JPS6230817A - Manufacture of martensitic stainless quenched steel stock - Google Patents

Abstract

PURPOSE:To extremely simplify the following descaling process or to make it unnecessary at all, by quenching and tempering cold rolled stock of martensitic stainless steel in inert gas atmosphere having an ultraflow temp. dew point. CONSTITUTION:Cold rolled stock of martensitic stainless steel is heated to 1,020 deg.C gaseous N2 or Ar atmosphere of <=30 deg.C dew point, then quenched, or further successively temper treated. Since generated oxidized scale in highly porous and has good reactivity with acid, fused alkali salt treatment, etc. are not needed at all, and complete descaling is possible by simple pickling or polish finishing just after quenching or tempering. In case quenching, tempering atmosphere is inert gas having <=-50 deg.C ultraflow temp. dew point, even if all of descaling treatments such as pickling and polish finishing are not carried out, not to mention molten alkali salt treatment, quenching member of martensitic stainless steel having beautiful surface is obtd.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for producing martensitic stainless steel, and particularly relates to a method for quenching or quenching and tempering the same, and a method for descaling the same. Used in the field of manufacturing hardened steel materials.

[Conventional technology]

Martensitic stainless steel is hardened by quenching and has excellent #4 toughness, so it is widely used for cutlery and spring materials. Martensitic stainless cold rolled steel materials used for these purposes are In the manufacturing process, rolling and annealing are repeated to achieve a predetermined thickness, and finally quenching or quenching and tempering is performed, followed by descaling treatment and, if necessary, a polishing finish.

In the above manufacturing process, the quenching treatment is generally performed in the atmosphere for 9
Because it is heated at a high temperature of 00 to 1,100 degrees Celsius and further tempered at a temperature of 200 to 800 degrees Celsius if necessary, a lumi oxide scale is generated on the surface of the steel material, and this oxide scale has no resistance to the inherent resistance of stainless steel. It is necessary to completely remove it from places where it impairs attractiveness and aesthetics.

However, since the oxide scale generated on the surface of martensitic stainless steel contains a large amount of Cr2O3 and is dense and strong in nature, it is very difficult to remove the scale. For this reason, the method for removing oxidized scale when martensitic stainless steel materials are quenched or quenched and tempered is to perform pretreatment with molten alkali salt treatment, and then pickle with nitric hydrofluoric acid and nitric acid. was.

However, the molten alkali salt treatment and the pickling treatment have the problem that waste liquid treatment is complicated, requires time and effort, and is expensive.

[Problem that the invention seeks to solve]

In view of the above-mentioned current state of the prior art, the present invention has been developed to provide the following advantages: When a martensitic stainless steel material undergoes a quenching or tempering process,
By creating a heating atmosphere for quenching and tempering in which the oxide scale generated on the surface of the steel material can be easily removed or does not need to be removed, the pretreatment for the pickling treatment for descaling - This eliminates the need for molten alkali salt treatment or even eliminates pickling treatment, which contributes to simplifying descaling treatment equipment, shortening descaling treatment time, and ultimately improving productivity and reducing production costs. The purpose of this invention is to provide a method for producing martensite stainless steel.

[Means and effects for solving the problems] The above objects of the present invention can be achieved by the following two inventions.

The gist of the first invention is as follows.

That is, in a method for producing a martensitic stainless steel cold rolled steel material, which comprises a step of quenching the martensitic stainless steel cold rolled steel material in an inert gas atmosphere having an ultra-low dew point, the cold rolled steel material is heated to a dew point of -30°C. A method for producing a martensitic stainless steel material, which comprises the following steps of quenching in an inert gas atmosphere, and a descaling step by pickling and/or polishing immediately after the quenching. .

The gist of the second invention is as follows.

That is, martensitic stainless steel quenching is characterized by having a step of annealing martensitic stainless steel cold-rolled steel material in an inert gas atmosphere with a dew point of -50°C or less, and after that, no descaling step is required at all. This is a method of manufacturing steel materials.

If hydrogen gas is used as the heating atmosphere for the quenching and tempering treatment of martensitic stainless steel, it will not be possible to obtain a light-obstructed quenched and tempered material without scale adhesion, but a large amount of hydrogen will enter the steel during heating. A hydrogen gas-containing atmosphere is not suitable because it causes significant embrittlement.

Therefore, an inert gas atmosphere is considered, but if only an inert gas is used, very thin and very dense scale will adhere during quenching of martensitic stainless steel, and it will be difficult to remove the scale. I found out. Furthermore, we obtained the knowledge that the cause of such dense scale formation is derived from trace amounts of moisture in the inert gas.

Next, the experiments that formed the basis of the present invention will be explained. 5U
A S420 J 2 marten type stainless steel plate (thickness 2.0+m) was used as a test material, and nitrogen gas with various dew points as shown in Table 1 was used at 1020°C in an atmosphere of 2. Gotsuga 8. After heating, the material was tempered in the atmosphere at 350° C. The descaling properties of the hardened and tempered material were investigated, and the results are also shown in Table 1.

From Table 1, in the case of both nitrogen gas and argon gas, if the dew point is below 130°C, molten alkali salt treatment as a pretreatment is not necessary during descaling, and simply pickling treatment is sufficient. It can be seen that descaling is possible. In the pickling treatment (nitric acid immersion, nitric acid electrolysis, or neutral salt electrolysis), the preferred conditions are listed below in terms of descaling performance and surface quality.

Table 1 Nitric acid immersion Concentration: 1-30% HNO solution
Temperature: Room temperature to 60°C Immersion time: 5 to 30 seconds Nitric acid electrolyte concentration: 1 to 30% HNO3 solution Temperature: Room temperature to 60°C Current density: 1 to 100 A/drn” Cathode treatment-anodic treatment or anodization electrolysis time (Anodizing time): 1 to 100 seconds Neutral salt electrolyte composition and concentration: 5 to 30% Na2SO, or 5 to 30% NaNO Solution temperature: Room temperature to 100°C Current density: 1 to 30 A/drn" Cathode treatment → Anodization or anodization Electrolysis time (anodization time): 1 to 100 seconds Martensitic stainless steel with a beautiful finish without roughening the surface by descaling under the above pickling conditions without molten alkali salt treatment You can get steel. Note that although nitric-fluoric acid immersion is possible for descaling, it cannot be used because the surface tends to become rough and it is difficult to set the conditions.

In addition, the oxide scale produced when quenching in an inert gas with a dew point of 130°C or less is very porous and highly reactive with acids, making it possible to simplify the descaling process as described above. However, even when the molten alkali salt treatment and pickling treatment were not performed at all, and polishing was performed with the quenched scale still attached, descaling was carried out extremely easily and a good polishing finish was achieved. .

If the dew point exceeds 130°C, the pickling conditions must be harsher than the above conditions unless pretreatment with molten alkali salt is performed. In that case, descaling is possible, but the texture may deteriorate. A problem will arise. Also, the dew point is ~30℃
If quenched materials are descaled by polishing alone, the scale is dense and strong, so the abrasive grains are worn out and it takes a very long time to completely descale, and this method reduces productivity. Therefore, it cannot be used in actual work. For these reasons, in the first invention, the inert gas atmosphere has a dew point of -30
Limited to below ℃.

Next, in the case of quenching at a dew point of 150° C. or lower, the scale produced is of such a scale that it is difficult to perceive it as temper color with the naked eye, and this oxide film is rich in #4 rustiness. Therefore, in this case, after quenching, there is no need for any descaling treatment, including a polishing process, and the product can be put to practical use as it is.

When the dew point exceeds 150°C, the resistance to oxide scale induction is poor, and a pickling or polishing process is essential. Therefore, in the second invention, the dew point of the inert gas during quenching is limited to -50°C or less. In the present invention, there are no particular limitations on the polishing process for surface conditioning performed after hardening. Furthermore, when tempering is performed, an atmosphere with a limited dew point of the inert gas of the present invention is suitable; however, if the tempering temperature is as low as 300°C or lower, the atmosphere must be an inert gas. For example, even if carried out in an oxidizing atmosphere such as the air, there is almost no oxide scale formation, and there is no particular limitation.

〔Example〕

A 5US420J2 stainless cold rolled steel plate cold rolled to a thickness of 06 was quenched at 1000°C in the atmosphere shown in Table 2. Next, tempering was performed at 350° C., and the quenched and tempered steel sheets were subjected to descaling treatment as shown in Table 2, if necessary.

All of these five examples have excellent surface properties and other internal qualities as quenched and tempered materials. Note that the purpose of polishing sample material No. 3 with a #320 belt grinder was to create gloss rather than descaling.

On the other hand, the descaling process is much simpler than the conventional descaling process, not to mention the molten alkali salt treatment.

〔Effect of the invention〕

As is clear from the above examples, the present invention provides martensitic stainless steel with a dew point of -30°C or below or -50°C.
By quenching in an inert gas atmosphere at 0°C or lower and tempering if necessary, the oxidized scale generated during C1 is easily removed or harmless, and the descaling efficiency in the next process, such as pickling, is improved compared to conventional methods. It is possible to reduce or eliminate descaling processing time, simplify or completely eliminate descaling processing equipment, reduce manufacturing costs, improve productivity, and take measures against pollution. I was able to achieve this effect.

Claims (2)

[Claims] (1) In a method for producing a martensitic stainless steel cold-rolled steel material comprising the step of quenching the martensitic stainless steel cold-rolled steel material in an inert gas atmosphere having an ultra-low dew point, the cold-rolled steel material is heated to a dew point of -30. A method for producing a martensitic stainless steel material, comprising the steps of quenching in an inert gas atmosphere at a temperature of .degree. C. or lower, and a descaling step by pickling and/or polishing immediately after the quenching. (2) A method for producing a martensitic stainless steel quenched steel material comprising the step of quenching the martensitic stainless steel cold rolled steel material in an inert gas atmosphere having an ultra-low dew point. A method for producing a martensitic stainless steel quenched steel material, comprising a step of quenching in an inert gas atmosphere at a temperature of 0.degree. C. or lower, and no descaling step is required thereafter.