SU1520140A1 - Steel - Google Patents

Abstract

The invention relates to the field of heat engineering, in particular, to methods of chemical-heat treatment of products, for example, their cementation and carbonitriding, and can be used in the engineering, aviation, automotive industry. The aim of the invention is to intensify the saturation process and reduce the consumption of endogas. The method of chemical heat treatment of products in continuous furnaces involves heating, saturating the surface layer, diffusion aging, and cooling before quenching using recycling of the process atmosphere at all stages of the process of chemical heat treatment. In the heating stages from 1000 K to the temperature of the cementation process and pre-quenching, the process atmosphere is circulated at a speed of 2.0-5.0 m / s, while the carrier gas is fed at the heating, saturation and diffusion holding stages. t at the time of loading and unloading of products. 1 tab.

Description

The invention relates to heat engineering, in particular, to methods of chemical-heat treatment of products, for example, their cementation and carbonitriding, and can be used in the engineering, aviation, automotive, tractor industry and in a number of other areas of national economy.

The purpose of the invention is to intensify the process of chemical heat treatment of products and reduce the consumption of endo gas.

With the method of chemical heat treatment of products in continuous furnaces, including heating, penetration of the surface layer, diffusion drain and cooling before quenching using technological atmosphere recirculation, when heated from 1000 K to the temperature of cement and heating before hardening, circulation of the technological atmosphere performed at a speed of 2.0-5.0 m / s. This makes it possible to drastically reduce the supply of fresh technological atmosphere, endogas oco6etfHo.

The proposed method of chemical heat treatment of products is carried out as follows.

In the space of the cementing (carbonitriding) furnace the fan

Yu

rys or other means of circulation of the technological atmosphere are established only in the heating and pressure zones in the intervals of specified temperatures or in the region of a controlled decrease in the surface concentration of the carburizer. The working space of the heated furnace is filled with a technological atmosphere consisting of a gas carrier and a carburizer. Products, for example, piston pins, loaded onto pallets with devices in the form of separate cages, are received from a external conveyor through a loading platform into the heating zone of the furnace working space at a specified time interval. The products are heated in technological-atmospheric streams circulating also near the surface of heaters and walls of the working space, which helps to level the temperature of parts (over the cross section of each charge. I Intensive circulation of the atmosphere

at the stage of heating in the region of existence. the creation of the changing gradient of the carbon potential of the atmosphere near the surface I of the products is accompanied — I C1 — a sharp acceleration of the restoration of the composition and the carbon-revitalizing capacity of the technological atmosphere. reduction of deviations in the mass of the hardened layer.

After the maximum saturation of the surface layer of the products, their heating is completed. At the stage of diffusion exposure, the intensity of carbon transfer across the gas – metal interface is 2-3 orders of magnitude lower than at the first stage and does not depend on the rate of circulation of the atmosphere by the technology. Flows of the circulating atmosphere from the heating zone flow into this zone, preventing the formation of local stagnant volumes of the technological atmosphere, since the pressure of the working space that separates the heating, cementation and diffusion exposure zones has been eliminated.

After the diffusion aging and the formation of a cemented layer from a predetermined thickness, the pallets with the products fall into the pressing zone, separated by the regime. This hundred

.

Q j JQ 25

50

55

thirty

35

40

45

Chemical heat treatment is carried out in a technological atmosphere flow circulating at a speed of 2.0-5.0 m / s, which ensures a stable value of the concentration of the carburizer on the surface of all products and the uniformity of the temperature of the charge before unloading.

The gas inlet is located in the heating zone and the technological atmosphere is discharged through the unloading platform onto the candle.

When the circulation rate of the technological atmosphere decreases in the process of heating below 2.0 m / s, the convective heat transfer from heaters to products located in the center of the charge box decreases and their heating slows down. This leads to an increase in the temperature differential across the load cross section and accelerated soot formation at cooler points of the charge shifted to the diffusion saturation zone.

Due to the increase in the duration of heating of some products and the background of the beginning of the carburizing process, deviations in the carbon content of the layer and thickness of the carburized layer increase. In addition, the fflepatypa surface of the heaters increases and the service life decreases, the deviations in the composition of the technological atmosphere of the furnace increase. The lower the recycling rate of the technological atmosphere of the furnace, the longer the recovery time of the composition of the technological atmosphere of the furnace.

In the deep (areas of the tank, where circulation due to local resistance is minimal or absent, the limiting erosion of the product surface does not correspond to the average carbon potential, but to the local composition of the technological atmosphere, and may last for an order of magnitude longer, contributing to additional slowing down of the process and increasing scatter on the quality of the carburized layer. In order to accelerate the carburization process, these products increase the supply of the carburizer, which contributes to a further deterioration in the quality va thermochemical processing acceleration sooting in cold areas congestive inactive atmo sphere, shorten the life of the heaters,

The table shows the comparative data of research in the implementation of the known and proposed methods.

Example 1 The working space of the grouting furnace is filled with the technological atmosphere. The fans are located in the heating and cooling zones. Subsets with piston fingers, placed on them in the form of separate cages, enter through the charging platform into the heating zone of the furnace with a specified time interval. The technological atmosphere circulates both around the load and near the surface of the heaters and the walls of the working- 5 atmosphere at the heating stage of 3.0 m / s, the circulating speed at the cooling stage - 1.5 m / s. of the technological atmosphere in the Dusty 1 furnace; s unevenly cooled by volume during the heating stage is 1.5 m / s, the cage, as the heat transfer from the cooling stage is 3.0 m / s. The circulating flow of technological atmosphere washes every cage in

the center of the cage is difficult (both by radiation and convection). In the process of pressing during the opening of the discharge valve, the composition of the technological atmosphere is periodically disturbed, and its speed of recovery is low,

directed transverse to its movement through the furnace.

When the circulation speed of the technological atmosphere at the heating stage is 1.5 m / s, the co-efficacy decreases on heat transfer from the heaters to the fingers, located both in the center of the charge and in its lower part, which leads to a slower heating, increasing the differential temperatures across the cage cross section and additional soot formation on colder fingers.

Slowing up the heating process also leads to a lag in the onset of carburization of the surface layer of cooler fingers, an increase in the deviation of carbon content and thickness of the carburized layer.

The slowing down of the circulation of the technological atmosphere in the heating zone affects the saturation zone and leads to a slower recovery of the composition of the technological atmosphere in both the heated zone and the saturation zone.

In order to speed up the carburizing process, it is necessary to increase the supply of the carburizer, which leads to a deterioration in the quality of chemical heat treatment, or to reduce the number of products of each charge supplied to the grouting furnace.

Example2. In contrast to the cementation conditions described in Example 1, the grinding rate of the process atmosphere in the furnace at the heating stage is 5.5 m / s. Accelerating the carburizing process

no layer is observed. However, to increase the rate of circulation, it is necessary to install a more powerful fan, which leads to a significant increase in energy costs, complication and cost of construction.

Example 3. Placed in a furnace set-ups with piston fingers after the completion of the processes of heating and diffusion saturation enter the stage of cooling before quenching. Technological circulation rate

the atmosphere at the stage of heating is 3.0 m / s; at the stage of cooling, 1.5 m / s. Paly1; s cool unevenly in terms of the volume of the charge, since the heat transfer from

the center of the cage is difficult (both by radiation and convection). In the process of subatmosphere at the stage of heating 3.0 m / s, at the stage of cooling, 1.5 m / s. Paly1; s cool unevenly in terms of the volume of the charge, since the heat transfer from

quenching when opening the discharge valve periodically disrupts the composition of the technological atmosphere, and its speed of recovery is low,

therefore, part of the products undergo partial decarburization. As a result of chemical heat treatment in an atmosphere of unstable composition and quenching with uneven volume

The cages with the temperature of the product have variations in the volume of the cage both in% C (0.3% C and above) and in hardness.

And Figure 4. The excess of the circulation speed of the technological atmosphere near the surface of the piston pins 5.0 m / s and no longer allows to evaluate the quality improvement efficiency, since the deviation in carbon concentration on the surface of products at the circulation speed of 2-5 m / s does not exceed 0.05% C, and products processed in bulk in baskets are about 0.1% C due to the sufficient rate of restoration of the composition of the technological atmosphere. At the same time, the uniformity of XI-mikro-thermal processing of products in the bulk of the charge does not exceed the specified values, and the complexity of the design of the device for recycling SII and an increase in energy consumption leads to an increase in production costs.

Invention Formula

The method of gas cementation of steel products, including heating, diffusion saturation with endogas regulation, cooling and subsequent

quenching, characterized in that, in order to intensify the process and reduce the consumption of endogas, at the pressing stage, endogasis is recycled at a speed of 2.0-5.0 m / s.

tion

40 34 39.7

38 34

22.0 22.0 31

28.0

58.0

5-8 5-8 3.3-4.0

0.71-0.90 0.14

Editor I. Derbak

Compiled by I. Petrov

Tehred L. Serdyukova Proofreader T.Paly

Order 6727/31

Circulation 942

 VIIIPI State Committee for Inventions and Discoveries at the State Committee for Science and Technology of the USSR PZOZZ, Moscow, Zh-35, Raushsk nab. 4/5

0,003 0,004 0,5

0.5 0.5

0.003 0.004 0.004

0.5-1.5 2.0-5.0

Subscription

Claims (1)

Claim The method of gas cementation of steel products, including heating, diffusion saturation with regulation of endogas, curing and subsequent hardening, characterized in that, in order to intensify the process and reduce endogas consumption, in the curing step, the endo gas is recycled at a rate of 2.05.0 m / s Way HTO time, h The volume of the furnace, m ³ Endoguea Consumption Forced recirculation rate of the process atmosphere, m / s Relative "D Actual U _r , and ³ In the process of diffusion During heating and saturation of the surface Famous 1 40 22.0 5-8 110-160 0.003 0.003 2 34 22.0 5-8 140-160 0.004 0.004 Before modernization 39.7 31 3.3-4.0 100-125 0.5 0.004 Proposed 1 " 38 28.0 0.71-0.90 20-25 0.5 0.5-1.5 2 34 28.0 0.14 4.0 0.5 2.0-5.0 Compiled by I. Petrov Editor I. Derbak Tehred L. Serdyukova Corrector T. Paly Order 6727/31 Circulation 942 Subscription V11IIPY State 113035, Committee for Inventions and Discoveries at the State Committee for Science and Technology of the USSR Moscow, W-35 ^z , Raushskaya nab., 4/5 Production and Publishing Plant Patent ¹ ', Uzhgorod, st. Gagarina, 101