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Analysis of peeling and lamination of molybdenum sheet in rolling process

Through a large number of molybdenum sheet rolling production, it is found that some batches of molybdenum sheet are seriously stratified in the warm rolling process. It is very easy to peel large area when rolling liquid is added in the rolling process from 1.5mm to 1.0mm, 1.0mm to 0.85mm, 0.75mm to 0.5mm.

From mo slab internal structure, the first in hot rolled slab internal structure should be sufficiently former molybdenum, polycrystalline sintered state exists in the relative rules of particle state, through the section layer of molybdenum metal profile can be seen that at this time under the action of external force on cracking easily, but at this time of the internal structure of mo slab is relatively stable, also can form a relatively ideal between molybdenum crystal as a whole.

When the molybdenum slab is heated to the maximum temperature of 1100-1150C, the internal grains of molybdenum and gold recombine with the recrystallization temperature of grains. When the molybdenum billet is rolled and calendered, its crystals will recombine and extrude to the rolling direction.

If the rolling area of the grain size of a molybdenum crystal is 0.1mm and the plate is rolled to 0.3mm when the plate is still 24 thickness, because the crystal recrystallizes from the outside to the inside, the deformation rate should be 98% larger, and the length of the molybdenum crystal after rolling will also change from 0.1mm to more than 9.8mm for deformation and elongation. At this time, the grains in the molybdenum plate also become sheet structure, such as elongated fish scales superimposed together to form a relatively stable metal body. At this time, the molybdenum plate goes through a round of 900-850°C/30min annealing and then goes to the next process of warm rolling.

In the process of hot rolling molybdenum plate from molybdenum slab to 3.0mm, there will be several situations, such as rolling when heating temperature does not reach the maximum reknot temperature, and the amount of pass deformation when molybdenum slab is opened.

Low furnace temperature is not reached more than 1150 ci of the ideal temperature sufficiently, molybdenum metal recrystallization temperature low rolling processing, the molybdenum gold inside crystal lamella structure under the large force to do with the unstable movement, though in the external view or want to stable, but the gold molybdenum internal mingled and again above the temperature of the permeability and sex difference, It is because of the instability of the lamellar structure that serious stratification occurs in the hot rolling process. Influence on the following 1.0, 0.8, 0.5mm rolling.

In the rolling process, there is a single pass rate and a total pass rate, and the pass rate has a single pass rate and a multi-pass rate. According to the deformation theory of molybdenum rolling, the deformation rate of single pass should be greater than 25%. However, according to the actual situation and equipment capacity, the requirement of equipment for rolling greater than 25% is higher. Therefore, it is necessary to control the disunity of deformation rate of single pass in rolling of single molybdenum billet. Multi-pass deformation rate of one fire heating is the total deformation rate of heating and rolling for many times. It is especially emphasized that when the molybdenum slab reaches 50%-60% deformation, it should be heated in the furnace and then rolled again.

In the process of rolling and rolling, the uneven deformation rate will also affect the internal structure of molybdenum plate, so it is necessary to prevent the inconsistent amount of pressing down as much as possible, and the single pressing down amount should be controlled in the range of 25%, which is conducive to the consistent extension of fish scale lamellar in molybdenum plate to strengthen the stability of tissue.

Therefore, the production requirement of thermal sharpening is to control the heating temperature of the blank at 1100-1150℃. In addition to shaping, the deformation rate of a single pass should be between 25-30%. When rolling below 8mm, it can be transferred to 1050℃ furnace body for rolling.

1050℃ low temperature furnace rolling to 3.0-3.5mm after annealing alkali washing to warm rolling, annealing temperature and heating time should be 900-850℃ annealing time 30-40min, such as heating time and heating temperature problems can be improved.

At this time of the internal structure of hot rolled plate is fine flake stack structure, on the surface of molybdenum to no obvious texture, but through a microscope to observe fine flake stack structure of cross section, through the warm rolling mill, make fine flake stack structure can further stretching, such as plant fiber organization structure, can be called a molybdenum metal fibre structure at this time. Due to rolling under recrystallization temperature, the internal work hardening of molybdenum and gold is serious and the internal stress is strengthened. Suppose in hot rolling sufficiently low temperature and the heating is not fully, so 3.0 3.5 mm hot rolled molybdenum plate structure is in unstable state, that is to say, the molybdenum fibre surface do not agree with the middle tier of the stress distribution, when using the rolling process by the mill rolling Di bearing surface occurs on the surface of the force applied to molybdenum plate deformation, the middle layer rolling deformation happened at the same time, However, the surface deformation resistance is small and the deformation rate is large, while the inner middle layer is large and the deformation rate is small. When the deformation of the two surfaces of the plate exceeds a certain range of values of the intermediate layer, the unstable structure is broken, the stress is released at this time, resulting in stratification.

The annealing process should be fully considered in the warm rolling process. According to the research, when the deformation of pure molybdenum plate reaches 50%, the internal stress should be eliminated by annealing. According to the annealing system of different thickness, the molybdenum sheet after annealing is beneficial to the subsequent rolling and rolling processing.

In cold rolling, every fiber body will have a warping stress zone to the outside of the sheet due to the strong pressure of rolling, which will cause the peeling phenomenon in the later processing. Although no rolling fluid peeling will not be significantly serious, but its internal has formed work hardening, internal stress increased. In 1.5 mm to 1.0 mm of annealing of rolling and annealing of molybdenum were on the premise of not dozen rolling fluid, 1.5 mm without annealing molybdenum plate do with internal stress and strain hardening, rolling molybdenum plate deformation of fiber layer of the inner small, fiber layer will processing aid slow release, the force at the same time, the deformation rate of molybdenum surface layer and center layer is small, a peeling chance is very small. If the rolling fluid is added, the friction coefficient of the fiber tissue on the surface of the molybdenum plate decreases and the deformation is large. The internal molybdenum fiber tissue was torn due to work hardening, which resulted in peeling phenomenon.

Because there is no systematic comparison of the percentage of stripping of annealed and unannealed molybdenum sheet plus rolling liquid, but through observation, it is found that the area of stripping of unannealed molybdenum sheet is less than that of unannealed molybdenum sheet, and most of the peeling part is the feeding port.

The flaking factor for rolling 0.85mm to 0.5mm molybdenum sheet is the same as that for rolling 1.0mm finished product.

1. According to the process improvement of sheet lamination of molybdenum plate, when the deformation rate of molybdenum plate reaches 50%, annealing system should be carried out to produce internal stress on work hardening.

2, change the rolling mode, the original relatively small fine fiber tissue into longitudinal sheet large fiber tissue, so that the metal fiber inside the molybdenum alloy is thicker, so as to improve the stability of the molybdenum metal internal structure.

3, strictly control the heating temperature and deformation rate.

4, replace the rolling fluid with large friction coefficient, so as to reduce the deformation rate inconsistency between molybdenum fibers.

5. In order to prevent the work hardening phenomenon of molybdenum plate in warm cold rolling, the thickness of hot rolling incoming plate should be 1.5-1mm when hot rolling 2.0mm finished product, 1.8mm hot rolling plate when cold rolling 0.5mm finished product, and 1.5mm hot rolling plate when cold rolling 0.5mm finished product.
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