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Rollers processed using powder metallurgy for asymmetric and traditional rolling of sheet metals
Section 5. Materials Science
DOI: http://dx.doi.org/10.20534/ESR-16-9.10-43-44
Djalalova Sevara Tukhtamuratovna, Senior teacher, the Faculty of Mechanics and Machine building
E-mail: kudratg@mail.ru Bakhadirov Kudratkhon Gayratovich, Tashkent State Technical University, Senior scientific researcher, the Faculty of Mechanics and Machine building E-mail: bahadirov@gmail.com
Rollers processed using powder metallurgy for asymmetric and traditional rolling of sheet metals
Abstract: In the article two different sintered alloys provided as options for increasing mechanical and other properties of rollers for asymmetric and traditional rolling of sheet metals. Martensitic steel AISI 440C and hard alloy Mo-TiC-Ni-W-Fe composition properties have been provided.
Keywords: rolling metal, sheet metal, hardness, material properties, microstructure.
The development of the metallurgical industry and metal forming is inextricably linked with the solution of topical scientific and technical issues of practical importance.
First, is the creation of sheet materials with increased performance and improved properties, structure, surface quality and accuracy of product dimensions. In this regard, an important role is played by rolling sheet metal using asymmetry development of modern high-performance, cost-effective manufacturing processes.
Reliability and performance tools Rolling mills are mainly determined by the state of their working bodies, which are the most wear. Measures to improve the durability due to high speed of the output system. This is due to severe working conditions due to heavy abrasion and heat. Today produced tool does not meet the requirements imposed on them. Currently, obtaining carbide tools from new alloys and powdered materials in the conditions of our country is relevant and has a scientific and practical importance [1].
Increased durability of tools is one of the basic and effective ways of increasing the service life of, in particular, the use of new materials. This would improve the quality of the tools is guaranteed, and at the same time, the need to cover the mills of the Republic of Uzbekistan due to increased longevity.
In particular, the preparation of the instruments local raw instrument greatly reduces costs and simplifies the process [2].
The studies have shown that one of the main tasks of the work was the choice of materials from local raw materials for the roller asymmetric and traditional rolling of sheet metal. Creating a new type of unit for the asymmetric rolling, which significantly increases the performance of the target material and the target product with high quality output.
Sintering processes can be divided into two basic types: solid state sintering and liquid phase sintering. Solid state sintering is carried out at a temperature at which the powder compacts complete sealing is achieved completely in the solid state, while the liquid phase sintering occurs when the liquid phase is present in the powder compact during sintering [3]. Liquid phase sintering is becom-
ing increasingly popular because of the time reduction sintering and thus its cost and performance advantages. It is widely used in the process of sintering of steels, tungsten carbide, hard alloys and superalloys. It is estimated that more than 70% of the sintered products processed by this method [2].
Sintered parts made of stainless steel are an important and growing segment of the industry of powder metallurgy. stainless steel powders were chosen to replace the powder metallurgy of ferrous alloys — for their superior characters such as corrosion resistance, oxidation resistance, wear resistance and mechanical properties (ductility and impact strength) [4].
Alloy interest in this work — AISI 440C (95X18 brand chromium steel), is a martensitic stainless steel family. The composition of the martensitic stainless steel such that they are able to transform into martensite. Due to the high hardenability inherent in these alloys, the quench rate needed to achieve the martensite is not high. Water and oil quenching are only used when working with thick sections. Typical formulations range from 12 to 18 wt% chromium (Cr) and from 0.1 to 1.2 wt% C. [5].
Alloy AISI 440C, in particular, a high content of carbon, straight chromium, high hardenability of a martensitic stainless steel has a good corrosion resistance in soft household and industrial applications, including fresh water, organic materials of weak acids of various petroleum products, in combination with an extremely high strength, hardness and abrasion resistance when in the hardened and tempered condition. It is used for parts requiring a combination of excellent wear resistance with moderate corrosion resistance. Typical applications are: ball bearings, camshafts, bushings, cutlery, chisels, knife blades, pump parts, surgical instruments, valve seats and other parts, which are requirements of high hardness and wear resistance, and operating at temperatures up to 500 0 C or have been exposed moderate corrosive environments. Low deformability of the group steels, however, significantly limits the applicability of the forged version [6]. This failure can be easily overcome by powder metallurgy (P/M) and metal injection molding (MIM) processing
Section 5. Materials Science
route, because of their ability to almost pure form. Full seal, however, is necessary to obtain optimal properties of structural parts.
The end result is the development of PM AISI 440C steel with high hardness, and minimal shrinkage moderate corrosion resistance in a cost effective manner.
To achieve this goal, the software used Thermocalc for the thermodynamic simulation and Taguchi method. Thermocalc software is a complete thermodynamic software that allows you to predict the material composition, structure and properties arising from a variety of materials processing. Therefore modeling using the program can produce phase diagrams, which are useful in determining the optimal combinations of these parameters that can produce the desired results [7].
Preliminary results obtained from the test samples of steel (AISI 440C with 1.2wt% C) previously sintered at Sintex a/s formed the core of the approach adopted for solving research problems. Sam-
ples were pressed at a pressure of550MPa and sintered at 1170 and 1 220 0 C respectively. On 500ppm boron in the form of FeB it was added to the liquid phase sintering agent. The samples sintered at 1220 o C was too much of the liquid phase and therefore appeared distorted. On the other hand, the samples sintered at 1170 o C had a very high density of about 7.63g/cm 3 and a surprisingly high hardness — 54HRc. While these values are within acceptable limits of these steels, the corrosion resistance, as defined in the cabinet saline was very poor. we had to determine a high degree of chromium depletion as a possible cause for the very poor corrosion properties of test steel Based on a review of results from Sintex A/S vis various literature. The optical micrograph of the samples sintered at 1170 o C (Fig. 4.1) clearly shows the presence of large amounts of carbides around previous austenite grain boundaries. These carbides are usually in the form of M 23 C 6 and M 7 C 3 chromium deplete the grain boundaries of the area around.
Figure 1. Optical micrograph of the test samples of steel AISI 440C, sintered at 1170 0 C
We consider the results of studies on the choice of local raw material for asymmetric and traditional rolling of sheet metal. In order to improve the technological and operational characteristics of the experimental unit it is recommended to use clips from the new production of molybdenum — titanium alloy.
At the choice of the local raw material for the work roll asymmetric and traditional rolling of sheet metal shown that materials obtained by sintering of refractory metal powders meet the requirements imposed on the rollers of rolling mills.
Sintering operation ensures that the powder particles are strongly coupled and that the doping is achieved better. Sintering is typically conducted in a reducing atmosphere in order to protect the surface of the powder against oxidation and possibly to reduce any existing oxides formed during atomization and processing. Commonly used for the sintering atmosphere, hydrogen, carbon monoxide, nitrogen and ammonia.
Powder metallurgy is a key component process of making porous, refractory materials, composite materials, high-strength alloys and special structural elements [8] listed below:
• Porous materials
• Refractory metals
• Special high-strength alloys
• Composite materials
• Structural parts
In order to improve the technological and operational characteristics of the experimental unit is proposed to use clips from the new production of molybdenum — titanium alloy (Table). Table 1. - The chemical composition of the sintered alloy of molybdenum system Mo-TiC-Ni-W-Fe
Content, wt.%
TiC Fe Ni W Мо
60-62 3,5-4,0 20-22 3,5-4,0 rest
Microstructure systems sintered Mo-TiC-Ni-W-Fe alloy molybdenum examined using metallographic microscope MIM-8 and a scanning-electron microscope SEM 200. Microsections Preparation was carried out in accordance with known methods.
References:
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