A method for preparing a martensitic sulfur-containing free-cutting stainless steel for aerospace applications

Abstract

The application discloses a preparation method of a martensite sulfur-containing free-cutting stainless steel for aviation, which comprises the following steps: adding industrial pure iron, a nickel plate, low-carbon chromium iron and a returned steel into an electric furnace to smelt, and adjusting the composition of the molten steel to control the composition; the percentage by weight of C is 0.22-0.25%, the percentage by weight of Si is 0.10-0.25%, the percentage by weight of Mn is 1.10-1.20%, the percentage by weight of P is 0.10-0.13%, the percentage by weight of Cr is 12.50-13.50%, and the percentage by weight of Ni is 1.65-1.90%; inserting sulfur powder sealed by a thin skin tube into the molten steel, stirring uniformly, then adding BaAlSi alloy to perform final deoxidization, and pouring into an electric slag blank after discharging; performing electric slag remelting on the electric slag blank, wherein the electric slag remelting slag system comprises 30-40 wt% CaF2 powder, 25-35 wt% Al2O3 powder, 20-30 wt% SiO2 powder, 3-7 wt% MgO powder and 3-7 wt% manganese metal particles; after the electric slag remelting ingot is obtained, the ingot is sent into a forging heat processing furnace to be heated, then forging is performed, the forged ingot is sent into an annealing furnace to be annealed, and the martensite sulfur-containing free-cutting stainless steel for aviation is obtained. The preparation method can effectively control the content of sulfur and manganese elements and improve the comprehensive yield of Y25Cr13Ni2.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of special steel metallurgy, and particularly relates to a preparation method of a martensitic sulfur-containing easy-to-cut stainless steel for aviation. BACKGROUND

[0002] Y25Cr13Ni2 is a martensitic sulfur-containing easy-to-cut stainless steel for aviation, and the chemical composition and weight percentage of the steel are as follows: C: 0.20-0.30%, Si: ≤0.50%, Mn: 0.80-1.20%, P: 0.08-0.15%, S: 0.15-0.25%, Cr: 12.00-14.00%, Ni: 1.50-2.00%, and the rest is Fe and inevitable impurities. In the Y25Cr13Ni2 sulfur-containing easy-to-cut stainless steel, sulfur forms MnS inclusions with manganese in the steel, interrupts the continuity of the base metal, produces under-cutting effect when the steel is cut at high speed, breaks the chip through stress concentration, and achieves the purpose of improving the cutting property of the steel. Therefore, in the easy-to-cut steel, sulfur is added as a beneficial element, which can improve the cut performance of the steel. However, sulfur is prone to segregation in the steel, which deteriorates the quality of the steel and reduces the plasticity of the steel at high temperature. It is a harmful element, which exists in the form of FeS with a lower melting point. The melting point of the existing FeS is only 1190℃, and the eutectic temperature of the eutectic body formed by Fe and S is lower, only 988℃. When the steel solidifies, the iron sulfide is precipitated at the original grain boundary. When the steel is hot worked at 1100-1200℃, the FeS on the grain boundary will melt, greatly weakening the bonding force between the grains, resulting in the hot brittleness of the steel. In order to prevent the brittleness caused by sulfur during the hot working of Y25Cr13Ni2, it is usually ensured that the steel contains sufficient manganese to form MnS inclusions with a higher melting point, and the mass content ratio of Mn and S in the steel is ≥5.

[0003] Electroslag remelting has the dual functions of refining and purification and sequential solidification forming, and the produced steel ingot has the advantages of compact organization, small and uniformly distributed inclusions, and high material performance. In the aviation industry and other industries with high safety factor requirements, the electroslag remelting method is usually used to smelt Y25Cr13Ni2.

[0004] However, there is a loss of sulfur and Mn elements during the electroslag remelting process, and the main reaction of the loss is as follows:

[0005] [S]+(O 2- )=(S 2- )+[O] (1)

[0006] (S 2- )+(O2)=(SO2)+(O2) (2)

[0007] [Mn]+[O]=(MnO) (3)

[0008] [Mn]+[S]=(MnS) (4)

[0009] The higher the oxygen content in the electrode rod, the more sufficient the kinetic conditions of the above reaction, that is, formula (1), formula (2) is more prone to occur, promotes the progress of the desulfurization reaction, and leads to the difficulty in controlling the content of sulfur elements in the steel. Meanwhile, the higher the sulfur content and oxygen content in the electrode rod, the more prone to formula (3), formula (4) occurs, promotes the burning loss of Mn elements, and leads to more difficult control of the content of manganese elements in the steel.

[0010] As can be seen from the above, using the electric furnace + electroslag remelting method to produce smelt Y25Cr13Ni2, there is a burning loss of sulfur elements and manganese elements in the electroslag remelting process, it is difficult to control the content of sulfur elements and manganese elements, and in order to improve the hot working performance of Y25Cr13Ni2 and the cutting performance of finished steel and other comprehensive performance indicators, it is required that the chemical composition of the electroslag ingot is uniform and meets the standard requirements, and the content of sulfur elements and manganese elements is accurately controlled, that is, the mass content ratio of Mn and S in Y25Cr13Ni2 should be ≥5, and the smelting difficulty of the electroslag remelting method is greater. Y25Cr13Ni2 has poor hot plasticity, low thermal conductivity, and martensitic transformation during the cooling process, and the cracking scrap situation is prominent. At present, the comprehensive yield of Y25Cr13Ni2 smelted by the electric furnace + electroslag remelting method is low (about 55%). SUMMARY

[0011] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a preparation method of a martensitic sulfur-containing easy-to-cut stainless steel for aviation, which can effectively control the content of sulfur elements and manganese elements and improve the comprehensive yield of Y25Cr13Ni2.

[0012] The technical scheme of the present application is as follows:

[0013] A preparation method of a martensitic sulfur-containing easy-to-cut stainless steel for aviation, specifically comprising the following steps:

[0014] S1: industrial pure iron, nickel plate, low-carbon chromium iron, and the return material of the steel grade are added into an electric furnace for smelting, and the composition of the molten steel is adjusted to the controlled composition, and the weight percentage is: C: 0.22-0.25%, Si: 0.10-0.25%, Mn: 1.10-1.20%, P: 0.10-0.13%, Cr: 12.50-13.50%, Ni: 1.65-1.90%;

[0015] S2: sulfur powder is loaded into a thin skin tube and sealed, inserted into the liquid steel, and stirred uniformly; then BaAlSi alloy is added in an amount of 1-1.5 kg per ton of liquid steel for final deoxidization, and then poured into an electroslag ingot; the amount of sulfur powder added is 0.27%-0.29% of the weight of the liquid steel, so that the control range of S in the electroslag ingot is 0.20-0.25%;

[0016] S3: the electroslag ingot of step S2 is subjected to electroslag remelting, and the electroslag remelting slag system used includes 30-40 wt% CaF2 powder, 25-35 wt% Al2O3 powder, 20-30 wt% SiO2 powder, 3-7 wt% MgO powder, and 3-7 wt% metallic manganese particles;

[0017] S4: immediately after the electroslag remelting ingot is produced, a cover is added for slow cooling, and when production conditions permit, the ingot is directly arranged for heating in a hot forging heat treatment furnace, then forging is performed, and after forging, the ingot is promptly boxed or buried in sand for slow cooling, and when production conditions permit, the ingot is directly arranged for annealing heat treatment in an annealing furnace, thereby obtaining the martensitic sulfur-containing free-cutting stainless steel for aviation.

[0018] Further, step S1 specifically includes the following steps:

[0019] S1.1: a bottom slag is added in an amount of 0.8%-1% of the charge loading in an electric furnace, and then industrial pure iron, nickel plate, low-carbon chromium iron, returned steel of the same grade, and the charge are loaded into the electric furnace for electric melting;

[0020] S1.2: after the charge is melted, part of the oxidized slag is removed by melting and cleaning, and then 0.8%-1.2 kg / t of Al block is added for pre-deoxidization, and then a reducing slag is added to form new slag; the adding amount of the reducing slag is 1%-3% of the weight of the liquid steel;

[0021] S1.3: after the slag material uniformly covers the liquid steel, silicon-calcium powder is used for multiple diffusion deoxidization, and the amount of silicon-calcium powder used for each deoxidization is 30 g, and the deoxidization time for each deoxidization is 3-5 min;

[0022] S1.4: after deoxidization is completed, the composition is adjusted to the control composition by taking a sample before the furnace is opened, thereby obtaining the liquid steel.

[0023] Further, the bottom slag and the reducing slag are both composed of CaO and CaF2, and the mass ratio of CaO to CaF2 in the bottom slag is 9:1; and the mass ratio of CaO to CaF2 in the reducing slag is 70%-80%:20%-30%.

[0024] Further, in step S2, the alkaline slag is first removed, acid slag material that has passed the roasting is added to cover the surface of the liquid steel, and then sulfur powder is added; the acid slag material is perlite or quartz sand, and the adding amount is 1%-1.5% of the weight of the liquid steel.

[0025] Further, in the electroslag remelting, the smelting current is 4200-4600 A, and the smelting voltage is 49-52 V.

[0026] Further, in the electroslag remelting, the smelting current is 4200-4600 A, and the smelting voltage is 49-52 V.

[0027] Further, in the step S4, the forging hot working process is: first, holding at the furnace loading temperature for greater than or equal to 1.5 h, the furnace loading temperature being less than or equal to 500 DEG C; then, heating to 800-900 DEG C and holding for greater than or equal to 1 h; further heating to 1130-1180 DEG C and holding for 1.5-2.0 h; the forging open forging temperature being greater than or equal to 1100 DEG C, and the stop forging temperature being greater than or equal to 850 DEG C.

[0028] Further, in the step S4, the forging hot working process is: first, holding at the furnace loading temperature for greater than or equal to 1.5 h, the furnace loading temperature being less than or equal to 500 DEG C; then, heating to 800-900 DEG C and holding for greater than or equal to 1 h; further heating to 1130-1180 DEG C and holding for 1.5-2.0 h; the forging open forging temperature being greater than or equal to 1100 DEG C, and the stop forging temperature being greater than or equal to 850 DEG C.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] 1. The present application carries out pre-deoxidation and diffusion deoxidation in the preparation of the electric furnace smelting composition, fully degasses and removes inclusions, controls the nitrogen and oxygen content in the molten steel, solves the problem of poor hot plasticity and finished product plasticity of Y25Cr13Ni2, adopts the electroslag remelting slag system with the added metal manganese particles in the electroslag remelting, the metal manganese particles are uniformly added after the other electroslag remelting slag is refined and the metal electrode is put in, and the balance slag is formed before the normal cutting amount of the large head of the electroslag ingot, thereby reducing the desulfurization reaction and the burning loss of manganese elements, and further facilitating the control of the content of sulfur elements and manganese elements and improving the comprehensive yield of Y25Cr13Ni2.

[0031] In the forging hot working process, the heating time in the low temperature section is prolonged, the forging stop forging temperature is increased, the two-phase zone forging cracking is prevented, recrystallization is facilitated, and work hardening is eliminated. The blank annealing system avoids the intermediate blank cracking by increasing the controlled cooling to 400 DEG C for 10-12 h and furnace cooling to less than or equal to 300 DEG C and then air cooling after furnace discharge.

[0032] 2. The aviation martensitic sulfur-free cutting stainless steel Y25Cr13Ni2 prepared by the present application meets the requirements of the aviation stainless steel standard (GJB2294-1995) in terms of physical and chemical and mechanical performance indexes; the chemical composition of the finished product rod is uniform, and the cutting performance is excellent.

[0033] 3、The comprehensive yield of the electroslag steel ingot is 75.77%, which effectively improves the comprehensive yield of the electroslag steel ingot and has remarkable economic benefits compared with the prior art. DETAILED DESCRIPTION

[0034] A preparation method of a martensitic sulfur-containing free-cutting stainless steel for aviation, specifically comprising the following steps

[0035] (1) primary smelting: adding 0.8% to 1% of the bottom slag (bottom slag composition: CaO: CaF2=9:1) to the charge of the electric furnace, then calculating and matching various metal raw materials such as industrial pure iron, nickel plate, low-carbon chromium iron, and the returned material of the steel grade, and then charging into the furnace for electric melting. Melt the charge at the maximum speed, remove part of the oxidized slag, add 0.8% to 1.2 kg / t of Al block for pre-deoxidation, then add reducing slag, and the adding amount of the reducing slag is 1% to 3% of the weight of the molten steel. The composition of the reducing slag is: CaO: CaF2=70% to 80%: 20% to 30% to form new slag; keep the slag evenly covering the molten steel, and use silicon-calcium powder for diffusion deoxidation for not less than 3 times, 3 to 5 minutes each time, and the dosage is about 30 g each time. After the composition is uniform, take the sample before the furnace (keep the white slag operation), and adjust the composition (except S) according to the composition of the sample before the furnace to control the composition: C: 0.22% to 0.25%, Si: 0.10% to 0.25%, Mn: 1.10% to 1.20%, P: 0.10% to 0.13%, Cr: 12.50% to 13.50%, and Ni: 1.65% to 1.90%. After sampling, keep deoxidation for 30 min. After alloying, remove the alkaline slag, add the roasted qualified acid slag (perlite or quartz sand) with an adding amount of 1% to 1.5% of the weight of the molten steel to cover the surface of the molten steel, seal the sulfur powder (sulfur powder adding amount: 0.27% to 0.29% of the weight of the molten steel; S control range: 0.20% to 0.25%) in a thin skin tube, insert it into the molten steel, and stir uniformly; add BaAlSi alloy for final deoxidation at an amount of 1 to 1.5 kg per ton of molten steel; and after 3 minutes of calming before pouring, the electroslag blank is obtained by pouring.

[0036] (2) electroslag remelting: electroslag remelting is performed on the electroslag blank. The specification of the electroslag remelted ingot is φ260 mm; the electroslag remelting smelting current is 4200 to 4600 A; and the electroslag remelting smelting voltage is 49 to 52 V.

[0037] The ratio of the five-component slag system in the electroslag remelting is: 30wt% to 40wt% of CaF2 powder; 25wt% to 35wt% of Al2O3 powder; 20wt% to 30wt% of SiO2 powder; 3wt% to 70wt% of MgO powder; and 3wt% to 7wt% of metallic manganese particles.

[0038] During the slag making of the electroslag remelting, CaF2 powder, Al2O3 powder, SiO2 powder, MgO powder and other slag materials are added first to make normal slag; then after the slag refining of the electroslag remelting is completed, the metal manganese particles are added evenly after the metal electrode is put in, the metal manganese particles are added evenly within 15 minutes, and before the normal cutting of the big head of the electroslag ingot, the "balanced slag" is formed.

[0039] (3) forging: after the electroslag remelting ingot is taken out, the cover is added for slow cooling, then the ingot is sent to a forging heat treatment furnace for heating, and then the ingot is forged; or when the production condition permits, the electroslag remelting ingot is directly arranged to be sent to the forging heat treatment furnace for heating, and then the ingot is forged. The forging heat treatment process is as follows: first, the temperature is kept for greater than or equal to 1.5 h at a furnace charging temperature, and the furnace charging temperature is less than or equal to 500 DEG C; then the temperature is increased to 800-900 DEG C, and the temperature is kept for greater than or equal to 1 h; and then the temperature is increased to 1130-1180 DEG C, and the temperature is kept for 1.5-2.0 h. The forging heating atmosphere is weak oxidizing or neutral; the forging starting temperature is greater than or equal to 1100 DEG C; and the forging stopping temperature is greater than or equal to 850 DEG C.

[0040] (4) annealing heat treatment: after forging, the ingot is boxed or buried in sand for slow cooling, and then the ingot is sent to an annealing furnace for annealing heat treatment; or when the production condition permits, the ingot is directly arranged to be sent to the annealing furnace for annealing heat treatment, so as to prevent the martensite transformation cracking caused by rapid cooling. During the annealing heat treatment of the forged intermediate billet, the temperature is increased to 760±5 DEG C, the temperature is kept for 6-8 h, and the cooling (cooling speed is less than or equal to 30 DEG C / h) is controlled to 400±5 DEG C, then the temperature is kept for 10-12 h, and then the furnace is cooled to less than or equal to 300 DEG C, and the ingot is taken out and air cooled, so as to avoid the cracking of the intermediate billet and the finished product.

[0041] The chemical composition and macrostructure of the aviation martensitic sulfur-containing free-cutting stainless steel Y25Cr13Ni2 prepared by the above method are shown in Table 1.

[0042]

[0043] In which, Mn / S = 1.06 / 0.185 = 5.73

[0044] As shown in Table 1, the chemical composition of the Y25Cr13Ni2 prepared by the method meets the standard requirements, and the mass content ratio of Mn / S in the steel is greater than 5, so that the hot brittleness phenomenon caused by sulfur can be effectively avoided.

[0045] Meanwhile, the physicochemical and mechanical properties of the aviation martensitic sulfur-containing free-cutting stainless steel Y25Cr13Ni2 produced by the method meet the requirements of the aviation stainless steel standard (GJB2294-1995); the chemical composition of the finished rod is uniform, and the cutting performance is excellent. The comprehensive material yield of the electroslag ingot reaches 75.77%, which is greatly improved compared with the prior art, and the economic benefit is remarkable.

[0046] Finally, it should be noted that the above-described embodiments of the present application are merely illustrative and are not intended to limit the scope of the present application. Those skilled in the art can make other changes and modifications to the embodiments described above on the basis of the above description. Here, all the embodiments cannot be exhaustively listed. Any obvious changes or modifications derived from the technical solutions of the present application are still within the scope of the present application.

Claims

1. A method for producing a martensitic sulfur-containing free-machining stainless steel for aerospace applications, characterized in that, Specifically comprising the following steps: S1: the industrial pure iron, nickel plate, low carbon chromium iron, the steel grade return material is added into the electric furnace to smelt, the initial adjustment liquid composition is to the control composition, according to the percentage by weight: C: 0.22~0.25%, Si: 0.10~0.25%, Mn: 1.10~1.20%, P: 0.10~0.13%, Cr: 12.50~13.50%, Ni: 1.65~1.90%; The steel grade is Y25Cr13Ni2; S2: sulfur powder is sealed in a thin skin tube and inserted into the liquid steel, and stirred uniformly; Then add BaAlSi alloy to each ton of molten steel to add 1~1.5kg for final deoxidation, and then pour into an electroslag blank; The amount of sulfur powder added is 0.27%~0.29% of the weight of the molten steel; S3: the electroslag blank of step S2 is electroslag remelted, and the electroslag remelting slag system used includes 30~40 wt% CaF2 powder, 25~35 wt% Al2O3 powder, 20~30 wt% SiO2 powder, 3~7 wt% MgO powder and 3~7 wt% metallic manganese particles; S4: after the electroslag remelting ingot is obtained, it is sent to a forging heat treatment furnace for heating, then forging is carried out, and after forging, it is sent to an annealing furnace for annealing heat treatment, thereby obtaining the martensitic sulfur-containing free-cutting stainless steel for aviation.

2. A method of producing a martensitic sulphur bearing free cutting stainless steel for aerospace applications according to claim 1, characterized in that, Step S1 specifically includes the following steps: S1.1: add 0.8%~1% of the bottom slag to the charge amount of the electric furnace, then add the industrial pure iron, nickel plate, low carbon chromium iron, and the steel grade return material to the electric furnace and send electricity to melt; S1.2: after the charge is melted, part of the oxidized slag is removed, and 0.8%~1.2 kg / t of Al block is added for pre-deoxidation, and then a reducing slag is added to form new slag; The amount of reducing slag added is 1%~3% of the weight of the molten steel; S1.3: after the slag material uniformly covers the liquid steel, multiple diffusion deoxidation is carried out with silicon-calcium powder, the amount of silicon-calcium powder used for each deoxidation is 30 g, and the deoxidation time for each deoxidation is 3~5 min; S1.4: after deoxidation, the composition is adjusted to the control composition by taking the sample before the furnace is taken, thereby obtaining the molten steel.

3. A method of producing a martensitic sulphur bearing free cutting stainless steel for aerospace applications according to claim 2, characterized in that, The bottom slag and the reducing slag are both composed of CaO and CaF2, wherein the mass ratio of CaO to CaF2 in the bottom slag is 9:1; The mass ratio of CaO to CaF2 in the reducing slag is 70%~80%:20%~30%.

4. A method of producing a martensitic sulphur bearing free cutting stainless steel for aerospace applications according to claim 1, characterized in that, In step S2, the alkaline slag is first removed, acid slag material that has passed the roasting is added to cover the surface of the molten steel, and then sulfur powder is added; The acid slag material is perlite or quartz sand, and the amount added is 1%~1.5% of the weight of the molten steel.

5. The method of producing a martensitic sulfur bearing free machining stainless steel for aerospace applications as claimed in claim 1, wherein, During electroslag remelting, the smelting current is 4200~4600 A, and the smelting voltage is 49~52 V.

6. A method of producing a martensitic sulphur bearing free machining stainless steel for aerospace applications according to claim 1, characterised in that, In step S3, during slag making for electroslag remelting, CaF2 powder, Al2O3 powder, SiO2 powder and MgO powder are first added for slag making, and after the slag material for electroslag remelting is refined, metallic manganese particles are uniformly added after the metal electrode, and the metallic manganese particles are uniformly added within 15 min.

7. A method of producing a martensitic sulphur bearing free cutting stainless steel for aerospace applications according to claim 1, characterized in that, In step S4, the forging hot working process is: first, holding for ≥1.5 h at the charging temperature ≤500 ℃; then, heating to 800-900 ℃, holding for ≥1 h; then, heating to 1130-1180 ℃, holding for 1.5-2.0 h; the open forging temperature is ≥1100 ℃, and the stop forging temperature is ≥850 ℃.

8. A method of producing a martensitic sulphur bearing free cutting stainless steel for aerospace applications according to claim 7, characterized in that, In the forging intermediate blank annealing heat treatment, when heating to 760±5 ℃, holding for 6-8 h, the cooling speed is ≤30 ℃ / h until 400±5 ℃, then holding for 10-12 h, and then furnace cooling to ≤300 ℃ and air cooling.

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