JPS60159156A - Mandrel alloy for piercing and expanding of seamless steel pipe - Google Patents

Abstract

PURPOSE:To increase the mechanical strength of a mandrel for piercing and expanding to be used in the stage of producing a seamless steel pipe and to improve the durability thereof by decreasing the content of Cr in an Ni-Cr low alloy steel, increasing the content of Ni therein and adding further Mo, W, etc. thereby forming said mandrel. CONSTITUTION:A steel material consisting of the compsn. which is contained therein with 0.1-0.25% C, 1-3% Cr, 1-9% Ni and 0.3-3% one kind of W or Mo or both in total is further incorporated therein with one or both of <1.5% Si and <1.5% Mn as a deoxidizing agent and in which the ratio of Ni/Cr is regulated to 1-3 is used as a mandrel for piercing and expanding in a device to be used for producing a seamless steel pipe. The mechanical strength of the mandrel at ordinary and high temp. is increased. Generation of a damage, crack, etc. on the surface of the mandrel by the high pressure between the pipe materials is prevented and the life of service time is increased in the stage of using the mandrel for piercing and expanding of the pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a core metal alloy for drilling and expanding pipes used in the production of seamless steel pipes.

Generally used for seamless steel pipe drilling, i! the gold is pressed longitudinally into a solid round piece of steel heated to approximately 1200° C. which is rotated and advanced by inclined mill rolls, thereby effecting axial perforation of the steel tube. The steel pipe drilled in this manner is similarly rotated and advanced by inclined rolling rolls, and the tube expansion core bar is heated to approximately 1000°C and press-fitted into the steel pipe borehole, thereby expanding the pipe. .

As a result, high temperature and high pressure act on the surface of the core metal for drilling and tube expansion, causing wear and plasticity of the core metal material.
C. Partial melting damage of wrinkles due to service, or galling or cracking due to seizure with the pipe material occurs, and the deformation and damage of the core bar caused by these progresses, and the core metal is damaged after a relatively short number of uses. Its use becomes impossible.

In order to prevent these damages that occur in core metals for drilling and tube expansion, the properties required of the alloy that forms the core metal differ depending on the type of damage as follows.

fi+ High mechanical strength at high temperatures is required to prevent wear and wrinkles.

(2) In order to prevent cracking, it is necessary to have high mechanical strength and extensibility at room temperature.

(3) In order to prevent the occurrence of partial melt damage, the addition of alloying elements with low solubility to the base metal in the composition of the core metal alloy should be kept as low as possible.

It is necessary to prevent these alloying elements from segregating at grain boundaries due to solidification segregation or grain boundary precipitation, resulting in a partial decrease in melting point and grain boundary embrittlement.

(4) In order to prevent galling and cracking due to seizure, a dense scale layer with insulation and lubrication properties is formed to an appropriate thickness on the surface of the core metal by scaling treatment. It is necessary to

In general, alloys for manufacturing this type of core metal have a composition by weight of CO13% to 0.4%, Cr3 to 4%, N
i1 to 1.5% is used.

In order to satisfy the above-mentioned requirements, the present 2 Haimei alloy has a core metal alloy composition with a lower content of C and Cr, a higher content of L and Ni, and a higher content of Mo and W. By newly adding one or both of them, the solid solution is hardened and the mechanical strength at room temperature and high temperature is increased, reducing the occurrence of the various damages mentioned above compared to conventional core metals of this type. It has now become possible to obtain an alloy that can be used to form a core metal that has better durability than conventional ones.

The composition of the alloy used to manufacture the core metal for drilling and expanding seamless steel pipes according to the present invention is, by weight, C: o, i to 0.25%, Cr: 1 to 3%, Ni: 1 to 9%. , one or both of MO and W total 0
．． 3% to 3%, the balance being Fe and unavoidable trace impurities, and is characterized by a Ni/Cr ratio value of 1 to 3. Furthermore, if necessary, as a normal deoxidizing agent, add 1.5% or less of Sl or 1.5% or less of Mn.
% or both may be mixed into the above composition.

Next, the reason for limiting the range of each component in the above composition will be explained.

C forms carbides with Fe and Cr, and is an effective element for increasing the mechanical strength of the alloy at room and high temperatures.At the same time, as the amount of Cr and Ni added increases, the solubility of C in the base metal increases. Therefore, C segregates at the grain boundaries due to solidification segregation during alloy casting and grain boundary precipitation during heat treatment, resulting in a partial decrease in melting point and grain boundary embrittlement, and also preferentially solidifies MO and W in carbides. It has contradictory dual properties of reducing the content of MO and W in the base metal by dissolving and absorbing it, and reducing solid solution hardening due to MO and W.

The core metal alloy of the present invention differs from conventional 6-karat alloys in order to prevent partial melt damage to 6-karat gold.
Since the mechanical strength at room temperature and high temperature is mainly determined by solid solution hardening, it is desirable that the C content be as low as possible. However, if the Ni content is too low, it becomes necessary to increase the Ni content in order to maintain the necessary mechanical strength, resulting in an economical cost increase. Furthermore, if the C content is low, the fluidity of the molten metal decreases, and the castability of the alloy deteriorates.

Therefore, the lower limit of the C content was set to 0.1% from the viewpoint of economy and castability, and the upper limit was set to 0.25% from the viewpoint of preventing partial melt damage to the core metal.

Si is added as necessary to adjust the deoxidation of the alloy, but
If there is too much Sl, the toughness of the alloy will decrease, and the scale will be removed during the school adhesion treatment, which is generally applied to this kind of core metal to add a dense thin layer of scale that has heat insulation and lubrication properties. Generates Firelight (FeO 5io2) to weaken the scale. Therefore, the upper limit of the Si content was set at 1.5%. There is no particular limit on the lower limit.

・Mn is also added to adjust deoxidation of the alloy as necessary.

Too much Mn makes the scale brittle as in the case of Si. Therefore, the upper limit of the Mn content was set at 1.5%. There is no particular limit on the lower limit.

Cr forms a solid solution in the alloy base metal or combines with C to form a carbide, and is an effective element for increasing the mechanical strength of the alloy at room temperature and high temperature, as well as improving the oxidation resistance of the alloy. . However, if the Cr content is too high, the oxidation resistance of the alloy will improve, which will cause the adhesion of scale to occur during the scale adhesion treatment, which is performed to attach scale with heat insulation and lubricity to the surface of the core metal. The layer becomes thinner, and galling damage due to seizure between the pipe material and the core metal occurs frequently. On the other hand, if the Cr content is too low, the mechanical strength of the alloy at room temperature and high temperature will decrease, and the core metal will be prone to wear, wrinkles, or cracks due to insufficient strength.

The alloy of the present invention overcomes this self-consistency by not forming carbides with C.
The problem was solved by adding enough Ni to the alloy to enhance the mechanical strength at room temperature and high temperature by solidly dissolving the entire amount in the alloy base metal, and by maintaining the Ni/Cr ratio between 1 and 3.

Examples of the influence of the Ni/Cr ratio on the non-mechanical properties of the alloys of the present invention at ambient and elevated temperatures are shown in FIGS. 1-4. Figure 81 shows the case where the C content is 1.4% and the test temperature is room temperature, Figure 2 shows the case where the Cr content is 1.4% and the test temperature is 900°C, and Figure 3 shows the case where the Cr content is 2. .8%
When the test temperature is room temperature, Figure 4 shows ('r content is 2.
8% and the test temperature is 900° C., and curve diagrams of the elongation % and tensile strength ?/- of the alloy according to the value of the N i /(' r ratio in each case are shown.

As can be seen from these curve diagrams, the tensile strength and elongation rate necessary to prevent cracking, which is one of the damages that reduce the durability of the core metal, are determined when the value of the N・i'/Cr ratio is 1. Below, the tensile strength goes from 45 sand/m4 to about 44 at 50 nights, which is insufficient, and when the Ni/Cr ratio is 3 or more, the elongation rate decreases significantly, making it unsuitable for preventing cracking. It turns out that there is something.

In addition, the high-temperature tensile strength of the alloy, which is necessary to prevent wear and wrinkles on the surface of the core metal, which is another damage that reduces the durability of the metal core, is difficult to maintain when the Ni/C:r ratio is 3 or more. 5
．． 2K? /- to about 5.3/-, which shows that the strength is insufficient, and at the same time, the elongation rate decreases significantly.

Based on the above results, the upper limit of the Cr content of the alloy was set at 3% to prevent galling due to seizure, and the lower limit was set at 1% to maintain the strength of the alloy. And the Ni content of the alloy is N1Z
The lower limit value is set to 1% to maintain the Cr ratio value from 1 to 3.
, the upper limit was set at 9%.

MO and W are elements that are dissolved in solid solution in the alloy base metal, combine with some l/)) and C to form carbides, and are particularly effective elements for increasing the high-temperature mechanical strength of the alloy.

On the other hand, increasing MO and W content reduces the oxidation resistance of the alloy. An example of the effect of adding one or both of MO and W on the high-temperature mechanical properties of the alloy of the present invention is shown in FIG. Figure 5 shows that the Cr content is 2.8% and the test temperature is 9.
Mo when the value of N i /CrO ratio is 2.0 at 00°C
, shows a curve diagram of the elongation rate and tensile IJ strength of the alloy according to changes in the content percentage of W or Mo+W.

According to this curve diagram, the added amount of MO and W (N1 type or 2 types) is effective in improving high temperature tensile strength up to 0.2%. 0.3
% to 1.5%, the high-temperature tensile strength of the striped alloy increases from 1.5% to 2.0%. The value increases rapidly and dramatically as the amount added increases. It can be seen that the high-temperature tensile strength begins to increase slowly again (with addition of 2.0% or more of potassium).

Among the metals manufactured using the alloy of the present invention, when drilling a solid round steel piece heated to a temperature of around 1200°C with a core metal for drilling, the material of the steel piece to be drilled is simply In the case of carbon steel, a core metal for drilling made of an alloy of the present invention containing 1.5% or less of one or both of MO and W is sufficient for the durability of conventional core metals. However, if the material of the perforated Z steel piece is special steel such as 13% chromium steel or F or 24% chromium steel, one of MO and W or one of MO and W may be used. It is necessary that the total addition amount of the two types is 5% to 3.0%, and in this case, the durability is 3 to 5 times that of conventional drilling core metals. (Please refer to the examples below.) If the amount of Mo and W added exceeds 3%, the elongation rate of the alloy decreases, and at the same time, the above-mentioned scale formation is caused by the treatment. The quality of the scale formed becomes weak.

Therefore, the lower limit of the amount of Mo and W added, or the total amount of both of them, in the alloy of the present invention was set to 0.3%, and the upper limit was set to 3%.

EXAMPLES The characteristics of the core metal alloy according to the present invention will be explained by summarizing several examples in a table. Table 1 summarizes the composition of the alloy of the present invention used in the multi-purpose test and the composition of a conventionally known comparative alloy.

Next, JI
A No. 10 room temperature tensile test piece according to the regulations of S-Z-2201, a high temperature tensile test piece according to the regulations of JIS-G-0567, and core bars for drilling with diameters from 13'71ijI to 149a were produced.

Room temperature tensile test is at room temperature, high temperature tensile test is at 900℃
The tests were conducted at a strain rate of 5% per minute.

The core for drilling was actually used in the drilling work of seamless steel pipes in parallel with the conventional 3 Cr I Nt @ steel type, and the durability was determined by the average number of holes per core for drilling. . The results of the above tests are summarized in Table 2.

As seen in Table 2, the room temperature mechanical strength of the alloys of the present invention is 1.5 times higher than that of the comparative alloys, except for Example 5.
The mechanical strength at high temperatures is 1.2 to 2 times greater than that of the comparative alloy.
It turns out that it is 4 to 3 times larger. The durability of the core metal for drilling made from the alloy of the present invention is approximately 3 to 6 times longer when the perforation tube material is carbon steel, compared to the core metal made from a comparative alloy. In the case of steel, it is seen to be 3 to 5 times more expensive.

Conventionally, core metal alloys for this type of drilling have a carbon content of 0.3% to 0.
．． 4%, which is higher than that of the uninvented alloy, and the value of the Ni/Cr ratio is usually 1 or less, that is, the Cr content is usually greater than the Ni content.

Therefore, as mentioned above, grain boundary segregation of carbides is likely to occur, which causes local melt damage. Furthermore, since the mechanical strength of conventional drilling core metals mainly depends on the dispersion hardening of carbides, there is no reduction in high-temperature mechanical strength at temperatures above 900°C, so wear and wrinkles do not occur on the core metal. In many cases, no improvement in durability could be expected. In contrast, with the alloy of the present invention, we have clarified the relationship between the various types of damage that occur in the core metal for drilling (the same applies to all core metals for tube expansion) and the material properties necessary to prevent such damage, and in particular, By designing the alloy so that its mechanical strength depends on solid solution hardening, we succeeded in achieving the above-mentioned excellent durability.

[Brief explanation of drawings]

FIG. 1 is a curve diagram showing the influence of the Ni/Cr ratio on the room temperature mechanical properties when the Cr content of the alloy of the present invention is 1.4%. FIG. 2 is a curve diagram showing the influence of the N 1 /Cr ratio on high-temperature mechanical properties when the Cr content of the invention alloy is 1.4%. FIG. 3 is a curve diagram showing the influence of the Ni/Cr ratio on the room temperature mechanical properties when the Cr content of the alloy of the present invention is 2.8%. FIG. 4 is a curve diagram showing the influence of the Ni/Cr ratio on high-temperature mechanical properties when the Cr content of the invention alloy is 2.8%. Figure 5 shows that the Cr content of the invention alloy is 2.8% and the Ni/C
FIG. 3 is a curve diagram showing the influence of MO and W addition amounts on high-temperature mechanical properties when the r ratio is 2.0. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Ni/CrwJ 2nd PI Ni /Cr ratio Figure 3 Nt / Cr 5 ['' 0 1-2 3 Mo, W, Mo◆W ('/,) Procedural amendment 1.8ゎao, 2yg 13El Director General of the Japan Patent Office Manabu Shiga 1, Indication of the case Patent application No. 11899/1989 2, Title of invention Core metal alloy for drilling and expanding pipes with seamless w4 approval 3, Amendment Relationship with the case of the person who filed the patent application Patent applicant Shinpo Kokusei Steel Co., Ltd. 4, agent 5, voluntary amendment 7, content of amendment fil The scope of the patent claims is amended as shown in the attached sheet. (2) In the 8th line from the bottom of page 4 of the specification, "C is 0.1 to 0.25 inches" and all "C is 0.14 to 0.18 inches" is corrected. (8) On page 6, line 6 of the specification, "from the perspective of 0.14," is corrected to "from the experimental standpoint of 0.141." (4) On page 6, line 7 of the specification, the statement ``From the viewpoint of io and 25 chi.''
This is corrected to "o and iss from an experimental standpoint (see examples below)". (5) Tables 1 and 2 on pages 14 and 15 of the specification are corrected as shown in the attached documents. 2. Claims (1) 1. C is 0.14 by weight. -, l, 0.18%
, 1 to 3 Cr, 1 to 9 Cr, 0.3 to 3 Cr in total of one or both of MO and W, the remainder being Fe and unavoidable trace impurities,
An alloy for forming a core metal for drilling and expanding seamless m-tubes, and having an N1ZCr ratio of 1 to 3. (2) Furthermore, if necessary, as a deoxidizing agent, Si is 1.5 or less, 1Mn is 1.5 or less (nJ, or both). The alloy described in .Applicant's representative Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) Weight r CdiO, 17zio, 25%, C
r 1 to 3%, Ni 1 to 9%, MO and W
0.31 to 3% in total of any one or two types,
The remainder consists of Fe and unavoidable trace impurities, and N
An alloy for forming a core bar for drilling and expanding seamless steel pipes having an i/Cr ratio of 1 to 3. (2) The alloy according to claim 1, further containing 1.5% or less of Si, 1.5% or less of Mn, or both as a deoxidizing agent, if necessary. .