JPH01179896A - Heat exchanger - Google Patents

Abstract

PURPOSE:To impart high-temperature strength to a tube plate of thick material and keep it from embrittlement or loss of its toughness by introducing specified ratios by weight in the use of such ingredients as C, Cr, Mo, Ni, N, P, S, Al, V, Nb, Mg, Ca, Si, Mn, and oxygen. CONSTITUTION:In the makeup of a tube state 4 of thick material, a part of a heat exchanger built of a barrel, tube plates 4, and heat exchanger tubes 3, the composition is made to comprise (in percentage ratios by weight) C (0.05-0.3, Cr (8-10), Mo (0.8-2.0), Ni (0.5 or less), N (0.02-0.10), P (0.01 or less), S(0.01 or less), Al(0.05 or less), V (0.01-0.5), Nb (0.01-0.15), (V+Nb should be in the range 0.1-0.6), Mg and/or Ca (0.001-0.01), Si (0.1 or less), Mn (0.5 or less), (Si+0.5Mn should be 0.25 or less), and oxygen (0.01 or less), the remaining components comprising Fe and unavoidable impurities. Such a composition enables a tube plate to have high-temperature strength and keeps it from embrittlement or loss of its toughness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention provides a high C.
The present invention relates to the use of r-ferritic steel, and relates to heat exchangers using thick inner materials that have excellent high-temperature strength, embrittlement resistance and stress relaxation properties during high-temperature use, and particularly to fast reactor steam generators.

[Conventional technology]

Ferritic steel, particularly 9Cr steel, is the mainstream material for heat exchanger tubes for fast reactors due to its oxidation resistance and high-temperature strength. Of these, US 0R is used as a material for thermal power plants.
MOa, 9Cr-IM developed at NL.

Since steel [EPRI Report RP1403 (1968)] has excellent properties, patent applications for 9Cr steel, which is an arrangement of wooden bells, have been published in Japan. For example, JP-A-62-103344 and JP-A-62-898.
Improvements in high temperature strength and toughness are being studied based on 90r-IMO-V-Nb steel, such as No. 42. However, no consideration was given to embrittlement and stress relaxation during high-temperature use, which are problems associated with thick-walled materials.

[Problem to be solved by the invention]

The 9Cr thread steel being developed by Koreashi is intended for thin-walled heat exchanger tubes, so it focuses on high-temperature strength and weldability, and reduces the toughness due to embrittlement during use, which is a problem with thick-walled materials. V:i was not taken into consideration, and there was a fear that brittle failure would occur if applied as is to thick inner materials. I cut it,
In order to improve toughness, it was necessary to sacrifice still strength, and it was considered difficult to achieve both.

In addition, stress relaxation is a problem in the thick inner material of steam generators for fast reactors, but this has not been particularly studied so far.

The purpose of this invention has been developed so far? It is an object of the present invention to provide a heat exchanger, particularly a steam generator for a fast reactor, using a thick-walled material that has a temperature strength comparable to that of Cr-based steel and suppresses a decrease in toughness due to embrittlement during use.

[Failure to solve the problem]

To summarize the present invention, the present invention relates to a heat exchanger, which comprises a body, a signboard, and a heat exchanger tube, and has a structure in which a plurality of heat exchanger tubes are aggregated by a tube sheet at the inlet and outlet of steam flowing inside the tube. In the heat exchanger, the tube sheet made of thick-walled material has a weight ratio of c:o, os to a3%, C
r: 8-10%, M.

208~2.0%, Ni: 0.5 or less, N: α02~
0.10%, p: o, o i% or less, S: 0
．． 01% or less, At: 0.05% or less, ■: α01~
0.5%, Nb: 0.01-0.15%, however, V+N
b: Contains α1-0.6%, and Mg and/or 1jCa: 0.001-0. ,01%, Si:
11% or less, Mn: 0.5% or less, and Si + 0
．． 5Mn: CL: 25% or less, oxygen: α: 01% or less, and the remainder includes Fθ and inevitable impurities.

An example of the heat exchanger of the present invention is a tube reactor steam generator.

A steam generator for a fast reactor will be explained with reference to FIG. That is, FIG. 1-1 is a local sectional view of a steam generator of a fast reactor, FIG. 1-2 is an enlarged view of a signboard, and FIG. 1-3 is a longitudinal sectional view thereof. In each figure, 1 means a steam inlet, 2 means a steam outlet, 3 means a heat exchanger tube, and 4 means a tube sheet.

To explain Fig. 1, steam enters from the inlet 1, branches from the signboard into the heat exchanger tube, ascends the heat exchanger tube in a helical shape, is collected at the tube plate on the outlet side, and exits from the outlet 2.

In order to improve embrittlement resistance during use while ensuring high temperature strength, C, Mo,
(2) Adjustment using additive elements such as Nb and N is difficult. Therefore, due to recent advances in manufacturing technology and methods of adding Mg and Ca as deoxidizers, there is a trend that Si and Mn, which were added as deoxidizers, are no longer needed.
I looked at the elements in layers. Sl and Mn have almost no effect on high-temperature strength, and are effective in reducing brittleness due to embrittlement.
In particular, since Sl promotes embrittlement, by reducing Si and Mn, it is possible to provide a thick inner material with improved embrittlement resistance during use while ensuring high temperature strength. Moreover, at the same time, the abrasiveness is improved, and there is also the effect that thermal stress generated due to temperature difference in the inner part of the thickness can be easily alleviated.

Furthermore, by adding a small amount of W to a steel type with reduced Sl and Mn, the toughness can be further improved.

C solidly dissolves in the matrix to increase the strength, and also precipitates fine carbides to increase the strength. It also has the effect of suppressing the precipitation of ferrite phase, which becomes hard and reduces high-temperature strength and toughness.

However, when the amount of addition increases, carbides aggregate and coarsen at grain boundaries, causing a decrease in strength and toughness. Therefore, the component range is a05 to 0.3%, especially 0.0
8 to α15chi is suitable.

Cr is an element that improves antioxidation performance, but if added in a large amount, it precipitates a ferrite phase and causes a decrease in strength and toughness, so a range of 8 to 10%, particularly 9%, is preferred.

MO can be solid-dissolved in the base to provide strength. However, when added in a large amount, it promotes precipitation of ferrite phase, leads to coarsening of Laves phase or carbide, and significantly reduces strength and strength. Therefore, the component range is 08-2.0
A spear, especially α9 to 1.2 chi, is suitable.

(2) and Nb form carbonitrides and increase high temperature strength. However, if a large amount is added, it will reduce the strength of C, NL7), which is solid-dissolved in the base and strengthen it, resulting in a decrease in strength.
V: 0.01-05%, Nb: 0.01-0.15%, V+Nb: 11-0.6%, especially V: 0.15-0.
25%, Nb: 0.05 to G, '10 are suitable.

N is dissolved in the base to improve its strength. However, if a large amount is cooled, coarse nitrides are formed and the dust quality decreases (102 to 0.10%, especially 0.06 to 0.07%).
% is preferred.

Since P and S segregate at grain boundaries and cause a decrease in toughness, (
It is necessary to keep it below 101%.

Although Sl 2 is effective as a deoxidizing agent, it promotes grain boundary segregation and coarsening of precipitates, leading to a decrease in toughness and making stress relaxation difficult to occur. Due to recent advances in manufacturing technology and the addition of Mg and Ca, deoxidizing agents are no longer required.
It is preferably 0.1% or less, particularly 0.05% or less.

Mn is effective in deoxidizing and improving weldability, but if added in large amounts, it increases quench hardenability and reduces casing toughness. In areas where the influence of heat is small, it is preferable to place emphasis on toughness and reduce it to 11% or less.

Also, due to the relationship between Sl and Mn, 34+0.5Mn is cL25
It is preferable that snoring ≠ seven happiness → chi or less.

N1 has the effect of completely suppressing the formation of δ ferrite, but adding multiple values causes weld cracking, so it is preferably kept at 0.5% or less, particularly 0.2% or less.

Mg and/or Ca are effective as debranching agents, but the efficiency does not increase even if they are added in large amounts, so aooi ~ 0.0
1% is good.

Although it is not necessary to add W, if it is added, it dissolves in the base and increases the toughness. Furthermore, W has the effect of preventing the precipitation of intermetallic compounds that cause embrittlement. However, if added in large amounts, workability and weldability will decrease, so W:0
．． O5 to 0.3%, particularly cL1 to 0.25% is preferred.

Although the AtU desorption effect is improved, adding a large amount impairs weldability and workability, so it is preferable to add 0.05% or less.

A high content of O does not adversely affect strength, ductility, and toughness, so it must be kept at 0.01% or less.

The steel of the present invention was heat treated at 1000 to 1100°C with a temperature of 0.
Normalize for 5 to 2 hours and heat at 720 to 780℃ for 1 to 4 hours.
Temper h. As a result of this heat treatment, the structure becomes entirely martensite.

Since the present invention is made of a material that prevents embrittlement and improves stress relaxation, it can be applied to boiler tube sheets.

〔Smile Shibe〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The invention is not limited to these examples.

Example 1 Table 1 shows comparison steels (scented 1 to 7) and steels of the present invention (scented 8 to 1).
6) Showing the chemical composition of 0. These steels were decomposed in A bath, rolled to a plate thickness of 20t, and 105
It was subjected to heat treatment of normalizing at 0° C. x 1 h and tempering at 760° C. x 1 h, and was subjected to an embrittlement test and a creep temporary pasting test. Note that the structure after heat treatment was completely martensite.

Example 2 Figure 2 shows S1 wrinkles (%, horizontal axis) and as-heat-treated and 550
3 is a graph showing the relationship between V notch Charpy absorbed energy (kgf-m, vertical axis) at 20° C. after heating for 3 DOOh. Heat treatment has almost no effect, but
When heated at 550℃ for 3000 hours, Si violet becomes 0.1%
Absorbed energy increases when below. In other words, heating embrittlement occurs! 1ll VC decreases.

Example 6 Figure 3 shows the Mn content (%, horizontal axis) and the as-heat-treated and 550
20 is a graph showing the relationship between V notch Charpy absorbed energy (kgf −m , vertical axis) at 20° C. after heating for 3000 hours. There is almost no effect up to heat treatment 1, but heating at 550° C. for 3000 hours increases. That is, heating embrittlement is less likely to occur.

Example 4 FIG. 4 is a graph showing the relationship between the absorbed energy (%, horizontal axis) of 1dsi+0.5Mn as-heat-treated and the absorbed energy Ckgf-m (vertical axis) after heating at 550° C. for 5000 hours. When the amount of Si+15Mn is 125% or less, almost no decrease in absorbed energy due to heating is observed.

Example 5 Figure 5 shows the W lid (%, horizontal axis) and the as-heat-treated and 550°C
, absorbed energy at 20℃ after heating for 3000h (
It is a graph showing the relationship between kgf·m1 (vertical axis). W is 0
．． If it exceeds 0.5%, the absorbed energy will increase, but 0.
．． If it exceeds 3%, the absorbed energy at 550° C. for 3000 hours will decrease.

Example 6 Figure 3 shows the comparison steel and the invention steel at 550°C for 5000h.
A graph showing the creep rupture strength of The creep rupture gi is the same for both the comparative steel and the steel of the present invention, but the creep rupture strength of Comparative Steel 7, which is indicated by ◇ in FIG. 3 and whose toughness has been improved by reducing N, is lower.

Example 7 Figure 7 shows a strain of 0.5 at 550°C. , 1% is a graph showing the relationship between time (h, horizontal axis) and relaxation of stress (~f/, , 2) (vertical axis). The steel of the present invention, which has improved toughness after high-temperature heating, easily relaxes stress and is effective in alleviating thermal stress generated in thick-walled materials.

〔Effect of the invention〕

According to the present invention, it is possible to provide a thick inner material that completely suppresses the decline in toughness due to embrittlement during use while ensuring high-temperature strength, and has excellent stress relaxation, so it is possible to provide a heat exchanger with a long life and high safety. , can provide fast reactor steam generators to the mark.

[Brief explanation of the drawing]

Figure 1-1 is a local cross-sectional view of the steam generator of a fast reactor;
Figure 2 is an enlarged view of the tube plate, Figures 1-3 are its longitudinal sectional views, and Figure 2
Figure 3 is a graph showing the relationship between 5BB1 and absorbed energy, Figure 3 is a graph showing the relationship between Mn wrinkles and absorbed energy, Figure 4 is a graph showing the relationship between Si+0.5Mn wrinkles and absorbed energy, and Figure 5 is a graph showing the relationship between Si+0.5Mn wrinkles and absorbed energy. FIG. 3 is a graph showing the creep rupture strength of comparative steel and steel of the present invention, and FIG. 7 is a graph showing stress relaxation. 1: Steam inlet, 2: Steam outlet, 6: Heat transfer tube, 4: Tube sheet Patent applicant Hitachi, Ltd.

Claims (1)

[Scope of Claims] 1. A heat exchanger consisting of a body, a tube plate, and a heat exchanger tube, and having a structure in which a plurality of heat exchanger tubes are gathered together by the tube plate at the inlet and outlet of steam flowing inside the tube. The tube sheet made of materials has a weight ratio of C: 0.05 to 0.3%, Cr:
8-10%, Mo: 0.8-2.0%, Ni: 0.5%
Below, N: 0.02-0.10%, P: 0.01% or less, S: 0.01% or less, Al: 0.05% or less, V: 0
．． 01 to 0.5%, Nb: 0.01 to 0.15%, however, contains V+Nb: 0.1 to 0.6%, and Mg
and/or Ca: 0.001 to 0.01%, S
i: 0.1% or less, Mn: 0.5% or less, and Si+
A heat exchanger characterized in that 0.5Mn: 0.25% or less, oxygen: 0.01% or less, and the balance contains Fe and inevitable impurities. 2. The heat exchanger according to claim 1, wherein the tube plate is made of a thick-walled material containing W: 0.05 to 0.3% by weight. 3. The heat exchanger according to claim 1 or 2, wherein the tube sheet is made of a thick-walled material with Mn: 0.1% by weight or less. 4. The heat exchanger according to any one of claims 1 to 3, wherein the heat exchanger is a fast reactor steam generator.