JP2007136509A - Build-up welding material for continuous casting roll, and roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a build-up welding material for a continuous casting roll which has high proof stress, high ductility and low thermal expansibility at high temperature and is excellent in thermal crack resistance, and to provide the rolls using the welding material. <P>SOLUTION: The build-up welding material for the continuous casting roll has a composition containing, by mass, ≤0.1% C, 10 to 15% Cr, 8 to 15% Mo, ≤5% W, ≤15% Co, 1 to 5% Al, 1 to 5% Ti and 0.01 to 0.1% N, and the balance Ni with inevitable impurities, and also satisfying Cr%/33+Mo%/25+W%/31≤1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a continuous casting roll overlay welding material and roll that have high yield strength, high ductility, and low thermal expansion characteristics at high temperatures and are excellent in heat crack resistance.

Conventionally, a continuous casting roll used at a high temperature of about 600 ° C. is in a harsh usage environment in which rapid heating and rapid cooling are repeated, and thus suffers damage such as thermal cracking and high-temperature oxidation. Maintenance in such a harsh use environment and an increase in manufacturing cost due to replacement have been an issue.
To solve such a problem, for example, as disclosed in JP-A-2001-340991 (Patent Document 1), C: 0.07% or less, Si: 1% or less, Mn: 1% or less, P : 0.003% or less, S: 0.03% or less, Ni: 3 to 5%, Cr: 15.5 to 17.5%, Cu: 3 to 5%, Mo: 1.5% or less, Nb: There has been proposed a continuous casting roll in which a built-up layer composed of 0.3 to 0.6%, the balance Fe and inevitable impurities is formed by welding.

  Further, as disclosed in JP-A-10-156500 (Patent Document 2), C: 0.03-0.3%, Si: 0.03-1.5%, Mn: 0.1 A weld metal layer composed of 3.0%, Ni: 0.5 to 10%, Cr: 10 to 20%, N: 0.05 to 0.5%, the balance Fe and inevitable impurities is formed on the roll surface layer. A build-up roll for heat-resistant cracking continuous casting characterized in that has been proposed. These are all Fe-based stainless steels.

  Further, as disclosed in JP 2002-239697 A (Patent Document 3), Cr: 17 to 22%, Co: 10 to 14%, Mo: 4 to 8%, W: 0.8 to 1 0.5%, Al + Ti: 3 to 5.5%, Si: 0.05% or less, Mn: 0.2% or less, C: 0.05% or less, Ni-based alloy powder composed of the balance Ni and inevitable impurities An overlaying roll for continuous casting in which a Ni-based austenitic alloy is deposited on the surface, which is a buildup roll for continuous casting in which a thickness of 2 mm or more is welded by a powder plasma arc overlay welding method, has been proposed. In recent years, however, the load applied to continuous casting rolls has been increasing due to higher speeds and higher temperatures in casting technology, and materials with excellent thermal crack resistance have been demanded.

  It is known that it is important to have high-temperature proof stress, high-temperature ductility, and low thermal expansion characteristics in order to improve the thermal cracking resistance of a continuous casting roll in such a use environment. As described above, Fe-based stainless steel generally has a lower high-temperature yield strength than Ni-based superalloys, whereas Ni-based superalloys have a relatively high thermal expansion coefficient, and these materials may not have sufficient thermal crack resistance. .

  On the other hand, various Ni-base superalloys are commercially available, but these are mainly developed as gas turbines and their peripheral materials, and many are developed on the assumption that they are used in a temperature range near 1000 ° C. In many cases, it has not been developed on the premise that the continuous casting roll is used at around 600 ° C. In general, these alloys are often used after being solution-treated at a temperature close to 1100 ° C. and then aging at a temperature of about 700 ° C. in order to eliminate solidification segregation and heterogeneous phase formation. However, clad rolls built for continuous casting have problems such as interfacial cracking and strength reduction of the roll material (core material), which makes it difficult to perform a solution treatment. Therefore, it is important to have good characteristics even in the process in which the solution treatment is omitted.

  Taking the above factors into consideration, we have made extensive developments, and at the operating temperature of around 600 ° C, we can suppress the formation of the brittle phase even in the process of omitting the solution treatment, exhibit high yield strength and high ductility, and have low thermal expansion. As Ni-base superalloy having characteristics, the inventors have disclosed C: 0.1% or less, Cr: 10-15%, Mo, as disclosed in JP-A-2005-144488 (Patent Document 4). : 8-15%, Co: 15% or less, W: 5% or less, Al: 1-5%, Ti: 1-5%, remaining Ni Ni did.

  This Patent Document 4 shows excellent heat cracking resistance as a continuous casting roll, but in a more severe use environment, the base component has high heat cracking resistance, so the number of heat resistant turtles generated on the roll surface is small. Thereafter, the applied thermal stress concentrates on the few thermal cracks, and as a result, although the number of thermal cracks is small, there may be deep cracks. Since such a deep crack leads to peeling of the overlay layer, there is a problem that early repair is required.

JP 2001-340991 A JP 10-156500 A Japanese Patent Laid-Open No. 2002-239697 JP 2005-144488 A

  In order to solve the above-mentioned problems, the inventors have made further developments, and as a result, have found the following extremely important findings for preventing the occurrence of deep cracks as a material for overlaying continuous casting rolls. . As described above, it is known that it is important to improve heat cracking resistance in a continuous casting roll that it has excellent high temperature proof stress, high temperature ductility, and low thermal expansion characteristics. It has been found that the heat cracking resistance can be greatly improved by including a predetermined amount of Ti and N in the Ni-based alloy for overlaying a casting roll.

  That is, by containing a predetermined amount of Ti and N, TiN is dispersed in the built-up layer, and this TiN becomes a stress concentration source and becomes a starting point of thermal cracks that occur during the use of continuous casting rolls. It has been found that finely dispersed particles can be obtained, and as a result, the thermal stress is alleviated by fine cracks, whereby large cracks and peeling of the surface layer causing damage to the continuous casting roll can be suppressed.

Patent Document 2 proposes a welding material in which 0.05 to 0.5% of N is added. In this example, Fe is a solid solution of N in the matrix as compared with the Ni-based alloy which is the material of the present invention. Since it is a base alloy, the form of nitride is different. The main effect of N addition in the Fe-based alloy is austenitization of the structure due to solid solution in the matrix. Furthermore, Fe ₃ N, Fe ₄ N, CrN, etc. are partially formed, and the effects of improving wear resistance and preventing crystal grain coarsening are also seen. However, in the Ni-base alloy having a small N solid solubility limit as in the present invention, the effect of N addition is different from that aimed at miniaturization of thermal cracks due to TiN dispersion by simultaneous addition with Ti.

As described above, the present invention includes a predetermined amount of Ti and N to disperse TiN in the build-up layer, and this TiN becomes a stress concentration source and the origin of thermal cracks that occur during use of the continuous casting roll. As a result, thermal cracks can be finely dispersed, and as a result, thermal stress is alleviated by fine cracks, so that large cracks and peeling of the surface layer that cause damage to the continuous casting roll can be suppressed. It is to provide a welding material for roll overlay for continuous casting.
The gist of the invention is that
(1) By mass%, C: 0.1% or less, Cr: 10-15%, Mo: 8-15%, W: 5% or less, Co: 15% or less, Al: 1-5%, Ti: 1-5%, N: 0.01-0.1%
A continuous casting roll overlay welding material characterized by comprising the balance Ni and unavoidable impurities and satisfying Cr% / 33 + Mo% / 25 + W% / 31 ≦ 1.

(2) The welding material for overlaying a continuous casting roll according to the above (1), characterized in that it is 1% or 2% by mass of Si: 0.5% or less and Mn: 0.5% or less.
(3) The welding material for continuous casting roll build-up according to the above (1) or (2), wherein S is 0.005% or less by mass%.
(4) Continuous casting roll build-up according to any one of the above (1) to (3), characterized in that one or two of Nb: 3% or less and Ta: 6% or less are used. Welding materials.

(5) Continuous casting roll build-up according to any one of (1) to (4) that satisfies 20 ≦ γ ′ phase amount ≦ 35%, LM absolute value ≦ 0.015%, Nv, Nv ′ ≦ 2.30 Welding materials.
However, γ ′: strengthened phase mainly composed of Ni ₃ Al LM absolute value: lattice constant mismatch of γ-γ ′ phase (Lattice Mismatch) Nv: average electron vacancy number of γ phase Nv ′: average electron of γ ′ phase Number of pores (6) A continuous casting roll comprising the welding material for overlaying a continuous casting roll according to any one of (1) to (5).

  As described above, according to the present invention, it is possible to provide a casting roll overlay welding material and a roll excellent in heat crack resistance.

The reasons for limiting the alloy components according to the present invention will be described below.
C: 0.1% or less C forms carbides with Ti, Cr, Mo, W, etc. at grain boundaries and strengthens the grain boundaries. However, if the content exceeds 0.1%, the Ti, Cr, Mo, and W concentrations in the grains decrease and adversely affect the yield strength and oxidation resistance, so the upper limit was made 0.1%.

Cr: 10-15%
Cr needs to be 10% or more in order to ensure oxidation resistance at high temperatures. However, if it exceeds 15%, a brittle intermetallic compound is precipitated and ductility is lowered. Therefore, the range was made 10 to 15%.

Mo: 8-15%
Mo is dissolved in the γ phase and has the effect of improving the high temperature yield strength and the effect of reducing the thermal expansion coefficient. Moreover, it is an element which has an effect which improves the corrosion resistance with respect to the fluorine contained in mold powder. However, if it is less than 8%, the effect is not sufficient. On the other hand, if it exceeds 15%, a brittle intermetallic compound is precipitated and ductility is lowered. Therefore, the range is 8-15%.

W: 5% or less W is an element that is dissolved in the γ phase and has the effect of improving the high-temperature yield strength and the effect of reducing the thermal expansion coefficient. However, if it exceeds 5%, a brittle intermetallic compound precipitates and the ductility decreases, so the upper limit was made 5%.
Co: 15% or less Co is an element having an effect of improving ductility. However, if it exceeds 15%, the cost increases, so the upper limit was made 15%.

Al: 1 to 5%
Al is an element that forms a γ ′ phase and improves high-temperature yield strength. However, if it is less than 1%, the effect is not obtained, and if it exceeds 5%, the ductility is lowered, so the range was made 1 to 5%. Ti: 1 to 5%
Ti generates TiN and becomes a thermal stress concentration source, and refines thermal cracks. Further, it replaces Al in the γ ′ phase and strengthens the γ ′ phase. However, if it is less than 1%, the effect is not sufficient, and if it exceeds 5%, the ductility decreases, so the range was made 1 to 5%.

N: 0.01 to 0.1%
N generates TiN, becomes a thermal stress concentration source, and refines thermal cracks. However, if it is less than 0.01%, the effect is not sufficient, and if it exceeds 0.1%, blowholes are likely to occur during welding, so the range was made 0.01 to 0.1%.

Cr% / 33 + Mo% / 25 + W% / 31 ≦ 1
When Cr% / 33 + Mo% / 25 + W% / 31 exceeds 1, brittle intermetallic compounds are produced, and ductility is lowered. Therefore, the upper limit is set to 1.
Si: 0.5% or less, Mn: 0.5% or less Si and Mn improve the hot-water flow when building up, but if over 0.5%, inclusions such as oxide precipitate and impact value Deteriorate mechanical properties. Accordingly, the upper limit is set to 0.5%.

S: 0.005% or less S can be suppressed to 0.005% or less to suppress high-temperature cracking during build-up. Therefore, the upper limit was made 0.005%. Preferably, it is suppressed to 0.003% or less.
Nb: 3% or less, Ta: 6% or less Nb and Ta are dissolved in the γ ′ phase to improve the yield strength. However, when the content exceeds 3% and 6%, respectively, the ductility is lowered. Were 3% and 6%, respectively.

20% ≦ γ ′ phase amount ≦ 35%, LM absolute value ≦ 0.015%, Nv, Nv ′ ≦ 2.30
When the amount of γ ′ phase is less than 20%, the yield strength is low, and when it exceeds 35%, the ductility is reduced and build-up cracking is liable to occur, so the range is set to 20 to 35%. Preferably, 23% ≦ γ ′ phase amount ≦ 30%.
On the other hand, if the LM absolute value exceeds 0.015%, the γ ′ phase aggregates and precipitates, and the ductility decreases. Furthermore, when Nv and Nv ′ exceed 2.30, a brittle phase is precipitated and ductility is lowered. Therefore, the upper limit was set to 0.015% and 2.30, respectively. Furthermore, it is preferably 0.010 mm and 2.28.

  Note that the LM absolute value described above represents a lattice constant mismatch of the γ-γ ′ phase, and Nv and Nv ′ are the average electron vacancy numbers of γ and γ ′, respectively, and Nv = ΣCxNx , And Nv ′ = ΣC ′ × Nx. Here, Cx and C′x are the concentrations of the X element constituting the γ and γ ′ phases, respectively, and Nx is the number of intrinsic electron vacancies of the X element.

  The average number of electron vacancies in a Ni-based alloy is limited to γ and γ ′ phase alloys in which γ ′ is uniformly precipitated in the γ matrix. It is limited within a range not exceeding the solid solubility of γ ′. If this limit is exceeded, even if initially only the γ and γ ′ phases are present, a phase such as the σ phase is precipitated in addition to the γ and γ ′ phases during long-term use, or the γ ′ phase is changed to the η phase. Or it transforms into a δ phase to deteriorate the properties. One of the quantities defining this limit is the average number of electron vacancies. If Nv and Nv ′ are 2.26 or less, the σ phase is not generated at all, and if it exceeds 2.41, the σ phase is always generated, and there are cases where the σ phase is generated or not in the middle. . Therefore, the average number of electron vacancies can be regarded as an amount that limits the boundary between γ or γ ′ and the σ phase.

  In calculating the LM absolute value or the like, if the composition of γ or γ ′ is determined, the lattice constant of γ or γ ′ is inevitably determined, and therefore LM is also determined. In the case of a forged material, the γ grain size is mainly affected by heat treatment conditions, and in the case of a cast material, it is affected by casting conditions such as the casting temperature, the mold preheating temperature, or the presence or absence of an inoculum in the mold. The γ ′ particle size is generally affected by heat treatment conditions, but when used as cast, it is affected by casting conditions.

Hereinafter, the present invention will be specifically described with reference to examples.
25 kg of base material is induction-melted in an Ar atmosphere, discharged from a nozzle with a diameter of 5 mm at 1600 ° C., atomized with N ₂ and Ar (comparative example) gas, and a powder having the component composition shown in Table 1 is produced. , And classified into -250/63 μm and used for the experiment. SUS329 was overlay welded (1 layer) on a low alloy roll (diameter 120 mm × length 1322 mm), and powder overlay plasma welding (2 layers) was performed on this powder. Further, this buildup roll was subjected to heat treatment at 600 ° C. for 4 hours.

  As an evaluation item, the evaluation of heat cracking resistance by a heat crack test is performed by rotating the build-up roll at 1.44 rpm, heating with a gas burner from above, spraying cooling water from below, and heating at 400 ° C. and cooling at 200 ° C. Thermal cycles were given 5000 times. Then, the cross section of the roll surface portion (4 sections of 150 mm × 40) was micro-observed and evaluated by the maximum crack depth. The results are shown in Table 1.

  As shown in Table 1, no. 1 to 10 are examples of the present invention. 11 to 26 are comparative examples. Comparative Example No. 11 has a high Cr content and W content, a large LM absolute value (Å), and a large Nv value. Furthermore, since the value of Cr% / 33 + Mo% / 25 + W% / 31 is high, the maximum crack depth is considerably large. Comparative Example No. 12 has a high Cr content and a high Mo content, a large LM absolute value (値), and a large Nv value. Furthermore, since the value of Cr% / 33 + Mo% / 25 + W% / 31 is high, no. Similar to 11, the maximum crack depth is quite large. Comparative Example No. No. 13 has a small amount of γ 'and a large LM absolute value, so that the maximum crack depth is large. Comparative Example No. No. 14 has a large maximum crack depth because the amount of γ ′ is small.

  Comparative Example No. No. 15 has a high Al content, a large amount of γ ′, a large LM absolute value, and a large Nv ′ value, so that the maximum crack depth is large. Maximum crack depth is quite large. Comparative Example No. No. 16 has a high C content, a high Ti content, and a large amount of γ ', so that the maximum crack depth is large. Comparative Example No. Since No. 17 has a high N content and a large LM absolute value, the maximum crack depth is large. Comparative Example No. No. 18 has a low N content and a large Nv ′ value, so that the maximum crack depth is large.

  Comparative Example No. Since No. 19 has high Si content, Mn content, and S content, the maximum crack depth is large. Comparative Example No. 20 is the Nb content, Comparative Example No. Since No. 21 has a high Ta content, the maximum crack depth is large. Comparative Example No. It can be seen that 22 to 26 have a large maximum crack depth because the N content is small. On the other hand, the present invention example No. Since all 1-10 satisfy | fills this invention condition, it turns out that it is very shallow compared with a comparative example about the maximum crack depth.

As described above, by containing a predetermined amount of Ti and N, TiN is dispersed in the build-up layer, and thermal cracks generated during use of a continuous casting roll in which this TiN becomes a stress concentration source are finely dispersed. As a result, the thermal stress is relieved by fine cracks, and a continuous casting roll overlay welding material with excellent heat cracking resistance that can suppress large cracks and peeling of the surface layer, which cause damage to the continuous casting roll, and manufactured by the same. Was able to provide a roll.


Patent applicant Sanyo Special Steel Co., Ltd. and 1 other
Attorney: Attorney Shiina

Claims (6)

% By mass
C: 0.1% or less,
Cr: 10 to 15%,
Mo: 8-15%,
W: 5% or less,
Co: 15% or less,
Al: 1 to 5%,
Ti: 1 to 5%,
N: 0.01 to 0.1%
A continuous casting roll overlay welding material characterized by comprising Ni, the balance Ni and inevitable impurities, and satisfying Cr% / 33 + Mo% / 25 + W% / 31 ≦ 1. % By mass
Si: 0.5% or less,
The welding material for overlaying continuous casting rolls according to claim 1, wherein Mn is one or two of 0.5% or less. The welding material for overlaying continuous casting rolls according to claim 1 or 2, wherein S is 0.005% or less in terms of mass%. % By mass
Nb: 3% or less,
The welding material for overlaying continuous casting rolls according to any one of claims 1 to 3, wherein Ta: 6% or less is used. The continuous casting roll overlay welding material according to any one of claims 1 to 4, wherein 20 ≦ γ ′ phase amount ≦ 35%, LM absolute value ≦ 0.015%, Nv, Nv ′ ≦ 2.30 are satisfied.
However, γ ′: strengthened phase mainly composed of Ni ₃ Al LM absolute value: lattice constant mismatch of γ-γ ′ phase (Lattice Mismatch) Nv: average electron vacancy number of γ phase Nv ′: average electron of γ ′ phase Number of holes A continuous casting roll comprising the welding material for overlaying a continuous casting roll according to any one of claims 1 to 5.