RU2230638C1 - Method for butt welding of carbon steel strips - Google Patents

Abstract

FIELD: welding of strips of hot rolled carbon steel designed for further cold rolling.

SUBSTANCE: method comprises steps of welding steel strips with thickness 2 - 6 mm before etching them by flashing-off end edges of strips; gradually approaching edges one to another for their welding and upsetting; selecting upsetting value according to thickness h of welded strips and taking into account carbon content in steel. When carbon content is less than 0.1%, selecting value

of upsetting

=(1.0 -1.1)h; when carbon content is in range 0.1 -0.3%,

= (1.12 -1.3)h. After duration of electrode working equal to 32 hours increasing upsetting value for first group of steels until

= (1.15 - 1.25)h and for second group of steels - until value

=(1.30 - 1.45)h.

EFFECT: possibility for increasing efficiency of equipment in cold rolling shop, lowered loss of metal due to decreased quantity of rejected metal in the result of enhanced rolling quality of welded seams.

2 ex

Description

The present invention relates to the welding of metals and can be used in butt welding of strip hot-rolled steel for subsequent cold rolling.

Butt welding of hot-rolled strips is carried out immediately before their etching on continuous etching units (NTA) to ensure the continuity of the process. The technology of such welding and equipment for its implementation are described, for example, in the book of A.I. Tselikova et al. Machines and assemblies of metallurgical plants. - M .: Metallurgy, 1988, v. 3, p. 381 and 382.

The strength of the weld during welding should be equal to the strength of the strip material (to avoid strip breaks during cold rolling). A high-quality seam provides the required performance of all units of the cold rolling workshop with minimal metal waste. The main indicator of the quality of welds is their “rolling” in a cold rolling mill, which is determined (in %%) by the ratio of torn joints to their total number for a rolled batch of strips.

It should also be noted that a poor-quality seam can be torn during the passage of metal at the NTA or at other stages of the cold rolling workshop (for example, during training after annealing).

A known method of welding hot-rolled strips, a distinctive feature of which is the underestimation of the thickness of the metal at the weld in comparison with the thickness of the welded strips, carried out in the process of removal of the weld and according to a certain relationship (see AS USSR No. 390884, class. 23 K 11 / 04, B 21 V 1/28, publ. 13.03.74 g.). There is also a known method of processing a weld on a rolling for cold-rolled sheets, in which the understatement of the thickness of the metal of the weld is produced from the edges of the strip with a uniform increase in the depth of understatement to its middle, with the determination of the thickness of the weld metal according to a specific relationship (see AS USSR No. 536025 , CL B 23 K 11/04, publ. 16.06.77).

A disadvantage of the known methods is the reduction (understatement) of the thickness of the metal in the weld area, which during cold rolling of strips with increased tension and speed can lead to their breakage with negative consequences.

The closest analogue to the claimed object is the technology of butt welding of steel strips with a thickness of 2-6 mm on the NTA, described in the book by Yu.D. Zheleznova et al. Improving the production of cold rolled sheet steel. - M .: Metallurgy, 1982, p. 19 and 20, tab. 6, 7 and 8.

This welding technology by continuously melting the end edges of the strips includes a gradual approximation of the edges, their welding and draft after welding and is characterized by the fact that the amount of draft Δ _os varies depending on the thickness of the welded strips “h”, within: Δ _os = (1,1 ... 1,7) h for all grades of steel.

The disadvantage of this technology is the invariance of the precipitation value to the carbon content in the welded steel, as well as to the duration of the butt welding machine electrodes (CCM), i.e. to their wear, which does not provide high quality (and rolling) welds.

The technical task of the invention is to increase the performance of the units of the cold rolling shop and reduce the yield of substandard metal by improving the rolling ability of welds.

To solve this problem, in the method of butt welding of carbon strip steel with a thickness of 2 ... 6 mm before etching by continuously melting the end edges of the strips, including the gradual approximation of the edges, their welding and draft after welding, when the carbon content in the steel is up to 0.1%, the precipitation Δ _{os is} taken, depending on the thickness h of the welded strips, equal to: Δ _os = (1.0 ... 1.1) h, and with a carbon content of more than 0.1% and up to 0.3% - Δ _os = (1 , 12 ... 1.30) h, and after 32 hours of operation of the electrodes, the Δ _os value for the first group of these steels is taken within (1.1 5 ... 1.25) h, and for the second group of steels - Δ _os = (1.30 ... 1.45) h.

The essence of the technical solution found is to vary the amount of metal precipitation during butt welding of strip steel (draft, i.e. the convergence of the ends of the strips, is the most important butt welding operation) depending on the carbon content in it, and also to change this value when the CCM electrodes are worn (after a certain welding time).

In addition, it was experimentally established (see below) that the value of Δ _os / h in most cases should be less than the known values (see Table 6-8 of the source selected as the closest analogue) even when the CCM electrodes are worn.

An experimental verification of the proposed method was carried out at the NTA sheet rolling shop No. 5 of OJSC “Magnitogorsk Iron and Steel Works”, evaluating the results of weldability in the cold rolling mill 2500 of this workshop, as well as the output of substandard strip rolling and increase the productivity of the units of the workshop.

For this purpose, when welding hot-rolled strip steel with a thickness of 2 ... 6 mm with different carbon contents before etching, the amount of metal deposition on the SSM NTA was varied depending on the total duration of welding (electrode working time).

The best results (an increase in weldability by 2 abs.% - up to 98% and a decrease in the yield of substandard products by 1.5 ... 2.0%) were obtained using the proposed welding technology. At the same time, an increase in productivity of all workshop units working with a welded strip was noted by 5 ... 7%.

Deviation from the recommended parameters of metal precipitation led to negative consequences, mainly due to the deterioration of the microstructure of steel. Thus, with an increase in Δ _os , a fine-grained structure was observed, which in some cases led to band breaks at the seams. A decrease in Δ _os (in comparison with the recommended values) caused coarsening of the steel grain, which worsened the plastic properties of the metal in the weld area, and also caused strip breaks (especially during cold rolling).

As it was established during metallographic studies, the noted negative phenomena were caused by the appearance of additional stresses in the heat-affected zone due to the large difference in the microstructures of the base metal and the resulting weld and “variability” of structures up to 2-3 points.

Butt welding was also carried out end-to-end on the NTA using the technology taken as the closest analogue (see table 8 in the book of Yu.D. Zheleznov and others). At the same time, weldability amounted to 94 ... 96% with a corresponding drop in production of workshop units and an increase in the output of substandard sheet, and on the SSM NTA, the duration of the working campaign of welding electrodes increased by 10% and their consumption decreased.

Thus, the pilot test confirmed the acceptability of the claimed technical solution to achieve the goal and its advantages over the known technology of butt welding of hot rolled strips.

According to the Central Control Laboratory of OJSC MMK, the introduction of the developed technology in the sheet rolling shop No. 5 of the plant will increase the profit from the sale of finished sheet metal (by reducing its cost and increasing production) by at least 5%.

Case Studies

1. Hot rolled strip steel with a thickness of h = 2 mm with a content of 0.07% of carbon is welded before etching with Δ _os = 1.05h = 1.05 · 2 = 2.1 mm. After 32 hours of precipitation of metal electrodes SSM value taking: Δ _oc = 1,2h = 1,2 · 2 = 2.4 mm.

2. Similar steel with a thickness of h = 6 mm and with a content of 0.2% carbon is butt welded to an NTA with Δ _os = 1.2h = 1.2 · 6 = 7.2 mm, and after 32 hours of operation of the welding electrodes: Δ _oc = 1.37h = 1.37 · 6≅8.2 mm.

Claims (1)

The method of butt welding of carbon strip steel with a thickness of 2 to 6 mm before etching by continuously melting the end edges of the strips, including the gradual approximation of the edges, their welding and draft, the value of which is selected depending on the thickness h of the welded strips, characterized in that the precipitation value is selected with taking into account the carbon content in steel, in this case, when the carbon content is up to 0.1%, the amount of precipitation ΔОс takes ΔОС = (1.0 ... 1.1) h, when the carbon content is more than 0.1 to 0.3%, ΔОС = (1.12 ... 1.3) h, and after 32 hours of operation of the electrodes, the amount of precipitation increased Chiva for a first group of said steel to Δos = (1,15 ... 1,25) h, for the second group - to Δos = (1,30 ... 1,45) h.