Rolling method for electron beam melting titanium blank

Abstract

The invention relates to a rolling method of an electron beam smelted titanium blank. The rolling method comprises the following steps: S1, carrying out surface pretreatment on the titanium blank smelted by an EB furnace; s2, preparing a boronizing medium, and ball-milling the boronizing medium into powder; s3, the titanium blank is placed in a boronizing medium, and boronizing treatment is conducted on the titanium blank; s4, the titanium blank subjected to boronizing treatment is fed into a stepping type heating furnace to be heated; and S5, the titanium blank is rolled to the target thickness through multi-pass rolling. According to the method, the surface of the electron beam smelting titanium blank is subjected to boriding treatment, the heating temperature of the titanium blank is increased to be higher than the phase transformation point, the plasticity of the titanium blank can be improved while high-temperature surface air suction of the titanium blank can be effectively avoided, and the surface quality of titanium blank rolling can be greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of titanium rolling production, in particular to a method for rolling an electron beam smelting titanium billet. Background Art

[0002] Titanium and titanium alloys have excellent properties such as high specific strength, good formability, high temperature resistance, and corrosion resistance, so they are widely used in the fields of chemical industry, aerospace, and ships. At present, the mainstream smelting process of titanium and titanium alloys is vacuum arc melting (VAR), but even using three vacuum arc melting cannot fundamentally guarantee the complete elimination of metallurgical defects of high and low density inclusions in titanium and titanium alloys. It is not easy to obtain highly homogeneous and pure ingots, and subsequent rolling is required after forging and blanking.

[0003] With the improvement of the metallurgical quality requirements of titanium and titanium alloys, electron beam melting (EBM) technology has developed rapidly. Electron beam melting technology not only eliminates the process of forging and blanking, but also the smelted titanium ingots can be directly rolled into coils, and solves the problem of high and low density inclusions in the smelting process of titanium and titanium alloys. A large amount of return material can be added, which is an important way to achieve the purification of titanium and titanium alloy materials and low-cost manufacturing. Compared with titanium and titanium alloy ingots after vacuum arc melting and forging, titanium ingots melted by electron beam have a coarser original grain size, which can reach the centimeter level. This leads to a significant difference in its surface oxidation behavior and rolling deformation behavior during heating and hot rolling compared with titanium billets melted by vacuum arc melting and forging.

[0004] Due to the coarse grains, high surface stress and cast defects of electron beam melted titanium ingots, the plastic deformation ability of titanium ingots is poor during hot rolling, and the surface of titanium ingots is prone to cracking and forming defects. The surface quality of hot-rolled titanium coils is poor, which damages the yield rate and increases the subsequent processing costs. Although increasing the hot rolling temperature of titanium ingots can improve the plasticity of titanium ingots, the surface air absorption of titanium ingots is serious when heated in the β phase region, which will also damage the surface quality of titanium coils.

[0005] Therefore, it is of great significance to develop a high-temperature rolling method for electron beam melted titanium billets to improve the surface quality of titanium coils rolled from electron beam melted titanium billets in order to address the problems existing in the rolling process of electron beam melted titanium billets. Summary of the invention

[0006] In view of the above problems, the purpose of the present invention is to provide a rolling method for electron beam melted titanium billets. By boronizing the surface of the electron beam melted titanium billet, the heating temperature of the titanium billet is increased to above the phase change point, thereby avoiding air absorption on the high-temperature surface of the titanium billet, while improving the plasticity of the titanium billet and improving the surface quality of the titanium billet rolling.

[0007] The technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for rolling an electron beam melted titanium billet, which specifically comprises the following steps:

[0009] S1. Surface pretreatment of titanium billet smelted in EB furnace;

[0010] S2, prepare the boronizing medium and ball grind it into powder;

[0011] S3, placing the titanium billet in a boriding medium to perform a boriding treatment on the titanium billet;

[0012] S4, sending the boronized titanium billet into a walking beam heating furnace for heating;

[0013] S5. Roll the titanium billet to a target thickness through multiple rolling passes.

[0014] Furthermore, the step S1 specifically includes: performing milling, chamfering and water grinding on the titanium blank in sequence to obtain a titanium blank with a smooth and flat surface, and the surface roughness Ra is required to be less than 5 μm.

[0015] Furthermore, in step S2, the boronizing medium is composed of a boron supplying agent, a catalyst and a filler.

[0016] Furthermore, the mass ratio of the boron supplying agent, the penetration catalyst and the filler is 1-2:1-2:1.5-3.

[0017] Furthermore, the boron supplying agent is a mixture of borax and ferroboron, and the mass ratio of borax to ferroboron is 10-12:1-2.

[0018] Furthermore, the penetration catalyst is a mixture of potassium fluoroborate and ammonium bicarbonate, and the mass ratio of potassium fluoroborate to ammonium bicarbonate is 1:1.

[0019] Furthermore, the filler is aluminum oxide.

[0020] Furthermore, the step S3 specifically includes: placing the titanium billet in a boronizing medium, keeping the temperature at 800° C. to 900° C. for 1 to 5 hours, so that the depth of the boronizing layer on the surface of the titanium billet reaches 20 to 30 μm.

[0021] Furthermore, in step S4, the heating temperature is 920°C to 980°C, and the time in the furnace is t=1.5×h, where t is the heating time in min, and h is the thickness of the titanium billet in mm.

[0022] Furthermore, in step S5, the pass reduction rate is 15%-35%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention improves the surface quality of the titanium billet through water grinding, reduces the surface roughness of the titanium billet, improves the boronizing effect and prevents the surface peeling defects of the titanium billet during hot rolling.

[0025] 2. The present invention forms a boronized layer with a thickness of several tens of microns on the surface of the titanium billet through boronizing treatment, and utilizes the boronized layer to prevent the titanium billet from absorbing air on the surface when heated above the phase transition point, thereby improving the surface quality of the titanium billet during rolling.

[0026] 3. The present invention increases the heating temperature of the titanium billet to above the phase transition point, thereby improving the plastic deformation capacity of the titanium billet and preventing crack defects from being generated due to insufficient plasticity during rolling of the titanium billet. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic flow chart of a method for rolling a titanium billet by electron beam melting. DETAILED DESCRIPTION

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] See attached Figure 1 The present invention provides a method for rolling an electron beam-melted titanium billet, which specifically comprises the following steps:

[0030] S1. Milling, chamfering and water grinding are performed on the titanium billet smelted in the EB furnace in sequence to obtain a titanium billet with a smooth surface, and the surface roughness is required to be Ra < 5μm.

[0031] S2, prepare the boronizing medium;

[0032] The boronizing medium is composed of a boron supply agent, a catalyst and a filler;

[0033] The mass ratio of the boron supply agent, the penetration catalyst and the filler is 1-2:1-2:1.5-3;

[0034] The boron supply agent is a mixture of borax and ferroboron, and the mass ratio of borax to ferroboron is 10-12:1-2;

[0035] The penetration catalyst is a mixture of potassium fluoroborate and ammonium bicarbonate, and the mass ratio of potassium fluoroborate to ammonium bicarbonate is 1:1;

[0036] The filler is alumina;

[0037] The boron supplying agent, penetration catalyst and filler are mixed in corresponding proportions and then ball-milled into powder.

[0038] S3. Perform boronizing treatment on the titanium billet, place the titanium billet in a boronizing medium, and keep it at 800°C to 900°C for 1 to 5 hours, so that the depth of the boronizing layer on the surface of the titanium billet reaches 20 to 30 μm.

[0039] S4. The titanium billet is placed in a step-beam heating furnace and heated at a temperature of 920°C to 980°C. The furnace time is t=1.5×h, where t is the heating time in min and h is the thickness of the titanium billet in mm.

[0040] S5. Roll the titanium billet to a target thickness through multiple rolling passes, with a reduction rate of 15% to 35%.

[0041] The method is further described below by means of specific embodiments:

[0042] Example 1

[0043] The titanium billet used in this embodiment is a TA1 pure titanium billet smelted in an EB furnace, with a thickness of 200 mm and a width of 1080 mm.

[0044] Firstly, the titanium billet is milled, chamfered and water-ground to obtain a titanium billet with a surface roughness of Ra=3.6μm; then the titanium billet is borided, placed in a boriding medium, and kept at 800℃ for 1h to make the depth of the boriding layer on the surface of the titanium billet reach 20μm; wherein the boriding medium consists of a boron supply agent, a catalyst and a filler, and the mass ratio of the boron supply agent, the catalyst and the filler is 1:1:1.5; the boron supply agent is a mixture of borax and ferroboron, and the mass ratio of borax to ferroboron is 10:1.2; the catalyst is a mixture of potassium fluoroborate and ammonium bicarbonate, and the mass ratio of potassium fluoroborate to ammonium bicarbonate is 1:1, and the filler is alumina; the borided titanium billet is then sent to a step-beam heating furnace for heating at 920℃ for 300min; finally, the titanium billet is rolled to the target thickness through multiple rolling passes, and the pass reduction rate is 15%.

[0045] The edge and surface quality of the titanium coil after rolling are good, with no defects such as cracking and meat falling off on the edge, and fewer defects such as peeling, pits and indentations on the surface. The surface defect rate is 5.2%.

[0046] Example 2

[0047] The titanium billet used in this embodiment is a TA2 pure titanium billet smelted in an EB furnace, with a thickness of 220 mm and a width of 1560 mm.

[0048] Firstly, the titanium billet is milled, chamfered and water-ground to obtain a titanium billet with a surface roughness of Ra=4.2μm; then the titanium billet is borided, placed in a boronizing medium, and kept at 850°C for 4h to make the depth of the boronizing layer on the surface of the titanium billet reach 25μm, the boronizing medium is composed of a boronizing agent, a catalyst and a filler, the mass ratio of the boronizing agent, the catalyst and the filler is 2:2:3, the boronizing agent is a mixture of borax and ferroboron, the mass ratio of borax and ferroboron is 6:1, the catalyst is a mixture of potassium fluoroborate and ammonium bicarbonate, the mass ratio of potassium fluoroborate and ammonium bicarbonate is 1:1, and the filler is alumina; then the titanium billet is sent to a step-beam heating furnace and heated at 950°C, with a furnace time of 330min; finally, the titanium billet is rolled to the target thickness by multiple rolling, and the pass reduction rate is 25%.

[0049] The edge and surface quality of the titanium coil after rolling are good, with no cracking or meat loss defects on the edge, and fewer defects such as peeling, pits and indentations on the surface. The surface defect rate is 4.8%.

[0050] Example 3

[0051] The titanium billet used in this embodiment is a TA10 titanium billet smelted in an EB furnace, with a thickness of 180 mm and a width of 1060 mm.

[0052] Firstly, the titanium billet is milled, chamfered and water-ground to obtain a titanium billet with a surface roughness of Ra=4.0μm; then the titanium billet is borided, placed in a boronizing medium, and kept at 900°C for 5h to make the depth of the boronizing layer on the surface of the titanium billet reach 30μm, the boronizing medium is composed of a boronizing agent, a catalyst and a filler, the mass ratio of the boronizing agent, the catalyst and the filler is 1:1:2, the boronizing agent is a mixture of borax and ferroboron, the mass ratio of borax and ferroboron is 10:1, the catalyst is a mixture of potassium fluoroborate and ammonium bicarbonate, the mass ratio of potassium fluoroborate and ammonium bicarbonate is 1:1, and the filler is alumina; then the titanium billet is sent to a step-beam heating furnace and heated at 980°C, with a furnace time of 270min; finally, the titanium billet is rolled to the target thickness by multiple rolling, and the pass reduction rate is 35%.

[0053] The edge and surface quality of the titanium coil after rolling are good, with no cracking or meat loss defects on the edge, and fewer defects such as peeling, pits and indentations on the surface. The surface defect rate is 5.4%.

[0054] Matters not described in detail in the present invention are all known technologies.

[0055] The embodiments described above are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for rolling an electron beam melted titanium billet, characterized in that: The method comprises the following steps: S1. Surface pretreatment of titanium billet smelted in EB furnace; S2, prepare the boronizing medium and ball grind it into powder; S3, placing the titanium billet in a boriding medium to perform a boriding treatment on the titanium billet; S4, sending the boronized titanium billet into a walking beam heating furnace for heating; S5. Roll the titanium billet to a target thickness through multiple rolling passes.

2. The method for rolling an electron beam melted titanium billet according to claim 1, characterized in that: The step S1 specifically includes: performing milling, chamfering and water grinding on the titanium blank in sequence to obtain a titanium blank with a smooth and flat surface, and the surface roughness Ra is required to be less than 5 μm.

3. The method for rolling an electron beam melted titanium billet according to claim 1, characterized in that: In the step S2, the boronizing medium is composed of a boron supplying agent, a catalyst and a filler.

4. The method for rolling an electron beam melted titanium billet according to claim 3, characterized in that: The mass ratio of the boron supplying agent, the penetration catalyst and the filler is 1-2:1-2:1.5-3.

5. The method for rolling an electron beam melted titanium billet according to claim 3, characterized in that: The boron supply agent is a mixture of borax and ferroboron, and the mass ratio of borax to ferroboron is 10-12:1-2.

6. The method for rolling an electron beam melted titanium billet according to claim 3, characterized in that: The penetration catalyst is prepared by mixing potassium fluoroborate and ammonium bicarbonate, and the mass ratio of potassium fluoroborate to ammonium bicarbonate is 1:

1.

7. The method for rolling an electron beam melted titanium billet according to claim 3, characterized in that: The filler is aluminum oxide.

8. The method for rolling an electron beam melted titanium billet according to claim 1, characterized in that: The step S3 specifically includes: placing the titanium blank in a boronizing medium, keeping the temperature at 800° C. to 900° C. for 1 to 5 hours, so that the depth of the boronizing layer on the surface of the titanium blank reaches 20 to 30 μm.

9. The method for rolling an electron beam melted titanium billet according to claim 1, characterized in that: In step S4, the heating temperature is 920°C to 980°C, and the time in the furnace is t=1.5×h, where t is the heating time in min, and h is the thickness of the titanium billet in mm.

10. The method for rolling an electron beam melted titanium billet according to claim 1, characterized in that: In step S5, the pass reduction rate is 15%-35%.

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