JPH0332490A - Built-up roll - Google Patents

Abstract

PURPOSE:To improve the impact characteristic and crack resistance of a hot rolling roll by specifying the alloy element compsn. of the built-up surface layer part of the roll. CONSTITUTION:The roll to be used in hot billet transter, or hot rolling, etc., is build-up welded and the surface layer part thereof is composed to consist essentially, by weight %, of iron and to contain 0.07 to 0.2% C, 0.5 to 2% Ni, 9 to 14% Cr, 0.2 to 1.5% Mo, 0.03 to 0.3% Nb, 0.1 to 1% V, and 0.2 to 2% W, and further to contain 0.3 to 2% Cu at need, by which the impact characteristics of the build-up weld metal is improved and the generation of weld crack is prevented.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a build-up roll, and more specifically, a build-up roll that is used under repeated heating and cooling at high temperatures and has excellent heat cracking resistance, abrasion resistance, and corrosion resistance. It is related to. (Prior art and problems to be solved) Hot rolls used for transferring or rolling high-temperature metal pieces, such as drawing rolls for continuous casting, are heated by contact with high-temperature metal pieces, and are heated by water or steam. The product is repeatedly cooled by water, resulting in extremely harsh operating conditions. In order to be used for a long time under such conditions, it is necessary to make the rolls from materials that have a high degree of wear resistance, corrosion resistance, and heat cracking resistance. Conventionally, such drawing rolls for continuous casting have been manufactured using 13Cr on the outer peripheral surface of a base roll made of low alloy steel.
- Overlay rolls made of Ni-based steel have been proposed and put into practical use. As 13cr-Ni steel, 13Cr-
There are 2Ni series, 13Cr-4Ni series, etc., and similar products include 13Cr series, 16Cr-3Ni series, etc. In addition, some yarns with some amount of Mo or V added to these component yarns are also seen. However, with such overlay rolls, there is a problem in that cracks occur on the roll surface due to thermal stress caused by repeated heating and cooling during use, significantly shortening the roll's service life, and improvement of this problem is desired. was. This problem is not limited to continuous casting drawing rolls, but also applies to other hot overlay rolls.In particular, hot overlay rolls with excellent heat cracking resistance or hot roll materials The reality is that development is desired. Needless to say, this type of overlay roll should have sufficient performance in terms of wear resistance and corrosion resistance. The present invention was made in response to such a need, and an object of the present invention is to provide a hot overlay roll having particularly excellent heat cracking resistance. (Means for Solving the Problems) In order to solve the above-mentioned problems, the inventors of the present invention have repeatedly produced various overlay welding materials, conducted performance tests, and conducted repeated studies. In doing so, we place particular emphasis on performance in terms of heat cracking resistance, and also evaluate items such as the impact properties of the weld metal being above a certain level and the absence of weld cracking. Promoted material development. As a result, with iron as the main component, C, Ni, Cr, Mo,
It was discovered that the above-mentioned problem can be solved by regulating Nb, V, and W within a predetermined range, or by forming an overlay welded part containing a small amount of Cu on the roll surface. , this is where the present invention is made. That is, the present invention provides a roll used in hot processes such as hot piece transfer or hot rolling, in which the roll surface layer contains iron as a main component, C: 0.07 to 0°2%, Ni: 0, 5
~2%, Cr: 9-14%, Mo2 0.2-1.5%,
Nb: 0.03~0.3%, V: 0°1~1% and W:
Contains 0.2 to 2%, and if necessary further Cu: 0, 3
The gist is a meaty roll characterized by having a composition containing ~2%. The present invention will be explained in further detail below. (Function) The reasons for limiting the chemical components of the roll surface layer in the overlay roll according to the present invention are as follows. C: 0.07 to 0.2% C has the effect of suppressing the formation of δ ferrite and making the structure martensite. It also combines with elements such as Nb and V to form carbides, which has the effect of improving high-temperature strength. Although it is related to other elements, it is necessary to contain 0.05% or more in order to make the structure martensite and ensure high-temperature strength. However, if it is contained in an amount exceeding 0.2%, weldability, particularly low temperature cracking properties, will deteriorate, residual austenite will be more likely to be formed, and heat cracking properties will decrease. Therefore, the appropriate amount of C is in the range of 0.05 to 0.2%. Ni: 0.5-2% Ni is an austenite-forming element and is effective in suppressing the formation of δ ferrite in the weld metal and improving the impact properties of the weld metal. In order to form a martensitic structure and improve impact properties, it is necessary to contain 0.5% or more. However, if the content exceeds 2%, retained austenite tends to grow, the coefficient of linear expansion increases, and heat cracking properties deteriorate. Therefore, the amount of Ni is set in the range of 0.5 to 2%. Cr: 9-14% In order to ensure sufficient corrosion resistance in the environment in which hot rolls are used, it is necessary to contain 9% or more of Cr. However, even if the content exceeds 14%, corrosion resistance is not improved much, and on the contrary, δ ferrite is more likely to be generated, resulting in deterioration of heat cracking property. Therefore, the amount of Cr is 9~
14% is appropriate. Mo: 0.2-1.5% Mo is effective in increasing the high temperature strength of weld metal,
In order to exhibit this effect, it is necessary to contain 0.2% or more. However, if the content exceeds 1.5%, it becomes difficult to suppress the formation of δ ferrite, and heat cracking properties are inhibited. Therefore, the amount of Mo is 0.3
The range is 1.5%. W: 0.2-2% W has the effect of increasing the high-temperature strength of the weld metal;
The effect is exhibited when the content is 2% or more. but,
If the content exceeds 2%, not only the degree of the effect will not change much, but also the heat cracking property will deteriorate due to the formation of δ ferrite. Therefore, WJi is 0.2~
The range shall be 2%. V: 0.1-1% (2) greatly contributes to increasing the high-temperature strength and softening resistance of the weld metal, and its effect becomes significant when it is contained at 0.1% or more. However, if the content exceeds 1%, the impact properties of the weld metal deteriorate, and there is a tendency for the slag removability in welding workability to deteriorate. Therefore, the appropriate V amount is in the range of 0°1 to 1%. Nb: 0.03 to 0.3% Nb contributes to an increase in high-temperature strength, similar to (2). The effect is exhibited when it is contained in an amount of 0.03% or more. However, if the content exceeds 0.3%, there is a tendency for the toughness of the weld metal to decrease significantly. Therefore, the amount of Nb is set in the range of 0.03 to 0.3%. Cu: 0.2-1% Cu is effective in improving corrosion resistance against high-temperature steam, so it can be added as necessary. When added, the effect is exhibited at 0.2% or more. However, if the content exceeds 1%, hot cracking tends to occur in the weld metal, so Cut is set in the range of 0.2 to 1%. The remainder is essentially iron, but St and Mn are each added in an amount of 0.1 to 1 as deoxidizing agent or to ensure strength.
% and 0.1 to 2%, and P and S may also be contained in very small amounts. It may be contained in the form of impurities. By forming the overlay weld metal having the above structure on the surface layer of the roll, it is possible to provide a hot roll having extremely excellent heat crack resistance and sufficient wear resistance and corrosion resistance. It goes without saying that when the overlay weld metal is formed only on the surface layer of the roll, the roll material (i.e., the base material) can be made of an appropriate material such as mild steel. The same effect can be obtained by manufacturing and attaching this to a roll material. Furthermore, it goes without saying that similar performance can be obtained even if the entire roll material is manufactured from materials having the above-mentioned component range according to the present invention. (Example) Next, an example of the present invention will be shown. Overlay Wj welding metal with the composition shown in Table 1 was overlay welded onto a mild steel plate by band arc welding under the following construction conditions, and 600
SR treatment was performed at ℃ for 2 hours. <Welding construction conditions> Material to be welded: 525C1 32tX 300wX 500 Q Welding method: Strip electrode submerged arc welding Electrode used: 1
3Cr steel (commercially available USB-410) 0.4mmtX 5
0mmw Polarity: DC, RP Welding current: 650A Welding voltage: 25V Welding speed: 19c/in Preheating, temperature between baths: 200-350°C Lamination method: 3-layer stacking with 4 passes and 1 layer (for collecting impact test pieces) After the SR treatment, a heat crack test piece and a weld metal impact test piece were taken from the welded part, various tests were conducted, and the heat crack property and impact performance were evaluated. The results are shown in Table 1. The heat crack test is performed by rapidly heating the surface of the test piece using a high-frequency coil, then cooling it with water from the surface, and repeating this process.Specifically, the test piece surface temperature is repeatedly heated to 700°C and 150°C. was performed 800 times. After the test, the specimen was cut and the maximum depth of the crack was measured. FIG. 1 shows the state of the heating coil and test piece in the heat crack test, and FIG. 2 shows the applied heat cycle pattern. The impact test was conducted at 20°C using a test piece having the shape of JIS Z 22024. Regarding the evaluation of the performance of overlay weld metal, we aimed to significantly exceed the performance of conventional overlay weld metal in terms of heat crack resistance, and the maximum crack depth was 0 under the above test conditions.
．． Those with a diameter of 4 mm or less were considered to be acceptable. Regarding impact performance, those whose absorbed energy at 20° C. was less than 0.5 kgf-s+ were judged to be rejected. Furthermore, those in which defects such as hot cracking occurred in the weld metal were also rejected. In Table 1, &1 to NQ8 are examples of the present invention, Nα9 to &
No. 19 is a comparative example and will be discussed as follows. Comparative Example &9, which did not contain any of Nb, V, and W, had insufficient strength at high temperatures and unsatisfactory heat cracking properties. In Comparative Example Halo, in which the amount of C was too low, δ ferrite was generated and the heat cracking property was deteriorated. C:! Comparative example NQll in which 1 is excessive and comparative example Nd in which Ni amount is excessive
I3 is because retained austenite was generated in both cases,
For &13, which did not satisfy the heat cracking property, it is possible that the above-mentioned performance deteriorated due to an increase in the coefficient of linear expansion. In Comparative Examples Na12 and &17 in which Nb or V was excessive, toughness deteriorated and heat cracking resistance decreased due to the formation of δ ferrite. Comparative Example Nα14, in which the amount of Cr was insufficient and the amount of C was excessive, did not satisfy heat cracking properties due to the formation of retained austenite. Comparative Example Na15 with an excessive amount of Cr, Comparative Example &16 with an excessive amount of Mo, and Comparative Example Nα18 with an excessive amount of W each did not satisfy the heat crack property due to the formation of δ ferrite. Comparative Example No. 19, in which the amount of Cu was excessive, was not subjected to an evaluation test because hot cracking occurred in the weld metal. In contrast to these comparative examples, inventive examples Na 1 to Na 8 were
It was confirmed that all of them had extremely excellent heat cracking properties as well as a predetermined impact performance.

[Margin 1 below 044 Among the weld metals obtained in Example 1, N111 of the present invention example. 3tX25X from N13 and &8 weld metal
Corrosion specimens of size 35 were taken and subjected to high temperature steam oxidation tests. The test conditions were 700°C x 8 hours, and the oxidation weight gain after the test was measured. As shown in Table 2, the test results show that N117 and &8 containing a predetermined amount of Cu have a smaller oxidation weight gain than Nal that does not contain Cu, and corrosion resistance is improved by adding a predetermined amount of Cu. It was confirmed that Table 2 In order to confirm the applicability to an actual machine, the overlay roll according to the present invention and the conventional overlay roll were respectively incorporated into the drawing roll in continuous casting equipment, and the degree of damage during use (
A comparative investigation was conducted regarding the degree of crack occurrence. The built-in overlay roll is a drive roll with a body of 380φ, and uses low-alloy heat-resistant steel as the roll material (base material).
The overlay weld metals having the compositions shown in the table are respectively formed. The installation position of the flesh-feeling roll according to the example of the present invention was the correction zone in the continuous casting roll group, and the flesh-feeling roll of the comparative example was also set in this zone. After each flesh-feel roll was installed, the state of crack occurrence on the roll surface and the maximum depth of cracks (measured with a crack meter) after approximately 3,000 charges were investigated. The results are shown in Table 4. As is clear from Table 4, the conventional flesh-feeling roll has continuous linear cracks on the roll circumference, as well as deep cracks. On the other hand, in the overlay roll according to the example of the present invention, although some short linear cracks were observed,
It was confirmed that the depth was shallow and the degree of damage was quite small. [Blank below] (Effects of the Invention) As detailed above, according to the present invention, a fleshy roll having excellent heat cracking resistance and sufficient performance in terms of wear resistance and corrosion resistance is provided. can do. It can be used as various hot rolls such as drawing rolls for continuous casting.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams explaining the procedure of the heat crack test. Figure 1 shows an overview of the test piece heating section, Figure 2 shows the test piece surface temperature pattern, and Figures 3 and 2 are diagrams explaining the procedure of the heat crack test. Figure 4 is a diagram showing the state of occurrence of cracks in the overlay roll of Example 3.
The figure shows an example of the present invention, and FIG. 4 shows a comparative example. 1... Test piece, 2... Thermocouple insertion hole, 3... Heating coil.

Claims (2)

[Claims] (1) In a roll used in hot processes such as hot piece transfer or hot rolling, the roll surface layer mainly contains iron, and
In weight% (hereinafter the same), C: 0.07-0.2%, N
i: 0.5~2%, Cr: 9~14%, Mo: 0.2~
1.5%, Nb: 0.03-0.3%, V: 0.1-1
% and W: 0.2 to 2%. (2) The overlay roll according to claim 1, wherein the roll surface layer further contains Cu: 0.3 to 2%.