材料
Abstract
Ultrasonic testing is an important technique for detection of rolling defects in steel bars. Ultrasonic testing is typically used to detect internal flaws, such as cracks and other discontinuities, that cannot be detected by visual inspection. GB／T 4162–91 regulates the ultrasonic testing of steel bars. This article discusses the purpose, scope, basic principles, test methods, and evaluation criteria of ultrasonic testing in accordance with GB／T 4162–91.
Introduction
Ultrasonic testing is a nondestructive testing technique used to detect flaws in metals such as steel bars. Ultrasonic testing uses high frequency sound waves to detect flaws in metal bars. These sound waves are transmitted into the metal and reflected back when they encounter a flaw. The reflected sound waves are analyzed to identify and locate the flaw.
Purpose
The purpose of ultrasonic testing in accordance with GB／T 4162–91 is to detect internal imperfections in steel bars caused by rolling or other forming processes. These imperfections may include cracks and other discontinuities.
Scope
GB／T 4162–91 applies to the ultrasonic testing of steel bars with cross-sections of up to 75 mm in diameter. GB／T 4162–91 is applicable to steel bars with a tensile strength of up to 630 MPa.
Basic Principles
Ultrasonic testing is based on the detection of sound waves reflected from flaws or discontinuities in metals. The sound waves are generated by an ultrasonic transducer, which is a device that converts electrical energy into mechanical energy. The transducer is mounted on the surface of the metal to be tested and transmits high frequency sound waves into the metal. When the sound waves encounter a flaw, they are reflected back to the transducer. The reflected waves are analyzed and converted into a signal that identifies and locates the flaw.
Test Methods
There are two types of ultrasonic testing in accordance with GB／T 4162–91: pulse-echo testing and time-of-flight diffraction (TOFD) testing.
Pulse-echo testing is the most common type of ultrasonic testing. During this type of test, an ultrasonic pulse is transmitted into the metal by the transducer. The pulse is reflected back when it encounters a flaw. The signal is then analyzed to detect and locate the flaw.
TOFD testing is similar to pulse-echo testing, except that it uses ultrasonic pulses of varying frequencies. The reflected signal is more complex than in pulse-echo testing and is used to detect smaller and/or deeper flaws. TOFD testing also offers improved resolution and sensitivity.
Evaluation Criteria
The signal from the reflected sound waves is analyzed to identify and locate the flaws. The signal is compared to a set of evaluation criteria to determine if a flaw is present. A flaw is considered present if the signal meets the evaluation criteria; if it does not meet the evaluation criteria, then the part is deemed acceptable.
Conclusion
Ultrasonic testing is an important technique used to detect flaws in steel bars caused by rolling or other forming processes. GB／T 4162–91 sets forth the requirements for ultrasonic testing of steel bars. The purpose, scope, basic principles, test methods, and evaluation criteria of ultrasonic testing are discussed in this article.
