Classified display and quantitative detection method for martensite and retained austenite in m‑a islands

Abstract

The invention relates to microstructure classified display and quantitative detection technology in iron and steel material, belongs to the field of iron and steel material, and particularly relates to a classified display and quantitative detection method for martensite and residual austenite in low-alloy granular bainite steel martensite / austenite island (M-A island). The method comprises steps: (1) a grinding and mechanical polishing method is used for preparing a low-alloy granular bainite steel metallographic sample; (2) an electrolytic polishing method is used for removing the stress layer on the surface of the metallographic sample, a nitric acid alcohol solution of 2wt% to 6wt% is then used for carrying out pre-corrosion for 5 to 15s, and absolute alcohol is finally used for ultrasonic cleaning for 10 to 20m; (3) the metallographic sample after ultrasonic cleaning is placed in a furnace free of atmosphere protection at the temperature of 150 to 300 DEG C for heat preservation for 2 to 6 hours, and when getting out of the furnace, the metallographic sample is placed in a dryer for air cooling till the room temperature; (4) the microscopic structure is observed in a metallographic microscope, wherein polygonal ferrite and bainitic ferrite are bluish violet, the martensite is brown and the residual austenite is off-white; and (5) distribution of each phase of the structure and quantitative analysis are carried out.

Description

technical field [0001] The invention relates to microstructure classification display and quantitative detection technology in iron and steel materials, and belongs to the field of iron and steel materials, in particular to martensite and residual austenite in a low-alloy granular bainite steel martensite / austenite island (M-A island) Classification display and quantitative detection method of celestial body. Background technique [0002] Low-alloy granular bainitic steel is widely used in large-scale hydrogenation reactors, nuclear power cylinders and certain material strength and high-temperature resistance due to its good strength and toughness, excellent resistance to hydrogen embrittlement and appropriate high-temperature creep resistance. There are certain requirements on the parts. However, with the continuous expansion of the scale of hydrogenation units and the continuous increase of nuclear power, the wall thickness of the hydrogenation reactor and the wall thickn...

AI Technical Summary

Problems solved by technology

The difficulty of using quantitative metallographic analysis technology to analyze the structure of granular bainitic steel lies in: the identification and extraction of the characteristic structure, using the traditional metallographic corrosion method, only the grayscale image of the microstructure can be obtained. The contrast is not obvious enough to distinguish

However, using the current color metallographic corrosion technology, it is also difficult to distinguish the martensite and retained austenite in the M-A island, resulting in some important details being ignored during the microstructure analysis, which is not conducive to the quantitative analysis of the characteristic microstructure

[0003] Chinese patent application (publication number CN101382494A, publication date 2009-3-11, applicant: Wuhan Iron and Steel (Group) Company), proposes a display and display of retained austenite or island martensite-austenite in TRIP steel Quantitative detection method, the main content is through the traditional color metallographic corrosion technology, using LePara reagent (sodium bisulfite solution and picric acid alcohol solution mixed in a certain proportion) to corrode the polished tissue, and the polygonal ferrite and shellfish in the tissue are corroded. However, under the metallographic microscope, the martensite and retained austenite in the M-A islands are white in the samples prepared by this corrosion method, which is difficult to detect on the metallographic Further quantitative statistics on the two

[0004] With the continuous development of research methods, although there are currently some methods that can clearly characterize the amount of retained austenite in the tissue (such as: using magnetic method or XRD to measure the amount of retained austenite in the tissue), the above methods are not only It is complex, and it is impossible to observe the comprehensive information of the amount, distribution, and size of M-A islands in the material organization intuitively

Under the scanning electron microscope, the electron backscattering technique (EBSD) can distinguish the martensite and austenite in the M-A island, and can also observe the distribution of the M-A island in the local area, but because the martensite and the matrix shellfish in the M-A island Identical ferrite structure, difficult to distinguish between martensite and bainitic ferrite in M-A islands

More importantly, the sample preparation and observation process of EBSD technology is complicated, which limits its wide application

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