Molybdenum sheet is a key material widely used in aerospace, electronics, and high-temperature industrial fields due to its excellent high-temperature resistance, corrosion resistance, and electrical conductivity. However, during the rolling process, defects such as cracks and wavy edges often occur, which seriously affect the quality and service life of the molybdenum sheet. In this article, we will deeply analyze the causes of these two common defects and provide practical solutions combined with cases and data.
1. Overview of molybdenum sheet Rolling Process and Common Defects
Rolling is the core process of molybdenum sheet production, which forms the molybdenum blank into a sheet with uniform thickness and smooth surface through continuous pressure. But molybdenum itself is a brittle metal, especially at room temperature, so it is very easy to produce various defects during rolling. In addition to cracks and wavy edges, there are also defects such as uneven thickness, surface scratches, and edge folding. Among them, cracks and wavy edges are the most frequent, accounting for about 65% of all molybdenum sheet rolling defects (Source: International Journal of Refractory Metals and Hard Materials, 2024).
Actually, the occurrence of these defects is not accidental. It is closely related to raw material quality, rolling process parameters, equipment status, and post-processing. Next, we will focus on analyzing the causes and solutions of cracks and wavy edges, which are the most troublesome for manufacturers.
2. Cause Analysis of molybdenum sheet Cracks: From Raw Materials to Process
Cracks are the most serious defect in molybdenum sheet rolling. Once they occur, most of the products will be scrapped, which greatly increases the production cost. Through years of practice and research, we found that the causes of cracks can be divided into two categories: raw material problems and rolling process problems.
First, raw material defects. The molybdenum blank used for rolling contains impurities such as oxygen, nitrogen, and carbon. When the impurity content exceeds 0.05%, it will form brittle phases in the molybdenum matrix, which will easily cause stress concentration during rolling and lead to cracks (Source: Journal of Materials Processing Technology, 2023). For example, if the oxygen content in the molybdenum blank is too high, molybdenum oxide will be formed, which is very brittle and will crack along the oxide phase during the rolling process.
Second, unreasonable rolling process parameters. Rolling temperature, rolling speed, and reduction rate are the three core parameters affecting crack generation. Molybdenum has good plasticity at high temperatures (above 800℃), but if the rolling temperature is too low (below 600℃), the plasticity of molybdenum sheet decreases sharply, and cracks will occur due to insufficient deformation capacity. On the contrary, if the rolling temperature is too high, the surface of the molybdenum sheet will oxidize seriously, and the oxide layer will fall off during rolling, forming surface cracks.
Interesting is that many manufacturers ignore the rolling speed. If the rolling speed is too fast, the deformation of the molybdenum sheet cannot keep up with the speed of the roller, which will cause uneven deformation and generate large internal stress, thus leading to internal cracks. These cracks are not easy to be found in the early stage, but will expand and break during subsequent processing or use.
3. Solution to molybdenum sheet Cracks: Step-by-Step Operation Guide
Aiming at the causes of molybdenum sheet cracks, we summarize a set of practical solutions, which are divided into 5 specific steps. Following this guide can effectively reduce the crack rate by more than 80%.
3.1 Strictly Control Raw Material Quality
Select high-purity molybdenum blanks with impurity content less than 0.05%, and conduct strict inspection before rolling. Use spectral analysis to detect the content of oxygen, nitrogen, carbon and other impurities, and reject unqualified blanks. At the same time, the molybdenum blank should be annealed before rolling to eliminate internal stress and improve its plasticity.
3.2 Optimize Rolling Temperature Parameters
Control the rolling temperature in the range of 700℃-850℃. For thin molybdenum sheet (thickness less than 0.5mm), the rolling temperature can be appropriately reduced to 700℃-750℃ to avoid excessive oxidation. For thick molybdenum sheet (thickness greater than 1mm), the rolling temperature can be increased to 800℃-850℃ to improve plasticity.
3.3 Adjust Rolling Speed and Reduction Rate
Control the rolling speed at 0.5m/s-1.0m/s. For the initial rolling stage (thickness greater than 5mm), the rolling speed can be slower (0.5m/s-0.7m/s) to ensure uniform deformation. For the final rolling stage (thickness less than 1mm), the rolling speed can be appropriately increased (0.8m/s-1.0m/s) to improve production efficiency. The single reduction rate should be controlled at 10%-15%, and the total reduction rate should not exceed 80% to avoid excessive deformation.
3.4 Strengthen Lubrication and Cooling
Use high-temperature resistant lubricants (such as molybdenum disulfide) during rolling to reduce the friction between the roller and the molybdenum sheet, avoid surface scratches and cracks caused by excessive friction. After rolling, cool the molybdenum sheet in air slowly, do not use water cooling, to prevent cracks caused by thermal stress.
3.5 Conduct Post-Rolling Annealing Treatment
Anneal the rolled molybdenum sheet at 900℃-1000℃ for 2-3 hours, then cool it to room temperature with the furnace. Annealing can eliminate the internal stress generated during rolling, refine the grain, and improve the toughness of the molybdenum sheet, thus reducing the possibility of crack expansion.
4. Cause Analysis and Solution of molybdenum sheet Wavy Edges
Compared with cracks, wavy edges are not fatal defects, but they will affect the flatness of the molybdenum sheet and cannot meet the requirements of high-precision applications (such as electronic components). Wavy edges refer to the phenomenon that the edges of the molybdenum sheet are curved up and down like waves after rolling.
The main cause of wavy edges is uneven deformation of the molybdenum sheet during rolling. Specifically, the deformation of the edge of the molybdenum sheet is greater than that of the middle part, or the deformation of the middle part is greater than that of the edge part. Why does this uneven deformation occur? There are three main reasons: uneven roller gap, inconsistent roller speed, and uneven temperature distribution of the molybdenum sheet.
However, it is worth noting that the uneven roller gap is the most common cause. Due to the long-term use of the roller, wear will occur, resulting in the middle part of the roller being slightly convex or concave, so that the gap between the upper and lower rollers is uneven. When rolling, the part with a larger gap has a smaller reduction rate, and the part with a smaller gap has a larger reduction rate, leading to uneven deformation and wavy edges.
4.1 Solutions to Wavy Edges of molybdenum sheet
According to the cause of wavy edges, the solution is mainly to eliminate uneven deformation. The specific methods are as follows:
First, check and adjust the roller gap regularly. Use a feeler gauge to detect the gap between the upper and lower rollers, ensure that the gap is uniform along the width direction of the roller, and the error does not exceed 0.01mm. If the roller is worn, it should be ground in time to restore the flatness of the roller surface.
Second, ensure the consistency of roller speed. Check the transmission system of the rolling mill regularly to avoid speed difference between the upper and lower rollers. If there is a speed difference, adjust the transmission ratio in time to ensure that the rollers rotate at the same speed.
Third, improve the temperature uniformity of the molybdenum sheet. When heating the molybdenum blank, use a uniform heating furnace to ensure that the temperature of each part of the blank is consistent, and the temperature difference does not exceed 20℃. This can avoid uneven plasticity caused by uneven temperature, thus reducing wavy edges.
5. Case Comparison: Effect of Different Solutions on molybdenum sheet Defects
To verify the effectiveness of the above solutions, we selected two manufacturers (Project A and Project B) with the same production scale and equipment for comparative experiments. Both manufacturers mainly produce molybdenum sheet with thickness of 0.3mm-2mm, and both have serious crack and wavy edge problems. The experimental period is 3 months, and the results are shown in the following table:
Indicators | Project A (Before Improvement) | Project A (After Improvement) | Project B (Before Improvement) | Project B (After Improvement) |
|---|---|---|---|---|
Crack Rate (%) | 18.6 | 2.3 | 17.9 | 2.1 |
Wavy Edge Rate (%) | 22.3 | 3.5 | 21.7 | 3.2 |
Product Qualification Rate (%) | 65.2 | 94.8 | 66.5 | 95.1 |
Production Cost per Ton (USD) | 8900 | 7200 | 8850 | 7150 |
We team found in the 2025 case that both projects achieved significant results after adopting the solutions proposed in this article. The crack rate and wavy edge rate were reduced by more than 85%, the product qualification rate was increased by nearly 30%, and the production cost per ton was reduced by about 19%. This fully shows that the solutions we proposed are scientific and practical, and can effectively solve the problem of molybdenum sheet rolling defects.
6. Common Misunderstandings in molybdenum sheet Rolling Defect Treatment
Warning: These misunderstandings will make the defect problem worse!
1. Blindly increasing the reduction rate to improve production efficiency. Many manufacturers want to shorten the production cycle, so they increase the single reduction rate to more than 20%, which leads to excessive deformation of the molybdenum sheet and a sharp increase in crack rate.
2. Using water cooling to speed up the cooling rate after rolling. Molybdenum sheet has poor thermal conductivity. Water cooling will cause a large temperature difference between the surface and the inside, generate large thermal stress, and lead to cracks.
3. Ignoring the lubrication effect. Some manufacturers think that lubrication only affects the surface finish, but in fact, insufficient lubrication will increase friction, cause uneven deformation, and lead to both cracks and wavy edges.
7. Practical Inspection Checklist for molybdenum sheet Rolling Defect Prevention
To help manufacturers better prevent rolling defects, we have formulated a practical inspection checklist. It is recommended to check item by item before and after rolling to ensure the stable quality of molybdenum sheet.
- Before rolling: Check the impurity content of the molybdenum blank (≤0.05%), check the flatness of the roller, check the uniformity of the roller gap (error ≤0.01mm), and check the heating temperature of the blank (700℃-850℃).
- During rolling: Check the rolling speed (0.5m/s-1.0m/s), check the lubrication status (uniform coating of lubricant), check the reduction rate (single ≤15%, total ≤80%), and check the surface condition of the molybdenum sheet in real time.
- After rolling: Check the surface of the molybdenum sheet for cracks and scratches, check the flatness (no wavy edges), check the thickness uniformity (error ≤0.02mm), and conduct annealing treatment (900℃-1000℃, 2-3 hours).
8. Conclusion: Key to Improving molybdenum sheet Rolling Quality
In summary, cracks and wavy edges in molybdenum sheet rolling are mainly caused by raw material defects, unreasonable process parameters, and equipment problems. To solve these problems, we must start from the source: strictly control raw material quality, optimize rolling process parameters, regularly maintain equipment, and strengthen process inspection.
Molybdenum sheet is a high-value-added material, and the control of rolling defects is crucial to improving product competitiveness. The solutions and operation guides proposed in this article are based on a large number of practical cases and data, which are highly operable. We believe that as long as manufacturers strictly follow these methods, they can effectively reduce the occurrence of rolling defects, improve product qualification rate, and reduce production costs.
In the future, with the continuous development of rolling technology, we will continue to explore more efficient and economical defect control methods to promote the healthy development of the molybdenum sheet industry.