A jig and a production method for a riserless steel ingot for a hollow forging

Abstract

The present application relates to a kind of riser-free steel ingot for hollow forging and production method, belong to smelting industrial technology field, solve the problem of low utilization rate of steel ingot, high riser proportion, high degree of element segregation in the production process of hollow forging in prior art.A kind of production method of riser-free steel ingot for hollow forging, comprising the following steps: step 1, molten steel smelting: control the composition of refining slag: CaO: 50-60%, CaF2: 5-10%, Al2O3: 25-30%, MgO+SiO2: 10-15%;Step 2, steel ingot auxiliary preparation before pouring and vacuum pouring: steel ingot auxiliary includes steel ingot mould, heat preservation cap and bottom disc, the upper part of the steel ingot mould is circumferentially processed with annular slot;Step 3, riser heating insulation treatment after pouring;Step 4, molten steel solidification forming, obtain riser-free steel ingot for hollow forging.Improve the utilization rate of steel ingot for hollow forging and metallurgical quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of smelting industry, and in particular to a jig for a riserless ingot for a hollow forge piece and a production method. BACKGROUND

[0002] With the rapid development of nuclear power, petrochemical industry and coal liquefaction projects, the number of large hollow forge pieces required is growing, and the supply and demand contradiction is becoming increasingly tense. The pressure vessel, evaporator and stabilizer in the nuclear power project all contain hollow forge pieces. The common hollow forge pieces include the upper cylinder and lower cylinder in the evaporator, the inlet and outlet connecting pipes, the core cylinder and the flange-pipe section cylinder in the pressure vessel, and the upper, middle and lower cylinders in the stabilizer. The most commonly used hydrogenation reactor in the petrochemical industry also needs to use a hollow forge piece-hydrogenation cylinder segment to be assembled and welded.

[0003] The hollow forge piece is mainly produced by using a solid ingot as a raw material. The production process is basically as follows: molten steel smelting, ingot casting, solid ingot blanking, upsetting, punching and hole expanding. The characteristics of the production process are that the forge piece only uses high-quality ingot body materials, and the riser and the nozzle material are finally discarded; at the same time, the middle region of the ingot is punched off by using a punching method; the ingot type used for producing the above-mentioned hollow forge piece is usually 150-500t, and in order to ensure the metallurgical quality of the forge piece, the proportion of the riser of the ingot is usually in the range of 15-20%, which causes low utilization rate of the ingot and high production cost of the hollow forge piece. Japan, France and other countries also use hollow ingot manufacturing technology to produce hollow forge pieces, but need to be poured in the atmospheric environment, which leads to difficult control of H, O and N gas content and difficult guarantee of the quality of the forge piece. SUMMARY

[0004] In view of the above analysis, the present application aims to provide a jig for a riserless ingot for a hollow forge piece and a production method, so as to solve at least one of the problems of low utilization rate of the ingot, high proportion of the riser and high degree of element segregation in the existing hollow forge piece production process.

[0005] In one aspect, the present application provides a production method for a riserless ingot for a hollow forge piece, which comprises the following steps:

[0006] Step 1, molten steel smelting: control the composition of the refining slag: CaO: 50-60%, CaF2: 5-10%, Al2O3: 25-30%, MgO+SiO2: 10-15%;

[0007] Step 2, preparation of the ingot jig before pouring and vacuum pouring: the ingot jig includes an ingot mold, a heat preservation cap and a bottom disc, the upper part of the ingot mold is circumferentially provided with an annular slot, and the opening direction of the annular slot is upward;

[0008] Step 3, riser heating and heat preservation treatment after pouring;

[0009] Step 4, the molten steel is solidified to form a riserless ingot for hollow forgings.

[0010] Preferably, the thickness of the ingot mold wall is 400-600 mm, and the height-diameter ratio is 1.3-1.5.

[0011] Further, the upper wall of the ingot mold is circumferentially processed with an annular groove, the center line of the groove is 1 / 4-1 / 2 of the thickness of the ingot mold wall away from the inner wall of the ingot mold, the depth of the groove is ≤1 / 4 of the height of the ingot mold, and the width of the groove is 50-100 mm.

[0012] It should be noted that the heat preservation cap includes an outer steel shell and an inner lining, and the outer steel shell is welded from a steel plate with a thickness of 5-10 mm.

[0013] Specifically, the inner lining is made of refractory material, and the main components of the refractory material are as follows in terms of mass percentage: Al2O3: 40-55%, SiO2: 35-52%, MgO: 3-10%, and the porosity is 65-80%, and the refractoriness is ≥1700℃.

[0014] Preferably, the ratio of the lower inner diameter of the heat preservation cap to the diameter of the upper inner wall of the ingot mold is 0.93-1.0.

[0015] Illustratively, the height of the heat preservation cap is the sum of the height of the riser and the reserved height, and the reserved height is 500-800 mm.

[0016] Further, the base disc includes a base disc body and a water gap, the water gap is paved with refractory material, the thickness of the refractory material is 50-70 mm, the mass fraction of Al2O3 in the refractory material is 70%-90%, and the base disc body and the water gap are paved with a steel plate in the shape of the part in contact with the molten steel, and the thickness of the steel plate is 10 mm.

[0017] It is worth noting that the preparation of the auxiliary tool before pouring includes baking the refractory material in the inner lining of the heat preservation cap at a temperature ≥350℃, and assembling the baked heat preservation cap, the ingot mold and the base disc into an ingot mold auxiliary tool in a vacuum chamber, and the temperature of the refractory material in the inner lining of the heat preservation cap before being placed in the vacuum chamber is ≥300℃.

[0018] On the other hand, the embodiment of the present application also provides an auxiliary tool for a riserless ingot for hollow forgings, which is used for the production of the riserless ingot for hollow forgings, and includes an ingot mold, a heat preservation cap and a base disc, the ingot mold is placed on the base disc, and the heat preservation cap is placed on the ingot mold.

[0019] The upper wall of the ingot mold is circumferentially processed with an annular groove, the center line of the groove is 1 / 4-1 / 2 of the thickness of the ingot mold wall away from the inner wall of the ingot mold, and the depth of the groove is ≤1 / 4 of the height of the ingot mold.

[0020] The heat preservation cap comprises an outer steel shell and an inner lining, the bottom disc comprises a bottom disc body and a water gap, the water gap is paved with refractory material, and the bottom disc body and the water gap are in contact with the molten steel and are paved with a steel plate in shape.

[0021] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0022] 1、 The present application combines the characteristics of the hollow forging requiring punching, changes the solidification heat transfer form of the ingot, and makes the composition segregation area and inclusions of the ingot without riser exceed the standard to be gathered in the core, which can be removed in the subsequent forging, so that the composition and metallurgical quality of the forging can meet the requirements of the corresponding technical conditions;

[0023] In the present application, the full refractory material lining type heat preservation cap and the heating and heat preservation treatment of the riser after pouring are adopted, so that the heat of the molten steel in the riser is mainly transferred to the air through the ingot mold, and the laying of refractory material on the bottom disc greatly reduces the heat conduction of the molten steel from the bottom of the ingot, realizes the solidification of the ingot along the diameter direction, and promotes the segregation and inclusions to the core.

[0024] 2、 The present application makes the heat transfer path longer by slotting along the upper mold wall of the ingot mold, greatly improves the heat insulation performance of the mold wall, prolongs the liquid state time of the molten steel in the riser, so that the feeding efficiency is higher, and the ingot utilization rate is improved; the slotting ratio is strictly controlled to ensure that the above heat transfer characteristics meet the strength requirements.

[0025] 3、 The present application further improves the heat preservation efficiency by baking the heat preservation cap before pouring and heating and heat preservation treatment of the riser after pouring, so that the riser ratio is lower and the ingot utilization rate is higher.

[0026] 4、 The present application cooperates the slotting of the mold wall, the use of low thermal conductivity heat preservation cap refractory material and the heat preservation measures before and after pouring, effectively improves the feeding efficiency of the riser, so that the riser ratio of the ingot is greatly reduced from 15%-16% to 2.45%-6%, the ingot utilization rate is significantly improved, and the production cost is reduced.

[0027] 5、 The present application accurately controls the composition of the refining slag during the smelting process of the molten steel, ensures that the molten steel reaches the required purity, controls O≤30ppm and S≤20ppm in the molten steel, and Al2O3≤5% in the inclusions, effectively reduces the segregation degree.

[0028] The technical solutions in the present application can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent description, and some advantages will become apparent from the description, or will be understood by those skilled in the art through implementation of the present application. The objects and other advantages of the present application can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0030] Figure 1 Auxiliary assembly drawing for the riserless ingot for hollow forge piece of the present application;

[0031] Figure 2 Schematic diagram of the riserless ingot for hollow forge piece of the present application;

[0032] Figure 3 Schematic diagram of the ingot mold for the riserless ingot for hollow forge piece of the present application;

[0033] Figure 4 Schematic diagram of the full refractory type heat preservation cap of the present application;

[0034] Figure 5 Pouring schematic diagram of the riserless ingot for hollow forge piece of the present application.

[0035] Reference signs:

[0036] 1 - riser; 2 - ingot body; 3 - nozzle; 4 - full refractory type heat preservation cap; 5 - ingot mold; 6 - heat preservation type base plate; 7 - refractory lining; 8 - steel shell; 9 - heating agent; 10 - grooving; 11 - steel plate; 12 - high-aluminum refractory; 13 - vacuum cover; 14 - vacuum chamber; 15 - ingot auxiliary. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which form a part of this application. The drawings show, by way of illustration, the principles of the present application and the preferred embodiments discussed in detail below to explain the present application.

[0038] In one aspect, one specific embodiment of the present application discloses a production method of a riserless ingot for hollow forge piece, comprising the following steps:

[0039] Step 1, molten steel smelting: control the composition of refining slag: CaO: 50-60%, CaF2: 5-10%, Al2O3: 25-30%, MgO+SiO2: 10-15%;

[0040] Step 2, preparation of auxiliary tool for steel ingot before casting and vacuum casting: the auxiliary tool for steel ingot includes a steel ingot mold, a heat preservation cap and a bottom plate, the upper mold wall of the steel ingot mold is circumferentially processed with an annular slot, and the opening direction of the annular slot is upward;

[0041] Step 3, heat preservation treatment of the riser after casting;

[0042] Step 4, solidification of the molten steel to form a riser-free steel ingot for hollow forgings.

[0043] It should be noted that the molten steel smelting process in step 1 includes electric furnace smelting and secondary refining; the refining is one of LF refining or RH refining, and the slag forming material is lime, aluminum oxide powder and fluorite;

[0044] After the refining is completed, the composition of the refining slag is required to meet the following requirements: CaO: 50-60%, CaF2: 5-10%, Al2O3: 25-30%, MgO+SiO2: 10-15%.

[0045] In order to ensure that the molten steel reaches the required purity, the composition of the refining slag is specifically required, and the removal of impurities such as sulfur and oxygen in the molten steel is indirectly controlled and reflected by the composition of the refining slag; when the composition of the refining slag meets the above requirements, the O in the molten steel can be controlled to be ≤30ppm, the S can be controlled to be ≤20ppm, and the Al2O3 in the inclusions can be controlled to be ≤5%.

[0046] The specific process is as follows: according to the requirements of the steel grade and the needs of the steelmaking process, the proportions and contents of various chemical components in the refining slag are pre-set; during the refining process, the composition of the refining slag is analyzed by sampling, and the amount of the slag forming material added is adjusted according to the analysis results to ensure that the composition of the slag meets the pre-set requirements; at the end of the refining process, the composition of the slag is detected again to confirm whether it meets the pre-set requirements, thereby indirectly verifying whether the purity of the molten steel reaches the expected target.

[0047] Further, the auxiliary tool for steel ingot used for producing the riser-free steel ingot for hollow forgings includes a steel ingot mold 5, a heat preservation cap 4 and a bottom plate 6; the steel ingot mold 5 is placed on the bottom plate 6, and the heat preservation cap 4 is placed on the steel ingot mold 5; the steel ingot mold is made of cast iron.

[0048] Specifically, the wall thickness of the steel ingot mold is 400-600mm, and the height-diameter ratio is 1.3-1.5.

[0049] Further, the upper mold wall of the steel ingot mold is circumferentially processed with an annular slot 10, the center line of the slot is 1 / 4-1 / 2 of the wall thickness of the steel ingot mold away from the inner wall of the steel ingot mold, the depth of the slot is ≤1 / 4 of the height of the steel ingot mold, the width of the slot is 50-100mm, and the specific formula is as follows:

[0050] 2H1 / (D1+D2)=1.3-1.5;

[0051] L2=(1 / 4~1 / 2)*L1;

[0052] L3=(1 / 6~1 / 4)*H1;

[0053] H1-mould height, mm;

[0054] D1-mould upper inner diameter, mm;

[0055] D2-mould lower inner diameter, mm;

[0056] L1-mould wall thickness, mm;

[0057] L2-distance between the center line of the slot and the inner wall of the mould, mm;

[0058] L3-slot depth, mm.

[0059] In the present application, since the full refractory lining type heat preservation cap 4 is adopted and the heat preservation treatment of the pouring riser is carried out after pouring, the heat of the molten steel in the riser is mainly transmitted to the air through the mould, the original heat transmission path from one surface to another surface is blocked through the circumferential slot in the upper mould wall, the heat transmission path of the hollow wall after the slot is longer, the heat insulation performance is improved through the way of increasing thermal resistance, reducing heat flux density and limiting heat flow channel, the liquid time of the molten steel in the riser is lengthened, so that the feeding efficiency is higher; when the slotting ratio is too large, the feeding efficiency of the molten steel in the riser is not obviously improved, and the supporting strength of the mould is reduced, so it is necessary to control the appropriate slotting size.

[0060] Further, the heat preservation cap comprises an outer steel shell 8 and an inner lining 7; the outer steel shell is welded by a steel plate with a thickness of 5-10 mm.

[0061] It should be noted that the inner lining material is refractory material, the main components of the refractory material are as follows in terms of mass percentage: Al2O3: 40-55%, SiO2: 35-52%, MgO: 3-10%; porosity 65-80%; refractoriness ≥ 1700℃; the parts in contact with the molten steel are all refractory materials, the thermal conductivity is controlled by controlling the composition and porosity of the refractory material to meet certain requirements, so as to improve the feeding effect of the molten steel in the riser.

[0062] The refractory material thermal conductivity needs to meet the following requirements: at 200℃, thermal conductivity ≤0.11W / m·k; at 600℃, thermal conductivity ≤0.14W / m·k; at 800℃, thermal conductivity ≤0.19W / m·k; at 1000℃, thermal conductivity ≤0.21W / m·k; at 1100℃, thermal conductivity ≤0.23W / m·k; at 1200℃, thermal conductivity ≤0.25W / m·k.

[0063] Preferably, the heat-insulating cap is in the shape of a circular truncated cone with the upper diameter being smaller than the lower diameter, and the ratio of the lower inner diameter of the heat-insulating cap to the diameter of the inner wall of the upper opening of the ingot mold is 0.93-1.0, preferably 0.93-0.98. ， The height of the heat-insulating cap is the sum of the height of the riser and the reserved height, and the reserved height is 500-800 mm, which is the space reserved for the heating agent.

[0064] The lower outer diameter of the heat-insulating cap is equal to the upper outer diameter of the ingot mold.

[0065] Further, the base tray is a heat-insulating base tray 6, which comprises a base tray body and a water gap, and the water gap is paved with refractory material 12, the thickness of the refractory material is 50-70 mm, and the mass fraction of Al2O3 in the refractory material is 70%-90%.

[0066] Paving the base tray with refractory material greatly reduces the heat conduction of molten steel from the bottom of the ingot, realizes the solidification of the ingot along the diameter direction, and promotes the segregation and inclusions to gather to the center.

[0067] Notably, the base tray body and the water gap are paved with steel plate 11 in the shape of the part in contact with the molten steel, and the thickness of the steel plate is 10 mm; the base tray paved with steel plate prevents the problem of foreign inclusions caused by the scouring of the flowing molten steel on the refractory material in the base tray at the initial stage of pouring.

[0068] Further, the preparation of the auxiliary tool before pouring in step 2 also comprises baking the heat-insulating cap lined with refractory material, and the baking temperature is ≥350℃; the baked heat-insulating cap, the ingot mold and the base tray are assembled into an ingot mold auxiliary tool, which is placed in a vacuum chamber 14, and the temperature of the heat-insulating cap lined with refractory material before being placed in the vacuum chamber is ≥300℃.

[0069] The baking of the heat-insulating cap lined with refractory material adopts assembly tongs.

[0070] Further, the heating and heat-insulating treatment of the riser after pouring in step 3 is to add heating agent 9 into the riser after the pouring of the ingot is completed, and the addition amount is 2 kg / t, and the physicochemical parameter indexes of the heating agent meet: the combustion time is ≥150 s, the extreme temperature is ≥1550℃, and the heat value is ≥1900 cal / g.

[0071] The baking of the heat-insulating cap in step 2 and the heating and heat-insulating treatment of the poured riser in step 3 mainly aim to improve the heat-insulating efficiency, so that the riser ratio is lower and the utilization rate of the ingot is higher.

[0072] In one possible design, the heating agent composition is: Al: 16.68%, Al2O3: 35.34%, SiO2: 21.74%, Fe2O3: 13.63%, CaO: 9.56%, C: 3.05%.

[0073] Because the ingot contains molten steel during casting, most of the molten steel enters the ingot after solidification, leaving only a small amount of molten steel (5% to 6%) in the ingot. As a result, the ingot has an extremely low riser ratio and can be considered a riser-free ingot.

[0074] On the other hand, a specific embodiment of the present invention also provides an auxiliary tool 15 for the production of hollow forgings without risers, which is used for the production of the hollow forgings without risers, including a steel ingot mold 5, a heat insulation cap 4 and a base plate 6, wherein the steel ingot mold is placed on the base plate and the heat insulation cap is placed on the steel ingot mold;

[0075] The upper part of the steel ingot mold has a circumferentially machined annular groove 10. The distance between the center line of the groove and the inner wall of the steel ingot mold is 1 / 4 to 1 / 2 of the steel ingot mold wall thickness, and the depth of the groove is ≤1 / 4 of the steel ingot mold height.

[0076] The heat-insulating cap includes an outer steel shell 8 and an inner lining 7. The chassis includes a chassis body and a sprue socket. The sprue socket is lined with refractory material 12. The parts of the chassis body and the sprue socket that come into contact with molten steel are lined with steel plates 11.

[0077] In summary, this invention, taking into account the need for punching in hollow forgings, modifies the solidification heat transfer mechanism of the steel ingot, causing excessive component segregation areas and inclusions in riserless steel ingots to accumulate in the core, which are then removed during subsequent forging. This ensures that the composition and metallurgical quality of the forging meet the corresponding technical requirements of the product. Furthermore, through the synergistic effect of circumferential grooving of the mold wall, control of the thermal conductivity of the refractory material in the insulation cap, and pre- and post-pouring insulation measures, the riser feeding efficiency is effectively improved, thereby significantly reducing the riser ratio of the steel ingot from the original 15%-16% to 2.45%-6%, significantly improving steel ingot utilization and reducing production costs.

[0078] The following describes the steel ingot auxiliary tooling and production method for hollow forgings according to the present invention, with reference to specific embodiments.

[0079] Example 1

[0080] This embodiment provides an auxiliary tool and production method for a 200t riserless steel ingot.

[0081] Steel ingots without risers, such as Figure 2 As shown, it is an optimized design based on a 229t ingot; the original ingot had a riser ratio of 15.41%, while the optimized ingot has a riser ratio of 2.45%.

[0082] The structural parameters of the steel ingot auxiliary fixtures are as follows:

[0083] Ingot mold: as shown in Figure 3 Fig. 1, the wall thickness of the ingot mold is L1 = 450 mm, the height of the ingot mold is H1 = 3942 mm, the upper inner diameter of the ingot mold is D1 = 2993 mm, the lower inner diameter of the ingot mold is D2 = 2638 mm, and the height-diameter ratio of the ingot mold is 2*H1 / (D1+D2) = 1.4; an annular groove is processed in the circumferential direction of the upper mold wall of the ingot mold, the center line of the groove is 150 mm away from the inner wall of the ingot mold, the depth of the groove is L3 = 800 mm, and the width of the groove is 50 mm.

[0084] Heat preservation cap: as shown in Figure 4 Fig. 2, the wall thickness of the steel shell 8 of the heat preservation cap 4 is L4 = 10 mm, and the heat preservation cap is welded by a steel plate; the lower inner diameter of the heat preservation cap is D3 = 2790 mm; the ratio of D3 to the upper inner diameter D1 of the ingot mold is 0.932, the lower outer diameter of the steel shell is D1+2*L1 = 3893 mm, and the height of the heat preservation cap is H3 = 1000 mm.

[0085] The main components of the refractory material used in the heat preservation cap 4 are Al2O3 = 54%, SiO2 = 42%, and MgO = 4%, and the porosity is 77%; the refractoriness of the refractory material is detected to be ≥1700°C, and the thermal conductivity of the refractory material is detected to meet the following requirements, as shown in Table 1:

[0086] Table 1 Thermal conductivity of the lining refractory material of the heat preservation cap in Example 1

[0087] Temperature / °C 200 600 800 1000 1100 1200 Thermal conductivity, W / m-k 0.102 0.133 0.179 0.201 0.226 0.243

[0088] Bottom disc: the high-alumina refractory material 12 is laid in the three holes of the bottom disc 6, and the thickness is 50 mm; the main component is Al2O3, and the content is 83%; the steel plate 11 is laid on the outer surface and the side surface of the high-alumina refractory material 12, and the thickness of the steel plate is 10 mm.

[0089] The steel ingot smelting and pouring process includes the following steps:

[0090] Step 1, steel ladle smelting: two ladles of molten steel are sequentially subjected to electric furnace smelting and secondary refining, and the slag-making material used in the secondary refining process of the two ladles of molten steel is 1800 kg of lime, 750 kg of aluminum oxide powder, and 300 kg of fluorite;

[0091] The composition of the secondary refining slag after control refining meets the requirements of Table 2.

[0092] Table 2 Composition of the secondary refining slag after control refining in Example 1

[0093] Steel ladle pass CaO CaF2 Al2O3 MgO + SiO2 First pass 54.38 9.73 26.81 9.08 Second pass 51.92 8.81 26.55 12.72

[0094] Step 2, preparation of steel ingot auxiliary tool, as shown in Figure 1 , Figure 5As shown: in the assembly of the tongs baking insulation cap, baking temperature is 412 ℃, placed in the vacuum chamber before the refractory temperature is 341 ℃;

[0095] The baked full refractory type insulation cap 4, new type ingot mold 5 and insulation type bottom disc 6 are assembled into the steel ingot auxiliary tool 15, and then placed in the vacuum chamber 14, covered with the vacuum cover 13, and vacuum casting is carried out.

[0096] Step 3: After the steel ingot casting is completed, the heating agent 9 is added into the riser: the amount of the heating agent 9 added is 400 kg (2 kg / t), which is used for the riser molten steel temperature rise, and the physical and chemical parameter index detection results of the heating agent 9 are as follows: the combustion time is 171 s, the extreme temperature is 1585 ℃, and the heat value is 2430 cal / g.

[0097] Step 4: The steel ingot is subsequently forged, shaped, heat treated and machined for flaw detection, the product ingot body 2 flaw detection and performance index can meet the technical condition requirements; the contents of the easily segregated elements C, Mn and Mo on the side of the product water gap 3 and the riser 1 are detected, as shown in Table 3, which meet the technical condition requirements.

[0098] The inner surface of the water / riser is the position closest to the core, the composition of the inner surface of the riser is the position with the highest element content, and the element content of the inner surface of the riser does not exceed the technical condition requirements, that is, it can be determined that the composition segregation (core area) exceeding the standard has been completely removed.

[0099] Table 3: Contents of easily segregated elements C, Mn and Mo on the side of the product water gap and the riser of Example 1

[0100]

[0101] Example 2

[0102] The present embodiment provides a 165t riserless steel ingot auxiliary tool and a production method.

[0103] The present riserless steel ingot is designed by optimizing the original 189t ingot type; the original ingot type riser proportion is 17.0%, and the optimized riserless steel ingot riser proportion is 4.9%.

[0104] The structural parameters of the steel ingot auxiliary tool are as follows:

[0105] The steel ingot mold: the wall thickness of the steel ingot mold is L1=400mm, the height of the steel ingot mold is H1=3864mm, the upper inner diameter of the steel ingot mold is D1=2740mm, the lower inner diameter of the steel ingot mold is D2=2412mm, and the height-diameter ratio of the steel ingot mold is 2*H1 / (D1+D2)=1.5; the upper part of the steel ingot mold is circumferentially processed with a ring-shaped slot, the center line of the slot is L2=150mm away from the inner wall of the steel ingot mold, the depth of the slot is L3=700mm, and the width of the slot is 50mm.

[0106] The heat preservation cap: the wall thickness L4 of the steel shell 8 of the heat preservation cap 4 is 10 mm, which is welded by steel plate; the lower inner diameter D3 of the heat preservation cap is 2603 mm; the ratio of D3 to the upper inner diameter D1 of the ingot mold is 0.95; the lower outer diameter of the steel shell is D1+2*L1=3540 mm; and the height H3 of the heat preservation cap is 1000 mm.

[0107] The main components of the refractory material used in the heat preservation cap 4 are Al2O3=53.5%, SiO2=41.8%, and MgO=4.7%, and the porosity is 76%; the refractoriness of the refractory material is detected to be greater than or equal to 1700 DEG C; and the thermal conductivity of the refractory material meets the following requirements, as shown in Table 4:

[0108] Table 4 Thermal conductivity of the lining refractory material of the heat preservation cap in Example 2

[0109] Temperature / °C 200 600 800 1000 1100 1200 Thermal conductivity, W / m-k 0.108 0.129 0.187 0.199 0.211 0.247

[0110] The base plate: the high-alumina refractory material 12 is laid in the three-well water gap 3 of the base plate 6, and the thickness is 50 mm; the main component is Al2O3, and the content is 82.5%; and the steel plate 11 is laid on the outer surface and the side surface of the high-alumina refractory material 12 in a random shape, and the thickness of the steel plate is 10 mm.

[0111] The steel ingot smelting and pouring process includes the following steps:

[0112] Step 1, steel ladle smelting: one ladle of molten steel is sequentially subjected to electric furnace smelting and secondary refining, and the slag-making material used in the refining process of the one ladle of molten steel is 2300 kg of lime, 850 kg of alumina powder and 350 kg of fluorite;

[0113] The composition of the refining slag after the control refining meets the requirements of Table 5.

[0114] Table 5 Composition of the refining slag after the control refining in Example 2

[0115] Steel ladle pass CaO CaF2 Al2O3 MgO + SiO2 Single pass 53.78 9.83 27.24 9.15

[0116] Step 2, preparation of the steel ingot auxiliary tool: the heat preservation cap lining refractory material is baked in the assembly tongs, the baking temperature is 462 DEG C, and the temperature of the refractory material before being placed in the vacuum chamber is 358 DEG C;

[0117] The fully refractory heat preservation cap 4, the new type of steel ingot mold 5 and the heat preservation type base plate 6 after being baked are assembled into the steel ingot auxiliary tool 15, and then are placed in the vacuum chamber 14, and the vacuum cover 13 is covered, so that the vacuum pouring is performed.

[0118] Step 3, after the steel ingot pouring is completed, the heating agent is added into the riser: the amount of the heating agent 9 added is 330 kg (2 kg / t), which is used for the temperature rise of the molten steel in the riser; and the physical and chemical parameter index detection results of the heating agent 9 are as follows: the combustion time is 171 s, the extreme temperature is 1585 DEG C, and the heat value is 2430 cal / g.

[0119] Step 4, the steel ingot is subsequently forged, heat treated and machined for inspection, the product inspection and performance indicators can meet the requirements of the technical conditions; the contents of the easily segregated elements C, Mn and Mo on the water gap and the riser side of the product are detected, as shown in Table 6, which meets the requirements of the technical conditions.

[0120] The inner surface of the water / riser is the position closest to the core, the composition of the inner surface of the riser is the position with the highest element content, and the element content of the inner surface of the riser does not exceed the requirements of the technical conditions, that is, it can be determined that the segregation of the composition (core area) exceeding the standard has been completely removed.

[0121] Table 6 Contents of easily segregated elements C, Mn and Mo on the water gap and the riser side of the product of Example 2

[0122]

[0123] Example 3

[0124] The present embodiment provides a 252t riser-free steel ingot auxiliary tool and a production method.

[0125] The present riser-free steel ingot is designed by optimizing the original 289t ingot; the original ingot riser ratio is 16.88%, and the optimized riser-free steel ingot riser ratio is 4.5%.

[0126] The structural parameters of the steel ingot auxiliary tool are as follows:

[0127] The steel ingot mold has a wall thickness of L1 = 500mm, a height H1 = 4167mm, an upper inner diameter D1 = 3285mm, a lower inner diameter D2 = 2889mm, and a height-to-diameter ratio of 2*H1 / (D1+D2) = 1.35; the upper part of the steel ingot mold is circumferentially processed with a ring-shaped slot, the center line of the slot is L2 = 170mm away from the inner wall of the steel ingot mold, the depth of the slot is L3 = 800mm, and the width of the slot is 50mm.

[0128] The heat preservation cap has a steel shell 8 with a wall thickness L4 = 10mm, which is welded from a steel plate; the lower inner diameter D3 of the heat preservation cap is 3170mm; the ratio of D3 to the upper inner diameter D1 of the steel ingot mold is 0.965, the lower outer diameter of the steel shell is D1+2*L1 = 4285mm, and the height H3 of the heat preservation cap is 1000mm.

[0129] The main components of the refractory material used in the heat preservation cap 4 are Al2O3 = 51%, SiO2 = 44%, and MgO = 5%, and the porosity is 77%; the refractoriness of the refractory material is detected to be ≥1700℃, and the thermal conductivity of the refractory material is detected to meet the following requirements, as shown in Table 7:

[0130] Table 7 Thermal conductivity of the lining refractory material of the heat preservation cap in Example 3

[0131] Temperature / °C 200 600 800 1000 1100 1200 Thermal conductivity, W / m-k 0.100 0.125 0.187 0.194 0.206 0.232

[0132] The base plate: the high-aluminum refractory 12 with a thickness of 50 mm is laid in the 3-waisted inner part of the water gap 3, and the main component is Al2O3 with a content of 83%; the steel plate 11 is laid along the shape on the outer surface and side surface of the high-aluminum refractory 12, and the thickness of the steel plate is 10 mm.

[0133] The ingot smelting and pouring process comprises the following steps:

[0134] Step 1, steel ladle smelting: two ladles of molten steel successively undergo electric furnace smelting and secondary refining, and the slag-making material used in the refining process of the two ladles of molten steel is 2300 kg of lime, 850 kg of aluminum oxide powder and 350 kg of fluorite;

[0135] The composition of the refining slag after control refining meets the requirements of Table 8.

[0136] Table 8 Composition of refining slag after control refining of Example 3

[0137] Steel ladle pass CaO CaF2 Al2O3 MgO + SiO2 First pass 53.22 8.89 25.97 11.92 Second pass 52.35 8.69 26.48 12.48

[0138] Step 2, ingot auxiliary preparation: the refractory material in the assembly tongs is baked to a temperature of 451 ℃, and the temperature of the refractory material in front of the vacuum chamber is 323 ℃;

[0139] The baked full-refractory heat-insulating cap 4, the new ingot mold 5 and the heat-insulating base plate 6 are assembled into the ingot auxiliary 15, and then placed in the vacuum chamber 14, and the vacuum cover 13 is covered, and vacuum pouring is performed.

[0140] Step 3, after the ingot pouring is completed, the heating agent is added into the riser: the amount of the heating agent 9 added is 504 kg (2 kg / t), which is used for heating the molten steel in the riser, and the detection results of the physical and chemical parameter indexes of the heating agent 9 are as follows: combustion time 171 s, extreme temperature 1585 ℃, and heat value 2430 cal / g.

[0141] Step 4, the ingot is subsequently forged, heat treated and machined for flaw detection, and the product flaw detection and performance indexes can meet the requirements of the technical conditions; the contents of the easily-segregated elements C, Mn and Mo on the side of the water gap and the riser of the product are detected, as shown in Table 9, and meet the requirements of the technical conditions.

[0142] Among them, the inner surface of the water / riser is the position closest to the center, the composition of the inner surface of the riser is the position with the highest element content, and the element content of the inner surface of the riser does not exceed the requirements of the technical conditions, that is, it can be determined that the segregation of the composition (the center area) that exceeds the standard has been completely removed.

[0143] Table 9 Contents of easily-segregated elements C, Mn and Mo on the side of the water gap and the riser of the product of Example 3

[0144]

[0145]

[0146] Comparative Example 1

[0147] The present comparative example provides a 200t riserless ingot auxiliary tool and a production method.

[0148] The main dimensions of the ingot auxiliary tool and the molten steel smelting and pouring process are the same as those of Example 1, except that the upper half of the ingot mold wall is not treated by slotting.

[0149] The 200t riserless ingot produced in Comparative Example 1 has a deep primary shrinkage hole, and the ingot body on the riser side is removed by forging by 140mm, and the ingot utilization rate is reduced by 3.55% compared with Example 1.

[0150] The contents of the easily segregated elements C, Mn and Mo on the riser side are shown in Table 10.

[0151] Table 10 Contents of easily segregated elements C, Mn and Mo on the riser side of the product of Comparative Example 1

[0152]

[0153] Comparative Example 2

[0154] The present comparative example provides a 200t riserless ingot auxiliary tool and a production method.

[0155] The main dimensions of the ingot auxiliary tool and the molten steel smelting and pouring process are the same as those of Example 1, except that the refractory material of the heat preservation cap is not baked when the ingot auxiliary tool is prepared in step 2.

[0156] The 200t riserless ingot produced in Comparative Example 2 has a deep primary shrinkage hole, and the ingot body on the riser side is removed by forging by 80mm, and the ingot utilization rate is reduced by 2.03% compared with Example 1.

[0157] The contents of the easily segregated elements C, Mn and Mo on the riser side are shown in Table 11.

[0158] Table 11 Contents of easily segregated elements C, Mn and Mo on the riser side of the product of Comparative Example 2

[0159]

[0160] Comparative Example 3

[0161] The present comparative example provides a 200t riserless ingot auxiliary tool and a production method.

[0162] The main dimensions of the ingot auxiliary tool and the molten steel smelting and pouring process are the same as those of Example 1, except that the composition of the refining slag in step 1 is not controlled according to the requirements of the present application, as shown in Table 12.

[0163] Table 12 Refining slag composition after refining of Comparative Example 3

[0164] Steel ladle pass CaO CaF2 Al2O3 MgO + SiO2 First pass 58.53 11.32 19.13 11.02 Second pass 57.36 12.65 20.79 9.2

[0165] The hollow forge piece produced in Comparative Example 3 has a flaw detection problem. The flaw detection result shows that at the water gap end, there are multiple Φ1.6-Φ3 mm intensive defects at a circumferential anticlockwise 1120-4300 mm, axial 0-220 mm, and depth 100-270 mm.

[0166] The contents of the easily segregated elements C, Mn, and Mo at the riser side of Comparative Example 3 are shown in Table 10.

[0167] Table 13 Contents of easily segregated elements C, Mn, and Mo at the product riser side of Comparative Example 3

[0168]

[0169] The 200 t, 165 t, and 252 t riserless steel ingot auxiliary and production method provided in Examples 1-3 are respectively designed by optimizing the 229 t, 189 t, and 289 t ingot type, and the riser proportion is reduced from the original 15%-16% to 2.45%-4.9%, which greatly improves the steel ingot utilization rate, indicating that the synergistic effect of the auxiliary design and various heat preservation measures of the present application effectively reduces the riser proportion and production cost of the steel ingot; and the contents of the easily segregated elements C, Mn, and Mo at the outer surface of the water gap and riser side, outer T / 4, T / 2, inner T / 4, and inner surface region after punching the core region are basically the same, indicating that the steel ingot without core for hollow forge piece preparation has no segregation, which can ensure that the composition and metallurgical quality of the forge piece can meet the requirements of the corresponding technical conditions;

[0170] As can be seen from Comparative Example 1 and Example 1, the upper half of the ingot mold wall is not subjected to slotting treatment, and the feeding efficiency is reduced, the steel ingot utilization rate is reduced by 3.55% compared with Example 1, and the content of the easily segregated elements at the inner surface of the riser is also slightly higher than that at the outer surface, outer T / 4, T / 2, and inner T / 4 position, which is not conducive to segregation control.

[0171] As can be seen from Comparative Example 2 and Example 1, the refractory material of the heat preservation cap is not baked before pouring, and the heat preservation efficiency is reduced, and the steel ingot utilization rate is reduced by 2.03% compared with Example 1.

[0172] As can be seen from Comparative Example 3 and Example 1, the refining slag composition is not controlled during the molten steel smelting process, which will increase the inclusion content in the molten steel, resulting in intensive defects at the water gap end of the forge piece.

[0173] In summary, the application combines the characteristics of the hollow forging needing punching, changes the solidification heat transfer mode of the ingot, makes the composition segregation area and the inclusions of the ingot exceeding the standard gather in the core, removes them in the subsequent forging, and makes the composition and the metallurgical quality of the forging meet the requirements of the corresponding technical conditions; through the cooperation of the circumferential slotting of the mold wall, the control of the thermal conductivity coefficient of the heat preservation cap refractory material, and the heat preservation measures before and after pouring, the efficiency of the feeding of the riser is effectively improved, thereby greatly reducing the riser proportion of the ingot, reducing the riser proportion of the ingot from 15%-16% to 2.45%-6%, significantly improving the utilization rate of the ingot, and reducing the production cost.

[0174] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for producing riserless steel ingots for hollow forgings, characterized in that, Includes the following steps: Step 1, Steelmaking: Control the composition of refining slag: CaO: 50~60%, CaF2: 5~10%, Al2O3: 25~30%, MgO+SiO2: 10~15%; Step 2, Preparation of steel ingot auxiliary tools and vacuum casting before casting: The steel ingot auxiliary tools include a steel ingot mold, a heat insulation cap and a base plate. The upper part of the mold wall of the steel ingot mold is circumferentially machined with an annular groove. The opening of the annular groove faces upward and is located on the top wall of the steel ingot mold. The base plate includes a base plate body and a sprue socket. The sprue socket is lined with refractory material. Step 3: Heat preservation treatment of riser after pouring; Step 4: Solidify the molten steel to obtain a riserless steel ingot for hollow forgings.

2. The production method according to claim 1, characterized in that, The wall thickness of the steel ingot mold is 400~600mm, and the height-to-diameter ratio is 1.3~1.

5.

3. The production method according to claim 2, characterized in that, The upper part of the ingot mold has a circumferentially grooved opening. The center line of the groove is 1 / 4 to 1 / 2 of the ingot mold wall thickness away from the inner wall of the ingot mold. The depth of the groove is ≤1 / 4 of the height of the ingot mold, and the width of the groove is 50 to 100 mm.

4. The production method according to claim 1, characterized in that, The heat-insulating cap includes an outer steel shell and an inner lining. The outer steel shell is welded from steel plates with a thickness of 5-10mm.

5. The production method according to claim 4, characterized in that, The lining material is a refractory material, and the main components of the refractory material, by mass percentage, are: Al2O3: 40~55%, SiO2: 35~52%, MgO: 3~10%; porosity 65~80%; refractoriness ≥1700℃.

6. The production method according to claim 1, characterized in that, The ratio of the lower inner diameter of the heat-insulating cap to the upper inner wall diameter of the steel ingot mold is 0.93~1.

0.

7. The production method according to claim 6, characterized in that, The height of the insulation cap is the sum of the riser height and the reserved height, which is 500~800mm.

8. The production method according to claim 1, characterized in that, The thickness of the refractory material is 50~70mm, and the mass fraction of Al2O3 in the refractory material is 70%~90%; the base body and the part of the nozzle that comes into contact with the molten steel are covered with steel plates that conform to the shape, and the thickness of the steel plates is 10mm.

9. The production method according to claim 1, characterized in that, The preparation of auxiliary tools before casting includes baking the refractory material lining the heat insulation cap at a temperature ≥350℃; assembling the baked heat insulation cap, steel ingot mold, and base into a steel ingot mold auxiliary tool, placing it in a vacuum chamber, and ensuring that the temperature of the refractory material lining the heat insulation cap is ≥300℃ before placing it in the vacuum chamber.

10. An auxiliary tool for producing riserless steel ingots for hollow forgings, used in the production method of riserless steel ingots for hollow forgings as described in any one of claims 1 to 9, characterized in that, It includes a steel ingot mold, a heat insulation cap, and a base plate, wherein the steel ingot mold is placed on the base plate and the heat insulation cap is placed on the steel ingot mold; The upper part of the ingot mold has a circumferentially machined annular groove. The opening of the annular groove is opened on the top wall of the ingot mold. The distance between the center line of the groove and the inner wall of the ingot mold is 1 / 4 to 1 / 2 of the thickness of the ingot mold wall. The depth of the groove is ≤1 / 4 of the height of the ingot mold. The heat-insulating cap includes an outer steel shell and an inner lining. The chassis includes a chassis body and a sprue socket. The sprue socket is lined with refractory material, and the parts of the chassis body and the sprue socket that come into contact with molten steel are lined with steel plates in a conformal manner.

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