JPS5919970B2 - Stainless steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention effectively utilizes the sensible heat held by the hot coil after hot rolling of ferritic or martensitic stainless steel for top annealing, thereby improving thermal economy and heat treatment efficiency. This invention relates to a method for heat treatment of steel.

Generally, when manufacturing cold-rolled steel strips or steel plates of ferritic or martensitic 1 stainless steel, a heat treatment process and a pickling process are carried out when cold rolling the hot coil after hot rolling. It is necessary to obtain metallurgical properties and surface conditions suitable for cold rolling.

In particular, ferritic and martensitic stainless steels change to an austenite phase when heated to high temperatures during hot rolling, but when the temperature of the material decreases after hot rolling, the rate of transformation of the austenite phase to the ferrite phase is slow, so the martensitic phase changes. Site transformation occurs and the material hardens. For this reason, conventionally, the coil that has been cooled after hot rolling is subjected to top annealing treatment to completely transform the austenite phase into the ferrite phase. In other words, in the past, in consideration of workability and metallurgical efficiency, such as problems in transporting the coil from the hot rolling process and problems in feeding the coil to the coil build-up line, after the hot coil was cooled to room temperature, Usually, the top was annealed by heating to a target temperature.

In other words, in the past, metallurgy was based on the idea that if the temperature is raised again from the high temperature region where martensitic transformation has not yet completed during the cooling process immediately after hot rolling and top annealing is performed, the decomposition of the γ phase and the diffusion phenomenon of carbide will be affected. Due to technical considerations and operational problems such as those mentioned above, it has become common practice to top-anneal the hot coil after it has been cooled to room temperature. Contrary to this common sense, the present invention relates to a heat treatment method that obtains various properties required for cold rolling by charging a hot coil after hot rolling into an annealing furnace in a high temperature state, thereby improving thermal economy. The aim is to shorten the heat treatment time. That is,
Based on many years of processing experience, even if a hot coil of 5-ferritic or martensitic stainless steel after hot rolling is charged into an annealing furnace in a high temperature state and annealed, the heating temperature will not increase from the conventional room temperature. We are confident that it is possible to obtain the same level of quality percentage compared to the top annealing process, and it has been found that significant benefits can be obtained in terms of thermal economy and work efficiency. . Therefore, the present invention
When manufacturing cold-rolled steel strips or steel plates of ferritic or martensitic stainless steel, the hot coil wound into a coil after hot rolling is heated in an annealing furnace at a high temperature.
There is also a method for heat treatment of tenremata steel, which is characterized by charging the steel. This method will be specifically explained below with reference to Examples.
Example 1 Stainless steel of the SUS430 grade was hot rolled, and the wound hot 1 coil was immediately transferred and charged into an annealing furnace.

The time required from removing the hot coil to charging it into the annealing furnace was approximately 30 minutes, and the temperature of the hot coil at the time of charging the annealing furnace was approximately 500°C at the outside of the coil, and approximately 700°C inside the coil.
It was °C. After top-annealing the hot coil in the high-temperature state using a conventional method, samples were taken to examine the metallographic state and quality characteristics. The results are shown in FIG. 1a and Table 1. For comparison, a conventional method in which the hot coil after hot rolling is cooled to room temperature and then charged into an annealing furnace was used for the same steel type as in the above example, using the same hot rolling conditions and the same annealing furnace. Samples were collected after top annealing and the metallographic state and quality characteristics were investigated.

The results are also shown in FIG. 1b and Table 1. It can be seen from the metallurgical micrograph (magnification XIOO) in FIG. 1 that the structure a of this example is substantially the same as the structure b of the conventional example.

Further, from the results in Table 1, it can be seen that there is no difference in quality percentage after top annealing between the present example and the conventional example. Example 2 The same treatment as in Example 1 was carried out except that SUS410 steel was used.

For comparison, a coil cooled to room temperature after hot rolling was placed in the same annealing furnace and top annealed for this SUS41O steel type. Samples of both annealed materials were taken and their quality characteristics were investigated. The results are shown in Table 2. From the results in Table 2, it can be seen that there is no difference in quality characteristics between this example and the conventional method.

The above examples show that even if hot-rolled hot-rolled coils of ferritic (SUS43O), martensitic (SUS41O) or stainless steel are charged into an annealing furnace in a high temperature state and top-annealed, the metallurgy will be improved. Although it can be seen that there is no difference in the physical characteristics between the two, the benefits obtained by implementing the method of the present invention can be evaluated as follows.

That is, as shown in Fig. 2, the hot coil after hot rolling is air-cooled by the {1 relatively gentle stiffness} line (however, curve 1 {1 in Fig. 2 is the outer part of the coil, and curve 2 is the outer part of the coil. After hot-rolling and winding, the temperature drop during transfer to an annealing furnace is rapid and small, and the material can be charged into an annealing furnace while maintaining a temperature of about 200 to 500°C. Therefore, it is possible to shift the coil temperature rise curve (Fig. 3-b) during normal top annealing to the left as shown by curve a (when charging at coil temperature Ta), and shorten the heating time by T. can. This T varies depending on the factory size, but it is approximately 200 minutes to 3 minutes.
00 minutes, the effect of improving operability is significant. Further, the amount of decrease in heating heat in the annealing furnace is expressed as q-X(T8tb)X↓η.

However, q - reduced heat amount (Kcal/k!?), C = specific heat (KcaIAg・°C), Ta - input coil temperature, Tb
= room temperature (input coil temperature according to the conventional method), η - thermal efficiency of the annealing furnace. From the implementation results of the method of the present invention, the annual processing amount is 6
On a scale of 10,000 tons, the contribution to energy saving and production efficiency is expressed as a ratio when the conventional method is set as 1.0, and the results shown in Table 3 are obtained.

[Brief explanation of the drawing]

Figure 1: Micrographs showing the structure of the present method a and conventional method b (magnification: .

Claims (1)

[Claims] 1. When a hot rolled coil of ferritic or martensitic stainless steel is annealed and then cold rolled to produce a cold rolled steel strip or steel plate, the hot coil wound into a coil after hot rolling is , a method for heat treatment of stainless steel, characterized in that the stainless steel is charged into an annealing furnace in a high temperature state where martensitic transformation has not yet been completed.