JP3508500B2 - Manufacturing method of austenitic stainless steel - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 18% Cr-8% Ni
Austenitic stainless steel with less streak pattern suitable for use in construction interior / exterior parts, bathtubs, various kitchen appliances, etc. that require particularly good surface aesthetics The present invention relates to a method for manufacturing a steel sheet. [0002] Austenitic stainless steels are widely used in the fields of building interior and exterior parts, bathtubs, various kitchen appliances, etc. because of their excellent workability and ridging resistance. However, in austenitic stainless steel, a striped pattern, that is, uneven luster, may occur on the surface of the steel sheet, which significantly impairs aesthetic appearance and reduces product value. It has become. For this reason, a method for producing an austenitic stainless steel sheet that prevents uneven gloss and has a stable gloss has been proposed, and there are many published techniques. For example, Japanese Patent Application Laid-Open No. Sho 62-17138 discloses a technique in which a predetermined amount of oil having a specific viscosity is applied before continuously annealing an austenitic stainless steel strip. This technique is intended to uniformly form an oxide scale layer on the surface of a steel strip to reduce unevenness in gloss after pickling due to uneven adhesion of rolling oil and rolling wear powder. Japanese Patent Application Laid-Open No. 7-155809 discloses a method in which the surface roughness of a roll used at the time of cold rolling is gradually reduced from rough to dense and then cold rolled. According to this, it is said that a stainless steel plate having a high gloss and a uniform glossy surface can be obtained without being largely affected by the previous history of the material to be rolled. [0004] However, Japanese Patent Application Laid-Open No. 62-17138 and Japanese Patent Application Laid-Open No.
All of the techniques disclosed in the above-mentioned publications have a problem that the equipment is remodeled and the manufacturing cost is increased. Accordingly, a main object of the present invention is to propose a method of manufacturing an austenitic stainless steel sheet with few streak patterns, which does not need to be concerned with the above-mentioned equipment remodeling, which the above-mentioned known technology has. is there. Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the manufacturing conditions in detail, particularly focusing on the hot rolling step. Austenitic system with less streak pattern without equipment remodeling by presuming that it is caused by surface gloss unevenness due to local difference in recrystallization behavior during It has been found that a stainless steel plate can be manufactured and the object of the present invention can be achieved. The present invention has been completed based on this finding, and the gist is as follows. In hot rolling an austenitic stainless steel slab by a rough rolling mill and a finishing rolling mill,
A method for producing an austenitic stainless steel, characterized in that rolling is performed so that the finish rolling end temperature FDT is higher than the finish rolling start temperature FET. Hereinafter, the present invention will be described more specifically based on experimental results. SUS 304 (0.05wt% C-
0.50wt% Si-1.05% Mn-0.033wt% P-0.02Swt% Al-
0.040 wt% N-18.2 wt% Cr-8.4 wt% Ni) and SUS316
(0.06% C-0.60wt% Si-1.02wt% Mn-0.035wt% P-
0.02S-0.024wt% N-16.9wt% Cr-10.6wt% Ni-2.2
After heating two stainless steel slabs (slab thickness 200 mm) having the composition of wt% Mo-0.020 wt% Ti) to 1260 ° C,
A 30 mm-thick sheet bar was obtained by rough rolling using a rolling mill including a stand. Next, this sheet bar was subjected to hot finish rolling by a rolling mill comprising seven stands to a thickness of 5.0 mm.
And two types of hot-rolled sheets having a diameter of 1.3 mm and wound at 650 ° C. Thereafter, the hot-rolled sheet having a thickness of 5.0 mm was subjected to hot-rolled sheet annealing, pickling, cold-rolled to a thickness of 0.4 mm, and then finish-annealed. Further, a hot-rolled sheet having a thickness of 1.4 mm was subjected to the test as it was after annealing. The hot-rolled sheet was annealed at 1150 ° C for SUS 304.
SUS 316 was performed at 1160 ° C. Finish annealing temperature is SUS 304
Was 1120 ° C, and SUS316 was 1135 ° C. In the obtained steel strip, the degree of occurrence of streak patterns on the surface of the steel sheet over the entire width of the coil is A (good) to D.
Indexed to (poor). For this indexing, the gloss was measured at 1 mm intervals with a gloss meter for the entire width of the coil.
When the glossiness difference between the measurement points adjacent to each other is less than 4, the surface streak index A is less than 4, and when there is less than 4 or more, the surface streak index B is less than 8. The surface streak pattern index C was defined as the case where it was present, and the surface streak pattern index D was defined as the case where 8 or more were present. Figure 1 shows the results.
Shown in FIG. 2A shows SUS 304, and FIG. 1B shows SUS 316. FIG. 1 shows that the hot finish rolling end temperature (FDT) of the SUS 304, SUS 316, hot rolled sheet and cold rolled sheet is the hot rolling start temperature (FE).
It can be seen that when higher than T), the streak pattern is greatly improved. From the above results, in the present invention, it is an essential requirement that the hot finish rolling end temperature (FDT) be higher than the hot rolling start temperature (FET). It is desirable that both the FET and the FDT are in the range of 900 to 1200 ° C. According to the present invention, it is not clear why the streak pattern can be improved by setting the hot finish rolling end temperature (FDT) higher than the hot rolling start temperature (FET), but it is inferred as follows. Is done. Austenitic stainless steel undergoes recrystallization during hot rolling, and the process of growing recrystallization nuclei immediately after processing proceeds. Here, it is considered that the streak pattern causes a local difference in recrystallization during hot rolling and surface gloss unevenness occurs. Therefore, in the present invention, the hot finish rolling end temperature (FDT) is set to the hot finish. By making the temperature higher than the rolling start temperature (FET), recrystallization is promoted between passes. Thus, it is presumed that a uniform structure was realized by actively utilizing the heat generated by the processing, and the streak pattern could be reduced. As described above, specific means for making the hot finish rolling end temperature higher than the hot rolling start temperature include, for example, increasing the rolling speed, increasing the working ratio, and adjusting the amount of water in the roll coolant. There are things to do. In addition, as a means for obtaining a more uniform structure, it is effective to perform oil lubrication rolling in addition to making the hot finish rolling end temperature higher than the hot rolling start temperature. The austenitic stainless steel to which the present invention is applied has a specific composition in which the Cr content is 15 wt%.
Any kind of austenitic stainless steel can be used. Alloy components other than Cr can be appropriately contained within the range contained in the austenitic stainless steel. Next, as for a method for producing a rolled material, not only ingot-bulking rolling but also a steel slab obtained by a continuous casting method can be applied. The heating temperature of the steel slab is suitably in the range of 1100 to 1400 ° C. from the viewpoint of surface quality and material properties. Following heating, hot rough rolling was performed, and then
According to the present invention, rolling is performed so that the hot finish rolling end temperature (FDT) is higher than the hot rolling start temperature (FET). As described above, after the hot rolling, particularly the hot finish rolling, is properly controlled by the present invention to obtain a hot rolled steel sheet, the cold rolling is performed by the steps of hot rolled sheet annealing, cold rolling and finish rolling annealing. Austenitic stainless steel sheets with few streak patterns can be used not only for steel sheets and cold-rolled steel strips, but also for hot-rolled steel sheets and hot-rolled steel strips that are not subjected to cold rolling or finish annealing as hot-rolled sheet annealing. Can be manufactured. EXAMPLE A continuous cast slab (thickness 200 mm) having the chemical composition shown in Table 1 was heated and then converted into a sheet bar using a three-stand rough rolling mill. Hot finish rolling was performed under various conditions by a machine to finish a hot rolled sheet. At this time, the finish rolling end temperature (FDT) and the finish rolling start temperature (FET) were controlled by changing the average strain rate in all stands of the finishing mill, but specific values differ depending on the steel type and the sheet thickness. Further, after pickling this hot-rolled sheet, cold rolling and finish annealing were performed to produce a steel strip. Further, for some of the samples, a steel strip was also manufactured by a process in which the cold rolling and the finish rolling were omitted from the above processes. Tables 2 to 4 show the production conditions of these steel strips. [Table 1] [Table 2] [Table 3] [Table 4] A test piece at a position 7 m from the tip of each of the obtained steel strips was sampled, and the streak pattern was evaluated. Specifically, in the evaluation of the surface streak pattern shown in Table 2, for the obtained steel strip, a steel sheet having a length of 300 mm in the rolling direction was sampled, and the occurrence degree of the streak pattern was indexed over the entire width of the steel sheet. Things. For the indexing, the gloss was measured at intervals of 1 mm with a gloss meter over the entire width of the coil, and the difference in gloss between adjacent measurement points was less than 4, and the surface streak pattern index A, less than 6 A surface streak pattern index B when 4 or more exist, a surface streak pattern index C when there is less than 8 and 6 or more, and a surface streak index D when 8 or more exist. did. Table 2 also shows the results. It can be seen that the inventive steel according to the present invention has greatly improved streak patterns regardless of the process after hot rolling. As described above, according to the present invention, it is possible to manufacture an austenitic stainless steel sheet having few streak patterns. In addition, according to the present invention, a stainless steel sheet with less streak pattern can be obtained by a step of performing cold rolling and finish annealing subsequent to a hot rolled sheet annealing or a step of omitting the hot rolled sheet annealing regardless of the steps after the hot rolling step. , Which greatly contributes to cost reduction of austenitic stainless steel sheets.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 Finish rolling end temperature FDT and finish rolling start temperature F
It is a figure which shows the influence which the temperature difference with ET gives to the generation | occurrence | production state of the streak pattern on the steel plate surface.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Susumu Sato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (56) References JP-A-61-246324 (JP, A) 8-277423 (JP, A) JP-A-10-280046 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 3/02 C21D 8/02

Claims (1)

(57) [Claims] [Claim 1] Austenitic stainless steel slab is
A method for producing austenitic stainless steel, comprising: performing hot rolling by a rough rolling mill and a finish rolling mill so that a finish rolling end temperature FDT is higher than a finish rolling start temperature FET.