RU2464140C2 - Method of making laminar rustproof steel - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy and may be used for production rustproof laminar steel billets and strips composed of carbon silicon-alloyed steel layer and at least one coated layer of rustproof steel. Basic layer is made to contain 0.8-4.0 wt % of silicon. Package is heated for rolling in vacuum chamber of rolling mill heating furnace at 800 - 1200°C and residual pressure not exceeding 1.33 Pa. Hot deformation of said package is performed by rolling at said mill chamber tightly communicated with heating furnace vacuum chamber at deformation of 12-60% in single pass. Rolled stock is cooled down to 300°C in cooling and discharge vacuum chamber tightly communicated with mill working vacuum chamber.

EFFECT: ruled out discontinuity of joint layer and high strength.

1 tbl, 10 dwg

Description

The invention relates to the metallurgical industry, namely the manufacture of vacuum-rolled blanks and strips of layered corrosion-resistant steel, consisting of a main layer of carbon steel alloyed with silicon, and at least one cladding layer of corrosion-resistant steel.

Known GOST 10885-85 "Hot-rolled sheet steel, two-layer corrosion-resistant. Technical conditions ”, in accordance with which two-layer sheets are made with a thickness of 4 to 120 mm. The manufacturing method is not regulated. The grades of carbon and low alloy steels of the base layer and steels of cladding layers, including corrosion-resistant chromium-nickel steels, are given.

Given the imperfection of the known methods for the manufacture of layered corrosion-resistant steels, GOST 10885-85 provides for the presence of discontinuity in the connection of layers and allows shear resistance of at least 150 MPa.

A known method of producing a clad sheet (patent EP No. 0132937 B1 dated 06/04/1984), comprising assembling a package of a base metal sheet and a clad metal sheet using a welded joint of sheets along their perimeter, purging with an inert gas the gap between the adjacent surfaces of the sheets, filling purge holes with fusible metal, heating the assembled bag to the temperature of hot deformation, rolling at a degree of deformation of 2% ... 20% per pass. The disadvantage of this method is that filling the gap between the sheets of the assembled package with an inert gas does not exclude the content of a certain amount of oxygen, oxidation of a part of the area of the connected surfaces and, as a result, discontinuities of up to 2% of the area of the connected surfaces.

A known method of manufacturing a clad sheet by hot rolling (patent EP No. 0201202 B2 dated 04/04/1986), comprising cleaning oxides of the joined surfaces of the base and clad metal sheets, laying sheets of the main, clad and cover layers; welding around the perimeter of the main and covering sheets; inert gas purging of the gap between the main and clad sheets; lowering the gas pressure in the gap between the sheets to 13.33 Pa and lower as the sheets folded together are heated until the temperature of the folded sheets reaches 100 ° C (evaporation and moisture removal from the gap will occur) during welding of the base and clad metal sheets and receiving a package; heating the bag to a temperature of 650-950 ° C for hot rolling, joining the surfaces of the base and clad sheets during hot rolling, and cooling the rolled bag to a temperature of 650 ° C or lower.

The disadvantage of this method is that the rolling of the package begins at a gas pressure of 13.33 Pa in the gap between the connected surfaces. At this pressure, gases contain oxygen, which during the heating of the package for rolling leads to the oxidation of the surfaces to be joined and to their discontinuity.

A known method of manufacturing bimetals (AS SU No. 937117 dated 11.26.1980), comprising assembling a steel package, heating it to a temperature not exceeding 1250 ° C, and rolling in two stages with intermediate isothermal holding after preliminary deformation with a degree from 30 to 50%. Exposure to rolling after deformation for 0.5 ... 2.0 hours at the temperature of the onset of hot rolling. Subsequent rolling of the package is carried out at a degree of deformation of 10% ... 30% and is completed at a temperature of 1100 ° C ... 1000 ° C.

The disadvantage of this method is that due to the presence of an oxide film on the contact surfaces, it does not allow to eliminate the discontinuity of the surfaces to be welded and to obtain high strength of the connection of steel layers.

A known method of rolling refractory metals in a vacuum rolling mill (Chernyshev V.N., Linetsky B.L., Krupin A.V. Processing of metals by pressure in controlled environments. - M., Metallurgy, 1993, p.245). In this method, preforms for rolling are heated in a vacuum chamber of a heating furnace of a vacuum rolling mill to a rolling temperature, hot deformation of a heated workpiece is carried out in a working vacuum chamber of a stand of a vacuum rolling mill, hermetically connected to a vacuum chamber of a heating furnace with a residual gas pressure of not more than 1.33 Pa . After rolling, the workpiece moves into the cooling and unloading chamber. A similar process for rolling a billet of laminated stainless steel is not described.

A known method of manufacturing a layered corrosion-resistant steel (large clad steel sheets: patents RU No. 2225781 from 02.14.2002, RU No. 2274528 from 05.06.2004, RU No. 2277464 from 08.16.2004), which includes the preparation ( machining to a given roughness R _a = 12.5 μm and degreasing) the contact surfaces of the base metal (steel slabs, steel ingots or tackle of carbon and low alloy steel grades, including 09G2S steel with silicon content up to 0.8%) and clad metal (tackle austenitic or ferritic stainless with hoists), assembly of the package from the main and cladding layers with a gap between them and its perimeter welding. After the sublayer is completed by manual welding, the gap between the contact surfaces is flushed with an inert gas, and then its preliminary evacuation to a pressure of 7 Pa. Then perform automatic submerged arc welding and additional evacuation to reduce the likelihood of oxidation of the contact surfaces when the package is heated. After heating the package, it is hot rolled to obtain a clad sheet of predetermined dimensions. The disadvantage of this method is the low strength and the presence of discontinuities in the connection of contact surfaces, reaching 1-2% per 1 m ² surface.

Closest to the technical nature of the present invention is a method for manufacturing rolling steel laminate material consisting of a base layer of carbon steel and at least one cladding layer of high alloy steel with special properties, including preparing the contact surfaces of the main and cladding layers, heating the bag under rolling, hot deformation of the package by rolling and cooling (patent RU No. 2234385 from 01.08.2003). In this method, the preform of the main layer is made of steel alloyed with silicon at its maximum content of 4 wt.% And other alloying elements. Obtained after assembly and welding along the perimeter, the layered package is heated to a temperature of hot plastic deformation, rolling is carried out at regulated relative deformation and heat treatment.

The disadvantage of this method is the low strength of the layered corrosion-resistant steel, because air remains in the gap between the contacting surfaces of the main and cladding layers, causing oxidation of the surfaces during heating to form a scale layer and, accordingly, discontinuities in the connecting layer.

The technical problem solved by the invention is the creation of a method for manufacturing layered corrosion-resistant steel, providing increased strength and eliminating discontinuities in the connecting layer.

The technical problem is solved in a method of manufacturing a layered corrosion-resistant steel, consisting of a base layer of carbon steel, alloyed with silicon, and at least one cladding layer of corrosion-resistant steel, including the preparation of contact surfaces of the base, containing from 0.8 to 4 wt. .% silicon and cladding layers, heating the package for rolling in a vacuum chamber of a heating furnace of a vacuum rolling mill at a temperature of 800-1200 ° C with a residual gas pressure of not more than 1.33 Pa, hot deformation of the package attack in the working vacuum chamber of the mill stand, hermetically connected to the vacuum chamber of the heating furnace, with a degree of deformation of 12 to 60% in one pass and cooling to a temperature of no higher than 300 ° C in the vacuum cooling and unloading chamber, hermetically connected to the working vacuum chamber rolling mill.

In order to achieve maximum strength of the connecting layer and save energy, the package for hot deformation is heated to a temperature selected from the interval 800-1200 ° C, and the package for rolling is heated at a residual gas pressure of not more than 1.33 Pa.

To increase the strength of the connection of the layers and reduce the formation of oxides on the surface of the rolled billet, cooling is carried out to a temperature not exceeding 300 ° C.

To save energy and reduce the load on the mill rolls, hot deformation of the package is carried out by rolling at a degree of deformation of 12 to 60% in one pass.

The technical effect is achieved due to the following combination of features: prepare the main layer containing from 0.8 to 4 wt.% Silicon; heat the bag for rolling in a vacuum chamber of a heating furnace of a vacuum rolling mill at a temperature of 800-1200 ° C with a residual gas pressure of not more than 1.33 Pa, conduct hot deformation of the bag by rolling in a working vacuum chamber of a stand of a vacuum rolling mill, hermetically connected to the vacuum chamber of the heating furnace, with a degree of deformation from 12 to 60% in one pass and cooling the rolled product to a temperature of no higher than 300 ° C in a vacuum cooling and unloading chamber, tightly connected to the working vacuum chamber about the camp.

The set of features characterizing the proposed method was not detected during patent information research, therefore, the technical solution meets the criterion of "novelty." Since the combination of distinctive features of the method of manufacturing layered corrosion-resistant steel does not follow from the known level of the described technological processes, but is achieved as a result of experimental studies, the technical solution meets the criterion of "inventive step".

A method of manufacturing a layered corrosion-resistant steel is illustrated by drawings, in which Fig. 1 shows the design of a package prepared for rolling, Fig. 2 shows samples rolled with different degrees of deformation, Fig. 3 shows the temperature dependence of the bond strength of the base and clad layers heating for rolling and degrees of deformation, Figs. 4-8 show the structure of the transition layer of samples after grinding and etching at a magnification of × 400; Fig. 9 shows a diagram of a device for testing specimens of layered corrosion-resistant steel for peeling the irrigation layer from the main, in Fig.10 - a laminated package with the main layer of carbon steel alloyed with 4% silicon.

Example.

For hot rolling in vacuum, an experimental batch of 4 groups of packages was made of steel of the main layer alloyed with silicon in wt.%: 0.8, 2, 3, 4, and a layer of clad steel 08X18H10T. Each package with a thickness of 15 mm was composed of blanks of the base layer 12 mm thick and 40 × 120 mm in size and 08X18H10T steel 3 mm thick and 40 × 120 mm in size. The surfaces of the workpieces were mechanically cleaned and degreased. The blanks were joined in a package with rivets at the edges (Fig. 1). Each bag was heated in a vacuum chamber of an electric heating furnace of a vacuum rolling mill and moved for rolling into a working chamber of a stand of a vacuum rolling mill connected to a vacuum chamber of a heating furnace.

The parameters characterizing the mode of heating and rolling are shown in table 1.

Rolled products (figure 2) were cooled to a temperature of 300 ° C in a vacuum cooling chamber with a residual gas pressure of 1.33 Pa, then in air to ambient temperature. In the regimes similar to those of heating, rolling and cooling of steel alloyed with silicon 0.8 wt.% (09Г2С), packages were rolled, the main layers of which were made of steel with a silicon content in wt.%: 2, 3, 4. In addition , carried out a similar rolling of packages and a study of rolled products with the main layer of steel st.3 with a silicon content not exceeding 0.37 wt.%.

In each mode characterized by three parameters (temperature, degree of deformation, and vacuum depth), at least two packets were rolled. Samples for metallographic studies and mechanical tests were cut from chilled steel. Tests of the connecting layer for separation were carried out using the device (Fig.9) according to a special technique. The results of the mechanical tests of the samples for separation of the clad layer are shown in table 1.

A diagram of the dependence of the bond strength of the layers on the heating temperature for rolling and on the degree of deformation is shown in Fig.3.

The test results showed that when the degree of deformation of the steel package is less than 12% and more than 60% at a temperature of 800-1200 ° C, the tear resistance is significantly lower than with degrees of deformation of 12-60%.

For steels with a silicon content in the main layer of up to 2, 3 and 4 wt.%, The data on the bond strength of the layers during tensile testing are similar to those obtained for rolled products with a base layer containing 0.8 wt.% Silicon, but for rolled products with the silicon content in the main layer is more than 4 wt.%, cracks are detected at the edges to a depth of 0.3 of the thickness of the main layer (Fig. 10), which leads to an increase in the allowance for the strip width and a decrease in the metal utilization coefficient.

All samples have a good connection of the layers without breaking the continuity. After polishing without etching, the boundary of the layers is indistinguishable. On the etched samples, especially at high magnifications, the layer boundary has a toothed appearance (Figs. 4-8). The boundaries between the cladding layers and the base layer are without discontinuities.

To obtain a strong connection of the layers, as well as to reduce the oxidation of rolled products and expensive furnace heaters made of refractory alloy, the degree of deformation of the package in one pass is 12-60% at a temperature of 800-1200 ° C and a residual gas pressure in the vacuum chamber of the rolling mill no more than 1, 33 Pa.

Table 1 Parameters of rolling packages of corrosion-resistant steel and the results of mechanical tests of rolled samples to break the clad layer from the main No. The silicon content in the steel of the base layer in wt.% The degree of deformation in one pass,% Heating temperature for rolling, ° С The residual gas pressure in the vacuum chamber of the rolling mill, Pa The tensile strength of the connection of the layers at separation, MPa one 2 3 four 5 6 one 0.8; 2; 3; four 10 800, 850, 900,
950, 1000,
1050, 1100,
1150, 1200 no more than 1,33 128 ... 272 2 12 194 ... 320 3 twenty 218 ... 332 four thirty 228 ... 396 5 40 232 ... 396 6 fifty 216 ... 402 7 60 204 ... 392 8 65 168 ... 366

Claims (1)

A method of manufacturing a layered corrosion-resistant steel, consisting of a base layer of silicon alloy carbon steel, and at least one cladding layer of corrosion-resistant steel, comprising preparing the contact surfaces of the base and cladding layers, heating the package for rolling, hot deformation of the package by rolling and cooling characterized in that a base layer is prepared containing from 0.8 wt.% to 4 wt.% of silicon, the package for rolling is heated in a vacuum chamber of a vacuum heating furnace rolling mill at a temperature of 800-1200 ° C with a residual pressure of not more than 1.33 Pa, hot deformation of the package by rolling is carried out in the working vacuum chamber of the mill stand, hermetically connected to the vacuum chamber of the heating furnace, with a degree of deformation from 12% to 60% per one pass, and the cooling of rolled products is carried out to a temperature of no higher than 300 ° C in a vacuum chamber for cooling and unloading, tightly connected to the working vacuum chamber of the rolling mill.

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