RU2341565C2 - Method of candy manufacturing from low-alloy steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes slab receiving, slabs heating till temperature 1200÷1300°C, rough and multipass finish rolling till defined thickness in regulated temperature range, cooling by water till winding temperature, at that slab is received from steel, containing wt %: 0.22-0.28 C; 0.15-0.35 Si; 1.0-1.4 Mn; 0.02-0.05 Al; not more than 0.02 Ca; not more than 0.03 Ti; not more than 0.4 Cr; not more than 0.4 Cu; not more than 0.010 S; not more than 0.015 P; not more than 0.012 N, the rest-iron, multipass finish rolling is implemented in temperature range from 960-1050 till 820-890°C, and cooling by water is implemented till winding temperature, equal to 580-660°C. At that at containing carbon in steel 0.22-0.24 wt % candies of thickness 3.5-5.0 mm are cooled by water till winding temperature 600-650°C, and at thickness more than 5.0 mm - till winding temperature 580-640°C. At contamination of carbon in steel more than 0.24 wt % candies of thickness 3.5-5.0 mm are cooled by water till winding temperature 610-660°C, and at thickness more than 5.0 mm - till winding temperature 600-650°C.

EFFECT: stability increasing of mechanical properties and yield ratio.

3 cl, 4 ex, 3 tbl

Description

The invention relates to the field of metallurgy, and more specifically to rolling production, and can be used in the manufacture of continuous broadband mills for electric welded straight-line tubing and casing pipes.

For the production of tubing and casing pipes, strips (hot rolled strips) of a thickness of 3.5-10.0 mm, a width of 950-1835 mm of low alloy steel, having the following set of mechanical properties are required (Table 1):

Table 1
Mechanical properties and weldability of strips (TS 105-496) σ _in , N / mm ² σ _t , N / mm ² δ,% Weldability not less than 520 320-470 not less than 20 satisfaction

Note: the axis of the samples coincides with the direction of rolling.

A known method of producing steel sheets, including smelting and continuous casting into slabs of low alloy steel containing, by weight. %:

Carbon 0.04-0.10 Silicon 0.01-0.50 Manganese 0.4-1.5 Chromium 0.05-1.0 Molybdenum 0.05-1.0 Vanadium 0.01-0.1 Boron 0.0005-0.005 Aluminum 0.001-0.1 Iron and impurities rest

The cast slabs are heated to a temperature of 1250 ° C and rolled with a total compression of at least 75%. Laminated sheets are subjected to quenching from the austenitic region and high-temperature tempering [1].

The disadvantages of this method are that the strip after rolling have low and uneven mechanical properties. This makes it impossible to use them for the manufacture of tubing and casing pipes. In addition, the need for thermal improvement (hardening and tempering) of the strips after rolling complicates and increases the cost of production.

There is also known a method of manufacturing a sheet of low alloy steel, including casting slabs of the following chemical composition, wt.%:

Carbon 0.02-0.3 Manganese 0.5-2.5 Aluminum 0.005-0.1 Silicon 0.05-1.0 Niobium 0.003-0.01 Iron rest

The slabs are heated to a temperature of 950-1050 ° C and rolled at a temperature above point A _r3 with a total compression of 50-70%. Laminated sheets are cooled in air [2].

With this method of production, the sheets have insufficient and uneven strength and ductility, insufficient weldability and are unsuitable for the manufacture of tubing and casing pipes.

The closest analogue to the present invention is a method for the production of strips of low alloy steel, including heating slabs, rolling into strips with a regulated temperature of the end of rolling and cooling with water to the temperature of the winding, moreover, the slabs are heated to a temperature of 1220-1280 ° C, the temperature of the end of rolling is maintained at the range of 820-880 ° C, and the temperature of the winding is set depending on the carbon content in the steel. In addition, low alloy steel has the following chemical composition, wt.%:

Carbon 0.15-0.24 Manganese 0.20-0.70 Silicon 0.10-0.40 Aluminum 0.01-0.07 Niobium 0.01-0.08 Chromium no more than 0.4 Nickel no more than 0.4 Copper no more than 0.4 Phosphorus no more than 0,020 Sulfur no more than 0,010 Nitrogen no more than 0,012 Iron the rest [3]

The disadvantages of this method are that the strips have unstable mechanical properties, which depend on the concentration of carbon in the steel and the thickness of the strip, which determines the speed of their cooling with water. In addition, the strips are characterized by insufficient weldability: when testing samples for breaking, their destruction occurs along the weld. All this leads to a decrease in yield.

The technical problem solved by the invention is to increase the stability of mechanical properties and yield.

To solve the technical problem in the known method for the production of strips of low alloy steel containing carbon, silicon, manganese, aluminum, chromium, copper, sulfur, phosphorus, nitrogen and iron, including heating the slab, rough and multi-pass finishing rolling to a given thickness with an end temperature rolling not lower than 820 ° С, water cooling to the winding temperature, according to the proposal, the slab is made of steel containing, wt.%:

Carbon 0.22-0.28 Silicon 0.15-0.35 Manganese 1.0-1.4 Aluminum 0.02-0.05 Calcium no more than 0,02 Titanium no more than 0,03 Chromium no more than 0.40 Copper no more than 0.40 Sulfur no more than 0,010 Phosphorus no more than 0.015 Nitrogen no more than 0,012 Iron rest

in this case, multi-pass finishing rolling is carried out in the temperature range from 960 ÷ 1050 ° C to 820-890 ° C.

In addition, when the carbon content in the steel is 0.22-0.24%, strips with a thickness of 3.5-5.0 mm are cooled with water to a coil temperature of 600-650 ° C, and with a thickness of more than 5.0 mm - to a coil temperature of 580 -640 ° С, and when the carbon content in the steel is more than 0.24%, strips with a thickness of 3.5-5.0 mm are cooled with water to a winding temperature of 610-660 ° С, and with a thickness of more than 5.0 mm - to a winding temperature of 600 -650 ° C.

The invention consists in the following. The chemical composition of steel, together with the temperature conditions of hot strip rolling, determine the level and stability of their mechanical properties and, as a result, the yield. When changing the carbon concentration in steel and the thickness of the strips, which determines the conditions for their cooling with water, the microstructure parameters and mechanical properties change.

The steel of the proposed chemical composition is the least sensitive by microstructure to temperature fluctuations in the interval of finishing rolling (from 960-1050 to a temperature not lower than 820 ° C), which stabilizes the mechanical properties of the strips. A change in the temperature of the strip windings depending on the specific carbon concentration in steel and the strip thickness compensates for the influence of these parameters on the formation of the final microstructure, which provides additional stabilization of the mechanical properties of the strips (with different carbon contents and different thicknesses) and increased yield.

Carbon in the low alloy steel of the proposed composition determines the strength properties of hot rolled strips. A decrease in carbon content of less than 0.22% leads to a drop in their strength properties below an acceptable level. An increase in carbon content of more than 0.28% affects the plastic properties of strips and their weldability.

When the silicon content is less than 0.15%, the deoxidation of the steel deteriorates, and the strength properties of the strips decrease. An increase in the silicon content of more than 0.35% leads to an increase in the number of silicate inclusions, reduces the uniformity of the mechanical properties of strips, ductility and weldability.

A decrease in the manganese content of less than 1.0% increases the oxidation of steel, worsens the weldability of the strips. An increase in manganese content of more than 1.4% increases the yield strength σ _t , the unevenness of the mechanical properties, which, in turn, leads to a decrease in yield.

Aluminum deoxidizes and modifies steel. By binding excess impurity nitrogen to nitrides, it inhibits its negative effect on the properties of strips. When the aluminum content is less than 0.02%, the complex of mechanical properties of strips decreases. An increase in its concentration of more than 0.05% leads to uneven properties of the strips.

Calcium contributes to steel modification and grinding of microstructure grains during fine hot rolling of strips in the temperature range from 960-1050 ° C to 820-890 ° C. Calcium enters steel when it is smelted from limestone and slag. However, an increase in calcium content of more than 0.02% leads to an increase in the number of non-metallic inclusions and a deterioration in the plastic properties and their uniformity of strips, which is unacceptable.

Titanium cleans the metal matrix of interstitial atoms. Carbide and nitride particles of the TiC _1,0 and TiN type harden steel without reducing its plastic properties. However, an increase in titanium content of more than 0.03% affects the uniformity of the strip properties and yield.

Chromium increases the strength of steel due to the formation of carbides. But an increase in the chromium content of more than 0.40% leads to a decrease in plastic properties and a deterioration in the quality of hot-rolled strips.

Copper is an impurity element. At a copper concentration of not more than 0.4%, it does not adversely affect the weldability of strips in the production of tubing and casing, but expands the possibilities of using scrap metal for smelting, which reduces the cost of production. At a copper concentration of more than 0.40%, the plastic properties and strip weldability deteriorate.

The steel of the proposed composition may contain in the form of impurities not more than 0.010% sulfur, not more than 0.015% phosphorus. At the indicated maximum concentrations, these elements in the steel of the proposed composition do not have a noticeable negative effect on the quality of the strips, while their removal from the steel melt significantly increases production costs and complicates the process. An increase in the concentration of these harmful impurities over the suggested values worsens the whole complex of mechanical properties of strips.

It has been experimentally established that at the temperature of the start of finish rolling above 1050 ° C, coarsening of austenitic grains occurs intensively in the steel of this composition due to their recrystallization after each pass. This, in turn, leads to the formation of a coarse-grained ferrite-pearlite microstructure as a result of the α → γ transformation, which ensures the uniformity of the properties of hot rolled strips. Lowering the temperature of the beginning of the finish rolling less than 960 ° C degrades the process ductility of steel strips of the proposed composition, does not allow to obtain a stable temperature of the end of rolling. It also impairs uniformity of properties and yield.

Lowering the temperature T _CP less than 820 ° C leads to excessive grinding of the microstructure, its hardening, lowering the plastic properties of hot-rolled strips.

A decrease in the winding temperature T _cm below 600 ° C for strips with a thickness of 3.5-5.0 mm made of low alloy steel of the proposed composition with a carbon content of 0.22-0.24% affects the plastic properties of the strips and the uniformity of mechanical properties along their length. The increase in T _cm above 650 ° C leads to a decrease in the uniformity and strength properties of strips with a thickness of 3.5-5.0 mm and yield.

A decrease in the winding temperature T _cm below 580 ° C for strips with a thickness of more than 5.0 mm made of low alloy steel of the proposed composition with a carbon content of 0.22-0.24% leads to hardening of the steel above the permissible level and a decrease in ductility. The increase in T _cm above 640 ° C leads to a decrease in the level and uniformity of the strength properties of strips with a thickness of more than 5.0 mm and yield.

A decrease in the winding temperature T _cm below 610 ° C for strips with a thickness of 3.5-5.0 mm made of low alloy steel of the proposed composition with a carbon content of more than 0.24% affects the plastic properties of the strips along their length. An increase in T _cm above 660 ° C leads to a decrease in the uniformity and strength level of strips with a thickness of 3.5-5.0 mm and yield.

A decrease in the winding temperature T _cm below 600 ° C for strips with a thickness of more than 5.0 mm made of low-alloy steel of the proposed composition with a carbon content of more than 0.24% leads to hardening of the steel above the permissible level and a decrease in ductility. The increase in T _cm above 650 ° C leads to a decrease in the uniformity of the strength properties of strips with a thickness of more than 5.0 mm and yield.

Method implementation examples

In converter production, low-alloy steels of various compositions are smelted and cast (Table 2).

1. Slabs of steel of composition 2 with a carbon content [C] = 0.22% of a thickness of 250 mm are loaded into methodological furnaces and heated to austenitization temperature T _a = 1250 ° C. The heated slabs are discharged onto the furnace rolling table of a continuous broadband mill 2000 and subjected to rolling in a roughing group of stands (rough rolling) to an intermediate thickness of 40 mm. Then, the roll at a temperature T _np = 1000 ° C is set into a continuous 7-stand finishing group of stands, where it is crimped to a final thickness of H = 4.5 mm. The regulated temperature of the end of rolling T _KP = 855 ° C is supported by a change in the rolling speed and intercell cooling of the strip.

The rolled strip is issued to the discharge roller table, where it is cooled with water to the temperature of the winding. Since the strip has a thickness of H = 4.5 mm, falling within the thickness range of 3.5-5.0 mm, and contains 0.22% carbon, the winding temperature is maintained equal to T _cm = 625 ° C. The cooled strip is wound onto a roll.

2. All the same operations as in example 1, only using slabs made of steel containing 0.24% carbon (composition 3), in the finishing group of stands the strips are rolled with a thickness of H = 8.0 mm, and the winding temperature is maintained equal T _cm = 610 ° C.

3. Slabs of steel of composition 4 with a carbon content [C] = 0.25% of a thickness of 250 mm are loaded into methodological furnaces and heated to austenitization temperature T _a = 1200 ° C. The heated slabs are discharged onto the furnace rolling table of a continuous broadband mill 2000 and subjected to rolling in a roughing group of stands (rough rolling) to an intermediate thickness of 40 mm. Then, the roll at a temperature T _np = 1050 ° C is set into a continuous 7-stand finishing group of stands, where it is crimped to a final thickness of H = 4.0 mm. The regulated temperature of the end of rolling T _KP = 830 ° C is supported by a change in the rolling speed and intercell cooling of the strip.

The rolled strip is issued to the discharge roller table, where it is cooled with water to the temperature of the winding. Since the strip has a thickness of H = 4.0 mm, falling within the thickness range of 3.5-5.0 mm, and contains 0.25% carbon, the winding temperature is maintained equal to T _cm = 635 ° C. The cooled strip is wound onto a roll.

4. All the same operations as in example 3, only in the finishing group of stands the strips are rolled with a thickness of H = 7.0 mm, and the winding temperature is maintained equal to T _cm = 625 ° C.

The options for rolling strips in various modes from steels of various compositions are given in Table 3.

From table 3 it follows that when implementing the proposed method (options No. 2, 3, 5-8), an increase in the stability of mechanical properties and yield of hot-rolled strips is achieved. In addition, strips are characterized by satisfactory weldability.

In the case of transcendental values of the declared parameters (options No. 1, 4, 8), the level and stability of the mechanical properties of the strips deteriorate, which is accompanied by a decrease in the yield. Also lower and unstable properties at zero yield are strips produced according to the prototype method (option No. 9).

The technical and economic advantages of the proposed method are that the heating of slabs of low alloy steel of the proposed composition, their subsequent hot rough and controlled finish rolling with a temperature of the end of rolling not lower than 820 ° C, cooling with water to a winding temperature, determined depending on the carbon content in low-alloy steel strip thickness, provides the formation of the optimal fine-grained ferritic-pearlite microstructure of steel. Due to this, it is possible to obtain a given level and increase the stability of mechanical properties and yield with satisfactory weldability of the strips.

table 2 The chemical composition of low alloy steels Composition number The content of chemical elements, wt.% FROM Si Mn Al Ca Ti Cr Cu S R N Fe one. 0.21 0.14 0.9 0.010 0.009 0.009 0.1 0.1 0.007 0.010 0.010 the rest. 2. 0.22 0.15 1,0 0,020 0.009 0.010 0.2 0.2 0.008 0.011 0.010 3. 0.24 0.20 1,2 0,035 0.010 0,020 0.3 0.3 0.009 0.013 0.011 -: - four. 0.25 0.22 1.3 0,040 0.015 0,025 0.3 0.3 0.009 0.014 0.012 -: - 5. 0.28 0.35 1.4 0,050 0,021 0,030 0.4 0.4 0.010 0.015 0.012 -: - 6. 0.29 0.36 1,5 0,060 0,030 0,032 0.5 0.5 0.011 0.016 0.013 -: - 7. 0.19 0.40 0.7 0,030 - - 0.3 0.4 0.011 0.010 0.011 -: -

Table 3 The modes of production of strips and indicators of their effectiveness Option No. Composition number T _a , ° C T _bp, ° C T _CP , ° C [FROM], % N mm T _cm , ° C σ _in , N / mm ² σ _t , N / mm ² δ,% Weldability Yield,% one. one 1310 1060 900 0.21 3,5 670 450-500 220-310 14-20 unsatisfied. - 2. 2 1300 1080 890 0.22 3,5 650 530 330 26 sat. 99.5 3. 2 1250 1065 885 0.22 4,5 625 540 395 28 sat. 99.7 four. 3 1270 1070 880 0.24 6.0 660 490-520 300-320 20-24 sat. 56.7 5. 3 1250 1065 885 0.24 8.0 610 540 320 28 sat. 99.7 6. four 1200 1050 830 0.25 4.0 635 530 340 27 sat. 99.6 7. four 1200 1050 830 0.25 7.0 625 550 470 22 sat. 99.8 8. 5 1210 1040 830 0.28 9.0 600 560 470 23 sat. 99.8 8. 6 1190 950 810 0.29 5,0 600 520-580 470-490 17-20 unsatisfied. 63.1 9. 7 1250 840 0.19 7.0 630 470-500 290-310 22 sat. -

Using the proposed method will increase the profitability of the production of strips for casing by 20-35%.

Information sources

1. Japanese application No. 61-163210, IPC C21D 8/00, 1986.

2. Japanese application No. 61-223125, IPC C21D 8/02, C22C 38/54, 1986.

3. RF patent 2264475, IPC C21D 8/02, 20.11.2005 - prototype.

Claims (3)

1. A method for the production of strips of low alloy steel, including obtaining a slab, heating a slab, roughing and multi-pass finishing rolling to a predetermined thickness in a regulated temperature range, water cooling to a winding temperature, characterized in that the slab is obtained from steel containing, wt.%: carbon 0.22-0.28 silicon 0.15-0.35 manganese 1.0-1.4 aluminum 0.02-0.05 calcium no more than 0,02 titanium no more than 0,03 chromium no more than 0.40 copper no more than 0.40 sulfur no more than 0,010 phosphorus no more than 0.015 nitrogen no more than 0,012 iron rest, while multi-pass finishing rolling is carried out in the temperature range from 960-1050 to 820-890 ° C. 2. The method according to claim 1, characterized in that when the carbon content in the steel is 0.22-0.24%, strips with a thickness of 3.5-5.0 mm are cooled with water to a winding temperature of 600-650 ° C, and with a thickness of more 5.0 mm - up to a winding temperature of 580-640 ° С. 3. The method according to claim 1, characterized in that when the carbon content in the steel is more than 0.24 wt.%, Strips with a thickness of 3.5-5.0 mm are cooled with water to a winding temperature of 610-660 ° C, and with a thickness of more than 5 , 0 mm - up to a winding temperature of 600-650 ° С.