JP2001200341A - Tool steel excellent in earth and sand wear property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold working tool steel for excavating tool, which is inexpensive and reduced in the number of manufacturing steps and which is prevented of fracture due to crack and chipping and improved in wear resistance to earth and sand, by making a cold working tool steel have high hardness (wear resistance) and toughness, properly regulating the grain size of carbides and the amount of retained austenite, respectively. SOLUTION: The cold working tool steel having high hardness and toughness and excellent earth-and-sand wear property has a composition consisting of, by weight, 0.65-1.40% C, <=2.0% Si, 0.10-2.0% Mn, 5.0-12.0% Cr, either or both of Mo and W within the range satisfying [Mo equivalent (Mo+1/2W)=0.5 to 5.0 and/or either or both of V and Nb within the range satisfying [V equivalent (V+1/2Nb)]=0.1 to 2.5, and the balance Fe with inevitable impurities and has a structure where the grain size of M7C3-type carbides is regulated to 5-15μm and a retained-austenite structure is allowed to remain by 5-20 vol.% in a martensitic structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alloy tool steel for a drilling tool such as a disc cutter, a chisel and a ripper point for a tunnel excavation, and more particularly to a steel alloy having a high carbide grain size and a high retained austenite content. The present invention relates to a cold tool steel which has high hardness (wear resistance) and high toughness, and has excellent earth and sand wear resistance.

[0002]

2. Description of the Related Art Conventionally, JIS-S
KD11 is widely used. However, plastic working technology
Tools to be used in accordance with the progress of
Stress load is large, and 60 HR
Even SKD11, which gives C hardness, has a coarse M₇C_Three
The wear resistance is secured by the type carbide, but M
₇C_ThreeMold carbides contribute to reduced mold life
I have. To solve such a problem, see, for example,
1442, JP-A-2-247357, JP-A-2-247357
JP-A-2-277745, JP-A-3-134136
And the inventions of JP-A-5-156407.
Is being planned.

[0003] Japanese Patent Application Laid-Open No. Hei 1-2201442 discloses that C: 0.90 to 1.35% and Si: 0.70% by weight%.
1.40%, Mn: 1.0% or less, S: 0.004% or less, Cr: 8.0 to 10.0, one or two of Mo and W
A species containing 1.5 to 2.5% of Mo + W / 2 and one or two of V and Nb of 0.15 to 2.5% of V + Nb / 2, the balance being Fe and unavoidable impurities; In a quenched and tempered structure, there is a rolling die steel in which the area ratio of M ₇ C ₃ type carbide is 2% or more and 9% or less, and the area ratio of MC carbide is 2.5% or less. Although the grain size is regulated in the present invention, it is intended mainly to improve toughness and to suppress crack propagation through the chain distribution of carbides. On the other hand, in order to obtain excellent earth and sand abrasion resistance, the present invention requires appropriate hardness, carbide amount and toughness. However, it does not disclose that both the grain size of the carbide and the retained austenite, which are important factors for obtaining these properties, are regulated.

Further, Japanese Patent Application Laid-Open No. 2-247357 discloses that
Japanese Unexamined Patent Publication (Kokai) No. Hei 1-2201442 further discloses a rolling die steel having a total amount of impurities of As, Sn, Sb, Cu, B, Pb, and Bi of 0.13% or less.
Further, Japanese Patent Application Laid-Open No. 2-277745 discloses that in a quenched and tempered structure, the total area ratio of one or two of MC-type residual carbide and M ₆ C-type residual carbide having a particle size of 2 μm or more is 3% or less, The area ratio of the M ₇ C ₃ type residual carbide having a particle size of 2 μm or more is regulated to 1% or less.

[0005] As in JP-A-1-201442, all of them are intended mainly to improve the toughness and to suppress crack propagation through the chain distribution of carbides. On the other hand, as described above, the present invention regulates both the particle size of the carbide and the retained austenite, and in particular, the particle size, M ₇ C ₃
It was found that crack generation and crack propagation due to cracks in the type carbide were major factors, and that when the particle size of M ₇ C ₃ carbide was 15 μm or less, sediment wear could be significantly reduced.

Japanese Unexamined Patent Publication No. 3-134136 also discloses the above-mentioned Japanese Unexamined Patent Publication No. Hei 1-2201442. Further, among the unavoidable impurities, P is 0.02% or less, S is 0.005% or less, and O is 30 ppm. Hereinafter, N is 300 ppm or less, and further, in the quenched and tempered structure, the area ratio of M ₇ C ₃ type residual carbide having a particle size of 2 μm or more is 8% or less, and the particle size is 2 μm.
A high-hardness, high-toughness cold tool having a total area ratio of one or two of MC-type residual carbides of at least m and M ₆ C-type residual carbides of 3% or less.

Further, Japanese Patent Application Laid-Open No. 5-156407 discloses that
After quenching and tempering, the M ₇ C ₃ type primary carbide has an area ratio of 4.0% or less, and the MC type primary carbide has an area ratio of 0.5% or less.
% Or less, the maximum particle size of the primary carbide is substantially 20 μm or less, resulting in a microstructure uniformly dispersed in the matrix.
High-performance rolling that can be quenched from a quenching temperature of 050 ° C. to 1100 ° C. to a temperature of 25 ° C./min at a quenching cooling rate of 25 ° C./min. It is in steel for dies.

Further, JP-A-6-212253 discloses that C: 0.75 to 1.75% and Si: 0.5 to 3.0.
%, Mn: 0.1 to 2.0%, Cr: 5.0 to 11.0
%, Mo: 1.3 to 5.0%, V: 0.1 to 5.0%, and the balance of Fe and impurities is 450 ° C.
A method for producing a cold tool steel characterized by tempering at the above temperature. That is, in each of JP-A-3-134136 and JP-A-5-156407,
The main purpose is to improve toughness and to suppress crack propagation through the chain distribution of carbides.

Japanese Patent Application Laid-Open No. Hei 6-212253 discloses that
By performing high-temperature tempering at a temperature of 450 ° C. or more, residual stress during quenching is removed, a stable structure is formed, and secondary hardening hardness is increased, and both hardness and toughness are excellent. Even when galling occurs or heat is generated in the tool due to electric discharge machining, the tool life is extended without cracking and the workability is greatly improved. However, if the tempering temperature is lower than 450 ° C., it cannot be sufficiently exhibited. On the other hand, according to the present invention, M
Were steel material the particle size of ₇ C ₃ -type carbide and 5~15μm by returning low temperature co, martensite by volume% 5-2
The purpose is to leave 0% of the retained austenite structure.

[0010]

The prior art described above is
The size of the carbide is regulated in terms of toughness and strength. The reason for this is to prevent the occurrence of minute defects due to the lack of the primary carbides and the prevention of cracks from becoming a propagation path. On the other hand, the present invention uses a cold tool steel having both high hardness and high toughness, because it does not use cemented carbide, it is inexpensive, has few manufacturing processes, suppresses breakage due to cracking and chipping, It is an object of the present invention to provide a cold tool steel for an excavating tool excellent in the quality.

[0011]

Means for Solving the Problems In order to achieve the above object, as a result of daily intensive studies, the inventors have found that the earth and sand abrasion resistance requires high hardness, an appropriate amount of carbides and an appropriate toughness. I found it. That is, the damage mechanism of the excavation tool is not only abrasion, but also micro-cracks caused by earth and sand biting into the tool, and cracks and chipping starting from the micro-cracks due to collision with gravel, rock, or the like. Therefore, it is necessary that the tool steel for the drilling tool contains a hard carbide that contributes to wear resistance and that the matrix has sufficient toughness. Therefore, in the present invention, a cold tool steel for an excavation tool excellent in earth and sand wear resistance by obtaining both appropriate hardness and toughness by regulating retained austenite.

The gist is as follows: (1) C: 0.65 to 1.40% by weight, Si:
2.0% or less, Mn: 0.10 to 2.0%, Cr: 5.
0 to 12.0%, any one of Mo or W or 2
The species is Mo equivalent (Mo + 1 / 2W): 0.5 to 5.0, the balance is composed of Fe and unavoidable impurities, the particle size of M ₇ C ₃ type carbide is 5 to 15 μm, and a part of austenite remains in the martensitic structure. A cold tool steel excellent in earth and sand abrasion characteristics characterized by having high hardness and high toughness by leaving a structure in a volume percentage of 5 to 20%.

(2) C: 0.65 to 1.40 by weight%
%, Si: 2.0% or less, Mn: 0.10 to 2.0%,
Cr: 5.0 to 12.0%, either V or Nb
V or equivalent (V + ／ Nb): 0.1 or more
2.5, consisting of Fe and unavoidable impurities, M ₇
The C ₃ -type carbide has a particle size of 5 to 15 μm and a martensite structure with a partly retained austenite structure of 5 to 20% by volume.
% Cold work steel with excellent earth and sand wear characteristics, characterized by having high hardness and high toughness by remaining%.

(3) C: 0.65 to 1.40 by weight%
%, Si: 2.0% or less, Mn: 0.10 to 2.0%,
Cr: 5.0 to 12.0%, either Mo or W
Mo equivalent (Mo + 1 / 2W): 0.5 to
5.0, one or two of V and Nb are V equivalents (V + ／ Nb): 0.1 to 2.5, the balance being Fe and unavoidable impurities, and the particle size of M ₇ C ₃ type carbide Cold tool steel excellent in earth and sand wear characteristics characterized by having high hardness and high toughness by leaving 5-20% by volume% of austenitic structure partially retained in martensite structure in 5-15 μm. . (4) In the above (1) to (3), the quenching temperature is 10
00-1080 ° C, tempering temperature 150-450 ° C, hardness H
It is a cold tool steel excellent in earth and sand wear characteristics characterized by being composed of RC55 or more.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting various components in the present invention will be described below. C: 0.65 to 1.40% C gives sufficient matrix hardness by quenching and tempering, and combines with Cr, Mo, V, etc. to form carbides, giving high-temperature strength and wear resistance. Element. 0.65% is necessary in order to secure the formation of a sufficient amount of carbides that contribute to wear resistance and the hardness as a tool steel for drilling,
If it exceeds 1.40%, coarse carbides are excessively precipitated during solidification, and the toughness is reduced. Further, the amount of retained austenite at the time of low-temperature tempering becomes too large, and conversely, the hardness is reduced. 65 to 1.40%.

Si: not more than 2.0% Si is mainly added as a deoxidizing agent, is an element effective for oxidation resistance and hardenability, and is solid-dissolved in the base to increase the base strength. , More than 2.0%,
Since the toughness is reduced, the upper limit is set to 2.0%. Mn: 0.10 to 2.0% Mn is an element added as a deoxidizing agent like Si to increase the cleanliness of steel and improve the hardenability. However, at 0.10% or less, the effect is negligible.
If added in excess of 2.0%, the cold workability is impaired and the toughness is reduced, so Mn is set to 0.10 to 2.0%.

Cr: 5.0 to 12.0% Cr combines with C to form a hard carbide, contributes to wear resistance, and is effective in improving hardenability. However, 5.0
%, The required wear resistance and hardenability are insufficient, and if added over 12.0%, coarse carbides are formed and the toughness is reduced. Therefore, Cr is 5.0 to 1
2.0%.

Mo and W are both important elements that form fine carbides and contribute to secondary hardening, and are elements that improve resistance to softening. However, the effect is M
o is twice as strong as W and W is twice as much as Mo to get the same effect. The effect of these two elements can be represented by the Mo equivalent (Mo + ／ W). In the component system of the present invention, Mo equivalent is required to be at least 0.5% or more. Conversely, excessive addition of Mo equivalents causes toughness to decrease, so the upper limit was made 5.0%.

V and Nb are both effective for secondary curing,
It forms hard carbides with C to greatly contribute to improvement of wear resistance and to refine crystal grains. However, the effect is V
Is twice as strong as Nb, and to obtain the same effect, Nb
Is twice as large as V. The effect of these two elements is V equivalent (V
+ 1 / 2Nb). In the component system of the present invention, in order to obtain a high temperature tempering hardness, at least 0.1% or more in V equivalent is necessary. Excessive addition degrades toughness, so the upper limit was made 2.5%.

Next, in the cold tool steel, the eutectic carbide which crystallizes during solidification is conventionally defined in terms of toughness or strength. The reason is that it is regulated in order to prevent the occurrence of minute defects due to the loss of the primary carbides and the prevention of cracks from forming a propagation path. However, as a result of elucidating this point in detail, the most significant feature of the present invention is that, in particular, breakage due to earth and sand wear as a tool steel having excellent earth and sand wear resistance is largely attributable to the particle size of M ₇ C ₃ type carbide. It is found that when the particle diameter of the M ₇ C ₃ type carbide is 15 μm or less, it is significantly reduced.

Next, the steel of the present invention has a quenching temperature of 1,000 to 1,000.
In quenching at 080 ° C. and tempering at 150 to 450 ° C., the formation of giant carbide harmful to toughness is suppressed, and an appropriate amount of residual carbide is obtained to obtain sufficient toughness while having a hardness of HRC 55 or more. In order to keep austenite, the balance between C and Cr is taken into consideration. Further, in order to improve wear resistance without deteriorating toughness, C, Cr, M
o, V is a well-balanced steel. That is, since it has sufficient hardness, excellent wear resistance, and sufficient toughness, it is a cold tool steel most suitable for use as a drilling tool.

[0022]

EXAMPLES The characteristics of the steel of the present invention will be described below as examples based on experimental results. Table 1 shows the chemical components of the test steel. Table 2 shows the results of the quenching and tempering hardness, the Charpy impact value, the retained austenite amount, and the earth and sand wear test of the test steels in Table 1. In the earth and sand abrasion test, a test piece processed to a diameter of 20 mm and a length of 100 mm was fixed,
It was inserted into a container filled with silica sand No. 4 earth and sand, and the container was continuously rotated at a rotation speed of 60 rpm for 4 hours, and then evaluated by measuring the abrasion amount of the test piece. Also, M ₇ C
_In the present invention, all the carbides having a size of 2 μm or more were regarded as M ₇ C ₃ type carbides.

[0023]

[Table 1]

[0024]

[Table 2]

As shown in Table 2, as shown in FIG. Nos. 1 to 4 are examples of the present invention. 5 to 10 are comparative examples. That is,
Each of the steels Nos. 1 to 4 of the present invention has an M ₇ C ₃ carbide particle size of 5 to 5.
15 μm, and according to the tempering conditions according to the present invention, HRC
High hardness of 55 or more was obtained, and these impact values were about 7 to 9 times that of the comparative steel (f) obtained by performing the same heat treatment on the conventional cold tool steel SKD11. It is clear that the amount is small and the sand and sand wear resistance is excellent. Further, the comparative steels (a) and (b) have different hardness and Charpy impact value, but both have a residual austenite amount of 0%. It turns out that earth-and-sand wear resistance is inferior to 1-4.

Next, in the comparative steel (c), since the retained austenite is too large, the steel No. of the present invention. It turns out that earth-and-sand wear resistance is inferior to 1-4. Further, if the M ₇ C ₃ carbide is too small or too large as in the comparative steels (d) and (e), the steel No. of the present invention will be described. It turns out that earth-and-sand wear resistance is inferior to 1-4. in this way,
It can be said that both proper retained austenite and M ₇ C ₃ carbide particle size are indispensable for having excellent earth and sand wear properties.

[0027]

As described above, the steel of the present invention has a high austenitic structure by partially leaving a retained austenite structure in a certain range of the grain size and martensite structure of M ₇ C ₃ carbide as a cold work tool steel. It is possible to provide a cold tool steel excellent in earth and sand abrasion characteristics having hardness and high toughness.

Claims (4)

[Claims] C. 0.65 to 1.40%, Si: 2.0% or less, Mn: 0.10 to 2.0%, Cr: 5.0 to 12.0% by weight% One or two of Mo and W are used at the Mo equivalent (M
o + ／ W): 0.5 to 5.0, the balance being Fe and unavoidable impurities, and the particle size of the M ₇ C ₃ type carbide is 5 to 1
A cold tool steel excellent in earth and sand wear characteristics, characterized in that it has high hardness and high toughness by leaving 5% to 20% by volume of a partly retained austenite structure in a martensite structure at 5 μm. 2.% by weight: C: 0.65 to 1.40%, Si: 2.0% or less, Mn: 0.10 to 2.0%, Cr: 5.0 to 12.0%, One or two of V or Nb is replaced with a V equivalent (V +
ＮNb): 0.1 to 2.5, the balance being Fe and unavoidable impurities, and the particle size of the M ₇ C ₃ type carbide is 5 to 15
A cold tool steel excellent in earth and sand wear characteristics, characterized in that it has a high hardness and a high toughness by leaving 5-20% by volume of a retained austenite structure in a martensite structure at a part size of μm. C .: 0.65 to 1.40%, Si: 2.0% or less, Mn: 0.10 to 2.0%, Cr: 5.0 to 12.0% by weight% One or two of Mo and W are used at the Mo equivalent (M
o + 1 / 2W): 0.5 to 5.0, any one or two of V and Nb are V equivalent (V +
ＮNb): 0.1 to 2.5, the balance being Fe and unavoidable impurities, the M ₇ C ₃ type carbide having a particle size of 5 to 15 μm, and a martensite structure with a partly retained austenite structure in volume%. A cold tool steel excellent in earth and sand wear characteristics characterized by having high hardness and high toughness by remaining 5 to 20%. 4. The method according to claim 1, wherein the quenching temperature is 1.
A cold tool steel having excellent earth and sand wear characteristics, comprising 000 to 1080C, a tempering temperature of 150 to 450C, and hardness of HRC55 or more.