JPH11211637A - Method for testing triaxial creep rupture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain data of a creep rupture in a state in which triaxial stress is applied. SOLUTION: In obtaining data of a triaxial creep rupture, a welded joint of Cr-Mo steel is utilized and a smooth test piece 11 is placed in a direction at right angles to the welding. A uniaxial load is applied to the smooth test piece 11, and the generation of cracks is detected by an ultrasonic inspection or electric resistance method. Moreover, a stress state of a part where the cracks are generated in the smooth test piece 11 is obtained by a creep analysis with creep characteristics at each part of the welded part taken into consideration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a triaxial creep rupture test method, and more particularly to a test method for acquiring basic data for design and evaluation of high-temperature equipment such as a thermal / nuclear power plant.

[0002]

2. Description of the Related Art For the design and evaluation of high-temperature equipment such as thermal power plants and nuclear power plants, creep rupture data of materials used in such equipment is indispensable. The most basic design data is obtained by a uniaxial test using a round bar test piece 1 as shown in FIG. In this test, usually, the round bar test piece 1 is heated in the electric furnace 2, the time until the specimen is broken by applying a load is measured, and the relationship between the load (stress) and the fracture time shown in FIG. Used for

[0003]

However, in general, the operating conditions of high-temperature equipment are in a multiaxial stress state, and it is necessary to obtain a relationship between a single-axis state and a multiaxial state. Therefore, a test under a biaxial stress condition is often performed by applying an internal pressure or an internal pressure and an axial load to a cross-shaped test piece as shown in FIG. 7 or a cylindrical test piece as shown in FIG.

By the way, in order to reproduce the conditions of the actual machine as it is, a test under a triaxial stress state is necessary. For the test under a triaxial stress state, a cross-shaped test piece shown in FIG. Axialization and tests using this test piece have been attempted. However, it is difficult to process the test piece, or it is difficult to break it from the test object part during the test, and it is inevitable that almost all of the test piece will break from the jig for load application, and creep rupture in triaxial stress state Successful data acquisition has been extremely difficult.

The present invention has been made in view of such circumstances, and after arranging a smooth test piece in a direction perpendicular to the welding direction by using a Cr-Mo steel welded joint, a uniaxial load is applied to the smooth test piece. By detecting crack initiation by ultrasonic inspection or electrical resistance method and determining the stress state of the crack initiation site in the smooth specimen by creep analysis considering the creep characteristics of each part of the weld, the triaxial stress An object of the present invention is to provide a triaxial creep rupture test method capable of acquiring creep rupture data in a state.

[0006]

According to the present invention, there is provided a triaxial creep rupture test method for acquiring triaxial creep rupture data, in which a smooth test piece is arranged in a direction perpendicular to a weld by using a Cr-Mo steel welded joint. After that, a uniaxial load is applied to this smooth specimen, crack initiation is detected by ultrasonic inspection or electric resistance method, and the stress state of the crack initiation part in the smooth specimen is evaluated by the creep characteristics of each part of the weld. This is a triaxial creep rupture test method obtained by creep analysis in consideration of

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a triaxial creep rupture test method using a Cr-Mo steel welded joint. Here, the smooth test piece 11 is a weld metal 14, a weld heat affected zone 12, a base material 13
And the whole including the screw portions 15 at both ends.

In this embodiment, a smooth test piece 11 of a welded joint is heated in an electric furnace and maintained at a high temperature, a uniaxial load is applied, and a weld heat-affected zone 12 in the smooth test piece 11 or a cross-section in a softened area is formed. Of cracks in the central part of the specimen is detected by ultrasonic inspection or electric resistance method. However, the stress state of the crack initiation portion inside the smooth test piece 11 is determined by the welded parts (base material 13, welding heat affected zone 12, welding metal 1).
Determined by creep analysis considering the creep characteristics of 4).

FIG. 2 is an explanatory view showing an outline of the case of a low alloy steel as an example of the structure of a Cr--Mo steel welded joint. When the base material is welded and heat-treated after welding, the heat affected zone
12 is formed on the side of the base metal 13 which is in contact with the weld metal 14, and narrow fine grains or a softened region having a width of several mm are generated on the base metal side. This fine grain or softened region has a lower creep strength and a faster creep deformation rate than the surrounding base metal and weld metal. This characteristic is basically the same for 9-12Cr steel. In addition,
In FIG. 2, region 1 is a pseudo-solid weld metal, region 2 is an unmixed region + remelted region (fusion region), region 3 is a heat-affected zone coarse-grained region, and region 4 is a heat-affected zone fine-grained region. , Region 5 indicates a heat-affected zone intercritical region, region 6 indicates a tempered heat-affected region, and region 7 indicates a non-heat-affected base material.

When a load is applied to such a welded joint at a high temperature in a direction perpendicular to the weld line, the deformation of the finely grained area (or softened area) 21 of the weld heat affected zone having a small width and a low strength as shown in FIG. The central portion 24 of the low-strength weld heat-affected zone fine grain region (or softened region), which is constrained by the surrounding high-strength weld metal 22 and base metal 23, is in a triaxial stress state.

The triaxial stress state depends on the diameter of the test piece, as shown in FIG. 4 showing the relationship between the test piece size and the stress state in the case of low alloy steel. Therefore, by changing the diameter of the test piece, it is possible to change the stress condition,
Testing under various stress conditions is possible. In FIG. 4, the relationship between the triaxiality index TF and the principal stresses σ1, σ2, σ3, and Mises equivalent stress σMises is TF = (σ1 + σ2
+ Σ3) / σMises.

Incidentally, the stress state of the crack initiation portion inside the test piece is determined by the respective portions of the welded portion (base metal 13, weld heat affected zone 12, weld metal 1).
Determined by creep analysis considering the creep characteristics of 4). When a crack is generated from the inside of the test piece in such a test, the detection of crack generation (lifetime) is performed by a non-destructive inspection such as an ultrasonic inspection or an electric resistance measurement.

[0013]

As described in detail above, according to the present invention, C
After arranging a smooth test piece in a direction perpendicular to the weld using a r-Mo steel welded joint, a uniaxial load is applied to the smooth test piece, and crack initiation is detected by ultrasonic inspection or an electric resistance method, In addition, a triaxial creep rupture test method that can acquire creep rupture data under triaxial stress conditions by obtaining the stress state of the crack initiation part in the smooth specimen by creep analysis considering the creep characteristics of each part of the welded part. Can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a triaxial creep rupture test method according to one embodiment of the present invention.

FIG. 2 is an explanatory view of a welded joint.

FIG. 3 is an explanatory diagram of a stress state in a weld joint creep rupture test.

FIG. 4 is a characteristic diagram showing a relationship between a test piece size and a triaxiality index TF.

FIG. 5 is an explanatory view of a uniaxial test using a round bar test piece.

FIG. 6 shows the fracture time and load (stress) in the uniaxial test of FIG.
FIG. 3 is a characteristic diagram showing a relationship with the graph.

FIG. 7 is a plan view of a cross-shaped test piece.

FIG. 8 is a perspective view of a test piece obtained by converting the cross-shaped test piece of FIG. 7 into three axes.

[Explanation of symbols]

 11: smooth specimen, 12: heat affected zone, 13, 23: base metal, 14, 22: weld metal, 21: fine grain area (or softened area) of heat affected zone.

Claims (1)

[Claims] 1. A method for acquiring triaxial creep rupture data.
In the axial creep rupture test method, after arranging a smooth test piece in a direction perpendicular to the weld using a weld joint of Cr-Mo steel, a uniaxial load is applied to this smooth test piece, and ultrasonic inspection or crack inspection is performed. A triaxial creep rupture test method characterized by detecting by an electric resistance method and determining a stress state of a crack initiation portion in a smooth test piece by creep analysis in consideration of creep characteristics of each portion of a welded portion.