JP3445994B2 - Method for manufacturing 22% Cr duplex stainless steel hot rolled steel strip - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled duplex stainless steel strip having an .alpha.-phase and a .gamma.-phase, especially a 22% Cr duplex stainless steel strip containing about 22 wt% of Cr. The present invention relates to a method for manufacturing a steel strip. [0002] Duplex stainless steel having an α phase and a γ phase has been applied to oil country tubular goods and the like because of its excellent corrosion resistance in a corrosive environment such as carbon dioxide gas and hydrogen sulfide gas. However, duplex stainless steel has poor hot workability, so hot rolling at high workability and strain rate, as in the case of general hot-rolled steel strip, causes defects such as edge cracks and reduces product yield. Greatly lower. [0003] Therefore, Japanese Patent Publication No. 54404/1990,
JP-B-7-65111, JP-A-5-255737
And Japanese Patent Application Laid-Open No. 6-81037, the slab is subjected to a working heat treatment prior to hot rolling, B addition and coarse bar heating are performed, a reduction in the width direction is applied, and the component adjustment is stricter. For example, a method for preventing ear cracks has been proposed. [0004] However, when the present inventors examined the method described in the above-mentioned patent publication, it was found that the occurrence of ear cracks was caused not by the precipitation of the σ phase but by the α phase in a specific temperature range. And 22wt% due to the difference in deformability between
In the case of a 22% Cr duplex stainless steel hot rolled steel strip containing Cr before and after, it was not always possible to prevent the occurrence of edge cracks. The present invention has been made to solve such a problem, and can reliably prevent the occurrence of ear cracks.
It is an object of the present invention to provide a method for producing a hot rolled steel strip of a% Cr duplex stainless steel. [0006] The above object is achieved by the following means. 1. In producing a 22% Cr duplex stainless steel hot rolled steel strip containing 21 to 23 wt% of Cr, a step of heating the slab having the above composition to 1050 to 1150 ° C and then rough rolling, and heating the rough bar after the rough rolling edge cracking consisting comprises a step, the rolling finishing at 900 ° C. or higher finishing temperature by
A method for producing a 22% Cr duplex stainless steel hot rolled steel strip excellent in preventing occurrence . The inventors of the present invention have conducted a laboratory study on the relationship between various hot rolling conditions and the occurrence of edge cracks using a slab for a 22% Cr duplex stainless steel sheet.
It became clear that the heating temperature before rolling and the rolling temperature had a great influence on the occurrence of edge cracks. FIG. 1 shows the relationship between the critical rolling reduction of ear cracking, the heating temperature and the rolling temperature. Here, the critical draft of the occurrence of ear cracks is the upper limit of the draft at which the ear cracks do not occur if the rolling is performed at a rolling reduction of less than this rolling reduction. Also confirmed that no ear cracks occurred. As shown in FIG. 1, the heating temperature is 1150 ° C.
When the rolling temperature is set to 900 ° C. or higher and the rolling reduction temperature is set to 900 ° C. or more, a critical rolling reduction of the occurrence of edge cracks of 40% or more is always obtained, and it can be seen that the generation of edge cracks can be reliably prevented. However, in the actual machine, the heating temperature is set to 1
If the temperature is set to 150 ° C. or lower, it becomes very difficult to perform rough rolling or finish rolling at 900 ° C. or higher. Therefore, in order to perform the rough rolling at 900 ° C. or higher, it is necessary to set the heating temperature to 1050 ° C. or higher. In order to finish roll at a finishing temperature of 900 ° C. or more, it is necessary to heat the rough bar to an appropriate temperature. The heating temperature of the rough bar may be appropriately set depending on the temperature of the rough bar before heating, the rolling conditions thereafter, and the like. As a method of heating the coarse bar, it is a simple method to heat the coarse bar by passing it through an induction heating coil or a tunnel furnace. EXAMPLE A slab having a thickness of 250 mm and a thickness of 2.8 and 4.5 mm was used under the hot rolling conditions shown in Table 2 using a slab having a thickness of 250 mm of the component system shown in Table 1.
No. 2 hot-rolled stainless steel strips 1 to 6 were manufactured. The thickness of the coarse bar at this time was about 30 mm, and the heating was performed by a method in which the coarse bar was passed through an induction heating coil to heat the entire width. Then, the presence or absence of an ear crack generated at the steel strip edge after winding was visually inspected. The results are shown in Table 2. Heating temperature from 1050
In the steel strips 3, 4, and 5 in which the finishing temperature was maintained at 900 ° C. or higher by heating the coarse bar within the range of 1150 ° C., no occurrence of ear cracks was observed. On the other hand, a steel strip 1 having a heating temperature of 1200 ° C.
Or a steel strip 2 having a finishing temperature of less than 900 ° C. because the coarse bar was not heated even when the heating temperature was 1150 ° C.
In the case, ear cracks were observed. The heating temperature is set to 1
The steel strip 6 at 000 ° C. was broken during rolling and could not be wound. This is considered to be due to the fact that the rough rolling itself was performed at a temperature much lower than 900 ° C., so that ear cracks were generated at the time of rough rolling, and the cracks started from the starting points at the time of finish rolling. [Table 1] [Table 2] Since the present invention is configured as described above, it is possible to reliably prevent the occurrence of ear cracks in 22% Cr.
A method for producing a hot-rolled duplex stainless steel sheet can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a relationship between a critical rolling reduction of occurrence of edge cracks, a heating temperature and a rolling temperature.

──────────────────────────────────────────────────続 き Continued on the front page (56) References JP-A-59-179714 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 3/02 C21D 9/46 C22C 38 / 00 C22C 38/44

Claims (1)

(57) [Claim 1] 22% Cr containing 21 to 23% by weight of Cr
In manufacturing a duplex stainless steel hot-rolled steel strip, a slab having the above composition is heated to 1050 to 1150 ° C., and then subjected to a rough rolling step, and a coarse bar after the rough rolling is heated to 90%.
A process of finishing rolling at a finishing temperature of 0 ° C. or more, and a method for producing a hot rolled 22% Cr duplex stainless steel strip excellent in preventing occurrence of edge cracks .