JPS61221385A - Method for descaling stainless steel material - Google Patents

Abstract

PURPOSE:To perform descaling easily without damaging heat treating furnace, by heat treating stainless steel material in a specified O2 atmosphere, then adhering aq. soln. of nitrate or ferric salt thereto at a specified temp., next, pickling said material. CONSTITUTION:If stainless steel material is charged into heat treating furnace of atmosphere contg. >=5% O2, then heat treated at about 1,100-700 deg.C, oxide film is formed on the surface of steel material. The steel is cooled to 700-300 deg.C, then aq. soln. of nitrate or ferric salt is adhered to said surface. Aq. soln. of these salts is penetrate into fine crack in scale, and the state easy for descaling is provided. Consequently, scale is removed simply by pickling in the following process. By the method, descaling is carried out easily, even if material contg. Pb in Cr stainless steel is used.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for descaling stainless steel materials, which removes an oxide film (scale) generated on the surface of stainless steel materials by heat treating the stainless steel materials. .

[Prior Art] Conventionally, when a stainless steel material is subjected to heat treatment such as annealing, scale is formed on the surface of the steel material, and in order to remove this scale, a mixture of lNO3-HF and l-1cQ is used.

The steel material after heat treatment was immersed in a descaling liquid such as H7SO4.

However, scale is insoluble in these descaling solutions, and a scale modification step is required to make the scale soluble in the descaling solution prior to the above descaling step. Such a scale modification process includes, for example, sodium immersion in which the steel material after heat treatment is immersed in a NaH salt bath.
The Hydride method and the HOOker method in which the steel material is immersed in a Na 0 H-Na NO 3 salt bath are available, but these methods require a large amount of energy to create the molten salt and require large-scale equipment. become.

As a means to solve this problem, for example,
3766 and Japanese Patent Publication No. 52-43767, there are methods in which stainless steel is coated with an alkali salt such as sodium chlorate or potassium chlorate and then heat treated, and the steel is heated while being cooled after heat treatment. A method of applying salt is known.

[Problems to be solved by the invention] However, in the former method, there is a problem in that the heat treatment furnace is attacked by volatilization of alkali, and both methods are suitable for chromium-based stainless steels containing lead. On the other hand, there was a problem that descaling was difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for descaling stainless steel materials, which solves the problems of the prior art described above and allows easy descaling of stainless steel materials containing lead.

[Means for Solving the Problems] The present invention, which was made to achieve the above object, has the following features: After heat treating stainless steel material in an atmosphere of 0.25% or more,
The method is characterized in that an aqueous solution of at least one of nitrates and ferric salts is applied to the steel material at a temperature of 0'C to 300C, and then pickled.

Here, the stainless steel material refers to nickel-based stainless steel and chromium-based stainless steel, and particularly refers to chromium-based stainless steel containing a spear. In addition, nitrate is Na
It refers to NO3, NH4NO3, and ferric salt refers to Fe.
CO3, Fe(NO3)3.

"e 2 (304) 3, etc." Attachment refers to methods such as spraying onto steel materials and immersion.

[Function] When a lead-containing chromium stainless steel material is heat treated at 1100° C. to 700° C. in an atmosphere of 5% or higher 02 in the heat treatment furnace, an oxide film is formed on the surface of the steel material. Next, the stainless steel material taken out from the heat treatment furnace was heated to 700℃~3
After cooling to 00°C, for example, Fe as a ferric salt is added.
An aqueous solution of CΩ3 is applied to the surface of the steel material.

At this time, fine racks are formed on the scale of the stainless steel material as it cools, and a second
A solution of iron salts penetrates to facilitate descaling.

Therefore, the HNO3-HF mixture for post-treatment.

Scale can be easily dissolved and removed using an acidic descaling solution such as HCΩ or HzSO4.

[Example] The present invention will be explained in detail below.

In Figure 1, P is added as a free-cutting element to stainless steel material.
Chromium stainless steel containing 0.03% b &1111
(SUS410), diameter 5.5mm, length 5Qmm
Cut it into a cylindrical shape and use it as a sample. This sample was placed in a heat treatment furnace and heat treated at 750° C. for 1 hour in an atmosphere of N2-5%02 in the furnace. After the heat treatment, while the sample was cooled to 600°C, an aqueous solution of FeCQ3'1O was sprayed onto the surface of the sample. After cooling in Trial 1, 3% by weight of HF and 15% by weight of HNO3 were sprayed onto the surface of the sample. The scale generated on the sample surface was dissolved and removed by immersion in the mixed solution at 40°C for 5 minutes.Then, the sample surface was brushed, washed with water, and dried, and the sample surface was visually observed to evaluate descaling performance. did.

In the above examples, the descaling property was 90% or more, and descaling was almost completely performed. Also, Na NO3 and N84 NO3 were used instead of FeCΩ3 aqueous solution.

A 10% by weight aqueous solution of Fe(NO3)3 nitrate was also able to achieve almost complete descaling.

On the other hand, as a comparative example corresponding to the conventional technology, an alkali salt (
When a saturated aqueous solution of Na 2 CO3) was used, the descaling performance was about 50%, which was incomplete. That is, in this example, even chromium-based suanless steel containing lead can be completely descaled.

Next, in the treatment process of the above example, only the concentration of 02 in the atmosphere in the heating furnace was changed, and the results are not shown in Figure 2. According to Figure 2, the results are shown in Figure 2. This results in better descaling properties. Therefore, in order to minimize scale on the surface of stainless steel, O
In this example, the 02 concentration is 5% or more, so it is easy to set the atmosphere of the heat treatment furnace.

Next, FIG. 3 shows the case where the atmosphere in the heat treatment furnace was kept constant at Nz+5%Q2 and only the temperature at which the FeCΩ3 aqueous solution was sprayed was changed. As is clear from the figure, 90
% or more, the treatment temperature is 30% or more.
0°C to 700°C is suitable, preferably 400'
100% descaling is possible at C~600'C.

Furthermore, in the above embodiment, since FeCQ3 or the like is attached to the steel material that is being cooled immediately after being taken out of the heat treatment furnace, there is also an energy saving effect.

[Effects of the Invention] As explained above, according to the present invention, the heat treatment furnace is not damaged due to the volatilization of the descaling solvent, and it can be applied not only to nickel-based stainless steel but also to chromium-based stainless steel containing Pb. Descaling can be easily performed even for

[Brief explanation of drawings]

FIG. 1 is a process diagram showing one embodiment of the present invention, and FIGS. 2 and 3 are graphs showing characteristics of the method according to the same embodiment.

Claims (1)

[Claims] After heat treating the stainless steel material in an atmosphere of O_25% or more, nitrate or secondary
attaching an aqueous solution of at least one of the iron salts to the steel material,
A method for descaling stainless steel material, which comprises then pickling.