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6Сетевое издание Совета ректоров вузов Большого Алтая
UDK 669.017
DEVELOPMENT OF A COMPOSITION FOR DIFFUSION SATURATION WITH BORON AND CHROMIUM TOOL STEEL
V. A. Butuhanov, B.S. Tsydypov, I.A. Garmaeva The East-Siberian state university of technology and management (Ulan-Ude, Russia) butuhanov_vyacheslav@mail.ru; bulvin@rambler.ru; dambi59@mail.ru
In given article are considered working out of structure of a plastering for diffusive saturation by a boron and chrome of a stamp from a steel L6, and also a choice of an optimum mode of thermal processing of a sated detail. Possibility of elimination of fragility of diffusive layers was analyzed at boronizing by addition in structure of a plastering of carbide of chrome. Results on measurement of microhardness of the received diffusive layers are resulted.
The decision of problems of increase of reliability and durability of details and the tool, first of all, is connected with hardening of blankets of products. Diffusive chemikal-thermal processing (CTP) allows to receive a new layer different from a core on a product surface and to provide a complex of necessary properties -physical, chemical, mechanical, etc. In cases when hardening of separate sites of details is required, apply himiko-thermal processing from a plastering which is more effective in comparison with other ways CTP: powder, liquid etc. from a plastering it is possible to carry To perspective methods CTP boronizing, chromium plating and the combined process - boronchromium-plating. Boronizing has the purpose improvement of physical and chemical characteristics boridic layers possessing high fragility, insufficient corrosion firmness and heat resistance.[1]
The given work is devoted working out of a chemical compound for boronchromium-plating to a working surface of a stamp from a steel L6. As the supplier of active atoms of a boron carbide - B4C is used. As the supplier of active atoms of chrome it is used феррохром. As the mix activator chloride of ammonium NH4Q was used. Also the plastering structure included following substances: graphite and bentonite. Graphite prevents a plastering to a surface of a sated product. Bentonite is binding substance.
The plastering contains a following parity of components, %:
5) ammonium chlorid (NH4C1) 3.
Dissolved in water to a pastelike condition the plastering is put on a strengthened surface of a stamp by means of a brush. Drying on air is spent at room temperature within 24 hours for prevention of formation of cracks. Then drying follows at temperature 2000C within 2 hours for full removal of a moisture. Saturation from a plastering is carried out at heating of a detail to 1050°C with endurance during 3 hours.
1) ferrous chrome
2) boron carbide (В4С)
3) graphite
4) bentonite
20 57
15 5
Grand Altai Council of HEI Chancellors Network Edition
The temperature of saturation of details from a plastering, a component 1050°C, is optimum as at temperature more low 900°C there is mainly a process of boronizing that leads to decrease in adhesion of a diffusive layer to a surface of a sated product. At temperature 950 0C the thickness of the strengthened layer makes only 10 microns, and saturation temperature above 1100 ° for the majority of steels leads to grain growth under the strengthened layer that in turn leads to decrease in impact strength and plasticity of metal under the strengthened layer and to decrease in working capacity of the tool.
The optimum should consider duration of saturation - 3 hours as at this endurance the diffusive layer with working thickness about 160 microns is formed. The microstructure of a diffusive layer is presented in drawing 1.
After process of saturation by a boron and chrome the product is exposed to the thermal processing including training and holiday.
Training is made from saturation temperature (1050 0C) in technical oil. The choice of oil as cooling environment is optimum from the point of view of maintenance necessary properties both strengthened boronchromum-plating a layer, and basic metal adjoining to it. [2,3]
After training the product is exposed to tempering. The holiday temperature, a component 480-560°C, is optimum as the fullest removal of the residual pressure leading to raised fragility of strengthened layers and low plasticity of the strengthened detail as a whole is provided. At temperature of tempering, a component less 480°C, there is an incomplete removal of hardening pressure and probably incomplete course of structurally-phase transformations that leads to the raised fragility of layers and decrease in impact strength of a core of a detail therefore firmness of the strengthened product decreases also. At temperature of low tempering, a component more 560°C, the detail core has low hardness that leads to chopping off the strengthened layer and to decrease in a resource of a detail.
Time of tempering making 3 hours, it is necessary to consider optimum. At smaller time of tempering there is a risk of incomplete removal of hardening pressure and an embrittlement of a core of a product as a result of adverse structure owing to what there is a probability of an exit of a product out of operation while in service because of peeling of the strengthened layer or as a result of high propensity of a material of a product to a flow.
Microhardness of a diffusive layer after saturation by a pine forest and chrome at temperature 1050 0C within 3 hours makes 14490 MPa. Hardness of a core of a stamp - 2570 MPa.
Training and tempering on the chosen mode allow to raise hardness of a diffusive layer and a stamp core. Microhardness of a diffusive layer after training from saturation temperature in oil and the subsequent tempering at temperature nearby 500 0C makes 18920 MPa. Hardness of a core of a stamp on Rocwell makes 37 HRC (3620 MPa).
Conclusions. Complex saturation by a pine forest and chrome allows to lower microhardness and to raise adhesion of a diffusive layer to a tool surface. The structure of a plastering for diffusive boroncromium-plating steels L6 is
Сетевое издание Совета ректоров вузов Большого Алтая
experimentally developed. The mode the stamp processings, including training in oil from temperature of saturation and the subsequent tempering is chosen.
References
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