Studying and investigating the identical rolling process in the angular channel of two-layer explosion-welded copper steel sheet

Master's degree thesis

Abstract

With the advancement of technology, the need to use new materials is felt. New methods have been developed to make new materials. Among the new materials in progress, we can mention double-layer sheets. These materials have composite properties of composite materials. The purpose of this research is to produce a double-layer sheet of 304L stainless steel and pure copper and to improve the mechanical properties of this sheet by using the uniform rolling process in the angled channel, which is one of the methods of severe deformation [1]. For this purpose, at first the double-layer sheet is produced through explosive welding [2], the samples matching the dimensions of the mold of the matching rolling machine are prepared in the angled channel. In the continuation of the process, mechanical work is done in different passes and the mechanical properties of the samples are examined and the results are analyzed. This method shows the increase of microhardness at different points of the cross-section of the double-layer sheet and the strength and states that the mechanical properties improve with the increase in the number of passes. The number of passes has an optimal value that, by repeating the process for a number greater than this optimal value, a drop in mechanical properties is observed. This method provides a new process for improving mechanical properties.

Keywords: uniform rolling in an angled channel, severe deformation, explosion welding, micro-hardness, strength

1-1-Introduction

Metal plates are among the most used sections in engineering applications. In many cases, it is necessary for the inside and outside of the screen to be placed in different environmental conditions, as a result, the two sides of the screen should have different characteristics. For example, one side of the plate is in the conditions of high working temperature or corrosive environment, while the other side of the pipe requires malleability and impact resistance as a structural component. It is obvious that such materials are difficult to find in the industry. Therefore, it seems necessary to combine and connect metals with different materials to create components with different characteristics. Bimetallic plates are widely used in various cases such as military, nuclear, petrochemical, chemical industries and also for applications such as boilers and converters. Connecting metals such as copper, aluminum, stainless steel, bronze, titanium, etc. to each other and the production of a composite sheet covers a wide range of structures required in related industries.

Improving the mechanical properties of materials can also be useful to a large extent in solving industry problems. One of the ways to strengthen the material is to reduce the grain size in the material. For this purpose, extreme plastic deformation processes can be used. Among these processes, the process of pressing in equal-angle channels and rolling in equal-angle channels, which is suitable for metal sheets.

One ??of the important things in the industrial use of materials is the strength and hardness and the desired lifespan of the materials, which leads to the lowering of the high costs of maintenance and repairs of equipment. Extreme plastic deformation is one of the methods of creating a nanostructure of fine grains and increasing the mechanical properties of metals. The uniform rolling process in the angled channel as one of the methods of plastic deformation leads to an increase in the hardness and strength of the parts produced from these sheets. According to the research conducted to investigate the uniform rolling process in the angled channel in multilayer composite sheets, factors such as friction, strain, strain rate, geometry, material properties and process speed should be investigated. In this way, based on the existing research, the research hypotheses are considered as follows:

There is a possibility of uniform rolling in the angled channel of the copper-steel double-layer sheet.

Performance of the uniform rolling process in the angled channel will reduce the size of the grains in the copper-steel double-layer sheet.

Execution of the process Uniform rolling in the angled channel will increase the strength and hardness of the copper-steel double-layer sheet.

1-2-Research objectives and statement of the problem

According to the subject of the research and previous research in this field in order to achieve a suitable and practical model, the objectives will be pursued as follows:

The process of uniform rolling in the angled channel is one of the processes of severe deformation, which is used to improve the mechanical and metallurgical properties of metal sheets. is placed Also, today, the use of multi-layer metal sheets is considered by researchers and industries due to the combination of different properties. Therefore, in this research, we investigate the identical rolling process in the angular channel of copper-steel double-layer sheets, and the following are investigated:

Changes in the strength of the samples

Changes in the hardness of the samples

Changes in the microstructure of the sheets due to the identical rolling process in the channel Angled

1-3-Research Background

Siegal et al. first introduced the equal pressing process in the angled channel as one of the extreme deformation methods that has the ability to fine-grain the structure in the micrometer range and in some cases the nanometer range, in 1970. But it was in the early nineties that this method was recognized as one of the effective methods for fine-grained coarse materials and obtaining suitable mechanical properties.

Azushima et al. have summarized and reviewed the methods of creating extreme plastic deformation to obtain very fine crystal grains. As a result, with this review, a complementary method was provided to create better properties. Reducing the grain size leads to an increase in yield stress and a decrease in ductility, so annealing process can be applied to increase ductility. Since the extreme plastic deformation method can create a nanometer microstructure in all metals that have a good deformability, the efficiency of this process can be increased by producing larger molds and using more. Kavacaj et al. In this research, the tested material is made of copper and strain, strain rate, temperature and stress were investigated for different mold angles. Also, the effect of friction and mold angle on stress, strain, strain distribution and inhomogeneity, shear deformation and torque on the rollers were investigated. The results showed that torsional deformation occurs for mold angles from 90 to 120 degrees, and it was also found that the strain decreases with the increase of the mold angle. In general, it can be concluded that all parameters decrease with the increase of the die angle.

Azimi et al., investigated the effect of different passes of the identical rolling process in the angled channel on the mechanical properties of aluminum 1100. These researchers reported that in the first pass of the process, the strength and hardness increase significantly and the malleability decreases. It was also reported that by applying more than 4 passes of the process, surface cracks are seen in the samples, which reduces the mechanical properties.

Park et al. These researchers reported that the outer part of the sample shows a grain pattern bent by shear deformation during uniform rolling in an angled channel, while the undeformed part of the sample shows initial graining perpendicular to the rolling surface. Except for the lower part of the sheet, which shows the curved graining, where the geometrical effects of the mandrel and the matrix alternately affect it, the maximum cutting angle, ?, is equal to 42 degrees.

Talebian et al. investigated the production of aluminum and steel multilayer sheets through severe deformation caused by rolling. These researchers reported that if the intermetallic compound created has a suitable thickness, a double or multilayer metal with suitable strength can be produced. It has been reported that the thickness of the intermetallic compound formed between aluminum and steel increases with increasing annealing time and temperature. Also, applying more plastic deformation causes strengthening and the possibility of achieving higher strength