Preparation method of ultrahigh-strength martensitic steel EBSD sample

Abstract

The invention relates to a preparation method of an ultrahigh-strength martensitic steel EBSD sample, and belongs to the technical field of metallurgical detection. The process comprises the following steps: 1) cutting; 2) grinding and polishing; (3) fine polishing; 4) ion grinding; and 5) detecting. According to the method, through sample preparation optimization, mechanical polishing and ion grinding are combined, so that a clear Kikuchi line pattern can be obtained in any area of martensitic steel, and residual strain and stress caused by surface mechanical sample preparation are removed at subsequent repeated erosion positions in the final stage of mechanical polishing, so that the Kikuchi line pattern can be obtained. The ion grinding time is greatly shortened; and the calibration rate during EBSD sample detection is improved. And the calibration rate of the collected sample reaches 90% or above.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgical detection and relates to a preparation method of an EBSD sample of ultrahigh-strength martensite steel. BACKGROUND

[0002] With the continuous progress of the steel industry technology, the application of ultrahigh-strength steel products is becoming more and more popular. The most common matrix structure of ultrahigh-strength steel is martensite, which is a multi-scale structure involving lath blocks, lath bundles and laths. EBSD technology is an important tool for analyzing the microstructure of materials, which can provide information such as crystal orientation, grain boundary characteristics, phase distribution, dislocation density and stress and strain of materials, and can be used to analyze the original austenite grain size, lath size, residual austenite distribution, dislocation density and stress and strain in the martensite steel, thereby providing theoretical support for the comprehensive performance of the martensite steel matrix.

[0003] As a surface analysis technology, EBSD only obtains information within tens of nanometers in thickness of the sample surface, so the sample requirements are extremely strict, and the sample must be conductive, smooth and free of residual stress. The preparation quality of the sample is directly fed back through the calibration rate, and the calibration rate is the most important factor to determine the quality of the EBSD analysis result. The preparation of the EBSD sample generally includes mechanical preparation, electrolytic polishing and ion milling. The mechanical polishing needs to be polished by polishing paste of different particle sizes after grinding, and generally needs to be polished to 50 nm or below, which has low polishing efficiency and low success rate. In the electrolytic polishing, the electrolyte, concentration and polishing parameters (temperature, time, current, etc.) are different for different steel types, and it is difficult to accurately control them. For martensite with high dislocation structure, it is also difficult to stably obtain the calibration rate by electrolytic polishing. Compared with mechanical polishing and electrolytic polishing, ion milling has the characteristics of good sample preparation effect, but the preparation time of the sample is relatively long, generally 3-4 hours. SUMMARY

[0004] In view of the deficiencies of the prior art, the application aims to provide a preparation method of an EBSD sample of ultrahigh-strength martensite steel. In the EBSD detection, clear Kikuchi line patterns can be observed in any detection area, so that the calibration rate is stably above 90%.

[0005] The technical scheme of the application is as follows: A preparation method of an EBSD sample of ultrahigh-strength steel martensite, comprising the following steps: 1) Cutting: cutting the sample by wire cutting, and the size of the sample is 12 mm x 12 mm x 5 mm; 2) Grinding and polishing: the sample is ground in sequence through 300#, 600#, 1000# and 2000# sandpaper, and then is coarsely polished to a mirror surface by using 2.5um diamond, at a polishing rate of 800-1000r / min; 3) Fine polishing: the sample is etched by 3%-4% nitric acid alcohol for 15-20s, and then is finely polished by using 1um diamond for 5-8min, at a polishing rate of 300-400r / min; after polishing, the sample is etched by 3%-4% nitric acid alcohol for 5-10s again; 4) Ion grinding: the sample is placed in an ion grinding instrument for polishing, argon ion acceleration voltage is selected as 8-10V, argon ion incident angle is 1 o ~3 o , and polishing time is 50-60min; 5) Detection: the polished sample is placed on a scanning electron microscope stage, an EBSD probe is inserted to collect and detect the morphology of the area, clear Kikuchi line patterns can be observed in any micro area of the detection area, and when the optimized MAD value of the Kikuchi line pattern in the image center is less than 0.5, the collection is carried out.

[0006] The present application combines mechanical polishing and ion grinding, removes residual strain and stress caused by surface mechanical sample preparation through subsequent repeated etching at the last stage of mechanical polishing, greatly shortens the ion grinding time and improves the calibration rate during EBSD sample detection. The outstanding features and significant effects of the present application mainly include: (1) efficiency improvement, compared with mechanical sample preparation, the present application does not need the longest vibration polishing in the last stage of mechanical sample preparation; compared with ion grinding, the grinding time is greatly shortened; (2) sample quality improvement, the EBSD calibration rate of the sample prepared by the present application is stably above 95%. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 EBSD image of Q1100 steel produced in Example 1.

[0008] Figure 2 EBSD image of Q1300 steel produced in Example 2. DETAILED DESCRIPTION

[0009] The following is illustrated by examples.

[0010] Example 1: preparation of EBSD sample of Q1100 ultrahigh-strength martensitic steel, including the following steps: 1) Cutting: the sample is processed by wire cutting, and the size of the sample is 12x12x5mm; 2) Grinding and polishing: the sample is ground in sequence through 300#, 600#, 1000# and 2000# sandpaper, and then is coarsely polished to a mirror surface by using 2.5um diamond, at a polishing rate of 800r / min; 3) Fine polishing: etching with 3% nitric acid alcohol for 12 s, then fine polishing with 1 um diamond for 6 min, polishing rate is 800 r / min, after polishing, etching with 3% nitric acid alcohol for 6 s; 4) Ion milling: placing the sample in an ion milling instrument for polishing, argon ion acceleration voltage is selected as 10 V, argon ion incident angle is 2 o , polishing time is 55 min; 5) Detection: placing the polished sample on a scanning electron microscope stage, inserting an EBSD probe to collect the morphology of the detection area, clicking on any micro area of the detection area can observe clear Kikuchi line patterns, in the center of the image, MAD of the Kikuchi line pattern is optimized, when the optimized MAD value is 0.42, collection is carried out, after collection, the calibration rate is 96.7%.

[0011] Example 2: preparation of EBSD sample of Q1300 ultra-high-strength martensitic steel, including the following steps: 1) Cutting: using wire cutting to process the sample, the size of the sample is 12 mm x 12 mm x 5 mm; 2) Grinding and polishing: grinding the sample through 300#, 600#, 1000# and 2000# sandpaper in turn, then coarsely polishing to a mirror surface with 2.5 um diamond, polishing rate is 900 r / min; 3) Fine polishing: etching with 3%-4% nitric acid alcohol for 13 s, then fine polishing with 1 um diamond for 7 min, polishing rate is 300 / min, after polishing, etching with 3% nitric acid alcohol for 8 s; 4) Ion milling: placing the sample in an ion milling instrument for polishing, argon ion acceleration voltage is selected as 10 V, argon ion incident angle is 3 o , polishing time is 60 min; 5) Detection: placing the polished sample on a scanning electron microscope stage, inserting an EBSD probe to collect the morphology of the detection area, clicking on any micro area of the detection area can observe clear Kikuchi line patterns, in the center of the image, MAD of the Kikuchi line pattern is optimized, when the optimized MAD value is 0.42, collection is carried out, after collection, the calibration rate is 94.3%.

Claims

1. A method of preparing an EBSD sample of ultra-high strength martensitic steel, characterized in that Comprising the following steps: 1) Cutting: The sample is processed by wire cutting, and the size of the sample is 12 mm x 12 mm x 5 mm; 2) Grinding and polishing: The sample is ground by 300#, 600#, 1000# and 2000# sandpaper in turn, and then is coarsely polished to a mirror surface by 2.5um diamond at a polishing rate of 800-1000r / min; 3) Fine polishing: The sample is etched by 3%-4% nitric acid alcohol for 15-20s, and then is finely polished by 1um diamond for 5-8min at a polishing rate of 300-400r / min, and then is etched by 3%-4% nitric acid alcohol for 5-10s; 4) Ion milling: The sample was placed in an ion milling instrument for polishing, the argon ion acceleration voltage was selected as 8-10 V, the argon ion incidence angle was 1 o ~3 o , and the polishing time was 50-60 min; 5) Detection: The polished sample is placed on the scanning electron microscope stage, the EBSD probe is inserted to collect the morphology of the detection area, and the clear kikuchi line pattern can be observed in any micro area of the detection area, and the MAD of the kikuchi line pattern in the image center is optimized, and the collection is carried out when the optimized MAD value is <0.5.

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