RU2344181C2 - Steel hot-rolled blank for shaping and method of rolling - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention concerns metal processing by pressure, particularly strip blank manufacturing for shaping. To improve plasticity properties of semifinished rolled products for steel strip blanks, carbon, manganese and silicon content depends on σ_t value and blank thickness h according to the following ratios: C'_e=(σ_t-262.5)/130 for h≥6 mm and C_e"=(σ_t-291)/124 for h<6 mm, where C_e=C+Mn/9+Si/3. A blank is hot-rolled from semifinished rolled product at specified temperature and cooled down at a rate depending on thickness h after rolling and specified flow limit according to the following ratio: V'_cool=(σ_t-297)/0.94, degree/s, for h≥6 mm and V"_cool=( σ_t-306):2.9 degree/s, for h<6 mm.

EFFECT: enhanced plasticity properties in semifinished rolled products for steel strip blanks.

2 cl, 2 ex

Description

The invention relates to the production of strip steel and can be used for the manufacture of billets.

Hot-rolled and cold-rolled strip steel with a given chemical composition and mechanical properties, which should ensure defect-free profiling of the workpiece (for example, the absence of cracking) and the required quality of bent profiles, for example long (angled, channel, trough, etc.), are used as a billet for the production of cold-rolled sections. )

The necessary properties of the billet for profiling determine the specification of its composition and modes of hot (cold) rolling. The requirements for this workpiece are described in sufficient detail in the book of S.F. Berezovsky "Production of bent profiles", Moscow: Metallurgy, 1985, pp. 11-14.

Known preform (sheet steel) for processing by molding, with the ability to deep stretch and stretch and containing carbon, manganese, chromium, vanadium and tungsten in predetermined quantities. However, the steel composition is not set depending on the thickness of the workpiece and its main mechanical indicator - the yield strength σ _t (see US Pat. No. 3442468, class C22C 39/50, publ. 13.02.72).

A known technology for the production of billets (tackle) from ageless low-carbon steel, which regulates the hot rolling regimes and, in particular, the compression in the descaler of a continuous hot rolling mill (see AS USSR No. 1533783, class B21B 1/02, publ. in BI No. 1, 1990). This technology is not acceptable for the production of the workpiece used in profiling.

The closest analogue to the claimed object is a hot-rolled billet for profiling and its rolling technology, described in the book of V.I. Anisimova et al. Extension of the range of rolled metal products - a reserve for savings, Chelyabinsk, Yu. Ural. Prince ed., 1980, pp. 16-20, 25-26 and table 4.

This preform with a specific chemical composition and σ _t (st3ps) is characterized by a relatively low content of basic elements (C, Mn, Si) and a constant σ _t for all thicknesses h of steel. A disadvantage of the known strip billet is the lack of a relationship between the values of h, σ _t and the content in steel C, Mn, Si (i.e., the carbon equivalent of С _е = С + Mn / 9 + Si / 3 (see the analogue in GOST 19281 “Rental from steel of increased strength ”, clause 4.3).

The rolling technology of the billet for profiling regulates the amount of compression in the last stand of the hot rolling mill, as well as the temperature of the end of rolling and strip winding. A disadvantage of the known technology is the lack of data on the cooling rate of the strips after rolling, which largely determines the mechanical properties of the finished product.

As a result of this, the known object does not provide defect-free profiling of strip steel and high quality of finished bent profiles.

The technical task of the present invention is to increase the plastic properties of a strip billet for profiling, which determine its acceptability for, for example, high-quality bent profiles with appropriate properties.

To solve this problem, in a roll for a hot-rolled steel strip billet for profiling, the content of carbon, manganese and silicon was determined by the carbon equivalent value depending on the yield strength and the thickness of the billet according to the following ratios:

для h≥6 мм и

для h<6 мм,

for h≥6 mm and

for h <6 mm

where C _e = C + Mn / 9 + Si / 3 is the carbon equivalent of steel, wt.%,

σ _t - yield strength, MPa,

h is the thickness of the strip, mm

262.5, 130, 291, 124 - empirical coefficients; The method of hot rolling a steel strip billet for profiling from rolled stock includes rolling with a given temperature, cooling and winding the strip, while cooling the strip is carried out at a speed determined depending on its thickness and yield strength in the following ratios:

, для h≥6 мм

, for h≥6 mm

, для h<6 мм,and

, for h <6 mm,

where V is the cooling rate, ° C / s,

σ _t - yield strength, MPa,

h is the thickness of the strip, mm

227, 0.94, 306, 2.9 - empirical coefficients.

The above mathematical relationships are obtained by processing the experimental data and are empirical.

The essence of the claimed technical solution is to optimize the chemical composition of the billet for profiling with a given thickness and with the required yield strength, hot rolling of which is carried out with a certain cooling rate on the discharge roller table of a broadband mill (i.e., after rolling is completed). The content of the three main elements in steel is determined by the proposed carbon equivalent. All this ensures the absence of cracking during profiling of the workpiece by increasing its plastic properties.

When implementing the claimed technical solution, before hot rolling the strip billet according to the required value of its yield strength and depending on the thickness, a tackle is selected (according to the accompanying documentation), the content of which C, Mn and Si corresponds to a predetermined carbon equivalent value C _e . After finding the necessary cooling rate V cool _. rolled products (also depending on h and σ _t steel) begin hot rolling of strips.

Experimental verification of the invention was carried out on a 2500 broadband hot rolling mill of OJSC Magnitogorsk Iron and Steel Works.

For this purpose, when rolling strips with a final thickness of 2 ... 8 mm from various steel grades, a tackle with different contents of C, Mn and Si was used, varying the cooling rate of the strips after hot rolling. The value of σ _{t was} set based on the data obtained as a result of research work on defect-free profiling carried out earlier at MMK. The results of the experiments were evaluated by the output of high-quality rolled products in the bent section workshop of the plant, in which the experimental billet was used.

The best results (yield of bent varietal profiles of the first grade within 99.6 ... 99.8% in the absence of crack formation in the profiling process) were obtained with the implementation of the proposed facility. Deviations from its recommended parameters worsened the achieved indicators. So, with a carbon equivalent of C _e (i.e., with a content of C, Mn and Si corresponding to its specific value) other than that determined by the above formulas, the yield of profiles of grade I did not exceed 98.3% and up to 0.3% of the bands gave cracking during profiling, since the actual value of σ _{t of the} workpiece differed from the required optimal values of this indicator.

Similarly, at cooling rates of hot rolled strips other than V _cool. determined by the proposed formulas (see above), the yield of bent profiles of grade I from the obtained billet did not exceed 98.5% and about 0.5% of the rolled products were rejected for cracks.

A control check of the workpiece and its production technology, selected as the closest analogue, led to 98% bent profiles of the first grade, and sorting into scraps by cracks reached 0.7%.

Thus, the experiments confirmed the acceptability of the technical solution found to achieve the goal and its advantages over the known object.

According to technical and economic studies conducted at the Central Control Laboratory of OJSC MMK, the implementation of the present invention in the production of hot-rolled strip steel billets for profiling will increase the yield of bent profiles of grade I by at least 1% with a corresponding reduction in waste and an increase in profit from sales rental.

Concrete example

1. The strip blank for profiling with a thickness of h = 6 mm should have a yield strength σ _t = 303 MPa.

Required carbon equivalent:

Based on the dependence C _e = C + Mn / 9 + Si / 3, the content of the main elements in the steel should be: [C] = 0.18; [Mn] = 0.9 and [Si] = 0.09 wt.%, I.e.

C _e = 0.18 + 0.9 / 9 + 0.09 / 3 = 0.18 + 0.1 + 0.03 = 0.31

Such chemical composition and σ _m = 303 MPa corresponds st3Gps GOST 380.

When hot rolling this workpiece, the cooling rate of the roll will be:

2. A blank for profiling from st.35 with a thickness of 3 mm

(carbon 0.33%, manganese 0.54% and silicon 0.18%) start rolling at a temperature of 1150 ° C, rolling ends at a temperature of 880 ° C, and winding is carried out at a temperature of 660 ° C.

Rolling is carried out with a total relative compression of 90% for 7 passes in the finishing group of the mill 2000, i.e. with an initial strip thickness of 32 mm. In the roughing group of stands, rolling begins with slabs 240 mm thick (5 passes).

When hot rolling this workpiece, the cooling rate of the roll:

The yield strength of the obtained preform for profiling 347 MPa.

Claims (2)

1. A tackle for a hot-rolled steel strip billet for profiling, the content of carbon, manganese and silicon in which it is established by the value of the carbon equivalent depending on the yield strength and the thickness of the billet according to the following ratios:

for h≥6 mm,

for h <6 mm
where C _e = C + Mn / 9 + Si / 3 is the carbon equivalent of steel, wt.%,
σ _t - yield strength, MPa,
h is the thickness of the strip, mm
262.5, 130, 291, 124 are empirical coefficients. 2. The method of hot rolling a steel strip billet for profiling from rolled according to claim 1, including rolling with a given temperature, cooling and winding the strip, while cooling the strip is carried out at a speed determined depending on its thickness and yield strength in the following ratios:

for h≥6 mm,
and

for h <6 mm
V is the cooling rate, ° C / s,
σ _t - yield strength, MPa,
h is the thickness of the strip, mm
297, 0.94, 306, 2.9 are empirical coefficients.