Brief introduction of residual austenite Austenite is a phase of iron, another common phase is martensite, and supercooled austenite refers to austenite that does not undergo martensite transformation under a certain degree of supercooling, and residual austenite refers to austenite that does not undergo transformation after martensite transformation. The retained austenite is always retained after quenching. Different types of steel have different amounts of austenite. For carbon steel, the remaining austenite can be observed in microstructure under the condition of carbon content greater than 0.4%. The higher the carbon content, the more austenite remains. Under the condition of the same carbon content, the residual austenite of alloy steel is more than that of carbon steel. The existence of residual austenite changes the properties of steel ring, such as making the elastic limit drop, the size of parts is not stable. Therefore, it is necessary to understand the transition of residual austenite during tempering in order to try to control it.

Other test method defects:

• Generally, it is lossy detection. The sample needs to be sliced.
• X ray method, however, is expensive in equipment, high in operation and slow in measurement. The depth of the test layer (only about 10 seats) is easily affected by the quality of the test surface.
• Metallographic method has a certain degree of subjectivity, and operators can make better judgment on metallographic recognition with a high degree of awareness. In particular, some hardening treatments are not particularly good, and when the dividing line between martensite and austenite is not obvious, the error is relatively large, time-consuming and laborious.

Development of magnetic measurement technology

• With the rapid development of electromagnetic method to evaluate product quality at home and abroad, for example, the United States USES barkhausen effect to evaluate materials [1]. Yoshiyong et al. used magnetostriction effect to check the heat treatment state and carbon content of steel [2]. The martensite content on steel surface was detected by eddy current method [3]. The content of high chromium cast iron residues was detected by magnetic method on equal use in ganzhai of wisco [4]. The detection of residual austenite in ductile iron by xiao ke ze et al. [5-6] in Inner Mongolia institute of technology makes the application of magnetic measurement method in the determination of retained austenite content in materials gradually mature. The mra-2 type residual austenite measuring instrument developed by AIT and luoyang bearing research institute has solved the problem of rapid, economical and simple measurement of residual austenite.
• After quenching, GCr15 bearing steel is ferromagnetic phase and non-ferromagnetic phase, in which austenite and carbides are non-ferromagnetic phase, the relative permeability is about 1.0, while martensite is ferromagnetic phase and the relative permeability is between 102 and 104. The difference between the two methods is used to establish the quantitative function relation between the unbalance current of bridge road and the residual austenite content of hardened steel, which can be used to detect the residual austenite content effectively.

Advantage of magnetic method for measuring residual austenite:

• Completely non-destructive, no damage to the workpiece;
• Rapid detection speed, detection of a workpiece in one minute can improve sampling frequency, so as to ensure timely adjustment of the process and improve product stability;
• Simple operation, good reproducibility and reproducibility of detection results, and computer software storage results, easy to call at any time to see.

Test conditions:

• Suitable for steel, cast iron and other ferromagnetic materials
• No dirt, oil film and oxide layer on the surface
• No strong electromagnetic interference within 3m.

Rma-2 parameters of residual austenite tester:

• Measuring the depth of the: 0.2～3ｍｍ
• Frequency range of measurement:20Hz～500Hz
• Single point test time is less than 10 seconds
• The sensitivity:＞1mA／1%Volume content of austenite
• Measuring range: 0～100%
• Repeated measurement error:≤ ±0.5%
• 电源:AC220±5％，50Hz±2％
• power≤100W
• The weight of the:10.00 Kg
• Sensor size:The standardφ7ｍｍ(customizable)

Other features:

• Instruments can be used with automation equipment (optional)
• Easy to use and mobile to use
• Software can be customized according to customer requirements (optional)
• On-line inspection

• ATTEN：Mr. CHENG
• TEL：+86 13910088723
• E-MAIL：kingcyy@126.com

Cost comparison of magnetic method and X-ray method:

Comparison of bearing ring paralympic content
The curve calibration

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