CN114018920A - Method for displaying delta ferrite in P91 and P92 steel - Google Patents
Method for displaying delta ferrite in P91 and P92 steel Download PDFInfo
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- CN114018920A CN114018920A CN202111269615.0A CN202111269615A CN114018920A CN 114018920 A CN114018920 A CN 114018920A CN 202111269615 A CN202111269615 A CN 202111269615A CN 114018920 A CN114018920 A CN 114018920A
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention relates to a method for quantitatively detecting the content of ferrite in a P91 and P92 steel metallographic structure and displaying delta ferrite in P91 and P92 steel, which is generally used at present for corroding at normal temperature by a picric acid hydrochloride alcohol solution or ferric chloride salt acid water solution, and the difference between the brightness of the delta ferrite and a matrix structure under a microscope is small. When the delta ferrite content is measured quantitatively by using an image analyzer, the delta ferrite cannot be automatically identified by the difference in image gray level. The delta ferrite in P91 and P92 steel is displayed by hot corrosion for 5-10 minutes by using a saturated picric acid aqueous solution, a matrix structure presents uniform and dense black by using a corroded sample, the delta ferrite presents high-brightness white, and delta ferrite areas in P91 and P92 steel can be automatically identified by an image analyzer to carry out quantitative determination on the content of the structure.
Description
Technical Field
The invention belongs to the field of physicochemical detection, and particularly relates to a method for displaying delta ferrite in P91 and P92 steels by quantitatively detecting the ferrite content in metallographic structures of the P91 and P92 steels.
Background
The P91 and P92 steels have excellent high-temperature performance and are largely used in the production of supercritical (super) boilers; in the production process of the seamless steel tube, a serious metallographic structure problem can be encountered, and delta ferrite can appear; the delta ferrite in the steel not only influences the shaping, toughness, strength and welding performance of the material, but also causes serious quality problems of inward and outward bending and the like in the production process of the seamless steel pipe. Therefore, in the quality control of P91 and P92 original steel billets, the content of delta ferrite needs to be accurately measured.
The image analyzer method provided by the standard GB/T15749-2008 quantitative metallographic determination method is the method with the highest efficiency in the quantitative metallographic determination at present. The method is to convert an optical image observed under a microscope into a digital image on a computer screen through a digital camera. And measuring the percentage of the number of pixels corresponding to the metallographic structure to be measured in the digital image to the total number of pixels of the picture to obtain the accurate content of the phase to be measured. The method has the premise that the metallographic structure to be detected and the matrix structure are required to present obvious brightness contrast by a specific corrosion method, and the image analyzer can automatically identify the metallographic structure through brightness difference of different pixels.
At present, in the industry, for metallographic structure corrosion of P91 and P92 steel types, a metallographic structure identification method is generally adopted for a quenched and tempered metallographic sample by adopting a picric acid hydrochloride alcohol solution or an iron chloride hydrochloric acid aqueous solution through normal-temperature corrosion. The metallographic structure corroded by the method can identify the δ ferrite and the tempered sorbite structure of the matrix, but the brightness difference between the two structures is small, so that when an image analyzer is used, the metallographic structure cannot be automatically identified through the difference of image pixel gray scale, and the subsequent quantitative determination of the δ ferrite content cannot be carried out.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a method for clearly and accurately displaying the delta ferrite in P91 and P92 steel by a corrosion method with safe operation and low cost, so that the obvious brightness contrast between the microstructure and a matrix is ensured, and the quantitative determination of the content of the delta ferrite by analysis software is facilitated.
The invention is realized by the following technical scheme:
1. a method for displaying delta ferrite in P91 and P92 steel is characterized in that: the method comprises the following steps:
step 1), preparation of a sample to be detected: after a sample to be detected is sawed, quenching and tempering heat treatment is carried out on the sample to be detected by using a resistance furnace, namely quenching is carried out at 1060 ℃, tempering is carried out at 760 ℃, and the sample to be detected after heat treatment is mechanically ground and polished to obtain a polished detection surface;
step 2), corrosive agent configuration: adding water into picric acid to obtain picric acid water solution, and heating the picric acid water solution to boil to obtain supersaturated picric acid water solution;
step 3), corroding a sample to be detected: putting a sample to be detected into a supersaturated picric acid aqueous solution, continuously heating the picric acid aqueous solution, keeping the solution in a boiling state, and carrying out hot corrosion for 5-10 minutes; taking out the corroded sample to be detected, cleaning the surface of the sample to be detected by using clean water and absorbent cotton to remove redundant reagents, dripping by using alcohol, and drying the surface of the sample to be detected;
step 4), observing a sample to be detected: observing the corroded sample to be detected under a metallographic microscope, wherein the matrix structure is compact black, and the delta ferrite is not corroded and is bright white; and selecting a delta ferrite structure area, taking a digital photo, and carrying out quantitative determination on the delta ferrite content by using an image analyzer.
In the step 1), in the preparation link of the sample to be detected, when a resistance furnace is used for carrying out quenching and tempering heat treatment on the sample to be detected, a tempered sorbite structure and delta ferrite are obtained.
The invention has the following beneficial effects: the invention uses picric acid aqueous solution to replace the normal temperature corrosion method of picric acid hydrochloride alcohol solution or ferric chloride hydrochloric acid aqueous solution to display delta ferrite in P91 and P92 steel. Under the microscope bright field, tempered sorbite of the matrix shows uniform and compact black after being corroded, and delta ferrite still keeps white with high brightness without being corroded. The delta ferrite and the matrix structure have obvious brightness difference in the acquired digital image, and pixels corresponding to the delta ferrite can be easily identified by using an image analyzer according to the difference of pixel gray levels to carry out quantitative determination on the tissue content. The grain size difference of the invention and the alloy steel corroded by the picric acid aqueous solution is that the grain size corrosion adopts short-time hot corrosion conventionally to display grain boundaries as a main purpose, and the invention adopts the picric acid aqueous solution to carry out longer-time hot corrosion to ensure that the matrix structure is over-corroded into a black area and simultaneously the brightness and the whiteness of delta ferrite are kept so as to carry out quantitative determination on the structure content.
Drawings
FIG. 1 is a graph (100X) showing the appearance of delta ferrite in P91 steel by room temperature corrosion for 1 minute using picric acid hydrochloride in alcohol.
FIG. 2 is a graph (100X) showing the delta ferrite morphology in P91 steel by using picric acid hydrochloride alcoholic solution for 5 minutes and normal temperature corrosion.
FIG. 3 is a graph (100X) showing the delta ferrite morphology in P91 steel by using picric acid hydrochloride alcoholic solution for 10 minutes and normal temperature corrosion.
FIG. 4 is a graph (100X) showing the delta ferrite morphology in P91 steel by room temperature corrosion using picric acid hydrochloride in alcohol for 30 minutes.
FIG. 5 is a delta ferrite morphology (100X) in P91 steel shown by 5-minute hot corrosion of picric acid water solution in example 1 of the present invention.
FIG. 6 is a delta ferrite morphology (100X) in P91 steel shown by 10-minute hot corrosion of picric acid water solution in example 1 of the present invention.
Detailed Description
The invention is further described with reference to the following figures and examples.
Example 1: a method for displaying delta ferrite in P91 and P92 steel sequentially comprises the following steps:
step 1), preparation of a sample to be detected: cold working in the central area of the P91 continuous casting billet is carried out to cut a sample to be detected, the sample to be detected is subjected to quenching and tempering heat treatment by using a box type resistance furnace: quenching at 1060 deg.C-tempering at 760 deg.C. Mechanically processing the heat-treated sample to remove the oxidized decarburized layer on the surface, using a grinding wheel to flatten the surface, using 240#, 500#, 800# metallographic abrasive paper to grind, and finally using W2.5 polishing paste to polish to obtain a polished surface to be detected;
step 2), corrosive agent configuration: dissolving 25g of picric acid in 100ml of water, and heating the picric acid aqueous solution to boiling to obtain a supersaturated picric acid aqueous solution;
step 3), corroding a sample to be detected: immersing the polished surface of a sample to be detected into a supersaturated aqueous solution of picric acid, continuously heating the aqueous solution of picric acid, keeping the boiling state of the solution, and carrying out hot corrosion for 5 minutes; taking out the corroded sample to be detected, cleaning the surface of the sample to be detected by using clean water and absorbent cotton to remove redundant reagents, dripping the reagent for a plurality of times by using alcohol, and drying the surface of the sample;
step 4), observing a sample to be detected: observing the corroded sample to be detected under a metallographic microscope, wherein the matrix structure is compact black, and the delta ferrite is not corroded and is bright white; and selecting a delta ferrite structure area, taking a digital photo, and carrying out quantitative determination on the delta ferrite content by using an image analyzer.
Step 5), effect comparison: and (3) carrying out corrosion treatment on the sample to be detected by using different methods, and comparing delta ferrite display effects.
The effect of normal temperature corrosion is shown in figure 1 when picric acid hydrochloride alcohol solution is used for 1 minute;
the effect of normal temperature corrosion for 5 minutes by using picric acid hydrochloride alcohol solution is shown in figure 2;
the effect of normal temperature corrosion for 10 minutes by using picric acid hydrochloride alcohol solution is shown in figure 3;
the effect of normal temperature corrosion for 30 minutes by using picric acid hydrochloride alcohol solution is shown in figure 4;
the effect is shown in figure 5 by using picric acid aqueous solution for 5 minutes;
the effect of hot etching using picric acid aqueous solution for 10 minutes is shown in FIG. 6.
Claims (2)
1. A method for displaying delta ferrite in P91 and P92 steel is characterized in that: the method comprises the following steps:
step 1), preparation of a sample to be detected: after a sample to be detected is sawed, quenching and tempering heat treatment is carried out on the sample to be detected by using a resistance furnace, namely quenching is carried out at 1060 ℃, tempering is carried out at 760 ℃, and the sample to be detected after heat treatment is mechanically ground and polished to obtain a polished detection surface;
step 2), corrosive agent configuration: adding water into picric acid to obtain picric acid water solution, and heating the picric acid water solution to boil to obtain supersaturated picric acid water solution;
step 3), corroding a sample to be detected: putting a sample to be detected into a supersaturated picric acid aqueous solution, continuously heating the picric acid aqueous solution, keeping the solution in a boiling state, and carrying out hot corrosion for 5-10 minutes; taking out the corroded sample to be detected, cleaning the surface of the sample to be detected by using clean water and absorbent cotton to remove redundant reagents, dripping by using alcohol, and drying the surface of the sample to be detected;
step 4), observing a sample to be detected: observing the corroded sample to be detected under a metallographic microscope, wherein the matrix structure is compact black, and the delta ferrite is not corroded and is bright white; and selecting a delta ferrite structure area, taking a digital photo, and carrying out quantitative determination on the delta ferrite content by using an image analyzer.
2. The method for indicating delta ferrite in P91 and P92 steel as claimed in claim 1, wherein: in the step 1), in the preparation link of the sample to be detected, when a resistance furnace is used for carrying out quenching and tempering heat treatment on the sample to be detected, a tempered sorbite structure and delta ferrite are obtained.
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2021
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