JPH05195158A - Steel pipe expander segment - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a segment for a steel pipe expanding machine, which has improved fracture resistance when expanding a steel pipe by improving toughness without lowering wear resistance. [Composition] C: 0.35 to 0.40% by weight, S
i: 0.80 to 1.00%, Mn: 0.40 to 0.50
%, P: 0.015% or less, S: 0.003% or less, C
r: 5.20 to 5.50%, Mo: 1.20 to 1.30
%, V: 0.80 to 1.00%, consists balance of Fe and impurities, the hardness is _H R _C45~52 steel pipe expanding machine segment 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a segment of a steel pipe expanding machine, and further improves toughness without lowering wear resistance to further improve fracture resistance during pipe expansion. It concerns the machine segment.

[0002]

2. Description of the Related Art A steel pipe expander used to increase the diameter of a steel pipe has, for example, a structure shown in FIGS. 1 and 2.

In the figure, 1 is a steel pipe, 2 is a pull rod,
Reference numeral 3 denotes a tapered cone having a regular polygonal cross section fitted on the outer circumference of the pull rod 2, and 4 denotes an external thread portion 2a of the end portion of the pull rod 2.
It is a nut that holds the cone 3 through the ring 5 by screwing into the.

As shown in FIG. 2, an inverted T-shaped groove 3a is formed on each surface of the regular polygonal cross section of the cone 3, and the cone 3 of the segment 6 is placed in the inverted T-shaped groove 3a. A T-shaped guide 6a fixed with a bolt 7 is fitted to the sliding surface side of and, and each segment 6 is slid in the same direction as the axial direction of the pull rod 2 on each surface of the cone 3 having a regular polygonal cross section. It is possible.

Reference numeral 8 is an annular flange that abuts the end of each segment 6, and 9 is a boom that supports the annular flange 8 and accommodates the pull rod 2.

In the steel pipe expander having such a structure, the pull rod 2 is moved to the position shown in FIG.
When the steel pipe 1 is arranged on the outer peripheral portion of the segment 6 in the state of being moved to the left of FIG. 1, and then the pressurizing cylinder is operated to move the pull rod 2 to the right of FIG. Although it moves to the right in FIG. 1, since each segment 6 is prevented from moving in the above direction by the annular flange 8 and the boom 9, it moves in the radial direction and the steel pipe 1
Is expanded from the inside, and the shape of the cross section and the longitudinal direction of the steel pipe 1 is corrected, the dimensions are adjusted, and the residual stress is uniformly diffused.

After that, when the pressurizing cylinder is operated to move the pull rod 2 to the left in FIG. 1, each segment 6 moves in the centripetal direction, so that the steel pipe 1 can be taken out.

In this case, the surface on which the steel pipe 1 is actually expanded at the outer peripheral portion of each segment 6 is referred to as an effective expansion surface, and the longitudinal dimension L is referred to as the effective expansion length. The feed pitch P of the steel pipe 1 per one time is usually shorter than the effective pipe length L.

In such a pipe expander, forward and backward movements are repeatedly performed by a pressurizing cylinder (not shown), and the outer peripheral sliding surface 3b of the tapered cone 3 having a regular polygonal cross section,
Friction sliding is frequently repeated between the inner surface side sliding surface 6b of each segment 6.

By the way, in the conventional steel pipe expanding machine of this type, particularly when expanding a thick steel pipe, a large momentary stress acts on the segment, which easily causes cracking, and therefore the segment has toughness. In addition to being necessary, it is necessary to have some degree of wear resistance (hardness) which is a property contrary to toughness because it is subjected to frictional sliding.

Therefore, as a means for realizing a high durability segment, there is a conventional method, for example, Japanese Patent Laid-Open No. 61-21334.
There is a special high carbon alloy tool steel obtained by improving JIS SKD11 disclosed in Japanese Patent No.

[0012]

This special high carbon alloy tool steel is a well-balanced material with good toughness in spite of high hardness, but with the recent increase in working stress due to the tendency toward ultra-thickness. As a result, the problem of segment cracking (cracking starting from the corner portion illustrated by C ₁ and C ₂ in FIG. 2) is emerging, and there is a problem that a higher performance material is required.

[0013]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above conventional problems, and improves toughness as compared with the conventional segment material without lowering the wear resistance and causes cracking during expansion of a steel pipe. It is an object of the present invention to provide a segment for a steel pipe expander capable of further preventing the above.

[0014]

The steel pipe expander segment according to the present invention has a weight percentage of C: 0.35 to 0.40.
%, Si: 0.80 to 1.00%, Mn: 0.40
0.50%, P: 0.015% or less, S: 0.003%
Hereinafter, Cr: 5.20 to 5.50%, Mo: 1.20
1.30%, V: 0.80~1.00%, consists balance of Fe and impurities, the hardness has a feature in that a configuration is _H R _C45~52, segments for such steel tube expansion machine The configuration according to the invention of (1) serves as means for solving the above-mentioned conventional problems.

Next, the reasons for limiting the chemical composition (% by weight) of the steel pipe expanding machine segment according to the present invention will be explained.

C: 0.35 to 0.40% C is an element effective for improving strength, transverse rupture strength and abrasion resistance, and has good segment strength, transverse rupture strength and abrasion resistance. In order to achieve this, the content must be 0.35% or more, but if it is too large, the wear resistance is improved, but the toughness decreases and the fracture resistance of the segment during expansion of the steel pipe deteriorates. The amount was 0.35 to 0.40%.

Si: 0.80 to 1.00% Si acts as a deoxidizing agent when steel is melted and is an element effective for enhancing the temper softening resistance of martensite. In order to obtain it, it is necessary to set it to 0.80% or more, but if it is too large, the toughness decreases and the fracture resistance of the segment during expansion of the steel pipe deteriorates, so the Si content is 0.80 to 1. The range was set to 00%.

Mn: 0.40 to 0.50% Mn acts as a deoxidizing agent and a desulfurizing agent at the time of melting the steel, enhances the cleanliness of the steel, improves the toughness, and improves the hardenability. Since it is an effective element for, it is necessary to set it to 0.40% or more to obtain such an effect.
If the amount is too large, the toughness is lowered and the segment breakage resistance during expansion of the steel pipe is deteriorated. Therefore, the Mn content is 0.4
The range was 0 to 0.50%.

P: 0.015% or less By reducing the P content, it is possible to improve the toughness and thereby to improve the fracture resistance of the segment when the steel pipe is expanded. Therefore, the P content is set to 0.015% or less.

S: 0.003% or less By reducing the S content, it is possible to prevent the deterioration of toughness due to the increase of the S content and to improve the fracture resistance of the segment when the steel pipe is expanded. Therefore, the S content is set to 0.003% or less.

Cr: 5.20-5.50% Cr combines with C or the like to form a composite carbide, which improves the strength and transverse rupture strength of the segment, and also improves the wear resistance. The toughness is improved to make the fracture resistance of the segment good at the time of expanding the steel pipe, but if it is too much, the toughness is rather lowered and the fracture resistance is deteriorated. Therefore, the Cr content is 5.20 to. The range was 5.50%.

Mo: 1.20 to 1.30% Mo is an element effective in forming carbides to strengthen the matrix and improve hardenability and temper softening resistance, so 1.20% or more. It is necessary to contain it, but if it is too much, the toughness is lowered and the fracture resistance of the segment at the time of expanding the steel pipe is deteriorated.

V: 0.80 to 1.00% V refines the crystal grains and improves the toughness to improve the segment breakage resistance during expansion of the steel pipe.
If it is too large, the hardenability deteriorates and it becomes impossible to obtain sufficient transverse rupture strength, so the content was made 1.00% or less.

The steel pipe expanding machine segment according to the present invention has a chemical composition as described above, further, the hardness after heat treatment is assumed to be H _R C45~52, hardness H _R C45 a is the wear resistance of the segment is not preferred because the ones drops below, if it is H R _C52 exceeded, it is not preferable because anti-crack loss of segments is deteriorated toughness is lowered, therefore, after the heat treatment Hardness is H
_R C45-52.

In addition, in order to further improve the sliding lubrication performance of the segment, it is also preferable to subject the surface to sulphonitriding treatment, if necessary.

For such a nitrosulfurization treatment, for example, a base mainly containing sodium cyanide (NaCN) is used as a sulfidizing agent, sodium sulfate (Na ₂ SO ₄ ) and sodium thiosulfate (Na ₂ S ₂ O _3). There is a lubricious surface hardening method that can be widely applied to various steel grades, cast iron, etc. by using a reducing salt bath additive containing).

[0027]

The steel pipe expander segment according to the present invention has the above-mentioned structure, and therefore, C, Si,
By optimizing the Mn, Cr, Mo, and V contents and regulating the P and S contents, the toughness was improved without decreasing the wear resistance, and the fracture resistance was improved. The occurrence of cracks during the expansion of steel pipes in the steel pipe expander segment will be reduced.

[0028]

EXAMPLE Steels having the chemical composition shown in Table 1 were smelted, quenched and tempered under the heat treatment conditions shown in Table 2, respectively, and then hardness, tensile strength, and Charpy impact value after tempering ( 2mmU notch test), bending test (8mmφ
When the flexure at break in (× 70 mm span) was examined, the results are shown in Table 2.

Further, with the alloy cast iron having the chemical composition shown in Table 3 as the counter material, the friction speed between each test material was 100 m.
m / sec, stroke: 200 mm, sliding surface dimension-fixed side: width 10 mm x length 20 mm, -moving side: width 12 m
A sliding test was conducted by the tester shown in FIG. 3 under the conditions of m × length 150 mm, lubricating oil: mineral oil. In the tester shown in FIG. 3, 11 is a fixed liner corresponding to a segment,
Reference numeral 12 is a pressure cylinder, 13 is a moving liner corresponding to a cone, 14 is a moving cylinder, and 15 is an oil groove.

When a sliding test was conducted in this way, the amount of wear and the seizure surface pressure were also the results shown in Table 2.

In the wear test, the amount of wear was measured after sliding back and forth 10,000 times at an average surface pressure of the actual machine of 30 kgf / mm ² . In addition, the seizure test has a surface pressure of 10 kgf.
/ Mm ² to 5 kgf / mm ^{2 in} increments, and the number of reciprocations at each surface pressure was 100 times, and the surface pressure at which seizure occurred was confirmed.

Further, when a pipe expansion test was carried out using an actual machine under the conditions shown in Table 4, the results shown in Table 2 were obtained for cracking and seizure.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

As is clear from the results shown in Tables 1 and 2, No. which satisfies the components and hardness of the present invention. 1-1 and No. In the case of 2-1, it was found that the Charpy impact value was large and did not break even in the bending test, and the toughness was extremely excellent. Further, the amount of wear in the sliding test was zero (unmeasurable), there was no problem of wear resistance, the seizure surface pressure was higher than the actual machine average surface pressure of 30 kgf / mm ² , and it was confirmed that there was no seizure problem. .. Furthermore, in the actual machine test, the occurrence of defects such as cracking and seizure was not recognized.

No. 1-1 material and No. 2-1
No. with the surface of the material subjected to sulfuritriding treatment 1-2 and N
o. It was found that in the case of 2-2, the seizure surface pressure was extremely large, and the safety against seizure was further improved. It should be noted that these materials have some wear in the sliding test because the softening layer on the outermost surface of the sulphidic nitriding layer is initially worn, and there is no problem in practical use.

On the other hand, in No. 3 having a large C content and Cr content, In No. 3, although the hardness is large and the abrasion resistance is considered to be extremely excellent, the amount of deflection at break in the bending test was small, and cracks were likely to occur in the actual machine test.

Further, No. 1 having a large C content and a small Mo content and a small Cr content. In Nos. 4 and 5, the wear resistance was good, but the toughness was low, and cracks were likely to occur in the actual machine test.

Further, in No. 3 having a low Si content and a high P content. In No. 6, the toughness was inferior, and cracks occurred in the actual machine test.

Furthermore, No. 3 has a small Cr content and a large P content and S content.
In No. 7, although the toughness was slightly good, the transverse rupture strength was low, and cracking occurred in the actual machine test.

Furthermore, the hardness of No. 1 which satisfies the components of the present invention is too low. In No. 1 to 3, it was found that wear was observed in the sliding test, and some warpage (plastic deformation) occurred in the entire segment even in the actual machine test, which was not practical. On the other hand, the hardness of No. ₃ which satisfies the components of the present invention and has a hardness exceeding HRC52. In Nos. 1 to 4, the seizure nitriding had a very high seizure surface pressure in the sliding test and was good, but the hardness was too high, so that the bending amount at break in the bending test was small and cracking occurred in the actual machine test.

[0044]

The steel pipe expander segment according to the present invention has a weight percentage of C: 0.35 to 0.40%, Si: 0.
80-1.00%, Mn: 0.40-0.50%, P:
0.015% or less, S: 0.003% or less, Cr: 5.
20 to 5.50%, Mo: 1.20 to 1.30%, V:
0.80 to 1.00%, consists balance Fe and impurities, since the hardness becomes assumed to be _H R _C45~52, toughness without lowering the wear resistance become favorable Therefore, the crack resistance at the time of expanding the steel pipe is further improved, and it is possible to cope with the recent tendency of increasing the manufacturing opportunities of high-strength thick-walled steel pipes, which is a remarkably excellent effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view ((a) in FIG. 1) and a cross-sectional description in the axial direction of a steel pipe, showing how a steel pipe expander using a steel pipe expander segment expands a steel pipe. It is a figure ((b) of FIG. 1).

FIG. 2 is a cross-sectional explanatory view showing a state in which a segment for a steel pipe expander is attached to a tapered cone.

FIG. 3 is an explanatory diagram showing an outline of a sliding tester used in an example of the present invention.

[Explanation of symbols]

 3 tapered cone 6 segment

Claims (2)

[Claims] 1. By weight%, C: 0.35 to 0.40%,
Si: 0.80 to 1.00%, Mn: 0.40 to 0.5
0%, P: 0.015% or less, S: 0.003% or less,
Cr: 5.20-5.50%, Mo: 1.20-1.3
0%, V: 0.80~1.00%, consists balance of Fe and impurities, the steel pipe pipe expansion machine segment, wherein the hardness is _H R _C45~52. 2. The segment for a steel pipe expanding machine according to claim 1, wherein the surface is subjected to a nitrosulfurization treatment.