JPH03169497A - Austenitic stainless steel welding material having excellent creep rupture ductility and brittleness resistance - Google Patents

Abstract

PURPOSE:To provide a welding material for high temp. structure by constituting the welding material with the specific wt.% of C, Si, Mn, P, Cr, Ni, Mo, Al, N and the balance of Fe and making the specific vol.% of delta-ferrite quantity. CONSTITUTION:The welding material is constituted of <=0.03wt.% C, <=1% Si, <=3% Mn, 0.01-0.07% P, 14-20% Cr, 6-10% Ni, 2-3% Mo, <=0.04% Al, 0.06-0.18% N and the balance of Fe. Further, the composition of the welding material is constituted so that the delta-ferrite quantity in the welding material thus obtd. is in the range of 1-12vol.% found from the equation. In the equation, Creq=Cr+Mo+1.5XSi and Nieq=Ni+0.5XMn+30X(C+N). By this method, the welding material having excellent creep rupture characteristic can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a Ni-Cr austenitic stainless steel welding material having excellent creep rupture ductility and embrittlement resistance at high temperatures.

(Conventional technology) Structural materials for fast breeder reactors currently under development include:
Austenitic stainless steels such as SUS304 and SUS31B are used, and these structural materials are used in the creep temperature range. The main stress applied to the structural materials of fast breeder reactors is thermal stress due to temperature fluctuations.

Creep fatigue characteristics are important because the residual stress caused by this thermal stress is repeatedly applied to structural materials during high-temperature operation in which the stress is relaxed by creep. by the way,
It has been revealed that this creep fatigue property has a correlation with creep rupture ductility, and stainless steel used as a structural material for fast breeder reactors is required to have excellent creep rupture ductility.

As such a stainless steel, the present inventors have invented a 316 series stainless steel plate having excellent creep rupture ductility (see Japanese Patent Laid-Open No. 82-23348).

However, since fast breeder reactors are large welded structures, the welded metal parts are also required to have excellent creep rupture ductility. Conventional high-temperature welding materials, such as SUS Y31B, do not have sufficient creep rupture ductility because carbides precipitate during creep, and SUS Y3L6L, which has a low carbon content, has excellent creep rupture ductility but has poor creep rupture ductility. Their strength was low, and none of them could be said to be sufficient for the structure of a fast breeder reactor. Furthermore, in these welding materials, from the δ-ferrite phase introduced to prevent hot cracking during welding,
The sigma phase, which is a brittle phase, tends to precipitate, leading to a decrease in toughness.

(Question 8 to be solved by the invention) In this way, the conventional SUS Y31B or S
US Y318L-based welding materials are inadequate as structural materials for fast breeder reactors in terms of either creep rupture ductility or creep rupture strength, and embrittlement resistance. The reason for this is that for the SUSY31B steel, C present in the steel precipitates as carbide at the interface between the δ-ferrite and austenite phases during use at high temperatures, and the sigma phase precipitates from the δ-ferrite phase. Seki. I'm in charge. That is, carbides precipitated at the interface cause interfacial embrittlement, causing a decrease in ductility or deterioration of creep rupture strength, and in the SUSY ale L system, the amount of C, which is a reinforcing element, is low, so the creep rupture strength is not sufficient. Furthermore, there was a problem in that the sigma phase easily precipitated from the δ-ferrite phase, resulting in a decrease in toughness.

The present invention solves these problems and provides an austenitic stainless steel welding material that has excellent creep rupture ductility, strength, and embrittlement resistance at high temperatures.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and the gist thereof is (1) C: 0.030% by weight. Below, SI: 1.0% or less, Mn: 3.0% or less, P: 0.01 to 0.07
%, Cr: 14.0-20.0%, Ni: 6.0
~IO, 0%, Mo: 2. O ~3,0%, Aj7
Twenty. 04% or less, N: 0.06-0. The welding material is a welding material containing 18% of Fe, with the remainder substantially consisting of Fe, and δ-
The composition of the welding material is configured such that the amount of ferrite is in the range of 1 to 12% by volume as determined by formula 1 below. Austenitic stainless steel welding material with excellent embrittlement resistance.

δ-Ferrite amount -70.29+3.2XCr. ．． −0.031x(Ni
．． ．． )2+15.881XCr. JNi. q-0.02
08xCr. ,xNi. ,-(1) [However, Cr*@-
Cr + No + 1.5XSi, Ni-q-Ni
+0.5×Mn+30X (C×N)] (2) In weight%, C: 0.030% or less, Si: 1
．． o% or less, M n + 3. 0% or less, P:
0. OL~0.07%, Cr:14.0~20.0%
, Ni:8. O ~ 10.0%, Mo2 2,0 ~ 3.0%, Ajl: 0.04% or less, N
: 0.08~0. A welding material containing t8% and W: 3.0% or less, with the remainder substantially consisting of Fe,
and δ in the weld metal part obtained by the welding material
-The amount of ferrite is determined by the following formula 1 in volume %
Welding of an austenitic stainless steel having excellent creep rupture ductility at high temperatures and excellent embrittlement resistance at high temperatures, characterized in that the composition of the welding material is comprised in a range of 1 to 12%. material.

δ-ferrite 'm-70.29+3.2XCr. -0.081X (NI.
q) 2+15.661xCr. Q/Ni*. -0.02
08xCr*, xNie. ”' (1) [However, Cr.
, -Cr+Mo+0.5×W+1.5XSi, Ni-q
-Ni + 0.5x Mn + 30x (C 1N)
〕It is in.

(Function) The technical basis for specifying the requirements of the present invention will be explained below.

The inventor conducted a systematic investigation on the chemical fraction and the amount of δ-ferrite with respect to the creep rupture characteristics of a welded metal part. Figures 1(A) and 1(B) show the influence of C and N amounts on creep rupture properties (test temperature: 550°C). (
A) It can be seen from the figure that by lowering C, the creep rupture ductility improves and the creep rupture strength decreases. On the other hand, for N, as shown in figure (B), C is 0.05
%, creep rupture strength increases with Nffi, but creep rupture ductility decreases. On the other hand, in a system with a low C content of 0.Ol%, the creep rupture strength improves with Nffi, but the creep rupture ductility does not decrease. That is, the possibility of developing a welding material with excellent creep rupture strength and creep rupture ductility was discovered by changing the reinforcing element from C to N.

Figure 2 shows such a low C material with excellent creep rupture properties.
High-N system (0.01%C-0.08%N-8%Ni-1
8%Cr-2.1%Mo) shows the influence of P on the creep rupture properties of weld metal parts.

It can be seen that by adding P, both creep rupture strength and creep rupture ductility are improved.

Hot cracking is a problem in welding austenitic stainless steel, and as a countermeasure to this problem, δ-ferrite is usually introduced into the weld metal. This δ
-As mentioned above, ferrite serves as a propagation path for creep cracks, so it is thought to have an effect on creep rupture characteristics. FIG. 3 shows the influence of the amount of δ-ferrite on the creep rupture characteristics, and it can be seen that there is an optimum value for the amount of δ-ferrite with respect to the creep rupture characteristics. In other words, in the conventional 0606%C-0.02%N system, carbide precipitation occurs during creep, so δ
- Although the influence of ferrite is significant, even in the 0.01% C-0.11% N system with improved creep rupture ductility, an optimum amount of δ-ferrite still exists, although the amount of change is somewhat small.

From the above research results, we found the possibility of creating a welding material with excellent creep rupture ductility that has creep rupture strength comparable to that of conventional materials.However, we need to study ways to further increase creep rupture strength without impairing creep rupture ductility. I did it. As a method for strengthening without impairing creep rupture ductility, solid solution strengthening is optimal, and N was used as a representative element, but other elements must be considered because N precipitates at 0.18% or more.

The present inventors selected W as an element with a high solid solution strengthening ability and high solubility, and investigated its effects. Figure 4 shows the results, 0.01%C-0
．． It can be seen that the creep rupture strength is improved by adding W to the 07%N-9%Ni-18%Cr-2,1%Mo system. However, if added in a large amount, the creep rupture ductility decreases, but this is due to the precipitation of intermetallic compounds containing W.

The reasons for limiting each component in the present invention will be described below.

First, in the component system of the present invention, C is an effective strengthening element, but since it precipitates as a carbide at the interface between the δ-ferrite and austenite phases, it impairs high-temperature mechanical properties such as creep rupture properties after long-term use at high temperatures. It is also a damaging element. From this point of view, Cffi was determined to be 0.030% or less, but if particularly high creep rupture ductility is required, it is desirable to set it to 0.020% or less.

Next, S1 is necessary as a deoxidizer, but if it exists in excess of more than 1.0%, it increases hot cracking susceptibility, so this value was set as the upper limit.

Mn is a deoxidizing element and at the same time has the effect of improving hot workability by fixing S in steel, but at 3%
If it exceeds this value, the creep rupture strength decreases, so this value was set as the upper limit.

P is an effective element in terms of creep rupture ductility because it precipitates in crystal grains as phosphide during high temperature holding and has a strengthening effect, and also has the effect of strengthening the phase interface. Since it occurs from 0.Ol%, the lower limit is set to 0.
It was set as 01%. However, since excessive addition significantly impairs weldability and hot workability, the upper limit has been set at 0.07%.
And so. In addition, especially when creep rupture ductility is required, it is desirable that the amount of P be 0.02% or more.

Ni is an essential element as an austenite forming element, and in order to control the amount of δ-ferrite within a predetermined range,
It is an element that is adjusted according to formula 1 in terms of composition balance with respect to the amount of Cr, which is a ferrite-forming element, and has the effect of suppressing the precipitation of σ-1 phase and χ-1 phase that deteriorate creep rupture properties, so it is 6% That's all. Addition of 10% or more causes δ
- As a result of increasing Crffi necessary for controlling the amount of ferrite, the overall alloy amount will be significantly increased, impairing weldability, so the upper limit was set at 10%.

Cr is an element that increases oxidation resistance, and for that purpose, l
4% or more is required, but if it exceeds 20%, the precipitation of the sigma phase from the δ-ferrite phase will be promoted during long-term heating at high temperatures, causing embrittlement due to the sigma phase, so the upper limit was set at 20%.

Mo is an element that has a solid solution strengthening effect, but at 2.0%
If it is less than 3.0%, it is insufficient, and if it exceeds 3.0%, it will cause embrittlement due to long-term heating at high temperatures, so the upper limit should be set at 3.0%.
And so.

L is a strong deoxidizing element, but if it is added in excess of 0.04%, it will combine with N in the steel due to high temperature and long-term heating.
The upper limit was set at 0.04% because it would distort the DN and impair creep rupture ductility.

N is an element that has a large solid solubility limit in austenitic stainless steel and has a strong solid solution strengthening effect.

Since this effect is more pronounced than 0.0B%, the lower limit was set at 0.06%. In addition, since adding more than 0.18% of N causes nitride precipitation during high-temperature use,
The upper limit was %.

The above is the basic breakdown system in the present invention, but in the present invention, it is effective to contain W within a predetermined range in order to further increase the strength. That is, since W has a solid solution strengthening effect like Mo and has a large solid solubility limit, it is an element that can increase creep rupture strength without impairing creep rupture ductility. However, 3.0%
If this value is exceeded, intermetallic compounds will precipitate during high-temperature use, reducing creep rupture ductility. Therefore, this value was set as the upper limit.

In addition to the above chemical fractionation, the amount of δ-ferrite must be at least 1% in order to ensure creep rupture ductility and to prevent hot cracking during welding. On the other hand, if the content of δ-ferrite exceeds 12%, the creep rupture ductility is impaired, so the upper limit was set at 12%.

Calculation of the amount of δ-ferrite in the present invention is based on Equation 1.

For each partial concentration used in the calculation of Equation 1, the concentration in the welding material is applied. The welding material of the present invention is applied to a base metal whose composition is close to that of the welding material, and welding is performed using a welding method that has little effect on the base metal composition or weld metal composition, so the weld metal composition can be almost reflected in the welding material composition. .

The effects of the present invention will be described in more detail below based on Examples.

(Example) Table 1 shows the chemical compositions of the welding materials of the present invention, comparative welding materials, and base metals. Table 2 shows welding conditions and actual measured values of δ-ferrite. The measured value of δ-ferrite is almost close to the value calculated from the set of welding materials. Table 3 shows the tensile properties and creep rupture properties at 550°C for the steels shown in Table 1. As is clear from these property investigation results, the welding material of the present invention is superior in creep rupture strength and creep rupture ductility after long-term use at high temperatures compared to comparative materials.

Table 2 (Effects of the Invention) As stated above, the welding material of the present invention has superior creep rupture properties compared to conventional welding materials, and is suitable for high-temperature structures used in creep regions. It is industrially extremely effective as a welding material.

[Brief explanation of the drawing]

Figure 1 (A). (B) is a diagram showing the influence of C and N content on creep rupture properties, Figure 2 is a diagram showing the influence of P content on creep rupture properties, and Figure 3 is a diagram showing the influence of δ-ferrite content on creep rupture properties. 4 are diagrams showing the influence of the amount of W on the creep rupture characteristics.

Claims (2)

[Claims] (1) In weight%, C: 0.030% or less, Si: 1.0
% or less, Mn: 3.0% or less, P: 0.01 to 0.07
%, Cr: 14.0-20.0%, Ni: 6.0-10
．． 0%, Mo: 2.0-3.0%, Al: 0.04% or less, N: 0.06-0.18%, and the remainder is a welding material consisting essentially of Fe, and A high-temperature method characterized in that the components of the welding material are configured such that the amount of δ-ferrite in the weld metal part obtained by the welding material is in the range of 1 to 12% by volume % determined by the following formula 1. An austenitic stainless steel welding material with excellent creep rupture ductility at high temperatures and excellent embrittlement resistance at high temperatures. δ-ferrite amount = -70.29+3.2×Cr_e_q-0.031×(
Ni_e_q)^2+15.661×Cr_e_q/N
i_e_q−0.0208×Cr_e_q×Ni_e_
q...(1) [However, Cr_e_q=Cr+Ho+1
．． 5×Si, Ni_e_q=Ni+0.5×Mn+30
×(C+N)] (2) In weight%, C: 0.030% or less, Si: 1.0
% or less, Mn: 3.0% or less, P: 0.01 to 0.07
%, Cr: 14.0-20.0%, Ni: 6.0-10
．． 0%, Mo: 2.0 to 3.0%, Al: 0.04% or less, N: 0.06 to 0.18%, and W: 3.0% or less, with the remainder being substantially The welding material is a welding material made of Fe, and the composition of the welding material is adjusted so that the amount of δ-ferrite in the weld metal part obtained by the welding material is in the range of 1 to 12% by volume % determined by the following formula 1. An austenitic stainless steel welding material having excellent creep rupture ductility at high temperatures and excellent embrittlement resistance at high temperatures. δ-ferrite amount = -70.29+3.2×Cr_e_q-0.031×(
Ni_e_q)^2+15.661×Cr_e_q/N
i_e_q−0.0208×Cr_e_q×Ni_e_
q...(1) [However, Cr_e_q=Cr+Mo+0
．． 5×W+1.5×Si, Ni_e_q=Ni+0.5
×Mn+30×(C+N)]