CN1064567C - Cooling control method used for steels after hot rolled - Google Patents

Abstract

The invention belongs to the field of controlled cooling after hot rolling of steel products. Mainly concerned with controlled cooling after hard-wire hot rolling. The control cooling method described in the present invention is divided into four stages; that is, the water cooling section from the hot rolling mill to the laying head section, the water vapor cooling section after the laying head, the natural cooling section at the outlet of the steam cooling device, and the coiler Rapid cooling section of the front section. The control cooling device of the present invention includes a sleeve water cooling device, a forced air cooling device and an air cooling device arranged behind the laying head. The steam cooling device is composed of a steam inlet pipe, a cooling chamber and an air extraction and water collection conduit.

Description

Controlled cooling method and controlled cooling device after steel hard wire hot rolling

The invention belongs to the field of controlled cooling after hot rolling of steel products. It is mainly suitable for controlled cooling after steel hard-wire hot rolling.

Controlling the cooling rate after hot rolling of steel hard wire can obtain a high proportion of better fine pearlite structure (that is, sorbite structure). This fine pearlite can improve the subsequent deep processing performance of hard wire, improve the yield and final performance of the product.

In the prior art, the Stelmore cooling method is a typical example of the controlled cooling method after the hot rolling of the wire rod ("High Speed Rolling Mill Wire Rod Production", Metallurgical Industry Press, 1995, page P330). The controlled cooling method adopts three-stage cooling method:

The first stage——rapid cooling stage, adopts sleeve type water spray cooling, and requires the wire rod to be cooled rapidly to the phase transition temperature after hot rolling;

The second stage——the air-cooling stage is a phase transition stage, and the cooling rate is controlled by air-cooling in order to obtain pearlite structure;

The third stage----rapid air cooling stage, accelerates cooling and reduces the formation of oxide scale.

In this method, due to the excessive cooling rate in the first stage, surface cracks are likely to occur on the surface of the wire, and at the same time, due to the rapid cooling structure formed on the surface, the core cannot be cooled to a certain temperature, thus limiting the final cooling temperature, and the entire wire cannot achieve phase transition. The phase transition temperature can only be reached after entering a certain area of air cooling in the second stage, so that the phase transition process in the second stage is not sufficient, and a satisfactory structure cannot be obtained.

The object of the present invention is to provide a controlled cooling method and a controlled cooling device after hard wire hot rolling of steel which can finally obtain better microstructure (sorbite) and excellent deep processing performance of the wire rod.

For one of object of the invention, a kind of method of controlled cooling after hard wire hot rolling of the present invention is divided into four stages, and accompanying drawing 1 is a process flow diagram of the present invention, and four stages are now described as follows:

The first stage——Water-cooled section, that is, the section from the hot rolling mill to the laying head, adopts sleeve water cooling, the cooling speed is controlled at 200-300°C/s, and the temperature before the wire enters the laying head is controlled at 750 Above ℃;

The second stage----water vapor cooling section, that is, the section under the jurisdiction of the steam cooling device after the laying machine, uses water vapor as the cooling medium, and the cooling speed of the water vapor cooling is controlled within the range of 20-30°C/s, and the wire rod is controlled in the conveying roller The running speed on the road is 0.8-1.3 m/s;

The third stage - the natural cooling section, that is, from the exit of the steam cooling device to the subsequent 6-meter section, natural cooling is adopted;

The fourth stage - the rapid cooling stage, that is, the section from the end of the third stage to the coiler, adopts forced air cooling.

The first stage is water-through cooling. By adjusting the water pressure and flow rate, the cooling rate is controlled at 200-300°C/s. The purpose is to reduce secondary oxidation, and to prevent the appearance of rapid cooling structures on the surface of the wire. The cooling rate should not be too high. Low, especially for large-scale wire rods, after the first stage of cooling, the temperature of the wire rods (that is, the temperature before entering the wire laying machine) is controlled above 750°C.

The second stage adopts steam cooling, the purpose of which is to stably cool the wire from above 750°C before entering the laying machine to 600-650°C, so as to provide sufficient conditions for the phase transformation of the third stage. In order to achieve this goal, one is to control the cooling speed, and the other is to control the running speed of the wire. It has been proved by experiments that the cooling speed of the steam cooling is controlled at 20-30°C/s, and the running speed of the wire on the conveying roller table is 0.8- 1.3 m/s. Water vapor cooling is realized by the vapor cooling device installed after the laying head. The steam cooling medium can be heated steam or water vapor generated by ultrasonic waves. The water vapor passing through the steam cooling device maintains a slight positive pressure at the inlet.

The third stage is the phase change stage. The temperature of the wire after being cooled by water vapor is 600-650°C. After the steam cooling, it is the third stage. Natural cooling is used to facilitate the phase change. The temperature of the wire can be kept stable at 600-650°C within a few minutes after steam cooling. During this period, the phase transformation from austenite to fine pearlite can be fully carried out, and finally a large amount of fine pearlite can be obtained.

The fourth stage is the rapid cooling stage. Forced air cooling is adopted to rapidly cool the wire below 230°C, the purpose of which is to reduce the formation of oxide scale and increase the yield of finished products.

In view of the second purpose of the present invention, the present invention is a controlled cooling device after hard-wire hot rolling of steel, which includes a sleeve water-through cooling device located behind the hot rolling mill and a forced air cooling device located in front of the coiler, and its technical solution yes:

A steam cooling device is installed behind the laying machine. The steam cooling device is composed of a steam inlet pipe, a cooling chamber, and an air extraction and water collection conduit; The tube is above the cooling chamber, the air suction and water collection conduits are below the cooling chamber, and the entire cooling chamber is located around the wire conveying roller table, that is, the conveying roller table and the wires running on it are all covered in the cooling chamber.

The present invention will be further described now in conjunction with accompanying drawing.

Accompanying drawing 1 is the process flow and related equipment schematic diagram of controlled cooling after hard-wire hot-rolled steel of the present invention.

Accompanying drawings 2 and 3 are respectively the front view and the left view structural schematic diagrams of the steam cooling device in the control cooling device after steel hard-wire hot rolling according to the present invention.

It can be seen from Fig. 1 that after being rolled by the hot rolling mill 1, the steel material 8 enters the cooling device 2 of the first stage for water cooling. Enter the third stage of natural cooling zone 5, the natural cooling zone is 6 meters long, and then enter the fourth stage of forced air cooling zone 6 after natural cooling, for forced air cooling, the wire is quickly cooled to below 230 ° C, and then the wire enters the coil Machine 7 collects and rolls into coils to become finished products and completes the entire controlled cooling process.

Seen from accompanying drawing 1, 2 and 3, the control cooling device after the hard wire hot rolling of steel product of the present invention comprises the sleeve water-piercing cooling device behind the hot rolling mill and the forced air cooling device before the coiler and A steam cooling device 4 is placed behind the laying machine 3, and the steam cooling device 4 is composed of a steam inlet pipe 10, a cooling chamber 11, and an air extraction and water collection conduit 12; It communicates with the cooling chamber 11, the steam inlet pipe 10 is above the cooling chamber 11, the air extraction and water collection conduit 12 is below the cooling chamber 11, and the entire cooling chamber 11 is located around the wire conveying roller table, that is, the conveying roller table and its The wire rods running above are all covered in the cooling chamber 11.

Compared with prior art, the present invention has following advantage:

(1) The cooling result can be controlled, and a large number of fine pearlite structures can be obtained in the metallographic structure, so the wire has good deep processing performance.

(2) During the cooling process, no cracks or cracks occur on the surface of the wire rod, and no quenching structure is generated, which ensures the final excellent performance of the wire rod.

(3) The finished product rate is high, and the cost of subsequent deep processing is reduced.

Example

According to the controlled cooling method and the controlled cooling device after steel hard-wire hot rolling described in the present invention, three batches of tests are carried out using No. 70 steel as a billet. After the wire rod is hot-rolled, it enters the controlled cooling stage. The controlled cooling process and parameters used in the three batches of tests are shown in Table 1. After cooling into a finished product, samples were taken for mechanical property test and metallographic structure inspection. The measured average mechanical properties and sorbite rate results are shown in Table 2.

Table 1 embodiment controls the process parameter of cooling

Table 2 The mechanical properties and sorbite rate of the wire rods of the examples after the implementation of controlled cooling

Claims (5)

1, the control cooling means after the hot rolling of a kind of steel rigid line comprises water-cooled and air cooling stage, it is characterized in that this control cooling means divides four-stage:

Phase I----water-cooled section, promptly hot-rolling mill adopts the sleeve spray to wear water cooling to the Laying head section, and cooling velocity is controlled at 200-300 ℃/second, and the temperature that wire rod enters before the Laying head is controlled at more than 750 ℃;

Second stage----steam cooling section, promptly vapour device for cooling institute area under one's jurisdiction section behind the Laying head is a cooling medium with steam, and the cold cooling velocity of steam vapour is controlled at 20-30 ℃ of/second scope, and the speed of service of control wire rod on rollgang is the 0.8-1.3 meter per second;

Phase III----natural cooling section, promptly from vapour device for cooling exit to subsequently 6 meters inner section, adopt the nature cooling;

Quadravalence section----is cooling stage fast, and promptly phase III end is adopted air blast cooling to rolling up the preceding section of collection machine.

2, cooling means according to claim 1 is characterized in that the steam cooling stage in second stage, keeps pressure-fired by the steam of vapour device for cooling at arrival end.

3, cooling means according to claim 1 is characterized in that the wire temperature in vapour device for cooling exit is controlled at 600-650 ℃ of scope;

4, cooling means according to claim 1 is characterized in that the cold cooling medium of vapour can be the steam of heating or the steam that produces with ultrasonic wave.

5, the control cooling device after the hot rolling of a kind of steel rigid line comprises the air blast cooling device before the sleeve that is positioned at behind the hot-rolling mill is worn water-cooling apparatus and is positioned at volume collection machine, it is characterized in that:

Settle a vapour device for cooling (4) in Laying head (3) back, this vapour device for cooling (4) is by steam inlet pipe (10), cooling chamber (11) and bleed and the conduit that catchments (12) is formed; Steam inlet pipe (10) and bleed and the conduit that catchments (12) all communicates with cooling chamber (11), steam inlet pipe (10) is in the top of cooling chamber (11), bleed and the conduit that catchments (12) is in the below of cooling chamber (11), whole cooling chamber (11) be in the wire rod rollgang around, promptly rollgang and in the above the operation the equal ladle cover of wire rod in cooling chamber (11).

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