Method for improving rolling surface quality of electron beam melting titanium blank

Abstract

The invention provides a method for improving the rolling surface quality of an electron beam melting titanium blank, which comprises the following steps: S1, pretreating the titanium blank to obtain the titanium blank with a smooth and flat surface; s2, the pretreated titanium blank is subjected to shot blasting treatment; s3, the titanium blank subjected to shot blasting treatment is heated; and S4, the heated titanium blank is rolled, and a titanium coil with the good edge and surface quality is obtained. The surface of the electron beam smelting titanium blank is subjected to shot blasting treatment, so that the surface plasticity of the hot-rolled titanium blank is improved, and the rolled surface quality of the titanium blank is improved.

Description

Technical Field

[0001] The invention relates to the technical field of titanium rolling production, and in particular to a method for improving the rolling surface quality of electron beam melted titanium billets. Background Art

[0002] Titanium and titanium alloys have excellent properties such as high specific strength, good formability, high temperature resistance and corrosion resistance. Therefore, they are widely used in chemical industry, aerospace, shipbuilding and other fields.

[0003] At present, the mainstream smelting process of titanium and titanium alloys is vacuum arc melting (VAR). However, even if three vacuum arc meltings are used, it 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 they need to be forged and blanked for subsequent rolling. With the improvement of metallurgical quality requirements for 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, and the smelted titanium ingots can be directly rolled into coils, but also solves the high and low density inclusions in the smelting process of titanium and titanium alloys, and can add a large amount of return materials. It 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, the titanium ingot melted by electron beam melting has a coarser original grain size, which can reach the centimeter level. This leads to its surface oxidation behavior and rolling deformation behavior during heating and hot rolling. It is quite different from the titanium billet melted by vacuum arc melting and forging. Because the titanium ingots produced by electron beam melting have coarse grains, large surface stress, and cast defects, the plastic deformation ability of the titanium ingots is poor during hot rolling, and the surface of the titanium ingots is prone to cracking and forming defects. The surface quality of the hot-rolled titanium coils is poor, which damages the yield rate and increases the subsequent processing costs.

[0004] Aiming at the problem of poor surface quality during the rolling process of electron beam melted titanium billets, it is of great significance to develop a method to improve the rolling surface quality of electron beam melted titanium billets. Summary of the invention

[0005] In accordance with the technical problems raised above, a method for improving the surface quality of electron beam melted titanium billets is provided. The present invention mainly ensures that the surface of the titanium billet is smooth and free of crack defects by milling, chamfering and water grinding the electron beam melted titanium billet. The titanium billet is then shot blasted to control the depth of the hardened layer on the surface of the titanium billet to be 100-200μm. The titanium billet is then sent to a step-type heating furnace for heating and insulation at 900℃-960℃. Finally, multiple rolling passes are performed to roll the titanium billet to the target thickness. The present invention improves the surface plasticity of the hot-rolled titanium billet and improves the surface quality of the titanium billet by shot blasting the surface of the electron beam melted titanium billet.

[0006] The technical means adopted by the present invention are as follows:

[0007] A method for improving the rolling surface quality of electron beam melted titanium billets comprises the following steps:

[0008] S1, pre-treating the titanium billet to obtain a titanium billet with a smooth surface;

[0009] S2, shot blasting the pretreated titanium blank;

[0010] S3, heating the titanium blank after shot blasting;

[0011] S4. Roll the heated titanium billet to obtain a titanium coil with good edge and surface quality.

[0012] Furthermore, in S1, the pretreatment includes: milling, chamfering, and water grinding the titanium blank, and the surface roughness Ra of the pretreated titanium blank is less than 5 μm.

[0013] Furthermore, in S2, the shot blasting pressure of the shot blasting treatment is 0.2-0.6 MPa, the shot blasting time is 20-60 min, and the shot blasting coverage is >200%.

[0014] Furthermore, the depth of the hardened layer on the surface of the titanium blank after shot blasting is 100-200 μm, and a uniform aluminum-rich layer with a thickness of 20-50 μm is formed on the surface of the titanium blank after shot blasting.

[0015] Furthermore, in S2, the shot blasting material for shot blasting is prepared from aluminum alloy cut wire shots with a diameter of 0.5-1.5 mm, and the hardness of the aluminum shots is 80-120 HV.

[0016] Furthermore, in S3, the titanium billet is placed in a walking beam heating furnace and heated at a temperature of 900°C to 960°C.

[0017] Furthermore, the time that the titanium billet is in the furnace is t=1.2×h, wherein t is the heating time, in min; and h is the thickness of the titanium billet, in mm.

[0018] Furthermore, in S4, the titanium billet is rolled to a target thickness through multiple rolling passes, and the rolling reduction rate of each pass is 15%-35%.

[0019] Furthermore, in S4, the surface defect rate of the titanium coil after rolling is less than 10%.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The shot blasting used in the present invention has a different effect from the traditional shot blasting in removing burrs and oxide scales on the ingot. The present invention forms a 100-200 μm fine-grained layer on the surface of the titanium billet through shot blasting, thereby improving the surface plasticity of the original cast titanium billet and helping to improve the surface quality of the titanium billet after rolling. In addition, the shot blasting material of the present invention is aluminum shot, which can form an aluminum-rich layer on the surface of the titanium ingot after shot blasting. Aluminum, as an α-Ti stabilizing element, can increase the phase transition point temperature on the surface of the titanium ingot. Raising the heating temperature of the titanium billet to above the phase transition point can not only cause the titanium billet to undergo a β phase transition and improve its plastic deformation ability, but also ensure that the surface of the titanium billet is in the α phase, thereby avoiding severe air inhalation during the surface phase transition.

[0022] Based on the above reasons, the present invention can be widely promoted in the fields of chemical industry, aerospace, shipbuilding, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] 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 labor.

[0024] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0028] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. Meanwhile, it should be clear that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0029] The present invention provides a method for improving the surface quality of electron beam melted titanium billets during rolling, that is, a method for rolling electron beam melted titanium billets to improve the surface quality of electron beam melted titanium billets during rolling. The method mainly comprises the following steps:

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

[0031] S2. Shot blasting is performed on the titanium billet. The shot blasting material is made of aluminum alloy wire cut shot with a diameter of 0.5-1.5mm. The hardness of the aluminum shot is required to be 80-120HV, the shot blasting pressure is 0.2-0.6MPa, the shot blasting time is 20-60min, and the shot blasting coverage is >200%. After shot blasting, the depth of the hardened layer on the surface of the titanium billet is 100-200μm. After shot blasting, a uniform 20-50μm thick aluminum-rich layer is formed on the surface due to the impact of the aluminum shot. Aluminum, as an α-Ti stabilizing element, will increase the phase transition temperature of the titanium billet surface.

[0032] S3. Place the titanium billet into a step-type heating furnace and heat it at 900°C to 960°C. The furnace time is t = 1.2×h, where t is the heating time in min and h is the thickness of the titanium billet in mm. Pure titanium is α-Ti below 882°C, which is a close-packed hexagonal lattice with poor deformation ability. Above 882°C, it will transform into β-Ti with a body-centered cubic lattice. The deformation ability will be significantly improved, but the surface air absorption will also be more serious. Since there is an aluminum-rich layer tens of microns thick on the surface of the titanium billet, the surface area of ​​tens of microns of the titanium billet is still α-Ti when heated at 900°C to 960°C, which can avoid serious surface air absorption, but the interior is transformed into β-Ti with excellent plasticity, which is beneficial to subsequent hot rolling deformation;

[0033] S4. Roll the titanium billet to the target thickness through multiple passes with a reduction rate of 15%-35% to obtain a titanium coil with good edge and surface quality.

[0034] The shot blasting used in the present invention has a different effect from the traditional shot blasting in removing ingot burrs and oxide scales. The present invention forms a 100-200 μm fine-grained layer on the surface of the titanium billet through shot blasting, thereby improving the surface plasticity of the original cast titanium billet and helping to improve the surface quality of the titanium billet after rolling. In addition, the shot blasting material of the present invention is aluminum shot, which can form an aluminum-rich layer on the surface of the titanium ingot after shot blasting. Aluminum, as an α-titanium stabilizing element, can increase the phase transition point temperature on the surface of the titanium ingot. Raising the heating temperature of the titanium billet to above the phase transition point can not only cause the titanium billet to undergo a β phase transition and improve its plastic deformation ability, but also ensure that the surface of the titanium billet is in the α phase, thereby avoiding severe air inhalation during the surface phase transition.

[0035] Example 1

[0036] The titanium billet used in this embodiment is a TA1 pure titanium billet smelted in an EB furnace, with a thickness of 210mm and a width of 1080mm. First, the titanium billet is milled, chamfered, and water-ground to obtain a titanium billet with a surface roughness of Ra=3.2μm; then the titanium billet is shot blasted, and the shot blasting material is prepared from aluminum alloy wire cut shot with a diameter of 0.6mm, the aluminum shot hardness is 85HV, the shot blasting pressure is 0.2MPa, the shot blasting time is 25min, the shot blasting coverage is 300%, and the depth of the surface hardened layer of the titanium billet after shot blasting is 110μm; then the titanium billet is sent to a step-type heating furnace and heated at 900℃, and the furnace time is 250min; finally, the titanium billet is rolled to the target thickness by multiple passes. The titanium curling edge and surface quality rolled by this method are good, there are no cracks or meat loss defects on the edge, and there are fewer defects such as peeling, pits and indentation on the surface, and the surface defect rate is 4.2%.

[0037] Example 2

[0038] The titanium billet used in this embodiment is a TA2 pure titanium billet smelted in an EB furnace, with a thickness of 180mm and a width of 1560mm. First, the titanium billet is milled, chamfered, and water-ground to obtain a titanium billet with a surface roughness of Ra=4.3μm; then the titanium billet is shot blasted, and the shot blasting material is prepared from aluminum alloy wire cut shot with a diameter of 1.2mm. The hardness of the aluminum shot is 110HV, the shot blasting pressure is 0.6MPa, the shot blasting time is 60min, the shot blasting coverage is 800%, and the depth of the surface hardened layer of the titanium billet after shot blasting is 186μm; then the titanium billet is sent to a step-type heating furnace and heated at 960℃, and the furnace time is 220min; finally, the titanium billet is rolled to the target thickness by multiple passes. The titanium curling edge and surface quality are good, there are no cracks or meat loss defects on the edge, and there are fewer defects such as peeling, pits and indentations on the surface, and the surface defect rate is 6.8%.

[0039] Example 3

[0040] The titanium billet used in this embodiment is a TA10 titanium billet smelted in an EB furnace, with a thickness of 150mm and a width of 1060mm. First, the titanium billet is milled, chamfered, and water-ground to obtain a titanium billet with a surface roughness of Ra=3.0μm; then the titanium billet is shot blasted, and the shot blasting material is prepared from aluminum alloy wire cut shot with a diameter of 1.0mm. The hardness of the aluminum shot is 96HV, the shot blasting pressure is 0.5MPa, the shot blasting time is 35min, and the shot blasting coverage is 500%. The depth of the surface hardened layer of the titanium billet after shot blasting is required to be 120μm; then the titanium billet is sent to a step-type heating furnace and heated at 920℃, and the furnace time is 180min; finally, the titanium billet is rolled to the target thickness by multiple rolling. The titanium curling edge and surface quality are good, there are no cracks or meat loss defects on the edge, and there are fewer defects such as peeling, pits and indentations on the surface, and the surface defect rate is 5.6%.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the rolling surface quality of electron beam melted titanium billets, characterized in that: The steps include: S1, pre-treating the titanium billet to obtain a titanium billet with a smooth surface; S2, shot blasting the pretreated titanium blank; S3, heating the titanium blank after shot blasting; S4. Roll the heated titanium billet to obtain a titanium coil with good edge and surface quality.

2. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 1, characterized in that: In S1, the pretreatment includes: milling, chamfering and water grinding the titanium blank, and the surface roughness Ra of the titanium blank after the pretreatment is less than 5 μm.

3. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 1, characterized in that: In S2, the shot blasting pressure of the shot blasting treatment is 0.2-0.6 MPa, the shot blasting time is 20-60 min, and the shot blasting coverage is >200%.

4. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 3, characterized in that: The depth of the hardened layer on the surface of the titanium blank after shot blasting is 100-200 μm, and a uniform aluminum-rich layer with a thickness of 20-50 μm is formed on the surface of the titanium blank after shot blasting.

5. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 1 or 3, characterized in that: In S2, the shot blasting material for shot blasting is prepared from aluminum alloy cut wire shot with a diameter of 0.5-1.5 mm, and the hardness of the aluminum shot is 80-120 HV.

6. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 1, characterized in that: In S3, the titanium billet is placed in a walking beam heating furnace and heated at a temperature of 900°C to 960°C.

7. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 6, characterized in that: The time of the titanium billet in the furnace is t=1.2×h, wherein t is the heating time, in min; h is the thickness of the titanium billet, in mm.

8. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 1, characterized in that: In S4, the titanium billet is rolled to a target thickness through multiple rolling passes, with a rolling reduction rate of 15% to 35%.

9. The method for improving the rolling surface quality of electron beam melted titanium billet according to claim 1, characterized in that: In the above S4, the surface defect rate of the titanium coil after rolling is less than 10%.

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