Smelting and forging heat treatment process method of 15Cr2NiMoV steel for natural gas compressor shell

Abstract

The invention provides a smelting and forging heat treatment process method of 15Cr2NiMoV steel for a natural gas compressor shell. A steel ingot is smelted and poured by adopting a process route of EBT electric arc furnace-LF furnace refining-VD vacuum refining-die casting. According to the 15Cr2NiMoV steel forge piece for the natural gas compressor shell, the heating temperatures of forge pieces of different specifications are controlled, a steel ingot is heated to a certain temperature to be forged, heat treatment is conducted after the forge piece is forged and formed, and good tissue and comprehensive mechanical properties are obtained. The 15Cr2NiMoV steel forge piece product for the natural gas compressor shell is manufactured by optimizing the component proportion and reasonably selecting smelting, forging and heat treatment processes, and the obtained material has high normal-temperature and high-temperature tensile strength and hardness, good low-temperature impact toughness and temper brittleness resistance and high creep strength and high-temperature endurance strength; according to the method, the product quality is improved, the rejection rate is reduced, and compared with the prior art, the method has great practical application value.

Description

Technical Field

[0001] The invention relates to the technical field of high-strength heat-resistant steel for natural gas compressors, and in particular to a smelting and forging heat treatment process method of 15Cr2NiMoV steel for natural gas compressor housings. Background Art

[0002] With the rapid development of natural gas pipeline construction, the number of natural gas pipeline compressor units, as core equipment, has increased rapidly, and the demand for compressor units has also increased day by day. Understanding pipeline compressor units and their application status will help the selection and use of units in pipeline construction. Compressors, as a common equipment in the natural gas production process, are widely used in all aspects of natural gas production. In order to obtain 15Cr2NiMoV steel forgings with excellent comprehensive performance, it is necessary to optimize the material composition ratio and reasonably select the smelting, forging and heat treatment processes of the forgings. Summary of the invention

[0003] The purpose of the present invention is to provide a preferred composition and smelting and forging heat treatment process of 15Cr2NiMoV steel for natural gas compressor housing, ensuring advantages in comprehensive properties such as strength, hardness, low-temperature impact toughness, resistance to temper brittleness and high-temperature endurance strength.

[0004] The technical solution of the present invention is a smelting and forging heat treatment process of 15Cr2NiMoV steel for natural gas compressor housing, wherein the chemical composition of 15Cr2NiMoV steel is composed of the following components by weight percentage: C: 0.13-0.18%, Si: 0.17-0.37%, Mn: 0.30-0.60%, P: ≤0.01%, S: ≤0.012%, Cr: 1.8-2.3%, Mo: 0.5-0.7%, Ni: 1.00-1.50, V: 0.10-0.12%, Al: 0.010-0.040%, Co: ≤0.03%, residual element As≤0.0 10%, Sn≤0.005%, Sb≤0.005%, Cu≤0.10%, gas elements [H]≤2ppm, [O]≤20ppm, [N]≤80ppm, the balance is Fe and inevitable impurities, the steel ingot is smelted and cast by the EBT arc furnace-LF furnace refining-VD vacuum refining-die casting process; the steel ingot is forged into a forging, the initial heating temperature of the steel ingot is set at 1220℃, the final forging temperature of each forging process is required to be greater than 800℃, in the final fire forming stage, the final forging temperature is greater than 750℃, and the forging ratio is greater than 6; the forging is heat treated after forging, and the heat treatment process comprises the following steps: Step 1: Normalizing + tempering, load the furnace at ≤400℃, heat to 950±10℃ at a speed of ≤120℃ / h and keep warm for 9h; then heat to 680±10℃ at a speed of ≤120℃ / h and keep warm for 12h, then take out of the furnace and air cool; Step 2, quenching + tempering: load the furnace at ≤400℃, heat to 940±10℃ at ≤120℃ / h, keep warm for 9h, and cool in water; load the furnace at ≤400℃, heat to 590±10℃ at ≤120℃ / h, keep warm for 12.8h, and cool in air; Step 3: Performance heat treatment, simulate post-weld heat treatment PWHT.max 650℃×45h, PWHT.min 650℃×20h. Load the furnace at ≤400℃, heat to 650±10℃ at a speed of ≤120℃ / h, and then air cool after exiting the furnace.

[0005] The chemical composition of 15Cr2NiMoV steel is optimized on the basis of the required range: C content is the main factor to ensure that the strength meets the requirements of the specification. If the C content is low, the strength cannot meet the requirements; if the C content is high, the low-temperature toughness and weldability of 15Cr2NiMoV steel will be reduced. Considering that this type of steel belongs to low-alloy steel, the C content is controlled at the upper limit; Mn can improve the strength of steel and weaken and eliminate the adverse effects of sulfur. Ni can improve the hardenability of steel and improve the low-temperature toughness of steel, so the Mn and Ni elements are controlled at the middle upper limit; Mo can improve the hardenability of steel and reduce the temper brittleness of steel, so the Mo element content should be controlled at the upper limit; V can improve the hardenability and high-temperature mechanical properties of steel and refine the grains, and has precipitation strengthening effect, but too much V is prone to forging cracks, so V is controlled at the middle limit; Ti has a similar effect to V, and TiC stabilizes carbides after heat treatment; Si is the main element for the formation of ferrite, which is a strengthening factor and a factor that promotes embrittlement. Si itself does not cause embrittlement, but promotes the embrittlement of P: when P is high, Si often squeezes P to the grain boundary (when the cooling speed of heat treatment after forging is slow, and the tempering parameter Pt value is greater than a certain value due to many tempering times, the embrittlement factor will also precipitate at the grain boundary); and O will also combine with Si to form SiO 2 The inclusion of oxides is concentrated at the grain boundaries, resulting in embrittlement at the grain boundaries; the appropriate amount of Si content can reduce the austenite transformation temperature, thereby inhibiting the precipitation of proeutectoid ferrite, which is conducive to the formation of fine bainite structure, thereby improving the strength and toughness of steel; the 15Cr2NiMoV steel used for natural gas compressor housing has extremely strict restrictions on harmful elements such as Cu, As, Sn, and Sb, and has extremely strict control requirements for the above harmful elements. At the same time, the material is required to have good purity, good plasticity, and toughness, so the requirements for harmful elements and gas elements such as S, P, H, O, and N are relatively strict.

[0006] Beneficial effects of the present invention: (1) The present invention optimizes the composition ratio and reasonably selects the smelting, forging and heat treatment processes, so that the 15Cr2NiMoV steel forgings have high room temperature and high temperature strength, hardness, good low temperature impact toughness, resistance to temper brittleness, high creep strength and high temperature endurance strength. After multiple production verifications, its room temperature strength, high temperature strength and hardness meet the technical standard requirements; at the same time, the brittle critical temperature Тк value is determined, and each performance index has a large margin; (2) The forging heat treatment process of the present invention is easy to implement. The present invention improves the quality of the product and reduces the scrap rate. Compared with the prior art, it has great practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The shape and size of the forging of Example 1; Figure 2 This is a metallographic micrograph of Example 1 after quenching and tempering; Figure 3 This is the metallographic micrograph of Example 1 after quenching + tempering + PWHT.min; Figure 4 This is a metallographic micrograph of Example 1 after quenching + tempering + PWHT.max. DETAILED DESCRIPTION

[0008] The present invention is further described in detail below.

[0009] Example 1 A 15Cr2NiMoV steel for a natural gas compressor housing, the chemical composition of the 15Cr2NiMoV steel consists of the following components by mass percentage: C: 0.16%, Si: 0.24%, Mn: 0.47%, P: 0.001%, S: 0.001%, Cr: 1.91%, Mo: 0.61%, Ni: 1.08, V: 0.10%, Al: 0.03%, Co: 0.02%, residual elements As≤0.003%, Sn≤0.001%, Sb≤0.001%, Cu: 0.04%, contained gas elements [H]≤2ppm, [O]≤20ppm, [N]≤80ppm, the balance is Fe and unavoidable impurities, a smelting process of 15Cr2NiMoV steel for a natural gas compressor housing, the above-mentioned 15Cr2NiMoV steel comprises the following manufacturing steps: (1) Charge: The charge is mainly composed of NiMo scrap steel and CrMo steel chips, with a carbon content of ≥0.6%. Carbon balls are added in the first batch and added in the middle of the charge; (2) Smelting and casting: The steel ingots are manufactured by using the EBT electric arc furnace - LF furnace refining - VD vacuum refining - mold casting process.

[0010] The obtained steel ingot is used to forge a forging, and the forging process comprises the following steps: Take the cylindrical forging with the dimensions of outer diameter φ=1920mm, inner diameter φ=1455mm, and length L=3573mm as an example. The weight of the forging is made of 50T steel ingots to a diameter of Φ1600mm, and forged with Φ1600mm round steel blanks. The initial forging temperature is 1220℃, the final forging temperature is 800℃, the forging times are 3 times, and the furnace is cooled after forging. Figure 1 shown.

[0011] The forging is heat treated, and the heat treatment process comprises the following steps: Step 1: Normalizing + tempering, load the furnace at ≤400℃, heat to 950±10℃ at a speed of ≤120℃ / h, and keep warm for 9h; then heat to 680±10℃ at a speed of ≤120℃ / h, and keep warm for 12h, then take out of the furnace and air cool; Step 2: Quenching + tempering: load the furnace at ≤400℃, heat to 940±10℃ at ≤120℃ / h, keep warm for 9h, and cool in water; load the furnace at ≤400℃, heat to 590±10℃ at ≤120℃ / h, keep warm for 12.8h, and cool in air; Step 3: Performance heat treatment, simulate post-weld heat treatment PWHT.max 650℃×45h, PWHT.min 650℃×20h. Load the furnace at ≤400℃, heat to 650±10℃ at a speed of ≤120℃ / h, and then air cool after exiting the furnace.

[0012] The performance of a 15Cr2NiMoV steel forging for a natural gas compressor housing prepared by the above smelting, forging and heat treatment work was tested: After normalizing + tempering, quenching + tempering + performance heat treatment at 650℃ for 45h (PWHT.max) and quenching + tempering + performance heat treatment at 650℃ for 20h (PWHT.min) respectively, the forgings were sampled for mechanical properties, microstructure, non-metallic inclusions and grain size testing, and the test results fully met the technical requirements. Figure 2 , Figure 3 , Figure 4 As shown in the figure, the metallographic microstructure is tempered martensite. The brittle critical temperature Тк value of 15Cr2NiMoV steel meets the technical requirements.

[0013] Product performance requirements: Room temperature tensile Rel≥490MPa, Rm / MPa=610MPa, A≥15%, Z≥55%; 350℃ high temperature tensile Rel≥440MPa, Rm≥540MPa, A≥14%, Z≥50%; body hardness ≤330HB; Тк≤-35℃; microstructure is tempered troostite structure, non-metallic inclusions: oxide ≤2.5, sulfide ≤2.0, silicate ≤3.5.

[0014] Quenching + tempering + Min.PWHT (650℃ holding for 20h), room temperature tensile Rel=588MPa, Rm / MPa=683MPa, A=25%, Z≥80%; 350℃ high temperature tensile Rel=612MPa, Rm / MPa=695MPa, A=19%, Z=77%; body hardness 207HB; Тк=-125℃; microstructure is tempered troostite structure, non-metallic inclusions: oxide 1.0, sulfide 1.0, silicate 1.0.

[0015] Quenching + tempering + Max.PWHT (650℃ insulation for 45h) Room temperature tensile Rel=585MPa, Rm / MPa=690MPa, A=25.5%, Z=79%; 350℃ high temperature tensile Rel=489MPa, Rm / MPa=591MPa, A≥19.5%, Z≥75%; Body hardness 207HB; Тк=-126℃; Microstructure is tempered troostite structure, non-metallic inclusions: oxide 1.0, sulfide 1.0, silicate 1.0.

Claims

1. A smelting and forging heat treatment process for 15Cr2NiMoV steel for natural gas compressor housing, wherein the chemical composition of 15Cr2NiMoV steel is composed of the following components by weight percentage: C: 0.13-0.18%, Si: 0.17-0.37%, Mn: 0.30-0.60%, P: ≤0.01%, S: ≤0.012%, Cr: 1.8-2.3%, Mo: 0.5-0.7%, Ni: 1.00-1.50, V: 0.10-0.12%, Al: 0.010-0.040%, Co: ≤0.03%, residual element As ≤0.010%, Sn≤0.005%, Sb≤0.005%, Cu≤0.10%, gas elements [H]≤2ppm, [O]≤20ppm, [N]≤80ppm, the balance is Fe and inevitable impurities, the EBT arc furnace-LF furnace refining-VD vacuum refining-die casting process is adopted to smelt and cast the steel ingot; the steel ingot is forged into forgings, the initial heating temperature of the steel ingot is set at 1220℃, the final forging temperature of each forging process is required to be greater than 800℃, in the final fire forming stage, the final forging temperature is greater than 750℃, and the forging ratio is greater than 6; the forging is heat treated after forging, and the heat treatment process comprises the following steps: Step 1, normalizing + tempering: load the furnace at ≤400℃, heat to 950±10℃ at a heating rate of ≤120℃ / h, and keep warm for 9h; then heat to 680±10℃ at a rate of ≤120℃ / h, and keep warm for 12h, then take out of the furnace and air cool; Step 2, quenching + tempering: load the furnace at ≤400℃, heat to 940±10℃ at ≤120℃ / h, keep warm for 9h, and cool in water; load the furnace at ≤400℃, heat to 590±10℃ at ≤120℃ / h, keep warm for 12.8h, and cool in air; Step 3: Performance heat treatment: simulate post-weld heat treatment PWHT.max 650℃×45h, PWHT.min 650℃×20h, load the furnace at ≤400℃, heat to 650±10℃ at a speed of ≤120℃ / h, and then air cool after exiting the furnace.

2. The smelting and forging heat treatment process of 15Cr2NiMoV steel for natural gas compressor housing according to claim 1 is characterized in that: The forgings are forged three times and furnace cooled after forging.

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