RU2361930C1 - Manufacturing method of hot-rolled mill products of heavy-duty - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: it is implemented steel making, containing, wt %: carbon 0.045-0.12, silicon not more than 0.50, manganese 0.35-1.15, aluminium 0.01-0.09, nitrogen not more than 0.010, niobium and/or titanium - 0.01-0.08, iron and unavoidable admixtures - the rest, pouring, hot rolling with finishing temperature in the range 830-880°C, cooling by water, winding of strips into coils in the range 510-640°C. Steel additionally contains, wt %: vanadium 0.01-0.08, calcium 0.0005-0.010, herewith total content of niobium, titanium and vanadium mustn't exceed 0.117 wt %.

EFFECT: strength properties increasing of steel at saving of formability and receiving of hot-rolled mill products of required strength grade.

7 cl, 6 tbl

Description

The invention relates to the field of metallurgy, and specifically to a technology for the production of high-rolled hot rolled products from low alloy steel, intended for the manufacture of automobile parts by stamping.

One of the defining qualities of an autosheet is its ability to stretch when stamping car parts. Hot rolled strips with increased strength and high ability to stretch, depending on the strength class, must correspond to a certain set of mechanical properties, for example, according to the requirements of the European standard EN 10149 (table 1):

Table 1 Strength Class * Mark The minimum yield strength (R _eH ), N / mm ² Temporary resistance (R _m ), N / mm ² Minimum elongation A,% <3 mm L _c = 80 mm > 3 mm L _c = 5.65√S ₀ 315 S315MC 315 390-510 twenty 24 355 S355MC 355 430-550 19 23 420 S420MC 420 480-620 16 19 460 S460MC 460 520-670 fourteen 17 500 S500MC 500 550-700 12 fourteen Note: * The strength class is laid down in the brand name according to EN 10292-04. The numerical value corresponds to the minimum yield strength.

A known method for the production of hot rolled strips of steel with a carbon content of up to 0.1 wt.%, In which, during hot rolling, the temperature of the end of rolling is taken equal to 860-890 ° C, the strip stripping is started 7-9 s after the end of rolling, and the winding temperature is taken equal to 640-700 ° C, while the training of the strips to obtain their matte surface is carried out in rolls with the height of the microroughness of barrels Ra = 2.2-2.7 microns and to obtain surface roughness with Ra = 2.9-4.0 microns [RF patent №2255990, IPC С21D 8/04, 07/10/2005].

The disadvantage of this method is that it does not provide the required level of mechanical properties of rolled strength classes from 315 to 500.

A known method for the production of hot rolled strips of steel with a carbon content in the range of 0.01-0.1%, in which during hot rolling the temperature of the end of rolling is taken equal to 780-800 ° C, cooling to a winding temperature is carried out at a speed of 9-13 deg / s , etching is carried out at 60-80 ° C, and training is carried out with a relative compression of 0.5-1.0% [RF Patent No. 2164248, IPC C21D 8/04, C21D 9/46, 03/20/2001].

The disadvantage of this method is that it does not provide the required level of mechanical properties of strength classes from 315 to 500.

The closest in technical essence and the achieved result is a method for the production of hot rolled strips, including the smelting of ultralow carbon steel with impurities of sulfur and nitrogen alloyed with titanium with an element content satisfying the ratio Ti / (4 · C + 3.43 · N + 1.5 · S ) = 1 ÷ 1.5, at which the hot rolling is completed at a temperature of 885-915 ° C, cooling is carried out to a temperature of 685-715 ° C, then the strips are trained with compression of 0.8-1.2% [RF Patent No. 2202630 , IPC C21D 8/04, 04/20/2003] - the prototype.

The disadvantage of this method is that it does not provide the required level of mechanical properties of rolled strength classes from 315 to 500.

The technical result of the invention is to increase the strength characteristics of steel while maintaining stampability, as well as to obtain hot-rolled steel of the required strength class.

The technical result is achieved by the fact that in the method of manufacturing hot rolled products of increased strength, including smelting low alloy steel, casting, hot rolling, water cooling, winding strips into coils, according to the invention, steel containing carbon 0.045-0.12% is smelted, silicon - not more than 0.50%, manganese - 0.35-1.15%, aluminum - 0.01-0.09%, nitrogen - not more than 0.010%; niobium and / or titanium - 0.01-0.08% of each, iron and inevitable impurities - the rest, while the temperature of the end of rolling is maintained in the range of 830-880 ° C, and the temperature of the winding is in the range of 510-640 ° C. Steel may additionally contain vanadium in an amount of 0.01-0.08%, as well as calcium in an amount of 0.0005-0.010%, while the total content of niobium, titanium and vanadium should not exceed 0.117 wt.%.

According to the invention, the content of carbon, manganese and the total content of niobium, titanium and vanadium are associated with the required strength class by the ratios:

where [C] is the carbon content in steel,%;

[Mn] is the manganese content in steel,%;

[Nb + Ti + V] is the total content of niobium, titanium, vanadium,%;

0.0002, 0.002, 0.0022, 0.15, 0.013 - empirical coefficients,%;

To _ol - dimensionless indicator, numerically equal to the required minimum yield strength.

The invention consists in the following. The mechanical properties of cold rolled sheet steel are affected by both the chemical composition of the steel and the modes of deformation-heat treatment.

Carbon is one of the reinforcing elements. When the carbon content is less than 0.045%, the strength properties of the steel are below an acceptable level. An increase in carbon content of more than 0.12% leads to a decrease in the ductility of steel, which is unacceptable.

Silicon in steel is used as a deoxidizer and an alloying element. When the silicon content in the steel is more than 0.50%, ductility sharply decreases, and embrittlement of steel takes place.

Manganese provides the desired mechanical properties. When the manganese content is less than 0.35%, the strength of the steel is below acceptable. An increase in the manganese content of more than 1.15% overly strengthens the steel, worsens its ductility.

Aluminum is introduced into steel as a deoxidizer. When the aluminum content is less than 0.01%, the ductility of the steel decreases, the steel becomes prone to aging. An increase in aluminum content of more than 0.09% leads to a deterioration in the complex of mechanical properties.

Nitrogen strengthens steel. With a nitrogen content of more than 0.010%, the steel becomes prone to aging.

Niobium, titanium and vanadium are used as alloying elements and provide the necessary strength properties. When the content of niobium, titanium, vanadium is less than 0.01%, it is not possible to obtain the required level of strength. An increase in the content of niobium, titanium or vanadium more than 0.08% is impractical due to excessive hardening of steel and deterioration of ductility.

Calcium is used in the range of 0.0005-0.010% as a highly active element for enhancing the deoxidizing effect of aluminum and removing phosphorus, sulfur, oxygen from the melt into slag, which leads to a change in the phase composition and an improvement in the shape (globulation) of oxide inclusions, as well as a decrease in their amount .

Hot rolling with temperatures of the end of rolling 830-880 ° C and winding 510-640 ° C provides the formation of an optimal metal texture with a predominant crystallographic orientation <111>, as well as a microstructure with high stability and uniformity. Below and above the stated temperature limits, the technical result was not achieved, namely, steel acquired a structure with a texture unfavorable for cold stamping and an uneven microstructure of the ferrite matrix.

It was experimentally established that the upper limit of the total content of niobium, titanium and vanadium is limited to 0.117%. With an increase in the total content of [Nb + Ti + V] over 0.117%, the ductility of rolled products deteriorates due to excessive hardening of steel.

It was established experimentally that for obtaining the desired strength grade carbon content, manganese, and the total content of niobium, titanium and vanadium should be regulated in accordance with the dependencies: [C] = (0.0002 · K _pr +0,002) ± 0,02, %; [Mn] = (0.0022 · K _pr -0,15) ± 0,20,%; [Nb + Ti + V] = (0,0002 · K _pr -0,013) ± 0,03,%.

Method implementation examples

Low oxygen steels were smelted in an oxygen converter, the chemical composition of which is given in Table 2.

Smelted steel was poured on a continuous casting machine into slabs with a cross section of 250 × 1280 mm. The slabs were heated in a heating furnace with walking beams to a temperature of 1250 ° C for 2.5-3.5 hours and rolled on a continuous broadband mill 2000 in strips 2.5-3.5 mm thick. The temperature of the strips at the outlet of the last mill stand is regulated. Hot rolled strips on the discharge roller table were cooled with water to certain temperatures and wound into rolls. Chilled rolls were subjected to hydrochloric acid etching in a continuous etching unit.

table 2
The chemical composition of low alloy steels Composition number The content of elements, wt.% FROM Si Mn Al N Nb Ti V Sa Fe and inevitable impurities one 0,03 0,03 0.30 0.05 0.006 0.004 0.003 0.003 0,0002 Ost. 2 0,045 0.003 0.35 0.05 0.005 0.010 0.005 0.005 0,0005 Ost. 3 0,07 0.20 0.70 0.01 0.005 0,030 0.010 0.005 0.005 Ost. four 0.08 0.42 0.82 0.04 0.010 0.002 0.002 0,080 0.010 Ost. 5 0.09 0.45 0.93 0.05 0.006 0.003 0,080 0.013 0,0004 Ost. 6 0.12 0.50 1.15 0.09 0.005 0,080 0,025 0.010 0,0007 Ost. 7 0.13 0.55 1.20 0.05 0.011 0,085 0.015 0,025 0.011 Ost. 8 (prototype) 0.003 - - - 0.005 - 0.051 - - Ost. Note: composition No. 8 contains sulfur in an amount of 0.008 wt.%

Table 3 shows the options for implementing the method of production of hot-rolled steel, as well as indicators of mechanical properties.

Table3
Technological parameters of the production of hot rolled products and indicators of mechanical properties Composition number The temperature of the end of rolling T _CP , ° C Winding temperature T _cm , ° С Yield strength σ _t (R _eH ), N / mm ² Tensile strength σ _in , (R _m ), N / mm ² Elongation δ ₈₀ , (A),% one 885 665 280 350 29th 2 880 640 345 405 26 3 855 620 380 455 23 four 845 580 435 505 21 5 840 550 475 530 17 6 830 510 515 560 fourteen 7 827 505 530 580 10 8 (prototype) 900 700 230-235 340-345 δ ₁₀ 38

Tables 4-6 indicate the required content of carbon, manganese and [Nb + Ti + V] according to dependencies (1), (2), (3).

Table 4
The minimum and maximum carbon content is calculated according to the relationship [C] = (0,0002 · K _pr +0,002) ± 0,02,% Composition number Content C, wt.% The required strength class K _pr C content, wt.% According to the relationship [S] = (0.0002 · K _pr +0,002) ± 0,02,% C _min C _max one 0,03 315 0,045 0,085 2 0,045 315 0,045 0,085 3 0,07 355 0,053 0,093 four 0.08 420 0,066 0.106 5 0.09 460 0,074 0.114 6 0.12 500 0,082 0.122 7 0.13 500 0,082 0.122 8 (prototype) 0,03 315 0,045 0,085

Table 5
Minimum and maximum manganese content, calculated according to the relationship [Mn] = (0,0022 · K _pr -0,15) ± 0,20,% Composition number The content of Mn, wt.% The required strength class K _pr Mn content, wt.% According to the relationship [Mn] = (0.0022 · K _pr -0,15) ± 0,20,% Mn _min Mn _max one 0.30 315 0.343 0.743 2 0.35 315 0.343 0.75 3 0.70 355 0.431 0.831 four 0.82 420 0.574 0.974 5 0.93 460 0.662 1,062 6 1.15 500 0.75 1.15 7 1.20 500 0.75 1.15 8 (prototype) - 315 0.343 0.743

Table 6
Minimum and maximum content [Nb + Ti + V], calculated according to the relationship [Nb + Ti + V] = (0,0002 · K _pr -0,013) ± 0,03,% Composition number The content of [Nb + Ti + V], wt.% The required strength class K _pr The content of (Nb + Ti + V), wt.% According to the relationship [Nb + Ti + V] = (0,0002 · K _pr -0,013) ± 0,03,% [Nb + Ti + V] _min [Nb + Ti + V] _max one 0.01 315 0.02 0.08 2 0.02 315 0.02 0.08 3 0,045 355 0,028 0,088 four 0,084 420 0,041 0,101 5 0,096 460 0,049 0.109 6 0.015 500 0,057 0.117 7 0.125 500 0,057 0.117 8 (prototype) 0.051 315 0.02 0.08

From tables 2-6 it is seen that in the case of the implementation of the proposed method (compositions No. 2-6) and the fulfillment of dependencies (1) - (3), mechanical properties with strength classes from 315 to 500 are achieved. and 7) and using the prototype method (composition No. 8), strength classes from 315 to 500 are not achieved: for composition No. 1, strength class 315 does not correspond to yield strength and tensile strength; for composition No. 7, the elongation class 500 does not correspond to elongation; for the prototype method (composition No. 8), the strength class 315 does not correspond to the yield strength and tensile strength.

Highly loaded car parts were made from rolling by stamping; there were no comments on stamping from the consumer.

Claims (7)

1. A method of manufacturing hot rolled steel of increased strength, including the smelting of low alloy steel, casting, hot rolling, water cooling, winding strips into coils, characterized in that the steel is smelted containing the components in the following ratio, wt.%:
carbon 0,045-0,12 silicon no more than 0.50 manganese 0.35-1.15 aluminum 0.01-0.09 nitrogen no more than 0,010 niobium and / or titanium 0.01-0.08 each iron and inevitable impurities rest
while the temperature of the end of the rolling support in the range of 830-880 ° C, and the temperature of the winding in the range of 510-640 ° C. 2. The method according to claim 1, characterized in that the steel further comprises vanadium in an amount of 0.01-0.08 wt.%. 3. The method according to claim 2, characterized in that the total content of niobium, titanium and vanadium does not exceed 0.117 wt.%. 4. The method according to any one of claims 1 to 3, characterized in that the steel further comprises calcium in an amount of 0.0005-0.010 wt.%. 5. The method according to any one of claims 1 and 2, characterized in that the carbon content is related to the required strength class by the dependence:
[C] = (0.0002 · K _pr +0,002) ± 0,02, wt.%
where 0,0002 is the empirical coefficient,%;
To _ol - dimensionless indicator, numerically equal to the required minimum yield strength;
0.002 - empirical coefficient,%. 6. The method according to any one of claims 1 and 2, characterized in that the manganese content is related to the required strength class by the dependence:
[Mn] = (0.0022 · K _pr -0,15) ± 0,20, wt.%
where 0,0022 is an empirical coefficient,%;
To _ol - dimensionless indicator, numerically equal to the required
minimum yield strength;
0.15 - empirical coefficient,%. 7. The method according to any one of claims 1 and 2, characterized in that the total content of niobium, titanium and vanadium is associated with the required strength class by the dependence:
[Nb + Ti + V] = (0,0002 · K _pr -0,013) ± 0,03, wt.%
where 0,0002 is the empirical coefficient,%;
To _ol - dimensionless indicator, numerically equal to the required
minimum yield strength;
0.013 - empirical coefficient,%.