A production method for heating large-size titanium billets using a steel rolling step heating furnace

Abstract

The present invention provides a production method for heating large-size titanium billets using a steel rolling step heating furnace. The present invention utilizes the existing steel rolling step heating furnace equipment and process conditions, considers the heating characteristics of titanium billets, combines the advantages of the step heating process with the soaking heating process, and realizes efficient heating production of large-size titanium billets of Φ600 and above; realizes batch rolling, and the hourly output reaches 40-60% of the steel output, meeting the quality requirements of subsequent production of special-size titanium materials, and the titanium rod yield rate is ≥94%. Moreover, the present invention utilizes the existing steel rolling step heating furnace equipment and process conditions, does not require additional equipment investment, can batch and efficiently heat and produce large-size titanium billets of Φ600 and above, and has extremely high economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of alloys, and in particular relates to a production method for heating large-size titanium billets by using a steel rolling step heating furnace. Background Art

[0002] The heating temperature of titanium billet is about 950℃, which is much lower than the heating temperature of steel billet, which is about 1230℃. If the titanium billet is heated by a walking beam heating furnace, the temperature will be too high or the heating will be uneven. If the heating temperature is too high, it will enter the β phase area, and the defects such as coarse structure and severe surface oxidation will be caused. The thermal conductivity of pure Ti is 16~18Wm at 100~1000℃. -1 k -1 , Ti alloy thermal conductivity 7~15Wm -1 k -1 , the thermal conductivity of steel is 30~50Wm -1 k -1 If large-sized titanium billets of Φ600 and above are not fully preheated and the heating speed when entering the furnace is the same as that of the steel billet, it is very easy to cause cracking in the core of the titanium billet and deformation, bending and jamming of the billet, resulting in major furnace shutdown and production accidents.

[0003] Existing titanium billet heating generally adopts induction heating and box-type resistance furnace heating. In induction heating, the current is induced on the surface of the billet, and the surface temperature rises rapidly, which is easy to cause local burning, and oxygen diffuses quite deeply in the metal; secondly, it is not easy to heat evenly, especially the radial temperature difference is large, which is not suitable for heating specifications above Φ200. The disadvantage of box-type resistance furnace heating is high power consumption and low heating efficiency.

[0004] At present, domestic titanium material processing enterprises basically use resistance furnaces for heating production. This technology can only heat small-sized billets and small unit weight titanium billets, and cannot achieve continuous production of large-sized titanium billets.

[0005] Existing reports use a method of using a steel rolling step heating furnace to heat 100-300 mm thick titanium billets, but the operation is complicated. It requires that a considerable number of steel billets be arranged in the middle of the titanium billet to absorb heat during the heating process of the titanium billet based on the steel rolling heating furnace. At the same time, the spacing of the billets needs to be calculated to prevent the titanium billet from being heated too quickly and at too high a temperature. The operation is cumbersome and is not suitable for large-scale production of titanium billets.

[0006] Existing reports use a continuous heating furnace to heat titanium billets with a maximum thickness of 500 mm. The furnace entry temperature is required to be 470°C, and the insulation is required to be more than 2.5 hours. This cannot be achieved in a steel rolling step heating furnace. The minimum furnace entry temperature of a steel rolling heating furnace is above 550°C, and insulation at the same temperature cannot be achieved. Summary of the invention

[0007] The purpose of the present invention is to provide a production method for heating large-size titanium billets using a steel rolling walking heating furnace, and to use the existing steel rolling walking heating furnace to realize batch heating production of titanium billets with a diameter of Φ600 and above. By changing the conventional heating mode of the walking furnace, the titanium billets are heated after being loaded as a whole in the walking furnace, replacing the mode in which the raw materials are heated and loaded and unloaded one by one in the furnace in a rhythmic forward step-by-step manner. The step-by-step heating mode of the billets in the walking furnace is adopted, combined with the step-by-step overall heating mode in which the billets are fixed after being loaded into the soaking furnace, and the advantages of two heating furnaces with different characteristics are combined, so that low-temperature slow heating, high-temperature fast heating, and heating strictly according to the process curve can be fully achieved, thereby realizing batch and efficient production, ensuring stable product quality, and at the same time significantly reducing energy consumption and improving the yield rate.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A production method for heating large-size titanium billets using a steel rolling walking beam heating furnace comprises the following steps:

[0010] 1) Before the titanium billet is loaded into the furnace, the temperature of each section of the walking beam heating furnace is controlled, wherein the temperature of the preheating section is 550-650°C; the temperature of the first heating section is 650-750°C; the temperature of the second heating section is 750-800°C; the temperature of the soaking section is 800-850°C;

[0011] 2) Under the temperature conditions of each stage in step 1), the titanium billet is loaded into the furnace as a whole;

[0012] 3) Heating the titanium billet;

[0013] 4) The titanium billet is taken out of the furnace.

[0014] The titanium billet of the present invention is a pure titanium billet or a titanium alloy billet;

[0015] Both pure titanium billets and titanium alloy billets are suitable for production by the method provided by the present invention; the pure titanium billets are industrial pure titanium TA1, TA2, TA3, TA4; the titanium alloy is TC4;

[0016] In step 1), before the titanium billet is loaded into the furnace, it is particularly important to control the temperature of each section of the step heating furnace. At this time, the billet is a cold billet. If the loading temperature exceeds the temperature described in step 2), the thermal stress caused by the temperature difference between the inside and outside will exceed its strength, directly leading to tearing of the core.

[0017] In step 2), the titanium billet is loaded into the furnace as a whole: the titanium billet is loaded into the walking beam heating furnace at a stepping rhythm of ≥5min / piece, and the overall loading capacity reaches 70-80%. Since there is no burner in the preheating section of the walking beam heating furnace, the heating cannot be controlled, so the 1 / 2-2 / 3 position near the tail of the preheating section cannot be loaded with steel. If a burner is installed in the preheating section, the furnace can be 100% loaded.

[0018] Furthermore, when the titanium billet is pure titanium billet, step 2) is specifically as follows: loading from the furnace tail to the furnace head, and not loading the 1 / 2 to 2 / 3 stations near the furnace tail in the preheating section, that is, leaving 8 to 12 stations at the furnace tail empty, so that the overall furnace loading capacity reaches 70 to 80%; then directly proceed to step 3) heating. The purpose is to achieve that each section of the heating furnace can independently control the temperature according to the process. Loading according to this requirement can prevent the cold material from entering the furnace due to excessive heating speed, causing bending deformation, and excessive internal and external thermal stress of the billet, causing internal tearing of the billet to cause serious rolling defects. At the same time, the overall charging and overall heating plan can be realized, and the step-by-step heating mode can be switched to the overall heating mode of the equalizing furnace.

[0019] Furthermore, when the titanium billet is a titanium alloy billet, step 2) is specifically as follows: loading from the furnace tail to the furnace head, not loading 2 / 3 to 1 station near the furnace head soaking section, that is, leaving 8 to 12 stations at the furnace head empty, so that the overall furnace loading capacity reaches 70 to 80%; after the titanium billet is loaded into the furnace as a whole, the temperature of each section is kept warm for 90±15 minutes according to step 1). Since titanium alloy is more easily deformed, it is kept warm during the overall loading in order to further reduce the temperature difference between the inside and outside of the billet, and to prepare for the transformation of the brittle deformation temperature of the core of the billet into plastic deformation; after the insulation is completed, the titanium billet in the furnace is moved at a stepping rhythm of 5 minutes / piece to fill the furnace head with materials, leaving 1 / 2 to 2 / 3 stations near the furnace tail in the preheating section, that is, leaving 8 to 12 stations at the furnace tail empty, so that the overall furnace loading capacity reaches 70 to 80%, and each section reaches the process setting temperature, creating conditions for subsequent efficient heating; and then directly proceed to step 3) heating.

[0020] In step 3), the heating of the titanium billet includes slow heating and rapid heating, specifically:

[0021] 3-1) Slow heating: The heating stage, heating stage 2 and soaking stage are heated to their respective target temperatures at a heating rate of 25-30℃ / h respectively; at this time, the heating rate needs to be controlled. If the heating rate is too fast, the billet will be heated unevenly, and the internal and external thermal stresses will be too large, resulting in direct deformation and bending of the billet or tearing of the core. At the same time, the heating rate in this temperature section is fast, and the energy consumption per ton of steel is large, which is neither economical nor environmentally friendly. The phase transition point of pure titanium is 850-900℃. In this temperature range, the billet absorbs a lot of heat and the temperature is difficult to heat up quickly; the phase transition point of TC4 titanium alloy is 950-1000℃. In this temperature range, it is difficult for the billet to heat up quickly to the specified temperature.

[0022] 3-2) Rapid heating: heating at a rate of 65-85°C / h.

[0023] In step 3-1), the target temperature of the first heating stage is 850±10°C, the target temperature of the second heating stage is 900±10°C, and the target temperature of the soaking stage is 950±10°C; after each stage is heated to the target temperature, it is kept warm until the first heating stage, the second heating stage and the soaking stage are all heated to their respective target temperatures;

[0024] In step 3-1), during the heating process, the furnace is stepped on the spot every 7 to 8 minutes to prevent the blank from being severely bent, which would make it impossible for the blank to move in the furnace and be taken out of the furnace.

[0025] Preferably, in step 3-1), after the first heating stage, the second heating stage and the soaking stage are heated to their respective target temperatures, the temperature is maintained; the temperature maintenance time is 60±15 min.

[0026] Further, in step 3-1), if the pure titanium billet is produced, after the first heating stage, the second heating stage and the soaking stage are heated to their respective target temperatures, step 3-2) can be performed for rapid heating; or, after the first heating stage, the second heating stage and the soaking stage are heated to the target temperature, they are kept warm for 60±15 minutes and then step 3-2) is performed for rapid heating;

[0027] In step 3-1), if the titanium alloy billet is produced, after the first heating stage, the second heating stage and the soaking stage are heated to their respective target temperatures, they are kept warm for 60±15 minutes and then the rapid heating is performed in step 3-2);

[0028] In step 3-2), when pure titanium billet is produced, the heating stage, the heating stage 2 and the soaking stage are heated to 1000±20°C at a heating rate of 65-85°C / h; each stage is heated to 1000±20°C and then kept warm. After the heating stage 1, the heating stage 2 and the soaking stage are all heated to 1000±20°C, they are kept warm for 60±15min.

[0029] In step 3-2), when a titanium alloy billet is produced, the first heating stage, the second heating stage and the soaking stage are all heated to 1125±15°C at a heating rate of 65-85°C / h; each stage is heated to 1125±15°C and then kept warm. After the first heating stage, the second heating stage and the soaking stage are all heated to 1125±15°C, they are kept warm for 60±15 minutes.

[0030] In step 3-2), during the heating process, step on the spot once every 7-8 minutes.

[0031] In step 4), rolling is performed at a discharging rhythm of 5 to 6 minutes per piece.

[0032] In the present invention, the flow ratio of air to high-coke mixed coal gas in the walking beam heating furnace is controlled between 1.8 and 2.2:1, and the high-coke mixed coal gas is appropriately increased to ensure that the titanium billet is heated in a slightly reducing atmosphere.

[0033] The invention provides a production method for heating large-size titanium billets by using a steel rolling step heating furnace, which can produce large-size titanium billets with a diameter of Φ600-800mm. The output of titanium billets reaches 40-60t / h; the surface quality is excellent, the overall oxidation and burning loss is less than 1.2%, and the head and tail loss is 1-1.5%. Hydraulic shears can be directly used online to replace fire cutting (fire cutting produces a lot of smoke), the production efficiency is high and environmentally friendly, and the titanium rod yield rate is ≥94%.

[0034] Compared with the prior art, the present invention utilizes the existing steel rolling step heating furnace equipment and process conditions, considers the heating characteristics of titanium billets, combines the advantages of the step heating process with the equalizing heating process, and realizes efficient heating production of large-sized titanium billets of Φ600 and above; realizes batch rolling, and the hourly output is 40% of the steel output, reaching 40-60t / h, and the product quality is stable, meeting the quality requirements of subsequent production of special-sized titanium materials. Compared with the conventional step heating furnace heating, which heats a maximum of 5-7 titanium bars at a time, the heating efficiency of the present invention is increased by more than 6 times. The present invention utilizes the existing steel rolling step heating furnace equipment and process conditions, does not require additional equipment investment, and can heat and produce large-sized titanium billets of Φ600 and above in batches with high efficiency, with extremely high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the process curve of conventional Φ600 steel billet step heating;

[0036] Figure 2 It is a heating curve diagram of a heating section of the step-by-step heating process of the pure titanium billet of the present invention;

[0037] Figure 3 This is a process curve diagram of step-by-step heating of TC4 titanium alloy according to the present invention;

[0038] Figure 4 This is a production site map;

[0039] Figure 5 The Φ600 pure titanium TA1 billet of Example 1 is taken out of the furnace;

[0040] Figure 6 The Φ600 pure titanium of Example 1 is rolled into a 150×150 product;

[0041] Figure 7 This is a photo of the flame cutting scene of Comparative Example 2, with heavy smoke;

[0042] Figure 8 Comparative Example 2 shows cracks during rolling. DETAILED DESCRIPTION

[0043] Example 1

[0044] A production method for heating large-size Φ600 pure titanium TA1 titanium billet using a steel rolling step heating furnace comprises the following steps:

[0045] 1) Before loading TA1 titanium billet into the furnace, control the temperature of each section of the heating furnace: preheating section temperature 550~650℃; heating section temperature 650~750℃; heating section temperature 750~800℃; soaking section temperature 800~850℃;

[0046] 2) Under the temperature conditions of each section in step 1), charge at a stepping rhythm of 5 to 6 minutes per section, from the furnace tail to the furnace head, with the preheating section close to the furnace tail, leaving 8 to 12 stations in the preheating section empty, and filling 70 to 80% of the stations in the furnace;

[0047] 3-1) The heating stage, the heating stage 2 and the soaking stage are all heated at a heating rate of 25-30°C / h, and the heating process is performed once every 8 minutes; the heating stage heating target temperature is 850°C, the heating stage 2 target temperature is 900°C, and the soaking stage target temperature is 950°C; after each stage is heated to the target temperature, keep the temperature, and wait until the heating stage, the heating stage 2 and the soaking stage are heated to their respective target temperatures; directly proceed to step 3-2);

[0048] 3-2) The first heating stage, the second heating stage and the soaking stage are all heated to 1000°C at a heating rate of 75°C / h; and kept warm for 60 minutes;

[0049] 4) Rolling at a rate of ≥5min / exit furnace.

[0050] The flow ratio of air to high-coke mixed gas in the heating furnace is controlled at 2.1:1, and the gas volume is appropriately increased to ensure that the titanium billet is heated in a slightly reducing atmosphere.

[0051] According to the production of Example 1, the average output of titanium billets reaches 50t / h; the surface quality is excellent, the overall oxidation loss is less than 1.2%, the head and tail loss is 1-1.5%, and hydraulic shears can be directly used online to replace fire cutting for cutting, and the titanium rod yield reaches 95.6%.

[0052] Example 2

[0053] A production method for heating a large-size Φ700 TC4 titanium alloy billet using a steel rolling walking beam heating furnace comprises the following steps:

[0054] 1) Before the titanium billet is loaded into the furnace, the temperature of each section of the walking beam heating furnace is controlled, including the preheating section temperature of 550-650℃; the heating section temperature of 650-750℃; the heating section temperature of 750-800℃; the soaking section temperature of 800-850℃;

[0055] 2) Load the materials at a stepping rhythm of 5min / piece, from the furnace tail to the furnace head. Do not load the materials in half of the stations near the furnace head in the preheating section, and leave 8 to 12 stations at the furnace head empty, so that the overall loading capacity reaches 70 to 80%; After the titanium billet is loaded into the furnace as a whole, keep the temperature of each section for 95min according to step 1); then move the titanium billet in the furnace at a stepping rhythm of 5min / piece, so that the furnace head is fully loaded, and leave 1 / 2 of the stations near the furnace tail in the preheating section, that is, leave 8 to 12 stations at the furnace tail empty, so that the overall loading capacity reaches 70 to 80%;

[0056] 3-1) The heating stage, the heating stage and the soaking stage are all heated at a rate of 25°C / h, and the heating process is performed at a constant speed every 8 minutes; the heating stage target temperature is 850°C, the heating stage target temperature is 900°C, and the soaking stage target temperature is 950°C; each stage is heated to the target temperature and then kept warm, and the heating stage, the heating stage and the soaking stage are heated to their respective target temperatures and kept warm for 65 minutes;

[0057] 3-2) Then, the heating stage 1, the heating stage 2 and the soaking stage are heated to 1125±15°C at a heating rate of 75°C / h; the temperature is kept for 60 minutes; during the heating process, the temperature is stepped on the spot once every 8 minutes.

[0058] 4) Rolling at a rate of ≥5min / exit furnace.

[0059] The flow ratio of air to high-coke mixed gas in the step heating furnace is controlled at 2:1, and the gas volume is appropriately increased to ensure that the titanium billet is heated in a slightly reducing atmosphere.

[0060] According to the production of Example 2, the average output of titanium billets reaches 40t / h; the surface quality is excellent, the overall oxidation loss is less than 1.2%, the head and tail loss is 1-1.5%, and hydraulic shears can be directly used online to replace fire cutting for cutting, and the titanium rod yield reaches 94.3%.

[0061] Example 3

[0062] A production method for heating Φ800 pure titanium TA2 titanium billet by using a steel rolling step heating furnace comprises the following steps:

[0063] 1) Before loading TA1 titanium billet into the furnace, control the temperature of each section of the heating furnace: preheating section temperature 550~650℃; heating section temperature 650~750℃; heating section temperature 750~800℃; soaking section temperature 800~850℃;

[0064] 2) Under the temperature conditions of each section in step 1), charge at a stepping rhythm of 6 minutes / piece, from the furnace tail to the furnace head, with the preheating section close to the furnace tail, leaving 8 to 12 stations in the preheating section empty, and filling 70 to 80% of the stations in the furnace;

[0065] 3-1) The heating stage, the heating stage and the soaking stage are all heated at a rate of 30°C / h, and the heating process is stepped on the spot once every 8 minutes; the heating stage heating target temperature is 850°C, the heating stage 2 target temperature is 900°C, and the soaking stage target temperature is 950°C; each stage is heated to the target temperature and then kept warm. After the heating stage, the heating stage 2 and the soaking stage are heated to their respective target temperatures, keep warm for 60 minutes;

[0066] 3-2) The heating stage 1, heating stage 2 and soaking stage are heated to 1000°C at a heating rate of 75°C / h; keep warm for 65 minutes;

[0067] 4) Rolling at a rate of ≥5min / exit furnace.

[0068] The flow ratio of air to high-coke mixed gas in the heating furnace is controlled at 2.2:1.

[0069] According to Example 3, the average output of titanium billets reaches 45 t / h, the surface quality is excellent, the overall oxidation loss is less than 1.2%, the head and tail loss is 1-1.5%, hydraulic shears can be directly used online to replace fire cutting for cutting, the shearing process is normal, and the titanium rod yield reaches 96.1%.

[0070] Comparative Example 1

[0071] A production method for heating Φ450 pure titanium TA1 billet by using a steel rolling step heating furnace, specifically comprising:

[0072] The alloy steel was heated according to the conventional step-by-step heating process, and the temperature control of each section was shown in Table 1;

[0073] Table 1 Process parameters of each stage of heating production in comparative example 1

[0074]

[0075] According to the production method of comparative example 1, serious bending in the furnace occurred, resulting in a steel jam accident.

[0076] Comparative Example 2

[0077] A production method for heating Φ700 titanium alloy TC4 billet using a steel rolling step heating furnace, specifically: heating by step, loading 3 billets at a time, and the heating process parameters are shown in Table 2;

[0078] Table 2 Heating process parameters of comparative example 2

[0079]

[0080] In the production process of Comparative Example 3, the billet did not crack during the heating process, but could not be cut by hydraulic shears. Flame cutting was used, which produced a lot of smoke and was accompanied by a strong explosion sound. The entire factory was affected, and the on-site operation did not meet the environmental protection requirements. In addition, during the online rolling process of 300×300, some transverse cracks occurred, and the yield rate of titanium rods was low, only 59.3%.

Claims

1. A production method for heating large-size titanium billets using a steel rolling walking beam heating furnace, characterized in that: The production method comprises the following steps: 1) Before the titanium billet is loaded into the furnace, the temperature of each section of the walking beam heating furnace is controlled, including the preheating section temperature of 550~650℃; the heating section temperature of 650~750℃; the heating section temperature of 750~800℃; the soaking section temperature of 800~850℃; 2) Under the temperature conditions of each section in step 1), the titanium billet is loaded into the furnace as a whole; 3) Heating the titanium billet; 4) Titanium billet is taken out of the furnace; The titanium billet is a pure titanium billet or a titanium alloy billet; Step 3) includes: 3-1) Slow heating: The heating stage 1, heating stage 2 and soaking stage are heated to their respective target temperatures at a heating rate of 25-30℃ / h; 3-2) Rapid heating: heating at a rate of 65-85℃ / h; In step 3-1), the target temperature of the first heating stage is 850±10℃, the target temperature of the second heating stage is 900±10℃, and the target temperature of the soaking stage is 950±10℃; after each stage is heated to the target temperature, it is kept warm until the first heating stage, the second heating stage and the soaking stage are all heated to their respective target temperatures; In step 3-2), when the pure titanium billet is produced, the heating stage, the heating stage 2 and the soaking stage are all heated to 1000±20°C at a heating rate of 65-85°C / h; each stage is heated to 1000±20°C and then kept warm. After the heating stage 1, the heating stage 2 and the soaking stage are all heated to 1000±20°C, they are kept warm for 60±15min; In step 3-2), when a titanium alloy billet is produced, the heating stage, the heating stage 2 and the soaking stage are all heated to 1125±15°C at a heating rate of 65-85°C / h; each stage is heated to 1125±15°C and then kept warm. After the heating stage, the heating stage 2 and the soaking stage are all heated to 1125±15°C, they are kept warm for 60±15 minutes; The production method is used to produce large-size titanium billets with a diameter of Φ600-800mm.

2. The production method according to claim 1, characterized in that In step 2), the titanium billets are loaded into the step heating furnace at a stepping rhythm of ≥5 min / piece, and the overall loading capacity reaches 70-80%.

3. The production method according to claim 1 or 2, characterized in that: When the titanium billet is a titanium alloy billet, the overall charging of the titanium billet into the furnace in step 2) is as follows: charging from the furnace tail to the furnace head, leaving 2 / 3-1 stations near the furnace head soaking section unloaded, so that the overall charging capacity reaches 70-80%; after the titanium billet is overall charged into the furnace, each section is kept warm for 90±15 min according to step 1), and after the insulation is completed, the titanium billet in the furnace is moved at a stepping rhythm of 5 min / station, so that the furnace head is fully loaded, and 1 / 2-2 / 3 stations near the furnace tail in the preheating section are left empty, so that the overall charging capacity reaches 70-80%.

4. The production method according to claim 1, characterized in that In step 3-1), when a titanium alloy billet is produced, after the first heating stage, the second heating stage and the soaking stage are heated to the target temperature, the temperature is maintained for 60±15 minutes.

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