JPH01205802A - Method for rolling to press weld internal defect of continuously cast stock - Google Patents

Abstract

PURPOSE:To press weld microporosities inside a rolled stock and to reduce the manufacturing cost and time by applying an intermediary compressive stress of a specifically proportional value to the deformation resistance of the stock to the stock between one or more pairs of stands. CONSTITUTION:As for hot continuous rolling of a continuously cast stock, an interstand compressive stress of >=25% of the deformation resistance value of the rolled stock is applied to the stock between one or more pairs of stands. Thus, microporosities inside the stock are press welded and steel bars and wires are manufactured by a two-heat-hot-charge method even if a continuously cast bloom of a large section is used. A small section continuously cast billet is rolled by a one-heat method. Hence, the manufacturing cost and time are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a rolling method for producing steel bars and wire rods by hot rolling using a continuous rolling mill using continuously cast blooms or billets as raw materials.

(Conventional technology) Steel bars and steel bars made from continuous casting blooms and billets are generally used.
In rolling wire rods, a continuous rolling mill with vertical and horizontal stands arranged alternately is used. In this case, a horizontal stand is used to reduce the thickness of the material, and a vertical stand is used to reduce the width of the material. In this rolling method, it is considered best to have no tension between the stands from the viewpoint of dimensional accuracy of the product.

However, during rolling in the intermediate and finishing rows, a tensile force of several percent of the material deformation resistance may be applied between the stands in order to improve the suitability of the material. On the other hand, in the case of coarse rows, the rolling down pattern changes depending on the size, so depending on the size, a compressive force may be generated between the stands, but this remains at a few percent or less of the material deformation resistance. Steel bars like this
In the rolling of wire rods, the cross-sectional shape of the material is close to square or circular, and the spread of the material in each pass is significantly larger than that in plate rolling. Therefore, internal defects (particularly in the center in the thickness direction and near the edges in the width direction) occur near the surface layer. porosity) tends to remain.

By the way, low carbon steel continuously cast bloom billets tend to have porosity in the center, and medium carbon steel is even more likely to have microporosity in the surface layer. If the width spread is small during unidirectional rolling, it will be sufficiently compressed and disappear in the rough rolling/intermediate rolling process, but if the width spread is significant in each pass, such as with long steel, the reduction will not penetrate to the center, and the center In some cases, porosity remains in the product without being crimped. Regarding microporosity near the surface layer, near the center of the end face where the width is significantly widened, the porosity is difficult to be compressed in the rolling direction and remains in the product. For this reason, when secondary processing a product, it may be necessary to cut using this porosity as a starting point.

Conventionally, in order to crimp such porosity, attempts have been made to increase the amount of reduction in the thickness direction and width direction, thereby crimping the porosity. As a result, in recent years, it has become common to use bloom as a material, and the cross-sectional size of bloom is also becoming larger, such as 300 mm x 40 h- or more. Furthermore, as cold-forged wire rods and steel bars require strict internal quality, ultrasonic inspection is performed at the billet stage after blooming and blooming to detect defects due to porosity in the surface layer or center. Only the billets of the seine net are sent to the production factory after being cleaned and reused.

(Problems to be Solved by the Invention) As described above, in the conventional tensionless rolling method, it is impossible to completely compress and eliminate the porosity in the slab with a normal rolling reduction amount. For this reason, conventionally, blooms with a large cross section were used as the material to increase the amount of reduction in the width and thickness directions.
I'm trying to crimp the porosity as much as possible. For this reason, the billet is first rolled from the bloom in a blooming mill, where it is turned into a cold material and inspected and maintained. Therefore, in addition to adopting a two-heat rolling method, cold treatment is required, resulting in significant cost and time loss (which goes against the current direct connection of steelmaking and rolling).

The most cost-effective method is to use a continuously cast billet with a small cross-section as a raw material, transport it to a product factory (steel bar mill, wire rod mill, etc.) using a hot charge, and roll it into a product in one heat. However, if the cross-sectional area of the continuously cast material is small (the rolling reduction rate will also decrease, and the possibility of residual porosity in the product increases), conventional rolling methods can reduce the residual porosity by using continuous cast billets with a small cross-section as the material. Risk is unavoidable, so for high-grade long steel products, two-heat rolling using a continuous casting bloom with a large cross section has conventionally been common, and this has been a factor in raising manufacturing costs and prolonging manufacturing time.

Therefore, an object of the present invention is to provide a method of rolling a high-grade long steel product by using a continuously cast billet with a small cross section and completely compressing and eliminating the porosity in the slab in one heat rolling process.

(Means for solving the problem) In order to achieve this purpose, the inventor has repeatedly conducted experiments and research,
I got the following idea.

By applying a strong inter-stand compression force between the stands of a continuous rolling mill, compression force is applied uniformly to the roll bite exit side during rolling of the upstream stand, allowing the reduction to penetrate to the center of the thickness direction, and reducing the pressure in the width direction of the material. It can be evenly penetrated even in the water. Further, when a compressive force is applied between the stands in this manner, the material is compressed (rolled down) in the longitudinal direction of the rolling direction, increasing the width and thickness. Therefore, the effect of compressing the porosity in the rolling direction can also be expected, especially within the roll bite where it is pressed. This method of applying compressive force to the material can be carried out between each stand, but if the material buckles between the stands due to the compressive force between the stands, not only will the porosity crimping effect be lost, but rolling will not continue. even becomes impossible. Buckling occurs when the distance between the roll axes between the stands is too large relative to the thickness and width of the material between the stands. Therefore, it is most effective to apply the compressive force for porosity compression during the bloom blooming process and the billet rough rolling process.

Thus, the gist of the present invention is that in continuous hot rolling of continuous casting materials, between at least one set of stands, the value of the hot deformation resistance of the material being rolled is doubled.
This is an internal defect crimping rolling method for continuous cast materials, which is characterized by giving an inter-stand compressive stress of 5% or more.

(Function) The magnitude of the compressive stress between the stands is adjusted by adjusting the rotational speed of the roll drive motor in the adjacent stands, and the compressive stress necessary for crimping internal defects such as porosity between the stands is applied to both rolls. occur between. The specific value of this compressive stress was determined experimentally. This experiment will be described next.

Experimental Apparatus FIG. 1 shows the arrangement of the rolling mill used in the experiment, in which a driven horizontal roll H1, a non-driven vertical roll v2, and a driven horizontal roll H3 are successively arranged, and rolls 81. The rolled material 1 is rolled in the direction of the arrow while applying a compressive force between V2. The specifications of this device are as follows.

H10-L diameter: 300mm V2C)-1Lt diameter? 200s- ■30-le diameter: 300-18l-V2 center distance 1m: 700s+mV2-H
Distance between 3 axes? 700m5 rolled forest material As shown in Figure 2, a billet with a square cross section (steel type SS 41) was used as the rolling material, and in order to confirm the effect of crimping internal defects (porosity) due to rolling, internal defects were Holes were formed to create artificial porosity. These holes (artificial porosity) consist of a hole 1a at the center of the thickness that simulates the porosity in the center, and holes 1b and 1c below the surface that simulates microporosity near the surface layer. Of these, 61b exists at the center of the thickness during horizontal rolling. These holes 1a,
For 1b and 1c, as shown in Figure 2, a hole with a diameter of 2 mm is made in the width direction in W inside the billet, a wire of the same diameter is inserted, leaving a space of 2 mm in length, and the rest are closed by welding. did.

The dimensions of this rolled material are summarized below.

Material thickness t: too-Material width W: 100m5+ Hole length 1: 2mm Hole diameter d: 21111 Distance*XIIX! : 10g+m distance)'+
+3'g: 40+ue positive And an experiment was conducted by preparing a large number of materials (billets) 1 provided with artificial porosity as described above.

The rolled material 1 was heated to 1250°C in both cases, and the rolling temperature in the former case was kept constant at 1100°C. In addition, the rolling reduction rate in Hl is constant, and the thickness of the material is to”100-
The pressure was reduced by 20% from fog to t+-8051 m. On the other hand, the amount of reduction in v2 was varied from 0 to 20 mm to change the compressive stress between both rolls and v2. In addition, the thickness was rolled down to 70 mm by the last driving horizontal roll H3.

In this experiment, the state of artificial volocity crimping in the old mill and one-bus rolling was investigated for each compressive stress. Figure 3 schematically shows the cross section of the material in the longitudinal direction of rolling before and after old rolling, and the material thickness ranges from to-100m to L+=80m.
The figure shows a state in which the circular cross section of the artificial porosity 1a collapses into an ellipse as the artificial porosity 1a is reduced to 1, and the cross-sectional area changes from S to S. Due to rolling, the cross-sectional area of porosity changes from S to S.
Therefore, as an index of the porosity bonding rate, the pore area reduction rate r - (se -St)/Ss
100%) means that the porosity is completely crimped. On the other hand, the plastic deformation of a material during rolling is determined by the relationship between the stress inside the material and the hot deformation resistance kf of the material, so internal defects (porosity)
As an index of the magnitude of compressive stress σ effective for crimping, σ
It is effective to use .

Next, the conditions and results of this experiment are summarized in Table 1. In this table, T, (to) is the hole 1as located at the center in both the thickness direction and width direction, and the hole 1as located at the center in the thickness direction and width. The hot deformation resistance kW of the 3541 material is 6.0, which shows the pore area reduction rate of 61b near the surface layer of the directional edge part.
It is constant at kg/smπ.

Table 1, Figure 4 is a graph showing the results of Table 1.

From the results shown in Table 1 and FIG. 4, the following conclusions can be drawn. As σhtt increases from 0.2 to 0.3, the pore area reduction rate increases rapidly and the porosity compression effect becomes noticeable, and σ/
At kf-0, 4, the center hole 1a is completely crimped (y
t-100%), further to σ, and γ at =0.6. =γ,
-100%, including the surface layer porosity 1b near the surface layer in the central part in the thickness direction and the end part in the width direction, where the crimping effect is the smallest.
All porosity is crimped.

Therefore, by repeating rolling at σ/kW -0.6 or more, the porosity in the center and near the surface layer can be completely compressed and eliminated. In addition, in this experiment, the effect of the compressive force between the stands begins to appear when σ/kt is 0.25.
or more, and if this value is 25% or more, the diameter is 2Il1
It can be expected that even if the porosity is quite large, on the order of m, the entire cross section will be completely crimped. In addition, by setting it to 60% or more, the porosity can be completely crimped.

Therefore, when carrying out the present invention, the compressive force between the stands should be such that σ/kt is sufficient for porosity bonding without causing buckling of the material, taking into account the above experimental results and the size of porosity within the material. The value should be selected to have an effect.

(Example) Implementation Team In this example, a steel bar with a side of 20 mm was produced from a continuous casting billet with a side of 180 mm in a continuous mill with a VH arrangement of 22 stands in total, including 6 stands in the rough row, 6 stands in the intermediate row, 1O Stan, and 6 stands in the finishing row. This is an example in which the method of the present invention is applied to a steel bar mill to be manufactured, and FIG. 5 shows the mill layout of this example.

The mill in this example has all stands individually driven, and H2
-V3, the rotational speed and output of each motor are set so that a compressive force of 2 kg/sm', which is 50% of the hot deformation resistance of the rolled material, acts between the stands between the stands. Table 2 shows the bus schedule for the coarse lines of this embodiment.

Note that the compressive force between the stands tends to increase the dimensional variation over the entire length, but in this example, the compressive force is applied only upstream of the coarse row, and the dimensional variation that occurs between 12 and V3 is It is sufficiently absorbed in the rolling of the 19 stands downstream, and there is no large difference in dimensions from the case without tension.

Table 2 This example uses a twisted horizontal tandem mill with 7 stands in the coarse row, 10 horizontal stands in the intermediate row, and 4 horizontal stands in the finishing row, and the -side is 125 mm 3! Continuous casting belay/
) is an example in which the method of the present invention is applied to the process of manufacturing a wire rod with a -side of 10+u+, and FIG. 6 shows the mill layout of this mill.

In this example, the first stand H1 and the second stand ■2
2.2k, which is 60% of the hot deformation resistance of the rolled material.
A compressive stress of "g/+*m" was applied between the stands, the material was twisted by 90 degrees at the exit side of the H2 stand, and introduced into the ■3 stand. The rough bus schedule for this example is shown in Table 3.

Table 3 (T): 90' twist implementation and 1 This example uses a continuous billet mill consisting of 8 stands of HV to cast a billet of 180 m on a side from a continuous casting plume of 300 mm thick x 300 mm wide. This is an example in which the method of the present invention is applied to a blooming factory that rolls .

In this mill, v2 is not driven, and 40% of the material deformation resistance is applied twice between Hl and V2 and between V4 and 85.
This gives a compressive stress between the stands corresponding to . Furthermore, dimensional fluctuations caused by these two compression rollings are reduced by light rolling with V8. The pass schedule for this embodiment is shown in Table 4.

In the case of this example, the dimensional accuracy of the babylet deteriorates by a few percent compared to the conventional method, but most of the microporosity, especially under the surface layer, is crimped and disappears due to the action of the compressive force, so that it can be transferred to the wire rod factory in the next process. Can be hot charged directly without maintenance.

Table 4 (Effects of the Invention) As described above, the present invention applies a compressive stress of 25% or more of the deformation resistance of the rolled material between arbitrary stands in continuous rolling of continuously cast plume billets, thereby The microporosity inside the rolled material is crimped. Therefore, even if a continuous casting bloom with a large cross section is used, steel bars and wire rods can be rolled in two heats and hot charging, and continuous casting billets with a small cross section can be rolled in one heat. As a result, manufacturing costs and time required for manufacturing can be significantly reduced.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the arrangement of a rolling mill used in an experiment to investigate the relationship between the magnitude of compressive force between stands and porosity crimping efficiency in the present invention. Figure 2 is a diagram showing the arrangement of a rolling mill used in an experiment using the apparatus shown in Figure 1. A perspective view showing a cross section of the rolled material used; FIG. 3 is a cross-sectional view schematically showing a longitudinal cross-section of the rolled material in FIG. 2 before and after the first horizontal rolling; FIG. 4 is a cross-sectional view showing compressive stress and A graph showing the relationship between porosity crimping efficiency; and FIGS. 5 to 7 are plan views showing the arrangement of rolling mills in the first to third embodiments of the present invention, respectively. 1: Rolled material

Claims (1)

[Claims] A continuous cast material characterized in that, in hot continuous rolling of the continuous cast material, an inter-stand compressive stress of 25% or more of the hot deformation resistance value of the material being rolled is applied between at least one or more stands. internal defect crimping rolling method.