SU1421430A1 - Method of producing rolled stock from low-pearlitic steel - Google Patents

Abstract

The invention relates to the field of ferrous metallurgy, specifically to the rolling industry. The purpose of the invention is to improve the quality of rolling and the effectiveness of the rolling process by optimizing temperature and speed conditions. After rolling the billet in the black cage, the tackle in the interfluid gap is cooled at an average speed of 1.5-5.0 C / s to the temperature of the completion of the rolling process, depending on the carbon equivalent of steel (C) at C, in - 0.37 rolling finish at 720 ° C, and with an increase or decrease in carbon equivalent by. every 0.02, the temperature of the end of rolling increases or decreases, respectively, by 10 ° C. 3 tab. but (/)

Description

The invention relates to ferrous metallurgy, specifically to the rolling production of thick plate, and can be used to produce high quality billets, for example, for large diameter pipelines operating under conditions of low temperatures.

The aim of the invention is to improve the quality of the rolling stock and the efficiency of the rolling process by optimizing the temperature and speed conditions.

The choice of the boundary values of the cooling rate is determined by the allowable differential temperature of the surface and in the middle of the rolled strip and the required rolling rate.

In tab. 1, the rationale for the proposed cooling rate range is experimental data on the temperature difference in the rolled steel thickness and the rolling rhythm provided by this cooling rate. The data were obtained with a cooled Denny rolled steel 40–80 mm thick from steel 09Г2ФБ (all rolled steel thicknesses that exist during controlled rolling).

As follows from the table. 1, a decrease in the average cooling rate of less than 1.5 ° C / s does not provide the rolling rhythm required by the technology, which leads to a decrease in the mill performance, and a cooling rate of 5.0 s / s leads to an increase in temperature thickness of rolled up to 161-179 С (permissible temperature difference is 100-150 С). Consequently, the optimum interval for average rates of cooling of the rolled billet when rolling metal perlite steels is 1.5-5.0 C / s.

The temperature of the end of rolling for low perlite dispersion hardening steels (of the type 09G2FB) is determined on the basis of experimental data near the point Аб | - real temperatures 680–730–6, and in experimental studies it was found that the rolling end temperature, which provides the most rational combination of strength and resistance properties, with a chemical composition characterized by a carbonic index; C, and an increase in carbon equivalent requires an increase in the temperature of the end of rolling (and vice versa). This is due to the effect of doped elements on the formation of a bainite structure, which adversely affects plastic rental properties

A quantitative relationship was established between these parameters — a change in carbon equivalent by 0.02 requires a corresponding change in the temperature of the end of rolling by 10 ° C.

In tab. Figure 2 shows the data on the mechanical properties of the rolled steel obtained at various temperatures at the end of rolling as a basis for the change in the temperature of the end of rolling as a function of the increase (decrease) in carbon equivalent.

Experienced rolling was carried out on rolled steel 09G2FB with a different carbon equivalent.

From tab. 2 that when rolling strips for the production of large diameter pipes operating under low temperature conditions from low alloy steel (0.29-0.41, the optimal end rolling temperature is 680-740 seconds. Experimental data are given in Table 2 It is also shown that with increasing or decreasing C, kb for every 0.02, the optimum complex of mechanical properties of Φ and 5 can be obtained by increasing (decreasing) the temperature of the rolling end by 10 C.

The use of the invention improves the quality of rolled strips for the production of large diameter pipes with a sufficiently high mill productivity. This effect is achieved by optimizing the temperature conditions of rolling. At the optimum cooling rate of the billet, the release activity of the dispersed carbide phases and nucleation of ferrite grains increases. In addition, the observance of the relationship between the chemical composition (carbon equivalent) and the end-of-rolling temperature provides for obtaining rolled products with stable mechanical properties when the chemical composition of the metal (workpiece-slab) changes.

The method is implemented as follows.

Steel slab 09G2FB

with C

eka

0.37 section 165 250 mm,

2900 mm long, heated in furnaces to 1150 ° C and subjected to rough rolling in 5 passes. From the roughing stand, a tackle is 70 mm thick at 960 ° C. For 20 seconds, tackle on the Schlepper is fed to the zone of accelerated cooling, while cooling in air to 950 ° C (cooling rate 0.5 C / s). In the zone of accelerated cooling, the metal is subjected to water-air cooling with an intensity of heat extraction of about 700 kcal / m s / s for 70 s, cooling down to, after which the shlepper is put into the finishing stand, where, after six passes, at a thickness of 19 4mm carry out final deformation (end of rolling) to a thickness of 17.6 mm. Water-air cooling of the rolling stock is carried out with the help of collectors with nozzles giving a flat jet of cooling water. The upper and lower headers provide uniform heat removal from both their surfaces of the rolling stock.

After the final rolling, the metal is cut to length and stacked for final cooling. ,

Other examples of a specific implementation of the method are given in table. 3

From tab. 3 it can be seen that the optimal average cooling rate of the tackle is 1.5–5.0 C / s with a carbon equivalent value of 0.37, the rolling process’s completion temperature is, and with increasing or decreasing carbon index

equivalent to a C, 0.37 by 0.02, the temperature of the end of rolling increases or decreases accordingly. This achieves an optimum set of mechanical properties GJ, S, which contributes to the improvement of the quality of rolling and the efficiency of the rolling process.

Using the proposed method of producing rolled steel from low-perlitic steel will improve the quality of rolled products for the production of large-diameter pipes and increase mill productivity.

Claims (1)

Formula invented Method for the production of rolled low-perlititic steel, including. roll of the workpiece in the roughing stand, cooling of the rolled stock in the interstand gap with temperature control of the end of rolling depending on the carbon equivalent of rolled steel and finishing rolling, characterized in in mezhkle. the co-gap is cooled at an average speed of 1.5-5, while rolling ends at 720 s at carbon equivalent steel C values "S 0.37, and at by increasing or decreasing the carbon equivalent value for every 0.02, the temperature of the end of rolling increases or decreases accordingly by 10 ° C. Table. one 50 56 68 2.0 86 80 72 59 47 100-150 30-65 110 129 143 161 179 37 31 28 25 22 Continuation of table Table 2 Table 3 105,143,161 41 28 25 .- Compiled by V.Ziselman Editor A.Vorovich Tehred M.Didyk Corrector M.Demchik Order 4364/8 Circulation 467 VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab ,, D, D / 5 1421430 8 Continuation of table 3 720 740 760 608 608 569 25 26 27 Subscription