Como detetar a qualidade da liga Hastelloy?

As a high-end corrosion-resistant material, the quality of Hastelloy alloy determines its service performance in extreme environments. Quality inspection should be carried out throughout the entire production process, using multi-level and multi-dimensional testing methods to ensure that material composition, organizational structure, and mechanical properties meet design standards. A scientific testing system is the core guarantee to avoid the risk of failure from raw material entry to finished product delivery. ​

Composition analysis is the fundamental step in quality testing, aimed at verifying whether alloy elements meet the grade standards. Spectral analysis techniques, such as direct reading spectrometers, can quickly determine the content of major and trace elements by detecting the wavelength and intensity of the excited light emitted by alloys, making them suitable for batch testing on production lines. For scenarios with higher precision requirements, chemical analysis methods accurately determine the proportion of each element through steps such as sample dissolution and titration reactions, especially identifying easily overlooked trace impurities (such as carbon and sulfur) that may cause hidden dangers such as intergranular corrosion. For complex shaped products such as castings, non-destructive composition analysis techniques can also be used to complete composition verification without damaging the workpiece. ​

Mechanical performance testing focuses on key indicators such as strength, plasticity, and toughness of materials. Tensile testing evaluates the deformation and fracture characteristics of materials under stress by applying axial tension to determine yield strength, tensile strength, and elongation. The impact test uses a pendulum to impact the specimen, measure the absorbed energy, and determine the material’s resistance to brittle fracture under low or high temperature loads, which is particularly important for Hastelloy alloys used in low-temperature environments. Hardness testing (such as Rockwell hardness and Vickers hardness) quickly evaluates the surface hardness of materials by the depth or indentation size of the indenter pressing into the surface, indirectly reflecting the heat treatment effect and wear resistance. ​

Microstructure testing can reveal structural defects within materials. Metallographic analysis can detect casting or processing defects such as segregation, inclusions, and porosity by preparing samples, grinding, polishing, and corrosion treatment, and observing grain size, precipitation phase distribution, and grain boundary state under a microscope. For welded parts, it is necessary to focus on checking the structural changes in the heat affected zone to avoid performance degradation caused by coarse grains. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can achieve more microscopic observation, identify nanoscale precipitates or microcracks, and provide a basis for material failure analysis. ​

Corrosion resistance testing is the core quality verification project of Hastelloy alloy. The salt spray test simulates the marine or industrial atmospheric environment by continuously exposing the sample in a salt spray box, observing the surface corrosion rate and pitting situation, and evaluating the resistance to atmospheric corrosion. The intergranular corrosion test (such as boiling nitric acid method, sulfuric acid copper sulfate method) is specifically used to detect the corrosion sensitivity of grain boundaries. By measuring the weight loss or bending test after soaking in a specific solution, it is determined whether there is a tendency for intergranular corrosion. For Hastelloy alloys that come into contact with specific media, targeted corrosion tests such as hydrofluoric acid immersion, high-temperature and high-pressure water corrosion, etc., need to be conducted to simulate the actual service environment. ​
In addition, non-destructive testing technology is widely used in finished product testing. Ultrasonic testing utilizes the principle of sound wave reflection to detect volumetric defects such as internal cracks and voids; Magnetic particle testing is applicable to ferromagnetic Hastelloy alloys (such as partially modified models) and can detect linear defects on or near the surface; Penetration testing is not affected by the magnetic properties of the material, but rather by the penetration of a penetrant into the defect and its coloration, providing a visual display of surface opening defects. ​

The quality inspection of Hastelloy alloy needs to develop targeted plans based on application scenarios, forming a complete verification system from composition, properties to microstructure. Only through strict testing can we ensure the safe and reliable service of materials in extreme environments such as chemical, aerospace, and marine engineering, and maximize their advantages in corrosion resistance and high strength. ​