JPS6115925A - Short-time heat treatment of same-metal welded part of low-temperature steel pipe containing ni - Google Patents

Abstract

PURPOSE:To improve remarkably the low-temp. toughness of the same-metal welded part by heat-treating the same-metal welded part under specified conditions when a low-temp. steel pipe contg. Ni is welded by using a same-metal welding material and then the same-metal welded part is hardened and tempered. CONSTITUTION:When a low-temp. steel pipe contg. Ni is welded by using a same-metal welding material and then the same-metal welded part is submitted to short-time hardening and tempering, the same-metal welded part is kept at 550-650 deg.C for 1-10min before the part is hardened to improve the low-temp. toughness of the same-metal welded part. The welding material is preferably composed of <=about 0.08% C, about 0.01-0.45% Si, about 0.3-1.0% Mn, <=about 0.01% P, <=about 0.01% S, <=about 0.035% O, <=about 0.01% N, and the remainder of an appropriate amt. of Ni, Fe, and inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides welded steel pipes made of Ni-containing low-temperature steel, such as U
The present invention relates to a method for manufacturing OE steel pipes using a cometal welding material, and particularly to a method of improving the low-temperature toughness of the weld by subjecting the cometal weld to a short-time heat treatment after welding.

As is well known, 2.5% Ni steel, 3.5% Ni steel, 5.5
%Ni steel or 9%Ni steel (! Warm steel is
Because it has high strength and toughness at extremely low temperatures, it is used as a material for various structures for the purpose of transporting and storing various low-temperature liquefied gases.

Conventionally, when welding structures made of such N1-containing low-decay steel, a high N1 austenitic welding material is usually used to ensure sufficient toughness of the welded part at extremely low operating temperatures. there were. However, when using austenitic welding consumables, the welding consumables contain large amounts of expensive Ni, resulting in extremely high costs.In addition, the weld zone (weld metal) is susceptible to hot cracking, and the base metal contains a large amount of Ni. There were problems such as the yield strength of the weld metal being lower than that of Ni low-temperature steel.

Therefore, in order to overcome these problems, by using a so-called co-metallic thread welding material that has almost the same composition system as the base metal low N1 steel, we are reducing costs, increasing the strength of the weld metal, and increasing the strength of the weld metal. Methods for reducing the hot cracking susceptibility of steel have been studied, and some results have been achieved, particularly in TIG welding and MIG welding. In other words, in TIG welding or MIG welding, since the incorporation of impurities into the weld metal during welding can be suppressed to a very small amount, austepite welding materials do not contain Ni, which is effective for improving toughness, and cometal welding. It is possible to ensure a certain degree of low-temperature toughness even when the material is welded, and at the same time, the above-mentioned advantages of using a co-metallic welding material can be achieved.

On the other hand, in submerged arc welding, which is known as a welding method with higher efficiency than TIG welding and MIG welding, it is difficult to suppress impurities such as oxygen that mix into the weld metal to a very small amount due to the influence of flux. , therefore Ni-containing
When a co-metallic welding material is used in submerged arc welding of low-temperature steel, it is difficult to ensure sufficient low-temperature toughness in the weld. Therefore, in this case, it may be possible to improve the low-temperature toughness of the co-metal weld by subjecting the co-metal weld to heat treatment such as quenching and tempering after welding.
For ordinary structures, it is often difficult to perform sufficient heat treatment after welding, and therefore it is actually difficult to use matching welding materials for submerged arc welding of ordinary structures made of Ni-containing low-temperature steel. It was said that

By the way, among the applications of N1-containing low-temperature steel, low i! For LJOE II pipes used as oxidizing gas transport pipes, it is relatively easy to heat treat the welded parts after welding for pipe making, and the tJOEl
It is expected to apply high-efficiency submerged arc welding to welding for pipe manufacturing and to use co-metallic welding materials, which have advantages such as low cost. That is, tJOE
Steel pipe 311! It is thought that by applying heat treatment after welding on the line, it is possible to improve low-temperature toughness, which is the biggest problem when applying alloy welding materials to submerged arc welding. However, heat treatment to improve low-temperature toughness has conventionally been carried out for a certain amount of time, that is, quenching and tempering treatments each require 15
It is said that it is necessary to take measures such as shortening the quenching time and lengthening the tempering time.
Batch processing of LIOE steel pipes exceeding 0- is impractical because it requires a huge furnace. On the other hand, in the method of heat-treating the pipe while transporting it using a pipe QT device, under conventional conditions, extremely low-speed transport or repeated processing is required, which poses a new problem of reduced processing efficiency.

In order to solve this problem, for example, Japanese Patent Laid-Open No. 54-1127
As proposed in Japanese Patent No. 21, research has been conducted to improve the low-temperature toughness of alloy welds of Ni-containing low-temperature steels by short-term heat treatment. The above proposed method uses ACsCs after submerged arc welding of Ni-containing low-temperature copper.
This is an attempt to improve the low-temperature toughness of the co-metal welded joint through a short heat treatment by performing tempering at a temperature of 900°C or less for 15 minutes or less, but according to experiments conducted by the present inventors. For example, although the proposed method improves the low-temperature toughness to a certain extent, it has been found that it is still not able to reach a fully satisfactory level.

In addition, in the case of the method proposed above, heating and holding l for quenching
The I gate and tempering heating opening are each within 15 minutes, and the lower limit of each holding time and the time from the start of heating to the completion of heating are not particularly stipulated, but according to the experiments conducted by the present inventors. It has been found that in order to obtain good low-temperature toughness under normal conditions, it is necessary to take more than 15 minutes from the start of temperature rise to the end of holding in each heating step. Therefore, even in the case of the method proposed above, the total processing time from the start of temperature rise to the start of cooling in each heat treatment process actually requires more than 15 minutes, so it is essential to reduce the pipe conveyance speed, and it is difficult to improve processing efficiency. I couldn't get it.

This invention was made against the background of the above-mentioned circumstances. When a co-metallic welding material is used for welding for manufacturing Ni-containing low-temperature steel pipes, the low-temperature toughness of the co-metallic weld can be improved in an extremely short period of time. The object of the present invention is to provide a method that can improve the performance by heat treatment.

In order to achieve the above object, the present inventors conducted various experiments and studies, and found that carbides in the weld metal were precipitated and agglomerated before quenching and tempering of N1-containing low-temperature steel alloy welds. We have obtained new knowledge that it is effective to improve the low-temperature toughness of co-metallic welds by short-time quenching and tempering. As a result of further experiments based on this knowledge, we found that by performing preliminary heat treatment at a temperature range of 550 to 650°C for 1 to 10 minutes before quenching, it was actually possible to quench and temper for a short time to contain Ni (Ni). [We have discovered that it is possible to improve the low-temperature toughness of alloy welded parts of copper alloys, and have come up with this invention.

That is, the present invention provides a method in which a Ni-containing low-temperature steel pipe is formed by welding using a cometal welding material, and after welding, the cometal welded part is subjected to a short quenching and tempering treatment. 1~ at a temperature of 550~650℃ before
It is characterized by being held for 10 minutes. By performing preliminary heat treatment in which the temperature is maintained at a temperature of 550 to 650°C for 1 to 10 minutes before quenching, the time from the start of temperature rise to the completion of temperature rise in each of quenching and tempering processes is within 10 minutes, and Short-time processing without post-retention,
In other words, it has become possible to significantly improve the low-temperature toughness of the co-metal welded joint without providing heating and holding as proposed in JP-A-54-112721, and as a result, the steel pipe after welding in the pipe making line can be improved. Even by heat treatment while transporting, it is possible to significantly improve the toughness without reducing the transport speed. Therefore, when high-efficiency sub-mark welding is applied as a welding method, it is possible to make full use of its high efficiency to form pipes at high speed, and at the same time, it is possible to manufacture high-quality pipes with excellent low-temperature toughness of the cometal weld. This makes it possible to manufacture steel pipes for N1g11i.

The heat treatment method of the present invention will be explained in more detail below.

The target base material in the method of the present invention is so-called N1-containing low-depletion steel, and steels with various Ni contents, such as 2.5%Ni steel, 3.5%Ni1%5%Ni11,6 %
N1 steel, 8%Nil, 9%Ni steel, etc. are known, but
This invention is applicable to any of these.

Further, the welding material used in the method of the present invention may be a welding material of a common metal thread having a composition close to that of the Ni-containing steel as the base material, and therefore in an amount close to that of the Ni-containing steel as the base material. Ferritic welding material containing Ni (
However, in reality, the base material is Ni! (The Ni content is slightly higher than that of the above). For example, the base material is 2.5%Nitg.
, 365% Ni steel, 5% N+PI, 996 N! t
In the case of A, the welding material contains 2.5 to 6 Ni.
%, 365 to 6%, 5 to 9%, or 9 to 13%.

In addition, the components other than Ni in these welding materials include GO, 08% or less, and 810.01 to 810.01% in the composition of the weld metal.
0.45%, MnO, 3-i0.0%, po, o
i% or less, so, oi% or less, OO, 035% or less,
It is desirable that the composition be such that N0 is 101% or less and the rest is compatible with N1 and l"e, which become unavoidable impurities, but if necessary, components can be included in the weld metal to the extent that they do not deteriorate the effect of heat treatment. There is no problem even if a certain amount of elements are added.

That is, the reason why the components of the weld metal have the above composition is as follows.

If C is higher than 0.08%, it becomes difficult to obtain a high-toughness, low-C tempered martensitic structure, and the toughness improvement effect by tempering is impaired, so it is desirable to keep it at 0.08% or less.

If S'i is less than 0.01%, it promotes an increase in the amount of oxygen in the weld metal and reduces the absorbed energy value after heat treatment, while if it exceeds 0.45%, it increases the tempering resistance, which makes it difficult to use the method of the present invention. Even with this, short-term heat treatment becomes difficult. Therefore, the optimum 3i in the weld metal for the method of the present invention is 0.01
It is desirable to set it to 0.45%.

~1n acts as a deoxidizing agent like Si, while N
It is an element that provides the necessary tensile strength together with i, but 0.
If it is less than 3%, degassing will be insufficient and the amount of oxygen in the weld metal will increase, and if it exceeds 1.0%, unlike Ni, it tends to deteriorate the toughness. Therefore, Mn in the weld metal is 0.3
~1.0% is appropriate.

Both P and S are impurities, and the lower the content, the better, but up to 0.01% each will not impede the good results obtained by the method of the present invention.

It is difficult to reduce 0 and N in submerged arc welding compared to MIG welding and TIG welding, and they tend to increase, but in order to satisfy low-temperature toughness after heat treatment, each must be 0.035% or less, 0.0
It is desirable that it be 1% or less.

In addition, Ni is an element necessary to give the weld metal the same mechanical properties as the base metal by adding it to the same level as Ni in the base metal, and is particularly effective in improving low-temperature toughness. As mentioned above, it is preferable to have the same or slightly higher level than the red copper plate.

On the other hand, it is common knowledge that the fewer other unavoidable impurities, the better. Furthermore, there is no problem in including other elements for the purpose of improving welding workability and properties of the weld metal, as long as they do not impair the effects of the short-time heat treatment according to the method of the present invention.

Furthermore, as a welding method, although it is highly efficient as mentioned above, the effect of this invention is most noticeable in the submerged arc welding method, which tends to deteriorate the low-temperature toughness of the welded part when welding is performed when a co-metallic welding material is used. However, it goes without saying that it can also be applied to other welding methods such as MIG welding and TIG welding.

In the method of the present invention, before quenching and tempering the cometal welded part of the Ni-containing low-temperature steel pipe welded using a cometal welding material by submerged arc welding or the like, as described above, 1-10 within the temperature range of 650℃
Perform preliminary heat treatment for bulking. That is, the material is preliminarily held in a temperature range lower than the quenching temperature, then heated to the quenching temperature for quenching, and further tempered.

The experiment that formed the basis of the finding that preliminary heat treatment before quenching and tempering is effective in improving low-temperature toughness as described above will be described below.

First, the present inventors set various patterns shown in FIGS. 1(A) to 1(D) as heat patterns for heating before quenching. Here, in Fig. 1 (A) to (D), 8 points are the temperature increase start point, 0 point is the cooling start point (quenching point), E point is the quenching temperature reached point, and A point is the temperature rise point before quenching. The 8 points indicate the holding temperature reached when holding at a low temperature, and the 8 points indicate the end point of the holding. Therefore, the heat pattern in Figure 1 (A) is when the temperature is raised monotonically from the heating start point S to the quenching temperature and then quenched immediately, and the heat pattern in Figure 1 (B) is when the temperature is raised to the quenching temperature and then If the material is held at a temperature for a short period of time and then quenched, Figure 1 (C) is used. If the material is held at a temperature lower than the quenching temperature before quenching, then heated to the quenching temperature and then quenched immediately, Figure 1 (D) is shown. Similarly, before quenching, the material is held at a temperature lower than the quenching temperature, and then once cooled to room temperature (point B), then heated to the quenching temperature, and immediately quenched.

Then, the quenching temperature was set to 790°C, and the time from the 8th point to the 0th point, that is, the time from the start of temperature rise to the start of quenching cooling, was 10
Quenching in each pattern of Figure 1 (A) to (C) in which the time from point 8 to point B and from point B to point 0 was kept within 10 minutes, respectively, in the pattern shown in Figure 1 (D). (Q) and normal tempering T>, QnT, Q−+
The low-temperature toughness of the co-metallic welds was evaluated by heat-treating the cometal welds after submerged arc welding of Ni-containing low-temperature steel using various combinations such as Q-+T, Q→Q4T-+T, Q→T→Q→T, etc. We investigated patterns and combinations that could sufficiently improve the results. Here, the conditions for making the matching welded part were as follows, and the Charpy impact test piece was taken so that its center was 7 inches below the surface of the base metal on the finishing side.

Base material steel plate: 3.5% N1 steel (plate thickness 20wm) Groove shape: As shown in Figure 5 (B) Welding wire: W4, W5 in Table 1 Flux: Ca F2-Ca 0-3i 02-A
i'203 series (non-fracturing type) Welding method: 2-electrode submerged arc welding (single-layer welding on both sides) As a result of these experiments, in the case of quenching with the patterns shown in Figure 1 (A) and (B), , No matter how you combine quenching and tempering, with one quenching and one tempering each,
Under the condition of S point → C point within 10 minutes, v Noti Charpy impact absorption energy VE-/+1/ at -101℃
did not reach 3 kgLi, whereas Fig. 1 (C),
In the case of pattern (D), by selecting the holding temperature at a low temperature before quenching (point A → point B), the value of VE-1°1 can be reduced to 5kof with one quenching and one tempering. −s+
It turns out that more than that can be reached. In other words, it has been found that by holding the steel at a temperature lower than the quenching temperature before quenching, the low-temperature toughness may be significantly improved by short-term heat treatment.

Furthermore, the present inventors conducted the following experiment in order to find an appropriate holding temperature for holding at a low temperature before quenching. In other words, the heat pattern of the quenching treatment is shown in Figure '1 (
As the pattern shown in C), after quenching at various holding temperatures (point A → point B) within the range of 100 to 790°C, tempering is performed using the heat pattern shown in Figure 1(A). The Charpy impact absorption energy at the center of the weld metal was examined after performing a restoration process. The results are shown in FIG. 2 in correspondence with the holding temperature. Furthermore, the quenching temperature (E.

0 point) is 790°C, temperature rising from the start of heating to the holding temperature @ (S-)A point) is 30 seconds, and holding R (A-=
8 points) was 5 minutes, the heating time from the holding temperature to the quenching temperature (B-E point) was 30 seconds, and quenching was performed immediately after reaching the quenching temperature (therefore, point E = point C). The total time from the start of temperature rise to quenching was 6 minutes. In addition, the tempering treatment temperature is 600℃, and the period from the start of temperature increase to the completion of temperature increase is 600℃.
The mixture was cooled at the same time as the heating was completed. The conditions for creating a matching weld in this experiment were as follows.

Base steel plate: 9% N11 (plate thickness 12.75 mm) Groove shape: As shown in Figure 5 (A) Welding wire: W3 in Table 1 Flux: Qa F2-Ca 0-8i 02-A
120s type (non-water fused type) Welding method: 2-electrode submerged arc welding (15I on both sides)
(i) Welding) From Figure 2, by setting the holding temperature before quenching within the range of 550 to 650°C, extremely excellent low-temperature toughness can be obtained, with impact absorption energy vE-+tt at -196°C being around 10 kC1r・m. , it can be seen that when held in a temperature range outside of 550 to 650°C, vE-tB is 5 kof-n or less, and low-temperature toughness is hardly improved. In other words, from this experimental result, 550 to 65
By holding the temperature in the 0°C temperature range for a short time (5 minutes in this example), the quenching process can be shortened (in this example, 6 minutes from point 8 where temperature rise starts to point E where temperature rise is completed) and tempering process can be shortened. It has been found that it is possible to significantly improve the U resistance of a co-metallic welded part of N1g1 hot-use steel by submerged arc welding (held for 6 minutes in this example). The reason why such a short heat treatment can sufficiently improve toughness is thought to be that holding the steel in the temperature range of 550 to 650°C before quenching promoted precipitation and agglomeration of carbides.

Although no particular experimental results were shown, the heating temperature was 550 to 650°C before quenching using a heat pattern as shown in Figure 1 (D).
When held at 550-650°C,
It has been confirmed that even when the material is cooled to room temperature and then heated to the quenching point, the low-temperature toughness is sufficiently improved in the same way as described above.

Next, the reasons for limiting the preliminary heat treatment conditions before quenching in the method of the present invention will be explained.

If the holding temperature in the preliminary heat treatment before quenching is less than 550°C or more than 650°C, a sufficient low-temperature toughness improvement effect cannot be obtained, as is clear from the experimental results in Figure 2. The temperature was within the range of 650°C.

Furthermore, if the holding time in preliminary heat treatment before quenching is less than 1 minute, a sufficient effect of improving low-temperature toughness will not be obtained, and if the holding time exceeds 10 minutes, the low-temperature toughness will not improve any further, and short-time heat treatment will not improve the low-temperature toughness any further. 550-650℃ because it cannot be achieved.
The holding time was within the range of 1 to 10 minutes.

Furthermore, Table 2 shows the results of examining the effectiveness of preliminary heat treatment before quenching in the method of this invention for Nil in various weld metals. The welded part used in this experiment was
Wires (common metal welding materials) shown in W1 to W7 in Table 1 as various N+ low-temperature steel base materials shown in Table 2, respectively.
and CaF2-8i 02-Ca 0-Al120a-based melting type non-water-crunched flanks were used, and were created by submerged arc welding. In addition, the heat pattern for quenching in the heat treatment after welding is the pattern shown in Figure 1 (C), and the holding temperature in the preliminary heat treatment (point A → point B) before quenching is 500 to 700℃.
00℃, the holding time was gradually changed within the range of 0.5 to 15 minutes, and the quenching temperature (points E and C) was 780℃ to 780℃.
The temperature was 820°C, and further tempering was performed using the heat pattern shown in Figure 1 (A), with the tempering temperature being 590 to 620°C.
The tempering time from the start of temperature rise to the completion of temperature rise is 3 to 1
It was set to 0 minutes.

As is clear from Table 2, when heat treatment was performed under conditions within the scope of this invention (experiment numbers 1.3.4.7 to 9.13 to
17), good toughness was obtained with short heat treatment (within 10 minutes for both quenching and tempering). On the other hand, in the case of the comparative method of Experiment No. 5.6, the retention before quenching (A-+
Good toughness could not be obtained because the temperature in point 8) was outside the temperature range of 550 to 650°C, and in the case of the comparative example of experiment number 2.10, the holding time before quenching was less than 1 minute, so good toughness was not obtained. was not obtained. Furthermore, in the case of experiment numbers 11 and 12, the holding time before quenching was too long, so although good toughness was obtained, the quenching treatment time was inappropriate when the pipe was transported while being transported.

An example in which the method of the present invention was actually applied to the production of a UOE steel pipe made of Ni-containing low-temperature steel will be described below.

Example 1 The welding wire shown in Table 1 W3 was used, and the flux was Qa F240%, Si Q224.0%, Ca
Two types of 20-inch LIOE steel pipes made of 9% Ni steel, namely, wall thickness 1
An experiment was conducted to manufacture a steel pipe A of 2.75 arms and a steel pipe B of 6IIIl in wall thickness. Note that tack welding after forming the raw copper plate into a tubular shape is performed using a diameter 1.
Lvl IG welding was performed using a 2 m (A) wire with a 100% Ar gas shield. Here, the material steel plate is a 9% Ni steel plate with a thickness of 12.75 +u (w
For A pipe A) and for one with a plate thickness of 611110 (for I pipe B
), and the groove shape of the welded part is as shown in Figure 5 (C).
The shape and dimensions were as shown in FIG. 5(D).

The welding conditions are as shown in the upper and middle rows of Table 3.

After welding, the above-mentioned steel pipes A and B are expanded and formed, and then heated in a heating furnace so that the steel pipe A has the heat pattern shown in Figure 3 (A), and the steel pipe B has the heat pattern shown in Figure 3 (B). Heat treatment was performed using a pipe quenching and tempering device by adjusting the output and conveyance speed. When the mechanical properties of the obtained UOE steel pipe A1B made of 9% Ni steel with two types of wall thickness were investigated, it was confirmed that it had excellent mechanical properties as shown in the upper and middle rows of Table 4. It was confirmed that the shape accuracy was also good. In addition, the tensile test is based on JIS
Z-3121 test piece, Charpy impact test is JIS
The test was conducted using a Z-3112 test piece, and in the case of steel pipe B, a half-size test piece was used.

Example 2 Using the wire shown as W4 and the welding wire shown as W5 in Table 1, and using the same flux as that used in Example 1, a wall thickness 2 made of 3.5% Ni steel was used.
An experiment was conducted to manufacture a 20-inch UOEgil pipe (hereinafter referred to as steel pipe C) of 0+am. Note that the raw steel plate was formed into a tubular shape, and the tack welding after shaping was performed by MIG welding with a 100% Ar gas shield using a wire with a diameter of 1.6 mm having the same composition as W4 in Table 1. The groove shape of the welded portion was as shown in FIG. 5(E), and the welding conditions were as shown in the lower row of Table 3.

After welding, the #l tube C was expanded and then heat treated for a short time using the heat pattern shown in FIG. When the mechanical properties of the heat-treated steel pipe C were examined, it was confirmed that it had excellent mechanical properties as shown in the lower part of Table 4, and it was also confirmed that the pipe precision was good. The tensile test piece was taken from the entire plate thickness according to JIS Z-3121, and the Charpy impact test piece was taken according to JIS Z-3121.
-3112, No. 4 test piece was collected mainly at 7IIIm below the surface of the base material on the Finishschung side.

As is clear from the above examples and the above-mentioned practical data, according to the heat treatment method of the present invention, N1q1.
When producing steel pipes by welding using a co-metal welding material, the low-temperature toughness of the co-metal joint can be sufficiently improved by short-term heat treatment. Therefore, if the heat treatment method of the present invention is applied, it is possible to improve the toughness of the welded joint without reducing the conveyance speed even when heat treatment is carried out while conveying the welded steel pipe in the pipe making line. This makes it possible to actually achieve alloy welding by submerged arc welding of Ni-containing low-temperature steel, which was considered difficult to put into practical use due to a decrease in toughness, making it possible to improve pipe manufacturing efficiency and reduce costs. .

As mentioned above, the method of this invention is not limited to submerged arc welding, but can also be applied to MIG welding and TI welding.
It can also be applied to G welding and the like, and these welding methods can also improve the low temperature toughness by -1.

Table 1 Table 4: Test results in Example 1.2 "vE-1"
Hello 96** Hello vE-101

[Brief explanation of drawings]

Figures 1 (A) to (D) are diagrams showing the heat patterns in the basic practical experiment of this invention, respectively, and Figure 2 shows the holding temperature in preliminary heat treatment before quenching and the low-temperature toughness (-196 'C) with. 3 (A) and (B) are diagrams showing the heat pattern of heat treatment in Example 1, (A) is the pattern for steel pipe A, and (B) is! 1! The pattern for B is shown. FIG. 4 is a diagram showing a heat pattern of heat treatment in Example 2, and FIGS. 5(A) to (E) are diagrams showing groove shapes of welded parts in basic practice or embodiments of the present invention, respectively.

Claims (1)

[Scope of Claims] A method of manufacturing a Ni-containing low-temperature steel pipe by welding using a co-metal welding material, and subjecting the co-metal welded portion to short-time quenching and tempering treatment after welding, comprising: 1. A short-time heat treatment method for a co-metal welded part of a Ni-containing low-temperature steel pipe, the method comprising holding the joint at a temperature of 550 to 650°C for 1 to 10 minutes before quenching.