Hot width reduction press tool and method for manufacturing the same

Abstract

To improve an alloy steel for build-up welding on the press face against a hot slab in a tool for hot-width compression pressing, enhance its wear resistance, heat crack resistance and high-temperature oxidation resistance, and further extend the service life.SOLUTION: A tool for hot-width compression pressing has an alloy steel for build-up welding on the press face against a hot slab, containing, in wt.%, C: more than 0.05% and 0.5% or less, Si: more than 0.2% and 0.9% or less, Mn: more than 0.4% and 1.2% or less, Cr: more than 9.0% to 11.0% or less, Mo: more than 2.0% to 3.5% or less, Ni: more than 1.5% and 3.0% or less, V: more than 0.1% and 0.5% or less, and W: more than 0.1% and 0.5% or less, with the balance being Fe and inevitable impurities.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a tool used when width reduction is performed on a hot slab such as a steel material by pressing, specifically, a tool for hot width reduction press having a build-up welding part of alloy steel on the pressing surface against the hot slab, and a manufacturing method thereof.

Background Art

[0002] In the production of steel materials, etc., a slab heated for hot rolling (referred to as a hot slab in this specification) is width-reduced by pressing to adjust it to a width suitable for the product size. Dies for this pressing are made as integral objects from materials such as ductile cast iron (FCD defined in JIS G5502), alloy steel for machine structures (SCM defined in JIS G4105), and hot work tool steel (SKT defined in JIS G4404), and are used.

[0003] Regarding the shape of the die, for example, Patent Document 1: Japanese Patent Laid-Open No. 60-203305 discloses that a die having an inclined part with a limited inclination angle on the inlet side in the slab advancing direction and subsequently having a parallel part can continuously perform width reduction to an arbitrary width without causing defects such as cracks on the surface and inside of the slab. Also, Patent Document 2: Japanese Patent Publication No. 4-33521 discloses that by providing an inclined caliper groove with limited dimensions on the slab pressing surface of a die having at least an inclined part on the inlet side in the slab advancing direction and subsequently having a parallel part, generation of slab surface flaws during rolling can be prevented.

[0004] Furthermore, Patent Document 3: Japanese Patent Laid-Open No. 11-25627 No. 1 (Patent No. 3563587) and Patent Document 4: Japanese Patent Laid-Open No. 2004-17076 (Patent No. 3711090) related to applications of the applicant's affiliated companies, etc., describe a tool for hot width reduction press having a build-up welding part of alloy steel containing C, Si, Mn, Cr, Mo, Ni, V, and W on the pressing surface against the hot slab of the tool for hot width reduction press, a manufacturing method thereof, and a die for hot width reduction press. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 60-203305 [Patent Document 2] Special Publication No. 4-33521 [Patent Document 3] JP-A-11-256271 (Patent No. 3563587) [Patent Document 4] Japanese Patent Publication No. 2004-17076 (Patent No. 3711090) [Overview of the project] [Problems that the invention aims to solve]

[0006] The slab pressing surface of hot width reduction presses has a problem where thermal cracks occur in addition to wear, and the degree of cracking expands with increasing use. If a slab is width reduced using a hot width reduction press with large thermal cracks, defects such as edge cracking will occur in the rolled material during subsequent hot rolling, so the hot width reduction press must be replaced. For example, when using the hot width reduction press tool manufactured as a single piece from the ductile cast iron mentioned above to reduce the width of hot slabs of ordinary steel for continuous hot rolling, replacement was required every 9 to 10 days in normal use, processing approximately 700 slabs per day.

[0007] When replacing a tool, continuous press operations must be stopped, reducing the operating rate of the entire process, including the preceding and succeeding processes, and impairing productivity. Furthermore, while hot width reduction press tools with enlarged cracks are reused after grinding away the cracks, this increases costs due to grinding costs and the need to maintain a larger number of spare hot width reduction press tools for replacement. Furthermore, as the grinding amount of the hot width reduction press tool increases, the change in the distance between the pair of tools on the left and right becomes larger, which interferes with the press operation. Therefore, shims are inserted to correct the tool thickness and extend the number of reuses, but this also increases the workload and time required for changing the hot width reduction press tool.

[0008] Furthermore, while hot-width reduction press tools made from the above-mentioned structural alloy steel and hot-work tool steel showed improved wear and thermal cracking compared to those made from ductile cast iron, the improvement was not significant, and they had to be discarded after 4-5 grinding cycles. In addition, the technologies described in Patent Documents 1 and 2 both relate to the shape of the mold, and therefore cannot be expected to extend the lifespan of the mold. Furthermore, the technologies described in Patent Documents 3 and 4 suppress the occurrence of thermal cracks on the slab pressing surface of a hot width reduction press tool by overlay welding alloy steel to the pressing surface against the hot slab, thereby extending the service life and reducing the frequency of tool replacement. However, there was a problem in that the ability to form an oxide film Cr2O3 was easily reduced, and high-temperature oxidation resistance could not be exhibited. The present invention aims to extend the service life and reduce the frequency of tool replacement in hot width reduction press tools by improving the alloy steel used for build-up welding to the pressing surface against the hot slab, thereby improving high-temperature oxidation resistance and further extending the service life. [Means for solving the problem]

[0009] Hot width reduction press tool according to the present invention to solve the above problems Manufacturing method This is a tool for reducing the width of a hot slab by pressing. In The pressing surface against the hot slab is made of an alloy steel containing, by weight %, C: greater than 0.05% and 0.5% or less, Si: greater than 0.2% and 0.9% or less, Mn: greater than 0.4% and 1.2% or less, Cr: greater than 9.0% and 11.0% or less, Mo: greater than 2.0% and 3.5% or less, Ni: greater than 1.5% and 3.0% or less, V: greater than 0.1% and 0.5% or less, with the remainder being Fe and unavoidable impurities. to a thickness of 15-60mm After build-up welding, the entire base material and the built-up weld are heated to a temperature of 500°C to 570°C. In a direction parallel to the pressing surface and perpendicular to the direction of movement of the hot slabThe method is characterized by holding the tool for hot width reduction pressing for t / 25 hours or more, depending on its thickness t (mm), and then cooling it. Furthermore, it is preferable to perform the build-up welding by block welding, and then perform peening treatment on the build-up welded area. [Effects of the Invention]

[0010] Hot width reduction press tool of the present invention Manufacturing method This refers to an alloy steel containing the above components on the pressing surface against the hot slab. The base material and the entire welded portion are built up with build-up welding to a thickness of 15 to 60 mm, and then cooled at a temperature of 500°C to 570°C for at least t / 25 hours, depending on the thickness t (mm) of the hot width reduction press tool in a direction parallel to the pressing surface and perpendicular to the direction of movement of the hot slab. Therefore, The resulting hot width reduction press tool is It offers excellent wear resistance and suppresses the occurrence and propagation of thermal cracks. Furthermore, its high-temperature oxidation resistance is improved, allowing for an even longer service life. Therefore, even if relatively inexpensive materials such as conventionally used carbon steel for machine structural use are used as the base material for hot width reduction press tools, the service life can be significantly extended. and ,above We can reliably and consistently manufacture excellent hot width reduction press tools like the one described. Therefore, the present invention significantly contributes to cost reduction by improving the press work rate of hot slabs, reducing the number of hot width reduction press tools required, and extending their lifespan, thereby increasing productivity. [Brief explanation of the drawing]

[0011] [Figure 1] A plan view showing an example of the use of a tool for hot width reduction pressing. [Figure 2] Cross-sectional view taken along arrow AA in Figure 1 for two types of hot width reduction pressing tools. [Figure 3] A diagram showing an example of block welding in the manufacturing method of a tool for hot width reduction pressing. [Modes for carrying out the invention]

[0012] The present invention will be explained with reference to an example of a hot width reduction press tool 2 shown in Figures 1 and 2. FIG. 1 is a plan view showing an example of use of a tool for hot width reduction pressing. While moving a hot slab 1 in the direction of the arrow, it shows a state where a width reduction press is performed in the width direction by a pair of tools 2 for hot width reduction pressing. FIG. 2 is an enlarged sectional view taken along the line A-A of FIG. 1 in two types of tools 2 for hot width reduction pressing. The slab pressing surface of the tool 2 for hot width reduction pressing may be flat as shown in (a), or may have a caliber 3 formed as shown in (b).

[0013] As the base material 4 of the tool 2 for hot width reduction pressing, similar to the above-mentioned conventional materials, alloy steel for machine structure (SCM defined in JIS G4105), hot work tool steel (SKT defined in JIS G4404) can be adopted. In addition, cheaper carbon steel for machine structure (such as S35C and S45C defined in JIS G4051) and similar steel materials (such as SF590 defined in JIS G3201) can also be adopted.

[0014] And, an alloy steel 5 is build-up welded on the slab pressing surface of the tool 2 for hot width reduction pressing. The components of the alloy steel 5, in weight %, contain C: more than 0.05% and less than or equal to 0.5%, Si: more than 0.2% and less than or equal to 0.9%, Mn: more than 0.4% and less than or equal to 1.2%, Cr: more than 9.0% and less than or equal to 11.0%, Mo: more than 2.0% and less than or equal to 3.5%, Ni: more than 1.5% and less than or equal to 3.0%, V: more than 0.1% and less than or equal to 0.5%, W: more than 0.1% and less than or equal to 0.5%, and the balance consists of Fe and inevitable impurities. The build-up welding can be carried out by MAG welding, for example, using a flux-containing wire having the above component composition.

[0015] The reasons for limiting each component range are explained below. C dissolves in the steel of the weld metal to improve its hardness and strength. In addition, it combines with Cr, Mo, V or W to form carbides, which has the effect of improving wear resistance. However, if its content is less than 0.05%, the desired effect cannot be obtained, and if it exceeds 0.5%, the toughness decreases and the heat resistance crack resistance decreases. Therefore, the C content is set to more than 0.05% and less than or equal to 0.5%.

[0016] Si (silicon) deoxidizes the weld metal during welding, improves its strength, and enhances the fluidity of the molten weld metal, thus preventing defects. However, if the Si content is below 0.2%, the desired effects cannot be obtained, and if it exceeds 0.9%, toughness decreases, leading to reduced thermal crack resistance. Therefore, the Si content was set to be between 0.2% and 0.9%.

[0017] Mn has the effect of deoxidizing the weld metal and improving its toughness during welding, but the desired effect cannot be obtained below 0.4%, and the effect saturates when added above 1.2%. Therefore, the Mn content was set to be between 0.4% and 1.2%.

[0018] Cr not only prevents high-temperature oxidation and steam corrosion, but also improves ductility (elongation, reduction of area), which suppresses the rate of thermal crack propagation. The optimal ductility is considered to be around 10.0%. Below 9.0% Cr content, the ability to form an oxide film (Cr2O3) decreases, and high-temperature oxidation resistance is not exhibited. Above 11.0%, the formation of a ferrite phase reduces ductility and leads to a decrease in thermal crack resistance. Therefore, the optimal Cr content is set between 9.0% and 11.0%, but between 9.5% and 10.5% is even better.

[0019] Mo is added to the weld metal to improve hardness and strength by solid dissolving in the steel, to increase high-temperature strength by bonding with carbon, and to provide resistance to tempering softening. Below 2.0%, the effect is not observed, and above 3.5%, toughness decreases, and thermal crack resistance deteriorates. Therefore, the Mo content was set to between 2.0% and 3.5%.

[0020] Ni is added to improve the toughness of the weld metal. Below 1.5%, this effect is not observed, and above 3.0%, hardness decreases and wear resistance declines. Therefore, the Ni content was set to be between 1.5% and 3.0%.

[0021] V is added as needed to further enhance high-temperature strength and temper softening resistance. Below 0.1%, no further effect is observed, and above 0.5%, toughness decreases, leading to a decline in thermal crack resistance, etc. Therefore, the V content was set to between 0.1% and 0.5%. The remainder consists of Fe and unavoidable components. Typical impurities include P and S. Since P and S embrittle the alloy, it is best to keep their content below 0.01%.

[0022] Water (W) is added to further improve high-temperature strength. Below 0.1%, this effect is not observed, and above 0.5%, toughness decreases and thermal crack resistance declines. Therefore, the W content was set to be between 0.1% and 0.5%.

[0023] As high-temperature strength increases, wear decreases, thermal cracking becomes less likely, and the crack propagation rate is suppressed due to improved high-temperature toughness, resulting in a significant improvement in the thermal crack resistance of tools used for hot width reduction pressing.

[0024] Furthermore, since the slab pressing surface of the hot width reduction press tool of the present invention has a build-up weld of such alloy steel, it has excellent wear resistance and suppresses the occurrence and expansion of thermal cracks. For this reason, even if a relatively inexpensive material such as the above-mentioned carbon steel for machine structures is used for the base material of the hot width reduction press tool, the service life can be significantly extended. Furthermore, hot width reduction press tools whose slab pressing surfaces have deteriorated due to wear or cracking can be reused by overlaying alloy steel with welding.

[0025] Furthermore, in the hot width reduction press tool of the present invention, it is preferable that the alloy steel 5 is overlay welded to a thickness d in the range of 15 to 60 mm. If the thickness d is less than 15 mm, the effect of extending the service life is not easily realized, and in the range of thickness d up to about 60 mm, the efficiency of the overlay welding work is good, and the number of times the tool can be reused by grinding away enlarged cracks is reduced, thus being suitable from a cost perspective as well.

[0026] Next, the method for manufacturing the hot width reduction press tool of the present invention will be described. After overlay welding the alloy steel 5 onto the slab pressing surface of the hot width reduction press tool 2, the entire assembly, including the base material 4 and the overlay welded alloy steel 5, is heat-treated at a temperature of 500°C to 570°C, with a holding time within this temperature range of t / 25 hours or more, depending on the thickness t (mm) of the hot width reduction press tool 2. It is desirable to preheat the hot width reduction press tool 2 to 400-500°C as a pre-welding step to reduce residual stress after welding.

[0027] As described above, overlay welding can be performed by MAG welding using, for example, flux-cored wire with the above-mentioned component composition. However, heat treatment under the above conditions is performed to remove residual stress in the overlay weld, densify the structure, and improve ductility. If the heat treatment temperature is below 500°C, no increase in strength due to secondary hardening will be obtained. If it exceeds 570°C, the hardness of the weld metal decreases, wear resistance decreases, and the base material softens, resulting in a decrease in strength. Furthermore, if the holding time in this temperature range is less than t / 25 hours, it becomes difficult to obtain the heat treatment effect across the entire slab pressing surface.

[0028] Furthermore, in the manufacturing method of a tool for hot width reduction pressing, it is preferable to perform overlay welding by block welding, and then perform peening treatment on the overlay weld. By performing peening on the weld after overlay welding, residual stress is reduced and the weld metal is strengthened. Furthermore, by performing the heat treatment after peening, residual stress is removed and the weld metal is further strengthened. [Examples]

[0029] To investigate the durability of the hot width reduction press tool 2 according to the present invention, three sets of hot width reduction press tools 2, each with the shape shown in Figure 1, were manufactured using S45C carbon steel for machine structural use as the base material 4. The slab pressing surface was flat as shown in Figure 2(a) and had a caliber as shown in Figure 2(b). The thickness t of the hot width reduction press tool 2 was 400 mm in all cases. Then, a layer of alloy steel 5, consisting of component A as shown in Table 1, was overlay welded to one set of slab pressing surfaces using MAG welding. The thickness d of the alloy steel 5 was set to 50-60 mm in all cases. As a comparative example, a hot width reduction press tool of the same shape made of ductile cast iron (hereinafter referred to as "Comparative Example A") was manufactured. Furthermore, one set of slab pressing surfaces was overlay welded by MAG welding with alloy steel 5 consisting of component B shown in Table 1 (component A in Table 1 of Reference 3) (hereinafter referred to as "Comparative Example B"), and one set of slab pressing surfaces was overlay welded by MAG welding with alloy steel 5 consisting of component C shown in Table 1 (component B in Table 1 of Reference 3) (hereinafter referred to as "Comparative Example C"). The thickness d of alloy steel 5 was the same in all cases, 50 to 60 mm. [Table 1]

[0030] The three sets of hot width reduction pressing tools according to the present invention and comparative examples B and C were all preheated to 400-500°C in an electric furnace. Then, using flux-cored wire consisting of the components shown in Table 1, block welding was performed in discrete areas in the order of the numbers shown in Figure 3 to mitigate the deformation of the base material 4. After welding each block, peening treatment was performed while the material was still red hot, and build-up welding was applied to the slab pressing surface. Next, a heat treatment was performed in an electric furnace at 500-570°C for 16 hours, followed by cooling to room temperature, and then finishing to the specified dimensions by mechanical grinding or other methods.

[0031] Using these three sets of welded hot width reduction presses and one set of ductile cast iron tools, we performed width reduction pressing on hot slabs for thin steel sheets. The slab sizes were 5,000 to 12,000 mm in length, 240 mm in thickness, and a difference of approximately 300 mm in width between before and after pressing. Approximately 700 hot slabs were pressed per day.

[0032] In Comparative Example A, both the flat and caliber-equipped hot width reduction press tools required replacement within 10 days due to the expansion of thermal cracks. Furthermore, the hot width reduction press tools in Comparative Example B, both the flat type and the type with a caliber, required replacement after 23 days, while the hot width reduction press tools in Comparative Example C, both the flat type and the type with a caliber, required replacement after 30 days. Furthermore, while Patent Documents 3 and 4 state that the hot width reduction press tools of Comparative Examples B and C, both the flat type and the type with a caliber, could be used without reassembly for 60 to 80 days with alloy steel component A and 80 to 100 days with component B as shown in Table 1, the results of subsequent tests were as described above. In contrast, both the flat and caliber-equipped hot width reduction press tools according to the present invention could be used for 40 days without reassembly. In other words, compared to Comparative Example A, the hot width reduction press tool according to this embodiment had approximately four times the processing volume in one cycle from crack cutting and removal to replacement, approximately 1.7 times the processing volume compared to Comparative Example B, and approximately 1.3 times the processing volume compared to Comparative Example C. [Explanation of symbols]

[0033] 1… Hot slab 2… Tools for hot width reduction presses 3… Caliber 4 … Base material 5 … Alloy steel

Claims

1. On the pressing surface against the hot slab in a hot width reduction press tool, by weight %, C: more than 0.05% and less than 0.5%, Si: more than 0.2% and less than 0.9%, Mn: more than 0.4% and 1.2% or less, Cr: more than 9.0% and less than 11.0%, Mo: more than 2.0% and less than 3.5%, Ni: more than 1.5% but not more than 3.0%, V: more than 0.1% and less than 0.5%, W: Contains more than 0.1% and 0.5% or less. The remaining alloy steel, consisting of Fe and unavoidable impurities, is built up with build-up welding to a thickness of 15 to 60 mm. The entire base material and the built-up weld are held at a temperature of 500°C to 570°C for at least t / 25 hours, depending on the thickness t (mm) of the hot width reduction press tool in a direction parallel to the pressing surface and perpendicular to the direction of movement of the hot slab, and then cooled. A method for manufacturing a hot width reduction press tool, characterized by the following:

2. The aforementioned build-up welding is performed by block welding, and then peening treatment is applied to the build-up weld. A method for manufacturing a hot width reduction press tool according to claim 1.

Images