JPS595860B2 - Method for determining embrittlement of austenitic stainless steel weld metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining embrittlement of austenitic stainless steel weld metal.

The composition of austenitic stainless steel weld metal is adjusted to contain an appropriate amount of δ-ferrite structure to prevent hot cracking during welding, but this δ-ferrite remains after welding. When heated in some way, such as by heat treatment or use at high temperatures, a very hardened and brittle phase (called sigma embrittlement)
This can lead to the destruction of structures such as equipment. Note that the degree of this σ phase embrittlement varies depending on the heating temperature or heating time. Conventionally, the degree of embrittlement has been determined by destroying a test piece manufactured according to the manufacturing and usage conditions of the structure, or by destroying a test piece actually cut out from the structure. Especially in the latter case, it damages the structure and significantly impairs the quality of the structure.

Therefore, there has been a need for a method for easily quantitatively determining the degree of embrittlement without damaging the structure. The present inventors conducted extensive research in response to such a request, and as a result, they discovered a method for easily and nondestructively quantitatively determining the degree of embrittlement due to heating of austenitic stainless steel weld metal. That is, the method of the present invention is characterized in that the presence or absence of embrittlement in an austenitic stainless steel weld metal is determined based on whether the amount of δ ferrite contained in the weld metal has decreased by 5% or less. Embodiments of the present invention will be described with reference to the drawings. The horizontal axis represents the amount of δ ferrite initially contained in the weld metal as measured by a ferrite meter, and the vertical axis represents the amount of decrease in δ ferrite, which is the basis of the present invention.

That is, the amount of δ ferrite was measured after heat treatment or during heating use, and the value obtained by subtracting the value from the initial amount of ferrite is displayed on the vertical axis. Note that the amount of δ ferrite can be easily measured from the weld metal surface using this ferrite meter without destroying the structure. As is clear from the drawings, the austenitic stainless steel weld metal was heat treated at 700°C for 5 hours (q), 15 hours (B) and 30 hours, but due to the amount of initial ferrite or changes in heating conditions. Regardless, if the amount of reduction in δ ferrite is 5% or more, cracks may occur in the weld metal, but if the amount of reduction is 5% or less, no cracks will occur. That is, the degree of embrittlement of the austenitic stainless steel weld metal can be evaluated by measuring the amount of decrease in the amount of δ ferrite from the initial amount of δ ferrite. Also, the above temperature is 700℃
Generally, when the base material is ferritic steel and the weld metal is a dissimilar metal such as stainless steel to make a joint, the annealing temperature is 600~
It is carried out at 700°C, and as the temperature increases, it tends to become brittle. Therefore, in the present invention, 70
0°C is selected, but even if heat treatment is performed at any temperature, for example in the range of 500 to 800°C, the weld metal will become brittle by reducing the amount of δ-ferrite reduction to 5% or less. Never. Also, in the drawings, the heat treatment time was 5 hours, 15 hours, and 30 hours, but the heat treatment temperature and storage time are generally determined depending on the material of the base material, plate thickness, etc., for example, 700°C. For materials heat treated for 15 hours at
In order to reduce the amount of ferrite reduction to 5% or less, the initial δ
A material with a ferrite content of 9% or less must be used.

Therefore, if a material containing an initial amount of δ ferrite of 10% or more is heat treated at the specified 700° C. for 15 hours, cracks will occur. As detailed above, the present invention has extremely great practical effects, such as being able to easily determine the embrittlement of a welded part of weld metal from the surface without destroying the structure. It is something.

[Brief explanation of the drawing]

The drawing is a curve showing the relationship between the initial amount of δ-ferrite and the amount of decrease in δ-ferrite for explaining one embodiment of the method for determining embrittlement of an austenitic stainless steel weld metal according to the present invention.

Claims (1)

[Claims] 1. Embrittlement of austenitic stainless steel weld metal, characterized in that the presence or absence of embrittlement in austenitic stainless steel weld metal is determined by the decrease in the amount of δ ferrite contained in the weld metal becoming 5% or less Judgment method.