304 stainless steel forgings are widely used in many industrial fields, and their quality is of vital importance. Nondestructive testing is a key means to ensure that there are no defects inside them.
Ultrasonic testing is one of the commonly used nondestructive testing methods. It uses the propagation characteristics of ultrasonic waves in stainless steel forgings. When ultrasonic waves encounter internal defects such as pores, slag inclusions or cracks, reflection, refraction and scattering phenomena will occur. By analyzing the time, amplitude and waveform of the reflected wave, the location, size and type of the defect can be determined. For example, when testing larger-sized 304 stainless steel shaft forgings, ultrasonic waves can be tested along the axial and radial directions to comprehensively check internal defects.
Radiographic testing also plays an important role. It uses X-rays or gamma rays to penetrate the forgings, making the film sensitive or the detector receive signals. Due to the different degrees of absorption of rays by defects and the matrix, different grayscale images will be formed on the film or detector. For volume defects such as shrinkage cavities and porosity inside 304 stainless steel forgings, radiographic testing can clearly present their shape and distribution, providing an intuitive basis for quality assessment.
Magnetic particle testing is suitable for detecting surface and near-surface defects of ferromagnetic materials. Although 304 stainless steel is weakly magnetic, it can also be used under certain conditions. After the forging is magnetized, surface or near-surface defects will cause magnetic field lines to be distorted, and magnetic particles will be adsorbed to form magnetic traces. For example, when detecting surface cracks in 304 stainless steel forgings, magnetic particle testing can quickly find tiny crack openings and determine their location and direction.
Penetrant testing is mainly aimed at surface opening defects. A penetrant containing a pigment or fluorescent agent is applied to the surface of the forging to penetrate the defect, and then the excess penetrant is removed and a developer is applied. The penetrant in the defect will be adsorbed and displayed. For minor scratches, cracks and other defects on the surface of 304 stainless steel forgings, penetrant testing can effectively detect them and ensure surface quality.
Eddy current testing is based on the principle of electromagnetic induction. When an alternating current passes through the detection coil, eddy currents will be generated on the surface of the 304 stainless steel forgings. If there are defects in the forging, the distribution and size of the eddy currents will change, resulting in changes in the impedance of the detection coil. By measuring and analyzing the impedance change, the surface and near-surface defects of the forgings can be determined, such as the wall thickness uniformity and surface defects of stainless steel forgings.
In practical applications, multiple non-destructive testing methods are often required to cooperate with each other. For example, ultrasonic testing is first used for large-scale preliminary screening to determine the areas where defects may exist, and then X-ray testing is used to further determine the detailed information of the defects in these areas, or magnetic particle testing and penetration testing are used to supplement the surface and near-surface defects to achieve accurate identification of internal defects in 304 stainless steel forgings.
Different non-destructive testing methods have their own advantages and disadvantages. Only by reasonably selecting and comprehensively applying these methods can the internal defects of 304 stainless steel forgings be fully and accurately detected, ensuring that their quality meets the requirements, ensuring safe and reliable use in various industrial scenarios, and promoting the high-quality development of related industries.
