JPS58130250A - Ferritic iron and steel material having improved brittleness caused by irradiation of neutron, and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a ferrite iron and steel material used for an atomic reactor pressure vessel, etc., which is obtained by adding a trace of Ti or/and Al into the ferrite iron and steel material, and has improved brittleness caused by irradiation of a neutron. CONSTITUTION:In a component adjusting process in case of melting and making ferrite iron and steel, a ferrite iron and steel material which has improved brittleness caused by irradiation of a neutron is obtained by adding a trace of Ti or/ and Al. As a result, in a state that impurity elements of Cu, P, S, etc. remain contained, brittleness caused by irradiation of a neutron due to the presence of these impurity elements of a very small quantity is improved remarkably, by a very simple method. Also, as for this iron steel material, its brittle state can be restored remarkably by annealing treatment, and it can be utilized effectively for an atomic energy industrial field.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvement of material deterioration due to neutron irradiation of ferritic steel materials used in nuclear reactor pressure vessels and the like.

Ferritic steel materials, represented by low-alloy steel and carbon steel, have traditionally been used as constituent materials for equipment that is exposed to neutron irradiation, such as the pressure vessels of nuclear reactors, and have the chemical compositions shown in Table 1. ing. However, as is well known in this steel material, due to the impurity elements contained in it, such as copper (Cu), phosphorus (P), sulfur (8), and vanadine M, ductility and toughness deteriorate when irradiated with neutrons. It causes so-called embrittlement such as low-density, which leads to deterioration of the material.
This may cause unexpected accidents. Therefore, when manufacturing pressure vessels and other equipment, careful examination of materials is essential from the standpoint of maintaining safety. However, the recent trend is toward an increase in the content of impurity elements, and countermeasures are being taken to prevent this. is becoming inevitable.

Therefore, for example, for copper (Cu), we carefully select scrap, that is, scrap steel, which is the raw material, and for phosphorus (P).
), for remaining impurity elements such as sulfur (S),
A special refining process is installed inside and outside the melting furnace to eliminate as much as possible, but this inevitably leads to an increase in manufacturing costs and an unavoidable increase in the cost of pressure vessels and other products. There is a certain drawback.

The present invention does not require any special considerations for the removal of impurity elements, which would lead to an increase in product cost, and uses an extremely simple method of adding a trace amount of a specific alloying element. This work was done by demonstrating that a ferritic steel material with less embrittlement due to neutron irradiation can be obtained. Next, the details will be explained using the drawings.

The present invention is made by an extremely simple method in which a trace amount of titanium (Ti) and/or aluminum (AJ), which are usually easily obtained, is added in the component adjustment step C2 during melting of steel. This feature significantly improves the embrittlement caused by neutron irradiation caused by the inclusion of trace impurity elements such as copper, phosphorus, and sulfur.
This study was made based on the fact that embrittlement can be significantly recovered by annealing, and this work also makes a significant contribution to the recently proposed annealing process for pressure vessels to recover from embrittlement.

Table 2 shows the results of a comparative experiment showing how the yield stress, tensile stress, and total elongation change during neutron irradiation for conventional steel materials and the steel material of the present invention, and the figure shows how the yield stress, tensile stress, and total elongation change during neutron irradiation. These are the results of a comparative experiment on the recovery behavior of oxidation. In addition, Table 3 shows the chemical composition of the steel materials used in the above-mentioned specific axis experiment results. In the table, the middle grade 0 is made by carefully selecting the scrap mentioned above and undergoing a special refining process to reduce Cu and P. It shows conventional steel materials with low S content, etc. The column below shows so-called A38 steel, which is currently used as reactor pressure vessel steel.
Standard values for the material composition of 3B steel are shown for reference. In addition, in the table, 5C indicates a steel material in which 0.5% by weight of copper is added to a zero steel material in order to investigate the influence of the inclusion of impurity elements, and 5C5A indicates a 1°C steel material ζ with copper added; 0.5% by weight of elemental aluminum (Al
) is added. Also, 5C5T is 0.0% compared to 5C steel.
Steel material with 5% by weight of titanium (Ti) added, 5C10T
is a steel material to which 1.0% by weight of titanium (T) is added to the above 5C steel in Table 2.

In addition, 5P in the table is a steel material that has been subjected to f'1 by adding 05% by weight of phosphorus (p) to O steel material in order to clarify the influence of phosphorus, and 5P5A is a steel material that has been subjected to f'1 by adding 05% by weight of phosphorus (p) to 5P steel material. It is a steel material made by adding (Al).

As Table 2 reveals, all of the steels tested were 11x l On, which is normally expected in a reactor pressure vessel.
/cTl and 1.2X10 n /crI (E>
1 & V) increases the yield stress and tensile stress upon neutron irradiation. In addition, the total elongation, which is largely related to embrittlement, decreases in all steel samples, but in particular, in 5C steel containing a trace amount of copper (Cu), it is 25.1% when not irradiated, but when irradiated with neutrons, it is 25.1%. 6.9% (
1,1xlo n/c++ri, 17% (1,2x10
n/crI), which showed the smallest value, and 5P steel containing a trace amount of phosphorus (p) showed the next smallest value, and the promotion of embrittlement caused by silver candles was clearly seen.

On the other hand, trace amounts of aluminum (A/) and titanium (Ti) were added to 5C steel. The decrease in total elongation was significant for 5c5A steel and 5C5T steel.

For example, in 5C5A steel, it is 9.9 cm,
5.3%, and 11.6% in 5C5T steel, 51
%, which is an improvement to a value close to 134% and 6.2% for 0 steel, which is steel containing low impurity elements. Similar results were also shown for 5C10T, in which the amount of titanium (Ti) added was greater than that of 5C5T.Furthermore, in 5P steel containing phosphorus, the total elongation was 0% of that of steel, but when aluminum (Al) was added, In the case of 5P5A with the addition of υ, it was 61%, which is close to 62% of the O steel material, showing a remarkable improvement.

Although not shown in Table 2, it can be easily inferred from the above results that an improvement effect is also exhibited when both aluminum (Al) and titanium (T1) are added. It has been clearly shown that the addition of alloying elements has a significant effect on reducing the total elongation, that is, improving embrittlement, caused by impurity elements.

Next, the figure shows steel materials 5C15C5A and 5C5T shown in Table 3.
, 1 for 5 CIOT. lX10 n/c++! (
These are the results of investigating the recovery behavior of total elongation when annealing was performed for 1 hour after neutron irradiation (E>1 MeV). As is clear from this, the A curve group plotted with white marks indicating the non-irradiated state and the B curve group plotted with black marks indicating the state during neutron irradiation, the annealing temperature The degree of recovery of the total elongation decreased by neutron irradiation increases as the 5C5A, 5C5T,
The recovery of 5C10T steel is remarkable, and the annealing temperature is 600℃.
(873°K), it has been shown that the elongation almost recovers to the full elongation when not irradiated.

This shows that application of annealing treatment to pressure vessels is an extremely advantageous condition for maintaining its strength2.

By the way, as in the present invention, titanium (T1) aluminum (
It is currently difficult to give a clear explanation as to why the addition of a small amount of Al) contributes to improving neutron irradiation embrittlement, but it is probably due to the addition of a small amount of titanium and aluminum that changes the state and properties of the internal composite. This is thought to be due to a change that weakens the susceptibility to embrittlement due to neutron irradiation. This can be seen in the attached reference photos, that is, the O steel material with low impurity content in Table 3, the 5C steel material with copper added to it, and this 5C steel material.
5C5T of the present invention with a trace amount of titanium (TI) added to steel
Steel material, when not irradiated with neutrons and 1.2 x 1020
This is considered to be evidenced by the photograph of the internal structure taken during neutron irradiation of n/crd (E>I Me V ). That is, photos (a), (b), (c), and (d) of O steel material and 50 steel material when not irradiated and when irradiated, and 5C5
As is clear from the comparison of the photo tel (f) of the T steel material when it is not irradiated and when it is irradiated, in the case of the 5C5T steel material, due to the addition of a trace amount of titanium (T), titanium carbide (TiC) with a grain size of around 02 μm is ) was observed, and this is thought to be due to the formation of an internal state with low neutron irradiation sensitivity, but this can easily be seen in ferritic low-alloy steels and carbon steels other than those shown in the examples above. Therefore, it can be inferred that neutron irradiation embrittlement, which is promoted due to the inclusion of trace amounts of impurity elements such as copper and phosphorus, will be improved for ferritic steel materials other than the examples.
;(I can do 1.

As is clear from the above explanation, according to the present invention, there is no need for any special consideration for removing impurity elements, which would lead to an increase in product costs, and the composition of the identified trace alloying elements is adjusted. Ferritic steel materials that contain impurity elements and are less susceptible to embrittlement due to neutron irradiation can be obtained by an extremely simple method of adding ferritic materials, making a remarkable contribution to the field of atomic crab industry.

[Brief explanation of the drawing]

The figure is a diagram showing the relationship between total elongation and annealing temperature, showing the recovery behavior of embrittlement caused by annealing treatment.

Claims (2)

[Claims] (1) A ferritic steel material with improved embrittlement due to neutron irradiation, which is characterized by adding a small amount of titanium or aluminum or both to the ferritic steel material to improve embrittlement caused by neutron irradiation. (2) A method for producing a ferritic steel material that improves neutron irradiation embrittlement, which is characterized by using a small amount of titanium in the component adjustment process during steel manufacturing.