Method for improving purity of stainless steel, 316LN stainless steel ingot, 316LN stainless steel forge piece and preparation method and application of 316LN stainless steel ingot and 316LN stainless steel forge piece

Abstract

The invention provides a method for improving the purity of stainless steel, a 316LN stainless steel ingot, a 316LN stainless steel forge piece and a preparation method and application of the 316LN stainless steel ingot and the 316LN stainless steel forge piece, and belongs to the technical field of smelting. The method for improving the purity of the stainless steel comprises the steps that raw materials are smelted, and molten steel is obtained; the molten steel is subjected to VODC refining, and refined molten steel is obtained; the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage which are sequentially carried out; a first deoxidizing agent is added in the VOH stage; mixing the refined molten steel with a second deoxidizing agent, and deoxidizing under the protection of argon to obtain deoxidized molten steel; the deoxidized molten steel is subjected to protective pouring, and a steel ingot is obtained; and the steel ingot is subjected to electroslag remelting, and the stainless steel ingot is obtained. VODC refining is adopted, the deoxidizing agent is added in the VOH stage, then the deoxidizing agent is added again, and the purity of the molten steel can be improved in cooperation with protective pouring and electroslag remelting.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting, and in particular relates to a method for improving the purity of stainless steel, a 316LN stainless steel ingot and a 316LN stainless steel forging, and a preparation method and application thereof. Background Art

[0002] 316LN stainless steel is a high performance austenitic stainless steel, which is widely used in applications requiring corrosion resistance, high strength and good weldability.

[0003] At present, the electric arc furnace smelting + AOD method is usually used to produce 316LN stainless steel ingots, but the ingots have many inclusions, resulting in poor mechanical properties of forgings. Summary of the invention

[0004] The object of the present invention is to provide a method for improving the purity of stainless steel, a 316LN stainless steel ingot and a 316LN stainless steel forging, and a preparation method and application thereof. The method provided by the present invention can improve the purity of stainless steel.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for improving the purity of stainless steel, comprising the following steps:

[0007] (1) smelting the raw materials to obtain molten steel;

[0008] (2) subjecting the molten steel obtained in step (1) to VODC refining to obtain refined molten steel; the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence; a first deoxidizer is added in the VOH stage;

[0009] (3) mixing the refined molten steel obtained in step (2) with a second deoxidizer, and deoxidizing the molten steel under argon protection to obtain deoxidized molten steel;

[0010] (4) performing protective pouring on the deoxidized molten steel obtained in step (3) to obtain a steel ingot;

[0011] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting to obtain a stainless steel ingot.

[0012] Preferably, the first deoxidizer in step (2) includes CaO, CaF 2 and FeSi.

[0013] Preferably, the dosage of the first deoxidizer in step (2) is 6-9 kg / t.

[0014] Preferably, in step (5), the voltage of the electroslag remelting is 80-86V, the current of the electroslag remelting is 16-18kA, and the time of the electroslag remelting is 9.5-10.0h.

[0015] The present invention also provides a 316LN stainless steel ingot prepared by the method described in the above technical solution, wherein the P content in the 316LN stainless steel ingot is ≤0.012wt%; the A-type inclusion rating in the 316LN stainless steel ingot is ≤2, the B-type inclusion rating is ≤1, the C-type inclusion rating is ≤1, and the D-type inclusion rating is ≤2.

[0016] The present invention also provides a 316LN stainless steel forging, which is prepared from the 316LN stainless steel ingot described in the above technical solution.

[0017] The present invention also provides a method for preparing the 316LN stainless steel forgings described in the above technical solution, comprising: sequentially forging, annealing, rough machining and solution treatment of the 316LN stainless steel ingot to obtain the 316LN stainless steel forgings.

[0018] Preferably, the initial forging temperature of the forging is 1150-1170°C, the final forging temperature of the forging is 920-940°C, the forging ratio of the forging is ≥3.0, the extension ratio of the forging is ≥2.0, and the total forging ratio is ≥4.0.

[0019] Preferably, the holding temperature of the solution treatment is 1140-1160° C., and the holding time of the solution treatment is 3-5 h.

[0020] The present invention also provides the use of the 316LN stainless steel forgings described in the above technical solution or the 316LN stainless steel forgings prepared by the preparation method described in the above technical solution in aerospace, ship power, medical equipment and nuclear power equipment.

[0021] The invention provides a method for improving the purity of stainless steel, comprising the following steps: smelting raw materials to obtain molten steel; performing VODC refining on the molten steel to obtain refined molten steel; the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence; adding a first deoxidizer in the VOH stage; mixing the refined molten steel with a second deoxidizer, and performing deoxidation under argon protection to obtain deoxidized molten steel; performing protective casting on the deoxidized molten steel to obtain a steel ingot; and performing electroslag remelting on the steel ingot to obtain a stainless steel ingot. The present invention conducts VODC refining on the molten steel obtained by smelting. During the refining process, vacuuming can improve the oxygen removal rate. At the same time, adding a deoxidizer in the VOH stage can further remove oxygen, reduce the content of inclusions, and further purify the molten steel. Subsequently, the deoxidizer is added again, and oxygen can be further removed under the protection of argon gas. The content of inclusions can be reduced to the maximum extent by protective pouring, and the purity of the molten steel can be improved. Then, electroslag remelting is performed to further reduce the content of inclusions, thereby improving the purity of the stainless steel ingot and further improving the mechanical properties of the forging. The experimental results show that the room temperature mechanical properties of the 316LN stainless steel forgings prepared by the method provided by the present invention are as follows: tensile strength is 610-630MPa; yield strength is 230-245MPa; longitudinal elongation after fracture is 65-68%, transverse elongation after fracture is 53-56%, and impact absorption energy is 123-135J. DETAILED DESCRIPTION

[0022] The present invention provides a method for improving the purity of a stainless steel ingot, comprising the following steps:

[0023] (1) smelting the raw materials to obtain molten steel;

[0024] (2) subjecting the molten steel obtained in step (1) to VODC refining to obtain refined molten steel; the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence; a first deoxidizer is added in the VOH stage;

[0025] (3) mixing the refined molten steel obtained in step (2) with a second deoxidizer, and deoxidizing the molten steel under argon protection to obtain deoxidized molten steel;

[0026] (4) performing protective pouring on the deoxidized molten steel obtained in step (3) to obtain a steel ingot;

[0027] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting to obtain a stainless steel ingot.

[0028] The method provided by the present invention is applicable to stainless steel of any chemical composition, and is preferably applicable to 316LN stainless steel.

[0029] Unless otherwise specified, the present invention has no particular limitation on the sources of the raw materials used, and the raw materials may be prepared using commercially available products or well-known preparation methods known to those skilled in the art.

[0030] The invention smelts raw materials to obtain molten steel.

[0031] In the present invention, the mass percentage of S in the raw material is preferably ≤0.020%; the mass percentage of P in the raw material is preferably ≤0.020%. The present invention can further improve the inclusion level by using pure raw materials with S≤0.020wt% and P≤0.020wt%.

[0032] The present invention has no special limitation on the composition of the raw materials, and the raw materials can be selected according to the actual steel type.

[0033] In the present invention, the smelting is preferably carried out in an electric arc furnace; the smelting preferably includes a melting period, an oxidation period and a reduction period carried out in sequence. The present invention has no special limitation on the model of the electric arc furnace, and instruments and equipment familiar to those skilled in the art can be used.

[0034] In the present invention, the temperature in the melting period is preferably 1540-1560° C. As an embodiment, the temperature in the melting period may be 1545-1555° C., or may be 1550° C.

[0035] In the present invention, it is preferred that a slag-forming agent is added during the melting period and carbon and oxygen are co-sprayed to form foamed slag.

[0036] In the present invention, the slag-forming agent is preferably FeO; the mass of the slag-forming agent is preferably 2-3% of the mass of the raw material. In the present invention, the slag-forming agent is beneficial to dephosphorization, promoting the floating of inclusions and gas and their removal with the slag flow.

[0037] In the present invention, the carbon spraying amount when the carbon and oxygen are co-sprayed is preferably 4-6 kg / t, more preferably 5 kg / t; the time for the carbon and oxygen co-spraying to make foamed slag is preferably 8-10 minutes; the oxygen blowing pressure when the carbon and oxygen are co-sprayed is preferably 0.30-0.50 MPa. As an embodiment, the oxygen blowing pressure can be 0.32-0.45 MPa, and can also be 0.35-0.40 MPa; the carbon and oxygen co-spraying can be blown with an oxygen blowing pipe. The present invention has no special limitation on the flow rate of carbon spraying when the carbon and oxygen are co-sprayed, and it can be sprayed within the above time. The present invention adopts an oxygen-enriched dephosphorization process during the melting period, and implements carbon and oxygen co-spraying, which can produce a strong carbon-oxygen reaction, causing the melt to boil, and impurities to float fully, thereby further achieving purification.

[0038] In the present invention, the basicity of the melt after the melting period is completed is preferably 2.5 to 3; the content of P in the melt after the melting period is completed is preferably 0.006 to 0.008 wt%.

[0039] In the present invention, the temperature of the oxidation period is preferably 1650-1670°C; the oxidation period is preferably carried out under oxygen blowing conditions; the pressure of the oxygen blowing is preferably ≥1.5MPa. As an embodiment, the temperature of the oxidation period can be 1655-1665°C, and can also be 1660°C. The present invention performs oxidative decarburization during the oxidation period to remove gas and inclusions in the melt, so that the decarburization amount of the melt is ≥40wt%, the C content is 0.8-1.0wt%, the P content is ≤0.08wt%, and the S content is ≤0.020wt%.

[0040] In the present invention, when the melt is boiled for 5 to 7 minutes during the oxidation period, a third deoxidizer is preferably added; the third deoxidizer is preferably SiMn; the mass of the third deoxidizer is preferably 0.1 to 0.3% of the mass of the melt, more preferably 0.2%. The addition of the deoxidizer in the present invention can pre-deoxidize the melt, so that the C content of the melt is ≤0.8wt%, the P content is ≤0.08wt%, and the S content is ≤0.020wt%.

[0041] In the present invention, the mass ratio of Si to Mn in the SiMn is preferably 1:(2-4), more preferably 1:3.

[0042] In the present invention, after the oxidation period, the melt is preferably deslagging. The present invention has no special limitation on the deslagging operation, and the operation well known to those skilled in the art can be adopted.

[0043] In the present invention, the reduction period is preferably entered when the temperature of the melt is 1700-1750° C. As an embodiment, the reduction period may be entered when the temperature of the melt is 1720° C.

[0044] In the present invention, the thin slag material, alloy raw material, reducing agent and composite deoxidizer are preferably added in sequence during the reduction period.

[0045] In the present invention, the thin slag material preferably includes lime and fluorite. The present invention has no special limitation on the amount of the thin slag material, and the C content in the melt can be adjusted to ≤1.0wt%.

[0046] In the present invention, the alloy raw materials preferably include ferrosilicon manganese, ferromanganese and ferrochrome. The present invention has no special limitation on the amount of the alloy raw materials, as long as the raw material composition meets the composition requirements of the prepared stainless steel.

[0047] In the present invention, the reducing agent preferably includes at least one of ferrosilicon powder, calcium carbide, carbon powder or AD powder; the amount of ferrosilicon powder is preferably 3-8 kg / t; the amount of calcium carbide is preferably 2-3 kg / t; the amount of carbon powder is preferably 0.5-2 kg / t; the amount of AD powder is preferably 5-8 kg / t. In the present invention, ferrosilicon powder, calcium carbide, carbon powder and AD powder are used to make white slag for deoxidation.

[0048] As an implementation mode, the amount of the ferrosilicon powder may be 4-5 kg / t; the amount of the calcium carbide may be 2.5-3 kg / t; the amount of the carbon powder may be 1-2 kg / t; and the amount of the AD powder may be 6-7 kg / t.

[0049] In the present invention, the retention time of the white slag after adding the reducing agent to make the white slag is preferably 15 to 25 minutes, more preferably 20 minutes. In the present invention, the retention time of the white slag after making the white slag is within the above range to fully perform reduction and deoxidation.

[0050] In the present invention, the composite deoxidizer preferably includes the following components in mass percentage: C 0.02-0.07%, Mn 10-30%, Si 5-15%, Al 0.4-1.2%, Ca 0.3-1% and Fe 50-75%. The composite deoxidizer is added during the reduction period to further improve the deoxidation effect and reduce the inclusion content.

[0051] In the present invention, the amount of the composite deoxidizer is preferably 6-10 kg / t. As an embodiment, the amount of the composite deoxidizer can be 8-9 kg / t. The present invention can further improve the deoxidation effect by limiting the amount of the composite deoxidizer to the above range, thereby reducing the inclusion content.

[0052] In the present invention, the temperature of the melt when the composite deoxidizer is added is preferably 1580-1620° C. As an embodiment, the temperature of the melt when the composite deoxidizer is added can be 1590-1610° C., or can be 1600° C.

[0053] In the present invention, 6 to 15 minutes after the composite deoxidizer is added to the melt, when the melt composition meets the required requirements and the melt temperature is 1690 to 1710°C, the melt is preferably transferred into a ladle, and then the slag is removed from the ladle and then the temperature is lowered to 1650 to 1700°C to obtain molten steel.

[0054] As an implementation method, after adding the composite deoxidizer into the melt for 10 to 15 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt can be transferred into a ladle, and then the slag is removed from the ladle and then the temperature is lowered to 1660 to 1680°C to obtain molten steel.

[0055] The present invention has no particular limitation on the operation of transferring the melt into the ladle, and the operation well known to those skilled in the art may be adopted.

[0056] In the present invention, the slagging in the ladle is preferably performed until the residue amount is ≤1.5kg / t.

[0057] The present invention has no special limitation on the operation of cooling the temperature to 1650-1700° C., and the operation well known to those skilled in the art can be adopted.

[0058] After obtaining the molten steel, the present invention performs VODC refining on the molten steel to obtain refined molten steel.

[0059] In the present invention, the VODC refining includes a VOD stage, a VCD stage, a VOH stage and a VD stage which are performed in sequence.

[0060] In the present invention, the vacuum degree of the VOD stage is preferably 100-120 mbar; the VOD stage is preferably top-blown oxygen and bottom-blown argon; the oxygen blowing amount of the VOD stage is preferably 450-650 mbar. 3 / h; the argon blowing amount in the VOD stage is preferably 4 to 6m 3 / h; the vacuum time of the VOD stage is preferably 1 to 1.5h; the temperature of the VOD stage is preferably 1600 to 1700°C. In the present invention, the VOD stage is a vacuum oxygen decarburization process. By limiting the process parameters of the VOD stage within the above range, the decarburization effect can be further improved, so that the carbon content in the melt is ≤0.80wt%.

[0061] As an embodiment, the vacuum degree of the VOD stage can be 110-115 mbar; the oxygen blowing amount of the VOD stage can be 500-550 mbar. 3 / h; the argon blowing amount in the VOD stage can be 4.5~5m 3 / h; the vacuuming time of the VOD stage can be 1.2 to 1.4 hours; the temperature of the VOD stage can be 1620 to 1680°C, or 1640 to 1660°C.

[0062] In the present invention, the vacuum degree of the VCD stage is preferably 15-20 mbar; the vacuum pumping time of the VCD stage is preferably 10-20 min; the VCD stage is preferably bottom-blown argon; the argon flow rate of the VCD stage is preferably 4-6 m 3 / h; the temperature of the VCD stage is preferably 1600-1700° C. In the present invention, the VCD stage is a vacuum carbon deoxidation process, and by limiting the process parameters of the VCD stage to the above range, the deoxidation effect can be further improved, thereby reducing the inclusion content in the molten steel.

[0063] As an implementation method, the vacuum degree of the VCD stage can be 16-18 mbar; the vacuum pumping time of the VCD stage can be 12-18 min, or 15-16 min; the argon flow rate of the VCD stage can be 4.5-5 mbar. 3 / h; the temperature of the VCD stage can be 1620-1680°C, or 1640-1660°C.

[0064] In the present invention, the first deoxidizer is added in the VOH stage; the first deoxidizer preferably includes CaO, CaF 2 and FeSi; the dosage of the first deoxidizer is preferably 6-9 kg / t. As an embodiment, the dosage of the first deoxidizer can be 7-8 kg / t. In the present invention, the VOH stage is a vacuum oxygen blowing heating process, and the deoxidation effect can be further improved by adding the first deoxidizer, thereby reducing the inclusion content in the molten steel; by limiting the type of the first deoxidizer to the above range, the inclusion content in the molten steel can be further reduced.

[0065] In the present invention, the mass ratio of Fe to Si in the FeSi is preferably (7-10), more preferably 1:8.

[0066] In the present invention, the vacuum degree of the VOH stage is preferably 15-20 mbar; the VOH stage is preferably top-blown oxygen and bottom-blown argon; the oxygen flow rate of the VOH stage is preferably 5-8 mbar. 3 / h; the argon flow rate in the VOH stage is preferably 4 to 6m 3 / h; the VOH stage preferably adopts aluminum addition to increase the temperature. The present invention has no special limitation on the time of the VOH stage, and sampling and analysis of each element composition can be within the specified requirements. The present invention has no special limitation on the amount of aluminum, as long as the melt temperature is increased to 1650-1670°C.

[0067] In the present invention, it is preferred to add aluminum first and raise the temperature before adding the first deoxidizer.

[0068] After the VOH stage is completed, the present invention preferably sequentially performs slagging and slagging on the melt obtained in the VOH stage.

[0069] The present invention has no special limitation on the slag making and slag removal operations. The aluminum content in the melt can be removed by using operations well known to those skilled in the art to ensure that the residual content can meet the requirements.

[0070] As an implementation method, the vacuum degree of the VOH stage can be 16-18 mbar; the oxygen flow rate of the VOH stage can be 5.5-6 mbar. 3 / h; the argon flow rate in the VOH stage can be 4.5~5m 3 / h.

[0071] In the present invention, the vacuum degree of the VD stage is preferably 0.5-1.5 mbar; the VD stage is preferably bottom-blown argon; the argon flow rate of the VD stage is preferably 4-6 m 3 / h; the vacuuming time of the VD stage is preferably 20-25 min; the temperature of the VD stage is preferably 1600-1700° C. In the present invention, limiting the process parameters of the VD stage within the above range can further reduce the inclusion content in the molten steel.

[0072] As an implementation method, the vacuum degree of the VD stage can be 0.8-1.2 mbar, or 1.0 mbar; the argon gas flow rate of the VD stage can be 4.5-5 mbar. 3 / h; the vacuuming time of the VD stage can be 22 to 24 minutes; the temperature of the VD stage can be 1620 to 1680°C, or 1640 to 1660°C.

[0073] After obtaining the refined molten steel, the present invention mixes the refined molten steel with a second deoxidizer and performs deoxidation under the protection of argon gas to obtain deoxidized molten steel.

[0074] In the present invention, the temperature of the refined molten steel is preferably 1610-1650°C.

[0075] In the present invention, the second deoxidizer is preferably CaSi powder; the dosage of the second deoxidizer is preferably 1-1.5 kg / t. As an embodiment, the dosage of the second deoxidizer can be 1.2-1.4 kg / t.

[0076] In the present invention, the mass ratio of Ca to Si in the CaSi powder is preferably 1:(2-4), more preferably 1:3; the particle size of the CaSi powder is preferably 3-5 mm. In the present invention, the CaSi powder is preferably dried before use. The present invention has no special limitation on the drying operation, and the operation well known to those skilled in the art can be used.

[0077] In the present invention, the mixing of the refined steel liquid and the second deoxidizer is preferably carried out in a tundish. In the present invention, the tundish is preferably bottom-blown with argon before use. The present invention can exhaust the air in the tundish by blowing argon at the bottom of the tundish to avoid the presence of oxygen; the use of a deoxidizer in the tundish for final deoxidation of the tundish can further reduce the oxygen content in the refined steel liquid, thereby reducing the content of inclusions.

[0078] The present invention has no special limitation on the model of the tundish, and any instrument or equipment familiar to those skilled in the art may be used.

[0079] The present invention has no special limitation on the operation of mixing the refined molten steel and the deoxidizer, and the technical scheme for preparing the mixed material well known to those skilled in the art can be adopted.

[0080] In the present invention, the deoxygenation time is preferably 20 to 30 minutes, more preferably 25 minutes. The present invention can further improve the deoxygenation effect by limiting the deoxygenation time within the above range.

[0081] After deoxidation, the present invention preferably performs sedation on the deoxidized melt to obtain deoxidized molten steel. In the present invention, the sedation time is preferably 6 to 7 minutes. The sedation of the present invention can remove gas and inclusions in the deoxidized molten steel and improve purity.

[0082] After obtaining the deoxidized molten steel, the present invention performs protective pouring on the deoxidized molten steel to obtain a steel ingot.

[0083] In the present invention, the protective pouring system is preferably inspected before the protective pouring. The present invention has no special limitation on the operation of inspecting the protective pouring system, as long as it is ensured to be dry, free of moisture, and the runner and steel mold are clean and free of pollution.

[0084] In the present invention, the temperature of the protective pouring is preferably 1550-1570°C, more preferably 1560°C; the flow rate of the protective pouring is preferably 5-7 mm / s, more preferably 6 mm / s; the atmosphere of the protective pouring is preferably argon; the flow rate of the argon is preferably 4-6 L / min, more preferably 5 L / min. The present invention adopts argon protective pouring to prevent secondary oxidation of deoxidized molten steel.

[0085] After the protective pouring is completed, the present invention preferably cools and demoulds the product obtained by the protective pouring in sequence to obtain a steel ingot.

[0086] In the present invention, the cooling time is preferably calculated according to Formula I:

[0087] T = 35R 2 (M)×1.2 Formula I;

[0088] Wherein, T is the cooling time, unit is h; R is the mold radius (ingot mold specification size), unit is m.

[0089] The present invention has no particular limitation on the demoulding operation, and any operation well known to those skilled in the art may be used.

[0090] After obtaining the steel ingot, the present invention performs electroslag remelting on the obtained steel ingot to obtain a stainless steel ingot. The present invention adopts electroslag remelting to further reduce the inclusion content, thereby improving the purity of the stainless steel ingot, and further improving the mechanical properties of the forging.

[0091] In the present invention, the voltage of the electroslag remelting is preferably 80-86V; the current of the electroslag remelting is preferably 16-18kA; and the time of the electroslag remelting is preferably 9.5-10.0h. As an embodiment, the voltage of the electroslag remelting can be 82-84V; the current of the electroslag remelting can be 16-17kA; and the time of the electroslag remelting can be 9.6-9.8h.

[0092] In the present invention, the slag system used in the electroslag remelting is preferably CaF 2 -Al 2 O 3 -CaO-MgO quaternary slag system. 2 -Al 2 O 3 The -CaO-MgO quaternary slag system is not particularly limited, and any quaternary slag system well known to those skilled in the art may be used.

[0093] In the present invention, the mass of the slag system is preferably 5 to 15% of the mass of the steel ingot.

[0094] The present invention has no particular limitation on the melting rate of the electroslag remelting, and it can be carried out at a uniform speed.

[0095] In the present invention, the electroslag remelting is preferably direct slag smelting of consumable electrodes; Si-Mn alloy powder is preferably added during the slag smelting period of the electroslag remelting; the amount of the Si-Mn alloy powder is preferably 2-3 kg / t. In the present invention, the Si-Mn alloy powder is a deoxidizer, which can improve the deoxidation effect.

[0096] In the present invention, the mass ratio of Si to Mn in the Si-Mn alloy powder is preferably 1: (2-4), more preferably 1: 3. The present invention has no particular limitation on the particle size of the Si-Mn alloy powder, and any particle size known to those skilled in the art can be used.

[0097] After electroslag remelting, the present invention preferably sequentially cools and anneals the product obtained by electroslag remelting.

[0098] The present invention has no particular limitation on the cooling operation, and any cooling operation well known to those skilled in the art may be used.

[0099] In the present invention, the holding temperature of the annealing treatment is preferably 820-840° C., more preferably 830° C.; the holding time of the annealing treatment is preferably 8-10 hours; the cooling method of the annealing treatment is preferably furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is preferably ≤300° C. The present invention has no special limitation on the operation of the furnace cooling and air cooling, and the operation well known to those skilled in the art can be adopted.

[0100] The present invention conducts VODC refining on the molten steel obtained by smelting, and vacuuming can improve the oxygen removal rate. Meanwhile, adding a deoxidizer in the VOH stage can further remove oxygen, reduce the content of inclusions, and further purify the molten steel. Subsequently, the deoxidizer is added again, and oxygen can be further removed under the protection of argon gas. The content of inclusions can be reduced to the maximum extent by protective pouring, and the purity of the molten steel is improved. Then, electroslag remelting is carried out to further reduce the content of inclusions, thereby improving the purity of the stainless steel ingot, and further improving the mechanical properties of the forging.

[0101] The present invention also provides a 316LN stainless steel ingot prepared by the method described in the above technical solution.

[0102] In the present invention, the P content in the 316LN stainless steel ingot is ≤0.012wt%; the A-type inclusion rating in the 316LN stainless steel ingot is ≤2, the B-type inclusion rating is ≤1, the C-type inclusion rating is ≤1, and the D-type inclusion rating is ≤2.

[0103] In the present invention, the chemical composition of the 316LN stainless steel ingot preferably includes, by mass percentage, C≤0.02%, Mn≤2.00%, Si≤0.75%, Cr 16.00-18.00%, Co≤0.05%, Ni10.00-14.00%, Mo2.00-3.00%, P≤0.012%, S≤0.005%, Cu≤0.10%, N0.10-0.16% and the balance Fe.

[0104] The 316LN stainless steel ingot provided by the present invention is an ultra-low P steel ingot, which is an austenitic heat-resistant stainless steel with corrosion resistance, high strength, high hardness and good welding performance. It is suitable for aerospace, ship power, medical equipment and nuclear power equipment, especially engineering structure fields such as fourth-generation nuclear power main pipeline components.

[0105] The present invention also provides a 316LN stainless steel forging, which is prepared from the 316LN stainless steel ingot described in the above technical solution.

[0106] The present invention also provides a method for preparing the 316LN stainless steel forgings described in the above technical solution, comprising: sequentially forging, annealing, rough machining and solution treatment of the 316LN stainless steel ingot to obtain the 316LN stainless steel forgings.

[0107] In the present invention, the initial forging temperature of the forging is preferably 1150-1170°C; the final forging temperature of the forging is preferably 920-940°C; the forging ratio of the forging is preferably ≥3.0; the extension ratio of the forging is preferably ≥2.0; and the total ratio of the forging is preferably ≥4.0.

[0108] As an embodiment, the initial forging temperature of the forging may be 1155-1160°C; the final forging temperature of the forging may be 925-930°C; the forging ratio of the forging may be 3.5-4.5; the extension ratio of the forging may be 2.5-3.5; and the total forging ratio may be 4.5-5.5.

[0109] In the present invention, the annealing holding temperature is preferably 820-840°C; the annealing holding time is preferably 8-10 hours. As an embodiment, the annealing holding temperature can be 830°C; the annealing holding time can be 8.5-9 hours. The present invention adopts annealing to remove the residual stress of forging and improve the mechanical properties of the forging.

[0110] In the present invention, the cooling method of the annealing treatment is preferably furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is preferably ≤300° C. The present invention has no special limitation on the operation of the furnace cooling and air cooling, and the operation well known to those skilled in the art can be adopted.

[0111] The present invention has no special limitation on the rough machining operation, and operations well known to those skilled in the art may be adopted.

[0112] In the present invention, the holding temperature of the solution treatment is preferably 1140-1160° C.; the holding time of the solution treatment is preferably 3-5 hours; and the cooling method of the solution treatment is preferably water cooling.

[0113] The present invention has no special limitation on the water cooling operation, and operations familiar to those skilled in the art may be adopted.

[0114] As an embodiment, the holding temperature of the solution treatment may be 1145-1150° C.; the holding time of the solution treatment may be 3.5-4 hours.

[0115] The present invention also provides the use of the 316LN stainless steel forgings described in the above technical solution or the 316LN stainless steel forgings prepared by the preparation method described in the above technical solution in aerospace, ship power, medical equipment and nuclear power equipment.

[0116] The present invention has no special limitation on the application of the 316LN stainless steel forgings in aerospace, ship power, medical equipment and nuclear power equipment, and the application operations familiar to those skilled in the art can be adopted.

[0117] The present invention adopts EAF (electric arc furnace) + VODC refining + argon protection pouring + electroslag remelting, which can reduce the content of non-metallic inclusions to the maximum extent, improve the purity of molten steel, and enhance the quality of steel. Among them, compared with the chemical composition of ASMESA-182316LN in the United States: C is optimized from ≤0.030wt% to ≤0.020wt%; S is optimized from ≤0.030wt% to ≤0.005wt%, reducing sulfide inclusions and eliminating sulfide band segregation; P is optimized from ≤0.040wt% to ≤0.012wt%, reducing phosphorus segregation, and improving resistance to stress corrosion, welding corrosion cracks and pitting corrosion.

[0118] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0119] Example 1

[0120] The preparation method of 316LN stainless steel ingot is:

[0121] (1) 10 steel with S≤0.020wt% and P≤0.020wt% is subjected to electric arc furnace smelting to obtain molten steel; the electric arc furnace smelting consists of a melting period, an oxidation period and a reduction period carried out in sequence;

[0122] In which, during the melting period, slag-forming agent FeO is added and carbon and oxygen are co-sprayed to form foamed slag, and the mass of the slag-forming agent is 3% of the mass of the scrap steel; the temperature during the melting period is 1560°C; the carbon spraying amount during carbon and oxygen co-spraying is 5kg / t; the time for carbon and oxygen co-spraying to form foamed slag is 10min; the oxygen blowing pressure during carbon and oxygen co-spraying is 0.50MPa; the basicity of the melt after the melting period is completed is 3, and P is removed to 0.006wt%;

[0123] The temperature of the oxidation period is 1660°C; the oxidation period is carried out under oxygen blowing conditions; the oxygen blowing pressure is 2.0MPa, so that the decarburization amount of the melt is ≥40wt%, the C content is 1.0wt%, P≤0.08wt%, and S≤0.020wt%; during the oxidation period, after the melt is boiled for 7 minutes, 0.2% SiMn by mass of the melt is added to make the C content of the melt ≤0.8wt%, P≤0.08wt%, and S≤0.020wt%; after the oxidation period is over, the melt is deslagging; the mass ratio of Si to Mn in SiMn is 1:3;

[0124] When the temperature of the melt reaches 1700°C and enters the reduction period, 200kg lime and 70kg fluorite are added to adjust the C content to ≤1.0wt%, and then 5kg / t ferrosilicon manganese, 5kg / t ferromanganese and 5kg / t ferrochrome are added, followed by the addition of a reducing agent, and the white slag is kept for 25 minutes after the white slag is made, and then 9kg / t of a composite deoxidizer is added when the melt temperature is 1600°C. After 15 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt is transferred to a ladle, and then the slag in the ladle is skimmed until the residue amount is ≤1.5kg / t, and then the temperature is reduced to 1650°C and transferred to a VODC vacuum refining furnace; the reducing agent is a mixture of ferrosilicon powder, calcium carbide, carbon powder and AD powder: the amount of ferrosilicon powder is 7kg / t; the amount of calcium carbide is 3kg / t; the amount of carbon powder is 2kg / t; the amount of AD powder is 7kg / t; the composite deoxidizer is composed of the following components in mass percentage: C 0.05%, Mn 25%, Si 15%, Al 1.0%, Ca 1% and Fe 57.95%;

[0125] (2) subjecting the molten steel obtained in step (1) to VODC refining to obtain refined molten steel; wherein the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence;

[0126] The vacuum degree of the VOD stage is 120mbar; the VOD stage is top blowing oxygen and bottom blowing argon; the oxygen blowing volume of the VOD stage is 630m 3 / h; the argon blowing volume in the VOD stage is 5m 3 / h; the vacuum time of the VOD stage is 1.5h; the temperature of the VOD stage is 1650°C, so that the C content in the melt is ≤0.80wt%;

[0127] The vacuum degree of the VCD stage is 18mbar; the vacuum pumping time of the VCD stage is 15min; the VCD stage is bottom-blown with argon; the argon flow rate of the VCD stage is 5m 3 / h; the temperature of the VCD stage is 1700℃;

[0128] In the VOH stage, aluminum is first added to raise the temperature to 1660°C, and then 9kg / t of deoxidizer CaO is added, followed by slagging and slagging. The vacuum degree in the VOH stage is 18mbar. In the VOH stage, oxygen is blown from the top and argon is blown from the bottom. The oxygen flow rate in the VOH stage is 8m 3 / h; the argon flow rate in the VOH stage is 5m 3 / h;

[0129] The vacuum degree of the VD stage is 1.0 mbar; the VD stage is bottom-blown argon; the argon flow rate of the VD stage is 5 m 3 / h; the vacuum time of the VD stage is 25min; the temperature of the VD stage is 1700℃;

[0130] (3) First, add 1.5kg / t dry CaSi powder to the bottom of the tundish, then blow argon at the bottom of the tundish to exhaust the air in the tundish, then pour the refined molten steel at 1610°C into the tundish for deoxidation for 25 minutes under argon protection, and then calm for 7 minutes to obtain deoxidized molten steel; wherein the mass ratio of Ca to Si in the CaSi powder is 1:3, and the particle size is 3-5 mm;

[0131] (4) Before pouring, the pouring system is checked to ensure that it is dry and free of moisture, and the runner and steel mold are clean and free of pollution. Then, the deoxidized molten steel obtained in step (3) is subjected to protective pouring, and then cooled and demolded in sequence to obtain a steel ingot. The protective pouring temperature is 1560° C., the protective pouring flow rate is 6 mm / s, the protective pouring atmosphere is argon, and the argon flow rate is 5 L / min. The cooling time is calculated according to formula I:

[0132] T = 35R 2 (M)×1.2 Formula I;

[0133] Where, T is the cooling time, in h; R is the mold radius (ingot mold specification size), in m;

[0134] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting, cooling and annealing treatment in sequence to obtain a 316LN stainless steel ingot; wherein the electroslag remelting adopts CaF 2 -Al 2 O 3 -CaO-MgO quaternary slag system, CaF 2 、Al 2 O 3, CaO and MgO have a mass ratio of 1:2:3:3, the mass of the quaternary slag system is 5% of the mass of the steel ingot, a 5t crystallizer, a crystallizer diameter of 1050mm, a consumable electrode is used for direct slagging, the consumable electrode diameter is 800mm, the voltage is 86V, the current is 17kA, 3kg / t of Si-Mn alloy powder is added during the slagging period, and the mass ratio of Si to Mn in the Si-Mn alloy powder is 1:3; the melting rate of the whole electroslag remelting process is uniform, and the electroslag remelting time is 10h; the holding temperature of the annealing treatment is 830℃; the holding time of the annealing treatment is 10h; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300℃.

[0135] Example 2

[0136] The preparation method of 316LN stainless steel ingot is:

[0137] (1) smelting 10 steel with S≤0.020wt% and P≤0.020wt% in an electric arc furnace to obtain molten steel; the electric arc furnace smelting consists of a melting period, an oxidation period and a reduction period carried out in sequence;

[0138] In which, during the melting period, slag-forming agent FeO is added and carbon and oxygen are co-sprayed to form foamed slag, and the mass of the slag-forming agent is 3% of the mass of the scrap steel; the temperature during the melting period is 1560°C; the carbon spraying amount during carbon and oxygen co-spraying is 6kg / t; the time for carbon and oxygen co-spraying to form foamed slag is 10min; the oxygen blowing pressure during carbon and oxygen co-spraying is 0.50MPa; the basicity of the melt after the melting period is completed is 3, and P is removed to 0.006wt%;

[0139] The temperature of the oxidation period is 1660°C; the oxidation period is carried out under oxygen blowing conditions; the oxygen blowing pressure is 2.0MPa, so that the decarburization amount of the melt is ≥40wt%, the C content is 1.0wt%, P≤0.08wt%, and S≤0.020wt%; during the oxidation period, after the melt is boiled for 7 minutes, 0.2% SiMn by mass of the melt is added to make the C content of the melt ≤0.8wt%, P≤0.08wt%, and S≤0.020wt%; after the oxidation period is over, the melt is deslagging; the mass ratio of Si to Mn in SiMn is 1:3;

[0140] When the temperature of the melt reaches 1700°C and enters the reduction period, 200kg lime and 70kg fluorite are added to adjust the C content to ≤1.0wt%, and then 5kg / t ferrosilicon manganese, 5kg / t ferromanganese and 5kg / t ferrochrome are added, followed by the addition of a reducing agent. After making white slag, the white slag is kept for 25 minutes, and then 8kg / t of a composite deoxidizer is added when the melt temperature is 1610°C. After 15 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt is transferred to a ladle, and then the slag in the ladle is skimmed until the residue amount is ≤1.5kg / t, and then the temperature is reduced to 1650°C and transferred to a VODC vacuum refining furnace; the reducing agent is a mixture of ferrosilicon powder, calcium carbide, carbon powder and AD powder, the amount of ferrosilicon powder is 7kg / t; the amount of calcium carbide is 3kg / t; the amount of carbon powder is 2kg / t; the amount of AD powder is 8kg / t; the composite deoxidizer is composed of the following components in mass percentage: C 0.05%, Mn 20%, Si 13%, Al 1.2%, Ca 1% and Fe 64.75%;

[0141] (2) subjecting the molten steel obtained in step (1) to VODC refining to obtain refined molten steel; wherein the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence;

[0142] The vacuum degree of the VOD stage is 110mbar; the VOD stage is top blowing oxygen and bottom blowing argon; the oxygen blowing volume of the VOD stage is 630m 3 / h; the argon blowing volume in the VOD stage is 5m 3 / h; the vacuum time of the VOD stage is 1.5h; the temperature of the VOD stage is 1700°C, so that the C content in the melt is ≤0.80wt%;

[0143] The vacuum degree of the VCD stage is 20mbar; the vacuum pumping time of the VCD stage is 15min; the VCD stage is bottom-blown with argon; the argon flow rate of the VCD stage is 5m 3 / h; the temperature of the VCD stage is 1700℃;

[0144] In the VOH stage, aluminum is first added and the temperature is raised to 1660°C, then 9kg / t of deoxidizer FeSi is added, and the mass ratio of Fe to Si in FeSi is 1:8, followed by slagging and slagging in turn; the vacuum degree in the VOH stage is 18mbar; the VOH stage is top-blown oxygen and bottom-blown argon; the oxygen flow rate in the VOH stage is 8m 3 / h; the argon flow rate in the VOH stage is 5m 3 / h;

[0145] The vacuum degree of the VD stage is 1.0 mbar; the VD stage is bottom-blown argon; the argon flow rate of the VD stage is 5 m 3 / h; the vacuum time of the VD stage is 20min; the temperature of the VD stage is 1700℃;

[0146] (3) First, add 1.5kg / t dry CaSi powder to the bottom of the tundish, then blow argon at the bottom of the tundish to exhaust the air in the tundish, then pour the refined molten steel at 1650°C into the tundish for deoxidation for 25 minutes under argon protection, and then calm for 7 minutes to obtain deoxidized molten steel; wherein the mass ratio of Ca to Si in the CaSi powder is 1:3, and the particle size is 3-5 mm;

[0147] (4) Before pouring, the pouring system is checked to ensure that it is dry and free of moisture, and the runner and steel mold are clean and free of pollution. Then, the deoxidized molten steel obtained in step (3) is subjected to protective pouring, and then cooled and demolded in sequence to obtain a steel ingot. The protective pouring temperature is 1560° C., the protective pouring flow rate is 6 mm / s, the protective pouring atmosphere is argon, and the argon flow rate is 5 L / min. The cooling time is calculated according to formula I:

[0148] T = 35R 2 (M)×1.2Formula I;

[0149] Where, T is the cooling time, in h; R is the mold radius, in m;

[0150] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting, cooling and annealing treatment in sequence to obtain a 316LN stainless steel ingot; wherein the electroslag remelting adopts CaF 2 -Al 2 O 3 -CaO-MgO quaternary slag system, CaF 2 、Al 2 O 3 The mass ratio of CaO and MgO is 1:2:3:3, the mass of the quaternary slag system is 5% of the mass of the steel ingot, the crystallizer is 5t, the diameter of the crystallizer is 1050mm, the consumable electrode is used for direct slagging, the diameter of the consumable electrode is 800mm, the voltage is 85V, the current is 18kA, 3kg / t of Si-Mn alloy powder is added during the slagging period, and the mass ratio of Si to Mn in the Si-Mn alloy powder is 1:3; the melting rate of the whole electroslag remelting process is uniform, and the electroslag remelting time is 10h; the holding temperature of the annealing treatment is 830℃; the holding time of the annealing treatment is 10h; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300℃.

[0151] Example 3

[0152] The preparation method of 316LN stainless steel ingot is:

[0153] (1) smelting 10 steel with S≤0.020wt% and P≤0.020wt% in an electric arc furnace to obtain molten steel; the electric arc furnace smelting consists of a melting period, an oxidation period and a reduction period carried out in sequence;

[0154] In which, during the melting period, slag-forming agent FeO is added and carbon and oxygen are co-sprayed to form foamed slag, and the mass of the slag-forming agent is 3% of the mass of the scrap steel; the temperature during the melting period is 1560°C; the carbon spraying amount during carbon and oxygen co-spraying is 5kg / t; the time for carbon and oxygen co-spraying to form foamed slag is 10min; the oxygen blowing pressure during carbon and oxygen co-spraying is 0.50MPa; the basicity of the melt after the melting period is completed is 3, and P is removed to 0.008wt%;

[0155] The temperature of the oxidation period is 1660°C; the oxidation period is carried out under oxygen blowing conditions; the oxygen blowing pressure is 2.2MPa, so that the decarburization amount of the melt is ≥40wt%, the C content is 1.0wt%, P≤0.08wt%, and S≤0.020wt%; during the oxidation period, after the melt is boiled for 7 minutes, 0.2% SiMn by mass of the melt is added to make the C content of the melt ≤0.8wt%, P≤0.08wt%, and S≤0.020wt%; after the oxidation period is over, the melt is deslagging; the mass ratio of Si to Mn in SiMn is 1:3;

[0156] When the temperature of the melt reaches 1710°C and enters the reduction period, 200kg lime and 70kg fluorite are added to adjust the C content to ≤1.0wt%, and then 5kg / t ferrosilicon manganese, 5kg / t ferromanganese and 5kg / t ferrochrome are added, followed by the addition of a reducing agent, and the white slag is kept for 25 minutes after the white slag is made, and then 8kg / t of a composite deoxidizer is added when the melt temperature is 1610°C. After 15 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt is transferred to a ladle, and then the slag in the ladle is skimmed until the residue amount is ≤1.5kg / t, and then the temperature is reduced to 1650°C and transferred to a VODC vacuum refining furnace; the reducing agent is a mixture of ferrosilicon powder, calcium carbide, carbon powder and AD powder, and the amount of ferrosilicon powder is 8kg / t; the amount of calcium carbide is 3kg / t; the amount of carbon powder is 2kg / t; the amount of AD powder is 8kg / t; the composite deoxidizer is composed of the following components in mass percentage: C 0.06%, Mn 30%, Si 15%, Al 1.2%, Ca 1% and Fe 52.74%;

[0157] (2) subjecting the molten steel obtained in step (1) to VODC refining to obtain refined molten steel; wherein the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence;

[0158] The vacuum degree of the VOD stage is 110mbar; the VOD stage is top blowing oxygen and bottom blowing argon; the oxygen blowing volume of the VOD stage is 600m 3 / h; the argon blowing volume in the VOD stage is 5m 3 / h; the vacuum time of the VOD stage is 1.5h; the temperature of the VOD stage is 1650°C, so that the C content in the melt is ≤0.80wt%;

[0159] The vacuum degree of the VCD stage is 20mbar; the vacuum pumping time of the VCD stage is 15min; the VCD stage is bottom-blown with argon; the argon flow rate of the VCD stage is 5m 3 / h; the temperature of the VCD stage is 1700℃;

[0160] In the VOH stage, aluminum is first added to raise the temperature to 1660°C, and then 8kg / t of deoxidizer CaF is added. 2 , followed by slagging and slagging; the vacuum degree of the VOH stage is 20mbar; the VOH stage is top blowing oxygen and bottom blowing argon; the oxygen flow rate of the VOH stage is 8m 3 / h; the argon flow rate in the VOH stage is 5m 3 / h;

[0161] The vacuum degree of the VD stage is 1.0 mbar; the VD stage is bottom-blown argon; the argon flow rate of the VD stage is 5 m 3 / h; the vacuum time of the VD stage is 25min; the temperature of the VD stage is 1700℃;

[0162] (3) First, add 1.5kg / t dry CaSi powder to the bottom of the tundish, then blow argon at the bottom of the tundish to exhaust the air in the tundish, then pour the refined molten steel at 1610°C into the tundish for deoxidation for 25 minutes under argon protection, and then calm for 7 minutes to obtain deoxidized molten steel; wherein the mass ratio of Ca to Si in the CaSi powder is 1:3, and the particle size is 3-5 mm;

[0163] (4) Before pouring, the pouring system is checked to ensure that it is dry and free of moisture, and the runner and steel mold are clean and free of pollution. Then, the deoxidized molten steel obtained in step (3) is subjected to protective pouring, and then cooled and demolded in sequence to obtain a steel ingot. The protective pouring temperature is 1560° C., the protective pouring flow rate is 6 mm / s, the protective pouring atmosphere is argon, and the argon flow rate is 5 L / min. The cooling time is calculated according to formula I:

[0164] T = 35R 2 (M)×1.2Formula I;

[0165] Where, T is the cooling time, in h; R is the mold radius, in m;

[0166] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting, cooling and annealing treatment in sequence to obtain a 316LN stainless steel ingot; wherein the electroslag remelting adopts CaF 2-Al 2 O 3 -CaO-MgO quaternary slag system, CaF 2 、Al 2 O 3 , CaO and MgO are in a mass ratio of 1:2:3:3, the mass of the quaternary slag system is 5% of the mass of the steel ingot, a 5t crystallizer, a crystallizer diameter of 1050mm, a consumable electrode is used for direct slagging, the diameter of the consumable electrode is 800mm, the voltage is 85V, the current is 16kA, 3kg / t of Si-Mn alloy powder is added during the slagging period, and the mass ratio of Si to Mn in the Si-Mn alloy powder is 1:3; the melting rate of the electroslag remelting process is uniform, and the electroslag remelting time is 10.0h; the holding temperature of the annealing treatment is 830℃; the holding time of the annealing treatment is 10h; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300℃.

[0167] The chemical composition of the 316LN stainless steel ingots prepared in Examples 1 to 3 is shown in Table 1; wherein the chemical composition analysis method of the 316LN stainless steel ingots in Table 1 is GB / T223.

[0168] Table 1 Chemical composition of 316LN stainless steel ingots prepared in Examples 1 to 3

[0169]

[0170] As can be seen from Table 1, compared with the original 316LN, the 316LN stainless steel ingot prepared by the preparation method provided by the present invention has C optimized from ≤0.030wt% to ≤0.013wt%; S optimized from ≤0.030wt% to ≤0.004wt%; and P optimized from ≤0.040wt% to ≤0.010wt%.

[0171] The non-metallic inclusion content of the 316LN stainless steel ingots prepared in Examples 1 to 3 was measured using the standard rating chart microscopic inspection method according to GB / T10561. The results are shown in Table 2.

[0172] Table 2 Non-metallic inclusion data of 316LN stainless steel ingots prepared in Examples 1 to 3

[0173]

[0174] It can be seen from Table 2 that the preparation method provided by the present invention can reduce the content of inclusions and improve the grade of inclusions.

[0175] Embodiments 4 to 6

[0176] A preparation method of a 316LN stainless steel forging comprises: forging, annealing, rough machining and solution treatment are performed on the 316LN stainless steel ingot prepared in Example 1 to obtain a 316LN stainless steel forging; wherein the initial forging temperature of the forging is 1160°C, the final forging temperature is 930°C, the forging ratio is 3.3, the elongation ratio is 2.5, and the total ratio is 4.3; the holding temperature of the annealing is 830°C, and the holding time is 10 hours; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300°C; the holding temperature of the solution treatment is 1150°C, the holding time is 5 hours, and the cooling method is water cooling.

[0177] Example 5

[0178] A preparation method of a 316LN stainless steel forging comprises: forging, annealing, rough machining and solution treatment are performed on the 316LN stainless steel ingot prepared in Example 2 to obtain a 316LN stainless steel forging; wherein the initial forging temperature of forging is 1160°C, the final forging temperature is 930°C, the forging ratio is 3.3, the elongation ratio is 2.5, and the total ratio is 4.3; the holding temperature of annealing is 830°C, and the holding time is 10 hours; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300°C; the holding temperature of the solution treatment is 1150°C, the holding time is 5 hours, and the cooling method is water cooling.

[0179] Example 6

[0180] A preparation method of a 316LN stainless steel forging is as follows: the 316LN stainless steel ingot prepared in Example 3 is subjected to forging, annealing, rough machining and solution treatment in sequence to obtain a 316LN stainless steel forging; wherein the initial forging temperature of forging is 1160°C, the final forging temperature is 930°C, the forging ratio is 3.3, the elongation ratio is 2.5, and the total ratio is 4.3; the holding temperature of annealing is 830°C, and the holding time is 10 hours; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300°C; the holding temperature of the solution treatment is 1150°C, the holding time is 5 hours, and the cooling method is water cooling.

[0181] The mechanical properties of the 316LN stainless steel forgings prepared in Examples 4 to 6 were tested, and the results are shown in Table 3. The room temperature tensile test used a Φ5 mm standard specimen, a WE-300 tensile testing machine, and a test temperature of 25 ° C to measure the tensile strength Rm and yield strength R P0.2 , elongation after fracture A; the impact performance adopts the Charpy pendulum impact test method of GB / T 229-2020 metal materials.

[0182] Table 3 Room temperature mechanical properties of 316LN stainless steel forgings prepared in Examples 4 to 6

[0183]

[0184] It can be seen from Table 3 that the 316LN stainless steel forgings prepared by the present invention have excellent room temperature mechanical properties.

[0185] It can be seen from the above examples that the 316LN stainless steel ingot prepared by the preparation method provided by the present invention has low inclusion content and the 316LN stainless steel forging has excellent mechanical properties.

[0186] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for improving the purity of stainless steel, comprising the following steps: (1) smelting the raw materials to obtain molten steel; (2) subjecting the molten steel obtained in step (1) to VODC refining to obtain refined molten steel; the VODC refining comprises a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence; a first deoxidizer is added in the VOH stage; (3) mixing the refined molten steel obtained in step (2) with a second deoxidizer, and deoxidizing the molten steel under argon protection to obtain deoxidized molten steel; (4) performing protective pouring on the deoxidized molten steel obtained in step (3) to obtain a steel ingot; (5) The steel ingot obtained in step (4) is subjected to electroslag remelting to obtain a stainless steel ingot.

2. The method according to claim 1, characterized in that In the step (2), the first deoxidizer includes at least one of CaO, CaF2 and FeSi.

3. The method according to claim 1 or 2, characterized in that: The dosage of the first deoxidizer in the step (2) is 6-9 kg / t.

4. The method according to claim 1, characterized in that: In the step (5), the voltage of the electroslag remelting is 80-86V, the current of the electroslag remelting is 16-18kA, and the time of the electroslag remelting is 9.5-10.0h.

5. The 316LN stainless steel ingot prepared by the method according to any one of claims 1 to 4, wherein the P content in the 316LN stainless steel ingot is ≤0.012wt%; the A-type inclusion rating in the 316LN stainless steel ingot is ≤2, the B-type inclusion rating is ≤1, the C-type inclusion rating is ≤1, and the D-type inclusion rating is ≤2.

6. A 316LN stainless steel forging, prepared from the 316LN stainless steel ingot according to claim 5.

7. The method for preparing the 316LN stainless steel forging according to claim 6, comprising: The 316LN stainless steel ingot is forged, annealed, rough machined and solution treated in sequence to obtain a 316LN stainless steel forging.

8. The preparation method according to claim 7, characterized in that: The initial forging temperature of the forging is 1150-1170° C., the final forging temperature of the forging is 920-940° C., the forging ratio of the forging is ≥3.0, the extension ratio of the forging is ≥2.0, and the total ratio of the forging is ≥4.

0.

9. The preparation method according to claim 7, characterized in that: The holding temperature of the solution treatment is 1140-1160° C., and the holding time of the solution treatment is 3-5 hours.

10. Application of the 316LN stainless steel forging according to claim 6 or the 316LN stainless steel forging prepared by the preparation method according to any one of claims 7 to 9 in aerospace, ship power, medical equipment and nuclear power equipment.

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