SU1312111A1 - Method for spheroidizing annealing of medium-carbon steels for cold upsetting - Google Patents

Abstract

The invention relates to ferrous metallurgy, in particular to the heat treatment of rolled products, and can be used for the manufacture of fasteners and other parts by cold heading. The goal is to increase the productivity of the process by speeding up spheroidization. The steel is heated to a temperature of 700–720 ° C, held for 30–35 minutes, then heated to a temperature of 755–765 ° C, and held for 20–25 minutes. Stirred with exposure at a temperature of 730-740 ° C for 15-20 minutes and at a temperature of 710-720 ° C for 80-100 minutes. The final preparation is carried out in air. 1 tab. g (L

Description

113

The invention relates to ferrous metallurgy, in particular, to thermal processing of rolled products, and can be used for the manufacture of fasteners and other parts using the method of cold heading,

The aim of the invention is to increase the productivity of the process by speeding up the spheroidization.

Exposure at 700-720 ° C during heating is performed in order to accelerate the subsequent spheroidization of cementite. Acceleration is achieved due to the fact that at this temperature the cementite plates are divided into smaller parts - subplates. If the shutter speed is lower than 700 ° C, this process is much slower, which lengthens the entire annealing process. When installed above 720C, along with the division of cementite plates, there is a partial redistribution of cementite with the formation of film imperfections at the grain boundaries of ferrite, which subsequently do not spheroidize for ten hours. Therefore, in the temperature range 700-720 C, they are chosen as the most technologically advanced. In this case, if the latch time is less than 30 minutes, the plates are not divided into parts in the entire volume of the metal and the subsequent spheroidization is not accelerated.

With a duration of more than 35 minutes, the initiation of film cementite at the grain boundaries of ferrite begins, which also complicates the spheroidization process and lengthens the annealing time. At 720–700 ° C, with a shutter speed of 30–35 minutes, plates are evenly divided into parts, which accelerates the spheroidization of cementite and reduces the annealing process as a whole. After annealing, a uniform granular pearlite structure is formed.

Although the aging in the process of heating at 700–720 ° C promotes the dividing of cementite plates into parts, spheroidization proceeds more quickly after a short-term heating and retention in the intercritical temperature range. This is due to the fact that at these temperatures pearlite is converted to austenite. Since heating and powering are short-lived, this transformation does not go to the end. AT

20

25

21 G12

In addition to ferrite and austenite, the microstructure of steel has under-dissolved cementite inclusions. Since the protruding gaps and edges of the cementite subplates first dissolve in austenite, the pdplates acquire a shape close to equiaxial. If a steel with a similar microstructure is dried below the effectoid temperature and depressed, then the eutectoid decay occurs by an abnormal mechanism with release of zntectoid cementite on the surface of the existing

 5 inclusions, as a result of which the structure of granular perlite is formed. Spheroidization is significantly accelerated if after heating during heating at 700–720 ° C, heating and soaking in the intercritical interior. is carried out at 755-765 ° C for 20-25 minutes, and then, during the cooling process, is carried out at intermediate temperature at 730-740 ° C for 15-20 minutes.

When heated to 755-765 and the top for a period of 20-25 minutes, the separation of cementite plates ends. their intensive dissolution begins. Below 755 ° C this process occurs much slower and even for 45 minutes does not provide the necessary degree of dissolution of cementite particles, and above 765 ° C cementite dissolves so quickly.

35 that already with a 10-minute hold, most of it goes into austenite, and the effect of the previous treatment on spheroidization at subcritical temperature is leveled.

40o

Heating and blowing up at 755-765 C, although they contribute to accelerating the onset of the conversion of perlite to austenite, they do not ensure the uniformity of this process in the bulk of the metal. With an increase in the retention time (more than 25 minutes) in certain parts of the matrix, the cementite dissolves completely, which also levels

50 the effect of pretreatment on subcritical spheroidization. A significant acceleration of spheroidization is achieved only in the case when, after heating and holding at 75555 765 C for 20-25 minutes in the process

the subsequent cooling is carried out at an intermediate temperature at 730-740 C.

This is due to the fact that after a sharp acceleration of the started stage of the growth

thirty

3, 1, of cementite particles at 755-765 ° C, the subsequent transformation of perlite into austenite at 730-740 ° C proceeds more smoothly and evenly, the process is easily controlled. After holding for 15–20 minutes, the degree of dissolution of cementite particles is provided, ensuring their number and globular shape are preserved. With a shutter speed below 730 ° C, near a temperature of eutectoid equilibrium (727 C), the release of austenite and, accordingly, the dissolution of cementite occurs very slowly, and slightly below the eutectoid temperature, for example, at 725 ° C, the austenite eutectoid disintegration occurs very slowly. If the intermediate transfer temperature is above 740 ° C, it accelerates

The entrainment of cementite and the nonuniformity of the dissolution process increase, which, with a charge of 12 minutes, leads to an almost complete dissolution of cementite and to the fact that the effect of the complex of the preceding operations is leveled. After holding in the process of heating at 700–720 ° C for a duration of 30–35 minutes, further heating and over

690 80

700 35

745 45

755 20

710 32

720 30

725 80

famous

758 18

765

15

780 10

740-760 10-30

fO ki in the intercritical temperature range at 755–765 ° C for 15–20 min and subsequent cooling with intermediate exposure at 730–740 ° C for 15–20 min. spheroidizing annealing at 710–720 ° C is completed in 80–100 min. depending on the heating temperature and the top up time in the previous stages.

Example. Testing the proposed method is carried out in a factory. Rolling steel 35 select section 23 mm is placed in a roller-type kiln through passage with a temperature of 710 C, 5 is kept at this temperature for 32 minutes, then transferred to a furnace zone with a temperature of 758 C, which is held for 18 minutes and cooled. In the cooling process, 20 shutter speeds are held at 735 ° C for 18 minutes and then a second shutter speed at 715 ° C for a duration of 90 minutes and then cooled in air. Steel of 10 other ce25 is treated in the same way.

.

The results of the experiments are given in the table.

700 150

710,100

355 (5.9)

175 (3)

715 90

720 85

725 120

680-690 300-420

160 (2.52)

145 (2.49)

292 (4.9)

330-450 (5.5-7.5)

513

As can be seen from the table, using the proposed method of spheroidizing annealing of medium carbon steels for cold heading will reduce the annealing time to 3 hours instead of 7.5 hours from what is known, increase the productivity of the process by 2.5 times and get the structure of granular pearlite in steel for cold heading at lower cost.

Claims (1)

The invention The method of spheroidizing annealing of medium carbon steels for cold Editor N. Gunko Order 1936/24 Compiled by V.Kitaisky Tehred A. Kravchuk Proofreader S. Cherni Circulation 550Subscribe VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, Projecto st., 4 sixteen landing, which includes heating to UZZ-TbO C, is held for 20-25 minutes, and staged cooling, characterized in that, in order to increase the productivity of the process during sph "spheroidization acceleration, during heating 700–720 ° C for 30–35 min, and staged cooling is carried out with a pin at 730–740 ° C for 15–20 min and at 710–720 ° C for 80–100 min, followed by air cooling.