Heavy Section Metallic Materials Impact Test Method Research

In recent years, the shipbuilding industry has grown rapidly under the marine strategy in our country, and the research of large-scale marine engineering structure has started, which has led to the rise of ocean engineering and manufacturing industry in China. Under this circumstance, the demand for large thickness structural steels and welded joints has risen, and the occurrence of major accidents increases accordingly. It was found that brittle fracture of thick plates and welded joints under low temperature is one of the main causes for these accidents, thus toughness research of large thickness steel plate and welded joints has become an increasingly important research subject.Nowadays, the main toughness researches of metallic materials and welded joints are CTOD, DWTT impact test, and Charpy pendulum impact test. Ship classification societies classify steels into different levels according to absorbed energies of Charpy pendulum impact test and decide for acceptance. According to rules of classification societies and GB/T 229-2007 Metallic materials. Charpy pendulum impact test method, impact specimen should be made into different sizes of (10×10×55)mm, (7.5×10×55)mm, (5×10×55)mm as standard specimen and supplementary specimen for the roughness test. For materials thicker than 10mm, the sampling methods are as follows according to CCS rules:for thickness not greater than 40mm, the impact test specimen should be near surface, which is that the distance between rolling surface and the edge of the specimen should be less than 2mm; for thickness over 40mm, the axis should be at 1/4 thickness of the specimen. The toughness of materials has great thing to do with its size, so there are limitations in the sampling rules of classification societies and national standards for the Charpy impact test specimen, which will cause difference between the impact toughness test results and the practical application of metallic materials leading to safety risks.There are limitations in specimen sampling method for Charpy impact test, thus this essay is comparing and analyzing the impact property results of spot sampling specimen with that of the through thickness sampling specimen based on the research results of impact energy connection between supplementary specimen and standard specimen of Charpy impact test, and the essay is also correcting and improving the temperature for normal Charpy impact test by data fitting, as well as analyzing and verifying the research results of micro fracture by scanning electron microscope.