KR900006351B1 - Precipitate quantitative measurement - Google Patents

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Description

Precipitate quantitative measurement

The accompanying drawings are perspective views showing specimens magnified and observed by a scanning electron microscope to measure the depth of corrosion in measuring the amount of precipitate in accordance with the present invention.

* Description of the main parts of the drawings

1 Psalm 11 Corroded Part

12: stripped portion 13: the interface

14: Scratches

The present invention relates to a quantitative measurement method of precipitates to accurately measure the amount of fine precipitates formed by Nb, V, Ti, etc. in a low alloy high tensile steel (HSLA-Steel) by a carbon replica in a transmission electron microscope (TEM). will be.

Conventional methods for measuring the amount of precipitates present in steel by carbon cloning in transmission electron microscopy include polishing the surface of steel specimens, corroding the polishing surface with a corrosion solution, and then present on the surface of the specimen corroded by carbon cloning. Extract the precipitates to measure the number of precipitates per unit area (ns) and average diameter (ds), and determine the number of precipitates per unit area (ns)

expression

......................................................(1)

........................................ ....(One)

A method of measuring the amount of precipitates in terms of volume fraction in terms of is known.

(In formula (1), fv: volume fraction of precipitates, ns: number of measured precipitates per unit area, ds: average diameter of measured precipitates, ss: standard deviation of the measured precipitate diameter and the average diameter), The volume (corrosion depth) of the specimen from which the precipitates are extracted is measured on the assumption that the average precipitate diameter (ds) is always constant. In practice, when the precipitates are corroded to extract carbon from the specimens, the depth of the specimens that are corroded is determined by It can be seen that it is changed as shown in Table 1 according to the heat treatment conditions.

TABLE 1

Average particle size of precipitates measured from the ds-surface.

nv-calculated precipitates per unit volume

Corroded Depth of te Specimen

However, in the conventional method, it is impossible to measure the corrosion depth of the specimen from which the precipitates are extracted, but it is assumed that the average diameter of the extracted extracts is constant. Because of this, lack of measurable determinism was a problem.

As a result, the lack of measurement accuracy results in a significant factor in the amount and distribution of the precipitates in mechanical properties and structure changes, which causes significant errors in the quality design of the high tensile steel, the material prediction, and the strength prediction model.

Therefore, accurate precipitation measurement has been required for the mechanical properties of the low alloy high tensile strength steel containing Nb, V and Ti, the model for predicting the transformation structure during cooling according to the operating conditions, and the strength prediction model.

Accordingly, the present invention is to provide a method for accurately measuring the amount of precipitate by means of measuring the change in the depth of the specimen corroded according to the composition of the steel and the heat treatment change conditions that the amount of precipitate could not be accurately measured in the conventional method. There is this.

Another object of the present invention is to provide a model or strength prediction model for predicting the mechanical properties of Nb, V, Ti-containing low alloy high tensile strength steel and the transformation structure during cooling according to the operating conditions. It is to make setting easy and good.

Hereinafter, the present invention will be described.

In the present invention, in the quantitative measurement of precipitates by measuring the amount of precipitates by a carbon cloning method in a transmission electron microscope, the step of finely polishing the surface of the steel specimen with a diamond powder of about 3μm, about half of the surface of the finely ground specimen After coating with Lacomit paint, the surface of the specimen is corroded with a corrosive solution, preferably a nital solution, the precipitates present on the surface of the corroded specimen by the carbon replica are extracted and the number of precipitates per unit area (ns) and Determination of the average particle diameter (ds) of the precipitate, peeling off the applied paint, and then observed by the scanning electron microscope the scratch marks on the boundary surface of the corroded portion and the peeled off portion with a scanning electron microscope to determine the corrosion depth ( measuring te); And the number of precipitates per unit area (ns)

.................................................(2)expression

......................... 2)

It relates to a method for measuring the amount of precipitate, including the step of converting to a volume fraction by.

In formula (2), fv 'is the volume fraction of precipitates, ns is the number of precipitates per unit area, ds is the average diameter of the measured mules, ss is the standard deviation between the diameter and the average diameter of the measured precipitates.

Hereinafter, the present invention will be described in detail with reference to the drawings.

As shown in the figure, in the first step of the present invention, the polished steel specimen surface 1 is finely ground with a diamond powder of about 3 μm, and about half (s) of the specimen surface is coated with Lacomit paint ( After coating with 2), corrode with corrosion solution for a certain time.

Next, the precipitates present on the corroded specimen surface are extracted with a carbon replica to measure the number of precipitates per unit area (ns) and the average diameter of the precipitates (ds).

Next, the paint 2 is peeled off, and the peeled portion 12, the corroded portion 11, and the portion of the scratched line 14 which is polished in contact with the interface 13 are magnified and observed with a scanning electron microscope. The corrosion depth (te) is measured by the geometric method of.

에 의해서 계산될 수 있다.That is, in the drawing, the corrosion depth te corresponds to "C",

Can be calculated by

Next, the number of extracts per unit area (ns)

.........................................................(2)expression

........................................ .......(2)

The quantitative measurement method for precipitates in accordance with the present invention is completed by converting to volume fraction by.

As the corrosion solution, various kinds of conventional corrosion solutions may be used, but it is preferable to use a 2% nital solution.

The scratch marks 14 on the surface of the specimen shown in the figure represent an ideal case magnified by scanning electron microscopy, and in reality, the scratch marks 14 are much larger than those shown in the figure. In addition, not all are formed in an equilibrium relationship with each other, but are also formed differently in depth.

However, there is no problem in measuring the actual corrosion depth according to the present invention, because the interface 13 between the corroded portion 11 and the peeled portion 12 of the various scratch marks 14 is peeled off. This is because the depth of corrosion te can be measured by selecting the scratched mark l4 having a predetermined depth, in contact with the?).

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

TABLE 2

Steel specimens composed of the components shown in Table 2 were heat-treated at 900 ° C. for 2 minutes, and then corroded under the conditions shown in Table 3 below.

As described above, the corroded specimen was observed by a scanning electron microscope to observe the relationship between the amount of precipitates and the depth (te) of the corroded specimen, and the results are shown in Table 3 below.

In addition, the number and the like of the precipitate extracted by the carbon replica for the specimen was observed by measuring with a transmission electron microscope and the results are shown in Table 3 below.

TABLE 3

* ds, dv: diameter of average precipitate obtained from surface area and volume distribution

fv: volume fraction of precipitate

ns, nv: number of precipitates present per unit surface area and volume, respectively

As shown in Table 3, it can be seen that the corrosion depth (te) of the specimen is changed according to the corrosion conditions, which is a conventional method that the corrosion depth (te) is always constant regardless of the heat treatment conditions and the corrosion time of the steel Means that the amount of precipitate cannot be measured accurately.

The steel grade having the composition shown in Table 2 of Example 1 was heat-treated at the temperature and time as shown in Table 4, and then subjected to the solubility formula, the conventional method, and the present invention for the specimen corroded for 20 seconds with 1% nital solution The sediment fraction values of the precipitates were measured and the results are shown in Table 4 below.

TABLE 4

1.56에 의해서 계산된 값이다.The theoretical value fv shown in Table 4 is the solubility limit equation log [Nb] [C + N] =

It is calculated by 1.56.

As shown in Table 4, it can be seen that the result of the conventional method is about 5-10 times more than the theoretical value, which means that the conventional method is inaccurate in measuring the amount of precipitates.

As described above, in the present invention, when the amount of fine precipitates (particularly, precipitates of low alloy high tensile steel) is measured by carbon cloning, the corrosion depth of the specimen from which the precipitates are extracted is measured by scanning electron microscopy. Considering the change in the extraction depth of the precipitate according to the change of the heat treatment conditions, it is possible to give a means for accurately measuring the number of precipitates per unit volume of the specimen.

Claims (1)

In the quantitative measurement of precipitates by measuring the amount of precipitates by a carbon cloning method in a transmission electron microscope, finely polishing the surface of the steel specimen with a diamond powder of about 3μm, about half of the surface of the finely polished specimens lakomit Applying with Lacomit paint and then eroding the specimen surface with a 2% nital solution; Determination of precipitates (ns) per unit area and the average diameter (ds) of the precipitates by extracting the precipitates present on the surface of the specimen corroded by the carbon replica: after the applied paint is peeled off, the corroded portion and the paint is peeled off Measuring the corrosion depth (te) by enlarging and observing the scratch marks upon polishing on the boundary surface of the portion with a scanning electron microscope; And the number of precipitates per unit area (ns)

........................................ ... (2) Precipitate quantitative measurement, characterized in that comprising the step of converting to a volume fraction.

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