JPS591786B2 - Steel for reactor vessels - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel resistant to radiation damage used in the manufacture of vessels for water-cooled power reactors (power reactors), which steel is subjected to neutron irradiation during use. It may also be used in other equipment whose structural materials are subjected to

The present invention is easily adapted for application in the manufacture of vessels for water-cooled high power reactors.

According to the prior art, steels previously used in nuclear reactor construction or specially developed for pressure vessels such as boiler shells and steam generator drums have improved resistance to radiation damage when exposed to radiation during service. show.

However, when used for a long time, the aforementioned steel becomes 2, OX
It has been found that the reactor vessel material tends to be less brittle when subjected to irradiation doses in excess of 1 o''N/CrIL (at a temperature of 290°C).

This considerably reduces the impact strength and significantly increases the transition temperature of the aforementioned materials.

As a result, the operational reliability and durability of the nuclear reactor become very poor.

Additionally, steels used for similar purposes known to those skilled in the art have the following compositions (% by weight):

i.e. 0.06-0.15% carbon, 0.15-0
．． 4% manganese, 0.16-1% silicon, 2.5-
8% nickel, 0.25-1.25% molybdenum,
0.5-0.9% chromium, 0.015% or less phosphorus,
0.015% or less sulfur, 0.08% or less aluminum, 0.006% or less nitrogen, 0.004% or less oxygen, and the balance iron.

However, the above-mentioned steel has an irradiation dose of 4 x 101
Applicable only to pressures not exceeding 9N/ff1 (E≧0.5MeV).

Steels with the following compositions (% by weight) have the highest properties.

Carbon 0.13 - 0.18 Manganese 0.3 - 0.6 Silicon 0.15 - 0.3 Nickel 1.0 - 1.6 Lirom 1.6 - 2.5 Upper 2° Den 0.5 ~0.7 Vanadium 0.01~0.12 Cerium 0.002~0.04 Copper 0.01~0.1 Antimony 0.0005~0.009 Tin 0
．． 0005～0.009 Phosphorus 0.002～
0.01 sulfur 0.001~0.01 iron balance 0.004~0.02 arsenic as an additive in the above-mentioned steel
Contains % by weight.

A steel of the above composition can be used at a temperature of 300 to 350° C. and an irradiation dose of 1×10 2 ON/C111 (E≧0.5 MeV).

A disadvantage of the steels referred to above is their susceptibility to embrittlement when exposed to radiation.

It is therefore an object of the present invention to overcome the above-mentioned drawbacks.

The object of the present invention is the resistance to radiation damage and therefore the flux (b) in the temperature range from 250 to 350°C.
lux) is 2x1o”ON/i (E≧0, 5 MeV)
To provide a steel for nuclear reactor vessels which will ensure improved operational reliability and durability of high power reactors whose vessels are subjected to severe service conditions. This is achieved by

In other words, this steel consists of iron, carbon, silicon, manganese,
A steel having a composition of chromium, nickel, molybdenum, vanadium, copper, antimony, cast iron, phosphorus, and arsenic, and according to the present invention, the above-mentioned components are contained in the following content (% by weight): Carbon 0.13 to 0 .18 Silicon 0.15-0.3 Manganese 0.3-0.6 Liromium 1.6-2.5 Nickel 1.0-2.0 Molybdenum 0.5-0.7 Vanadium 0.01 ~0.12 Copper 0.01~0.05 Antimony 0.0005~0.009 Tin 0
．． 0005~0.009 phosphorus o, ooi
~0.005 Arsenic 0.00
05 0.002 iron An atom characterized in that the total amount of phosphorus and arsenic, which is the balance and is contained in the above-mentioned composition, is expressed by the following relationship: P +5 As≦1xlO”% by weight It is steel for furnaces.

A chromium content of 1.6 to 2.5% by weight improves the hardenability, ensures uniformity of strength and ductility, increases impact strength and lowers the transition temperature.

If the chromium content in the steel is less than 1.6% by weight, the required mechanical properties of the steel, in particular the strength properties and critical low temperature brittleness, cannot be achieved.

It is undesirable for the chromium content to be more than 2.5% by weight, since this leads to the formation of complex carbides and, therefore, to a decrease in impact toughness.

A nickel content in the range of 1.0 to 2.0% by weight provides the necessary mechanical strength and viscosity (toughness) in large thickness forgings.

When the nickel content in the steel is lower than 1.0% by weight, the strength and viscosity of large thickness forgings are insufficient.

Conversely, if the nickel content is greater than 2.0% by weight, the resistance to irradiation will be weakened.

The molybdenum content in the steel in the range of 0.5 to 0.7% by weight, together with chromium and nickel, provides the steel with the necessary strength and sufficiency for long-term service in the temperature range of 250 to 350 °C. provides excellent thermal stability.

If the molybdenum content in the steel is lower than 0.5% by weight, the thermal stability and strength of the steel will decrease.

Conversely, if the molybdenum content is more than 0.7% by weight, the impact strength will drop sharply.

A carbon content of 0.13 to 0.18% by weight in the steel
without lowering the critical temperature of brittleness or with a thickness of 65
It is possible to manufacture steel characterized by increased strength without impairing the processing characteristics of forged products of 0 mm or more.

If the carbon content in the steel is lower than 0.13% by weight, the strength is reduced.

Conversely, if the carbon content in the steel is more than 0.18% by weight,
Impact strength (elasticity) is significantly reduced.

A silicon content in the steel within the above range (0.15 to 0.3% by weight) allows complete deoxidation and the production of dense steel ingots.

If the silicon content in the steel is lower than 0.15% by weight, deoxidation is incomplete.

Conversely, if the silicon content in the steel is more than 0.3% by weight,
This will result in the formation of non-metallic inclusions that will adversely affect impact toughness.

A manganese content of 0.3 to 0.6% by weight provides the necessary strength and yield point.

If the manganese content in the steel is lower than 0.3% by weight, its strength and yield point will decrease.

Conversely, a manganese content greater than 0.6% by weight has a detrimental effect on the weldability of the steel.

A vanadium content of 0.01 to 0.12% by weight ensures a fine grain structure of the steel, which increases the impact toughness and lowers the transition temperature of the steel.

If the vanadium content is lower than 0.01% by weight, strength and weldability are reduced.

A vanadium content of more than 0.12% by weight increases the tendency to brittle fracture and increases the transition temperature.

0.0005 to 0.002% by weight arsenic content and 0.001 to 0.005% by weight phosphorus content.
In combination with a copper content of 0.01 to 0.05% by weight, this ensures a high resistance of the steel to radiation damage and considerably improves the mechanical and service properties of the steel.

If the arsenic content in the steel is more than 0.002% by weight, it significantly worsens the resistance of the steel to radiation.

Reducing the arsenic content below 0.0005% by weight is undesirable, as it requires a charge of extra purity and makes the steel considerably more expensive.

If the phosphorus content in the steel is more than 0.005% by weight,
Makes steel's resistance to radiation considerably worse.

Reducing the phosphorus content below 0.001% by weight is undesirable since it requires a charge of special purity and makes the steel considerably more expensive.

Similarly, if the copper content in the steel is greater than 0.05% by weight, it significantly impairs the resistance of the steel to radiation.

Reducing the copper content below 0.01% by weight is undesirable, as it requires a charge of extra purity and makes the steel considerably more expensive.

The total amount of phosphorus and arsenic contained in the steel of the present invention is expressed by the following relational expression.

p+5As≦1×10−2 wt% If this relational condition is fulfilled, the steel with the proposed composition has good technical properties and the 250 in wire bundle
It is aimed at manufacturing high-pressure cases (containers) for high-power reactors that are used for long periods at operating temperatures of 350 to 350°C.

A total content of phosphorus and arsenic greater than 0.01% by weight worsens the resistance of the steel to radiation.

The antimony content is preferably 0.0005 to 0.009% by weight, and the antimony content in the steel is preferably 0.0005 to 0.009% by weight.
．． If the amount is more than 0.09% by weight, thermal embrittlement of the forged product with a large thickness will occur.

Reducing the antimony content below 0.0005% by weight is undesirable since it requires a charge of extra purity and makes the steel considerably more expensive.

Similarly, it is preferred that the tin content is between 0.0005 and 0.009% by weight, with the tin content in the steel being 0.009% by weight.
If the amount is more than % by weight, thermal embrittlement of the forged product with a large thickness will occur.

Reducing the tin content below 0.0005% by weight is undesirable since it requires a charge of extra purity and makes the steel considerably more expensive.

The main component of steel is iron.

In addition to the above-mentioned components, the steel proposed herein contains the following additives (wt%): sulfur, o, oio or less, antimony, 0.009 or less, tin, 0.009 or less.

A sulfur content of more than 0.01% by weight increases the tendency to brittle fracture.

The steel of the invention is produced in an open hearth or electric arc furnace using conventional melting methods using suitably treated charge materials.

When going through the process of melting steel in an open hearth, first molten steel is made in a basic open hearth, and then molten steel with a specified content, particularly low content of phosphorus and arsenic, is obtained in an acidic open hearth.

In addition, when going through the process of melting steel in an arc furnace, molten steel with a specified content is obtained by a complete oxidation method in a basic arc furnace.

The molten steel thus obtained is cast into a mold in a vacuum chamber (processed by the so-called vacuum steel ingot casting method) to obtain a cast product (steel ingot) of forgeable quality.

Four examples are shown in Table 1.

The first three examples relate to the folding invention and represent embodiments of the proposed chemical composition of steel, and the fourth example is for comparison and represents the chemical composition of the prior art. There is.

Table 1 also shows the changes in steel properties due to the proposed deformation mode in the chemical composition.

As is clear from Table 1, Examples 1 to 3 according to the present invention
Unlike the comparative example 4, this steel is characterized by a higher irradiation resistance.

The steel composition of Example 1 has a total content of P+5As=5xlO-3% by weight, and the steel is irradiated with a neutron flux of 2 x 102 ON/d (E≧0.5 MeV, 250 to 290
℃), i.e. there is no change in its transition temperature (which is 0 ℃).

For the steel composition of Example 2, P+5As=0.7xlO-3% by weight
under the same irradiation conditions as in Example 1, the steel becomes slightly brittle, i.e. its transition temperature change is 1
It is 0°C.

For the steel composition of Example 3, P+5As=1.0X10''wt%
The steel is embrittled to some extent under the same irradiation conditions as in Example 1, but the change in its transition temperature is 30 °C.

Further embrittlement is not desirable.

On the other hand, in the case of Example 4 (comparative example), the steel composition has a total content of P+5As=3xlO-2% by weight, and under the same irradiation conditions as Example 1, the transition temperature change of the steel is 90 °C. However, this steel does not meet the requirements placed on vessel steels for the manufacture of high power reactors.

Claims (1)

[Claims] 1 The following composition (wt%): Carbon 0.13 to 0.18% Silicon 0.15 to 0.3% Manganese 0.3 to 0.6% Lirom 1.6 to 2 .5% Nickel 1.0 - 2.0% Upper 2° Density 0.5 - 0.7% Vanadium 0.01 - o, 12% Copper 0.01 - 0.05% Antimony 0.0005 - 0.009 %tin
0.0005-0.009% Phosphorus o, ooi
~ 0.005% Arsenic 0.000
5 to 0.002% and a balance of iron, and the total amount of phosphorus and arsenic in the composition is represented by the following formula: % formula %.