Method for the production of long-rolled products of circular cross section

 

(57) Abstract:

The invention relates to the field of metallurgy, in particular to the production of rolled round cross-section for subsequent drawing. Method for the production of long-rolled products of circular cross section comprises hot rolling a steel with a carbon content of 0.6 to 1.0, manganese not more than 1.5 and silicon is not more than 1.0 wt.%, accelerated cooling water to the bulk temperature 770-850oWith subsequent cooling to bulk temperature 750oWith that conduct, not less than for a time determined from the expression , where Kin- an empirical coefficient equal to 2.55, D - diameter of the rent, mm, MT - manganese content, wt. %, further cooling leads in two stages, the first stage cooling with surface temperature not below twith= 721 - of 9.8 Mn + 28,6 Si,oC, where mn and Si content of manganese and silicon, by weight. % to the surface temperature tp=(748 - S)10oC, where C is the carbon content, wt.%, spend time, not exceeding 3, the second stage cooling lead to a temperature not exceeding tto=715 - S,oC, where C is the carbon content, wt.%, in a period of time not less than 35 C. the Invention provides homogeneous sorbet tositsa to the field of ferrous metallurgy, in particular the production of long-rolled products of circular cross section for the subsequent drawing.

There is a method of controlled cooling of the cable rod directly after leaving the last stand of the mill, including intensive cooling water temperature rolling up to 850-600oWith rod supplied with the speed of 50-80 m/s, followed by slow cooling in the unfolded coils to 620-680oWith further cooling of the wire rod in coils (Nodes, I. , Babich C. K., Sails Century. Century. and other Structure and properties of the cable wire rod and wire after controlled cooling, Steel, 1983, 11, S. 66-69).

The disadvantage of this method is to obtain an inhomogeneous structure in the cross section and the length of the rod and the large variation of mechanical properties along the length of the roll. This is due to the fact that granular carbides that occur during slow cooling in air with a heating surface hardened layers, don't completely dissolve, resulting in patterns tempering of martensite, reducing technological plasticity steel, resulting in the process of drawing to increased breakage.

The closest analogue of the present invention is a rolling steel cable, cooling water at a rate not less than 1000oC/C directly on the output of the last stand of the mill within 0.1-0.2 s to bulk temperature 770-850oWith, exposure time, determined from the expression:vyd= (0,15-0,50)d2CRcyclic cooling, comprising alternating processes of cooling and holding period of the cycle of 0.1-0.3 s and a speed of 250 to 500oC/C to bulk temperature of 650-750oWith, wherevydthe time of exposure, with; dCR- the diameter of the rent, cm, and then the cooling coils in the air (A. C. the USSR 1379318, CL 21 D 1/02, 8/06, publ. 07.03.88.).

Signs nearest analogue, coinciding with the essential features of the claimed invention:

1. Hot rolling steel with a carbon content of 0.6 to 1.0, manganese not more than 1.5 and silicon is not more than 1.0 wt.%.

2. Accelerated cooling water to the bulk temperature 770-850oC.

3. Cooling to bulk temperature 750oC.

4. Further cooling.

The known method does not provide trajectory optimization of cooling for a specific chemical composition eutectoid steels for the following reasons.

When leaving the last stand prevremeni, determined from the expression: vyd= (0,15-0,50)d2CRwherevyd- extract from; dCRthe diameter of rent, see For rod diameter 5.5 mm, the shutter speed ranges from 0,045 to 0,151 seconds, which is not sufficient for the complete alignment process temperature in the cross section. The time specifies the duration of the equalization of temperature in the cross section, does not take into account the effect of the chemical composition of the steel and its effect on hardenability, which is a decisive factor in the subsequent formation of a given microstructure. So, if you increase the carbon content of the steel from 0.01% to 0.8% offset temperature - transformation with 910oWith up to 723oWith that it is important to select the cooling rate and the duration of the equalization of temperature in the cross section. Without varying the exposure after rapid cooling in the surface layers of the rod due to the dual phase recrystallization -- is formed of relatively fine-grained structure of austenite (above point A1) undergoing air diffusion transformation with the formation of heat stable carbides, which, depending on the excess temperature AND1have different morphology, thus determining the formation of abnormal spirtnogo perlite, globes of cementite which masked the subsequent imposition of quasilattices transformations at temperatures above 800oWith an abnormality manifested in the form of structurally free cementite along the boundaries of former austenite grains.

Double circular cooling, including alternate cooling processes and alignment with the period of the cycle of 0.1 and 0.3 seconds and a speed of 250 and 500oC/C to bulk temperature of 650 and 750oWith a few stabilizes the process of phase transitions, but does not consider isothermal aging, which are determined based on thermokinetic diagrams for different types of steels, and time to equalize the temperature over the cross section of the car and allows you to get completely across the cross section and length of rolled homogeneous structure of sorbitol. Because the decrease in decay time of austenite after rapid pre-cooling water is not regulated by specific chemical composition of the steels and their thermokinetic diagrams, it is not possible to obtain a homogeneous sorbitol structure and uniform distribution of properties across the section and the length of the car.

The basis of the invention is the task of the CA is th the chemical composition of the steels and kinetics of phase transformations is achieved to optimize the path of cooling, providing a homogeneous sorbitol structure and uniform distribution of properties across the section and the length of the car.

The problem is solved in that in the method of production of long steel products of circular cross section, comprising hot rolling a steel with a carbon content of 0.6 to 1.0, manganese not more than 1.5 and silicon is not more than 1.0 wt.%, accelerated cooling water to the bulk temperature 770-850oWith subsequent cooling to bulk temperature 750oWith further cooling, according to the invention the cooling to bulk temperature 750oTo spend not less than a time determined from the expression

< / BR>
where Kin- an empirical coefficient equal to 2.55, D - diameter of the rent, mm, Mn - manganese content, wt.%, and further cooling leads in two stages, the first stage cooling with surface temperature not below tc=721-9,8 Mn+28,6 Si,oC, where Mn and Si content of manganese and silicon weight. % to the surface temperature tp=(748-S)10oC, where C is the carbon content, wt. %, spend time, not exceeding 3 seconds, the second stage cooling lead to a temperature not exceeding tto=715-S,oC, where C is Roderigo composition to the bulk temperature 750oWith not less than a time determined from the expression

< / BR>
due to the influence of the diameter of the rolled product range and its hardenability, a significant impact on which has a Mn content in the steel. The claimed time necessary for a more complete alignment of the bulk temperature, because the temperature difference on the surface of the rod and in the center reaches 450oWith and more. For eutectoid composition of steels duration of the diffusion process with the increase of the phase boundary increases, therefore, the accelerated cooling without alignment to the mass-average temperature = 750oWith, and further stabilization of the temperature leads to the formation of bainite structures and increase the strength properties up to excessive levels, which complicates the subsequent drawing and increases the breakage of the wire.

Further cooling is carried out in two stages. At the first stage regulates the surface temperature of the rod, which should not be less than determined from the expression tc=721-9,8 Mn+28,6 Si,oC, where Mn and Si content of manganese and silicon, wt.%, before the surface temperature tp=(748-S)10oC, where C is the carbon content, weight. %. The cooling on this floor is l A1width when the cooling rate is more than 100oC/C does not exceed 1oFor sarbatoarea perlite and up to 10oFor coarse pearlite during cooling rates exceeding 1000oWith a/C. So for the stable entrance in the temperature zone of existence sorbitol patterns produce cooling at a given speed corresponding to the kinetics of phase transformations for a specific chemical composition of steel.

In the second stage, the cooling air lead time for at least 35 seconds, which is sufficient for the collapse of the stable temperature of the supercooled austenite in the structure of sorbitol and due to the diffusion of carbon to the surface layers decrease beoperating layer on the surface of the car is less than 1.0%.

In the proposed method takes into account the chemical composition of the steel, the cooling control is carried out on bulk temperature with its regulation on sites, which is pre-determined using a mathematical model.

Regulated by the exposure time, which is determined by considering thermokinetic diagrams, phase transformations, which also provides the time for equalizing the temperature behold the bit structure and accordingly, properties throughout the cross section and length of rental.

Example.

On a wire mill 300-3 OJSC MMK rolled party rod of steel chemical composition, wt.%: With - 0,71, MP is 0.65, Si - 0,27, diameter 5.5 mm with rolling rate of 50 m/s

Part of the party wire rod produced in accordance with the proposed method. Directly at the exit of the finishing stand wire rod is subjected to accelerated cooling to bulk temperature 800oIn once-through cooling devices, nozzles which deliver the water under pressure of 1.5 MPa. Then, the wire rod is cooled with air to a bulk temperature 750oWith over a 2.4 seconds, i.e., not less than for a time determined from the expression

< / BR>
where KV is the empirical coefficient equal to 2.55, D - diameter of the rent, mm, MT - manganese content, wt.%.

Next, wire rod coils are laid on and provide cooling in two stages. In the first stage, cooling the surface temperature of 725oS, i.e. not below tc= 721 - 9.8 MP + 28,6 Si,oC, where mn and Si content of manganese and silicon weight. % to the surface temperature of 600oWith appropriate expression tp= (748-S)10oC, where C is the carbon content, wt.%, spend, the de - carbon content in wt.% within 35 seconds.

The second part of the party wire rod produced by the method closest analogue: accelerated cooling water lead with a speed of 2500oC/C directly to the outlet of the finishing stand for 0.1 second to bulk temperature 800oWith the equalization of temperature in the cross section in the course of 0.045 seconds (corresponding to 0.15 dCR2), two cyclic cooling cycle of 0.1 seconds and a speed of 250oC/C to bulk temperature 750oWith cooling coils in the air.

The results of metallographic studies of the rod cooled by the proposed method when the values of the inventive process parameters and by a known method showed that the structure of the wire rod processed by the proposed method consisted of a homogeneous fine sorbitol across the section and the length in the presence of de-carbonized surface layer is less than 1%, and the structure of the wire rod processed by a known method, consisted in the surface layers of the lamellar pearlite and in the whole cross-section of sorbitol with up to 40% of lamellar pearlite in the total mass and inclusions bainite structures. In the process soon is Alicia patterns of sorbitol over the whole cross section, with greater temperature stability than lamellar pearlite, there is a restoration of this structure after heating and subsequent cooling, which provides bezopasnosti process lug when processed by the present method. For machining steel according to the method, the presence in the surface layers of the lamellar pearlite in the microstructure up to 40% leads to the formation of structures quenching that subsequent drawing lead to the emergence of micro-cracks, which leads to increased breakage.

Optimization of the trajectory cooling, taking into account the chemical composition of the steel and the kinetics of phase transformations, ensures the completion of phase transitions along the length of the rebellion and across the cross-section rod of medium-carbon and high-carbon (cable car) steel grades that will allow to process wire rod in the hardware industry, directly received after the camp without prior heat treatment. Uniform sorbitol structure throughout the cross section and length of rental with rental of heating eliminates additional licensing before further drawing.

Method for the production of long-rolled products of circular cross section, ukscone cooling water to the bulk temperature 770-850oWith subsequent cooling to bulk temperature 750oWith further cooling, wherein the cooling to bulk temperature 750oTo spend not less than a time determined from the expression

< / BR>
where Kin- an empirical coefficient equal to 2.55;

D - diameter of the rent, mm;

MP - manganese content, wt. %,

and further cooling leads in two stages, the first stage cooling with surface temperature not below

twith= 721-9,8 Mn+28,6 Si,oC,

where mn and Si content of manganese and silicon, by weight. %,

before the surface temperature

tn= (748-S)10oWITH

spend time, not exceeding 3, the second stage cooling lead to a temperature not exceeding

tto= 715-S,oWITH,

where C is the carbon content, wt. %,

in a period of time not less than 35 C.

 

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FIELD: rolling-mill machinery.

SUBSTANCE: the invention presents an installation for rolled metal cooling and is dealt with metal rolling, in particular with cooling of rolled metal. The installation for rolled metal cooling contains a body with an inlet branch-pipe and two rows of outlet branch-pipes displaced from each other by a half step. Value of a step of the outlet branch pipes in each row does not exceed four internal diameters of the branch-pipes. Across the body opposite to an entry of the inlet branch-pipe a dissector is installed. Along the body opposite to the outlet branch-pipes there are two entire central plates and two fragmentary lateral plates forming two longitudinal funnel-shaped cavities, turned by their narrow parts to each row of outlet branch-pipes. Fragmentariness of the lateral plates is created at the expense at least of one cutout in the base of each plate, at the longitudinal butts of which there are two perpendicularly fixed damping plates facing inside the funnel-shaped cavities. The invention allows to increase evenness, flexibility and efficiency of the rolling metal cooling process and ensures reliable operation of the installation.

EFFECT: the invention allows to increase evenness, flexibility and efficiency of the rolling metal cooling process and ensures reliable operation of the installation.

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