RU2799195C1 - Method for the production of hot-rolled pickled steel - Google Patents

Abstract

FIELD: hot-rolled pickled steel.

SUBSTANCE: method for the production of hot-rolled pickled steel includes the smelting of steel containing, wt.%: 0.04-0.15 C, max 0.1 Si, 0.7-1.2 Mn, max 0.010 S, max 0.03 P, max 0.25 Cr, max 0.3 Ni, not more than 0.3 Cu, 0.01-0.08 Al, not more than 0.015 N, not more than 0.08 Nb, 0.01-0.05 Ti, not more than 0.01 V, Fe, and the rest is inevitable impurities. Casting of steel, its hot rolling, coiling of strips into a roll and pickling are carried out. The roughing stage of hot rolling starts at a temperature of 1090-1220°C and finished at a temperature of 1000-1150°C. The finishing stage of hot rolling starts at a temperature of 950-1030°C and finished at a temperature of 820-920°C. The winding of the strips is carried out at a temperature of 490-600°C. Rolled products are etched at a temperature of the ends of the rolls of not more than 100°C.

EFFECT: increase in the strength properties of rolled products.

5 cl, 2 tbl

Description

The invention relates to the field of metallurgy and can be used in the production of hot-rolled pickled steel with a thickness of 2.0-6.0 mm, intended for the manufacture of wheel disks.

A known method for the production of hot-rolled steel for cold stamping, including the smelting of low-carbon steel, casting, hot rolling, winding strips into coils, according to which steel is smelted containing components in the following ratio, wt.%: carbon 0.002-0.015, silicon 0.005-0.050, manganese 0.05-0.50, phosphorus 0.005-0.09, sulfur 0.003-0.020, copper 0.1-0.6, aluminum 0.02-0.07, nitrogen 0.002-0.007, titanium 0.0005-0, 0040, niobium not more than 0.060, iron and inevitable impurities - the rest, subject to the following conditions:

Sef.=[C]-CTi-CNb≥0.0006% and Sef+0.05[P]≥0.003%,

where is sef. - effective content of carbon not bound by titanium or niobium;

[C] - total carbon content in steel;

CTi is the content of titanium bonded carbon, with CTi=0 at [Ti]/[N]<3.43 and CTi=([Ti]-3.43N)/4 at [Ti]/[N]≥3.43 ;

CNb is the content of carbon bound by niobium, CNb=Nb/7.74;

[P] - phosphorus content in steel,

and after winding the strip, etching and/or training is carried out [Patent RU No. 2307175, IPC C21D 8/04, C22C 38/16, 2007].

Specified in the way the chemical composition does not allow to obtain a structure that ensures the stability of the properties in the finished product.

The closest analogue to the claimed object is a method for the production of hot-rolled steel for automobile wheels, including smelting, out-of-furnace processing, continuous casting, heating the slab for hot rolling, rolling it in the roughing and finishing continuous groups of stands of a broad-strip mill to obtain a strip, cooling the strip with water at the outlet roller table with subsequent winding into a roll, according to which steel of the following chemical composition is smelted, wt.%:

Carbon 0.06-0.11

Silicon not more than 0.30

Manganese 0.50-0.80

Sulfur no more than 0.007

Niobium 0.02-0.06

Titanium no more than 0.025

Calcium 0.001-0.007

Iron and inevitable impurities the rest,

at the same time, rolling in the finishing group of stands is carried out with an acceleration of 0.01-0.05 m/s ² , the temperature of the end of hot rolling is set at 860-930°C, after which differential cooling of the upper and lower surfaces of the strip is carried out, and in the process of cooling the strip with a thickness from more than 5.5-6.0 mm, water is supplied by opening all pipe valves at the top and bottom of the strip immediately after it leaves the last stand of the hot rolling mill, and in the process of cooling the strip with a thickness of 3.0-5.5 mm - by opening each the fourth pipe valve at the top and bottom of the strip after the strip reaches the coiler, while the coiling temperature is 620-680°C [Patent RU No. 2602206, IPC B21B 1/26, 2016].

The disadvantage of this method are insufficient strength properties.

The technical result of the invention is to increase the strength properties of rolled products in relation to the prototype while maintaining satisfactory formability, increasing the usable steel after stamping and bending.

The technical result is achieved by the fact that in a method for the production of hot-rolled pickled steel, including steel smelting, casting, hot rolling, winding of strips into a coil and pickling, steel is smelted containing, wt.%:

C 0.04-0.15

Si no more than 0.1

Mn 0.7-1.2

S no more than 0.010

P no more than 0.03

Cr not more than 0.25

Ni no more than 0.3

Cu not more than 0.3

Al 0.01-0.08

N no more than 0.015

Nb no more than 0.08

Ti 0.01-0.05

V not more than 0.01

Iron and inevitable impurities the rest,

at the same time, the rough rolling stage starts at a temperature of 1090-1220°C and ends at a temperature of 1000-1150°C; 490-600°C, and the pickling of rolled products is carried out at a temperature of the ends of the roll is not more than 100°C.

The resulting rolled product is characterized by a tensile strength of 460–670 MPa, a yield strength of 400–600 MPa, and a relative elongation of at least 14%.

The thickness of the finished rolled products is 2.0-6.0 mm.

For rolled products with a thickness of 2.0-3.99 mm, the rolling end temperature is 820-900°C, the coiling temperature is 520-600°C, for rolled products with a thickness of 4.0-6.0 mm, the rolling end temperature is 840-920°C and the coiling temperature is 490-570°C.

The microstructure of the resulting rolled products consists of at least 98% ferrite and up to 2% pearlite, with a grain size of 10-13 points.

The essence of the invention

The chemical composition and the homogeneous structure obtained after hot rolling make it possible to provide a range of required properties necessary to ensure the processing of rolled metal products by the end user.

When the carbon content is 0.04%, the required strength characteristics after hot rolling are not achieved. Above 0.15% carbon, elongation is reduced, which can cause processing problems for the customer.

Silicon and manganese provide the desired mechanical properties due to solid-soluble hardening, the hardening mechanism of which is associated with the interaction of manganese and silicon atoms dissolved in the crystal lattice. When the silicon content in steel is more than 0.1%, ductility decreases sharply. With a manganese content of less than 0.7%, the strength of the steel is below the permissible. An increase in the manganese content of more than 1.2% excessively strengthens the steel, degrades its ductility.

Sulfur and phosphorus are harmful impurities that degrade the mechanical properties of hot-rolled sheets. However, when the content of phosphorus is not more than 0.030% and sulfur is not more than 0.010%, their harmful effect is weak.

Chromium, nickel and copper harden steel, but at their concentration of more than 0.25%, 0.3% and 0.3%, respectively, the ductility of the steel decreases and its formability and flexibility deteriorate.

Aluminum was introduced to deoxidize steel and reduce casting defects. When the aluminum content is less than 0.01%, the ductility of steel decreases, the steel becomes prone to aging. An increase in the aluminum content of more than 0.08% leads to a deterioration in its mechanical properties below an acceptable level and a decrease in formability and flexibility.

Nitrogen is an element that hardens steel. An increase in the nitrogen content of more than 0.015% leads to a decrease in ductility and contributes to the aging of steel.

The minimum titanium content (0.01%) is determined by the requirement to release some nitrogen in the form of titanium nitride. An increase in the content of titanium more than 0.05% and niobium above the upper limit (0.08%), in addition to a negative effect on formability and a decrease in the magnitude of the HV effect, leads to an increase in the cost of steel.

Vanadium strengthens the ferrite matrix. With a vanadium content of more than 0.010%, the formability deteriorates and the cost of steel increases.

The rough rolling step starts at a temperature of 1090-1220°C and ends at a temperature of 1000-1150°C. It has been experimentally established that if the temperature of the beginning of rough rolling is higher than 1220°C, this will lead to the formation of cracks and breaks during rolling. At temperatures below 1090°C, undissolved large non-metallic inclusions remain in the steel, which reduces its ductility and mechanical properties of rolled products. At a temperature of the end of rough rolling above 1150°C, the diversity of the microstructure increases and the complex of mechanical properties of rolled products decreases. At a temperature of the end of rough rolling below 1000°C, the steel has low technological ductility, which negatively affects the formability and flexibility of the steel.

Finish rolling starts at a temperature of 950-1030°C and ends at a temperature of 820-920°C. These temperatures are chosen in order to increase the density of defects in the crystal structure of the metal and their ordered distribution (substructure), which leads to the multiple formation of ferrite volumes during the polymorphic γ→α transformation and further formation of the required structure.

The winding of the strips is carried out at a temperature of 490-600°C. This range ensures the uniformity of the formation of ferrite grains and the required mechanical properties of the finished product.

Pickling of rolled products is carried out at a temperature of the ends of the roll of not more than 100 ° C, because at higher temperatures, the solutions of the pickling unit will boil. Also, high-temperature metal will adversely affect the components of the unit, which can lead to malfunctions.

For rolled products with a thickness of 2.0-3.99 mm, the rolling end temperature is 820-900°C, the coiling temperature is 520-600°C, for rolled products with a thickness of 4.0-6.0 mm, the rolling end temperature is 840-920°C and the coiling temperature is 490-570°C. These temperature ranges ensure the uniformity of the ferrite-pearlite structure and obtaining the required physical and mechanical properties.

The homogeneous microstructure of the resulting rolled product consists of ferrite-pearlite grains with a size of 10-13 points, without impurities such as manganese sulfides. This structure is achieved by an optimally selected chemical composition in combination with the developed technological rolling conditions.

Implementation examples:

Steel was smelted in a converter, out-of-furnace treatment was carried out and poured into slabs. Then the slabs were transferred to the rolling mill-2. On the mill 2000 rolled slabs to a final thickness of 2.0-6.0 mm at a temperature of the beginning of rough rolling 1090-1220°C and finish rolling at a temperature of 820-920°C. Then the rental was wound into a roll at a temperature of 490-600°C. After that, the rolled metal was subjected to pickling at a temperature of the ends of the roll not exceeding 100°C.

Table 1 shows the chemical compositions of smelted slabs with different content of elements. Table 2 shows the technological parameters and mechanical properties of the resulting hot-rolled pickled steel. Examples 1-4 are examples of the invention, examples 5-6 of the prototype.

Subject to the specified ranges of chemical composition and technological parameters (examples No. 1-4), the following mechanical properties of the resulting rolled products were achieved: yield strength 400-600 MPa, tensile strength 460-670 MPa and relative elongation of at least 14%.

When performing examples of the prototype (examples No. 5-6) were obtained low strength properties and observed defects after testing.

The test for formability and flexibility of rolled products was carried out on press-bending machines and the indicator of good formability was determined from the presence of cracks after deformation, if there were no cracks, the rolled product was good.

Tests have shown that the use of the proposed method for the production of hot-rolled pickled steel in compliance with the specified parameters makes it possible to ensure high mechanical properties of rolled products (yield strength 400-600 MPa, tensile strength 460-670 MPa, relative elongation of at least 14%) and ensure good formability and flexibility.

Table 1

Chemical compositions of steel

Fuse C Si Mn S P Cr Ni Cu Al N Nb Ti V 1 0.11 0.02 1.04 0.008 0.01 0.05 0.03 0.05 0.034 0.005 0.072 0.019 0.0035 2 0.09 0.019 0.76 0.003 0.009 0.032 0.01 0.01 0.040 0.004 0.046 0.016 0.003 3 0.08 0.03 0.83 0.007 0.011 0.05 0.02 0.05 0.038 0.007 0.050 0.015 0.002 4* 0.05 0.09 0.87 0.006 0.013 0.03 0.03 0.04 0.032 0.005 0.038 0.014 0.0042 5* 0.08 0.15 0.68 0.002 - - - - - - 0.022 0.015 - 6* 0.09 0.12 0.52 0.003 - - - - - - 0.044 0.005 -

table 2

Controlled parameters and obtained mechanical properties

Example Rolled thickness, mm Tnch, °C Тkch, °C Tnp, °C Tkp, °C Tcm, °C Tt, °C Grain score Mechanical properties Presence of defects
(after bending
and stampings) Tensile strength,
σ _in MPa Yield strength, σ _t MPa Relative elongation, δ % 1 5.9 1102 1079 1013 890 569 36.5 eleven 576 484 32 No 2 2 1141 1095 953 843 533 32.6 10 605 450 26 No 3 4.8 1105 1088 998 845 532 25 13 590 445 24 No 4 3 1100 1062 982 855 525 27 12 525 467 thirty No 5 3.6 - - - 917 660 - 10 483 410 29 Yes 6 6.0 - - - 912 636 - eleven 510 400 31 Yes

Claims (7)

1. A method for the production of hot-rolled pickled steel, including steel smelting, casting, hot rolling, winding strips into coils and pickling, characterized in that steel is smelted containing, wt%: C 0.04-0.15 Si no more than 0.1 Mn 0.7-1.2 S no more than 0.010 P no more than 0.03 Cr no more than 0.25 Ni no more than 0.3 Cu no more than 0.3 Al 0.01-0.08 N no more than 0.015 Nb no more than 0.08 Ti 0.01-0.05 V no more than 0.01 Fe and unavoidable impurities rest, while the roughing stage of hot rolling starts at a temperature of 1090-1220°C, and ends at a temperature of 1000-1150°C, the finishing stage of hot rolling starts at a temperature of 950-1030°C, and ends at a temperature of 820-920°C, winding of strips carried out at a temperature of 490-600°C, the pickling of rolled products is carried out at a temperature of the ends of the rolls is not more than 100°C. 2. The method according to claim 1, characterized in that the resulting rolled product has a tensile strength of 460-670 MPa, a yield strength of 400-600 MPa and a relative elongation of at least 14%. 3. The method according to claim 1, characterized in that the thickness of the finished product is 2.0-6.0 mm. 4. The method according to claim 1, characterized in that for a thickness of rolled products of 2.0-3.99 mm, the temperature of the end of rolling is 820-900°C, the winding temperature is 520-600°C, and for rolled products with a thickness of 4.0- 6.0 mm, the rolling end temperature is 840-920°C and the coiling temperature is 490-570°C. 5. The method according to claim 1, characterized in that the microstructure of the resulting rolled products consists of at least 98% ferrite and up to 2% pearlite with a grain size of 10-13 points.