KR100302399B1 - Method for evaluating weldability of welded thin sheet with ease - Google Patents

Abstract

The present invention relates to a test part toughness evaluation test method of a thin plate that can be easily quantified by quantifying the weld toughness of the thin plate more accurately and simply,

A specimen prepared by welding the thin plate and the thin plate was welded, the both ends of the specimen were fixed, and a crack was generated by applying a force by a punch to the fracture toughness measurement site to evaluate the fracture toughness of the welded part and the base metal. In the test method comprising the step of forming a through-hole in the portion for evaluating the fracture toughness to have a direct line having a size smaller than the diameter of the punch; including, through the coincidence of the center of the through-hole and the punch It is characterized by fracture toughness by quantifying the state in which the largest deformation and crack occurred around the hole as it is.

Description

Test method for evaluation of toughness of welded sheet with easy quantification {METHOD FOR EVALUATING WELDABILITY OF WELDED THIN SHEET WITH EASE}

The present invention relates to a method for evaluating weld toughness of a thin plate that can be easily quantified by quantifying weld toughness of a thin plate more accurately and simply.

In general, the weld heat affected zone (HAZ) of the welded structure is very complicated and various structures are formed according to the difference in the weld heat history and the surrounding conditions during welding, the mechanical properties such as hardness and brittleness change.

In addition, the triaxial nonuniform residual stress and hydrogen absorption generated during welding act in combination with the discontinuity of the structure, resulting in deterioration of fracture toughness of HAZ.

Therefore, accurate fracture strength evaluation of welded metal and HAZ together with the base metal has been an important task in the evaluation of the safety of welded structures. Especially in the case of low alloy steel for pressure vessels, tensile test, Charpy test, It is mandatory to carry out NDT tests.

As a conventional method for evaluating the fracture toughness of steel welds, a wide test, a cross welded test and a double length test have been performed. However, in the case of the weld heat affected zone, the microstructure gradient is formed as well as the mixing ratio of the mouth tool and the micro component is varied according to the distance from the fusion boundary. It is known that it is greatly nourished by the field.

Therefore, in order to accurately evaluate the fracture strength of the welded part, it is important to accurately evaluate the inherent strength and toughness of each of the continuously changing welded microstructures.

Recently, the SP (small punch) test, which has been developed for the development of candidate materials for fusion reactors, is a so-called bulge test that determines the transition temperature and carbonaceous fracture toughness, which are characteristics related to the fracture toughness of metal materials. It is known that it is used for the strength evaluation of composite materials and coating materials, as well as the locations that can be obtained in a very small volume, and in addition, it is known that it may be applied to material evaluation in the case of non-uniform structure. However, not only the test data by this method is small but also the fracture area is uneven during the test by such a method, and in order to evaluate the weld toughness of the desired part, it is possible to perform complex equations or predict the Although it is to quantify the weld toughness of the site, this method is complicated and it is difficult to accurately evaluate the weld toughness.

The present invention has been made in order to solve such a conventional problem, the object of the present invention is to provide a quantitative weld weld toughness evaluation test method of the thin plate that can be quantified by measuring the toughness of the weld plate more accurately and simply. have.

1 is a conceptual diagram for evaluating the weld toughness of a thin plate by a conventional method

Figure 2 is a problem derivation diagram showing the location of cracks generated by the conventional method

Figure 3 is a conceptual diagram for evaluating the weld toughness of the thin plate by the method of the present invention

4 is an explanatory view showing a crack occurrence situation when the weld toughness evaluation of the thin plate is made by the method of the present invention.

Explanation of symbols on the main parts of the drawings

10 ... lamination

12 ... welds

13 ... through hole

14 ... crack

As a technical configuration for achieving the above object, the present invention,

To prepare the specimen by connecting the thin plate and thin plate by welding, to fix the both ends of the specimen, and to observe the occurrence of cracking by applying the force by the punch to the fracture toughness measurement site, to evaluate the fracture toughness of the welded part and the base metal In the test method,

And forming a through hole in the specimen to have a diameter of a size smaller than that of a punch in a portion for evaluating fracture toughness.

In order to quantify the state of the largest deformation and cracks in the periphery of the through-hole by matching the center of the through-hole and the punch as it is to characterize the fracture toughness characterized in that the toughness of the weld weld toughness evaluation test method By.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

FIG. 1 shows a schematic configuration for evaluating the toughness of a welding portion 112 welded to and connected to a thin plate 110 and a thin plate 110 by a conventional method, and not shown a welded thin plate 110. It is fixed to an Instron universal testing machine and the like, and the punch 120 positioned above the weld 112 of the thin plate 110 is gradually lowered to measure the deformation of the weld according to the displacement of the punch 120.

However, in this conventional method, the thinnest portion is formed at a portion slightly away from the center of the punch, not at the center portion of the punch (a position for evaluating weld characteristics), so that a crack 114 (see FIG. 2) occurs. Therefore, SP energy (E _SP ), which is used as a criterion for evaluating fracture toughness (measured energy to the point of failure, measured by the area under the load displacement curve), shows the weldability to the central specimen of the punch. It wasn't. Of course, in order to correct this, we infer weldability to the center part of the punch by using SP energy for the part which is actually broken by a prediction method such as a complicated equation or simulation, but this is very complicated and lacks accuracy. Was.

3 schematically shows a configuration for measuring weld toughness of a thin plate according to the method of the present invention, which forms a through hole 13 in the weld 12 of the thin plate specimen 10 and the through hole 13 thereof. It is seen that the punch 20 is located at the top.

Of course, the size of the through hole 13 should be smaller than the diameter of the punch 20, more precisely even after the size of the through hole 13 is increased by the force of the punch 20 It should be smaller than the diameter of (20).

In the manufacture of the specimen, the position of the through hole 13 is formed in a portion for toughness evaluation of the base material or the HAZ tissue part.

In the manufacture of the specimen, the precision of the through hole 13, etc. is not a big problem, which is to form the through hole 13 in the same manner even if a fine notch is formed in the inner surface of the through hole 13. This is because cracking occurs in the through hole 13 when the toughness is evaluated by the method of the present invention.

In order to evaluate the toughness of the weld by the method according to the present invention, after fabricating the specimen as described above, by fastening four bolts to the upper and lower dies of the specimen jig (not shown) with a uniform force It is fixed (usually using a torque wrench) and the punch 20 is lowered at a constant speed by an Instron universal testing machine.

In addition, the fracture surface observation uses a scanning electron microscope (SEM).

When the appropriate time elapses after the lowering of the punch 20, a crack occurs in the specimen. In the present invention, the crack 14 always occurs in the through hole 13.

This is predicted, when the weld fracture fracture toughness of the thin plate is evaluated by the method of the present invention, the largest deformation occurs around the through hole 13 formed in the weld 12, and thus cracks 14 in the through hole 13. ) Is very important in terms of reproducibility.

That is, in the welded portion 12 in which the through hole 13 is formed, a portion having weak toughness causes cracks 14, whereas a portion having high toughness does not generate cracks 14. If the crack 14 is generated in the through hole 13 formed in the welded portion 12 of the specimen 10 by the lowering of the 20, the structure of the welded portion 12 corresponding to the crack 14 generated at this time and By quantifying the size of the crack 14 and the force exerted on the punch 20, the values become characteristics that evaluate the weld fracture fracture toughness of the thin plate.

In addition, SP energy (E _sp ), which is a criterion for evaluating the fracture toughness of the specimen 10, is defined as the area under the load displacement curve as the required energy up to the fracture occurrence point observed by the scanning electron microscope. Find the ductile-brittle transition temperature from the curve of the SP energy and its test temperature.

Therefore, cracks are generated in unwanted portions as in the prior art, and thus fracture toughness of the weld portion 12 can be directly evaluated without having to infer weld fracture fracture toughness of the desired portion based on the test result.

That is, in the present invention, when a through hole is formed in a part of a specimen for evaluating fracture toughness, and the punch is moved in a state where the through hole and the center of the punch coincide, the maximum deformation and subsequent crack in the through hole part are always achieved. As a result, it is possible to quantify the force applied to the punch at the time when such a crack occurs, as it is, as the evaluation value for the fracture toughness of the thin plate weld portion.

As described above, according to the test method for evaluation of toughness of a welded thin plate according to the present invention, a hole having a diameter smaller than a punch is formed in a desired portion for toughness evaluation of the welded portion or the base metal connected to the thin plate, and When a crack is generated by the action of the punch, the fracture toughness of the thin plate welded portion can be accurately characterized by a simple method of quantifying the state thereof.

Claims (1)

(Correct) A specimen prepared by connecting the thin plate and the thin plate by welding, fixing both ends of the specimen and applying cracking force by applying a punch to the fracture toughness measurement site, and fracture fracture toughness of the welded part and the base metal In the test method for evaluating, And forming a through hole in the specimen to have a diameter of a size smaller than that of a punch in a portion for evaluating fracture toughness. Easily quantitative weld joint toughness evaluation test method characterized in that the characteristics of fracture toughness by quantifying the state of the largest deformation and cracks generated around the through hole by matching the center of the through hole and the punch as it is.