JPS6311844A - High-temperature embrittlement damage detection method for ferrite-containing stainless steel members - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to engineering plants and atomic couplants used in high-temperature environments, and particularly to high-temperature embrittlement of ferrite-containing stainless steel actual machine parts used therein. Relating to a damage detection method.

[Conventional technology]

Ferrite-containing stainless steel is known to suffer from aging embrittlement when used at high temperatures for long periods of time. In particular, 475°C embrittlement progresses with long-term aging even at relatively low temperatures.
There is a need for a technique to non-destructively detect the degree of embrittlement using an actual device, but the only technology that can be found in this regard is Japanese Patent Application Laid-Open No. 61-28859.

[Problem that the invention seeks to solve]

It is already known that ferrite-containing stainless steels suffer from aging embrittlement when used at high temperatures for long periods of time.

At a relatively high temperature of about 600° C. or higher, σ phase embrittlement occurs due to the precipitation of a phase, and in a range of 400 to 500° C., so-called 475° C. embrittlement occurs.

Among the above embrittlement factors, the mechanism of 475°C embrittlement is not well understood.

Conventionally, measures taken to deal with embrittlement damage include avoiding heat treatment of ferrite-containing stainless steel members in the above-mentioned temperature range, or avoiding long-term use of actual equipment in that temperature range. .

However, as mentioned above, 475° C. embrittlement may occur during long-term use even in a temperature range of 400° C. or lower, and it seems that sufficient consideration is required when using actual ferrite-containing stainless steel parts at high temperatures.

However, conventionally, there is no effective method for non-destructively detecting the degree of embrittlement damage in actual machine parts made of ferrite-containing stainless steel.

An object of the present invention is to provide a method that can effectively and non-destructively detect the degree of embrittlement of a ferrite-containing stainless steel member used in a high-temperature environment.

゛ [Function] ゛ Ferrite-containing stainless steel has excellent stress corrosion cracking resistance and is relatively inexpensive, so it is beginning to be widely used, but when used at high temperatures for long periods of time, the ferrite phase decomposes and forms a brittle σ phase. This causes embrittlement. Furthermore, depending on the operating temperature, 475°C brittleness may occur.

The present invention is characterized by non-destructively detecting the degree of 475°C embrittlement damage, in particular, among the embrittlement damage caused by high-temperature, long-term use of ferrite-containing stainless steel members.

As a result of various studies on the embrittlement of ferrite-containing stainless steel caused by high-temperature heating, the inventors discovered a phenomenon in which the corrosivity of the ferrite region decreases as embrittlement progresses. By utilizing this phenomenon, the degree of embrittlement of ferrite-containing stainless steel can be evaluated very easily. In other words, according to the present invention, if the relationship between the degree of embrittlement and the corrosivity of the ferrite region is determined experimentally and a master curve is prepared in advance, the progress of embrittlement can be determined by measuring the amount of ferrite in the member. The degree can be detected.

To evaluate the corrosion resistance of the ferrite region, a part of this member is immersed in a solution, and a polarization curve is taken using a potentiostat as shown in FIG. That is, the ratio iR of the passivation limit current iC when the corrosion potential is polarized to the anode side from the natural potential and the reactivation current density iH in the process of returning to the previous natural potential after passivation. It is easy to determine by the size of /iC.

〔Example〕

An embodiment of the present invention will be described below.

Table 1 shows the normal temperature IN values of 20%Cr-10%Ni ferrite-'austenitic duplex stainless steel as received and samples subjected to various high-temperature aging in the receiving machine. (This shows the iR/iC ratio in a 12sO4 aqueous solution. A tendency for the iR/iC value to increase as the aging heat treatment time increases. Figure 1 shows the iR/iC ratio of the sample material after each aging heat treatment. According to this, which shows the relationship between the ratio and Charby absorbed energy (toughness value),
It can be seen that there is a good correspondence between the iR/iC ratio and Charby absorbed energy.

Next, a cylindrical member made of 20% Cr-10% Ni ferrite-austenite dual-phase stainless steel was prepared. Next, based on the results of this experiment, an embrittlement damage detection system for ferrite-containing stainless steel was created. FIG. 1 shows its block diagram. In the corrosion cell 1, a part of the member is polarized by a potentiostat 2. The resulting corrosion current i passes through a 12og converter 3 and enters a computer 5. Further, the corrosion potential Ec enters the computer 5 through the potentiostat 2. Based on the obtained i and Ec, the potentiostat is controlled by a computer through the potential scanner 4 to obtain i, iC and iR, respectively, and calculate the ip/iC ratio. iR obtained in advance/
The degree of embrittlement is calculated from the miter curve of the iC ratio and the degree of embrittlement and displayed on the display board 6.

Using this detection system, the degree of embrittlement of a 20%Cr-10%Ni ferrite-austenite dual-phase stainless steel cylindrical member was measured after long-term heat aging treatment at 450°C. The results are shown in Table 2. The predicted value and the measured value show good agreement. As described above, according to this example, the degree of embrittlement of ferrite-austenite dual phase stainless steel can be measured non-destructively.

Table 2 [Effects of the Invention] According to the present invention, the degree of embrittlement of ferritic stainless steel members used at high temperatures can be detected non-destructively and quickly, so embrittlement damage can be prevented. safety can be increased.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embrittlement damage detection system according to an embodiment of the present invention, and Fig. 2 shows the reactivation current (in)/passivation limit current (iC) ratio under each aging heat treatment condition and each test temperature. Relationship diagram of Charby absorbed energy in , 3rd
The figure is a schematic diagram showing the polarization characteristics of embrittled ferrite-containing stainless steel. 1... Corrosion cell, 2... Potentiostat, 3.
...Qog converter, 4...Potential scanner, 5
...computer, 6...display board.

Claims (1)

[Claims] 1. A ferrite-containing stainless steel, characterized in that the degree of embrittlement of the ferrite-containing stainless steel member during high-temperature, long-term use is detected by measuring the electrochemical properties of the ferrite-containing stainless steel. A method for detecting high-temperature embrittlement damage in steel members. 2. In claim 1, the corrosion potential of the member in a solution is passedivated to the passivation limit current i_C when polarized toward the anode side from the natural potential, and then returned to the original natural potential. From the size of the ratio i_R/i_C to the reactivation current density i_R in the process of
High-temperature embrittlement damage detection for ferrite-containing stainless steel members, characterized in that the toughness value of the member is determined from a master curve of i_R/i_C and toughness values determined in advance, and the presence or absence of the possibility of embrittlement damage is determined. Method. 3. The ferrite-containing stainless steel according to claim 2, characterized in that the i_R/i_C of the member is automatically measured, and the degree of embrittlement is read from the master curve given in advance and displayed. A method for detecting high-temperature embrittlement damage in parts.