JP2002235144A - Wear resistant high strength steel, cutting edge, bucket tooth and bucket lip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a wear resistant high strength steel which has excellent hardenability, weldability, machinability and cost effectiveness as well as hardness, temper softening resistance and impact resistance. SOLUTION: The steel has a composition containing, by weight, 0.25 to 0.35% C, 1.00 to 1.50% Si, 0.50 to 1.50% Mn, <=0.020% P, 0.008 to 0.015% S, <=1.2% Ni, 0.30 to 0.55% Cr, 0.15 to 0.50% Mo, 0.005 to 0.050% Ti, and 0.0005 to 0.0050% B, and in which the value of R defined by the following formula of R=1.2×Si (wt.%)+0.3×Ni (wt.%)+0.3×Cr (wt.%)+5×Mo (wt.%) is >=2.5. The steel is produced by hot rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wear-resistant tough steel used for parts of construction machines and civil engineering machines, and a cutting edge, a bucket tooth and a bucket lip in an excavator using the wear-resistant tough steel. .

[0002]

2. Description of the Related Art Among components used for construction machines and civil engineering machines, steel materials used for parts subjected to earth and sand wear in direct contact with earth and rock require high wear resistance. Various measures have been proposed for increasing hardness, a property most closely related to wear properties. Further, according to the purpose of use of the steel material, various measures have been taken to enhance other properties besides hardness, such as impact resistance and weldability.

For example, (1) Japanese Patent Application Laid-Open No. 2-179842 discloses that, in the component system proposed in Japanese Patent Application Laid-Open No. 61-174326, the Mn content is reduced, the Mo content is increased, and Cr, B, sol. A
A high-toughness wear-resistant steel plate which has a wear resistance equal to or higher than that of a conventional wear-resistant steel plate by adjusting the contents of l, N, etc., and also has toughness and delayed fracture resistance has been disclosed. .

[0004] (2) In JP-60-243250 discloses, in order to improve the weldability of high hardness wear steel _{H B} ≧ 500, wherein _{P H = C + Mn / 10} + Mo
/ 6 + Cr / 15 + 3V + 40P + of _{weldability P H} value indicated by 100B is summarized as steel is 1.0% or less excellent high hardness wear steel is disclosed.

Further, (3) Japanese Patent No. 2970309 discloses that a specific low-alloy steel is subjected to a specific heat treatment so as to obtain a stable ferrite and martensite.
A method for producing a wear-resistant steel material that forms a phase structure so as to obtain a steel material having good wear resistance and excellent workability and weldability is disclosed.

[0006] (4) In Japanese Patent Application Laid-Open No. 10-204575, required amounts of C, Si, Mn, Cr, M
o, Nb, and V are contained, and a combination of specific rolling and heat treatment forms a composite precipitate of Cr, Mo, and V with V as a nucleus during use. There is disclosed a tough and wear-resistant member having sufficient toughness to satisfy workability, breakage resistance and burn-out crack resistance.

[0007]

Generally, sediment-resistant steel is used under severe conditions such as hard rock excavation to relatively mild conditions such as sediment loading. Parts such as cutting edges and bucket teeth and bucket lips, especially in excavators such as large excavators, are used under particularly severe conditions. Essential characteristics required for this type of component include the following three characteristics. Sufficient initial hardness to obtain abrasion resistance, Temper softening resistance so that initial hardness does not easily soften due to frictional heat generated when being violently rubbed against soil rock during use. Impact resistance (toughness) that can withstand the impact force generated in the event of a severe collision, and in addition to these characteristics, it is also desirable to add additional characteristics. Quenching properties to obtain the required hardness, weldability that can be easily welded to construction machine working equipment, etc., machinability that allows easy machining, and economic efficiency.

However, the steel materials described in the above publications (1) to (3) do not sufficiently satisfy the above-mentioned characteristics (1) to (3), and are indispensable especially for wear-resistant steel used under severe conditions. No consideration is given to tempering softening resistance, which is a characteristic. Further, in the steel material described in the above-mentioned publication (4), although it is intended to improve hardness, softening resistance, impact resistance and hardenability,
Since this is a method of forming a composite precipitate of Cr, Mo, and V with V as a nucleus, it is necessary to add a large amount of expensive Cr, Mo, and V, and this has to sacrifice economy. There is a problem. In addition, there is a problem that the weldability is not satisfactory.

[0009] As described above, all of the prior arts are specialized only in some of the above-mentioned required characteristics, and particularly the temper softening resistance and the mechanical strength which are considered important in heavy excavation. It can be said that there is almost no object aimed at improving the machinability required during processing.

The present invention has been made in view of these problems, and has excellent hardness, tempering softening resistance, impact resistance, hardening properties, weldability, machinability, and economy. To provide a wear-resistant tough steel suitable for use under severe conditions such as hard rock excavation, and to provide a cutting edge, a bucket tooth and a bucket lip formed of the wear-resistant tough steel. It is assumed that.

[0011]

Means for Solving the Problems and Functions / Effects In order to achieve the above object, the present inventors newly developed the following formula: R = 1.2 × Si to maintain sufficient temper softening resistance. (Wt%) + 0.3 × Ni (wt%)
An index of R value defined by + 0.3 × Cr (wt%) + 5 × Mo (wt%) is introduced, and it is found that R ≧ 2.5 is necessary from the relationship between the R value and the tempering temperature. In order to satisfy the required and other required characteristics, an appropriate range of the added amount of each component was found by various tests.
In short, the wear-resistant tough steel according to the first invention has C: 0.2
5 to 0.35 wt%, Si: 1.00 to 1.50 wt%
%, Mn: 0.50 to 1.50 wt%, P: 0.020
wt% or less, S: 0.008 to 0.015 wt%, N
i: 1.2 wt% or less, Cr: 0.30 to 0.55 wt
%, Mo: 0.15 to 0.50 wt%, Ti: 0.00
5 to 0.050 wt%, B: 0.0005 to 0.005
Including 0 wt%, the following formula: R = 1.2 × Si (wt%) + 0.3 × Ni (wt%)
An R value defined by + 0.3 × Cr (wt%) + 5 × Mo (wt%) is 2.5 or more, and is manufactured by hot rolling.

[0012] The steel material has the highest hardness in the as-quenched state, but is subjected to unexpectedly high-temperature tempering due to the generation of frictional heat due to intense friction with earth and rock.
The smaller the decrease in hardness during high-temperature tempering, in other words, the higher the tempering temperature when the decrease in hardness is constant, the higher the temper softening resistance. Therefore, in the present invention,
The constant value of the hardness decreases with _{H RC} (Rockwell Hardness) 10
The point, the remains of quenching from the _hardness, the _{H RC} 10
The tempering temperature (° C.) for lowering the point is T-ΔH
_RC 10, and the following formula: R = 1.2 × Si (wt%) + 0.3 × Ni (wt%)
+ 0.3 × Cr (wt%) + 5 × introducing an indication that R value defined by Mo (wt%), appropriate from the relationship between the R value and the tempering temperature T-ΔH _{R C} 10 R-value It defines the range.

That is, R value and tempering temperature T-ΔH _RC
10 is a fixed relation (proportional relation) as shown in FIG.
430 ° C, which is generated by normal rock excavation
In order to reduce the hardness to 10 points by _HRC ,
It has been found that the value needs to satisfy R ≧ 2.5. In addition, other necessary properties other than the tempering softening resistance, in other words, hardness, impact resistance, hardenability, weldability,
In order to satisfy each property of machinability and economy, a plurality of steel grades were prepared and the appropriate range of the amount of each component added was determined by various tests. The reasons for limiting the addition ratio of each component are as follows.

[0014] C: 0.25~0.35wt% C is an element necessary for obtaining a hardness, the amount added to obtain _H RC 45 or more hardness by quenching and tempering 0.2
It is necessary to be 5 wt% or more. The amount of addition is 0.35
If the content exceeds wt%, the toughness significantly decreases, so the upper limit is set to 0.35 wt%. It should be noted that those requiring weldability are desirably 0.30 wt% or less.

Si: 1.00 to 1.50 wt% Si is an element necessary for imparting temper softening resistance, and the lower limit of the addition amount is 1.00 to obtain the effect.
wt%. On the other hand, if the addition amount is too large, the toughness is reduced, and the austenitizing temperature is increased to make quenching difficult, so the upper limit is set to 1.50 wt%.

Mn: 0.50 to 1.50 wt% Mn is an element effective for improving hardenability and toughness, and at least 0.5 wt% is necessary in order to sufficiently obtain the effect of hardenability. Further, if the addition amount is too large, the weldability is reduced, so the upper limit is set to 1.50 wt%.

P: 0.020 wt% or less P is likely to segregate at the grain boundary and lowers weldability and toughness. Therefore, it is desirable that the amount of P added is small. The upper limit is set to 0.020 wt% in consideration of economy in steelmaking.

S: 0.008 to 0.015 wt% S has harmful effects such as precipitation of inclusions and reduction in toughness and lamella tearing in a welded portion, but has an effect of improving machinability. If the addition amount exceeds 0.015 wt%, the toughness is reduced, and if it is less than 0.008 wt%, the machinability is significantly reduced.
wt%.

Ni: 1.2 wt% or less Ni has a slight effect on imparting tempering softening resistance by the combined addition of Si, Cr and Mo. However, if the added amount is too large, it is uneconomical.
wt%.

Cr: 0.30 to 0.55 wt% Cr has the effect of improving the temper softening resistance by the combined addition of Si, Ni and Mo. Further, it is an element effective for improving hardenability and toughness. However, if the addition amount is too large, the weldability is lowered and it is uneconomical, so the addition range is set to 0.30 to 0.55 wt%.

Mo: 0.15 to 0.50 wt% Mo has the effect of improving the tempering softening resistance by the combined addition of Si and Ni. Further, it is an element effective for improving hardenability and toughness. However, if the addition amount is too large, the weldability is lowered and it is uneconomical, so the addition range is made 0.15 to 0.55 wt%.

Ti: 0.005 to 0.050 wt% Ti binds preferentially to N as TiN, and serves to prevent B from binding to N and losing effectiveness. However, if the addition amount is too large, the toughness is reduced as inclusions, so the addition range is 0.005 to 0.050 wt%.

B: 0.0005 to 0.0050 wt% B has the effect of significantly improving the hardenability when added in a small amount. However, if the addition amount is too small, a sufficient effect cannot be obtained, and if the addition amount is too large, the weldability is reduced. Therefore, the addition range is 0.0005 to 0.0050 wt%.

According to the wear-resistant and tough steel according to the present invention, the following effects can be obtained by defining the R value and the amount of each component added as described above. (1) Hardness of _HRC 45 or more can be obtained by quenching and tempering. (2) Hardness difference in hardness and 430 ° C. After tempering after quenching can be obtained a steel having a 10 point or less temper softening resistance at H _RC. (3) Sufficient bending toughness can be obtained. (4) A steel plate having a thickness of up to 80 mm and a center strength of _HRC4
Hardenability of 0 or more can be obtained. (5) Sufficient weldability can be obtained. (6) It is possible to obtain a steel having machinability that allows easy drilling of bolt holes. (7) It is economical with relatively few expensive additional elements.

Next, a second invention provides a method for heating and quenching the wear-resistant tough steel of the first invention at 850 to 900 ° C.
Tempering at 150 to 250 ° C., the surface hardness _H RC 48
To a cutting edge in an excavator, wherein The third invention is a wear-resistant tough steel of the first aspect of the invention, after the water quenched and heated to 850 to 900 ° C., and tempered at 150 to 250 ° C., the surface hardness was _H RC 48-55 The present invention relates to a bucket tooth in an excavator. Furthermore, the fourth invention provides the wear-resistant tough steel of the first invention by 850 to 850.
After heating to 900 ° C and water quenching, 150-250
℃ tempering at relates bucket lip at the excavator, characterized in that the surface hardness was H _RC 48-55.

As described above, the cutting edge or the bucket tooth or the bucket lip is machined from the wear-resistant and high-strength steel according to the first aspect of the present invention.
After heating to 900 ° C and water quenching, 150 to 25
By tempering at 0 ° C., the surface hardness _H RC. 48 to
55 products can be obtained. According to the cutting edge or the bucket tooth or the bucket lip obtained in this way, the time until the wear can be greatly extended, and the life can be greatly improved as compared with the conventional product.

[0027]

Next, specific examples of a wear-resistant tough steel, a cutting edge, a bucket tooth and a bucket lip according to the present invention will be described with reference to the drawings.

Inventive steels A to A having the compositions shown in Table 1
Various tests were performed for each of C and comparative steels D to J. The test results are also shown in Table 1.

[0029]

[Table 1]

In Table 1, the column of "R value" is shown.
Is given by the formula R = 1.2 × Si (wt%) + 0.3 × Ni (w
t%) + 0.3 × Cr (wt%) + 5 × Mo (wt%)
The value calculated in the above shows an index of temper softening resistance
It is. In addition, “T−ΔH _RC"10 ℃" column is quenching
From the hardness as it is, H_RCTo lower 10 points
It shows the tempering temperature. Furthermore, "surface hardness"
In the column, a steel plate with a thickness of 80 mm
After water quenching from the night temperature, tempering at 200 ° C
2 shows the surface hardness of each of the samples. Also,
The column of “bending deflection” is a figure from the surface side of the sample.
2 and a bending test shown in FIG.
The amount of deflection at the time of breaking when performing a bending test with the testing device 2
It is shown. Further, the column of “weld crack” indicates the thickness 2
After tempering a 5mm steel plate under the above conditions, processing the groove
Butt welding to check for harmful cracks (no cracks
X =, cracked = x).

As is clear from the test results, the steels A, B and C of the present invention can obtain satisfactory results in any of the items of temper softening resistance, surface hardness, bending deflection and weld cracking. Was. On the other hand, in Comparative Steel D, the surface hardness was low due to the small amount of C (carbon), and in Comparative Steel E, welding cracks occurred due to the large amount of Cr. Further, in the comparative steel F, since the amount of C (carbon) is large, the toughness (the amount of flexure) is reduced, and a weld crack is generated. In the comparative steel G, the toughness is reduced due to the large amount of Si. Further, in the comparative steel H, the tempering softening resistance is reduced due to the low Si value and the low R value,
In Comparative Steel I, welding cracks occurred due to a large amount of Mo. In Comparative Steel J, weld cracking occurs due to a large amount of Mn.

Next, the steel A of the present invention and the comparative steels D, G
About, to manufacture a steel plate having a thickness of 80 mm by hot rolling,
A bucket tooth 3 for a hydraulic shovel having a shape shown in FIG. 4 was machined from this steel plate, heated to 900 ° C., then water-quenched and tempered at 180 ° C. FIG. 5 shows the distribution of the cross-sectional hardness of the tooth of the steel A of the present invention at this time. As is clear from FIG. 5, the hardness from the surface to the center is _HRC 48 or more. Here, the bucket tooth 3 is fixed to a front end edge of a bucket lip 5 provided at a front portion of the bucket 4 in the hydraulic shovel as shown in FIG. 6 by bolting. In addition,
The bucket tooth 3 used in this embodiment has a symmetrical shape at the base end and the tip end with respect to the bolt hole. The side tooth tips are reused.

Next, the bucket teeth manufactured by the steel A of the present invention and the comparative steels D and G were respectively used as a tooth, a tooth and a tooth, and these teeth were mounted on a bucket of a large hydraulic excavator for about 260 hours of practical use. Tested. The test results of this practical test are shown in FIG. As is clear from FIG. 7, the wear amount is 150 mm.
The operating time to reach is about 250 hours for the tooth, 157 hours for the tooth and 200 hours for the tooth, and the life of the tooth is 1.6 times that of the tooth and 1.25 times that of the tooth. It became.

Although the above practical test was performed on a bucket tooth, similar practical test results can be obtained for a cutting edge of an excavator, a bucket lip 5 (see FIG. 6), and the like. FIG. 8 shows the cutting edge 6 attached to the leading edge of the bucket 4A by bolting. FIG. 9 shows a cutting edge 9 which is attached to the leading edge of a blade 8 attached to the tip of the frame 7 of the bulldozer by bolting. Thus, the wear-resistant tough steel according to the present invention satisfies the desired required properties in all properties of hardness, tempering softening resistance, impact resistance, hardenability, weldability, machinability and economy. Particularly, it is suitable for use in parts used under severe conditions such as hard rock excavation, especially bucket teeth, cutting edges, bucket lips, and the like.

[Brief description of the drawings]

[1] Figure 1 is a graph showing the relation between the R value and the tempering temperature T-ΔH _RC 10.

FIGS. 2A and 2B are diagrams showing a bending test piece shape.

FIG. 3 is a schematic view of a bending test apparatus.

FIGS. 4A and 4B are views showing a bucket tooth shape.

FIG. 5 is a diagram showing a sectional hardness distribution of a bucket tooth.

FIG. 6 is a perspective view of a bucket showing a mounting state of a bucket tooth.

FIG. 7 is a graph showing practical test results.

FIG. 8 is a perspective view of a bucket showing an attached state of a cutting edge.

FIG. 9 is a perspective view of a blade showing an attached state of a cutting edge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bending test piece 2 Bending test apparatus 3 Bucket tooth 4, 4A bucket 5 Bucket lip 6, 9 Cutting edge 7 Frame 8 Blade

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C21D 6/00 C21D 6/00 LHF term (Reference) 2D015 JA06 KA01 4K042 AA25 BA02 BA03 BA05 BA11 CA02 CA06 CA08 CA10 CA12 DA01 DA02 DC02 DD02

Claims (4)

[Claims] 1. C: 0.25 to 0.35 wt%, Si:
1.00 to 1.50 wt%, Mn: 0.50 to 1.50
wt%, P: 0.020 wt% or less, S: 0.008-
0.015 wt%, Ni: 1.2 wt% or less, Cr:
0.30 to 0.55 wt%, Mo: 0.15 to 0.50
wt%, Ti: 0.005 to 0.050 wt%, B:
0.0005-0.0050 wt%, and the following formula: R = 1.2 × Si (wt%) + 0.3 × Ni (wt%)
A wear-resistant tough steel characterized by having an R value defined by + 0.3 × Cr (wt%) + 5 × Mo (wt%) of 2.5 or more and manufactured by hot rolling. 2. The wear-resistant tough steel according to claim 1, wherein
After heating to 0 to 900 ° C and water quenching, 150 to 2
Tempered at 50 ° C., the cutting edge in the excavator, characterized in that the surface hardness was _H RC 48-55. 3. The method according to claim 1, wherein the wear-resistant tough steel is 85%.
After heating to 0 to 900 ° C and water quenching, 150 to 2
Tempered at 50 ° C., bucket tooth in excavator, characterized in that the surface hardness was _H RC 48-55. 4. The method according to claim 1, wherein
After heating to 0 to 900 ° C and water quenching, 150 to 2
Bucket lip in excavator, characterized in that tempering at 50 ° C., the surface hardness was _H RC 48-55.