RU2490081C2 - Method of rolling section bars from hard-to-deform steels - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention may be used in rolling of section bars from hard-to-deform steels for critical parts. Proposed method comprises heating of continuously-cast billet to austenitising temperature, multi-pass reduction in rolls with passes at roughing and finishing with specified total reduction and rolling end temperature. Rolling at roughing passes is performed at from 1140-1290°C of deformation start to 1000-1100°C of deformation end and total reduction of 2.2-8.4 at maximum-to-minimum reduction ratio in every pass making at least 1.2 and not over 1.6.

EFFECT: intensified mechanical crystallite grinding without with dynamic and static recrystallisation of deformed austenite grains.

1 dwg, 6 ex, 1 tbl

Description

The invention relates to rolling production and can be used in the rolling of long sections from hardly deformable steels for critical products.

A known method for the production of rolled products, including the production of continuously cast billets, heating the billets to an austenitic temperature of 1150-1280 ° C, rough rolling with a total compression ratio of 40-92%, and finish rolling with a total compression ratio of 50-70% and a temperature of the end of rolling 680- 1050 ° C [1].

The disadvantages of this method are that it does not provide high quality profiles of difficult to deform steels, the result of which is a decrease in yield.

The closest analogue to the present invention is a method for the production of high-quality profiles, including heating, continuously cast billets to austenitizing temperature, multi-pass compression in rolls with calibers for roughing and finishing passes with a regulated total hood from 4 to at least 15 (depending on the steel group) and the temperature of the end of rolling 860-1000 ° C [2].

The disadvantages of this method are the low quality of long sections from hard to deform steels, which is manifested in the form of cracks, gaps, profile failures. As a result, the yield is reduced.

The technical task of the invention is to improve the quality and yield of profiles from hard to deform steels.

To solve the technical problem in the known method of rolling long sections from difficult to deform steels, including heating a continuously cast billet to austenitizing temperature, multi-pass compression in rolls with calibers for roughing and finishing passes with regulated total drawing and temperature of the end of rolling, according to the invention, rolling in rough passages lead in the temperature range from 1140-1290 ° C to 1000-1100 ° C with a total hood λ = 2.2-8.4 with a ratio of the maximum and minimum itelnyh preform reductions in each of the passes of not less than 1.2 and not more than 1.6.

Figure 1 shows, by way of example, a conversion diagram for the transverse profile of a workpiece in a square-to-oval calibration system. The blank of the square section is shown by the dashed line. The figure 2 shows a plot of the distribution of the relative compression e across the width of the oval caliber during compression according to the scheme in figure 1.

The invention consists in the following. A continuously cast billet of hardly deformed steel structurally consists of large crystallites and is characterized by low technological ductility. To suppress the negative impact of the cast structure on the quality of finished high-quality profiles, it is necessary to increase the hood in draft passes. However, an increase in hoods leads to the appearance of cracks and transverse tears in the rolled metal, which has a low technological ductility.

During the experiments, the conditions of deformation in rough passages of workpieces made of continuously difficult to deform continuously cast steels were determined, under which both the destruction of crystallites and the dispersion of microstructural components were ensured, and the formation of cracks and gaps in the metal was excluded. It was found that in the temperature range from 1140-1290 ° C to 1000-1100 ° C with a ratio of the maximum and minimum relative compressions of the workpiece in each of the passages, which is at least 1.2 and not more than 1.6, due to the appearance of an additional shear deformation components of a regulated value intensifies mechanical grinding of crystallites without the need to increase the hood, leading to the appearance of defects. At the same time, under the indicated deformation-thermal action, dynamic and static recrystallization of deformed austenitic grains occur in steel. The boundaries of recrystallized grains retain high strength and are not prone to the formation of germinal cracks and tears. The multi-cycle deformation-thermal action alternating along rough passages with shear components of deformation provides sequential dispersion and homogenization of the initial microstructure. As a result, after reaching the total draw at λ = 2.2-8.4 with rough passages, hard-to-deform steel acquires increased technological ductility. Due to this, there is an increase in the quality and yield of profiles.

It was experimentally established that if the temperature of the start of rough rolling, T _n, is higher than 1290 ° C, this does not exclude the oxidation of the intergranular boundaries of cast hardly deformed steel. This leads to the formation of cracks and tears during rolling. At a temperature T _n below 1140 ° C, large non-metallic inclusions that are not dissolved in austenite are retained in the steel, which reduces its ductility and the mechanical properties of long sections.

When the temperature of the finish of roughing passes T _{cc is} below 1000 ° C, hard-to-deform steel has low technological ductility, which leads to non-fulfillment of the profile in calibers. An increase in T _cc over 1100 ° C contributes to an increase in the variety of microstructures and to a decrease in the complex of mechanical properties of varietal profiles.

If the total extraction λ after rough passes is less than 2.2, then fragments of cast crystallites will remain in the microstructure of the steel of the finished profiles, their quality will deteriorate. At λ greater than 8.4, the appearance of cracks and tears on the workpiece is not excluded.

In cases where the ratio of the maximum ε _max and minimum ε _min relative compressions in caliber is less than 1.2, shear deformations are not sufficient for fracture of crystallite fragments. When the ratio of ε _max to ε _min more than 1.6, the uneven deformation in the caliber will lead to the formation of cracks and breaks in the workpiece, reducing quality and yield.

Method implementation examples

A continuously cast square billet of 150 × 150 mm square from hard-to-heat-treating heat-resistant steel of the grade 40X10C2M (GOST 5945-95) is heated in a methodical furnace with gas heating to the austenitizing temperature T _n = 1215 ° C and delivered to the furnace rolling table of a section rolling mill 350. Then, the heated billet is transported to the draft 5-stand group carry out its multiple compression in rolls with a system of calibers "square" - "oval" (Figure 1) with a total hood λ = 5,3. In each of the oval and square calibers, the workpiece is rolled with a variable compression ε along the width B of the caliber. The maximum reduction in caliber is ε _max = 14%, and the minimum ε _min = 10%. The ratio of the maximum and minimum relative compressions of the workpiece is equal to:

ε _max : ε _min = 1.4

The required values of ε _max and ε _min set the depth of the incisions of the streams on the rolls forming the caliber.

A variable compression λ, along the width B of the gauge, ensures the growth of the shear component of the plastic deformation of the workpiece, which contributes to the mechanical study of the cast structure, grinding and homogenization of the structural components.

Rough rolling is completed at a temperature of T _cc = 1050 ° C. In the temperature range of rough rolling from T _n = 1215 ° C to T _KCH = 1050 ° C due to the grinding of the microstructure from the action of shear deformation and controlled recrystallization, the technological plasticity of hard-deformed heat-resistant steel is increased, the formation of cracks and ruptures is eliminated, and the desired profile is achieved.

After the rough rolling is completed, the obtained oval-shaped strip is assigned to the finishing group of stands in which the “oval” -circle is crimped into a strip of circular cross section with a diameter of 20 mm.

The finished strip is characterized by high dimensional accuracy, the absence of defects in the form of cracks and sunsets, and high mechanical properties due to the fine-grained homogeneous microstructure of hard-deformed steel. The result is an increase in yield to a value of Y = 99.6%.

Implementation options of the proposed method for rolling profiles of hardly deformable steels and indicators of their effectiveness are given in the table.

Table. Deformation-thermal regimes of rolling of long sections from hardly deformed steels and their effectiveness No. p / p T _n , ° C ε _max / ε _min T _cd , ° C µ Fur. St. va Profile Defects Y% one. from 1D 900 2.1 unsuccessful. presence. 85.5 2. 1140 1,2 1000 2.2 double absent. 99.5 3. 1215 1.4 1050 5.3 double absent. 99.6 four. 1290 1,6 1100 8.4 double absent. 99,4 5. 1300 1.7 1200 8.6 unsuccessful. presence. 83.9 6. 1180 - not regl 19.9 unsuccessful. presence. 85.5

High-quality profiles that do not meet the mechanical requirements for heat-resistant steel grade 40X10C2M are used for less demanding products.

From the data presented in the table, it follows that the implementation of the proposed method (options No. 2-4) is achieved by improving the quality and yield of profiles from difficult to deform steels. With exorbitant values of the declared parameters (options No. 1 and No. 5), as well as in the prototype method (option No. 6), there is a decrease in quality and yield.

The technical and economic advantages of the proposed method consist in the fact that the implementation of the proposed deformation-thermal regimes using experimentally determined values of compression unevenness over the width of the caliber contributes to the appearance of additional regulated shear deformations that improve the development of the cast steel structure, which improves the quality of long sections from hard to deform steels and yield. A side effect is the expansion of the range of rolled profiles from continuously cast billets in the direction of increasing the cross-sectional area of the finished profiles.

As the base object adopted the known method [2]. Using the proposed method will increase the profitability of the production of varietal profiles for critical purposes by 15-20%.

Literary sources

1. RF patent No. 2041962, IPC B21B 1/46, 1995;

2. RF patent No. 2243834, IPC B21B 1/46, 2005.

Claims (1)

A method of rolling long sections from difficult to deform steels, including heating a continuously cast billet to austenitizing temperature, multi-pass compression in rolls with calibers for roughing and finishing passes with regulated total drawing and temperature of the end of rolling, characterized in that the rolling in roughing passes is carried out in the temperature range from 1140-1290 ° C to 1000-1100 ° C with a total hood of 2.2-8.4 with a ratio of the maximum and minimum relative compressions of the workpiece in each of the passages, I not less than 1.2 and not more than 1.6.