A rolling method for titanium billets smelted in an EB furnace

Abstract

The present application provides a rolling method of titanium billet smelted by EB furnace. The method firstly heats for a long time in low temperature zone of 850-880 DEG C, to ensure the uniformity of the temperature of the titanium billet; then heats for a short time in high temperature zone of 900-950 DEG C, to refine the grain of the titanium billet by phase transition while avoiding the surface oxide film of the titanium billet being too thick under high temperature, to affect the surface quality. Meanwhile, aiming at the characteristics of the titanium billet smelted by EB furnace, such as coarse grain, poor plastic deformation capacity and easy cracking at the edge of the billet, after the low temperature heating and high temperature heating are completed, the two-pass small reduction rolling and small deformation amount side pressing are adopted, which is not only beneficial to the control of the rough rolling shape, but also can refine the edge grain and improve the edge quality. Finally, through multi-pass rolling, the target thickness is reached. Through test, the edge and surface quality of the obtained titanium coil is good, the edge is not cracked and the meat defect is not dropped, and the surface defect rate is less than 7%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rolling production of titanium billets, and particularly relates to a production method of titanium billets smelted by an EB furnace. BACKGROUND

[0002] Titanium and titanium alloy have excellent characteristics such as high specific strength, good formability, high temperature resistance, corrosion resistance, etc., and thus are widely used in the fields of chemical industry, aerospace, ships, etc.

[0003] At present, the mainstream smelting process of titanium and titanium alloy is vacuum arc melting (VAR), but even using three times of vacuum arc melting cannot fundamentally ensure that the metallurgical defects of high and low density inclusions in titanium and titanium alloy are completely eliminated, and it is not easy to obtain high homogenization and pure ingot, and the ingot still needs to be subjected to subsequent rolling after being forged and opened.

[0004] With the improvement of the metallurgical quality requirements of titanium and titanium alloy, electron beam melting (EBM) technology has rapidly developed. The electron beam melting technology not only eliminates the process of forging and opening, but also solves the problem of high and low density inclusions in the smelting process of titanium and titanium alloy, and a large amount of returned material can be added, which is an important way to realize the purification of titanium and titanium alloy materials and low-cost manufacturing.

[0005] Compared with the titanium and titanium alloy ingots after the process of forging and opening by the VAR furnace, the ingots directly produced by the EB furnace have a more bulky original grain size, which can reach centimeter level, resulting in a large difference in surface oxidation behavior and rolling deformation behavior in the process of heating and hot rolling compared with the titanium billets smelted by the VAR furnace. However, the rolling process of the titanium billets smelted by the EB furnace is still the same as that of the titanium billets smelted by the VAR furnace, which results in poor edge and surface quality of the titanium coil rolled from the titanium billets smelted by the EB furnace, and reduces the yield while increasing the processing cost in the later stage. SUMMARY

[0006] Therefore, the present application aims to provide a rolling method of titanium billets smelted by an EB furnace. By using the method, the edge and surface quality of the titanium coil rolled from the titanium billets is good, and the edge has no cracking and meat loss defects, and the surface has less defects such as peeling, pits and indentation.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] The present application provides a rolling method of titanium billets smelted by an EB furnace, which comprises the following steps:

[0009] S1: heating the titanium billets in a low temperature zone of 850-880℃, then heating in a high temperature zone of 900-950℃, and then performing phosphorus removal treatment on the heated titanium billets;

[0010] The time of heating in the low-temperature zone is greater than the time of heating in the high-temperature zone.

[0011] S2: rolling the titanium blank after the phosphorus removal treatment by two passes while applying side pressure, and then rolling the obtained titanium blank to obtain a titanium coil;

[0012] The pass reduction rate of the two-pass rolling is 10-15%.

[0013] Preferably, the deformation amount of the side pressure is 2-5%.

[0014] Preferably, the titanium blank in step S1 is pretreated before heating in the low-temperature zone.

[0015] Preferably, the pretreatment comprises milling, chamfering and then water grinding the titanium blank.

[0016] Preferably, the surface roughness Ra of the titanium blank after the pretreatment is less than 5 microns.

[0017] Preferably, the time t1 / min of heating in the low-temperature zone is (0.8-1.2) x thickness of the titanium blank / mm.

[0018] Preferably, the time t2 / min of heating in the high-temperature zone is (0.2-0.4) x thickness of the titanium blank / mm.

[0019] Preferably, the phosphorus removal treatment is performed by using high-pressure water.

[0020] Preferably, the pressure of the high-pressure water is 22-30 MPa.

[0021] Preferably, the rolling after applying the side pressure is performed by multi-pass rolling.

[0022] Preferably, the multi-pass rolling is performed by 6-10 passes.

[0023] Preferably, the pass reduction rate of the multi-pass rolling is 15-35%.

[0024] Preferably, the thickness of the titanium coil is 4-10 mm.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] The present application provides a rolling method of titanium billet smelted by EB furnace, which firstly heats for a long time in low temperature zone to ensure the uniformity of the temperature of the titanium billet, and then heats for a short time in high temperature zone to refine the grain of the titanium billet and avoid the over-thickening of the surface oxidation film of the titanium billet in high temperature, which affects the surface quality. Meanwhile, aiming at the characteristics of the titanium billet smelted by EB furnace, such as the coarse grain, poor plastic deformation capacity and easy cracking of the edge of the titanium billet, after the low temperature heating and high temperature heating, the two-pass small reduction rolling and small deformation amount side pressing are carried out, which is not only beneficial to the control of the rough rolling shape, but also can refine the edge grain and improve the edge quality.

[0027] Through test, the edge and surface quality of the titanium coil rolled from the titanium billet is good, the edge has no cracking and meat loss defects, the surface has less peeling, pit and indentation defects, and the surface defect rate is less than 7%, and the calculation formula of the surface defect rate is: the length of the surface defects of the titanium coil / the total length of the titanium coil*100%. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0029] In view of the poor edge and surface quality of the titanium coil rolled from the titanium billet smelted by EB furnace in the prior art, the present application provides a rolling method of titanium billet smelted by EB furnace, which comprises the following steps:

[0030] S1: heating the titanium billet in 850-880℃ low temperature zone, then heating in 900-950℃ high temperature zone, and then performing dephosphorization treatment on the heated titanium billet;

[0031] The heating time in the low temperature zone is greater than the heating time in the high temperature zone.

[0032] S2: performing two-pass rolling on the dephosphorized titanium billet while applying side pressing, and then rolling the obtained titanium billet to obtain a titanium coil;

[0033] The pass reduction rate of the two-pass rolling is 10-15%.

[0034] According to the present application, the titanium blank is first heated in a low temperature zone of 850-880°C, and then heated in a high temperature zone of 900-950°C. In the present application, the titanium blank is preferably pretreated before being heated, and the pretreatment comprises milling, chamfering and water milling of the titanium blank. The manner of milling, chamfering and water milling is not particularly limited in the present application, and can be carried out according to the techniques well known to those skilled in the art. The present application requires that the titanium blank has a surface roughness Ra < 5 μm, or even Ra < 4 μm, after the above-mentioned pretreatment, so as to obtain a titanium blank with smooth and flat surface.

[0035] After the pretreatment is completed, the titanium blank with smooth and flat surface is subjected to low temperature zone heating treatment and high temperature zone heating treatment. In the present application, the time of low temperature zone heating is generally greater than that of high temperature zone heating. In the present application, the time t of the heating of the titanium blank in the zones is t = c x h, wherein t is the heating time, the unit is min, c is the heating time coefficient, and h is the thickness of the titanium blank, the unit is mm. In the present application, the heating time coefficient c1 of the titanium blank in the low temperature zone of 850-880°C is 0.8-1.2, and the heating time coefficient c2 of the titanium blank in the high temperature zone of 900-950°C is 0.2-0.4. That is, in some embodiments of the present application, the time t1 / min of the low temperature zone heating is (0.8-1.2) x the thickness of the titanium blank / mm, and the time t2 / min of the high temperature zone heating is (0.2-0.4) x the thickness of the titanium blank / mm. The present application can ensure the uniformity of the temperature of the titanium blank by long time heating in the low temperature zone, and can avoid the over-thickening of the oxidation film on the surface of the titanium blank at high temperature, which affects the surface quality, by short time heating in the high temperature zone.

[0036] After the high temperature zone heating treatment is completed, the titanium blank is oxidized at high temperature, and a dense phosphor film is formed on the surface of the titanium blank. If the phosphor film cannot be removed before rolling, it will be pressed into the surface of the titanium blank by the roller during rolling, which affects the surface quality. The residual phosphor film also accelerates the wear of the roller and reduces the service life of the roller. Therefore, the titanium blank after the high temperature zone heating is preferably subjected to phosphor removal treatment in the present application. In some embodiments of the present application, high pressure water is preferably used for the phosphor removal treatment, and the pressure of the high pressure water is 22-30 MPa, preferably 25-28 MPa.

[0037] The present application is aimed at the characteristics of the titanium blank smelted by EB furnace, such as coarse grain, poor plastic deformation ability and easy cracking at the edge during rolling. After the phosphor removal treatment is completed, the obtained titanium blank is subjected to two passes of small reduction rate rolling and small deformation amount side pressing, which is not only beneficial to the control of the rough rolling shape, but also can refine the edge grain and improve the edge quality. In the present application, the pass reduction rate of the two passes of rolling is preferably 10-15%, more preferably 12-13%. At the same time, the deformation amount of the side pressing is preferably 2-5%, more preferably 3-4%.

[0038] Then, according to the present application, the obtained titanium billet is rolled, and the rolling is multi-pass rolling until the target thickness is reached. In the rolling process, the pass reduction rate is preferably 15-35%, more preferably 20-30%. In some embodiments of the present application, the rolling is to a thickness of 4-10 mm of the final hot-rolled titanium coil.

[0039] It is tested that the titanium coil rolled from the titanium billet has good edge and surface quality, and the edge has no cracking and meat loss defects, and the surface has less peeling, pits and indentation defects, and the surface defect rate is less than 7%.

[0040] In order to further illustrate the present application, the following examples are used to illustrate the present application in detail. The experimental raw materials used in the following examples of the present application are all commercially available.

[0041] Example 1

[0042] The titanium billet used in this example is a TA1 pure titanium billet smelted by an EB furnace, with a thickness of 200 mm and a width of 1080 mm. First, the titanium billet is milled, chamfered and water ground to obtain a titanium billet with a surface roughness Ra of 3.6 μm; then the titanium billet is heated in zones, first at 880 °C for 240 min, and then at 950 °C for 40 min; then the titanium billet is high-pressure water dephosphorized, with a high-pressure water pressure of 30 MPa; then the titanium billet is rolled in two passes with small reduction, with pass reduction rates of 10% and 12% respectively, while small deformation amount side pressing is applied, with side pressing deformation amounts of 3% and 5% respectively; finally, the titanium billet is rolled in 8 passes, with pass reduction rates of 15-35%, and the thickness of the final hot-rolled titanium coil is 8.0 mm.

[0043] The titanium coil has good edge and surface quality, and the edge has no cracking and meat loss defects, and the surface has less peeling, pits and indentation defects, and the surface defect rate is 4.2%, and the calculation formula of the surface defect rate is: the length of the titanium coil surface defect / the total length of the titanium coil x 100%.

[0044] Comparative Example 1

[0045] The titanium billet used in this example is a TA1 pure titanium billet smelted by an EB furnace, with a thickness of 200 mm and a width of 1080 mm. First, the titanium billet is milled, chamfered and water ground to obtain a titanium billet with a surface roughness Ra of 3.6 μm; then the titanium billet is heated in zones, first at 880 °C for 240 min, and then at 950 °C for 40 min; then the titanium billet is high-pressure water dephosphorized, with a high-pressure water pressure of 30 MPa; then the titanium billet is rolled in two passes with small reduction, with pass reduction rates of 10% and 12% respectively, without side pressing; finally, the titanium billet is rolled in 8 passes, with pass reduction rates of 15-35%, and the thickness of the final hot-rolled titanium coil is 8.0 mm.

[0046] Compared with Example 1, since no side pressure is applied during the two passes of rolling in this comparative example, the titanium edge quality is poor, a large number of cracks and meat loss occur, and thus the surface pits and indentation defects increase, and the surface defect rate reaches 15.5%.

[0047] Example 2

[0048] The titanium blank used in this example is TA2 pure titanium blank smelted by EB furnace, with a thickness of 220 mm and a width of 1560 mm. First, the titanium blank is milled, chamfered and water ground to obtain a titanium blank with a surface roughness Ra = 4.2 μm; then the titanium blank is heated in zones, first at 870 ℃ for 200 min, and then at 910 ℃ for 60 min; then the titanium blank heated out of the furnace is high-pressure water dephosphorized, with a high-pressure water pressure of 25 MPa; then the titanium blank is rolled in two passes with a small reduction rate, with a pass reduction rate of 12% and 15% respectively, while a small deformation amount of side pressure is applied, with a side pressure deformation amount of 2% and 3% respectively; finally, 9 passes of rolling are carried out, with a pass reduction rate of 15-35%, and the final hot-rolled titanium coil has a thickness of 4.0 mm.

[0049] The titanium edge and surface quality are good, with no cracks and meat loss defects in the edge, and fewer peeling, pits and indentation defects on the surface, with a surface defect rate of 5.8%.

[0050] Comparative Example 2

[0051] The titanium blank used in this example is TA2 pure titanium blank smelted by EB furnace, with a thickness of 220 mm and a width of 1560 mm. First, the titanium blank is milled, chamfered and water ground to obtain a titanium blank with a surface roughness Ra = 4.2 μm; then the titanium blank is heated in zones, first at 870 ℃ for 200 min, and then at 910 ℃ for 60 min; then the titanium blank heated out of the furnace is high-pressure water dephosphorized, with a high-pressure water pressure of 25 MPa; then the titanium blank is rolled in two passes with a small reduction rate, with a pass reduction rate of 12% and 15% respectively, while a small deformation amount of side pressure is applied, with a side pressure deformation amount of 2% and 3% respectively; finally, 9 passes of rolling are carried out, with a pass reduction rate of 15-35%, and the final hot-rolled titanium coil has a thickness of 4.0 mm.

[0052] Compared with Example 2, since the low-temperature zone heating time is too short and the high-temperature zone heating time is too long in this comparative example, the titanium blank surface is severely oxidized and absorbed, resulting in an increase in the peeling defects of the hot-rolled titanium coil, and the surface defect rate reaches 20.4%.

[0053] Example 3

[0054] The titanium blank used in the example is TA10 pure titanium blank smelted by EB furnace, with thickness of 180 mm and width of 1060 mm. Firstly, the titanium blank is milled, chamfered and water ground to obtain a titanium blank with surface roughness Ra = 4.0 μm; then the titanium blank is heated in zones, first heated at 850 ℃ for 240 min, and then heated at 900 ℃ for 70 min; then the titanium blank heated out of the furnace is dephosphorized by high-pressure water, with high-pressure water pressure of 22 MPa; then the titanium blank is rolled by two passes with small reduction, with pass reduction of 10% and 15% respectively, while small deformation amount of side pressing is applied, with side pressing deformation amount of 2% and 5% respectively; finally, the titanium blank is rolled by 8 passes, with pass reduction of 15-35%, and the final hot-rolled titanium coil has thickness of 4.0 mm.

[0055] The titanium coil has good edge and surface quality, with no cracking and meat loss defects, less peeling, pits and indentation defects, and surface defect rate of 6.4%.

[0056] Comparative Example 3

[0057] The titanium blank used in the example is TA10 pure titanium blank smelted by EB furnace, with thickness of 180 mm and width of 1060 mm. Firstly, the titanium blank is milled, chamfered and water ground to obtain a titanium blank with surface roughness Ra = 4.0 μm; then the titanium blank is heated in zones, first heated at 850 ℃ for 240 min, and then heated at 900 ℃ for 70 min; then the titanium blank heated out of the furnace is dephosphorized by high-pressure water, with high-pressure water pressure of 22 MPa; then the titanium blank is rolled by two passes with small reduction, with pass reduction of 10% and 15% respectively, while small deformation amount of side pressing is applied, with side pressing deformation amount of 2% and 5% respectively; finally, the titanium blank is rolled by 8 passes, with pass reduction of 15-35%, and the final hot-rolled titanium coil has thickness of 4.0 mm.

[0058] Compared with Example 3, since the pass reduction is too large in the two passes of rolling in the comparative example, the hot-rolled titanium coil has poor shape, and the peeling defects of the titanium coil increase, with surface defect rate of 12.3%.

[0059] The above description of disclosed examples enables one skilled in the art to make or use the application. Numerous modifications to these examples will be apparent to those of skill in the art, and the general principles defined herein can be applied to other examples without departing from the spirit or scope of the application. Therefore, the present application is not to be limited to the examples presented but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rolling method of an EB furnace smelted titanium billet, characterized by, The method comprises the following steps: S1: heating the titanium billet smelted by EB furnace in a low temperature zone at 850-880 ℃, then heating in a high temperature zone at 900-950 ℃, and then performing phosphorus removal treatment on the heated titanium billet; The time of the low temperature zone heating is greater than the time of the high temperature zone heating; S2: performing two passes of rolling on the titanium billet after the phosphorus removal treatment while applying side pressure, and then rolling the obtained titanium billet to obtain a titanium coil; The pass reduction rate of the two passes of rolling is 10-15%, and the deformation amount of the side pressure is 2-5%.

2. The rolling method according to claim 1, characterized in that, The titanium billet in step S1 is pretreated before the low temperature zone heating; The pretreatment comprises milling the surface of the titanium billet, chamfering, and water grinding treatment.

3. The rolling method according to claim 2, characterized in that, The surface roughness Ra of the titanium billet after the pretreatment is less than 5 μm.

4. The rolling method according to claim 1, characterized in that, The time t1 / min of the low temperature zone heating is (0.8-1.2)×thickness of the titanium billet / mm.

5. The rolling method according to claim 4, characterized in that The time t2 / min of the high temperature zone heating is (0.2-0.4)×thickness of the titanium billet / mm.

6. The rolling method according to claim 1, characterized in that, The phosphorus removal treatment is performed by using high pressure water; The pressure of the high pressure water is 22-30 MPa.

7. The rolling method according to claim 1, characterized in that, The rolling after the side pressure application is performed by using multi-pass rolling; The passes of the multi-pass rolling are 6-10 passes.

8. The rolling method according to claim 7, characterized in that The pass reduction rate of the multi-pass rolling is 15-35%.

9. The rolling method according to claim 1, characterized in that, The thickness of the titanium coil is 4-10 mm.