RU2171159C2 - Method of production of structural wear-resistant powder steel - Google Patents

Abstract

FIELD: powder metallurgy. SUBSTANCE: method includes preparation of powder mixture of components included in steel composition; pressing of mixture in closed mold to obtain porous briquette; heating of porous briquette in protective atmosphere up to 1000- 1100 C and heat treatment by pressing. In so doing, introduced additionally into powder mixture is high- temperature fluorolignin in closed mold to attain residual porosity in it up to 7-17%. Subsequent heating of briquette is conducted at rate of 15-25 C/s and held at this temperature for 7- 17 min. EFFECT: higher wear resistance of produced structural wear-resistant steel. 6 tbl, 1 ex

Description

 The invention relates to powder metallurgy and, in particular, to methods for manufacturing high-density non-porous structural powder steel for general engineering purposes with improved machinability.

 A known method of obtaining structural wear-resistant powder steels (Dorofeev YG Dynamic hot pressing of porous powder billets. - M .: Metallurgy, 1977), including the operation of preparing a powder mixture of the components that make up the steel; pressing the powder mixture of the components included in the steel, pressing the powder mixture to obtain a porous briquette with a residual porosity of 20-30%, sintering the briquette in a protective atmosphere for 40-60 minutes, hot pressure treatment of the heated briquette to obtain a non-porous material.

 Steel obtained by this method has high physical and mechanical properties: tensile strength 300-400 MPa, hardness 60-120 HRB. Steel obtained in this way has low wear resistance.

As a prototype, a method has been adopted for producing powder wear-resistant structural steels (Yu.G. Dorofeev "Dynamic hot pressing of porous powder billets", M .: Metallurgy, 1977), including the steps of preparing a powder mixture of the components that make up steel, pressing the powder mixture in closed a mold to obtain a porous briquette with a residual porosity of 20-30%, heating the briquette in a protective atmosphere for 7-15 minutes at a temperature of 1000-1100 ^o C, which corresponds to a heating rate of 1.1-2.6 ^o C / min, hot processing q by heating heated briquette to obtain non-porous material. The steel obtained by this method has high physical and mechanical properties, which, depending on the composition of the steel, vary in the range: tensile strength 290-390 MPa, hardness 60-120 HRB. However, the steel obtained by this method has low wear resistance.

 The authors were faced with the task of increasing the wear resistance of structural powder steel by alloying it with a high-temperature polymer.

The problem is solved in that a high-temperature polymer is additionally introduced into the powder mixture of the components that make up the steel, which is used as fluorine-lignin in an amount of 2.0-10.0 wt.%. Then the powder mixture is successively pressed in a closed mold to obtain a porous briquette with a porosity of 7-17%, heating this briquette in a protective atmosphere with a heating rate of 15-25 ^o C / s to 1000-1100 ^o C and incubated for 7- 17 minutes

 To prevent intense burnout of high-temperature fluorine lignin, the porous powder briquette is more dense, with a residual porosity of 7-17%. With such residual porosity, the number of open pores in the briquette sharply decreases, the cross section of open pores narrows, and, as a result, the fluorine lignin burnup is negligible.

 The introduction of fluorine lignin helps to obtain a dense briquette, because reduces friction between particles of iron powder.

When a porous briquette is heated before hot pressure treatment in a protective medium in the range of 1000-1100 ^o C, the high-temperature fluorine-lignin polymer decomposes into its constituent elements. Hydrogen, released, interacts with oxides, reducing them, carbon and fluorine interact with particles of steel powder, forming on their surface a shell of carbide (cementite) and iron fluoride, which increase both the hardness and strength of the surface of the particles. In this case, the plastic properties of the particles themselves remain high. Thus, the decomposition of fluorine lignin creates the conditions for the formation of a compact structure characterized by high strength characteristics, increased hardness and wear resistance without reducing plastic properties.

 The essence of the invention is illustrated by an example implementation of the method, which consists in carrying out the following operations.

 1. Preparation of a powder mixture from iron powder ПЖВ 2.160.26 GOST 9849-86 and powder of a high-temperature polymer fluorine-lignin 2-10 wt.%.

 2. Pressing the powder mixture in a closed mold to obtain a porous briquette with a residual porosity of 7-17%.

3. Heating the briquette at a speed of 15-25 ^o C / s to a temperature of 1000-1100 ^o C in a protective atmosphere, holding it at this temperature for 7-17 minutes.

4. Hot pressure treatment by the method of precipitation in a closed mold with a value of the specific reduced work of the seal 220-250 MJ / m ³ .

 The test results of steel samples obtained in accordance with the proposed method are presented in table. 2-6.

 The properties of powder steel significantly depend on the used iron powder, therefore, to compare the physicomechanical properties, samples were made of iron powder ПЖВ 2.160.26 GOST 9849-86 according to the prototype method. In the table. 1 shows the results of testing samples made by the prototype method.

 From the above data it follows that when the content of the high-temperature polymer fluorine-lignin is less than 2 wt.%, The wear resistance is not better than that of the prototype, and if it contains more than 10 wt.%, The mechanical properties are worse than that of the prototype.

 When the content of the high-temperature polymer fluorine-lignin in the range of 2-10 wt. % physical and mechanical properties are better than that of the prototype, and wear resistance is 2.5-4 times higher. Thus, the amount of the introduced high-temperature fluorine-lignin polymer in the range of 2-10 wt.% Should be considered optimal.

 To determine the optimal residual porosity of the preform according to the above technology, samples were obtained for the residual porosity of 5 to 20%. The test results of the samples are given in table. 3.

 From the above data it follows that with a residual porosity of less than 7%, the physical and mechanical properties are worse than that of the prototype, and with a residual porosity of more than 17%, wear resistance is at the level of the prototype. With a residual porosity of 7-17%, the physical and mechanical properties are better than that of the prototype, and the wear resistance increases by 3-4.5 times. Thus, the residual porosity of 7-17% should be considered optimal.

To determine the optimal heating rate, samples were obtained according to the above technology at different heating rates of porous briquettes from 10 to 30 ^o C.

 The test results are given in table. 4.

From the above data it follows that at a heating rate of less than 15 ^o C / s, the wear resistance is not better than that of the prototype, and at a heating rate of more than 25 ^o C / s, a deterioration in physical and mechanical properties is observed. When the heating rate is in the range of 15-25 ^o C / s, the physicomechanical properties and wear resistance are better than that of the material obtained by the technology adopted as a prototype. Thus, the optimal should be considered a heating rate of 15-25 ^o C / s.

From the table. 5 shows that the optimal heating temperature is the interval 1000-1100 ^o C.

 From the table. 6 shows that the optimal exposure time is a time interval of 7-17 minutes

Exposure at a temperature of 1000-1100 ^o C is necessary so that the carbon and fluorine formed during the decomposition of fluorine lignin diffuse into iron powder particles. When holding for less than 7 min, diffusion does not occur completely. When holding for more than 17 min, the diffusion of carbon and fluorine deep into the powder leads to depletion of its surface layers, which results in deterioration of the mechanical characteristics of steel. Additional saturation of the surface layers with carbon and fluorine does not occur, because fluorine lignin decomposes completely during this time.

Thus, from the test results of the prototypes it became clear that the optimal modes of the method are as follows:
- the amount of introduced high-temperature polymer fluorine-lignin 2-10 wt.%;
- pressing a porous briquette with a residual porosity of 7-17%;
- high-speed heating briquette 15-25 ^o C / s.

 As can be seen from the description, the proposed method has an inventive step. Thus, the test results obtained allow us to judge the high wear resistance of powder structural steel while maintaining high physical and mechanical characteristics.

 A patent information search showed that objects with a combination of the main distinguishing features of the proposed method were not found.

Claims (1)

The method of obtaining structural powder wear-resistant steel, which consists in preparing a powder mixture of the components that make up the steel, pressing the mixture in a closed mold to obtain a porous briquette, heating it in a protective atmosphere to 1000-1100 ^o C and hot pressure treatment to obtain a non-porous material, characterized in that the high-temperature polymer fluorine-lignin in an amount of 2-10 wt. %, pressing the briquette of the powder mixture in a closed mold is carried out until porosity of 7-17% is reached, and its subsequent heating to 1000-1100 ^o C is carried out at a speed of 15-25 ^o C / s and the briquette is held at 1000-1100 ^o C within 7-17 minutes

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