SU1217896A1 - Method of machining weld joints of steel strips - Google Patents

Description

The invention relates to rolling production and can be used in workshops where butt-welding is performed by flashing steel strips advantageously on high carbon and medium carbon steels for subsequent cold rolling.

The aim of the invention is to achieve the productivity and quality of welded joints by increasing ductility.

The invention is legal as follows.

Steel strips of high carbon and (1) carbon steel steels are welded, the seam is cooled to 450-600 ° C, then deburring is started, and simultaneously with deburring, the heating is heated to the surface temperature of the welded joint 650-730 ° C in 2-4 seconds kept at this temperature for 5–10 s, then cooled to 500–550 ° C for 10–15 s, then in air. Starting the deburring at a temperature of the seam below increases the cooling time, and with accelerated cooling, for example, stitching of the seam with gas or liquid medium, fragile structures are formed akalki. The subsequent increase in their plasticity requires a long time of weld treatment and reduces productivity.

The start of deburring at a weld temperature of more than 600 ° C leads to a deterioration in the quality of the weld due to the formation of a coarse-grained structure. In addition, deburring the weld with simultaneous heating of the welded joint from temperatures more leads to the formation of coarse perlite in the weld zone in the case of machining of welded joints from medium carbon and high carbon steels. Such seams have low reliability and are destroyed during further processing of the strips. Improving the reliability of welded joints by their subsequent heat treatment leads to an increase in the weld processing time to 7–8 min, which unacceptably reduces productivity

Heating the weld during the stripping process to the temperature of the weld surface below increases the required lead (more than

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10 s) at this temperature to remove the surface work hardening, as well as due to a long holding, leads to a weakening of the seam, reducing its reliability.

Heating the weld to a temperature above 730 ° C leads to coarsening of the grain in the weld zone, which reduces the reliability of the joint.

Heating the seam to a holding temperature (650-730 ° C) for less than 2 s requires very large mosch heaters, which is impractical because the seam is usually heated in the jaws of the welding machine by passing the current from the machine's welding transformer. Increasing this time (more than 4 s) reduces performance.

The adjustment time (at a seam temperature of 650-730 C) of less than 5 s does not ensure the removal of the surface work hardening from the incisors during deburring, and more than 10 s reduces the productivity and strength of the seam.

Slow cooling of the seam up to 500-550 C in 10-15 s ensures a seam of high reliability. Accelerating the cooling of the seam (less than 10 s) leads to a decrease in the reliability of the joint due to increased brittle, surface layers of the seam, and an increase in the cooling time of the seam (more than 15 s) reduces productivity.

Slow cooling to the temperature below is impractical because it reduces productivity, slow cooling to temperatures above 550 C does not provide the required ductility of the surface layers of the weld.

Example. At the butt-welding machine installed in the line of the continuous pickling unit of the sheet-rolling shop, the welds were welded at the ends of the strips made of steel grades 45, 50 and 65G. The dimensions of the welded strips: thickness 2.5-5.0 mm, thickness 250-465 mm. At the butt welding machine, the ends of the strips were welded by reflowing, the joint was cooled, deburring and heat treatment of the welded joint were made. Heat treatment was carried out by passing an electric current through the seam. The change in temperature, heating and cooling time during the heat treatment process was carried out by changing the value of the electrical

Current and time switch settings Minimum cooling time | (the maximum cooling rate of the seam in air was obtained by stopping the supply of electric current through the seam (time less than 10 s).

The temperature of the welded joint was determined with a pyrometer. When machining welded joints by the stopwatch, the treatment time from the start of the flashing process to the end of slow cooling was determined. The quality of the seam (its plasticity) was determined by the angle when testing for bending, as well as in the process of further processing of the metal, the rolling properties of the welded joints of the bands on the five-year continuous cold-rolling mill 630 were recorded.

Heating of the welded joint after cooling to 450-600 ° C began simultaneously with deburring of bur.

The table shows the processing modes and test results of welds.

Analysis of the table shows that a decrease (less than 450 C) and an increase (more) in the temperature of the start of deburring leads to a deterioration in the quality of the weld (experiments Nos. 4 and 5). Reduces the quality of the weld is low (less than 650 C) and high (more than 730 ° C) heating temperature or insufficient time (less than 5 s) exposure at a given Tetf perratura weld (experiments No. 7, 8 and 11). An increase in the heating time of a welded joint, an overhang after heating reduces the productivity and reduces the quality of the welded joint (experiments Nos. 13 and 14). Reducing the cooling time after heating and losing leads to a deterioration in the quality of the seam (test No. P), and the increase in this time (more than 15 s) is impractical because it reduces productivity without increasing the quality of the seam.

The treatment time of the seam according to the proposed method is 39-47 s. This provides an average productivity of continuous pickling.

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unit, for example when processing strips of steel grade 65G size 3.0 X 465 mm 31.2 t / h. At the same time, during the processing of such strips by the prototype method, the processing time of a welded joint is 1 min, and the average productivity of a continuous pickling unit is 4.2 t / h. In this case, the weldability of the seams on the mill is 80%, the bend angle of the seam does not exceed 50. Reduced time around. processing of welded joints of 65G steel strips by a known method for up to 3 minutes leads to the destruction of the seams

 in the line of the continuous pickling unit and its stop.

Thus, it was experimentally established (experiments no. I, 2, 3, and 6) that the treatment of welded joints by the proposed method provides improved performance by reducing the processing time and welding, the quality of welded joints (the bend angle of the welds is 90 degrees: 99, 1 -

99.6%). I

The proposed processing method

welded joints increase the productivity of the process and due to this, the productivity of the entire unit, which uses butt welding, is sharply increased. The productivity of continuous aggregates (for example, continuous pickling aggregates) is largely determined by the processing time of welded joints, which is drastically reduced when using the proposed method. In addition, the proposed method improves compared with the known quality of welded joints. This is especially important in the subsequent cold rolling of strips from medium-carbon and high-carbon steel grades with welded joints, when the mill productivity depends on the rolling capacity of the seams, subsequent to the redistribution of the aggregates and product quality. Reducing the processing time of welded joints also provides energy savings on processing.

 Compiled by I. Lipgart Editor T, Parfenova Tehred L. Mikesh Proofreader M. Samborska

Order 1084/32 Circulation 552Subscription

VNIIPI USSR State Committee

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

Branch PPP Patent, Uzhgorod, st. Design, 4.

Claims (1)

METHOD FOR PROCESSING WELDED COMPOUNDS OF STEEL BARS mainly from medium-carbon and high-carbon steels, including cooling the weld after welding, deburring and heat treatment of the welded joint, characterized in that, in order to increase productivity and quality of welded joints, cooling after welding is carried out to 450-600 ° C ^ stripping of the grit is carried out with simultaneous heating to the surface temperature of the welded joint 650-730 ° C for 2-4 s, and heat treatment _{β is} carried out by exposure at 650–73O ^q C for 5–10 s and cooling to 500–550 ° C in 10–15 s. Ш_ · .. _ 1217896>