JPH0613756B2 - Ferrite grain boundary developing solution and etching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a revealing solution that clearly reveals ferrite crystal grain boundaries of steel regardless of the material, and an etching method using the revealing solution.

[Conventional technology]

The grain size of steel significantly affects the mechanical properties and workability of steel. Therefore, it is important to quantitatively grasp the size of these crystal grains, that is, the crystal grain size, in order to know the various properties of the steel, and the test methods for the austenite crystal grain size and ferrite crystal grain size are specified in JIS, ASTM, etc. Has been done. In such a grain size test, it is necessary to first expose the crystal grain boundaries by etching the observation surface of the crystal grains. Has been used.
This is a nitric acid alcohol solution in which nitric acid is mixed with ethyl alcohol or methyl alcohol to be about 5%.
The etching was carried out by immersing a steel material whose polished surface was polished and mirror-finished in this nitric acid alcohol solution for several seconds to 1 minute, washed with water, and dried.

[Problems to be Solved by the Invention]

However, in the above-mentioned nitric acid alcohol solution and the etching method using this solution as an exposing liquid, the exposed ferrite crystal grain boundaries may be unclear like Ti-added steel, for example. Further, when investigating the recrystallization temperature region due to annealing of the thin steel sheet, the appearance of ferrite grain boundaries due to etching was unclear, so the structure after cold rolling was observed as if recrystallization did not begin, and There was a problem that the recrystallization temperature could not be obtained.

The present invention solves the above problems, and clearly reveals the ferrite crystal grain boundaries of the steel material, which has been difficult to appear conventionally.
It is an object of the present invention to provide an exposing solution that can reveal ferrite crystal grain boundaries that have been conventionally revealed, but are not always clear, and an etching method using the revealing solution.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present inventors have conducted various studies on the composition of the grain boundary expressing liquid and completed the present invention. That is, in the present invention, 0.1 ml of picric acid is added to 100 ml of water.
5-0.6g and sodium dodecylbenzene sulfonate 1.
0-8.0 g was dissolved, and further hydrochloric acid or sulfuric acid 1.0-5.0 ml was added, a ferrite crystal grain boundary developing solution (hereinafter referred to as Ferrist reagent), and an etching method using the above-mentioned Ferrast reagent, That is, the steel material is immersed in a Ferrast reagent, the corrosion product is generated on the surface and then taken out to remove this corrosion product, washed with water, dried and immersed in a nitric acid alcohol solution, taken out from this solution and washed with water,
An etching method characterized by drying, and immersing the steel material in a Ferrast reagent heated to 60 to 90 ° C., removing the corrosion product generated on the surface after taking out from this reagent, washing with water, and drying. The present invention relates to a characteristic etching method.

[Action]

In the ferast reagent of the present invention, picric acid has the effect of selectively dissolving ferrite crystal grain boundaries to expose the grain boundaries, but if this content is less than 0.5 g per 100 ml of water, the dissolution rate is low, while If it exceeds 6.0 g, it will be difficult to control dissolution, so the content should be 100 ml of water.
The amount was 0.5 to 6.0 g.

Sodium dodecylbenzene sulphonate has the effect of alleviating the above-mentioned action of dissolving picric acid, but if its content is less than 1.0 g per 100 ml of water, the above effect is insufficient. However, the effect is not increased, so the content should be 1.0-
It was 8.0 g.

Hydrochloric acid or sulfuric acid is added to adjust the pH of the Ferrast reagent to be acidic and promote the action of picric acid, but if the addition amount is less than 1.0 ml with respect to 100 ml of water, the above effect is insufficient, while 5.0 ml is added. If it exceeds the above range, it becomes difficult to selectively control the dissolution of the crystal grain boundaries, so the addition amount is set within the above range.

〔Example〕

 Hereinafter, description will be made based on examples.

First, the method of preparing the Ferrast reagent, but 100 ml of water
Into a container, 0.5 to 6.0 g of picric acid is dissolved while heating, and 1.0 to 8.0 g of sodium dodecylbenzene sulfonate is added and dissolved while stirring. After the dissolution is completed, hydrochloric acid or sulfuric acid is added and mixed in the range of 1.0 to 5.0 ml. Since the degree of corrosion of the steel surface during etching differs depending on the steel type to be etched, for example, if it is necessary to suppress the corrosion of the steel surface as a whole, increase the content of sodium dodecylbenzene sulfonate, and also the ferrite crystal grains themselves. If it is necessary to suppress the corrosion of the above, the content of hydrochloric acid, sulfuric acid or picric acid is reduced, etc., and each chemical is appropriately adjusted within the above range. In this example, picric acid was 2.5 g, sodium dodecylbenzene sulfonate was 6.0 g, and the amount of hydrochloric acid added was 1.0 ml.

Next, as an etching method using the above-mentioned Ferrast reagent, for example, a steel material is immersed in a 5% nitric acid alcohol solution for about 5 seconds, and the degree of corrosion of the surface is observed to judge the ease or difficulty of corrosion. , According to which one of the following two methods is adopted. That is, if the surface of the steel material is relatively easily corroded, the steel material with the observation surface polished and mirror-finished is immersed in a Ferrast reagent at room temperature to form a corrosion product on the observation surface, which is then taken out from the reagent and washed with water. After-corrosion products are removed, washed again with water, dried with warm air, and then 5
% Nitric acid alcohol solution for 10 to 20 seconds, taken out, washed with water, and dried (hereinafter referred to as etching A method). If the surface of the steel material is relatively unlikely to be corroded, the steel material with a mirror-finished observation surface is immersed for 1 to 5 minutes in a Ferrast reagent heated to about 60 to 90 ° C. and taken out from the reagent. After that, a method of removing the corrosion product generated on the surface, washing with water and drying (hereinafter referred to as etching B method) is used. In the etching B method,
In this example, the heating temperature of the Ferrast reagent was 70 ° C. and the immersion time of the steel material was 5 minutes.

As a method of removing the corrosion product generated on the observation surface, it is optimal to use a buff cloth without damaging the observation surface.
When a clear ferrite grain boundary cannot be obtained by observing the etching surface with a microscope, the etching by the above etching method A or etching method B is repeated again.

FIGS. 1 to 4 show the metallographic structures obtained when etching was performed by the etching A method or the etching B method of the present invention using the Ferrast reagent of the present invention prepared as described above for various steels. And micrographs showing the metal structures obtained when etching was performed by the conventional method, respectively. FIG. 1 shows the case where a rimmed steel sheet was used as the test material, and FIG. 2 and FIG. Are all Ti-containing low alloy steel sheets, FIG. 2 is as-rolled, FIG. 3 is after annealing at 800 ° C., and FIG. 4 is when Si-containing magnetic steel sheet is used.

In Fig. 1 using a rimmed steel sheet as the test material, (a)
The figure shows an example of the present invention when etching was performed by the etching A method using a Ferrast reagent, and the figure (b) shows a conventional example when etching was performed for about 40 seconds in a 5% nitric acid alcohol solution. From FIG. 1, it can be seen that the ferrite crystal grain boundaries are clearer in the case of the present invention example than in the conventional example.

In FIG. 2, (a) shows the case where etching is performed by the etching B method using a Ferrast reagent (example of the present invention),
(B) The figure shows the case of etching in a 5% nitric acid alcohol solution for about 60 seconds (conventional example).
In the present example using the low alloy steel containing i, it can be seen that the ferrite grain boundaries cannot be discriminated at all in the conventional example, whereas the grain boundaries appear unclearly in the example of the present invention. In addition, FIG. 3 shows a second example of the annealed material containing Ti.
When the etching is performed under the same etching conditions as shown in the figure, (a) shows the example of the present invention and (b) shows the conventional example. In each case, the ferrite grain boundaries are clearly shown as compared with FIG. 2, and it is understood that the sharpness is particularly high in the examples of the present invention.

In FIG. 4, (a) shows the case where etching is performed by the etching A method using Ferrast reagent (invention example),
(B) is a case where etching is performed in a 5% nitric acid alcohol solution for about 60 seconds (conventional example). However, in the present example for a Si-containing magnetic steel sheet, the present invention is compared with the conventional example. It can be seen that the ferrite grain boundaries are clearer in the example.

〔The invention's effect〕

As described above, in the ferrite grain boundary test, using the ferrite grain boundary developing solution of the present invention containing picric acid, sodium dodecylbenzene sulfonate and hydrochloric acid or sulfuric acid in a predetermined range, the etching method of the present invention By applying, it is possible not only to clearly express the ferrite crystal grain boundaries, which have been difficult to express up to now, but also to express the ferrite crystal grain boundaries that have been conventionally revealed more clearly. This is not only effective in checking the quality of steel products, but also provides a useful tool in the research and development of steel products.

[Brief description of drawings]

1 to 4 are micrographs of a metal structure obtained by etching according to the method of the present invention and the conventional method.
The figure shows the case of using a rimmed steel sheet as the sample material, and the figure 2 shows the case of using a Ti-containing low alloy steel sheet as rolled.
Similarly, when a low alloy steel sheet containing Ti is used after annealing, FIG. 4 is a case where an electromagnetic steel sheet containing Si is used.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-52-23698 (JP, A) JP-A-59-219473 (JP, A) JP-A-62-238380 (JP, A)

Claims (3)

[Claims] 1. A ferrite grain boundary expression characterized by dissolving 0.5 to 6.0 g of picric acid and 1.0 to 8.0 g of sodium dodecylbenzene sulfonate in 100 ml of water, and further adding 1.0 to 5.0 ml of hydrochloric acid or sulfuric acid. Discharge. 2. A steel material is immersed in the ferrite grain boundary developing solution according to claim 1 to form a corrosion product on the surface and then taken out to remove the corrosion product, washed with water and dried, and then nitric alcohol. An etching method comprising immersing in a solution, removing from the solution, washing with water, and drying. 3. A steel material is immersed in a ferrite grain boundary developing solution according to claim 1 heated to 60 to 90 ° C., and the corrosion product formed on the surface after removal from the developing solution is removed. An etching method characterized by washing with water and drying.