JPS6164823A - Method and apparatus for heat treating martensitic stainless steel after arc welding - Google Patents

Abstract

PURPOSE:To improve the resistance of martensitic stainless steel to weld crack, stress corrosion cracking and unstability rupture and the fatigue strength by heating the weld zone of the steel and a region close to the weld zone under specified conditions when the steel is heat treated after arc welding. CONSTITUTION:Martensitic stainless steel as a base metal is arc welded with a welding electrode of similar composition and heat treated. During the heat treatment after the arc welding, the weld zone of the steel and a region close to the weld zone are heated so as to give 18,000-22,000 Larson-Miller parameter P represented by the equation [where T is the heating temp. ( deg.C), and t is the holding time (hr)].

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to arc welding of martensitic stainless steel, and in particular, decreases in hardness, recovery of toughness, and The present invention relates to a post-arc welding heat treatment method for martensitic stainless steel that can reduce residual stress, etc., and a treatment apparatus therefor.

[Technical background of the invention and its problems] Generally, when arc welding a structure made of martensitic stainless steel, typically 13% Cr steel, post-heat treatment is performed to remove residual stress from the structure. Perform annealing. This annealing treatment is generally performed with the structure housed in a furnace. However, when performing welding work on a large structure or at an outdoor installation site, the above-mentioned annealing process cannot be easily performed.

However, if welding work is absolutely necessary for repairs, etc., welding rods made of common metal martensitic stainless steel or austenitic stainless steel with good welding performance specified by JIs, D309, etc. After welding with a rod, the weld and the region near the weld of the structure are heated to a temperature below the Ar1 transformation temperature at which the crystalline path changes to perform local annealing.

However, when welding with an austenitic stainless steel welding rod, the weld has approximately 40 to 9/mt
A very high tensile residual stress of tr2 results. Residual stress also occurs due to thermal expansion.

These residual stresses are hardly removed by the above-described local post-annealing heat treatment. In addition, because the welding rod and the structure have different chemical compositions, the color of the welded part may differ from the surrounding area, and the intergranular corrosion resistance in corrosive environments may deteriorate.
There are drawbacks such as reduced stress corrosion resistance, cracking susceptibility, etc.

On the other hand, when welding is carried out using a welding rod made of martensitic stainless steel, which is a common metal, it is possible to easily reduce the hardness of the welded structure by locally heating the welded part. The degree of recovery of notch toughness and the degree of reduction of residual stress vary greatly depending on the heating conditions such as the temperature of the local heating and the heating holding time, making it difficult to obtain a good post-heat treatment result.

[Purpose of the Invention] The present invention has been made based on the above circumstances, and its purpose is to reduce the residual stress and hardness generated in the welded part and the area near the welded part during arc welding of martensitic stainless steel. rise.

Can reduce notch toughness, etc., and improve weld cracking resistance, stress corrosion cracking resistance, etc. An object of the present invention is to provide a method for post-arc welding heat treatment of martensitic stainless steel, which can improve ff1 unstable fracture resistance and fatigue strength, and a treatment apparatus therefor.

[Summary of the Invention] The method for post-arc welding heat treatment of martensitic stainless steel according to the present invention provides a method for post-arc welding heat treatment of martensitic stainless steel, which is performed after performing arc welding using a matching welding rod. The heat applied to the area near the
The Ranson mirror parameter P is expressed by the following formula, where the bottom is the heating temperature (°C) and t is the heating holding time (hr).
The value of is set to be 180oO or more and 22000 or less.

P-(273+T)・(20+Iogt) However, 50
0≦T≦(Ar1 transformation temperature) In a post-arc welding heat treatment apparatus for martensitic stainless steel according to another invention, a temperature detection unit detects a welded portion of martensitic stainless steel and a region near the welded portion during post-heat treatment. The heating temperature T (°C) at the time of heating is detected, and a timer is used to calculate the heating holding time t (hr
), the above-mentioned Ranson Miller parameter P is calculated by the parameter calculation unit from the heating holding time t measured by the timer and the heating temperature T detected by the temperature detection unit,
Furthermore, the value of the Ranson Miller parameter P calculated by this parameter calculation unit is 18000 or more and 220
When the temperature becomes 00 or less, the end display section displays the end of the post-heat treatment.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an apparatus for post-arc welding heat treatment of martensitic stainless steel according to an embodiment. That is, 1 in the figure is a structure formed of martensitic stainless steel, such as 13% Cr steel, and a welded part of this structure 1 and a post-weld heat treatment area 2 including this welded part are heated by a heating burner 3. The flame 4 heats the area locally. A thermocouple 5 for detecting the heating temperature of the post-heat treatment area 2 is attached at a position a certain distance away from the post-heat treatment area 2,
The temperature detected by this thermocouple 4 is determined by a temperature calculation unit 6 as the normal heating temperature of the post-heat treatment area 2 based on the thermal conductivity of the structure 1, the distance between the post-heat treatment area wt2 and the thermocouple 5, etc. Converted to T. These thermocouples 5 and temperature calculating section 6 constitute a temperature detecting section.

The heating temperature T (° C.) of the post-heat treatment region 2 outputted from the temperature calculation unit 6 is tested by the temperature comparison unit 7 to see whether it satisfies equation (1).

500≦T≦(Arll variable temperature (1) Then, in the temperature comparison section 7, the heating temperature T (℃) is a low temperature of less than 500℃ or a value exceeding the Ar1 transformation temperature at which a change in the crystal structure occurs. If there is, the abnormality is displayed on the temperature abnormality display section 8 as a temperature abnormality.

When the heating temperature T (℃) satisfies the condition of equation (1),
It is sent to the parameter calculation unit 9 which calculates the Ranson Miller parameter P. A heating holding time t (hr) is inputted to this parameter calculating section 9 from a heating time timer 1o. The heating holding time t (hr) is input to the parameter calculation unit 9 by inputting a pulse signal at constant minute time intervals Δt from the heating start time, taking into account that the heating temperature changes during heating. be exposed. Then, the parameter calculation section 9
is calculated using the temperature Ti sent out from the temperature comparator 7 at that time every time a pulse signal is input from the heating time timer 10 at a constant time interval of t (adding the unit Ranson Miller parameter Pi shown in equation 2). I will do it.

Ti = (273+Ti)・(20+logΔ
t) Therefore, the Ranson Miller parameter P at that point becomes (Equation 31).

The Ranson Miller parameter P calculated by the parameter calculation unit 9 is sent to the condition comparison unit 11 (it is determined whether or not Equation 4 is satisfied.

18000≦P≦22000 (4)
When the condition comparison unit 11 satisfies equation (4),
A display command signal is sent to the end display section 12.

After receiving the display command signal, the completion display section 12 indicates that the heating of the post-heat treatment region 2 of the structure 1 under the optimum conditions has been completed using, for example, an indicator lamp or a warning buzzer.

With the post-arc welding heat treatment equipment for martensitic stainless steel constructed in this way, the operator can
The heating timer 10 is activated at the same time as the heating of the post-heat treatment area 2 after arc welding is started with the flame 4 of the heating burner 3. Then, the heating temperature Ti of the post-heat treatment area 2 at that point detected by the thermocouple 5 and corrected by the temperature calculation unit 6
A unit Ranson mirror parameter Ti corresponding to a constant interval Δt is calculated by the parameter calculating section 9 and sequentially added according to equation (3). Then, the regular Ranson mirror parameter P after the addition is sent to the condition comparison section 11 at regular time intervals, and the Ranson mirror parameter P
When the value of (41) is satisfied, a display instructing to stop heating is displayed on the end display section 12.
When a heating stop instruction is displayed on 2, the heating burner 3 can be stopped.

In addition, during heating, the heating temperature T of the post-heat treatment area 2 becomes (1).
If the condition is no longer satisfied, a temperature abnormality will be displayed on the temperature abnormality display section 8, so the output of the heating burner 3 may be adjusted so that the temperature abnormality is not displayed on the temperature abnormality display section 8.

Next, as a method of applying heat to the post-heat treatment region 2 of the structure 1 made of martensitic stainless steel as described above, the Ranson Miller parameter P is adopted, and the Ranson Miller parameter P The value of (4
) The reason why the residual stress, increase in hardness, and decrease in notch toughness of the weld can be most effectively improved is explained below.

That is, the inventor has created 13 compounds having the chemical components shown in the table below.
%Cr-4%N1 martensitic stainless steel (J
Is, equivalent to 5C85) to 13% Cr, which is the conventional coin
Distance Y (s) from the center of the weld line, residual stress σ (K9/2), and Vickers hardness (Hv
) was determined through experiments.

The measurement results are shown in Figure 2. In the figure, σX indicates residual stress in the X direction, and σY indicates residual stress in the Y direction. As is clear from the figure, the residual stress σ in the welded part after welding is a compressive stress of about 10υ/12. However, this welded part has a martensitic composition and has an extremely high Vickers hardness of about 400 HV. Therefore, it is considered that local embrittlement of the welded portion progresses significantly.

Figure 3 shows that after welding under the above conditions, the welded area was welded for 15 minutes.
This figure shows the relationship between the distance Y (ms+) from the weld line center, the residual stress σCK9/m2>, and the Vickers hardness (HV) when locally heated to 600°C. As is clear from the figure, the Vickers hardness of the welded part is approximately 3.
00HV, but the residual stress is about 70 to 9/1
It has risen to a very high value of around ars2. this is,
This is thought to be the result of the superimposition of the stress relaxation effect and the softening tendency of the welded part during the heating holding time (15 minutes).

In this way, depending on the heating conditions of the post-heat treatment, the hardness of the weld may be reduced by performing the post-heat treatment.
On the contrary, residual stress may increase.

In particular, FIG. 4 shows the relationship between residual stress σ and heating holding time t using heating temperature T as a parameter. As is clear from the figure, the residual stress σ may exhibit a maximum value depending on the heating conditions such as the heating holding time t and the heating temperature T. For example, if the heating temperature T is 550°C, the jilt during heating and holding is approximately 1
At 5 minutes, the residual stress σ reaches the maximum value of rJ90/am. Therefore, if we use this method of organizing the experimental results, the best value for the heating conditions of the post-heat treatment between the heating temperature T and the heating holding time at. It is difficult to find it easily.

Therefore, the inventor introduced the Ranson Miller parameter P in equation (5), which indicates a type of heat amount to be added to the post-heat treatment region.

P-(273+T)・(20+Ioot) (5) However, T and t are the heating temperature ("
C) and heating holding time (hr).

Ranson Miller parameter P, residual stress σ, and Vickers hardness (HV) in the welds in Figures 2 and 3
Figure 5 shows the relationship between In addition, in FIG. 5, changes in the Charpy absorbed energy value vE (phantom-TrL) at 0° C., which indicates a type of notch toughness characteristic, are also collectively shown. As is clear from the figure, the residual stress, Vickers hardness, and Charpy value are each calculated by the Ranson Miller parameter P
It shows a certain tendency with respect to the value of . That is, after the residual stress rapidly increases to about P-16000 and reaches its maximum value,
It gradually decreases as the Ranson Miller parameter P increases. Further, the Vickers hardness decreases as the running miller parameter P increases, and finally approaches the value of the base material. On the other hand, the Charpy value exhibits a trapezoidal characteristic as shown in the figure, and the Ranson Miller parameter P exhibits a substantially constant maximum value within a specific range.

Therefore, the value of the Ranson Miller parameter P that satisfies both the residual stress and Vickers hardness below a certain value and the Charpy value above a certain value is 18,000 as shown in the figure.
It can be understood that it is above and below 22,000.

Note that the post-heat treatment area must naturally be heated to a certain minimum temperature or higher, so the heating temperature T is 50°C.
The temperature must be 0°C or higher. Further, if the heating temperature T is too high, a change in the crystal structure occurs, so it needs to be below the Ar1 transformation temperature.

In this way, by setting the amount of heat applied to the post-heat treatment area 2 in the post-heat treatment at the value of the Ranson Miller parameter P described above, the residual stress and Vickers hardness of the welded part after the post-heat treatment can be reliably reduced to below a certain value. At the same time, it is possible to maintain the Charpy value above a certain value. Therefore, the heating conditions for post-heat treatment can be easily set to the best values.
It can improve the residual stress, increase in li' degree, decrease in notch toughness, etc. that occur in the weld zone and the area near the weld zone during arc welding of martensitic stainless steel, and the weld zone can be resistant to weld cracking, stress corrosion cracking, and unstable fracture. It can improve durability and fatigue strength.

In addition, the operator should check the concentration abnormality display section 8 and the end display section 12.
The post-heat treatment area 2 is heated with the heating burner 3 while monitoring, and the heating can be stopped when the stop command is displayed on the end display section 12. By adopting the Ranson Miller parameter P, the post-heat treatment apparatus The operation is not particularly complicated.

Note that the present invention is not limited to the embodiments described above. For example, as shown in FIG. 6, a heating control section 13 is provided to which the output signals of the temperature comparison section 7 and the condition comparison section 11 are input, and when a temperature abnormality is sent from the temperature comparison section 7, the heating burner 3 The heating burner 3 may be automatically stopped when the Ranson Miller parameter P determined by the condition comparing section 11 satisfies the condition of equation (4).

[Effects of the Invention] As explained above, according to the present invention, the residual stress and hardness increase that occur in the weld zone and the region near the weld zone during arc welding of martensitic stainless steel.

It is possible to provide a post heat treatment method and post heat treatment apparatus for arc welding of martensitic stainless steel, which can improve the reduction in notch toughness, etc., and improve weld cracking resistance, stress corrosion cracking resistance, unstable fracture resistance, and fatigue strength resistance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a post-arc welding heat treatment apparatus for martensitic stainless steel according to an embodiment of the present invention, and Figs. 2 and 3 show the relationship between Ranson Miller parameters, residual stress, and Gockers hardness. Characteristic diagram showing the relationship,
Figure 4 is a characteristic diagram showing the relationship between heating holding time and residual stress, Figure 5 is a characteristic diagram showing the relationship between Ranson Miller parameters, residual stress, Vickers hardness, and Charpy value.
The figure is a block diagram showing a post-heat treatment apparatus for arc welding of martensitic stainless steel according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Structure, 2... Post heat treatment area, 3... Heating burner, 4... Flame, 5... Thermocouple, 6... Temperature calculation part, 7... Temperature comparison part , 8... concentration abnormality display section,
9... Parameter calculation section, 10... Heating time timer, 11... Condition comparison section, 12... End display section, 13
...Heating control section. Applicant's representative Patent attorney Takehiko Suzue Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) In arc welding of martensitic stainless steel, in which a martensitic stainless steel base material is arc welded using a matching welding rod, and then a post heat treatment is performed, the martensitic stainless steel is The heat applied to the steel weld and the area near this weld is
A martensitic stainless steel characterized in that the value of the Ranson Miller parameter P expressed by the following formula is 18,000 or more and 22,000 or less, where T is the heating temperature (°C) and t is the heating holding time (hr). post-arc welding heat treatment method. P=(273+T)・(20+logt) However, 500≦T≦(Ar1 transformation temperature) (2) In arc welding of martensitic stainless steel in which a martensitic stainless steel base material is arc welded using a matching welding rod and then post heat treatment is performed, the martensitic stainless steel A concentration detection unit that detects the heating temperature T (°C) when the steel weld and the region near the weld is heated, and a heating retention time t (hr ); a parameter calculation unit that calculates a Ranson Miller parameter P expressed by the following formula from the heating holding time t measured by the timer and the heating temperature T detected by the temperature detection unit; The martensitic stainless steel is characterized in that the martensitic stainless steel is provided with an end display section that displays the end of post-heat treatment when the value of the Ranson Miller parameter P calculated by the parameter calculation section is 18,000 or more and 22,000 or less. Heat treatment equipment after arc welding. P=(273+T)・(20+logt) However, 500≦T≦(Ar1 transformation temperature)