In the weld toughness index, some specifications are not required, and it requires the same level of toughness for welds of various strength levels. For example, for submarine steel, according to the specifications of the Japanese Defense Agency [6, 7], the welding metal of various strength grades or welding wire requires the impact absorption at -50 °C to be not less than 27 J; The yield strength includes four grades of 460, 630, 800 and 940 MPa, and the welding method is applicable to electrode arc welding, submerged arc welding, MIG welding and the like. In addition to the requirements for the impact absorption of the deposited metal, the drop joint test is carried out on the welded joint. The specified strike strength is selected according to the yield strength grade and the thickness of the test plate. It is required that the sample fracture does not occur at -50 °C. Toughness assessment from these two aspects should be more scientific. The US Military Standard (MIL) assesses the toughness of welding materials used in submarines. Some aspects are consistent with Japan, but there are also differences. For the evaluation of the toughness of deposited metal, the Charpy V-shaped impact test was adopted in the early stage, and the impact absorption work at -50 °C was required to be not less than 27, 47 or 68 J. The improvement of these impact absorption work was not caused by the increase of strength. It is determined based on factors such as the toughness reserve of the welding material. Later, it was changed to dynamic tear test (DT test). The thickness of the commonly used sample is about 16mm (5/8å‹). The width and length of the sample are 41mm and 180mm respectively. The processing of the crack source gap is more strict. Claim. The test temperature is 30 °F (about 0 ° C), and the minimum tear work requirements are 610, 645, 680 and 780 J (450, 475, 500 and 575 ft-1b). The determination of these values ​​is not linear with the increase of strength, but is directly related to the toughness reserve of the material. For example, the weld DT with a yield strength of 920 MPa or higher requires 645 J (475 ft-1b), and the yield strength. For welds greater than or equal to 700 MPa, the DT value is required to be ≥780 J (575 ft-1b). In the past few years, the Charpy V-type impact test and the dynamic tear test were used together, and only one method of dynamic tear test was used. In the assessment of the toughness of welded joints, it is very different from Japan. The United States uses the explosion test [8]. The thickness of the test plates is 25mm (1å‹) or 38mm (1.5å‹). After butt welding, it becomes a square with a side length of 510mm. Or 640mm, the weld is in the center. The test temperature is 30 °F (about 0 ° C). After 3 explosions, it is desirable that the thickness reduction rate reaches 7%, and no debris is required. Cracks passing through the entire thickness are allowed, but the cracks should not extend to the support area. Inside. The US military standard defines this method as an approved test or an appraisal test, and only the welding material that passes this test can be used for submarine construction. Once the test is passed, as long as the weld core composition, the coating formulation and raw materials, manufacturing techniques and processes of the welding material are not changed, the test is not carried out and only the toughness test of the deposited metal is carried out (Charpy V-shaped or dynamic) Tear test), and the purpose of this toughness test is mainly to control the quality stability of the welding material. Therefore, the absorption work of deposited metal can be considered as a relative judgment to control the quality of welding consumables. When a certain welding material is used in a specific structure such as a ship, bridge, pressure vessel, vehicle, elevated structure, etc., it should be based on the characteristics of the structure, the force (whether static or dynamic, low-cycle fatigue or high-cycle fatigue), environment Conditions, etc., put forward specific requirements, and some also require special evaluation tests, and at the same time determine the toughness index of the deposited metal that meets the safety requirements. Neither the higher the toughness index, the better, nor the need to reduce the toughness in order to reduce costs. It is not entirely reasonable to use the toughness index of the steel to require the welding material. After the steel is welded, the coarse-grained area in the heat-affected zone is significantly grown due to the grain growth, so that the toughness is greatly reduced, so in order to ensure the heat-affected zone With good toughness, there should be higher requirements for the toughness of the base metal. At present, the welding material standards at home and abroad are formulated by the welding material standardization body. Although the strength grades of high-strength steel welding materials are not completely consistent, the toughness indexes of deposited metals under various strength levels are the same. There are mainly two systems [9]: First, the European system, impact absorption work requirements ≥ 47 J The countries around the Pacific, such as the United States, China, Japan, South Korea, etc., adopt another system, that is, the impact absorption work requirement is greater than 27 J. After 2000, the International Organization for Standardization (ISO) recognized both systems and placed them in the same standard according to the two systems A and B. Such as ISO18275-2005, ISO16834-2006 and ISO18276-2005, respectively, the welding rod, solid welding wire and flux cored wire standard for high-strength steel, in which the yield strength of the deposited metal is uniformly divided into the following three standard A systems. 5 grades, namely 550, 620, 690, 790 and 890 MPa grade; and the impact absorption of deposited metal does not change with the strength grade, it is a fixed value, that is, the A system requires AkV ≥ 47J; the B system requires AkV ≥ 27 J . However, under the same impact energy conditions, it is divided into several test temperatures, usually +20, 0, -20, -30, -40, -50, -60, -70 and -80 °C. The test temperature can be selected based on the temperature of the structure or the requirements for toughness reserve to meet the different needs for toughness. For example, ships operating in the southern rivers of China have higher ambient temperatures and higher test temperatures. Ships operating in northern rivers have lower ambient temperatures and should be selected for lower test temperatures. Some structures are subjected to dynamic loads or fatigue loads. Compared with structures that are only subjected to static loads in the same area, the same strength of welding consumables can be used, but there should be a greater reserve in toughness to ensure that under dynamic load or fatigue load. For safe operation, it is necessary to select a welding material that meets the 47 J or 27 J impact absorption work at a lower test temperature. 3 Conclusion In the welding joint strength matching, for low-strength steel grades, equal or super strong matching can be used; for high-strength steel grades, equal or low-strength matching should be adopted, and super-strong matching is unfavorable. In terms of weld toughness index, there are several cases, one is that the toughness requirement is increased as the weld strength is increased; the other is that the same impact absorption work is required for the welds of various strength levels. However, the test temperature is changed, the harsher the use conditions of the product, the lower the corresponding test temperature; there is also the same requirement for the impact absorption work and the test temperature, but the hammer joint or explosion of the welded joint is also required. Test and use this as an approval test. Previous page