50~100℃ / h and held for 1~4h. Then the temperature is increased to 1080℃~1130℃ at a rate of ≤50℃ / h and held for 1~3h. After exiting the furnace, Step 2) Variable speed cooling is performed.

[0007] Step 2) Variable speed cooling: Within 50 seconds after the heat preservation in Step 1), the workpiece is hoisted into a water tank for water cooling. The water temperature is controlled below 30℃. The water tank should be thoroughly stirred. Water cooling: Control the cooling rate ≥150℃ / min until the workpiece surface temperature reaches 500℃~550℃, and then perform air cooling. Air cooling: Control the cooling rate ≤30℃ / min until the workpiece surface temperature is in the range of 150℃~250℃. Then, load the workpiece into the heating furnace. After completing Step 2), prepare to perform composite stabilization treatment.

[0008] Step 3) Composite stabilization treatment: The furnace temperature is ≤400℃. The temperature is increased to 890-910℃ at a heating rate of 50-100℃ / h and held for 2-4 hours. Then the furnace is cooled to 840-860℃ and held for 1-2 hours. Then the furnace is cooled to 790-810℃ and held for 1-2 hours. After the holding is completed, the furnace is removed and air-cooled to room temperature.

[0009] It is suitable for improving the grain size of TP347H seamless steel pipes with an outer diameter ≥650mm, wall thickness 80mm-100mm, and length ≥6000mm, thereby improving the quality of TP347H seamless steel pipes.

[0010] The chemical composition of steel grade TP347H is as follows: C = 0.05%, Si = 0.56%, Mn = 0.95%, Cr = 18.59%, Ni = 11.33%, S = 0.003%, P = 0.020%, Nb = 0.40%, with the balance being iron.

[0011] Compared with the prior art, the process of the present invention has the following advantages: The advantages of the heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipe according to the present invention are as follows:

[0012] 1. For the first time, a combined heat treatment process of stepped solution treatment + variable speed cooling + composite stabilization is adopted, which effectively combines the stepped solution treatment, variable speed cooling and composite stabilization processes.

[0013] 2. NbC is fully dissolved during the low-temperature stage, and grain boundary migration and growth are inhibited during the high-temperature stage.

[0014] 3. Variable speed cooling can quickly cross the sensitization range, avoid σ phase precipitation, and alleviate and reduce residual stress.

[0015] 4. Multi-temperature zone stabilization treatment promotes uniform precipitation of nano-sized NbC, pins grain boundaries, and refines grains. The TP347H seamless steel pipe produced according to this invention not only improves the mixed grain and coarse grain phenomena but also enhances its quality. Detailed Implementation

[0016] Example 1: A heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipe. Steel grade: TP347H; Chemical composition: C = 0.05%, Si = 0.56%, Mn = 0.95%, Cr = 18.59%, Ni = 11.33%, S = 0.003%, P = 0.020%, Nb = 0.40%, balance: iron; Specifications: Φ828mm * Φ633mm * 6600mm; Heat treatment process as follows:

[0017] Step 1) Stepped solution treatment: The furnace temperature is 300℃. The temperature is increased to 450℃ at a rate of 80℃ / h and held for 2 hours. Then the temperature is increased to 650℃ at a rate of 80℃ / h and held for 2 hours. Then the temperature is increased to 950℃ at a rate of 80℃ / h and held for 2 hours. Then the temperature is increased to 1100℃ at a rate of 50℃ / h and held for 1 hour. After the furnace is removed, Step 2) Variable speed cooling is performed.

[0018] Step 2) After the heat preservation in Step 1) is completed, perform variable speed cooling: within 43 seconds after the heat preservation is completed, the workpiece is lifted into a water tank for water cooling (initially water temperature 28℃). Six pumps are turned on in the water tank to stir thoroughly. Water cooling (cooling rate 150℃ / min) is performed until the surface temperature of the workpiece reaches 500℃. Then air cooling (cooling rate 30℃ / min) is performed until the surface temperature of the workpiece is 150℃. Then the workpiece is placed into the heating furnace and Step 3) composite stabilization treatment is performed.

[0019] Step 3) After step 2) is completed, perform composite stabilization treatment: the furnace temperature is 400℃, and the temperature is increased to 900℃ at a rate of 80℃ / h and held for 4 hours. Then the furnace is cooled to 850℃ and held for 2 hours. Then the furnace is cooled to 800℃ and held for 2 hours. After the holding period, the furnace is removed and air-cooled to room temperature.

[0020] After production according to the above heat treatment process, the test results according to ASTM E112 standard are shown in Table 1:

[0021] Table 1 Test Results

[0022]

[0023]

[0024] After the production of ultra-large diameter TP347H seamless steel pipes using the improved heat treatment process of this invention, the grain size test results meet the requirements.

[0025] Example 2: A heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipes. Steel grade: TP347H; Chemical composition: C = 0.49%, Si = 0.57%, Mn = 0.87%, Cr = 18.19%, Ni = 11.52%, S = 0.025%, P = 0.019%, Nb = 0.44%, balance: iron; Specifications: Φ929mm * Φ694mm * 6600mm; Heat treatment process as follows:

[0026] Step 1) Stepped solution treatment: The furnace temperature is 350℃. The temperature is increased to 450℃ at a rate of 80℃ / h and held for 2 hours. Then the temperature is increased to 650℃ at a rate of 80℃ / h and held for 2 hours. Then the temperature is increased to 950℃ at a rate of 80℃ / h and held for 2.5 hours. Then the temperature is increased to 1100℃ at a rate of 50℃ / h and held for 1.5 hours. After the furnace is removed, Step 2) Variable speed cooling is performed.

[0027] Step 2) After the heat preservation in Step 1) is completed, perform variable speed cooling: within 46 seconds after the heat preservation is completed, the workpiece is lifted into a water tank for water cooling (initially water temperature 25℃). Six pumps are turned on in the water tank to stir thoroughly. Water cooling (cooling rate 150℃ / min) is performed until the surface temperature of the workpiece reaches 500℃. Then air cooling is performed (cooling rate 30℃ / min) until the surface temperature of the workpiece is 150℃. Then the workpiece is loaded into the heating furnace and Step 3) composite stabilization treatment is performed.

[0028] Step 3) After step 2) is completed, perform composite stabilization treatment: the furnace temperature is 400℃, and the temperature is increased to 900℃ at a rate of 80℃ / h and held for 4 hours. Then the furnace is cooled to 850℃ and held for 2 hours. Then the furnace is cooled to 800℃ and held for 2 hours. After the holding period, the furnace is removed and air-cooled to room temperature.

[0029] After production according to the above heat treatment process, the test results according to ASTM E112 standard are shown in Table 2:

[0030] Table 2 Detection Results

[0031]

[0032]

[0033] After production using the heat treatment process of the present invention to improve the grain size of ultra-large diameter TP347H seamless steel pipe, the grain size test results meet the requirements.

Claims

1. A heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipes, characterized in that: The process steps are as follows: Step 1) Stepped solution treatment: The furnace temperature is ≤350℃. The temperature is increased to 400℃~500℃ at a rate of 50~100℃ / h and held for 1~3h. Then the temperature is increased to 600℃~700℃ at a rate of 50~100℃ / h and held for 1~3h. Then the temperature is increased to 950℃~1000℃ at a rate of 50~100℃ / h and held for 1~4h. Then the temperature is increased to 1080℃~1130℃ at a rate of ≤50℃ / h and held for 1~3h. After the furnace is removed, Step 2) Variable speed cooling is performed. Step 2) Variable speed cooling: Within 50 seconds after the heat preservation in Step 1), the workpiece is hoisted into a water tank for water cooling. The water temperature is controlled below 30℃. The water tank should be thoroughly stirred. Water cooling: Control the cooling rate ≥150℃ / min until the workpiece surface temperature reaches 500℃~550℃, and then perform air cooling. Air cooling: Control the cooling rate ≤30℃ / min until the workpiece surface temperature is in the range of 150℃~250℃. Then, load the workpiece into the heating furnace. After completing Step 2), prepare to perform composite stabilization treatment. Step 3) Composite stabilization treatment: The furnace temperature is ≤400℃. The temperature is increased to 890~910℃ at a heating rate of 50~100℃ / h and held for 2~4h. Then the furnace is cooled to 840~860℃ and held for 1~2h. Then the furnace is cooled to 790~810℃ and held for 1~2h. After the holding is completed, the furnace is removed and air-cooled to room temperature.

2. The heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipe according to claim 1, characterized in that: It is suitable for improving the grain size of TP347H seamless steel pipes with an outer diameter ≥650mm, wall thickness 80mm-100mm, and length ≥6000mm, thereby improving the quality of TP347H seamless steel pipes.

3. The heat treatment process for improving the grain size of ultra-large diameter TP347H seamless steel pipe according to claim 1, characterized in that: The chemical composition of steel grade TP347H is as follows: C=0.05%, Si=0.56%, Mn=0.95%, Cr=18.59%, Ni=11.33%, S=0.003%, P=0.020%, Nb=0.40%, with the balance being iron.

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