Ultra-pure smelting method for high-performance Cr-Ni-W shaft steel and high-performance Cr-Ni-W shaft steel

Abstract

The invention belongs to the field of ultra-pure smelting processes of high-performance Cr-Ni-W series high-strength steel, and particularly relates to an ultra-pure smelting method of high-performance Cr-Ni-W shaft steel and the high-performance Cr-Ni-W shaft steel. According to the method, vacuum induction melting is adopted, furnace charge is heated and melted in a magnetic induction mode, the whole melting process is completed in vacuum, and no slag participates in the metallurgy process. The smelting mode has a good effect of removing gas and non-ferrous metal impurities, and alloy elements are basically not burnt. In the vacuum consumable remelting process, inclusion particles float to the surface of a molten pool and are gradually adsorbed by the wall of a crucible under the action of an electric arc, so that the inclusion content in the alloy can be further reduced, and the purity of a cast ingot is improved; and meanwhile, reasonable cooperation of current and voltage, melting speed and cooling is adopted in the melting process, and the component and structure uniformity of Cr-Ni-W series high-strength steel finished product cast ingots is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the field of ultrapure smelting technology of high-performance Cr-Ni-W series high-strength steel, and specifically relates to an ultrapure smelting method of high-performance Cr-Ni-W shaft steel and high-performance Cr-Ni-W shaft steel. Background Art

[0002] Cr-Ni-W series high-strength steel is a structural alloy steel characterized by low gas and impurity content, high alloy content, and excellent strength and toughness. Cr-Ni-W series high-strength steel is commonly used to manufacture large-section carburized parts requiring high strength, good toughness, and low notch sensitivity, such as large gears, drive shafts, crankshafts, and spline shafts; and high-strength parts subject to heavy loads and vibration, such as connecting rods, gears, and crankshafts in heavy and medium-sized machinery.

[0003] The shipbuilding industry is a modern, comprehensive, and strategic industry that provides technical equipment for water transportation and marine resource development. It serves as the foundation and crucial support for China's implementation of its maritime power strategy. This industry places high demands on the development of high-end marine equipment in my country. Cr-Ni-W series high-strength steels, used in ship crankshafts and transmission systems, require high performance, long life, and high reliability. This in turn demands that the raw materials possess ultra-high purity, ultra-low inclusion levels, and a superior balance of strength and toughness.

[0004] Conventional Cr-Ni-W series high-strength steels are generally smelted in electric arc furnaces or electric arc furnaces + electroslag remelting. It is difficult to significantly improve the purity of the materials in conventional smelting process technology and cannot meet high performance requirements. In order to meet the high requirements of high-end marine equipment for Cr-Ni-W series high-strength steels, the present invention proposes to use an ultra-pure smelting process technology of vacuum induction + vacuum consumable remelting to significantly reduce the level of residual elements and gas content, and obtain Cr-Ni-W series high-strength steels with ultra-high purity, ultra-low inclusion levels and better toughness. Tables 1 and 2 are the requirements for residual elements and gas content and non-metallic inclusion levels in the industry standards and the technical specifications for smelting Cr-Ni-W series high-strength steels of the present invention (hereinafter referred to as "enterprise standards"), respectively.

[0005] Table 1 Residual element and gas content requirements (unit: wt%)

[0006]

[0007]

[0008] Table 2 Non-metallic inclusion level requirements

[0009] Summary of the Invention

[0010] To address the shortcomings of the aforementioned prior art, the present invention provides a method for melting ultrapure Cr-Ni-W series high-strength steel and the resulting high-performance Cr-Ni-W shaft steel. This method utilizes a smelting process combining vacuum induction melting and vacuum consumable remelting to produce a Cr-Ni-W series high-strength steel with ultra-high purity, ultra-low inclusion levels, and enhanced toughness. This steel can be used to manufacture high-performance, high-strength steel for key components in transmission systems for high-end marine equipment.

[0011] The technical solution of the present invention is:

[0012] A method for smelting ultrapure Cr-Ni-W series high-strength steel includes vacuum induction melting and vacuum consumable remelting. The composition of the Cr-Ni-W series high-strength steel, measured by mass percentage, includes: C 0.16-0.18%, Si 0.28-0.35%, Mn 0.38-0.60%, P ≤ 0.006%, S ≤ 0.004%, Cr 1.40-1.60%, Ni ≤ 4.20-4.40%, Cu ≤ 0.10%, W 0.90-1.10%, Al ≤ 0.016%, Ti ≤ 0.02%, H ≤ 0.00010%, O ≤ 0.0010%, N ≤ 0.0018%, and the remainder is Fe. Vacuum induction melting is used to heat and melt the charge using magnetic induction. The entire melting process is completed under vacuum, and no slag is involved in the metallurgical process. This smelting method effectively removes gas and nonferrous metal impurities, with minimal burn-off of alloying elements. During vacuum consumable remelting, inclusion particles rise to the surface of the molten pool and are gradually absorbed by the crucible wall under the action of the arc, further reducing the inclusion content in the alloy and improving the purity of the ingot. Simultaneously, the smelting process utilizes a reasonable combination of current, voltage, melting rate, and cooling to ensure uniform composition and microstructure of the finished Cr-Ni-W series high-strength steel ingots.

[0013] The smelting method of the ultra-pure high-performance Cr-Ni-W shaft steel specifically comprises the following steps:

[0014] 1) Vacuum induction melting

[0015] ① Load the materials in the order of pure iron → metal Ni plate, metal W → pure iron;

[0016] ② The vacuum degree during the melting stage is ≤4.1Pa, high vacuum is maintained throughout the melting process, and the melting is slow to facilitate degassing; samples are taken for analysis of C, S, Ni, W, Al, P, and N;

[0017] ③ Electrode rod composition control: C0.16~0.18%, Si0.28~0.35%, Mn0.50~0.80%, P≤0.006%, S≤0.004%, Cr 1.40~1.60%, Ni≤4.20~4.40%, Cu≤0.10%, W0.90~1.10%, Al≤0.016%, Ti≤0.02%, H≤0.00015%, O≤0.0015%, N≤0.0020%, and the rest is Fe;

[0018] ④After the electrode rod mold is cooled and demoulded, it should be sent for annealing in time;

[0019] 2) Vacuum consumable remelting:

[0020] The diameter of the consumable ingot corresponding to the induction mother electrode is Vacuum consumable remelting is divided into three stages: arc starting stage - steady state stage - hot capping stage;

[0021] ① Arc starting stage: current is 3-15kA, voltage is 20-25V, and arc starting time is 100-150min;

[0022] ② Steady-state stage: the vacuum degree is maintained at ≤2Pa, the steady-state current in the normal melting stage is 8-12kA, the steady-state voltage is 20-25V, the steady-state melting rate is 4.0-7.0kg / min, and the smaller the fluctuation, the better;

[0023] ③Hot sealing stage: the current is 4-10kA, the voltage is 20-24V, and the hot sealing time is 30-80min. After remelting, the product is cooled under vacuum for 40-100min and then the vacuum is broken. After demoulding, the product is sent for stress annealing.

[0024] 3) Hot forging

[0025] Heat the vacuum consumable ingot to 1150-1200℃, keep it warm for 3-6 hours, then take it out of the furnace for forging. The starting forging temperature is 950-1050℃, and the final forging temperature is 850-950℃.

[0026] 4) Post-forging heat treatment: The bars are air-cooled after forging and then normalized.

[0027] Furthermore, in step 1) (2), when N ≤ 30 ppm, metallic Cr and Ni are added to the steel, and stirring and refining are carried out, and samples are taken for analysis of C, Cr, W, Ni, and N; when N ≤ 30 ppm, Mn is added to fine-tune the chemical composition, and stirring is carried out until there are no bubbles, and then samples are taken for measurement of all elements and gaseous N; after N ≤ 30 ppm is qualified, pouring is carried out, and the pouring temperature is 1560-1600°C.

[0028] Furthermore, in step 1) in ④, the annealing process is to heat the electrode rod to 680±20°C and keep it at this temperature for 20 to 30 hours, then cool it to below 500°C in the furnace at a cooling rate of ≤50°C / h, and then take it out of the furnace and air-cool it to room temperature.

[0029] Furthermore, after the electrode is annealed in step 1), it is polished and flattened to remove the oxide scale.

[0030] Furthermore, in step 2) ②, when the current and voltage are fixed (horizontal power control), the current I (unit: kA) is proportional to the melting rate v (unit: kg / min), and the ratio K (unitless) = [I] / [v], K is between 1.14 and 3.

[0031] Furthermore, in step 2) in ③, the composition of the vacuum consumable ingot is controlled as follows: C 0.16-0.18%, Si 0.28-0.35%, Mn 0.38-0.60%, P ≤ 0.006%, S ≤ 0.004%, Cr 1.40-1.60%, Ni ≤ 4.20-4.40%, Cu ≤ 0.10%, W 0.90-1.10%, Al ≤ 0.016%, Ti ≤ 0.02%, H ≤ 0.00010%, O ≤ 0.0010%, N ≤ 0.0018%, and the rest is Fe.

[0032] Furthermore, in step 3), the number of upsetting and drawing is determined according to the specifications of the finished product, the intermediate billet is kept at a temperature of 1050-1100° C. for 1-3 hours, and the cumulative forging ratio is ensured to be 4-6.

[0033] Furthermore, in step 4), the rod is heated to 850-950°C and kept at this temperature for 5-9 hours, then taken out of the furnace and air-cooled. It is then heated to 650-700°C and kept at this temperature for 25-30 hours, then cooled to below 500°C and taken out of the furnace and air-cooled.

[0034] The present invention also provides an ultra-pure high-performance Cr-Ni-W shaft steel prepared by the smelting method of the above-mentioned ultra-pure high-performance Cr-Ni-W shaft steel; the composition of the high-performance Cr-Ni-W shaft steel, calculated by mass percentage, includes: C 0.16-0.18%, Si 0.28-0.35%, Mn 0.38-0.60%, P ≤ 0.006%, S ≤ 0.004%, Cr 1.40-1.60%, Ni ≤ 4.20-4.40%, Cu ≤ 0.10%, W 0.90-1.10%, Al ≤ 0.016%, Ti ≤ 0.02%, H ≤ 0.00010%, O ≤ 0.0010%, N ≤ 0.0018%, and the rest is Fe. Detailed description of the invention:

[0036] A smelting method for ultra-pure high-performance Cr-Ni-W shaft steel

[0037] 1) Vacuum induction melting:

[0038] ① Raw material requirements: Use high-purity Ni, Cr, and Mn metals, and use special pure iron ingredients. All metal materials must have accurate composition. The metal materials and alloy materials used must be clean and free of oil, rust, dust, oxide scale, and other contaminants.

[0039] ②Charging requirements: Charge in the order of pure iron → metal Ni plate, metal W → pure iron. The melting stage requires slow melting to maintain the best degassing state of the melt and add materials in this state.

[0040] ③ Melting Requirements: The vacuum level during the melting stage must be ≤4.1Pa. High vacuum must be maintained throughout the melting process, and the melting process must be slow to facilitate degassing. Samples must be taken for analysis of C, S, Ni, W, Al, P, and N. When N is ≤30ppm, metallic Cr and Ni are added to the steel, followed by stirring and refining. Samples must be taken for analysis of C, Cr, W, Ni, and N. When N is ≤30ppm, Mn is added to fine-tune the chemical composition. Stir until there are no bubbles, and then sample for analysis of all elements and gaseous N. After N is ≤30ppm and passes the test, pouring can begin at a temperature of 1560-1600°C.

[0041] ④ Electrode rod composition control: C0.16~0.18%, Si0.28~0.35%, Mn0.50~0.80%, P≤0.006%, S≤0.004%, Cr 1.40~1.60%, Ni≤4.20~4.40%, Cu≤0.10%, W0.90~1.10%, Al≤0.016%, Ti≤0.02%, H≤0.00015%, O≤0.0015%, N≤0.0020%, and the rest is Fe.

[0042] ⑤ After the electrode rod mold cools and is demolded, it is promptly annealed. The annealing process involves heating the electrode rod to 680±20°C for 20-30 hours, then cooling it in a furnace at a rate of ≤50°C / hour to below 500°C, then removing it from the furnace and air-cooling it to room temperature. After annealing, the electrode is polished, flattened, and scaled.

[0043] 2) Vacuum consumable remelting:

[0044] The diameter of the consumable ingot corresponding to the induction mother electrode is Vacuum consumable remelting is divided into three stages: arc starting stage - steady state stage - hot capping stage.

[0045] ① Arcing Stage: Current: 3-15kA, voltage: 20-25V, arcing time: 100-150 minutes. The primary task is to ignite the arc and quickly and reliably transition it to a stable combustion phase, ensuring that the molten metal essentially covers the bottom of the vessel, laying the foundation for normal melting and ingot formation. Adjust the current and voltage within the set range based on actual conditions.

[0046] ② Steady-state stage: The vacuum is maintained at ≤2Pa. During the normal melting stage, the steady-state current is 8-12kA, the steady-state voltage is 20-25V, and the steady-state melting rate is 4.0-7.0kg / min, with the smallest fluctuations being preferred. The matching of process parameters such as voltage, current, vacuum, and melting rate directly impacts ingot quality, with the steady-state current and melting rate being particularly critical. If the melting rate is too fast, ingot segregation can easily occur; if the melting rate is too slow, the melting time will be too long, resulting in energy waste, increased costs, and reduced production efficiency. A reasonable melting rate can reduce or even eliminate internal segregation in the ingot, improve the first-time yield, and significantly reduce energy consumption. The present invention proposes that during the normal stable melting stage, when the current and voltage are fixed (horizontal power control), the current I (unit: kA) is proportional to the melting rate v (unit: kg / min), with the ratio K (unitless) = [I] / [v]. When K is between 1.14 and 3 and the melting rate is kept as constant as possible, an ingot with uniform structure and low segregation can be obtained. The ratio K is related to the specific heat capacity of the steel grade. The larger the specific heat capacity, the smaller the ratio K.

[0047] ③ Hot-capping stage: Current is 4-10kA, voltage is 20-24V, and hot-capping time is 30-80 minutes. The main task is to compensate for head shrinkage. Proper control of current, voltage, and hot-capping time is crucial to improve shrinkage and porosity in the ingot head and reduce impurities such as gas in the head.

[0048] After remelting, the product is cooled under vacuum for 40 to 100 minutes and then the vacuum is broken. After demoulding, it is sent for stress annealing.

[0049] The composition of the vacuum consumable ingot is controlled as follows: C 0.16~0.18%, Si 0.28~0.35%, Mn 0.38~0.60%, P≤0.006%, S≤0.004%, Cr 1.40~1.60%, Ni≤4.20~4.40%, Cu≤0.10%, W0.90~1.10%, Al≤0.016%, Ti≤0.02%, H≤0.00010%, O≤0.0010%, N≤0.0018%, and the rest is Fe.

[0050] 3) Hot forging

[0051] Heat the vacuum consumable ingot to 1150-1200°C, hold it for 3-6 hours, then remove it from the furnace for forging. The start forging temperature is 950-1050°C, and the final forging temperature is 850-950°C. The number of upsetting and drawing passes is determined by the finished product specifications. The intermediate billet is held at 1050-1100°C for 1-3 hours. Ensure a cumulative forging ratio of 4-6.

[0052] 4) Post-forging heat treatment

[0053] After forging, the bar is air-cooled and then normalized. The bar is heated to 850-950℃ and kept at this temperature for 5-9 hours before being taken out of the furnace and air-cooled. Then, it is heated to 650-700℃ and kept at this temperature for 25-30 hours. The bar is then cooled to below 500℃ and air-cooled.

[0054] Compared with the existing technology, the present invention has the following advantages:

[0055] 1. In the vacuum induction melting process of the present invention, a pure and uniform mother electrode is obtained by using high-purity and clean raw materials for smelting, adopting a reasonable charging sequence, strict vacuum requirements, and a slow melting speed.

[0056] 2. During the vacuum consumable melting process, the present invention utilizes appropriate current and voltage settings during the arc starting, steady-state, and hot-capping stages to control the melting rate during the steady-state stage, thereby ensuring uniform composition and microstructure of the Cr-Ni-W series high-strength steel consumable ingot. Furthermore, the vacuum degree during the melting process is maintained at ≤2 Pa, further enabling gas removal.

[0057] The Cr-Ni-W series high-strength steel obtained using the above method has excellent comprehensive performance. The performance indicators of the Cr-Ni-W series high-strength steel smelted by double vacuum smelting were compared with those prepared by electric furnace + electroslag. The tensile strength of the Cr-Ni-W series high-strength steel smelted by double vacuum smelting increased by 6.2% to 16.1%, the yield strength increased by 39.1% to 53.5%, the elongation increased by 12.0% to 52.4%, the cross-sectional shrinkage increased by 7.1% to 18.9%, and the V-notch impact energy increased by 40.5% to 82.3%. The strength and toughness of the Cr-Ni-W series high-strength steel smelted by double vacuum smelting are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a photo of non-metallic inclusions in the Cr-Ni-W series high-strength steel prepared in Example 1.

[0059] Figure 2 This is a photo of non-metallic inclusions in the Cr-Ni-W series high-strength steel prepared in Example 2.

[0060] Figure 3This is a photo of non-metallic inclusions in the Cr-Ni-W series high-strength steel prepared in Example 3.

[0061] Figure 4 This is a photo of non-metallic inclusions in the Cr-Ni-W series high-strength steel prepared in Comparative Example 1.

[0062] Figure 5 This is a photo of non-metallic inclusions in the Cr-Ni-W series high-strength steel prepared in Comparative Example 2.

[0063] Figure 6 This is a photo of non-metallic inclusions in the Cr-Ni-W series high-strength steel prepared in Comparative Example 3. DETAILED DESCRIPTION

[0064] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0065] The specific chemical compositions of Examples 1 to 3 and Comparative Examples 1 to 3 of the Cr-Ni-W series high-strength steel of the present invention are shown in Table 3; the non-metallic inclusion ratings of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 4; the mechanical properties of Examples 1 to 3 and Comparative Examples 1 to 3, including tensile strength, yield strength, elongation, reduction of area, and V-notch impact energy, are shown in Table 5.

[0066] Table 3 Chemical composition (wt / %)

[0067]

[0068]

[0069] Table 4 Non-metallic inclusions

[0070]

[0071]

[0072] Table 5 Mechanical properties

[0073]

[0074] Example 1

[0075] The chemical composition and mass fraction of the Cr-Ni-W series high-strength steel in this embodiment are shown in Table 3. The Cr-Ni-W series high-strength steel in this embodiment is prepared by the following steps:

[0076] 2) Vacuum induction melting

[0077] The materials are loaded in the order of pure iron → Ni metal plate, and then W metal → pure iron. The vacuum during the melting stage is 3.1-3.7 Pa, and the melting is slow to facilitate degassing. After nitrogen content is qualified as ≤30ppm, Φ520mm electrodes are cast at a temperature of 1575°C. The electrode rod composition is: C 0.18%, Si 0.31%, Mn 0.80%, P 0.006%, S 0.004%, Cr 1.60%, Ni 4.40%, Cu 0.10%, W 1.10%, Al 0.016%, Ti 0.02%, H 0.00015%, O 0.0015%, N 0.0020%, and the remainder is Fe.

[0078] After the electrode rods have cooled and been demolded, they are promptly annealed. The annealing process involves heating the electrode rods to 660°C and holding for 28 hours. They are then furnace-cooled to 480°C at a rate of 40°C / hour, removed from the furnace, and air-cooled to room temperature. After annealing, the electrodes are polished to remove the oxide scale.

[0079] 3) Vacuum self-consumption

[0080] Will The induction electrode is put into a vacuum consumable furnace for refining. The consumable ingot has a diameter of Vacuum consumable remelting is divided into three stages: arc starting stage, steady-state stage, and hot-capping stage. ① Arc starting stage: The current gradually increases from 3kA to 12.8kA, the voltage gradually increases from 20V to 24.6V, and the arc starting time is 116 minutes. ② Steady-state stage: During normal melting, the steady-state current is 9.7-12kA, the steady-state voltage is 21.8-25V, and the steady-state melting rate is 5.5kg / min. The ratio K of current I (unit: kA) to melting rate v (unit: kg / min) is 1.76-2.18. During normal melting, the vacuum degree is always maintained at ≤1.5Pa. ③ Hot-capping stage: The current gradually decreases from 9.5kA to 4kA, the voltage is 21.5-24V, and the hot-capping time is 45 minutes.

[0081] After remelting, the ingots were cooled under vacuum for 55 minutes before vacuum was broken. After demolding, they were hot-annealed. The composition of the consumable ingots was consistent with that of the finished product, as shown in Table 3.

[0082] 3) Hot forging

[0083] The vacuum consumable ingot was heated to 1180°C and held for 5 hours before being removed from the furnace for forging. The starting forging temperature was 950°C and the final forging temperature was 850°C. The intermediate billet was held at 1050°C for 3 hours. The cumulative forging ratio was 5.

[0084] 4) Post-forging heat treatment

[0085] After forging, the bars are air-cooled and then normalized. The bars are heated to 890°C for 7 hours, then removed from the furnace for air-cooling. They are then heated to 675°C for 28 hours, cooled to 400°C, and removed from the furnace for air-cooling.

[0086] Example 2

[0087] The chemical composition and mass fraction of the Cr-Ni-W series high-strength steel in this embodiment are shown in Table 3. The Cr-Ni-W series high-strength steel in this embodiment is prepared by the following steps:

[0088] 1) Vacuum induction melting

[0089] The materials are loaded in the order of pure iron → Ni metal plate, and then W metal → pure iron. The vacuum during the melting stage is 2.1-3.2 Pa, and the melting is slow to facilitate degassing. After nitrogen content is qualified as ≤30ppm, Φ520mm electrodes are cast at a temperature of 1560°C. The electrode rod composition is: C 0.17%, Si 0.35%, Mn 0.73%, P 0.005%, S 0.001%, Cr 1.40%, Ni 4.28%, Cu 0.05%, W 1.02%, Al 0.010%, Ti 0.01%, H 0.00010%, O 0.0011%, N 0.0018%, and the remainder is Fe.

[0090] After the electrode rods are cooled and demolded, they are promptly annealed. The annealing process involves heating the electrode rods to 680°C and holding for 25 hours. The rods are then furnace-cooled to 400°C at a rate of 50°C / hour, removed from the furnace, and air-cooled to room temperature. After annealing, the electrodes are polished to remove the oxide scale.

[0091] 2) Vacuum self-consumption

[0092] Will The induction electrode is put into a vacuum consumable furnace for refining. The consumable ingot has a diameter of Vacuum consumable remelting is divided into three stages: arc starting stage, steady-state stage, and hot-capping stage. ① Arc starting stage: The current gradually increases from 4.5kA to 15kA, the voltage gradually increases from 21.8V to 25V, and the arc starting time is 100 minutes. ② Steady-state stage: During the normal melting stage, the steady-state current is 8-10.6kA, the steady-state voltage is 20-23.8V, and the steady-state melting rate is 4kg / min. The ratio K of the current I (unit: kA) to the melting rate v (unit: kg / min) is 2-2.65. During the normal melting process, the vacuum degree is always maintained at ≤1.7Pa. ③ Hot-capping stage: The current gradually decreases from 10kA to 5kA, the voltage is 20-23.5V, and the hot-capping time is 30 minutes.

[0093] After remelting, the ingots were cooled under vacuum for 40 minutes before vacuum was broken. After demolding, they were hot-annealed. The composition of the consumable ingots was consistent with that of the finished product, as shown in Table 3.

[0094] 3) Hot forging

[0095] The vacuum consumable ingot was heated to 1150°C, held for 6 hours, and then removed from the furnace for forging. The starting forging temperature was 1000°C, and the final forging temperature was 900°C. The intermediate billet was held at 1100°C for 1 hour. The cumulative forging ratio was 4.

[0096] 4) Post-forging heat treatment

[0097] After forging, the bars are air-cooled and then normalized. The bars are heated to 850°C and held for 9 hours before being air-cooled. They are then heated to 700°C and held for 25 hours before being cooled to 500°C before being air-cooled.

[0098] Example 3

[0099] The chemical composition and mass fraction of the Cr-Ni-W series high-strength steel in this embodiment are shown in Table 3. The Cr-Ni-W series high-strength steel in this embodiment is prepared by the following steps:

[0100] 1) Vacuum induction melting

[0101] The materials are loaded in the order of pure iron → Ni metal plate, and then W metal → pure iron. The vacuum during the melting stage is 3.0-4.1 Pa, and the melting is slow to facilitate degassing. After nitrogen content is qualified at ≤30ppm, Φ520mm electrodes are cast at a temperature of 1600°C. The electrode rod composition is: C 0.16%, Si 0.28%, Mn 0.50%, P 0.003%, S 0.002%, Cr 1.55%, Ni 4.20%, Cu 0.03%, W 0.90%, Al 0.012%, Ti 0.01%, H 0.00012%, O 0.0009%, N 0.0019%, and the remainder is Fe.

[0102] After the electrode rods are cooled and demolded, they are promptly annealed. The annealing process involves heating the electrode rods to 700°C and holding for 20 hours. They are then furnace-cooled to 500°C at a rate of 45°C / hour and air-cooled to room temperature. After annealing, the electrodes are polished to remove the oxide scale.

[0103] 2) Vacuum self-consumption

[0104] Will The induction electrode is put into a vacuum consumable furnace for refining. The consumable ingot has a diameter of Vacuum consumable remelting is divided into three stages: arc starting stage, steady-state stage, and hot-capping stage. ① Arc starting stage: The current gradually increases from 4.2kA to 12.6kA, the voltage gradually increases from 22.8V to 25V, and the arc starting time is 150 minutes. ② Steady-state stage: During normal melting, the steady-state current is 10.5-11.9kA, the steady-state voltage is 23.5-25V, and the steady-state melting rate is 7kg / min. The ratio K of current I (unit: kA) to melting rate v (unit: kg / min) is 1.5-1.7. During normal melting, the vacuum degree is always maintained at ≤2Pa. ③ Hot-capping stage: The current gradually decreases from 9kA to 5.7kA, the voltage is 21.3-23.8V, and the hot-capping time is 80 minutes.

[0105] After remelting, the ingots were cooled under vacuum for 90 minutes before vacuum was broken. After demolding, they were hot-sent for annealing. The composition of the consumable ingots was consistent with that of the finished product, as shown in Table 3.

[0106] 3) Hot forging

[0107] The vacuum consumable ingot was heated to 1200°C and held for 3 hours before being removed from the furnace for forging. The starting forging temperature was 1050°C and the final forging temperature was 950°C. The intermediate billet was held at 1080°C for 2 hours. The cumulative forging ratio was 6.

[0108] 4) Post-forging heat treatment

[0109] After forging, the bars are air-cooled and then normalized. The bars are heated to 950℃ and kept at this temperature for 5 hours before being taken out of the furnace and air-cooled. They are then heated to 650℃ and kept at this temperature for 30 hours before being cooled to 380℃ and air-cooled.

[0110] Figures 1 to 3 These are photos of non-metallic inclusions in the Cr-Ni-W series high-strength steels prepared by the double vacuum smelting method in Examples 1 to 3. Figures 4-6 The following are photos of non-metallic inclusions in the Cr-Ni-W series high-strength steels produced by the electric furnace + electroslag smelting method in comparative examples 1 to 3. It is clear that the Cr-Ni-W series high-strength steels produced by the double vacuum smelting method have higher purity.

Claims

1. A method for smelting ultrapure high-performance Cr-Ni-W shaft steel, characterized in that: The steps include: 1) Vacuum induction melting ① Load the materials in the order of pure iron → metal Ni plate, metal W → pure iron; ② The vacuum degree during the melting stage is ≤4.1Pa, high vacuum is maintained throughout the melting process, and the melting is slow to facilitate degassing; samples are taken for analysis of C, S, Ni, W, Al, P, and N; ③ Electrode rod composition control: C0.16~0.18%, Si0.28~0.35%, Mn0.50~0.80%, P≤0.006%, S≤0.004%, Cr 1.40~1.60%, Ni≤4.20~4.40%, Cu≤0.10%, W0.90~1.10%, Al≤0.016%, Ti≤0.02%, H≤0.00015%, O≤0.0015%, N≤0.0020%, and the rest is Fe; ④After the electrode rod mold is cooled and demoulded, it should be sent for annealing in time; 2) Vacuum consumable remelting: The diameter of the consumable ingot corresponding to the induction mother electrode is Vacuum consumable remelting is divided into three stages: arc starting stage - steady state stage - hot capping stage; ① Arc starting stage: current is 3-15kA, voltage is 20-25V, and arc starting time is 100-150min; ② Steady-state stage: the vacuum degree is maintained at ≤2Pa, the steady-state current in the normal melting stage is 8-12kA, the steady-state voltage is 20-25V, the steady-state melting rate is 4.0-7.0kg / min, and the smaller the fluctuation, the better; ③Hot sealing stage: the current is 4-10kA, the voltage is 20-24V, and the hot sealing time is 30-80min. After remelting, the product is cooled under vacuum for 40-100min and then the vacuum is broken. After demoulding, the product is sent for stress annealing. 3) Hot forging Heat the vacuum consumable ingot to 1150-1200℃, keep it warm for 3-6 hours, then take it out of the furnace for forging. The starting forging temperature is 950-1050℃, and the final forging temperature is 850-950℃. 4) Post-forging heat treatment: The bars are air-cooled after forging and then normalized.

2. The smelting method of the ultrapure high-performance Cr-Ni-W shaft steel according to claim 1, characterized in that: In step 1) (2), when N ≤ 30 ppm, metallic Cr and Ni are added to the steel, and stirring and refining are carried out. Samples are taken for analysis of C, Cr, W, Ni, and N. When N ≤ 30 ppm, Mn is added to fine-tune the chemical composition. The steel is stirred until there are no bubbles. Then, samples are taken for measurement of all elements and gaseous N. After N ≤ 30 ppm is qualified, the steel is poured at a pouring temperature of 1560-1600°C.

3. The smelting method of the ultrapure high-performance Cr-Ni-W shaft steel according to claim 1, characterized in that: In step 1) in step ④, the annealing process is to heat the electrode rod to 680±20°C and keep it at this temperature for 20 to 30 hours, then cool it to below 500°C in the furnace at a cooling rate of ≤50°C / h, take it out of the furnace and air-cool it to room temperature.

4. The smelting method of the ultrapure high-performance Cr-Ni-W shaft steel according to claim 1, characterized in that: After the electrode is annealed in step 1), it is polished, flattened, and the oxide scale is removed.

5. The smelting method of ultrapure high-performance Cr-Ni-W shaft steel according to claim 1, characterized in that: In step 2) ②, when the current and voltage are fixed, the current I is proportional to the melting speed v, and the ratio K = [I] / [v], K is between 1.14 and 3.

6. The smelting method of ultrapure high-performance Cr-Ni-W shaft steel according to claim 1, characterized in that: In step 2) in ③, the composition of the vacuum consumable ingot is controlled as follows: C 0.16-0.18%, Si 0.28-0.35%, Mn 0.38-0.60%, P ≤ 0.006%, S ≤ 0.004%, Cr 1.40-1.60%, Ni ≤ 4.20-4.40%, Cu ≤ 0.10%, W 0.90-1.10%, Al ≤ 0.016%, Ti ≤ 0.02%, H ≤ 0.00010%, O ≤ 0.0010%, N ≤ 0.0018%, and the rest is Fe.

7. The smelting method of ultrapure high-performance Cr-Ni-W shaft steel according to claim 1, characterized in that: In step 3), the number of upsetting and drawing is determined according to the specifications of the finished product, the intermediate billet is kept at a temperature of 1050-1100° C. for 1-3 hours, and the cumulative forging ratio is ensured to be 4-6.

8. The method for smelting ultrapure high-performance Cr-Ni-W shaft steel according to claim 1, characterized in that: In step 4), the rod is heated to 850-950°C and kept at this temperature for 5-9 hours, then taken out of the furnace and air-cooled. It is then heated to 650-700°C and kept at this temperature for 25-30 hours, then cooled to below 500°C and taken out of the furnace and air-cooled.

9. An ultrapure, high-performance Cr-Ni-W shaft steel produced by the smelting method of any one of claims 1 to 8; the high-performance Cr-Ni-W shaft steel comprising, by mass percentage, the following: C0.16~0.18%, Si0.28~0.35%, Mn0.38~0.60%, P≤0.006%, S≤0.004%, Cr 1.40~1.60%, Ni≤4.20~4.40%, Cu≤0.10%, W0.90~1.10%, Al≤0.016%, Ti≤0.02%, H≤0.00010%, O≤0.0010%, N≤0.0018%, and the rest is Fe.

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