SU1216220A1 - Method of temperature hardening of reinforcement bars - Google Patents

Description

The invention relates to rolling production, in particular to the accelerated cooling of rolled products in the stream of hot rolling mills for the purpose of thermal strengthening.

The aim of the invention is to increase the strength and plastic properties of reinforcing bars by compensating for the residual tensile stress of rolling origin,

FIG. 1 shows a scheme for crimping an oval billet; coming out of the roughing stand in the rolls of the finishing stand in a circle in FIG. 2, a drawing of the drawing in FIG. 3, a drawing of the stress of rolling origin; in fig. 4 is a cross-section of the car after leaving the finishing stand in FIG. 5 is a plot of stresses of a thermal origin with uniform cooling, and a perforation shaft in FIG. .6 is the total voltage of the stressor by a known method; in fig. a circuit for cooling a rod section according to the proposed method; Fig. 8 shows a junction of thermal stresses during cooling in accordance with the proposed method; Fig. 9 shows the resulting residual stress diagram when cooled by the proposed method.

The reinforcing bar in cross section is a round rod with inclined ribs around the perimeter. In the deformation zone of the finishing stand, where an oval is set into a round caliber due to uneven rolling across the width of the caliora, the draws are also distributed unevenly. the resulting rental) is approximately 2 times. This trend, as shown by an analysis of rebar rods, persists in almost all of the profile-sizes from No. 12 to No. 36. After the rolls leave the calibration, the stretch ends are equalized, but residual stresses of rolling origin arise .

In the most compressed places, where there is the most stretching, compressive stresses occur, and in the least compressed; Locally, tensile stresses (Fig. 3).

162202

The appearance of an unlikely scheme of residual stresses has a different effect on the stability of austenite. The compressive stresses increase the stability of austenite, and the tensile stresses decrease it. This contributes to the formation of a heterogeneous structure over the rod section. During heat treatment of such a rod, immediately after the finishing stand, residual stresses are fixed in it, and tensile residual stresses significantly deteriorate the strength characteristics of thermally strengthened

15 rental.

The distribution of residual thermal stresses with uniform cooling has the form shown in FIG. 4 and 5. In this case, the tension of the secondary voltage in the central part {near the center is summed with the residual tensile stresses of rolling origin, and the following picture appears

3 (FIG. 6) of the total residual stresses that adversely affect the mechanical properties of heat-treated rolled products.

To compensate for q using

30 thermal stresses tensile stresses of rolling origin, it is necessary to cool the rolled around the perimeter only in those places where the rolled got the smallest stretch (Fig. 7 and Fig. 3, these areas are shown with a segment m). B. In this case, thermal stresses occur on the cooling surface, similar to FIG. 5, only localized in the regions bounded by the chords in. and

 rri (fig 7). In order not to get the impression that these thermal residual stresses lie in the same ROTATING rolling residual stresses (Fig. 2), the arrangement of thermal stresses is given in d; metrii (Fig. 8).

With the addition of thermal stresses with uneven cooling (Fig. 8) with rolling residual

 stresses (fig. 3), it is necessary to fold only the stresses located in the central part of the rod. 3, as a result of the addition, the following picture of the location of the exact stresses of thermal and rolling origin (Fig. 9) is obtained.

Example. At mill 350 several hundred kilograms were rolled.

3

t

reinforcing rods number 20 of steel 20 HS thermally strengthened. In the area of thermal strengthening with a length of 16–18 m at a rolling speed of 7–8 m / s, the rods were accelerated by a known method, i.e., the temperature decreased from 1020 ± 20 C to 450 C with uniform cooling along the perimeter in two stages. The installation was positioned after the stand, thus providing a postdeformation suspension of 1.8–2.1 s. Then accelerated cooling was carried out in several modes with uneven cooling of the perimeter parts of reinforcing bars. The total length of the sprayer cooling section (non-uniform) was 8 m, and the cooling section in the pass-through (uniform) chambers was 10 m. The cooling intensity on the sprayer cooling section and in the pass-through chambers was changed by the cooling water flow rate and the number of sprayers used .

Established several modes of uneven cooling in the sprayer cooling section. After uneven cooling, the average temperature of the reinforcing bars was 900 s (1 cooling mode). The temperature was measured to an optical pyrometer, and in the temperature range of BOO-BOO C and 600-400 ° C using an OPIR-50 pyrometer after the cooling section at a distance of 15 m. After uneven cooling, the average temperature was 820-850 ° C (II cooling mode) , III mode - 750-780 С, IV mode - 700-750 ° С.

Cooling mode

the way

88.3 87.4 89.7 89.9 88.6

16220 "

Water consumption for cooling in each mode on the sprayer section was 100, 140, 158 and 165, respectively, at a temperature of 5 cooling water of 14 C. Then

together with the sprayer device, water was fed into the through-flow cooling chamber with a flow rate so that after the cooling section the temperature of the reinforcing bars was 400-450 ° C.

At the cooling water flow rates in the sprayer cooling plots in 1 - IV modes, the chambers are in chambers

The t5 throughflow cooling to achieve a temperature of 450 ° C was 220, 190, 177 and 160. Samples of thermo strengthened rods cooled according to the known regime and

20 according to the claimed method, they investigated the mechanical properties on a tensile machine. The results of the mechanical tests are shown in the table.

25 Analysis of the test results shows that the mechanical properties of reinforcing bars thermo strengthened by a known method are the lowest with the mechanical properties of reinforced bar

30 round rods, thermo-strengthened in G mode, are lower than the requirements of GOST 10884-81 for AT-V class, and in II and IV modes generally comply with the requirements of GOST 10884-81, but there are attacks on either strength

40

or plastic properties. The best combination of strength and plastic properties was obtained by cooling the reinforcing bars according to the III cooling mode.

Mechanical properties

9.9 9.6 8.6 8.6 10.1

3

3

2.8

3

3

92.5 87.1 88.0 89.6 96.1 91.3

97.5

115.2 113.4 112.6 115.3 108.3 107.5 109.8 108.6

Table continuation

9.9

11.1

11.0

15.4

18.1

13.8

11.1

15.2

16.4

17.3

16.8

7,6

5.6

6.5

4.2

3

3

3

3.2

3.4

3

3.4

3

3

3

3

3

3.1 2.8 3

Fi.Z

Fig.b

Cfnpyu Soffbt Pw. 7

L | L

-YALSHPGs-E I /

9

Compiled by V.Kitaisky Editor R.Tsitsika Tehred A. Babinets Proofreader A.Zimokosov

Order 963/30 Circulation 552Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Filial PPP Patent, g, Uzhgorod, st. Project, 4

Claims (1)

METHOD OF TEMPERATURE REINFORCEMENT BARS mainly with a diameter of 18 mm and more, including austenization of the workpiece, rolling, two-stage cooling until the average cross-section temperature is 550-625 ° C with a cooling rate in the second stage of 400 600 deg / s and final cooling in air, different from I mean that, in order to increase the strength and plastic properties of reinforcing bars by compensating for the residual tensile stresses of rolling origin, at the first stage of cooling, local cooling is less crimped during rolling sections of the perimeter of the rods to a temperature on their surface below 500 C, reducing the total temperature of the rods to 750-800 C, and then carry out general cooling of the rods. 1216.220