JPWO2010047137A1 - Continuous casting roll - Google Patents

Abstract

An object of the present invention is to provide a continuous casting roll that is excellent in wear resistance and corrosion resistance in addition to general heat crack resistance. SOLUTION: In mass%, C: 0.07% or less, Si: 0.2-1.5%, Mn: 3% or less, Cr: 13-20%, Ti: 0.5-4%, N : A roll for continuous casting which includes 0.1 to 0.5%, the balance Fe and inevitable impurities, and a build-up weld layer satisfying 1 ≦ Ti / N ≦ 20 on the roll surface. Here, the Mo may further contain 0.3 to 3% Mo, and the Co may further contain 0.5 to 3% by mass%. [Selection] Figure 1

Description

  The present invention relates to a buildup roll for continuous casting that is provided in a continuous casting facility and has excellent corrosion resistance and wear resistance.

  The continuous casting equipment at steelworks is equipped with a number of rolls that transport slabs, such as guide rolls and pinch rolls. These rolls receive contact loads from high-temperature slabs over a long period of time. Due to repeated heating and cooling by heating with a piece and cooling with cooling water, severe damage such as wear, thermal cracking, high temperature steam oxidation, etc. is caused.

  In addition, low melting point mold powder that prevents contact between the mold and the molten steel is supplied to the mold of the continuous casting facility. In this case, the roll located in the area close to the mold comes into contact with fluorine contained in the mold powder, and the roll is corroded. Therefore, as a countermeasure against damage to the roll, overlay welding or self-fluxing alloy spraying is performed on the roll surface.

Conventionally, as a welding material for overlay welding, Fe-based stainless steel such as 13Cr-Ni (Ni: 1-6), 17Cr-4Ni (SUS630) stainless steel, Ni-based alloy or Ni-based self-fluxing alloy spraying is used. Materials are used.
JP 2002-348638 A JP 2006-263807 A JP 2007-136509 A

  In recent years, there has been a strong demand for higher casting speeds, improved production performance and slab yield, and the surface temperature of rolls has risen, making the use environment of rolls more severe than before. Yes. Especially for top rolls (foot rolls, support rolls, guide rolls, etc.) directly under the mold, in addition to thermal crack resistance, which is a general required characteristic of continuous cast rolls, further improvement in roll wear resistance and corrosion resistance is required. It is like that.

  Here, in 13Cr—Ni (Ni: 1-6) Fe-based stainless steel, martensite is the main strengthening structure, and therefore, the hot strength is low and the wear resistance and corrosion resistance are poor. In addition, since 17Cr-4Ni (SUS630) Fe-based stainless steel uses a steel-rich intermetallic compound phase for the strengthened structure, it has higher wear resistance and corrosion resistance than 13Cr-Ni (Ni: 1-6) Fe-based stainless steel. However, in view of changes in the usage environment of the roll, further improvements in wear resistance and corrosion resistance are required.

  Accordingly, an object of the present invention is to provide a continuous casting roll that is excellent in wear resistance and corrosion resistance in addition to general heat crack resistance.

  In order to solve the above problems, the continuous casting roll of the present invention is (1) mass%, C: 0.07% or less, Si: 0.2 to 1.5, Mn: 3% or less, Cr: Overlay weld layer containing 13 to 20%, Ti: 0.5 to 4%, N: 0.1 to 0.5%, remaining Fe and inevitable impurities, and satisfying 1 ≦ Ti / N ≦ 20 On the roll surface.

  Here, the “roll surface” means the surface of the roll base material of the roll for continuous casting, and when another surface treatment layer (for example, a sprayed layer) is formed on the surface of the roll base material. The surface treatment layer becomes the “roll surface”. Further, even if the overlay welding layer of the present invention is formed on the surface of the roll base material and a thin sprayed layer is formed on the surface for the purpose of dispersion of thermal cracks (for example, Japanese Patent No. 1242246), this thin Even when the sprayed layer disappears during use and the surface becomes a build-up weld layer, it is included in the continuous casting roll of the present invention.

  (2) In the configuration of (1), Mo: 0.3 to 3% can be included by mass%. According to the configuration of (2), Mo is dissolved in the metal matrix, and the strength at high temperature can be improved.

  (3) In the configuration of (1) or (2), Co: 0.5 to 3% can be included in mass%. According to the configuration of (3), the heat resistance of the build-up weld layer is increased, and the strength at high temperature can be improved.

  (4) In the configurations of (1) to (3), Ni: 1 to 5% can be included in mass%. According to the configuration of (4), the corrosion resistance of the build-up weld layer can be increased.

  It is preferable to set C: 0.05% or less in terms of mass%, and it is preferable to set Ti: 0.5-3% in mass%, and N: 0.15-0.3 in mass%. % Is preferable, and it is preferable to set 1 ≦ Ti / N ≦ 15 by mass%.

  ADVANTAGE OF THE INVENTION According to this invention, the roll for continuous casting excellent in abrasion resistance and corrosion resistance can be provided.

Embodiments of the present invention will be described with reference to the drawings.
(Embodiment)
FIG. 1 is a schematic view of a continuous casting apparatus. The continuous casting apparatus 1 of this embodiment includes a tundish 2, a mold 3, a support roll 4, and a cooling spray 5. The dundish 2 is formed in a box shape whose upper side is open, and stores molten steel H poured from a ladle (not shown). An immersion nozzle 7 extending in the vertical direction is provided at the bottom of the dundish 2, and the tip of the immersion nozzle 7 extends into the mold 3 positioned below the dandish 2.

  The mold 3 is formed in a cylindrical shape from a water-cooled steel plate, and casts molten steel H flowing from the dundish 2 through the immersion nozzle 7. Copper or the like can be used for the mold 3.

Mold powder 11 is injected into the mold 3. Thereby, molten steel is interrupted | blocked from air | atmosphere, while being able to prevent heat insulation and oxidation, it can prevent that molten steel adheres to the surface of the mold 3. FIG. The mold powder 11 is composed of a powder mainly composed of an oxide such as CaO, SiO ₂ , MgO, or Al ₂ O ₃ , and Li ₂ O, NaF, CaF, etc. are added to reduce the viscosity. Yes.

  A plurality of support rolls 4 are arranged in a downstream direction from the lower end of the mold 3, and convey the slab cooled by the mold 3 while supporting it. A plurality of cooling sprays 5 are provided along the support roll 4, and the cooling water is sprayed from the gaps between the adjacent support rolls 4 toward the slab.

  In the above-described configuration, the molten steel H injected from the ladle (not shown) into the dundish 2 is injected into the mold 3 while the flow rate is adjusted by the immersion nozzle 7 at the bottom of the dandish 2. The molten steel H injected into the mold 3 is cooled (temporarily cooled) at the contact portion that contacts the inner wall surface of the mold 3 and solidifies. As a result, a slab having a solidified layer on the surface and an unsolidified molten steel H inside is generated.

  The unsolidified slab drawn from the lower end portion of the mold 3 is conveyed downstream while being supported by the support roll 4, and is cooled by cooling water sprayed from the cooling spray 5 during conveyance. At this time, the support roll 4 slides and wears due to the contact load received from the slab. Moreover, it receives loads such as thermal cracking and high-temperature steam oxidation due to the heat cycle by heating with the slab and cooling with cooling water. Furthermore, the mold powder injected into the mold 3 comes into contact with the support roll 4, and the fluorine contained in the mold powder and the base material of the support roll 4 cause a chemical reaction, and the support roll 4 is corroded.

  Therefore, in this embodiment, overlay welding excellent in corrosion resistance and wear resistance is performed on the surface of the support roll 4. Next, the composition of the build-up weld layer welded to the surface of the support roll 4 will be described.

  The weld layer welded to the support roll 4 of the present embodiment is in mass%, C: 0.07% or less, Si: 0.2 to 1.5, Mn: 3% or less, Cr: 13 to 20%, Ti: 0.5-4%, N: 0.1-0.5%, balance Fe and inevitable impurities, and 1 ≦ Ti / N ≦ 20. In addition, as a build-up welding method, a well-known method (for example, submerged arc welding method, powder plasma arc welding method) can be used.

  The characteristics required for continuous casting rolls are mainly "corrosion resistance", "wear resistance", and "heat crack resistance". Among these characteristics, as a method for improving wear resistance, corrosion resistance, A method of dispersing carbides as hard particles in a ductile and tough metal matrix for maintaining heat cracking resistance is known. However, when the support roll 4 is heated to a high temperature in contact with the slab, chromium having a high affinity with carbon is combined with the carbon to produce carbide, and this carbide precipitates at the grain boundaries. As a result, thermal cracking is easily promoted along the crystal grain boundary, the chromium concentration in the metal matrix is lowered, and the heat crack resistance and corrosion resistance of the support roll 4 are lowered.

  On the other hand, in the build-up weld layer of this embodiment, the carbon content is limited to a low value of 0.07% by mass or less so as not to lower the corrosion resistance, and is a hard factor that improves wear resistance. As a substitute for the carbide of particles, a large amount of titanium having excellent corrosion resistance is contained, and further, this titanium is reacted with nitrogen having a strong affinity to precipitate nitride, thereby improving the wear resistance. That is, unlike carbon, it does not combine with chromium and precipitate at the grain boundaries. Thereby, since the fall of the chromium density | concentration in a metal matrix can be suppressed, it can have wear resistance, maintaining heat cracking resistance and corrosion resistance.

  In other words, it is possible to provide the support roll 4 in which chromium is evenly distributed in the metal matrix and includes titanium nitride. As will be described below, the support roll 4 is excellent in corrosion resistance, wear resistance, and heat crack resistance.

  Next, the reason for limitation of each material which comprises this overlay welding layer is demonstrated.

(About C)
The present invention is based on the knowledge that wear resistance, corrosion resistance, and the like are satisfied by using Ti and N instead of C. Therefore, the C content needs to be set as low as possible. However, since C is an inevitable element mixed from a welding material or the like, the content rate cannot be reduced to 0%. Therefore, only the upper limit value is defined for C.

(About Si)
When the Si content is high, embrittlement of the welded layer that has undergone build-up welding occurs, and the toughness decreases. For this reason, the upper limit of the Si content is preferably 1.5% by mass, and more preferably 1.0% by mass. Si can lower the viscosity of the molten metal during welding, increase fluidity and improve weldability. It is also an effective element for removing impurities such as oxygen due to refining action. For this reason, the lower limit of the Si content is preferably 0.2% by mass, and more preferably 0.3% by mass. Since Si is an inevitable element, it is contained at least 0.2% by mass.

(About Mn)
When the content of Mn is high, the weld layer welded by overlay welding becomes brittle and the toughness decreases. For this reason, the upper limit of the Mn content is preferably 3% by mass, more preferably 2% by mass. Mn can reduce the viscosity of the molten metal during welding, increase the flow and improve the weldability. It is also an effective element for removing impurities such as oxygen due to refining action. For this reason, the lower limit of the Mn content is preferably 0.2% by mass, more preferably 0.8% by mass. In addition, since Mn is an inevitable element, it is contained at least 0.2% by mass.

(About Cr)
If the Cr content is too high, the toughness decreases. For this reason, the upper limit of the Cr content is preferably 20% by mass, and more preferably 17% by mass. If the Cr content is low, the corrosion resistance and oxidation resistance cannot be improved. For this reason, the lower limit of the Cr content is preferably 13% by mass, and more preferably 15% by mass.

(About Ti)
When the Ti content is high, a brittle metal compound is generated and the toughness is lowered. For this reason, the upper limit of the Ti content is preferably 4% by mass, and more preferably 3% by mass. Further, Ti improves corrosion resistance, and reacts with N instead of Cr to generate nitrides with excellent wear resistance. For this reason, when the Ti content is low, the amount of nitride produced is reduced, and the wear resistance cannot be improved. For this reason, the lower limit of Ti is preferably 0.5% by mass.

(About N)
N forms a solid solution in the matrix metal to increase the tempering resistance and combine with Ti to form a nitride having excellent wear resistance. In addition, since nitride is finely dispersed in the matrix and does not precipitate unevenly at grain boundaries like carbide, it contributes to the improvement of thermal crack resistance. For this reason, the lower limit of the N content is preferably 0.1% by mass, more preferably 0.15% by mass. When the content of N is high, blow holes are likely to occur when overlay welding is performed. For this reason, the upper limit of the N content is preferably 0.5% by mass, and more preferably 0.3% by mass.

(About the ratio of Ti and N)
As described above, the present invention aims to generate nitrides by reacting Ti with N, thereby improving the wear resistance of the overlay weld layer. It is necessary to set the ratio of N. Ti / N is preferably 1 to 20, and more preferably 1 to 15.

  Ni can also be included in the build-up weld layer. If the Ni content is high, the cost increases. For this reason, the upper limit of the Ni content is preferably 5% by mass, and more preferably 3.5% by mass. If the Ni content is low, sufficient corrosion resistance cannot be obtained. For this reason, the lower limit of the Ni content is preferably 1% by mass, and more preferably 1.5% by mass. Ni can be omitted when the required corrosion resistance can be ensured by the nitride of Ti and N.

  Mo can also be included in the build-up weld layer. Mo is an effective element in that it dissolves in the metal matrix and the strength at high temperature is improved. For this reason, the lower limit of the Mo content is preferably 0.3% by mass, and more preferably 0.5% by mass. When the Mo content is high, the toughness is lowered and the cost is increased. For this reason, the upper limit of the Mo content is preferably 3% by mass, and more preferably 1.5% by mass. Mo may be omitted.

  Co can also be included in the overlay weld layer. Co is an effective element in terms of improving heat resistance and improving strength at high temperatures. For this reason, the lower limit of the Co content is preferably 0.5% by mass, and more preferably 1% by mass. If the Co content is high, the workability is lowered and the cost is increased. For this reason, the upper limit of the Co content is preferably 3% by mass, and more preferably 2% by mass. Note that Co can be omitted.

  Next, an Example is shown and this invention is demonstrated concretely.

The following corrosion resistance test and wear resistance test were conducted.
(Corrosion resistance test)
A weld layer having the composition shown in Table 1 was formed on the surface of an SS400 flat plate (300 × 400 × 40 t). Arc welding was used as a welding method, and a weld layer composed of 8 layers was formed. A test piece (20 h × 30 w × 4 mmt) was cut out from the entire welded steel portion which is not easily affected by dilution.

  Table 2 shows the test conditions for the corrosion resistance test. As shown in Table 2, each test piece was immersed in a 5% by mass hydrofluoric acid aqueous solution and allowed to stand for 100 hours. The temperature of the hydrofluoric acid aqueous solution was normal temperature (20 ° C.).

The results of the corrosion resistance test are shown in Table 5. Corrosion weight loss is evaluated quantitatively. When the corrosion weight loss is 3.8 (mg / mm ² ) or less, it is evaluated as “Excellent” and when it is 3.8 to 4.2 (mg / mm ² ). Was evaluated as good, and when it was larger than 4.2 (mg / mm ² ), it was evaluated as poor as x.
(About wear resistance test)
A build-up weld layer having the composition shown in Table 1 was formed on the surface of a carbon steel pipe S25C (φ90 × 100). After forming the build-up weld layer consisting of three layers, the thickness of the build-up weld layer is cut to 5 mm by machining, and the cut carbon steel pipe S25C is cut in the radial direction to obtain a test piece (φ100 × 10 t) Was made.

  A test apparatus for the abrasion resistance test will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating a schematic configuration of a test apparatus for an abrasion resistance test. In the figure, the test apparatus includes a counter roller 21 and a test piece (hereinafter referred to as a test piece roller) 22. The counterpart roller 21 rotates around the rotation shaft 21a, and the test piece roller 22 rotates around the rotation shaft 22a extending in a direction parallel to the rotation shaft 21a. The rotation shaft 21a is connected to a first rotation motor (not shown) via a transmission gear (not shown). When the first rotation motor is driven, the counter roller 21 rotates around the rotation shaft 21a. The test piece roller 22 is pressed against the surface of the counterpart roller 21. The rotation shaft 22a of the test piece roller 22 is connected to a second rotation motor (not shown) via a transmission gear (not shown), and when the second rotation motor is driven, the test piece is rotated around the rotation shaft 22a. The roller 22 rotates.

  A high frequency heating coil 23 extending in the circumferential direction of the counterpart roller 21 is provided at a position slightly spaced from the outer surface of the counterpart roller 21. When an alternating current is passed through the high-frequency heating coil 23, a high-density eddy current is generated near the surface of the counterpart roller 21, and the counterpart roller 21 is heated by the Joule heat. Near the surface of the test piece roller 22, a cooling water spray nozzle 24 is provided at a position different from the counterpart roller 21. The cooling water sprayed from the cooling water spray nozzle 24 is supplied to the test strip roller 22 to cool the test strip roller 22.

  In the above-described configuration, when the cooling water spray nozzle 24 is operated by energizing the high-frequency heating coil 23, the test piece roller 22 is heated at the contact position with the counterpart roller 21 and is supplied from the cooling water spray nozzle 24. It is cooled at the position of contact with water.

  Further, the test piece roller 22 is pressed against the surface of the mating roller 21 to be in frictional contact, and the first and second rotating rollers are used so that the rotation speed of the test piece roller 22 is slower than that of the mating roller 21. The drive of the motor is controlled. Thereby, the build-up weld layer formed on the surface of the test piece roller 22 can be worn by the rotating action of the counterpart roller 21. Therefore, the wear resistance of the test piece roller 22 can be evaluated under a temperature environment in which heating and cooling are repeated.

  Table 3 shows the test conditions for the abrasion resistance test. As shown in Table 3, the pressing force of the test piece roller 22 against the counterpart roller 21 is 147 (N), the rotational speed of the counterpart roller 21 is 500 rpm, the rotational speed of the test piece roller 22 is 490 rpm, and a high frequency The heating temperature by the heating coil 23 was 500 ° C., and the test time was 5 hours. Note that the slip ratio of the counterpart roller 21 and the test piece roller 22 was 2%.

After the test time, the wear amount of the test piece roller 22 was measured to evaluate the wear resistance. The amount of wear was a value obtained by multiplying the pressing force (147 (N)) against the test piece roller 22 by the sliding distance (travel distance, that is, the rotation speed x the circumference of the test material (m)). Calculation was performed by gradually reducing the volume of the overlay weld layer. Table 4 shows the results of the abrasion resistance test. The amount of wear is quantitatively evaluated, and when the specific friction amount is 1.2 (mm ³ / N · m) or less, it is evaluated as “Excellent” as ◎, and 1.2 to 1.7 (mm ³ / N · m · In the case of m), it was evaluated as “Good” as good, and when it was larger than 1.7 (mm ³ / N · m), it was evaluated as “Poor” as poor. In addition, about weldability, it was visually evaluated whether it was poor in welding.

It is the schematic of a continuous casting apparatus. It is the schematic of a test apparatus.

Explanation of symbols

2 Tundish 2
3 Mold 4 Support roll 5 Cooling spray

Claims (8)

  In mass%, C: 0.07% or less, Si: 0.2-1.5%, Mn: 3% or less, Cr: 13-20%, Ti: 0.5-4%, N: 0.1 A continuous casting roll having a build-up weld layer containing 0.5% and the balance Fe and inevitable impurities and satisfying 1 ≦ Ti / N ≦ 20 on the roll surface.   The continuous casting roll according to claim 1, wherein, in mass%, Mo: 0.3 to 3% is included.   The roll for continuous casting according to claim 1 or 2, characterized by containing Co: 0.5 to 3% by mass%.   The continuous casting roll according to any one of claims 1 to 3, wherein Ni is contained in an amount of 1 to 5% by mass.   The continuous casting roll according to any one of claims 1 to 4, wherein C is 0.05% or less in terms of mass%.   The roll for continuous casting according to any one of claims 1 to 5, wherein Ti is 0.5 to 3% by mass.   The roll for continuous casting according to any one of claims 1 to 6, wherein N is 0.15 to 0.3% in mass%. The roll for continuous casting according to any one of claims 1 to 7, wherein, in mass%, 1≤Ti / N≤15.

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