JPS6210219A - Manufacture of as-rolled feritic stainless steel sheet having superior ridging resistance - Google Patents

Abstract

PURPOSE:To manufacture an as-rolled ferritic stainless steel sheet having superior ridging resistance by hot rolling a ferritic stainless steel at a specified draft and a specified rate of strain in a specified temp. range. CONSTITUTION:When a ferritic stainless steel is hot rolled to a prescribed thickness, hot rolling is carried out at >=20% draft and >=150<-1> rate of strain in the temp. range of 1000-500 deg.C in at least one pass. The stainless steel contains about 0.12% C and about 10-20% Cr and is heated to about 800-1250 deg.C in the form of a slab before the hot rolling. Thus, a steel sheet having improved ridging resistance is obtd. in simplified manufacturing stages because a cold rolling stage can be eliminated.

Description

[Detailed Description of the Invention] (Industrial Application Field) Regarding the production of ferritic stainless steel sheets, especially the regulation of rolling conditions, this specification omits the cold rolling process and the recrystallization annealing process to improve ridging resistance and processability. This article describes the results of development research that revealed that it is possible to manufacture thin steel sheets with good properties.

Needless to say, ferritic stainless steel is cheaper than austenitic stainless steel, and has features such as no stress corrosion cracking, so it is widely used in various kitchen utensils, automobile parts, etc. On the other hand, in order to prevent pollution caused by plating, it is used as a substitute for plated parts, and the number of people using it is increasing.

However, when cold-rolled thin steel sheets made of ferritic stainless steel are press-formed, unique irregularities along the rolling direction called ridging tend to occur, which significantly impairs the surface beauty of the molded product. There is no denying the fact that ferritic stainless steel is an obstacle to expanding its uses.

(Prior art) Many studies have been conducted on the causes of this ridging, and it is now known that hot-rolled sheets have large stretching in the rolling direction originating from the hot rolling or casting structure, and orientations that are crystallographically close to each other. It is thought that this is because a band-like structure having .

All conventional adhesive run prevention measures are aimed at preventing or destroying this band-like tissue.For example, US Pat.
No. 16) proposes to improve the ridging property by performing low-temperature hot rolling and box annealing at 800 to 830"C, followed by cold rolling and annealing. On the other hand, JP-A-51 -450・～7 in Publication No. 128720
The occurrence of ridging is prevented by rolling with a reduction rate of 15 inches or more in the temperature range of 00°C, followed by annealing, cold rolling, and final annealing. It is taught that the occurrence of ridging can be improved by performing hot rolling with a rolling reduction of 20 inches or more and then performing hot rolled plate annealing-cold rolling-annealing.

All of these methods are extremely effective means for preventing ridging, but the biggest drawback of the conventional ferritic stainless steel sheet manufacturing process is that the process steps are extremely long, and therefore the energy required to produce the final product is extremely low. , not only requires a huge amount of manpower and time, but also causes various problems in product quality during these long processes.

In particular, it is essential that the manufacturing procedure for ferritic stainless steel sheets for processing includes a cold rolling process (rolling temperature below 300°C), and this cold rolling process not only aims to reduce the desired thickness; Another aim is to use the plastic strain introduced by cold working to promote the growth of crystal grains with the (111) orientation, which is advantageous for deep drawability, in the final annealing process. The problem that is being solved by cold working as described above is that the deformation resistance in the temperate zone is significantly higher than in hot working, so the energy required for rolling is enormous, and the rolling rolls are severely worn. Rolling problems such as slips are also likely to occur. Further, in the annealing process, unavoidable problems include surface concentration of impurity elements and deterioration of surface beauty due to surface oxidation.

On the other hand, it can be rolled at a relatively high temperature range of 500 to 1000'C, and the cold rolling process and recrystallization annealing process can be omitted.
Furthermore, the present invention focuses on the fact that if good ridging resistance and workability are obtained, the above-mentioned problems can be eliminated and there are great manufacturing advantages. 0 (Means for solving the problem) In the process of rolling to a plate thickness, at least one pass is
At a temperature range of 00°C, reduction rate of 20 inches or more, strain rate of 1
508 or more, the method for manufacturing an Azrold 7 elite stainless steel sheet (first invention) is characterized in that it is rolled at a rolling speed of at least one pass. Reduction rate of 20 in the temperature range of 1000 to 500℃
% or more, the strain rate is 1508 or more, and the strain rate (-) and friction coefficient (μ) satisfy ■/μ≧500. The method for producing a rolled ferritic stainless steel sheet (second invention) further improves workability and advantageously achieves this.The explanation will begin with the research results that form the basis of this invention.

As sample material: C: 0.05chi, si: 0.21%
, Mn: o, 13%, P: 0.022%, S: 0.
006chi, qr: 1 6.5 1%,'N
i: 0.10%, Al: 0.02% and N: 0. A factory hot-rolled sheet of ferritic stainless steel with a thickness of 3.0 plates was used, with OR3chi (each is wt%), and the remainder was essentially Fe. The hot-rolled sheet was heated to 850 ° C. After soaking, 1 bath 10%, 2
0 inch and 30% rolling were performed. At this time, the strain rate was changed by changing the rolling speed. Figure 1 shows the relationship between strain rate and Lang index, and the ridding index strongly depends on the strain rate. It has been shown that the ridging resistance is significantly improved by using 0 lubricating oil. At the same time, an experiment was conducted in which the friction coefficient between the rolled material and the roll during hot rolling was varied by changing the lubrication conditions. Mineral oil was applied to the roll using a sprayer in varying amounts to vary the coefficient of friction (μ).

Figure 2 shows the ratio of strain rate) to friction coefficient (μ) ``t/
The influence of μ on the i value after annealing is shown. shi/μ is 500
With the above, r was significantly improved.

Note that the strain rate (-) was determined according to the following formula.

Here, n: Rotation speed of the rolling roll r: Reduction rate (%) / l OO R: Radius of the rolling roll (Ill) Ho = Rolling plate thickness (10 m) The inventors conducted research based on this basic data. heavy ′
As a result, we have found that by regulating the manufacturing conditions as described below, it is possible to manufacture stainless thin steel sheets with excellent ridging resistance and press formability.

Although the mechanisms of high strain rate rolling and lubricated rolling are not necessarily clear, they are thought to have a close relationship with changes in the texture of the rolled material and working strain.

Regarding the relationship with steel composition, the effect of high strain rate rolling does not essentially depend on the steel composition, but the purity targeted by this invention is a:o, xz% or less, ar:lO~20chi. 7 elite stainless steel containing 15
0 S-1 or more provides complete ridging resistance.

Next, as for the method of manufacturing the rolled material, not only ingot-blurring rolling but also steel slabs obtained by continuous casting can be applied.

However, if the heating temperature of the steel billet is too low, the rolling load will increase and scratches are likely to occur, while if it is too high, the crystal grains will become coarse. °C is preferred.

It goes without saying that the so-called Co-DR (continuous casting-direct rolling) method, in which rolling is started without reheating the billet after continuous casting, is also applicable. The methods of casting rolled material (sheet bar caster method and strip caster method) also have great economic merit from the viewpoint of process saving, and are also advantageous as a method for producing the rolled material of the so-called plate of this invention.

The hot rolling process is the most important in this invention, and in order to improve the desired ridging resistance, at least one bath is carried out at a temperature range of 1000 to 500°C, with a reduction rate of 20% or more and a strain rate of 150 S. It is essential to carry out hot rolling in the above manner. In order to improve workability, at least one bath is carried out at a temperature range of 1000 to 500°C with a reduction rate of 20.
It is essential to perform rolling at a strain rate of 150 B-1 or higher, and under conditions where the strain rate) and the friction coefficient (μ) satisfy the relationship -/μ≧500.

Regarding the rolling temperature, rolling at high temperatures exceeding 1000°C makes it difficult to ensure ridging resistance and workability by controlling the strain rate, while rolling at temperatures below 500°C results in a significant increase in deformation resistance and makes recrystallization difficult. 1000 to become
Unless the zero strain rate, which is limited to ~500°C, is 150 S-1 or higher, it is not possible to secure a material with excellent ridging resistance as desired.

The number of rolling passes and the distribution of the rolling reduction ratio may be arbitrary as long as the above conditions are satisfied. The arrangement and structure of the rolling mill, roll diameter and tension, type of lubricating oil, lubrication method, etc. have no essential influence.

In addition, recrystallization annealing treatment is not required in principle, but due to material requirements, heat retention or soaking treatment may be performed on the runout table after rolling and during the winding process, or if necessary, some heat treatment may be performed after rolling. It does not prohibit the use of

Regarding pickling, the steel strip obtained by the above procedure has a thinner oxidized layer because it is rolled at a lower temperature than conventional methods, and can be used for a wide range of purposes without pickling. In addition to shot blasting and acid removal, mechanical removal is also possible.
The ridging resistance of ferritic stainless steel is determined by applying at least 1 bath of rolling according to the present invention at a temperature range of 1000 to 500°C at a rolling reduction rate of 20 inches and a strain rate of 0 (effect). ) 150 S
−1 or more, and in addition, the workability is
However, as explained in the background of the experiment, if the temperature range of 1000 to 500°C, the reduction rate of 20% or more and the strain rate of 1508 or more are not satisfied, the cast structure will be significantly improved. There is no effect due to insufficient crushing, and no improvement in workability is observed when the C/μ is 500.

(Example) Steels having the compositions shown in Table 1 (B) to (F) were processed into sheets of 20 to 40 plate thickness by continuous casting in a converter and rough rolling or converter and seed per caster. A steel billet manufactured by continuous casting was heated to 1100°C, soaked, and then roughly rolled. This sheet bar was rolled using a rolling mill consisting of 6 rows to form a steel slab of 1.0 to 8. A thin copper strip having an OB plate thickness was made, and at this time, the highest strain rate was achieved at the last row of stands, and lubricated rolling was also performed at the last row of stands. Table 2 shows the rolling conditions of the last row stand and the material properties of the thin steel strip.

The r value in Table 2 is 15% using JI3 No. 5 test piece.
Measured by the three-point method after applying a tensile strain of (r
C was determined as + r + 2 rD) / 4.

The ridging property was evaluated by using a JI3 No. 5 test piece cut out from the rolling direction, applying a tensile strain of 15%, measuring the surface irregularities using a surface roughness meter, and evaluating the ridging property according to the following criteria.

Riding rank Steel plate waviness height 1 (Good) 10~2 Q ptn5 (
Poor) 〉70μm Ratings of 1 and 2 indicate ridging properties that pose no practical problems.

(Effects of the Invention) According to the first invention, the ridging resistance of the ferritic stainless steel sheet is significantly improved by controlling the temperature and processing conditions in at least one bath of the rolling process, and according to the second invention, the lubrication conditions during rolling are further improved. The addition of control operations can also bring about a marked improvement in processability.

In addition, the cold rolling process can be omitted, and the rolled material is compatible with the sheet bar caster method, strip caster method, etc., and the manufacturing process of ferritic stainless thin steel sheets for processing can be simplified.

[Brief explanation of the drawing]

Figure 1 is a graph of the relationship between strain rate and rank index, and Figure 2 is a graph of the relationship between strain rate, friction coefficient ratio, and r value. F-relaxing〈〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉0

Claims (1)

[Claims] 1. In the step of rolling ferritic stainless steel to a predetermined thickness, at least one pass is performed at a temperature range of 1000 to 500°C, a reduction rate of 20% or more, and a strain rate of 150 s^.
- A method for producing an azurold ferritic stainless steel sheet having excellent ridging resistance, the method comprising rolling at a rolling temperature of 1 or higher. 2. In the process of rolling ferritic stainless steel to a predetermined thickness, at least one pass is performed at a temperature range of 1000 to 500°C, with a reduction rate of 20% or more and a strain rate of 150 s^.
An azurolled ferritic stainless steel sheet with excellent ridging resistance and workability, which is characterized by being rolled under conditions where the strain rate (■) and friction coefficient (μ) satisfy −ﾆ1 or more and the strain rate (■) and friction coefficient (μ) satisfy ■/μ≧500. manufacturing method.