JPS62275511A - Hot rolling roll having excellent wear resistance and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the hot rolling roll which has the excellent wear resistance and tensile strength and reuses the core by forming an underlaying weld layer of a specific alloy on the roll core surface and then forming an upperlaying weld layer of a specific alloy on the underlaying weld layer surface with dispersing NbC powders on the underlaying layer surface. CONSTITUTION:A selected one of a Co base alloy, a Ni base alloy, a stainless steel, and a chrome base low alloy steel is underlay welded on the roll core surface. Then, an upperlaying weld layer of selected one of an austenitic stainless steel, a Co base alloy, and a Ni base alloy having an excellent ductility is formed on the underlaying layer surface. In that time, the upperlaying weld is performed by use of a torch having an excellent sealing capability at a temp. in the 450-600 deg.C range of the preheating and interpass temps. with NbC powders containing <=0.15wt% free carbon dispersed on the underlaying layer surface.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a hot roll with excellent wear resistance and a method for manufacturing the same.

[Conventional technology]

With the advancement of rolling technology, rolling rolls have been strongly required to improve their performance in terms of materials, and improvements have been made to manufacturing methods, materials, etc. 6. The characteristics required of hot rolling rolls are wear resistance. sex.

These include heat cracking resistance, seizure resistance, and high tensile strength.

Currently, Adamite rolls and high Cr cast iron rolls are often used for hot rolling. These rolls have been improved in wear resistance and seizure resistance by increasing carbon content and alloying, and increasing precipitated carbides. However, the method of increasing carbides by increasing carbon content and alloying has the problem that if the carbides increase, the toughness of the mesh-like precipitates decreases and the tensile strength and heat cracking resistance deteriorate. Since there are limits to using the ingredients alone, it has been proposed to improve the roll characteristics by changing the manufacturing method.

For example, JP-A-58-167007 has 5KD on the roll surface.
-11 powder is plasma sprayed, then vacuum sintered at about 1050°C, and then heated to 1150°C and hot forged. That is, this is a method of manufacturing rolling rolls with excellent wear resistance and tensile strength by using a material with excellent tensile strength as the roll core material and overlaying an alloy with excellent wear resistance on the surface by thermal spraying. However, this method has a problem of high cost due to complicated steps. In particular, large rolls require huge equipment costs for vacuum sintering equipment, hot forging equipment, etc., and hot forging and heat treatment make carbides finer and more spheroidal, so even if extreme deterioration in toughness can be prevented.

Since 5KD-11 has a carbide area ratio of about 20%, there are problems such as no significant improvement in wear resistance can be expected.

In addition, JP-A-50-110909 discloses a method in which cemented carbide powder is mixed and shaped into a roll and integrated by sintering, which has excellent wear resistance, heat cracking resistance, and seizure resistance. Since it is impossible to regenerate the remaining part (roll core), the cost of the roll increases, and there are disadvantages in that it is impossible to manufacture large rolls and the toughness is poor.

Furthermore, JP-A-58-181470 discloses a surface hardening method, which uses an alloy powder mainly composed of Co--Cr, NbC powder, VC powder, Ti
This is a method in which at least one type of C powder is mixed and supplied to form a weld metal on the surface of the metal base material, but the preheating temperature of the roll core material, the type of core material, etc. are appropriately selected and various conditions are applied. However, it was found that it could not be used as a rolling roll because the bonding strength between the roll core material and the built-up layer was insufficient, and a flesh-like metal without defects could not be obtained.

[Problem that the invention seeks to solve]

An object of the present invention is to solve the above-mentioned problems of the prior art, provide an inexpensive hot roll that has excellent wear resistance, heat cracking resistance, seizure resistance, and tensile strength, and whose roll core material can be repeatedly reused, and a method for manufacturing the same. is to provide.

[Means and operations for solving the problems] The above objects of the present invention are achieved by the following two inventions.

The gist of the first invention is as follows.

That is, a Co-based alloy underlaid on the surface of the roll core material,
An underlay welding layer made of one type selected from Ni-based alloys, stainless steel, and chromium-based low alloy steel, and an austenitic stainless steel in which NbC powder overlaid on the surface of the underlay layer is dispersed; This hot roll has excellent wear resistance and is characterized by having an overlay weld layer made of one selected from Co-based alloys and Ni-based alloys.

The gist of the second invention is as follows.

That is, the step of welding one type selected from Co-based alloy, Ni-based alloy, stainless steel, and chromium-based low alloy steel to the surface of the roll core material, and the step of welding austenitic stainless steel to the surface after the under-filling. Steel, Co-based alloy and Ni
One type selected from the base alloys is overlaid using a torch with excellent shielding properties in the preheating/bath temperature range of 450 to 600°C while dispersing NbC powder with a free carbon content of 0.15% or less. A method for manufacturing a hot roll having excellent wear resistance, comprising the steps of welding.

If an alloy layer containing ultra-hard carbide dispersed can be firmly bonded to the surface of a roll core material with excellent tensile strength, a desired roll with excellent wear resistance can be obtained.
When the technology of 181470 was applied to rolling rolls, surface cracks 2 as shown in Figures 1 (A) and (B) occurred when the preheating and interpass temperatures were low, but if the preheating temperature was increased, these cracks could be eliminated. However, in NbC, Fig. 1 (E) and (F
Porosity 6 as shown in ) occurred, and sound overlay welding could not be performed. In addition, there are other defects in overlay welding.
Lamellar cracks 4 shown in Figures (C) and (D), Figure 1 (G), (
Inclusion 8 shown in H) was observed.

The present inventors investigated the causes of these defects and reached the following conclusion. In other words, due to insufficient ductility of the matrix, the preheating and inter-pass temperatures are increased, resulting in oxidation of the unwelded surface, and NbC, which has poor oxidation resistance at high temperatures, reacts with carbide C and oxide film 0□. It becomes C○ or co2 and porosity occurs. For these reasons, it is thought that these defects can be prevented if the preheating and interpass temperatures can be lowered by using a highly ductile matrix, so a test was conducted using a highly ductile matrix. However, within the range of conditions required to obtain the ultra-hard carbide dispersion rate and the necessary ultra-hard alloy layer for rolling rolls, surface cracks occur, so preheating is required to prevent the formation of an oxide film on the unwelded parts of the base metal. - It was not possible to lower the temperature between the baths.

In addition, the reason why the surface crack inhibition temperature did not decrease even after changing to a high ductility matrix was due to the thickness of the cemented carbide and the small weaving width to ensure gas shielding properties, which resulted in a large penetration amount. This is because the mixing ratio of the core roll alloy steel in the matrix became high and the ductility of the matrix could not be improved.

For this reason, we decided to underlay the surface of the core material roll with an alloy that has excellent heat resistance, oxidation resistance, and ductility, with the aim of preventing matrix metal deterioration due to penetration of the core material and preventing oxidation of unwelded parts. .

Inconel 600, which has excellent ductility, is used as an underlay alloy.
Three alloys were used: austenitic stainless steel and stellite Nα21, which contained a small amount of C and no W, and two layers were underlaid on the surface of the roll core material. The components and high-temperature ductility of Stellite &21 are shown in Table 1 and Figure 2, respectively.

The results showed that the surface crack prevention temperature decreased and the preheating and interpass temperatures could be lowered by more than 100°C.

Table 1 After the above-mentioned underlaying, plasma transferred arc welding (hereinafter P
Top welding was carried out using the TA method (referred to as the TA method), and the occurrence of surface flaws was investigated, and the results are also shown in Table 2.

From Table 2, in the case where TiC was used as the carbide, fine lamellar cracks remained in the 5US316L underlay, but no delamination occurred in the underlay on Inconel 600 and Stellite Nα2. However, inclusions were generated in the bead overlapping portions in all cases, and it was not possible to obtain a build-up that could be used as a roll material.

In the case where NbC was used as the carbide, the incidence of porosity was significantly reduced by underfilling. In this case as well, the effect of the 5US316L underlay was small, and fine porosity frequently occurred in the matrix. 5U
The occurrence of porosity with S316L is thought to be due to its inferior oxidation resistance compared to other alloys and the high amount of oxygen in the powder, so it is desirable to use 5US316L powder, which has a low oxygen content. In the lower row, the free carbon of NbC is 0.15% or less, and 5US316L has a low oxygen content.
was used as a matrix in the overlay weld metal, so no porosity occurred at all.The hardness of the overlay metal in the examples of the present invention shown in Table 2 was 3rd.
As shown in the table, there is no problem as a roll material.

Table 3 Also, for comparison with the examples of the present invention, hot abrasion tests were conducted on conventional adamite rolls and high Cr cast iron rolls, and the results of the examples and conventional examples are shown in Figs. The indications in the figure and the test conditions are shown in Table 4.

From the results shown in Figures 3 to 6, the abrasion resistance of the examples of the present invention is more than 10 times better than that of conventional Adamite rolls, the surface roughness is approximately 1/2 smooth, and furthermore, in the hot abrasion test, It was found that no thermal cracking occurred, making it an excellent material for rolls.

The present inventors have developed a hot roll with excellent wear resistance using a Co-based alloy or a Ni-based alloy as the underlay alloy.
I: Since we achieved some success with J construction, we applied for a patent application in 1986-032.
513, but the following problems still remain. In other words, (a) the hot roll disclosed in Japanese Patent Application No. 61-032513 has excellent wear resistance;
Since a Co-based alloy or a Ni-based alloy was used as the underlay alloy, an increase in cost could not be avoided.

(b) Moreover, Co-based alloys or Ni-based alloys are susceptible to hot cracking when the welding speed is increased, and as a result, it is difficult to employ high-efficiency welding methods.

In order to solve the remaining problems mentioned above, as a result of research, we decided to take the following measures for the underlay welding material.

(a) Use an alloy with a small amount of expensive metal components such as Co, Ni, etc.

(b) Cr to prevent oxidation of surface metal due to welding heat
Use an alloy with a content of 9% or more.

(c) NbC used in the overlay metal reacts with oxygen.

In order to prevent C○ or Co2 from being generated and causing porosity in the weld metal, the oxygen content of the underlay material is set to 500 ρρm or less.

(d) In order to prevent weld cracking during overlay welding, a material with good ductility is used for the underlay welding layer.

(e) An underlay material with good thermal shock resistance is used to prevent thermal cracks generated in the overlay weld layer, which is a hardened alloy, from propagating to the base metal due to thermal shock during rolling.

(f) Use an underlay material that has a tensile strength that can withstand deformation during rolling.

(g) Use an underlay welding material that can be used for high-efficiency welding with a high deposition rate, such as band arc welding, submerged arc welding, carbon dioxide arc welding, and MIG welding.

As the underlay welding material to be underlayed on the surface of the roll core material, the present inventors have selected No. 5 as one that satisfies the conditions listed above.
We have reached the conclusion that the materials shown in the table are the most suitable, and will explain the results of experiments using these materials.

The present inventors used various underlay welding materials shown in Table 5 under the welding conditions shown in Table 6, and then under the proper welding conditions shown in Table 7, which was found in Japanese Patent Application No. 61-03253. The occurrence of surface flaws such as surface cracks, single-layer cracks, porosity, and inclusions was investigated for hot rolls subjected to overlay welding by the PTA method, and the results are also shown in Table 7.

As is clear from Table 7, no defects were observed in the fleshy part, and it was found that both the bottom weld and the top weld were sound weld layers. In addition, the hardness of the overlay metal shown in Table 7 is 8th.
As shown in the table, Hs reached 58 to 79, and the hardness was satisfactory as a roll material.

Table 5 Table 6 Table 8 From the above experiments and the reasons for limitations described at the same time, it has become clear that the overlay conditions according to the present invention should be limited as follows.

(a) On the surface of the roll core material, one type selected from Co-based alloy, Ni-based alloy, stainless steel, and chromium-based low alloy steel is under-welded.

(b) On the surface of the underlay layer, an overlay welding layer made of one selected from highly ductile austenitic stainless steel, Co-based alloy, and Ni-based alloy is formed.

(c) In the case of overlay welding, NbC powder containing 0.15% or less of free carbon is dispersed and overlaid.

If the free carbon content of the NbC powder exceeds 0.15%, porosity increases, so the content was limited to 0.15% or less.

(d) Preheating and interpass temperature for overfill welding is 450 to 600.
Limited to a temperature range of ℃. The reason for this limitation is that weld cracking is inhibited at temperatures above 450°C, but when temperatures exceed 600°C, penetration becomes deep and the carbide dispersion rate decreases. Furthermore, in order to make the dispersion of the carbide powder uniform, the above 450 to 60
The preheating pass temperature is selected from a temperature range of 0°C depending on the overlay welding layer and is maintained within a temperature range of ±25°C using a heating temperature that can maintain welding heat input and dissipated heat in equilibrium.

(e) Also, to prevent air from being sucked in during overfill welding to prevent the occurrence of porosity.

A torch with an integral outer cylinder with excellent shielding properties should be used.

〔Example〕

Example 1 The present invention was applied to a universal mill horizontal roll made of hot-rolled H-section steel whose shape is shown in FIG. That is, as detailed conditions are shown in Table 9, the roll core is 1°, with emphasis on weldability,
SCM430 forged steel rolls with C<0.3% and carbon equivalent <0.6% were used.

Co-based alloy stellite Nα2 is coated on the surface of this roll core 10.
1 was welded in two layers using the PTA method.

Next, it was finished by machining to form the underlay layer 12 with a thickness of about 4 m.

The underlay layer 12 was mixed with 40% by volume of Stellite Nn21 powder whose components are shown in Table 10 and 60% by volume of NbC powder whose components are shown in Table 11 with free carbon reduced to 0.03% or less. One layer (
Superalloy overlay welding of approximately 4 mm) was performed to form the overlay layer 14.

The welding conditions are shown in Table 7, and the preheating and interpass temperature was 50
The temperature was 0 to 550°C. After top welding, 600℃XlOH
Stress relief annealing was performed, and the rolling roll was finished in Table 9 by machining. There were no cracks or other flaws in PT (penetrant testing) after machining. In addition, the surface hardness after cutting is 8th
As shown in the figure, Hs<Hs is 68 to 82, which is excellent.

Table 10 Table 11 Using this roll H250X 125 x 6 x
No. 9 H-beam steel was rolled to 1500 mm, but the wear after rolling was minimal and it was possible to reuse it by re-cutting to 0.1 mm. This amount of wear is approximately 1 of that of the conventional C: 2% Adamite roll.
/1o, and an H-beam steel with a good surface and no seizure flaws was obtained. As for thermal cracking, slight cracking occurred initially, but it did not progress after that and had no effect on the product.

Table 12 The wear resistance of the cemented carbide overlay roll of this example was significantly improved, the roll core material could be used repeatedly, the roll consumption rate was halved, and there was no seizure on the product. Rolling efficiency was improved by eliminating rolling pauses due to roll maintenance.

Example 2 The present invention was applied to a round bar intermediate rolling roll whose shape is shown in FIG. That is, as detailed conditions are shown in Table 9, an SCM forged roll was used as the roll core 10. Note that round bar intermediate rolling is performed by caliperless rolling, so it is a flat roll. This roll has a problem of heat cracking because the rolling speed is slow and the contact length of the rolled material is long with respect to the roll diameter, so we focused on heat cracking resistance and used high ductility 5US316L stainless steel for the matrix of overlay welding. .

Other underlayment, NbC powder, and welding conditions are shown in Table 9 and are the same as in Example 1.

Figure 10 shows the hardness after finish cutting and before rolling. Further, Fig. 11 shows the amount of wear after rolling for 500 hours for the upper roll and the lower roll. Measurements were made at 16 locations as shown in Figure 12, and the amount of wear was measured at D as shown in Figure 13.
Shown in quantity.

This amount of wear is about 1/3 of that of conventional Adamite rolls, and while conventional rolls had the problem of biting of the rolled material, the roll of this example has good biting properties and can perform stable rolling. , a reduction in the frequency of roll replacement, an improvement in product dimensional accuracy, a reduction in roll unit consumption, etc. The amount of wear is shown by the amount D shown in FIG. 13.

This amount of wear is about 173 for the conventional Adamite roll,
In addition, conventional rolls had the problem of biting of the rolled material, but the roll of this example has better biting properties (stable rolling, reduced roll change frequency, improved product dimensional accuracy, 0-
We were able to achieve effects such as reduction in fuel consumption per unit of production.

Example 3 Hot roll according to the present invention, conventional Adamite roll, high Cr cast iron roll and Japanese Patent Application No. 61-032513
(hereinafter referred to as the earlier application).

A hot abrasion test was conducted on 82 types of rolls, and a comparative test was conducted on the characteristics of each roll.

Examples of the present invention have special compositions as shown in Table 13. The roll is a roll in which a 14Cr-V steel as shown in Table 14 is underlaid on a roll core material of 5 steel, and 5US316L in which 60% by volume of NbC powder is dispersed is overlaid and welded thereon.

Table 13 Table 14 On the other hand, the herol shown in the earlier application is JISSCM430
This is a roll in which Stellite Corner 21 is underlaid on the core material of the roll, and Inconel 600 in which 60% by volume of NbC powder is dispersed is overlaid on it, and the B roll is JIS 30M.
430 roll core material is underlaid with Stellite Nα21,
5US31 with 60% by volume of NbC powder dispersed thereon
This is a roll topped with 6L.

The above comparative test results are No. 14.15 and 16.1, respectively.
As shown in Figure 7. The display symbols in the figure and hot wear test conditions are as shown in Table 15.

As is clear from the comparative test results shown in Figures 14 to 17, the example of the present invention has a wear resistance of 1 point compared to the conventional Adamite roll.
C
It was found that the wear resistance was almost the same as that of the rolls with tip mA and B, which were underlaid with o-based Sesterite Nα21, and that they were excellent as roll materials.

Example 4 The present invention was applied to a universal mill vertical roll made of hot-rolled H-section steel having a shape as shown in FIG.

As the roll core material, the same AS as shown in Table 13 is used.
C special cast steel is used, and the roll core material 10 is preheated to 350°C, and while maintaining the temperature at 350±50°C, a 14th layer is applied to its surface.
Two layers of 14Cr-V steel having the same composition as shown in the table were welded using a submerged arc welding method, and then finished by machining to form an underlay layer 12 with a thickness of about 4 m. This underlay welded core material 10 is preheated to 525°C, and ±25°C
In the lower layer J'J l 2, Stellite 21 powder with the same composition as shown in Table 10 was reduced to 40% by volume and free carbon was reduced to 0.03%, and as shown in Table 11. Using a welding material containing 60% by volume of NbC powder of the same composition, one layer of cemented carbide with a thickness of about 4 nn was welded by PTA to form the overlay layer 14. The overlay welding conditions were the same as those shown in Table 8 of Example 1, and the preheating and interpass temperatures were 500°C.
The temperature was set at ~550°C.

After overlay welding, stress relief annealing was performed at 600° C. for 10 hours, and the product was then machined into a hot rolled roll. After machining, penetrant testing (CPA) was carried out and there were no defects such as cracks.

Moreover, the surface hardness after cutting and finishing is as shown in FIG.

1-Is was 64-72, which was excellent.

Next, a practical test was conducted on the hot rolling roll manufactured according to the present invention. In other words, using this roll, H25
0x125x6x9 H section steel was rolled 1500 times,
Abrasion after rolling was minimal, and reuse was possible by recutting 0.1 m.

This amount of wear is approximately 1/1 of that of the conventional C:2% Adamite roll.
1o, and also has a good surface H without any seizure flaws.
A shaped steel was obtained. As for thermal cracking, slight cracking occurred initially, but it did not progress after that and had no effect on the product.

〔Effect of the invention〕

As is clear from the above embodiments, the present invention provides underlay welding consisting of one type selected from Co-based alloy, Ni-based alloy, stainless steel, and chromium-based low alloy steel, which is underlayed on the surface of the roll core material. One type selected from austenitic stainless steel, Co-based alloy, and Ni-based alloy is heated at 450 to 600°C while dispersing NbC powder with free carbon content of 0.15% or less on the layer and the surface after underlaying. Over-welding using a torch with excellent shielding properties in the preheating and interpass temperature range provides excellent wear resistance, heat cracking resistance, seizure resistance, and tensile strength, and the roll core material can be reused repeatedly I was able to get a roll. As a result, it was possible to significantly reduce the roll consumption rate, and since there was no seizure, there was no need to stop rolling due to roll maintenance, and rolling efficiency was significantly improved.

Furthermore, although the roll performance is excellent, the welding point of patent application No. 61-032513, which uses Co-based alloy or Ni-based alloy as the underlay welding layer, has problems in terms of cost. This can be completely solved by underlaying various types of stainless steel such as ferritic steel or chromium-based low alloy steel, which can significantly reduce manufacturing costs including material costs, welding costs, and construction time. Ta.

[Brief explanation of drawings]

Figures 1 (A) to (H) each show defective aspects of the roll, (A) is a plan view showing surface cracks, (B) is a sectional view taken along the line B-B of (A), and (C) is a plan view showing layered cracks,
(D) is a cross-sectional view taken along the line D-D of (C), (E) is a plan view showing porosity, (F) is a cross-sectional view taken along the line F-F of (E), and (G) is an inclusion. , (II) is a sectional view taken along the line H-H in (G), FIG. 2 is a diagram showing the elongation of Stellite NQ21 at high temperatures, and FIGS. 3 to 6 are examples and comparative examples. Figure 3 is a diagram showing the relationship between load and specific wear amount, Figure 4 is a diagram showing the relationship between slip rate, ratio If, and wear amount, and Figure 5 is a diagram showing the relationship between slip rate, ratio If, and wear amount. A diagram showing the relationship between load and surface roughness, Figure 6 is a diagram showing the relationship between slip rate and surface roughness, and Figure 7 is a cross-sectional view showing an example of a universal mill horizontal roll finished with H-beam steel. , Figure 8 is a diagram showing the surface hardness of the horizontal roll example, Figure 9 is a sectional view showing the round bar intermediate rolling roll example, and Figure 1o is a diagram showing the surface hardness of the round bar intermediate rolling roll example. 11 is a diagram showing the amount of wear after 500 hours of rolling of the round bar intermediate rolling roll example, and FIG. 12 is a diagram showing the wear amount of the round bar intermediate rolling roll example 81! 13 is a partial sectional view of the roll showing the wear amount of the roll, 14-1
Figure 7 shows the hot abrasion test results of Examples and Comparative Examples of the present invention, Figure 14 shows the relationship between load and specific wear amount, Figure 15 shows the relationship between burr rate and specific wear amount, and Figure 16 shows the relationship between burr rate and specific wear amount. Figure 17 is a diagram showing the relationship between load and surface roughness, Figure 17 is a diagram showing the relationship between filler ratio and surface roughness, and Figure 18 is an example in which the present invention is applied to a universal mill vertical roll finished with H-beam steel. FIG. 19 is a diagram showing surface hardness in a vertical roll embodiment of the present invention. 10... Roll core material, 12... Underlay layer, 14...
Top weld layer. Agent Patent Attorney Takeo Nakaji Figure 1 Figure 21; λ, L (℃) Figure 3 too 200 300 t (kqf
) Figure 4 3.8 al 9.6
14.2 slip 1! (%) Figure 5 +00 200 300, fr
t (kq f) Figure 6! , 8 6.1 9.6
142 Suriya (%) Mass compilation ←l Figure 14-+00 200 300
jItrt t:wvfr Figure 15 3.8 6.1 9.6
14.2 Su, Beso 4! (z> Fig. 16 I guest T (k?su) Fig. 17 31 Berry - (n≦→ Fig. 18

Claims (2)

[Claims] (1) Co-based alloy, Ni underlay on the surface of the roll core material
An underlay welding layer made of one type selected from a base alloy, stainless steel, and chromium-based low alloy steel, and an austenitic stainless steel in which NbC powder overlaid on the surface of the underlay layer is dispersed, Co 1. A hot roll having excellent wear resistance, comprising an overlay weld layer made of one type selected from base alloys and Ni-base alloys. (2) On the surface of the roll core material, a material selected from Co-based alloy, Ni-based alloy, stainless steel, and chromium-based low alloy steel is used.
A step of welding a seed underlay, and dispersing NbC powder with a free carbon content of 0.15% or less of one type selected from austenitic stainless steel, Co-based alloy, and Ni-based alloy on the surface after underlaying. Preheat to 450-600℃ while
A method for manufacturing a hot roll with excellent wear resistance, comprising the steps of over-welding using a torch with excellent shielding properties in the bath temperature range.