JP2020079438A - Method for manufacturing hot-rolled austenitic stainless steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of ferrite in steel to a level at which no harmful effect occurs in a post-process while preventing coarsening of the structure during heat treatment after processing an intermediate product without changing the component system of the steel sheet. Provided is a method for manufacturing an austenitic stainless hot-rolled steel sheet, which is possible and suitable for a material for a clock and a material for a housing of an information communication device. SOLUTION: An austenitic stainless steel slab obtained by an ingot forming method or a continuous casting method is soaked under the conditions of a treatment temperature of 1150 to 1300 ° C. and a treatment time of 3 to 8 hours to increase the amount of ferrite in the steel. Is adjusted to 2.0% or less, or the relative magnetic permeability of the steel is adjusted to 1.020 or less, and then the soaking material is hot-rolled. [Selection diagram] Fig. 1

Description

  TECHNICAL FIELD The present invention relates to a method for producing an austenitic stainless hot rolled steel sheet suitable for materials for timepieces and information communication device housings, and particularly to an austenitic stainless hot rolled steel sheet capable of improving polishability and low magnetic permeability without lowering corrosion resistance. Manufacturing method.

  Conventionally, austenitic stainless hot rolled steel sheets of SUS316 series and SUS316L series, which are excellent in corrosion resistance and decorativeness, have been widely used as materials for timepieces used for wristwatch exterior parts and the like, and information communication equipment housings used for smartphone housings and the like. ing. The SUS316-based and SUS316L-based austenitic stainless steels contain a large amount of Cr and Mo in order to improve the corrosion resistance, but these Cr and Mo are elements that easily generate ferrite, and even if the hot-rolled sheet is annealed, ferrite May remain. If this ferrite remains in the steel sheet, streaks will occur during polishing, and the decorativeness and polishability will deteriorate, and the relative permeability will also increase, making it unsuitable as a watch material or a material for information and communication equipment housings. Becomes Therefore, in order to eliminate this ferrite from the steel sheet, it is sufficient to shift the annealing condition, which is the heat treatment after the intermediate product processing, to the high temperature/long time side, but excessive annealing causes orange peel due to the increase of crystal grains. Not only the decorativeness and free-cutting property are deteriorated, but also the strength of the steel material is deteriorated.

Therefore, as a technique capable of solving the above problems, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2004-176078) below, C: 0.10% or less by mass%, Si: 0.20- 1.00%, Mn: 0.50 to 2.00%, S: 0.050 to 0.300%, Ni: 10.00 to 15.00%, Cr: 14.0 to 18.00%, Mo : 1.00 to 3.00%, Al: 0.020% or less, Ca: 0.0010 to 0.0080%, O: 0.0040 to 0.012%, balance Fe and unavoidable impurities An austenitic free-cutting stainless steel consisting of is disclosed.
According to such a technique, not only excellent corrosion resistance and polishability, but also hot forging, cold forging, attention to productivity improvement such as cutting, especially austenitic stainless steel suitable for wristwatch exterior parts etc. It is said that it can be provided.

JP 2004-176078 A

However, although it is possible to suppress the generation of ferrite in steel and improve the polishability, etc. by changing the composition system as in the above-mentioned conventional technique, a drastic change in the composition system is Other quality items (such as mechanical properties) will inevitably be affected, which may cause deviations from the component range requested by the customer, or change to the conventional process for manufacturing processed products. There is also a possibility that it will have an adverse effect.
Therefore, the main problem of the present invention, without changing the composition system of the steel sheet, while preventing the coarsening of the structure during heat treatment after processing the intermediate product, adversely affect the amount of ferrite in the steel in the subsequent step. It is an object of the present invention to provide a method for producing an austenitic stainless hot rolled steel sheet suitable for a timepiece material and a material for an information communication device housing, which can be reduced to a level that does not exist.

  In order to solve the above problems, the method for producing an austenitic stainless hot rolled steel sheet according to the first aspect of the present invention is a slab of austenitic stainless steel obtained by an ingot making method or a continuous casting method at a treatment temperature: 1150 to 1150. It is characterized in that the soaking treatment is performed under the conditions of 1300° C. and treatment time: 3 to 8 hours to adjust the amount of ferrite in the steel to 2.0% or less, and then the soaking treatment material is hot rolled. To do.

  In this invention, the amount of ferrite in the steel is reduced to 2.0% or less by performing soaking treatment under the predetermined conditions at the stage of the slab, so that heat treatment such as subsequent hot rolling or annealing after intermediate product processing is performed. Is not required to be shifted to a high temperature/long time side, and even if such treatment is performed as in the conventional case, the amount of ferrite in the steel is reduced to such an extent that the residual ferrite does not cause an adverse effect.

  The method for producing an austenitic stainless hot rolled steel sheet according to the second aspect of the present invention is a slab of austenitic stainless steel obtained by an ingot making method or a continuous casting method, at a treatment temperature of 1150 to 1300° C. and a treatment time of 3 to. The steel is soaked under the condition of 8 hours to adjust the relative magnetic permeability of the steel to 1.020 or less, and then the soaked material is hot-rolled.

  In the present invention, the relative magnetic permeability of the steel is adjusted to 1.020 or less by performing the soaking process under the predetermined conditions at the stage of the slab. It will be suitable.

In the present invention, the soaking treatment is preferably performed in a continuous slab heating furnace.
Conventionally, the soaking process is performed in a batch heating furnace, but by performing the slab soaking process using a continuous slab heating furnace, the austenitic stainless hot-rolled steel sheet that is the target can be manufactured efficiently and economically. You will be able to.

  Furthermore, in the present invention, it is preferable to add a unique configuration described in the embodiments described later.

  According to the present invention, without changing the composition system of the steel sheet, while preventing coarsening of the structure during heat treatment after processing the intermediate product, the ferrite content in the steel is reduced to a level at which no adverse effect occurs in the subsequent process. It is possible to provide a method for producing an austenitic stainless hot-rolled steel sheet suitable for a watch material or a material for an information communication device housing.

It is a graph which shows the relationship between the 1240 degreeC soaking process time and the ferrite amount in steel in each layer of a slab. It is a graph which shows the relationship between the soaking process time at 1240 degreeC, and the relative magnetic permeability of steel. It is a graph which shows the relationship between the soaking process temperature and the relative magnetic permeability of steel in a soaking time of 6 hours.

The method for producing an austenitic stainless hot-rolled steel sheet of the present invention is a slab of austenitic stainless steel obtained by an ingot making method or a continuous casting method under the conditions of treatment temperature: 1150 to 1300° C. and treatment time: 3 to 8 hours. Characterized by soaking the ferrite content in the steel to 2.0% or less or adjusting the relative permeability of the steel to 1.020 or less, and then hot rolling the soaked material. And
First, the reasons for limiting each condition of the soaking treatment before hot rolling constituting the method for producing an austenitic stainless hot rolled steel sheet according to the present invention will be described.

FIG. 1 shows the steel type No. of Table 1 below. It is a graph which investigated using the material of (alpha), and shows the relationship between the 1240 degreeC soaking process time in each slab layer, and the ferrite amount in steel. Specifically, the steel grade No. manufactured by the continuous casting method was used. Samples of 25 mmT×25 mmW×30 mmL size divided in the thickness direction from the central portion in the width direction of the α slab (195T×1280W) were sampled and heated in an Ar atmosphere electric furnace at a heating temperature of 1240° C. for 1 to 6 It was kept heated for a certain period of time. Then, the result of cooling to room temperature by air cooling and measuring the amount of ferrite in the steel in a cross section in the direction perpendicular to the casting with a ferrite scope manufactured by Fisher is shown in FIG.
The portions other than the chemical components shown in Table 1 are Fe and inevitable impurities.

  As shown in this figure (graph), when the heat treatment temperature (soaking treatment temperature) is 1240°C, the ferrite content in the steel increases until the heat treatment time (soaking treatment time) reaches approximately 1 hour, but then decreases. It can be seen that the amount of ferrite in the steel in all the layers in the thickness direction becomes 2.0% or less after approximately 3 hours.

FIG. 2 shows the steel type No. of Table 2 below. 6 is a graph showing the relationship between the soaking treatment time at 1240° C. and the relative magnetic permeability of steel examined using the β material. Specifically, the steel grade No. manufactured by the continuous casting method was used. Samples of 25 mmT x 25 mmW x 10 mmL size were taken from the slab thickness center of the β slab (test materials A and B; 200T x 1266W) and the center in the width direction, and the heating temperature was 1240°C in an Arema furnace in an Ar atmosphere. The heating and holding were performed for 2, 4 and 6 hours. Then, it cooled to room temperature by air cooling, and measured the relative magnetic permeability of the steel according to ASTM A342 test method 4 using the FERROMASTER by Stefan Mayer Instruments company for the cross section in the casting right angle direction.
The portions other than the chemical components shown in Table 2 are Fe and inevitable impurities.

  As shown in this figure (graph), when the heat treatment temperature (soaking treatment temperature) is 1240°C, although the relative magnetic permeability of the steel tends to increase immediately after the start of the soaking treatment, the heat treatment time (soaking treatment time) is 2 hours. In the case where the heat treatment temperature exceeds 3 hours, the relative magnetic permeability of the steel tends to decrease in proportion to the heat treatment time. In the case where the heat treatment temperature exceeds 3 hours, the relative magnetic permeability of the steel is 1.020 or less, which is suitable for watch materials. It can be seen that the relative magnetic permeability further decreases as the treatment time increases.

  FIG. 3 shows the steel type No. of Table 2 above. It is a graph which investigated using the material of (beta), and shows the relationship between the soaking process temperature in 6 hours of soaking|uniform-heating, and the relative magnetic permeability of steel. Specifically, steel type No. manufactured by the continuous casting method. Samples of 25 mmT×25 mmW×10 mmL size were taken from the slab thickness center and the width direction center of the β slab (test materials A and B; 200T×1266W) and heated in an Arema furnace in an Ar atmosphere at heating temperatures 1200, 1240, It was heated and held at 1260° C. for 6 hours. Then, it cooled to room temperature by air cooling, and measured the relative magnetic permeability of the steel based on ASTM A342 test method 4 using the FERROMASTER by Stefan Mayer Instruments company for the cross section in the casting right angle direction.

  As shown in this figure (graph), when the heat treatment time (soaking treatment time) is set to 6 hours, the relative magnetic permeability of steel is 1.020 or less, which is suitable for watch materials, even if the heat treatment temperature (soaking treatment temperature) is 1200°C. It can be seen that the relative magnetic permeability becomes lower as the heat treatment temperature rises.

  To summarize the above, the effect of the soaking treatment before hot rolling largely depends on the treatment temperature and the treatment time, and as a result of comprehensively judging each of the above data, as described above, the soaking treatment temperature is Within the range of 1150 to 1300° C., the soaking time is within the range of 3 to 8 hours, and the amount of ferrite in the steel is 2.0% or less, or the relative permeability of the steel is 1.020 or less. It is preferable to adjust. By doing so, the hot-rolled steel sheet obtained by hot-rolling the soaked material can proceed the subsequent manufacturing steps in the same manner as conventional ones without changing the composition system of the steel sheet. Therefore, it is possible to prevent coarsening of the structure during heat treatment after processing the intermediate product, and it is possible to reduce the amount of ferrite in the steel to a level that does not cause any adverse effect in the post-process. It is suitable for body material.

  Further, generally, the soaking treatment is a heat treatment performed on the ingot in a batch type, but the soaking treatment of the present invention performed at the slab stage is performed by a walking beam type continuous heating furnace or a pusher type continuous heating furnace. It is preferable to use such a continuous slab heating furnace. By using such a continuous slab heating furnace, the slab soaking process can be carried out efficiently and economically.

Claims (3)

An austenitic stainless steel slab obtained by the ingot casting method or the continuous casting method is subjected to a soaking treatment under the conditions of a treatment temperature: 1150 to 1300° C. and a treatment time: 3 to 8 hours, so that the amount of ferrite in the steel is 2.0%. Adjust to the following, then hot-roll the soaked material,
A method for producing an austenitic stainless hot-rolled steel sheet characterized by the above. The austenitic stainless steel slab obtained by the ingot casting method or the continuous casting method is subjected to a soaking treatment under the conditions of a treatment temperature: 1150 to 1300° C. and a treatment time: 3 to 8 hours so that the relative magnetic permeability of the steel is 1.020 or less. And then hot rolling the soaked material,
A method for producing an austenitic stainless hot-rolled steel sheet characterized by the above. The method for producing an austenitic stainless hot rolled steel sheet according to claim 1 or 2,
A method for producing an austenitic stainless steel hot rolled steel sheet, wherein the soaking treatment is performed in a continuous slab heating furnace.