JP2003315226A - Evaluation method for toughness in welding-heat influence part of steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the reproducibility and the universality of a Charpy impact test in a welding-heat influence part of a steel material, to facilitate to compare and evaluate the steel material and to select its welding condition. <P>SOLUTION: The method is for evaluating the toughness in the welding-heat influence part of the steel material. In the evaluation method for the toughness in the welding-heat influence part of the steel material, a V-shaped or I-shaped groove is worked at the steel material, a gas shielded arc welding operation or a submerged arc welding operation is performed to the groove by using a welding wire which contains 12% or more of Ni in terms of mass % with respect to the total mass of the wire and which contains 34% or more of Cr+Ni, a notch working operation is executed to a test piece sampled from the heat influence part of the welding operation, and the Charpy impact test is performed. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the toughness of a welded heat-affected zone of a thick steel material used for construction, bridges, shipbuilding and the like. 2. Description of the Related Art Steel materials used in the fields of construction, bridges, shipbuilding, etc., are almost always joined by welding.
At the time of this welding, the base metal portion at the peripheral portion of the weld metal is heated to cause transformation or the like, and a region where the structure changes is generated. This portion is referred to as a welding heat affected zone (hereinafter, referred to as HAZ). H
AZ is made of a different material from the steel part which is not affected by heat, and many of them have lower performance than steel. For example, in the Great Hanshin Earthquake, many fractures were found at or near welded joints such as beam-column joints, column-column joints, and column bases, and it was pointed out that the HAZ material had a large effect. I have. [0003] However, the material of the HAZ, particularly the absorbed energy and brittle fracture rate in the Charpy test for evaluating the toughness, of course vary depending on the welding conditions. Poor sex. For these, see Structural Journal of Japan, Vol. 7, No. 27, September 2000, pp. 23-3.
No. 7 describes in detail "Proposal of HAZ Toughness Evaluation Method for Building Steel Material and Results of Toughness Evaluation". The evaluation of HAZ toughness in multi-layer welding tends to be somewhat overestimated, and a method for evaluating HAZ toughness in one-bead welding has been proposed. That is, in the HAZ portion of a general steel material, a portion closer to the welding heat source has a higher maximum temperature and is heated to a higher temperature, so that the crystal grains tend to be coarsened and toughness is reduced. However, when multi-layer welding is performed, the region of the coarse crystal grains is heated again by the next welding pass. In this reheating, the maximum heating temperature is lower because the welding heat source is farther than in the previous time, and the crystal grains become finer by recrystallization, and the toughness is improved. If a test piece is collected from the reheated portion, the toughness is naturally evaluated to be high. On the other hand, in the one-bead welding, the reheating phenomenon does not occur, and the evaluation is performed with coarse grains, which is a severe evaluation. In addition, this one-bead method also has a slight effect on the wire aiming position and the like, as well as the groove shape, and further improvement is necessary in practical use. This is because the boundary between the molten (welded) metal and the steel (base metal) (called the fusion line) has a curved shape, and the notch of the Charpy test specimen is not necessarily parallel to the fusion line, and as a result, This is because the performance at a position separated by a certain equal distance from the melting line is not evaluated. [0005] Therefore, when conducting a precise study, a method called a "reproduced heat cycle test" in which a test piece subjected to a heat cycle in accordance with actual welding is prepared, processed into a Charpy test piece and tested. Has evaluated its performance. However, this requires equipment capable of controlled rapid heating and rapid cooling, and is unsuitable for simply evaluating steel material performance. The composition, strength, or Charpy impact test values of steel materials are specified in standards such as JIS and are subject to quality assurance.
Although the performance values obtained by the tests are important necessary characteristics, as described above, the evaluation method is not always well-developed, and when the HAZ performance is specially required, it is individually specified. It is the actual situation that a so-called construction test or the like is conducted. SUMMARY OF THE INVENTION Accordingly, the present invention provides a test method capable of easily performing the HAZ Charpy test with reproducibility and universality. It is an object to provide a method for facilitating selection and facilitating selection of welding conditions. [0007] The present inventors have studied how to improve the reproducibility of the HAZ Charpy test in evaluating the material quality of the HAZ, and as a result, have found out how to make a vertical fusion line. I figured out what was important. From the results, the gist of the present invention is as follows as described in the claims. (1) A method for evaluating the toughness of a heat-affected zone of a steel material, in which a re-shaped or I-shaped groove is formed on the steel material, and the groove is formed by adding Ni in an amount of 12% by mass% to the total mass of the wire. % Or more, and using a welding wire containing 34% or more of Cr + Ni, perform gas shielded arc welding or sub-mark welding, and notch a test piece taken from the heat affected zone of the welding. And evaluating the toughness of the heat affected zone of a steel material by performing a Charpy test. FIG. 1 is a schematic view showing a Charpy test piece sampled from a one-bead welding with a groove in order to explain an embodiment of the present invention. A weld bead 2 is formed on a steel material 1 having a groove-shaped groove, and a Charpy test piece 3 having a notch 4 formed on a heat-affected zone thereof is sampled. The broken line 5 in the figure indicates the (highest reached) isotherm of the heat-affected zone (HAZ). If the Charpy test notch can be made along the isotherm,
Although the properties of the HAZ heated to that temperature can be accurately evaluated, as shown in FIG. 1, the notch of the Charpy test is processed vertically, so the notch over the heated area has a certain range with the highest temperature. Processing is performed, which causes a reduction in the universality of the performance values obtained by the Charpy test. Therefore, by welding under such conditions that the isotherm is perpendicular to the Charpy test specimen sampling surface,
By making the notch and the isotherm parallel to the extent that there is no practical problem, the universality of the test performance value can be increased. According to the present invention, in order to obtain this vertical isotherm, the amount of heat input to welding is used to melt the welding wire as much as possible by using a R-shaped groove or an I-shaped groove to reduce the melting of the steel material. Is the way. Therefore, the component of the wire contains 12% or more of Ni and 34% or more of Cr + Ni, and gas-shielded arc welding or sub-marked arc welding using this welding wire is performed. It is characterized in that a Charpy test piece notched in the heat-affected zone is sampled and tested. In addition,% at this time shows the mass% with respect to the total mass of a wire. By containing 12% or more of Ni, the electric resistance of the wire is increased and the melting temperature of the wire is decreased. Most of the heat input to the welding is consumed for the melting of the wire, and the melting of the steel material is reduced. Since the welding is performed while maintaining the original shape of the steel material vertical wall side of the tip or the I-shaped groove, the isotherm of the HAZ portion becomes vertical. Furthermore, when the wire is made into a flux cored wire, the melting of the wire is increased and the melting of the steel material is reduced, so that a more vertical isothermal region can be obtained. However, when a medium Ni concentration wire is used, the weld metal has a structure called martensite,
Cracks occur in the weld metal. To prevent this, an appropriate amount of Cr is added. It is necessary to increase the amount in the lower Ni region, and the content of Cr + Ni is set to 34% or more. That is, when the Ni content is 12%, the Cr content is 22% or more.
Is more than 34%, it can be used without Cr. In the case of submerged welding, it is possible to add Cr from the flux to prevent cracks in the weld metal, but a different phase is easily formed, and addition from the wire is desirable from the viewpoint of accelerating the melting of the wire. It is also possible to use Mo instead of Cr. This is because Mo also has the same property of promoting ferrite formation as Cr. [0011] Table 1 shows an outline of the embodiment. Implementation NO.1-5
Are examples of the present invention, and Examples 6 to 9 are comparative examples. Implementation NO.
1 is an example of the present invention, which is a 30 mm thick 400N / mm ² steel for building use, one end face is a right angle, the other end face is inclined at 40 °, the bottom part is rounded with a radius of 3 mm, and cut to a depth of 15 mm. Butted steel is made to make a groove, and JISZ33
23YF309 (Ni: 12.6, Cr: 24%) type,
Using a flux cored wire of 1.2 mm diameter,
20A 26V Speed 23cm / min Heat input 2.5kJ / mm, Shear
MAG welding of 20% CO ₂ -80% Ar gas, and the center of the weld metal in the thickness direction was set as the center of the Charpy test specimen, and JISZ22 of 0.5 mm from the melting line at the V notch position.
Five V-notch Charpy test specimens No. 02 were sampled and tested at 0 ° C. As a result, the melting line was almost straight, and the fracture surface after the Charpy test showed no difference depending on the location.
There was little variation in Charpy absorbed energy and brittle fracture ratio, and the results were good. Execution No. 2 is also an example of the present invention.
And Les shaped grooving 5mm thick depth 15mm in building 490 N / mm ² steel, 45 ° tilt, this JISZ3332 YGT
9 Ni-2 (Ni: 57%) system, using a 1.4 mm diameter wire, 350 A 32 V speed 19 cm / min Heat input 3.5 kJ
/ mm, shield gas 2% O ₂ -98% Ar MIG welding, and using the center of the weld metal in the thickness direction as the center of the Charpy test piece, a V notch test piece 0.5 mm from the notch position melting line. Five were taken and tested at 0 ° C. Also in this case, the melting line was almost straight, the fracture surface after the Charpy test showed no difference depending on the location, and there was little variation in the Charpy absorbed energy and the brittle fracture ratio. The embodiment No. 3 is also an example of the present invention.
90 N / mm ² steel, 25 mm deep, 45 ° inclined groove processing is performed, and JISZ3332 YGT9Ni-2 (Ni:
58, Mo: 13%) system, 4mm diameter wire, and high basicity molten flux, 550A 34V speed 24cm / min Heat input 4.7kJ / mm SAW, thickness direction of the weld metal The center of the Charpy test specimen as
Five V-notch test pieces of 1.0 mm from the melting line at the notch position were sampled and tested at -20 ° C. Also in this case, the melting line was almost straight, the fracture surface after the Charpy test showed no difference depending on the location, and the distribution range of the Charpy absorbed energy and the brittle fracture ratio was small, which was a good result. The embodiment No. 4 is also an example of the present invention.
80N / mm ² steel, 15mm deep, 45 ° inclined groove processing, Inconel 82 (Ni: 73%) series,
Using a 3.2mm diameter wire and a high basicity firing type flux, 450A 32V speed 21cm / min Heat input 4.1kJ / m
m SAW, and the center of the weld metal in the thickness direction is set as the center of the Charpy test specimen, and 0.5 m from the melting line at the notch position.
Five V-notch specimens of m length were taken and tested at -20 ° C. Also in this case, the melting line was almost straight, the fracture surface after the Charpy test showed no difference depending on the location, and the distribution range of the Charpy absorbed energy and the brittle fracture ratio was small, which was a good result. Embodiment No. 5 is also an example of the present invention, in which an I-shaped groove having a gap of 5 mm is assembled from 490 N / mm ² steel for construction having a thickness of 15 mm and Inconel 625 (Ni; 62, Cr; 22).
%), 1.2A wire, 220A 26V speed 1
9cm / min heat input 1.8kJ / mm, shield gas 5% CO ₂ −
Two layers of MIG of 95% Ar were used, and five welded V-notch Charpy test pieces of 1 mm were taken from the notch position melting line with the overlapped portion of the weld metal as the center of the Charpy test piece.
Tested in ° C. This is because the fracture surface after the Charpy test has a fine structure reheated at the center of the test piece, but there is no difference in this amount, and the distribution range of the five Charpy absorbed energy and the brittle fracture ratio The results were also small and good results, and it was confirmed that the evaluation of toughness including the reheated portion could be stably performed. Example No. 6 is a comparative example using the same steel material and groove as in Example 1 and generally used JISZ3312.
A joint was prepared by carbon dioxide welding using a 1.2 mm diameter wire of YGW11 (without Ni and Cr), and a Charpy test was also taken and tested in the same manner as in Example 1. This was because the penetration from the center of the weld metal to the surface was greater than the bottom, and the melting line was curved. The fracture surface of the weld metal is also observed at the part where the fracture surface after the Charpy test is on the surface side of the weld metal, and the fracture surface of the weld metal is not uniform. It was not. Embodiment No. 7 is also a comparative example, which uses the same groove as in Embodiment 2 and uses JISZ3321 Y308L (N
i: 10, Cr: 21%) system, using a 1.4 mm diameter wire, 350 A 32 V speed 19 cm / min Heat input 3.5 kJ
/ mm, shield gas 2% O ₂ -98% Ar MIG welding test. Both the test piece collection and the test were performed in the same manner as in Example 2. However, this is a crack in the weld metal,
A stable test could not be performed. Implementation No. 8 is also a comparative example,
The groove shape was a 50 ° V groove, and the other conditions were the same as in Example 4. As a matter of course, the melting line was oblique, and the weld metal was recognized on the fracture surface of the Charpy test piece. The test included the weld metal, and was not a test of only the heat-affected zone of steel. Example No. 9 is also a comparative example.
80 N / mm ² steel was machined into a 15 mm deep, 50 ° slanting groove, and JIS Z3183 S804-H4 (N
i: 2, Cr: 0.6%) system, 4mm diameter wire and high basicity sintering type flux, 550A 33V speed 31cm / min Heat input 3.5kJ / mm SAW, and weld metal With the center in the thickness direction as the center of the Charpy test piece,
5 Notch specimens 0.5 mm from the V-notch position melting line
The samples were collected and tested at -20 ° C. Also in this case, the penetration near the surface of the weld metal was larger than the bottom of the weld metal, the melting line was inclined, the weld metal was observed on the fracture surface after the Charpy test, and the test was not limited to the weld heat affected zone only . [Table 1] According to the present invention, the performance of the heat-affected zone in welding of a steel material, in particular, the reproducibility in the evaluation of toughness in the Charpy test and the universality thereof can be improved.
Thereby, the steel material provider and the user can easily evaluate the performance of each steel plate and compare it, and can easily select the steel material or the welding conditions. For this reason, the reliability of the performance of the steel structure is enhanced, and a significant industrially useful effect is exhibited, such as a rational selection of steel materials.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of sampling a Charpy test specimen from a heat-affected zone of a weld formed by one-bead welding at a groove. [Description of Signs] 1: Steel material having a groove, 2: welding bead, 3: Charpy test piece, 4: Notch position of Charpy test piece, 5: welding heat affected zone

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Shigeru Ohkita             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation             Company Technology Development Division F-term (reference) 2G052 AA11 AD32 AD52 EB13 EC00                       GA05                 2G055 AA03 BA14 EA10 FA01                 2G061 AA13 AB04 AC04 BA20 CA01                       CB08 CB19

Claims (1)

Claims: 1. A method for evaluating the toughness of a heat affected zone of a steel material, comprising the steps of: forming a R-shaped or I-shaped groove on the steel;
In the groove, Ni was added in an amount of 1% by mass based on the total mass of the wire.
Using a welding wire containing not less than 2% and not less than 34% Cr + Ni, gas shielded arc welding or sub-mark welding is performed, and a notch is formed on a test piece taken from a heat affected zone of the welding. A toughness evaluation method for a weld heat affected zone of a steel material, wherein a Charpy test is performed after processing.