JPH08260093A - Metal band saw barrel material excellent in fatigue strength in weld zone and metal band saw - Google Patents

Abstract

PURPOSE: To produce a metal band saw barrel material in which the main body maintains high fatigue strength and the fatigue strength of the weld zone and heat affected zone is good and to produce a metal band saw. CONSTITUTION: This metal band saw barrel material excellent in the fatigue strength in the weld zone is the one having a compsn. contg., by weight, 0.40 to 0.50% C, <=1.0% Si, <=1.5% Mn, 1.0 to 1.5% Cr, one or two kinds of Mo and W by 0.5 to 0.9% by Mo+1/2W, 0.1 to 0.5% V and 0.01 to 0.1% Al, and the balance Fe with impurities, and <=0.2% Nb may be added to the same compsn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses high speed steel as a blade material,
The present invention relates to a metal band saw body and a metal band saw that are welded to this blade material.

[0002]

2. Description of the Related Art A metal band saw is a high-speed steel blade material and an inexpensive low-grade steel body material that are subjected to electron beam welding, laser beam welding, inert gas welding, etc. to save the cost of expensive high-speed steel. After integrating the body and the body material, heat treatment according to the blade cutting and high speed steel of the blade material, that is, about 1200 ~ 1220 ℃
Quenching and tempering at around 540-570 ℃. The body material is desired to have high toughness and high fatigue strength without undergoing coarsening of crystal grains even when subjected to the same heat treatment as high-speed steel. In response to this requirement, the applicant of the present application has examined a material capable of ensuring sufficient properties even under the same heat treatment condition as that of the high-speed steel, and the Japanese Patent Publication Nos. 49-16008, 54-5366 and 55-32778. Issue, Japanese Patent Publication No. 56-11744, Japanese Patent Publication No. 59-10991
Japanese Patent Publication No. 61-12022, Japanese Patent Laid-Open No. 02-115353, Japanese Patent Laid-Open No. 04-
We have developed and commercialized a new alloy steel disclosed in No. 354852.

[0003]

Generally, a metal band saw has a blade member and a body member welded to each other, and after cutting the blade,
Both ends of the heat-treated band-shaped body are butt-welded to each other to form an endless shape, and then the welded part is locally annealed for finishing. The operation of the metal band saw is to cut the material to be cut (mainly steel material) held between the wheels while rotating between two wheels provided in the cutting machine. A tension is applied between the wheels of the metal band saw so that the material to be cut does not have a bend, and at the same time, a bending stress is repeatedly applied along the wheels during driving. Further, the wheel is inclined with respect to the horizontal, and the metal band saw is also subjected to torsional stress corresponding to the inclination of the wheel. Therefore, the metal band saw body is exposed to harsh conditions in which tensile stress, bending stress, and repetitive torsional stress are applied during driving. Particularly in recent saw machines, the stress applied to the metal band saw has been further increased due to prevention of bending and bending, downsizing, and improvement of cutting ability.

The applicant of the present application has developed and put into practical use the steels described in the above-mentioned publications as a body material for obtaining a high fatigue strength against such severe stress, and as a result, the breaking life of the metal band saw is Significant improvements have been made. However, recent metal band saws have improved fatigue strength of the body material as a result of the development of the body material, but on the other hand, endlessly welded parts (more specifically, the welded part and its peripheral part). Heat-affected zone: The weld zone is typified below)
The current situation is that it has reached 50%. Generally, in order to weld a metal band saw endlessly, butt welding is performed in which both ends of a body material are abutted with each other and melted and pressed under a strong current to weld and join, followed by short-time low-temperature annealing. In order to keep the fatigue strength of the welded portion good, the soundness of the welded portion is important.

As described above, in order to weld the metal band saw endlessly, both ends of the body material of the same material are melted and welded to each other, but the characteristics of the butt welded portion are as follows.
It depends greatly on the composition of the body. The inventor does not reduce the fatigue strength of the body material, does not generate blowholes during the welding of the blade material and the body material, and further, the soundness of the butt weld portion when the both ends of the body material are welded into an endless shape. The development was carried out focusing on the importance of the composition, that is, the combination of compositions in which the difference in hardness between the hardness of the body material and the hardness of the welded part is important after the short-time low-temperature annealing following welding.

Hereinafter, unless otherwise specified, the welded portion means a joint portion between both ends of the body material. When observing the welded portion in more detail, in the welded portion after welding, a molten layer, a re-quenched layer that is most affected by the heat of fusion in the vicinity of the molten layer, and a high temperature tempered layer around the re-quenched layer Each layer is present and exhibits different hardness distributions. Then, following the welding, a local short-time anneal is performed to soften and reduce the hardness of each of the above layers. At this time, the most desirable state is that the hardness of the body material body adjusted to an appropriate hardness and the hardness level between the layers are the same, and the variation in the hardness of minute portions is small.

From this point of view, when reviewing the developed materials for conventional metal band saw body materials, the main focus was on strengthening the body material and improving fatigue strength, and as a result of progressing toward higher alloying, welding Even if the body material hardness and the body-level hardness are adjusted by adjusting the conditions and local annealing conditions, the hardness varies in the minute parts between the layers of the welded part, and the welded part is prematurely damaged. It turned out that it was the cause of. An object of the present invention is to secure a high fatigue strength of a body material, and in particular, a metal band saw body material and a metal band saw body having a good fatigue strength, in which the difference in hardness of the welded portion is equal to the average hardness of the body material body and has little variation. Is to provide.

[0008]

[MEANS FOR SOLVING THE PROBLEMS] A metal band saw body having excellent fatigue strength of a welded portion of the present invention has a Vickers hardness of at least 45 by heat treatment under the same conditions as the high speed steel of the blade.
It is necessary to secure 0HV or higher and to show high fatigue strength. Therefore, the body material is
After quenching at around 540-570 ° C, which is the tempering condition for high-speed steel, which can suppress the coarsening of crystal grains, 450-5
There is a need for a chemical composition that gives a hardness of 50 HV. In the present invention, further, both ends of the body material after the heat treatment are butt-welded, and then the weld portion in a locally annealed state at a low temperature for a short time is healthy, and the hardness difference between the body material body and the weld portion is In order to minimize it, it is not possible to achieve it only by a composition that simultaneously satisfies the heat treatment conditions and hardness characteristics of the body material described above,
More strict compositional restrictions are required.

In the metal band saw body of the present invention, which is greatly restricted in the production as described above, a minimum amount of V is essentially added, and MC type carbides are formed together with a small amount of Nb added as necessary. Therefore, it is to prevent the crystal grains from coarsening even in high temperature quenching. In addition, after tempering at around 540 to 570 ° C, which is the tempering condition for high-speed steel for blade materials, the hardness of 450 to 550 HV, which is the proper hardness for use as a metal band saw, and appropriate wear resistance are imparted. Therefore, in order to form a carbide and increase the temper softening resistance, it is necessary to add C, Cr, (Mo, W).

Further, the above-mentioned elements of C, Cr, (Mo, W), when welding the both ends of the body, even if the body around the molten layer undergoes high temperature tempering due to the heat of fusion, the body is still It requires a minimum addition to increase the temper softening resistance to the extent that it does not fall below the hardness of the body. On the other hand, C, Cr, (Mo, W, in order to impart an appropriate tempering softening resistance capable of softening the molten layer and the re-quenched layer to the same level as the hardness of the body by the local short-time annealing performed after welding. It is necessary to limit the content of each element in () to a narrow range. In particular, when the addition amount of these elements increases, the hardness of the molten layer and the re-quenched layer portion becomes higher than the hardness of the main body, so if the local annealing conditions are changed to high temperature or long time, Since there is a problem that the hardness of the portion around the welded portion subjected to high temperature tempering becomes too lower than the hardness of the main body, the upper limit of the content is severely limited. That is, C is 0.40 to 0.50%, Cr is 1.0 to 1.5%, and Mo is in a range that satisfies all the above characteristics.
It was found that one or two of W and W are restricted to the range of 0.5 to 0.9% at Mo + 1 / 2W.

Further, Ni added for the purpose of imparting toughness to many commercialized body materials produces retained austenite after welding and is transformed into an unstable martensite structure by subsequent short-time annealing. It was found that the hardness of the welded portion was locally harder than that of the body of the body, and Ni is not added to the body of the present invention. In the present invention, due to such a strict limitation of the composition range, both ends of the body material are welded to each other by butt welding, and subsequently the hardness of the welded portion after the local annealing is performed and the average hardness of the body material body. This is the first metal band saw with a hardness difference of ± 30 HV or less.

That is, in the first invention of the present invention, C 0.40 to 0.50% by weight, Si 1.0% or less, Mn 1.5% or less, Cr 1.
0-1.5%, 1 or 2 types of Mo and W are 0.5 with Mo + 1 / 2W
-0.9%, V 0.1-0.5%, Al 0.01-0.1%, balance F
A metal band saw body excellent in fatigue strength of a weld, characterized by comprising e and impurities. The second invention is C 0.40 to 0.50% by weight, Si 1.0% or less, Mn 1.5%.
Below, Cr 1.0 to 1.5%, Mo and W 1 or 2
+ 1 / 2W 0.5-0.9%, V 0.1-0.5%, Al 0.01-0.1%,
A metal band saw body excellent in fatigue strength of a weld, characterized by containing 0.2% or less of Nb and the balance Fe and impurities.

According to a third aspect of the present invention, the hardness difference between the hardness of the welded portion and the average hardness of the body of the body is ± 30 HV or less after both ends of the body are welded together and then locally annealed. A fourth aspect of the present invention is a metal band saw excellent in fatigue strength of a welded portion, in which both ends of a body material having the composition described in the first invention or the second invention are butt-welded together, and A metal band saw excellent in fatigue strength of a weld, characterized by having a hardness difference of ± 30 HV or less between the hardness of the weld after the local annealing and the average hardness of the body material.

[0014]

[Function] The reasons for limiting the chemical components will be described below. C
Is an important element for ensuring the strength and toughness of the body material and the weld, and for making the annealed structure of the weld a stable martensite phase. Further, C combines with carbide forming elements such as Cr, Mo, W, V, and Nb to precipitate as fine carbides in the tempering at around 540 to 570 ° C, and has the effect of increasing the softening resistance to the tempering. Further, in the tempering of the body material, a hardness of 450 HV or more is obtained, and in order not to reduce the hardness of the welded part after annealing as compared with the body body, C is required to be at least 0.40% or more. .

On the other hand, the addition of C exceeding 0.50% is 540 to 57
When tempered near 0 ° C, the hardness becomes 550 HV or higher, which not only reduces the fatigue strength of the body itself, but also increases the amount of retained austenite in the welded part, making it impossible to obtain hardness in the annealed state. Therefore, the upper limit is 0.50%. Si has an effect as a deoxidizing agent at the time of melting, and also has an effect of increasing temper softening resistance. If too much is added, the hardness of the welded part during butt welding becomes high after short-time low-temperature annealing.
Is 1.0%. The desirable Si range is 0.6% or less.

Like Si, Mn is added as a deoxidizing agent during melting, but if it is too much, the cold workability of the body is impaired, so the upper limit of Mn is made 1.5% or less. The desirable range of Mn is 1.0% or less. Cr enhances the hardenability of the body material, increases the tempering softening resistance near 540 to 570 ° C to secure the hardness of 450 ° C or higher as described above, and also has the effect of preventing the hardness of the welded portion from decreasing. Have. Therefore, at least 1.0% of Cr is required, but if it is too large, the re-quenched layer part of the heat-affected zone will have a high hardness even after the annealing treatment, and the whole heat-affected zone will be uneven. The upper limit is set to 1.5% because the hardness distribution will be uniform.

Both Mo and W are effective in increasing the temper softening resistance of the body material and ensuring high hardness even when heat treatment is performed simultaneously with the high speed steel. It is an element important for preventing the decrease in hardness, and it is necessary to add one or two. Of these, Mo is an element effective in improving toughness and W is improving wear resistance, and Mo + 1 / 2W can be appropriately selected within a range of 0.5 to 0.9%. To obtain the above effect,
Mo + 1 / 2W requires 0.5% or more. However, if a large amount of addition is made, carbides of Mo and W in the secondary hardening tend to agglomerate, resulting in a decrease in toughness, and the hardness of the welded portion becomes too high, so the upper limit is made Mo + 1 / 2W to be 0.9%.

V forms MC type special carbides, and the whole amount does not melt into the matrix even at the quenching temperature of high speed steel, prevents coarsening of crystal grains at the time of quenching, and increases temper softening resistance. It is an important element for preventing the deterioration of the strength of the body and the hardness of the welded part.
One of the features of the present invention is that V is essentially added while Cr,
By controlling the amount of addition of elements such as Mo, W, and Nb that increase the temper softening resistance to the minimum, the proper hardness of the metal band saw body is ensured, and the difference in hardness of the welded portion due to butt welding is further improved. The point is that it can be controlled small. A minimum of 0.1% is required to bring out the effect of V above,
With many additions, MC-type primary carbides that crystallize during solidification tend to agglomerate, which lowers the toughness of the body body and causes the hardness of the weld to become too high, so the upper limit of V is made 0.5%.

Al is a strong deoxidizing agent and is an element that changes the morphology of non-metallic inclusions produced during the melting of the body material.
That is, the Mn or Si oxide-based inclusions generated in the molten metal during melting are reduced by addition of Al to Al ₂ O ₃ , which results in blowholes generated during welding of the blade material and the body material. Has the effect of preventing. Further, Al is an element effective in binding to N in the molten metal to form fine AlN and suppressing the coarsening of crystal grains. In order to obtain the above-mentioned effect of Al, at least 0.01% is required, but if it is too much, Al ₂ O ₃ generated will become coarse and reduce toughness, so the upper limit is set.
0.1% Nb forms a high melting point MC type carbide,
Since it has the effect of preventing the crystal grains of the body material from becoming coarse during simultaneous quenching with the blade material of high-speed steel, it is added as necessary. However, if the amount is too large, MC type carbides tend to aggregate, so the upper limit is preferably 0.2%.

Ni is an element effective for improving hardenability and toughness in a material plastically worked by ordinary forging, rolling, etc., but like the body materials of the present invention, the body materials are welded to each other. In that case, fine segregation with high Ni concentration is likely to be generated in the molten layer,
This segregated portion becomes retained austenite. Subsequently, when a short-time annealing is performed, this retained austenite part undergoes martensitic transformation, and becomes an unstable structure in which the variation in the microhardness of the molten layer part becomes large. Ni is not added. Further, the metal band saw of the present invention, the notch fatigue test result of the welded portion performed in the examples described below, and the result of measuring the micro hardness distribution of the welded portion, the hardness of the welded portion after the local annealing and the body material. If the difference in hardness from the average hardness of the main body exceeds ± 30 HV, the fatigue strength of the welded part decreases, so the hardness difference should be ± 30 HV or less. Further, as a desirable composition of the metal band saw, it is preferable to use a body material having the composition of the first invention or the second invention.

[0021]

EXAMPLES The present invention will be described below based on examples. (Example 1) In order to evaluate a metal band saw body according to the present invention (hereinafter referred to as the present invention steel), the present invention steels, conventional steels and comparative steels shown in Table 1 were melted. In particular, as a comparative steel, a material in which Ni, Cr, Mo and C were changed so that the compositional limitation of this patent becomes clear was examined.

[0022]

[Table 1]

The steels of the present invention, conventional steels, and comparative steels were each melted by 20 kg to be ingoted, then slabbed, followed by hot rolling, annealing, cold rolling, and annealing. thickness
Finished to a flat material 1.0 mm wide and 30 mm wide. Then this material 1200
Hardness, fatigue characteristics, hardness distribution of the butt weld portion, and fatigue characteristics of the butt weld portion were investigated by carrying out quenching at ℃ and tempering at 560 ° C., and these results are shown in Table 2. After the butt welding, the burr (bulging part) generated by the welding is removed, and 700
Annealing was performed by energizing at 20 ° C. for 20 seconds, and the surface was polished and used for the experiment. For the fatigue test of the body material, a test piece having the shape shown in Fig. 1 was used. Also, as shown in Fig. 2, the fatigue test of the welded portion had the same shape as the test piece of the body material, and the notch bottom and the welded portion were The ones that were matched were used. Further, the hardness was measured such that the edge surface of the flat material traverses the welded portion in the longitudinal direction as shown in FIG.

[0024]

[Table 2]

The fatigue test was carried out with a tensile stress of 294 N / mm ² and 882 N.
A tensile stress of / mm ² was applied with a sine load, evaluated by the number of repetitions until breakage, and shown as an average value of values obtained by performing 5 tests under the same conditions. In addition, the hardness distribution of the butt weld is shown in FIG.
Micro Vickers 1 kg
The hardness distribution of the body material body-heat-affected zone-melting area-heat-affected zone-body material body was measured by using, and the hardness increasing portion was shown as + Δ and the hardness falling portion was shown as -Δ with respect to the body material body. . It can be seen from Table 2 that the steel of the present invention has a small change in hardness of the welded portion, a high fatigue strength of the welded portion, a small difference from the fatigue strength of the body material, and a small fracture of the welded portion.

Among these, the conventional steel 11 containing 0.75% of Ni and containing Cr in a larger amount than the steel of the present invention, the hardness of the welded portion is large on the high hardness side as compared with the hardness of the main body, and Like the invention steel, Ni is not added and the Cr content is 1.
It turns out that it should be 5% or less. Also, comparative steel No. 21
From 24 to 24, when there is an element out of the composition range of the steel of the present invention, the hardness of the welded portion largely varies, which affects the decrease in fatigue strength.

(Embodiment 2) In order to confirm the above experimental results, actual band saws were manufactured for the steels of the present invention Nos. 1 and 3 and the conventional steels of Nos. 11 and 12 and set on a saw machine. Table 2 shows the results obtained by investigating the time until the material was fractured by idling with the tension increased by a certain amount. As a result, the present invention steel N
o.1 is 32.7 hours on average, No.3 is 66.9 hours,
In all cases, the body material body was fractured. On the other hand, in the case of conventional steel No. 11, the average of 3 pieces was 51.3 hours (of which 2 were weld fractures),
In addition, No. 12 was 54.9 hours (of which, 1 weld fracture)
Met. From the above results, it is understood that the steel of the present invention is excellent as a metal band saw body material.

[0028]

As described above, even if the body material of the present invention is subjected to the same heat treatment as the blade material of the high speed steel, there is no coarsening of crystal grains and a predetermined hardness can be obtained. Fatigue strength of the material body is high, the fluctuation of the hardness of the butt weld is small, and the same hardness as the body material body can be obtained. As a result, it is effective as a metal band saw that has better fatigue strength than conventional materials.

[Brief description of drawings]

FIG. 1 is a view showing the shape of a fatigue test piece of a flat material (plate thickness 1 mm).

FIG. 2 is a diagram showing the shape of a fatigue test piece of a welded flat material (plate thickness 1 mm).

FIG. 3 is a diagram showing an example of a hardness measurement position of a weld and a measurement result.

Claims (4)

[Claims] 1. C. 0.40 to 0.50% by weight, Si 1.0% or less, Si 1.0% or less, Mn 1.5% or less, Cr 1.0 to 1.5%, one or two of Mo and W are 0.5 to 0.9% at Mo + 1 / 2W, and V 0.1-0.5%, Al
Metal band saw body with excellent fatigue strength of the weld, which contains 0.01 to 0.1% and the balance Fe and impurities. 2. C 0.40 to 0.50% by weight, Si 1.0% or less, Si 1.0% or less, Mn 1.5% or less, Cr 1.0 to 1.5%, one or two kinds of Mo and W at Mo + 1 / 2W 0.5 to 0.9%, V 0.1-0.5%, Al
A metal band saw body excellent in fatigue strength of a weld, which contains 0.01 to 0.1% and 0.2% or less of Nb, and the balance Fe and impurities. 3. The hardness difference between the hardness of the welded portion after the both ends of the body material are butt-welded together and subsequently the local annealing is performed and the average hardness of the body material is ± 30 HV or less. A metal band saw with excellent fatigue strength of the welded part. 4. The hardness of the welded body and the average hardness of the body of the body, after both ends of the body of the composition according to claim 1 or 2 are welded together by butt welding and then locally annealed. A metal band saw with excellent fatigue strength in welds, characterized by a hardness difference of ± 30 HV or less.