Auxiliary tool and production method of riser-free steel ingot for hollow forge piece

Abstract

The invention relates to an auxiliary tool and a production method of a riser-free steel ingot for a hollow forge piece, belongs to the technical field of smelting industry, and solves the problems of low steel ingot utilization rate, high riser proportion and high element segregation degree in the production process of the hollow forge piece in the prior art. The invention relates to a production method of a riser-free steel ingot for a hollow forge piece. The production method comprises the following steps: step 1, smelting molten steel: controlling the components of refining slag: 50-60% of CaO, 5-10% of CaF2, 25-30% of Al2O3 and 10-15% of MgO + SiO2; 2, a steel ingot auxiliary tool is prepared before pouring and is subjected to vacuum pouring, wherein the steel ingot auxiliary tool comprises a steel ingot mold, a heat preservation cap and a base plate, and an annular open groove is machined in the circumferential direction of the mold wall of the upper portion of the steel ingot mold; 3, after pouring, dead head heating and heat preservation treatment is conducted; and 4, solidifying and forming the molten steel to obtain the riser-free steel ingot for the hollow forge piece. The utilization rate and metallurgical quality of the steel ingot for the hollow forge piece are improved.

Description

Technical Field

[0001] The invention relates to the technical field of smelting industry, in particular to an auxiliary tool and a production method of a riser-free steel ingot for a hollow forging. Background Art

[0002] With the rapid development of my country's nuclear power, petrochemical and coal liquefaction projects, the number of large hollow forgings required is growing, and the contradiction between supply and demand is becoming increasingly tense. Pressure vessels, evaporators and pressurizers in nuclear power projects all contain hollow forgings. Common hollow forgings include the upper and lower cylinders in the evaporator, the inlet and outlet pipes, the core cylinder and the vessel flange-pipe section cylinder in the pressure vessel, and the upper, middle and lower cylinders in the pressurizer. The most commonly used hydrogenation reactor in the petrochemical industry also needs to be welded with hollow forgings-hydrogenation cylinder sections for its main structure.

[0003] Hollow forgings are mainly produced with solid steel ingots as raw materials, and the production process is basically: molten steel smelting-ingot casting-solid steel ingot blanking-upsetting-punching-expanding. The characteristics of its production process are that only high-quality steel ingot body materials are used for forgings, and the risers and nozzle materials will eventually need to be discarded; at the same time, the middle area of ​​the steel ingot is punched out by the punching method; the steel ingots used to produce the above-mentioned hollow forgings are usually 150-500t ingots, and in order to ensure the metallurgical quality of the forgings, the proportion of the risers of the steel ingots is usually in the range of 15-20%, resulting in low ingot utilization and high production costs of hollow forgings. Countries such as Japan and France also use hollow steel ingot manufacturing technology to produce hollow forgings, but they need to be cast in an atmospheric environment, which makes it difficult to control the H, O, and N gas content and the quality of the forgings is difficult to ensure. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide an auxiliary tool and a production method for a riserless steel ingot for hollow forgings, so as to solve at least one of the problems of low ingot utilization, high riser ratio, high degree of element segregation, etc. in the existing hollow forging production process.

[0005] On the one hand, an embodiment of the present invention provides a method for producing a riser-free steel ingot for a hollow forging, comprising the following steps:

[0006] Step 1, molten steel smelting: control the composition of refined slag: CaO: 50-60%, CaF 2 : 5-10%, Al 2 O 3 :25-30%,MgO+SiO 2 : 10-15%;

[0007] Step 2, preparation of steel ingot auxiliary tools and vacuum casting before pouring: the steel ingot auxiliary tools include 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 groove, and the opening direction of the annular groove faces upward;

[0008] Step 3: Heat and insulation treatment of the riser after pouring;

[0009] Step 4: The molten steel is solidified and formed to obtain a riser-free steel ingot for hollow forgings.

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

[0011] Furthermore, the upper mold wall of the ingot mold is circumferentially processed with an annular groove, 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 ingot mold wall thickness, the depth of the groove is ≤1 / 4 of the ingot mold height, and the groove width is 50 to 100 mm.

[0012] It should be noted that the thermal insulation cap includes an outer steel shell and an inner lining, and the outer steel shell is welded by steel plates with a thickness of 5 to 10 mm.

[0013] Specifically, the lining material is a refractory material, and the main components of the refractory material are calculated by mass percentage: Al 2 O 3 :40~55%、SiO 2 : 35-52%, MgO: 3-10%; porosity 65-80%; refractoriness ≥1700℃.

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

[0015] Exemplarily, the height of the insulation cap is the sum of the riser height and the reserved height, and the reserved height is 500-800 mm.

[0016] Furthermore, the chassis includes a chassis body and a nozzle cavity, and a refractory material is laid in the nozzle cavity, and the thickness of the refractory material is 50-70 mm. 2 O 3 The mass fraction is 70%-90%; the chassis body and the nozzle socket are in contact with the molten steel and are paved with steel plates in accordance with the shape, and the thickness of the steel plates is 10mm.

[0017] It is worth noting that the preparation of auxiliary tools before pouring includes baking the refractory material lining of the insulation cap, and the baking temperature is ≥350°C; the baked insulation cap, ingot mold and chassis are assembled into ingot mold auxiliary tools, which are placed in a vacuum chamber, and the temperature of the refractory material lining of the insulation cap is ≥300°C before being placed in the vacuum chamber.

[0018] On the other hand, an embodiment of the present invention further provides an auxiliary tool for a riserless steel ingot for hollow forgings, which is used for producing the riserless steel ingot for hollow forgings, and comprises a steel ingot mold, a heat preservation cap and a chassis, wherein the steel ingot mold is placed on the chassis, and the heat preservation cap is placed on the steel ingot mold;

[0019] The upper mold wall of the steel ingot mold is circumferentially processed with an annular groove, 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 thickness of the steel ingot mold wall, and the depth of the groove is ≤ 1 / 4 of the height of the steel ingot mold;

[0020] The insulation cap comprises an outer steel shell and an inner lining, the chassis comprises a chassis body and a nozzle socket, refractory materials are laid in the nozzle socket, and steel plates are laid in the chassis body and the nozzle socket in contact with the molten steel.

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

[0022] 1. The present invention combines the characteristics of hollow forgings that need to be punched, and by changing the solidification heat transfer form of the steel ingot, the excessive component segregation area and inclusions of the riser-free steel ingot are gathered in the core, and are removed during subsequent forging. The forging composition and metallurgical quality can meet the corresponding technical requirements of the product;

[0023] The present invention adopts a full refractory lined insulation cap and performs heating and insulation treatment on the riser after pouring, so that the heat of the molten steel in the riser is mainly transferred to the air through the ingot mold, and the refractory material is laid on the bottom plate to greatly reduce the heat of the molten steel from the bottom of the ingot, thereby achieving solidification of the ingot along the diameter direction and promoting the segregation and inclusions to gather toward the center.

[0024] 2. The present invention makes grooves along the circumferential direction of the upper mold wall of the steel ingot mold to make the heat transfer path longer, greatly improve the heat insulation performance of the mold wall, and prolong the time that the molten steel in the riser remains in liquid state, thereby making the shrinkage compensation efficiency higher and improving the utilization rate of the steel ingot; the groove ratio is strictly controlled to ensure the above-mentioned heat transfer characteristics while ensuring that the strength meets the use requirements.

[0025] 3. The present invention further improves the insulation efficiency by baking the insulation cap before pouring and performing heating and insulation treatment on the riser after pouring, thereby making the riser ratio lower and the utilization rate of the steel ingot higher.

[0026] 4. The present invention effectively improves the shrinkage compensation efficiency of the riser through the synergistic effect of circumferential grooves in the mold wall, the use of insulation cap refractory materials with low thermal conductivity, and insulation measures before and after pouring, thereby greatly reducing the riser ratio of the steel ingot. The riser ratio of the steel ingot is reduced from the original 15%-16% to 2.45%-6%, which significantly improves the utilization rate of the steel ingot and reduces the production cost.

[0027] 5. The present invention ensures that the molten steel reaches the required purity by accurately controlling the composition of the refined slag during the molten steel smelting process, controlling O≤30ppm, S≤20ppm, and Al in the inclusions 2 O 3 ≤5%, effectively reducing the degree of segregation.

[0028] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0030] Figure 1 It is an assembly diagram of an auxiliary tool for a riser-free steel ingot for a hollow forging of the present invention;

[0031] Figure 2 Schematic diagram of a riser-free steel ingot for a hollow forging of the present invention;

[0032] Figure 3 It is a schematic diagram of a steel ingot mold for a hollow forging without a riser;

[0033] Figure 4 This is a schematic diagram of a full refractory thermal insulation cap of the present invention;

[0034] Figure 5 It is a schematic diagram of casting a riser-free steel ingot for a hollow forging of the present invention.

[0035] Reference numerals:

[0036] 1- riser; 2- ingot body; 3- nozzle; 4- all-refractory insulation cap; 5- ingot mold; 6- insulation chassis; 7- refractory lining; 8- steel shell; 9- heating agent; 10- slot; 11- steel plate; 12- high-alumina refractory material; 13- vacuum cover; 14- vacuum chamber; 15- ingot accessories. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0038] On the one hand, a specific embodiment of the present invention discloses a method for producing a riser-free steel ingot for hollow forgings, comprising the following steps:

[0039] Step 1, molten steel smelting: control the composition of refined slag: CaO: 50-60%, CaF 2 : 5-10%, Al 2 O 3 :25-30%,MgO+SiO 2 : 10-15%;

[0040] Step 2, preparation of steel ingot auxiliary tools and vacuum casting before pouring: the steel ingot auxiliary tools include 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 groove, and the opening direction of the annular groove faces upward;

[0041] Step 3: Heat and insulation treatment of the riser after pouring;

[0042] Step 4: The molten steel is solidified and formed to obtain 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 refining outside the furnace; the refining is one of LF refining or RH refining, and the slag-making materials are lime, alumina powder and fluorite;

[0044] After refining, the composition of the refined slag is required to meet the following requirements: CaO: 50-60%, CaF 2 : 5-10%, Al 2 O 3 :25-30%,MgO+SiO 2 : 10-15%.

[0045] In order to ensure that the molten steel reaches the required purity, the composition of the refined slag is clearly required, and the removal of impurities such as sulfur and oxygen in the molten steel is indirectly controlled and reflected through the composition of the refined slag; when the composition of the refined slag meets the above requirements, O≤30ppm, S≤20ppm in the molten steel, and Al in the inclusions can be controlled 2 O 3 ≤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 refined slag are pre-set; during the refining process, the composition of the refined slag is analyzed by sampling, and the amount of slag-making materials added is adjusted according to the analysis results to ensure that the composition of the slag meets the preset requirements; at the end of the refining process, the composition of the slag is tested again to confirm whether it meets the preset requirements, thereby indirectly verifying whether the purity of the molten steel has reached the expected target.

[0047] Furthermore, the steel ingot auxiliary tools used in the production of the riserless steel ingot for hollow forgings include a steel ingot mold 5, a heat preservation cap 4 and a chassis 6; the steel ingot mold 5 is placed on the chassis 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 400-600 mm, and the aspect ratio is 1.3-1.5.

[0049] Furthermore, the upper mold wall of the steel ingot mold is circumferentially processed with an 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 thickness of the steel ingot mold wall, the depth of the groove is ≤ 1 / 4 of the height of the steel ingot mold, and the width of the groove is 50 to 100 mm. 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-ingot mold height, mm;

[0054] D1-inner diameter of ingot mold, mm;

[0055] D2-inner diameter of ingot mold, mm;

[0056] L1-ingot mold wall thickness, mm;

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

[0058] L3-groove depth, mm.

[0059] In the present invention, since a full refractory lined insulation cap 4 is adopted and the riser is subjected to heating and insulation treatment after pouring, the heat of the molten steel in the riser is mainly transferred to the air through the ingot mold. The original heat transfer path directly from one surface to another is blocked by the circumferential grooves on the upper mold wall of the ingot mold. The heat transfer path of the hollow wall after the grooves is longer. The thermal insulation performance is improved by increasing the thermal resistance, reducing the heat flux density and limiting the heat flow channel. The molten steel in the riser remains in liquid for a longer time, thereby making the shrinkage compensation efficiency higher. When the groove ratio is too large, the shrinkage compensation efficiency of the molten steel in the riser is not significantly improved, and the supporting strength of the ingot mold is reduced, so it is necessary to control the appropriate groove size.

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

[0061] It should be noted that the lining material is a refractory material, and the main components of the refractory material are calculated by mass percentage: Al 2 O 3 :40~55%、SiO 2: 35-52%, MgO: 3-10%; porosity 65-80%; refractoriness ≥1700℃; all parts in contact with molten steel are refractory materials. By controlling the composition and porosity of refractory materials, the thermal conductivity coefficient can meet certain requirements, thereby improving the shrinkage feeding effect of molten steel at the riser.

[0062] The requirements for the thermal conductivity of the refractory material to be met are as follows: at 200°C, the thermal conductivity is ≤0.11W / m·k; at 600°C, the thermal conductivity is ≤0.14W / m·k; at 800°C, the thermal conductivity is ≤0.19W / m·k; at 1000°C, the thermal conductivity is ≤0.21W / m·k; at 1100°C, the thermal conductivity is ≤0.23W / m·k; at 1200°C, the thermal conductivity is ≤0.25W / m·k.

[0063] Preferably, the outer shape of the heat preservation cap is a truncated cone with an upper diameter smaller than a lower diameter, and the ratio of the lower inner diameter of the heat preservation cap to the upper inner wall diameter of the ingot mold is 0.93-1.0, preferably 0.93-0.98. ， Ensure that no transverse cracks will occur at the root of the riser when the steel ingot solidifies; the height of the insulation cap is the sum of the riser height and the reserved height, and the reserved height is 500-800mm, which is the reserved space 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] Furthermore, the chassis is a heat-insulating chassis 6, which includes a chassis body and a nozzle cavity, and a refractory material 12 is laid in the nozzle cavity, and the thickness of the refractory material is 50-70 mm. 2 O 3 The quality fraction is 70%-90%.

[0066] Laying refractory materials on the chassis greatly reduces the heat dissipation of molten steel from the bottom of the ingot, realizes the solidification of the ingot along the diameter direction, and promotes the gathering of segregation and inclusions towards the center.

[0067] It is worth noting that the chassis body and the nozzle socket are in contact with the molten steel and are paved with a steel plate 11, the thickness of which is 10 mm. The steel plate is laid on the chassis to prevent the flowing molten steel from scouring the refractory material in the chassis at the initial stage of pouring, thereby generating foreign inclusions and causing the product to fail the flaw detection.

[0068] Furthermore, the preparation of auxiliary tools before pouring described in step 2 also includes baking the refractory material lining of the insulation cap, and the baking temperature is ≥350°C; the baked insulation cap, ingot mold and chassis are assembled into an ingot mold auxiliary tool, which is placed in the vacuum chamber 14, and the temperature of the refractory material lining of the insulation cap before placing in the vacuum chamber is ≥300°C.

[0069] The refractory material lining of the insulation cap is baked using assembly tongs.

[0070] Furthermore, the post-pouring riser heating and insulation treatment in step 3 is to add a heat-generating agent 9 into the riser after the pouring of the steel ingot is completed, with an addition amount of 2 kg / t, and the physical and chemical parameter indicators of the heat-generating agent meet the following requirements: burning time ≥ 150 s, extreme temperature ≥ 1550°C, and calorific value ≥ 1900 cal / g.

[0071] The main purpose of baking the insulation cap in step 2 and heating and heat-insulating the riser after pouring in step 3 is to improve the insulation efficiency, thereby reducing the riser ratio and increasing the utilization rate of the steel ingot.

[0072] In one possible design, the heat-generating agent composition is: Al: 16.68%, Al 2 O 3 : 35.34%, SiO 2 : 21.74%,Fe 2 O 3 : 13.63%, CaO: 9.56%, C: 3.05%.

[0073] When the steel ingot is poured, there is molten steel in the insulation cap. After solidification, most of the molten steel enters the steel ingot. A small amount of molten steel accounts for 5% to 6% of the remaining molten steel in the insulation cap. The riser ratio of the resulting steel ingot is extremely low, and it can be considered as a riser-free steel ingot.

[0074] On the other hand, a specific embodiment of the present invention further provides an auxiliary tool 15 for a hollow forging without a riser steel ingot, which is used for producing the hollow forging without a riser steel ingot, and comprises a steel ingot mold 5, a heat preservation cap 4 and a bottom plate 6, wherein the steel ingot mold is placed on the bottom plate, and the heat preservation cap is placed on the steel ingot mold;

[0075] The upper mold wall of the steel ingot mold is circumferentially processed with an 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 thickness of the steel ingot mold wall, and the depth of the groove is ≤ 1 / 4 of the height of the steel ingot mold;

[0076] The insulation cap includes an outer steel shell 8 and an inner lining 7, and the chassis includes a chassis body and a nozzle socket, in which a refractory material 12 is laid, and the chassis body and the nozzle socket in contact with the molten steel are laid with a steel plate 11 in accordance with the shape.

[0077] In summary, the present invention combines the characteristics of hollow forgings that need to be punched, and by changing the solidification heat transfer form of the steel ingot, the excessive component segregation area and inclusions of the riser-free ingot are gathered in the core, and are removed during subsequent forging, so that the forging composition and metallurgical quality can meet the corresponding technical conditions of the product; through the circumferential grooving of the mold wall, the control of the thermal conductivity of the refractory material of the insulation cap and the synergistic effect of the insulation measures before and after pouring, the shrinkage compensation efficiency of the riser is effectively improved, thereby greatly reducing the riser ratio of the steel ingot, and the riser ratio of the steel ingot is reduced from the original 15%-16% to 2.45%-6%, which significantly improves the utilization rate of the steel ingot and reduces the production cost.

[0078] The steel ingot auxiliary tool and production method for hollow forgings of the present invention are described below in conjunction with specific implementation methods.

[0079] Example 1

[0080] This embodiment provides a 200t riser-free steel ingot auxiliary tool and a production method.

[0081] There is no riser ingot, such as Figure 2 As shown, it is designed by optimizing the 229t ingot shape; the original ingot shape has a riser ratio of 15.41%, and the riser ratio of the optimized riser-free ingot is 2.45%.

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

[0083] Ingot mold: Figure 3 As shown, the wall thickness of the ingot mold is L1=450mm, the height of the ingot mold is H1=3942mm, the upper inner diameter of the ingot mold is D1=2993mm, the lower inner diameter of the ingot mold is D2=2638mm, and the height-to-diameter ratio of the ingot mold is 2*H1 / (D1+D2)=1.4; the upper mold wall of the ingot mold is circumferentially processed with an annular groove, the distance between the center line of the groove and the inner wall of the ingot mold is L2=150mm, the depth of the groove is L3=800mm, and the groove width is 50mm.

[0084] Thermal cap: Figure 4 As shown, the wall thickness L4 of the steel shell 8 of the insulation cap 4 is 10mm, and it is welded from steel plates; the lower inner diameter D3 of the insulation cap is 2790mm; the ratio of D3 to the upper inner diameter D1 of the steel ingot mold is 0.932, the lower outer diameter of the steel shell is D1+2*L1=3893mm, and the height H3 of the insulation cap is 1000mm.

[0085] The main component of the refractory material used in the insulation cap 4 is Al 2 O 3 =54%, SiO 2 =42%, MgO=4%, porosity 77%; the refractoriness of the refractory material is tested to be ≥1700°C, and the thermal conductivity of the refractory material meets the following requirements, as shown in Table 1:

[0086] Table 1 Thermal conductivity of refractory materials for lining of insulation cap in Example 1

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

[0088] Chassis: High-aluminum refractory material 12 is laid in the 3 nests of the chassis 6 water outlets, with a thickness of 50mm, and the main component is Al 2 O 3 , content 83%; a steel plate 11 is laid in the outer surface and side of the high-aluminum refractory 12, and the thickness of the steel plate is 10mm.

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

[0090] Step 1, smelting of molten steel in batches: 2 batches of molten steel are successively smelted in an electric furnace and refined outside the furnace. The slag-making materials used in the refining process of the 2 batches of molten steel are 1800kg lime, 750kg alumina powder and 300kg fluorite;

[0091] The composition of the refined slag after refining is controlled to meet the requirements of Table 2.

[0092] Table 2 Composition of refined slag after refining in Example 1

[0093] Ladle CaO <![CDATA[CaF 2 ]]> <![CDATA[Al 2 THE 3 ]]> <![CDATA[MgO+SiO 2 ]]> First Pack 54.38 9.73 26.81 9.08 Second Pack 51.92 8.81 26.55 12.72

[0094] Step 2: Prepare the steel ingot auxiliary tools, such as Figure 1 , Figure 5 As shown: the refractory material in the insulation cap is baked in the assembly clamp, the baking temperature is 412℃, and the refractory material temperature is 341℃ before being placed in the vacuum chamber;

[0095] The baked all-refractory heat-insulating cap 4, the new steel ingot mold 5 and the heat-insulating bottom plate 6 are assembled into a steel ingot auxiliary tool 15, and then placed in a vacuum chamber 14, covered with a vacuum cover 13, and vacuum casting is performed.

[0096] Step 3, after the ingot pouring is completed, a heat-generating agent is added into the riser: the amount of heat-generating agent 9 added is 400 kg (2 kg / t), which is used to heat the molten steel in the riser. The physical and chemical parameter index test results of the heat-generating agent 9 are: burning time 171 s, extreme temperature 1585 ° C, and calorific value 2430 cal / g.

[0097] Step 4, the steel ingot is subsequently subjected to forging, heat treatment and machining for flaw detection. The flaw detection and performance indicators of the product ingot body 2 can meet the requirements of the technical conditions. The contents of the easily segregated elements C, Mn and Mo on the sides of the product nozzle 3 and the riser 1 are detected, as shown in Table 3, which meet the requirements of the technical conditions.

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

[0099] Table 3 Contents of easily segregated elements C, Mn and Mo on the nozzle and riser sides of the product of Example 1

[0100]

[0101] Example 2

[0102] This embodiment provides a 165t riser-free steel ingot auxiliary tool and a production method.

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

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

[0105] Ingot mold: The wall thickness of the ingot mold is L1=400mm, the height of the ingot mold is H1=3864mm, the upper inner diameter of the ingot mold is D1=2740mm, the lower inner diameter of the ingot mold is D2=2412mm, and the height-to-diameter ratio of the ingot mold is 2*H1 / (D1+D2)=1.5; the upper mold wall of the ingot mold is circumferentially processed with an annular groove, the distance between the center line of the groove and the inner wall of the ingot mold is L2=150mm, the depth of the groove is L3=700mm, and the groove width is 50mm.

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

[0107] The main component of the refractory material used in the insulation cap 4 is Al 2 O 3 =53.5%, SiO 2 =41.8%, MgO=4.7%, porosity 76%; the refractoriness of the refractory material is tested to be ≥1700°C, and the thermal conductivity of the refractory material meets the following requirements, as shown in Table 4:

[0108] Table 4 Thermal conductivity of refractory materials for lining of insulation cap in Example 2

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

[0110] Chassis: High-aluminum refractory material 12 is laid in the 3 nests of the chassis 6 water outlets, with a thickness of 50mm, and the main component is Al 2O 3 , content 82.5%; a steel plate 11 is laid on the outer surface and side of the high-aluminum refractory 12, and the thickness of the steel plate is 10mm.

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

[0112] Step 1, smelting of molten steel in batches: 1 batch of molten steel is successively smelted in an electric furnace and refined outside the furnace, and the slag-making materials used in the refining process of 1 batch of molten steel are 2300kg lime, 850kg alumina powder and 350kg fluorite;

[0113] The composition of the refined slag after refining is controlled to meet the requirements of Table 5.

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

[0115] Ladle CaO <![CDATA[CaF 2 ]]> <![CDATA[Al 2 THE 3 ]]> <![CDATA[MgO+SiO 2 ]]> Single Pack 53.78 9.83 27.24 9.15

[0116] Step 2, steel ingot auxiliary tool preparation: bake the refractory material in the insulation cap in the assembly clamp, the baking temperature is 462°C, and the refractory material temperature is 358°C before being placed in the vacuum chamber;

[0117] The baked all-refractory heat-insulating cap 4, the new steel ingot mold 5 and the heat-insulating bottom plate 6 are assembled into a steel ingot auxiliary tool 15, and then placed in a vacuum chamber 14, covered with a vacuum cover 13, and vacuum casting is performed.

[0118] Step 3, after the ingot pouring is completed, a heat-generating agent is added into the riser: the amount of heat-generating agent 9 added is 330 kg (2 kg / t), which is used to heat the molten steel in the riser. The physical and chemical parameter index test results of the heat-generating agent 9 are: burning time 171 s, extreme temperature 1585 ° C, and calorific value 2430 cal / g.

[0119] Step 4: The steel ingot is subsequently subjected to forging, heat treatment and machining for flaw detection. The flaw detection and performance indicators of the product can meet the requirements of the technical conditions. The contents of the easily segregated elements C, Mn and Mo on the nozzle and riser sides of the product are detected, as shown in Table 6, which meet the requirements of the technical conditions.

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

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

[0122]

[0123] Example 3

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

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

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

[0127] Ingot mold: The wall thickness of the ingot mold is L1=500mm, the height of the ingot mold is H1=4167mm, the upper inner diameter of the ingot mold is D1=3285mm, the lower inner diameter of the ingot mold is D2=2889mm, and the height-to-diameter ratio of the ingot mold is 2*H1 / (D1+D2)=1.35; the upper mold wall of the ingot mold is circumferentially processed with an annular groove, the distance between the center line of the groove and the inner wall of the ingot mold is L2=170mm, the depth of the groove is L3=800mm, and the groove width is 50mm.

[0128] Insulation cap: The wall thickness L4 of the insulation cap 4 steel shell 8 is 10mm, and it is welded from steel plates; the lower inner diameter D3 of the insulation 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 insulation cap is 1000mm.

[0129] The main component of the refractory material used in the insulation cap 4 is Al 2 O 3 =51%, SiO 2 =44%, MgO=5%, porosity 77%; the refractoriness of the refractory material is tested to be ≥1700°C, and the thermal conductivity of the refractory material meets the following requirements, as shown in Table 7:

[0130] Table 7 Thermal conductivity of refractory materials for lining of insulation cap in Example 3

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

[0132] Chassis: High-aluminum refractory material 12 is laid in the 3 nests of the chassis 6 water outlets, with a thickness of 50mm, and the main component is Al 2 O 3 , content 83%; a steel plate 11 is laid in the outer surface and side of the high-aluminum refractory 12, and the thickness of the steel plate is 10mm.

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

[0134] Step 1, smelting of molten steel in batches: 2 batches of molten steel are successively smelted in an electric furnace and refined outside the furnace. The slag-making materials used in the refining process of the 2 batches of molten steel are 2300kg of lime, 850kg of alumina powder and 350kg of fluorite;

[0135] The composition of the refined slag after refining is controlled to meet the requirements of Table 8.

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

[0137] Ladle CaO <![CDATA[CaF 2 ]]> <![CDATA[Al 2 THE 3 ]]> <![CDATA[MgO+SiO 2 ]]> First Pack 53.22 8.89 25.97 11.92 Second Pack 52.35 8.69 26.48 12.48

[0138] Step 2, steel ingot auxiliary tool preparation: bake the refractory material in the insulation cap in the assembly clamp, the baking temperature is 451°C, and the refractory material temperature is 323°C before being placed in the vacuum chamber;

[0139] The baked all-refractory heat-insulating cap 4, the new steel ingot mold 5 and the heat-insulating bottom plate 6 are assembled into a steel ingot auxiliary tool 15, and then placed in a vacuum chamber 14, covered with a vacuum cover 13, and vacuum casting is performed.

[0140] Step 3, after the ingot pouring is completed, a heat-generating agent is added into the riser: the amount of heat-generating agent 9 added is 504 kg (2 kg / t), which is used to heat the molten steel in the riser. The physical and chemical parameter index test results of the heat-generating agent 9 are: burning time 171 s, extreme temperature 1585 ° C, and calorific value 2430 cal / g.

[0141] Step 4: The steel ingot is subsequently subjected to forging, heat treatment and machining for flaw detection. The flaw detection and performance indicators of the product can meet the requirements of the technical conditions. The contents of C, Mn and Mo, which are easily segregated elements, on the nozzle and riser sides of the product are tested, as shown in Table 9, which meet the requirements of the technical conditions.

[0142] The inner surface of the water / riser is the closest to the core, and the composition of the inner surface of the riser is the position with the highest element content. If the element content on the inner surface of the riser does not exceed the technical requirements, it can be determined that the excessive component segregation (core area) has been completely removed.

[0143] Table 9 Contents of easily segregated elements C, Mn and Mo on the nozzle and riser sides of the product of Example 3

[0144]

[0145]

[0146] Comparative Example 1

[0147] This comparative example provides a 200t riser-free steel ingot auxiliary tool and production method.

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

[0149] The 200t riser-free steel ingot produced in Comparative Example 1 has a deeper shrinkage cavity depth, and the ingot body on the riser side of the steel ingot is removed by forging by 140 mm. The utilization rate of the steel ingot is reduced by 3.55% compared with that in Example 1.

[0150] The contents of C, Mn and Mo, which are easily segregated elements 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] This comparative example provides a 200t riser-free steel ingot auxiliary tool and production method.

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

[0156] The 200t riser-free steel ingot produced in Comparative Example 2 has a deeper shrinkage cavity depth, and the ingot body on the riser side of the ingot is removed by forging by 80 mm. The utilization rate of the ingot is reduced by 2.03% compared with that in Example 1.

[0157] The contents of C, Mn and Mo, which are easily segregated elements 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] This comparative example provides a 200t riser-free steel ingot auxiliary tool and production method.

[0162] The main dimensions of the ingot auxiliary tool and the molten steel smelting and pouring process are the same as those in Example 1, except that the control of the refined slag composition in step 1 does not meet the requirements of the present invention, as shown in Table 12.

[0163] Table 12 Refined slag composition after refining in Comparative Example 3

[0164] Ladle CaO <![CDATA[CaF 2 ]]> <![CDATA[Al 2 THE 3 ]]> <![CDATA[MgO+SiO 2 ]]> First Pack 58.53 11.32 19.13 11.02 Second Pack 57.36 12.65 20.79 9.2

[0165] The hollow forgings produced in comparative example 3 have flaw detection problems. The flaw detection results show that: at the nozzle end, the circumference is 1120-4300mm counterclockwise, the axial direction is 0-220mm, and the depth is 100-270mm, and multiple Φ1.6-Φ3mm dense defects are found.

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

[0167] Table 13 Contents of easily segregated elements C, Mn and Mo on the riser side of the product of comparative example 3

[0168]

[0169] The auxiliary tools and production methods for 200t, 165t and 252t riser-free steel ingots provided in Examples 1 to 3 are respectively designed by optimizing the ingots of 229t, 189t and 289t. The riser ratio is reduced from the original 15% to 16% to 2.45% to 4.9%, and the utilization rate of the steel ingot is greatly improved, indicating that the synergistic effect of the auxiliary tool design and various insulation measures of the present invention effectively reduces the riser ratio and production cost of the steel ingot; and after the core area is punched out, the contents of C, Mn and Mo, which are easily segregated elements, are basically the same in the outer surface of the water inlet and the riser side, the outer T / 4, T / 2, inner T / 4 and the inner surface area, indicating that the steel ingot prepared for the hollow forging without the core has no segregation, which can ensure that the forging composition and metallurgical quality can meet the corresponding technical conditions of the product;

[0170] It can be seen from Comparative Example 1 and Example 1 that the upper half of the ingot mold wall is not grooved, the shrinkage compensation efficiency is reduced, the ingot utilization rate is reduced by 3.55% relative to Example 1, and the content of segregation-prone elements on the inner surface of the riser is slightly higher than that on the outer surface, outer T / 4, T / 2, and inner T / 4 positions, which is not conducive to segregation control.

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

[0172] It can be seen from Comparative Example 3 and Example 1 that if the composition of the refined slag is not controlled during the molten steel smelting process, the inclusion content in the molten steel will increase, causing dense defects to appear at the nozzle end of the forging.

[0173] In summary, the present invention combines the characteristics of hollow forgings that need to be punched, and by changing the solidification heat transfer form of the steel ingot, the excessive component segregation area and inclusions of the riser-free ingot are gathered in the core, and are removed during subsequent forging, so that the forging composition and metallurgical quality can meet the corresponding technical conditions of the product; through the circumferential grooving of the mold wall, the control of the thermal conductivity of the refractory material of the insulation cap and the synergistic effect of the insulation measures before and after pouring, the shrinkage compensation efficiency of the riser is effectively improved, thereby greatly reducing the riser ratio of the steel ingot, and the riser ratio of the steel ingot is reduced from the original 15%-16% to 2.45%-6%, which significantly improves the utilization rate of the steel ingot and reduces the production cost.

[0174] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for producing a riser-free steel ingot for hollow forgings, characterized in that: The steps include: Step 1, molten steel smelting: control the composition of refined 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 pouring: the steel ingot auxiliary tools include 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 groove, and the opening direction of the annular groove faces upward; Step 3: Heat and insulation treatment of the riser after pouring; Step 4: The molten steel is solidified and formed to obtain a riser-free 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 400-600 mm, and the height-to-diameter ratio is 1.3-1.

5.

3. The production method according to claim 2, characterized in that: The upper mold wall of the ingot mold is circumferentially processed with an annular groove, 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 ingot mold wall thickness, the groove depth is ≤1 / 4 of the ingot mold height, and the groove width is 50 to 100 mm.

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

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 are, by mass percentage, Al2O3: 40-55%, SiO2: 35-52%, MgO: 3-10%; the porosity is 65-80%; and the refractoriness is ≥1700°C.

6. The production method according to claim 1, characterized in that: The ratio of the lower inner diameter of the heat preservation 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, and the reserved height is 500-800 mm.

8. The production method according to claim 1, characterized in that: The chassis includes a chassis body and a nozzle socket, in which refractory material is laid, the thickness of the refractory material is 50-70mm, and the mass fraction of Al2O3 in the refractory material is 70%-90%; the chassis body and the nozzle socket are laid with steel plates in contact with the molten steel, 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 pouring includes baking the refractory material lining of the insulation cap, and the baking temperature is ≥350°C; assembling the baked insulation cap, ingot mold and chassis into an ingot mold auxiliary tool, placing it in a vacuum chamber, and the temperature of the refractory material lining of the insulation cap before placing it in the vacuum chamber is ≥300°C.

10. An auxiliary tool for a hollow forging without a riser steel ingot, characterized in that: Used for producing the riser-free steel ingot for hollow forgings as claimed in any one of claims 1 to 9, comprising a steel ingot mold, a heat preservation cap and a bottom plate, wherein the steel ingot mold is placed on the bottom plate, and the heat preservation cap is placed on the steel ingot mold; The upper mold wall of the steel ingot mold is circumferentially processed with an annular groove, 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 thickness of the steel ingot mold wall, and the depth of the groove is ≤ 1 / 4 of the height of the steel ingot mold; The insulation cap comprises an outer steel shell and an inner lining, the chassis comprises a chassis body and a nozzle socket, refractory materials are laid in the nozzle socket, and steel plates are laid in the chassis body and the nozzle socket in contact with the molten steel.

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