SU804187A1 - Method of producing castings - Google Patents

Description

(54) METHOD FOR GETTING CASTINGS

one

The invention relates to destructive production, mainly to the manufacture of parts (metalworking equipment, and can be used in the manufacture of castings, operating under conditions of thermal and mechanical and mechanical loads, such as molds of open-hearth furnaces.

The technological process of producing such castings involves the manufacture of the mold and the pouring of molten steel into it. In order to eliminate casting defects of shrinkage — threefold and increase in the mechanical properties of the metal, in the process of pouring the mold, microcoolers are introduced into the melt — metal shot. The metal of such castings is characterized by increased mechanical and service properties in connection with the favorable growth of microcoolers on the crystallization process. For example, the introduction of iron powder PZH-1K, PZH-2K or reduced

steel grit having an oxide-free surface makes it possible to obtain a quality structure and. mechanical properties approaching those of a deformable metal.

However, it is not possible to increase the duration of exploitation of Tasht castings operating under conditions of heat exchange.

Known crtoco6 production of steel castings with the introduction into the melt when pouring the microdes of iron coolers - iron powder PZH-2K in the amount of 1-2% 2.

In spite of this, it is not possible to increase the durability of castings, the volumes of which work under conditions of thermal cycles and mechanical loads.

As a rule, the volumes of parts experiencing significant mechanical loads are structurally quite massive and with a high margin of safety. However, the massiveness of the volume is contraindicated in the case of operation during warm weather. At the same time, due to high temperature gradients, thermal stresses arise from the volume of parts, which often lead to boxing, formation of traditionals, and their further intensive development to reject limits. Exceeding the thermal stress of the ultimate strength of the material accelerates the destruction of the part. The most sensitive to destruction is the interface areas of massive and thin-walled volumes in detail. In these cases, thermal cracks originate primarily and propagate deep into the material at almost the same speed as in the metal without introducing micro-refrigerators. The main reason for this material behavior is to maintain the same level of thermal conductivity and linear expansion coefficient and, accordingly, ypoBi current thermal stresses. The purpose of the invention is to increase the service life of castings by reducing the stresses acting at the interface of the thick-walled and thin-walled volumes, each of which is subjected to thermal and mechanical loads. This goal is achieved by the fact that in the method of obtaining castings, mainly muld open-hearth furnaces, including pouring the molten metal into the mold and introducing it into it. microcoolers, scale additionally introduced into the molten metal with a volume ratio of scale and microcaps (Ol-l): 10. Scale, mixed with liquid metal, decomposes and leads to the formation of cells - gas voids, uniformly distributed in the metal . Microcoolers, taking heat from a liquid metal to heat and melt, leading to the formation of centrv crystal in metal. talization and accelerate its crystallization. The metal most quickly crystallizes in the thin-walled areas of the casting. In these areas, the melt quickly solidifies and the gas cells formed are fixed. In massive areas, the metal is in the liquid state for a long time and gases in a significant amount have time to stand out, as a result of which, in solid areas subjected to mechanical stress, the metal solidifies. Thus, the metal of the thin-walled parts of the parts exposed to heat cycles, the shutter 874 has the presence of gas cells-voids, and the massive - monolithic. Since the thermal conductivity of a metal with gas void cells is lower than solid, the heat transfer at the interface between thin-walled and thick-walled volumes decreases dramatically and the strength characteristics remain high. Favorable conditions are created to reduce the rate of nucleation and growth of cracks, slowing down the destruction of the material, which leads to an increase in the duration of operation of parts. In the EXPERIMENTAL production, blanks are produced, ф 110 and 1 О mm high (without taking into account the height of profits) of 35 L. steel. The number of introduced refrigerators is 3% of the weight of the metal in the mold, and the size of the granules is 0.5-3 mm. Scale is introduced at a volume ratio of 1: 1 and 1: 1 micro-coolers and micro-refrigerators. The grain sizes of o7 saline are in the range of 0.2-1.5 mm. Samples in the form of rods f 1O mm and 150 mm high are made from metal of castings. One of the ends of the samples is heated in a shaft electric furnace with a temperature in the shaft of 1OOO C and at the same time the temperature of the ends of the samples is measured with a potentiometer with an accuracy of ± 5%. On the surfaces of the heated and opposite ends of the samples, hot junctions of chromel-alumel thermocouple thermocouple wires f 0.2 mm are welded. It was found that the temperature on the surface of a prototype cast from a metal according to the proposed method with the introduction of scale in a volume ratio with microcoolers 0.5: S is 84 O lower than the temperature on the surface of a control sample cast from a comparable metal. In this case, the temperature values (when the heated end is kept in the furnace for 180 seconds) for the test and control samples are 836 and 920 C, respectively, which is explained by the reduction of the effective thermal conductivity of the metal, depending in each case on the size of the check. the uniformity and frequency of their pattern.

The value of this coefficient is estimated by the formula

0 Я15-П5, .К) |

where 6T | sZx is the temperature gradient;

d - coefficient of thermal conductivity;

P is the number of cells;

. - cell uniform distribution coefficient;

5 - area c, with body;

 averaged cell area The temperature also affects the mechanical properties of the samples. Thus, for different values of temperature T, the values of stresses 6 g arising during deformations are also different. For example, for steel St ZO L at temperatures of 836 and 92 ° C, the values of, for example, Yarin 6b are in the ranges of 6.8-6.9 and 4.34, 4 kg / mm2, respectively. Thus, the mechanical / strength of metal products used in various conditions (heat shifts, mechanical loads) obtained by the proposed method increases almost 1.6 times, which determines the increased durability of the casting operation as a whole.

As indicated above, cell sizes should be defined and uniformly distributed in the volume. The size of a gas bubble cell is due to a complex of factors, the main factors of which include the size introduced with micro-refrigerated dross grains, and the characteristics of solidification of the melt. Practically, it has been established that the use of scale grains more than 1.5 mm thick for carbonaceous melts leads to the formation of coarse

903

.0.05: 1.0 878 0.1: 10

836

0.5: 10

gaseous voids, dramatically reducing the strength characteristics of the metal. Grains delicate less than 0.2 mm thick do not fully seize into the metal, as they are carried away by the upward flows of gas emitted from the metal rotating in the vortex funnel, which is necessarily used in suspension casting. When okashshi hit the liquid metal of 5-carbon steel, the reaction proceeds

sz g + | b rk C02,

which results in cells filled with gas. KogagchesteZo

The introduced scale is also important for the number of gas cells formed, their size and uniform distribution. So. entering insufficient or excessive amounts of

LINES lead to the formation of gas cells in such a way that the purpose of the invention cannot be achieved. In the first case, the number of gas cells formed is insufficient to have a significant effect on the change in the thermal conductivity of the steel and, therefore, on a dry scale, affect the random characteristics of the parts. The increased amount of scale leads to the emergence of a large gaseous gas shell and enhanced boiling of the metal.

In a unique way, what is the most satisfied predelak {and additionally introduced scale

in volume ratios with microcoolers, it is (0, G): 1O. The results of thermal conductivity of samples with different amounts of injected dross together with micro refrigerators are shown in the table.

1.6

Unevenly

More uniform - 2.4 but

4.9

Evenly

84

Claims (1)

Claim A method of producing castings, mainly of open-hearth furnace furnaces, comprising pouring molten metal into a mold and introducing micro nickel ₃₅ nickels into it, characterized in that, in order to increase the life of the castings, an additional amount of mill scale is introduced into the molten metal with a volume ratio of mill scale of ₄₀ kills ( 0.1-1): 10.