JPS59159931A - Production of steel material - Google Patents

Abstract

PURPOSE:To obtain a steel material having extremely fine and uniform carbide structure with less variance in components and structure with high productivity by hot rolling a carbon steel or alloy steel contg. C in a specified amt. then subjecting the steel to patenting followed by low temp. annealing. CONSTITUTION:A carbon steel or alloy steel contg. >=0.4wt% and more preferably <=1.3wt% C is hot rolled at a temp. of preferably the Ar3 transformation point or above and under such condition under which the rolling end temp. attains particularly 750-850 deg.C. The carbon steel or alloy steel after the hot rolling is once cooled and is reheated or the steel is subjected to patenting at a constant holding temp. of preferably 400-650 deg.C at a prescribed plate thickness, width or wire diameter in succession to the above-mentioned hot rolling. The carbon steel or the like is thereafter subjected to low temp. annealing at a temp. of preferably the heating austenite transformation point (Ac1 transformation point) or below and the intended steel material having the fine and uniform structure of carbide is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a steel material having a fine and uniform carbide structure.

Conventionally, as a method for producing this type of steel material, there has been a method in which steel of a predetermined composition is hot-rolled, then subjected to spheroidizing annealing, then cold-rolled, and then low-temperature annealed.

However, in such conventional methods, as spheroidizing annealing, a long time heat treatment was performed under the conditions of, for example, 8 hours of heating + 4 hours of soaking + 10 hours of slow cooling (770°C pass 650°C), Although it is a continuous type, it has the problem of having to heat-treat each coil using a discontinuous furnace such as a punch furnace, resulting in poor productivity and variations in the spheroidization process between the inner and outer parts of the coil. This has the drawback of easily causing variations in product characteristics.

The object of the present invention is to provide a manufacturing method that can produce steel materials such as copper strips, steel wires, and steel bars with high productivity that have small, extremely fine, and uniform carbide structures.

This invention involves hot rolling carbon steel or alloy steel with a C content of 0.4% by weight or more, applying patenting to a predetermined plate thickness, plate width, or wire diameter, and then low-temperature annealing. This method is characterized in that steel materials such as copper strips, steel bars, and steel wires having a uniform and fine carbide structure are obtained. In the method for manufacturing a steel material according to the present invention, after the C content is rolled, annealing and cold rolling are performed as necessary, and this cold rolling is further repeated with low temperature annealing as necessary, It also includes the steps of applying patenting after that, then low-temperature annealing, and then cold rolling if necessary.

The steel to which this invention is applied is carbon steel or alloy steel with a C content of 0.4% by weight or more, specifically, for example, C: 0.4 to 1.3% by weight, Si: 1 .0% by weight
Hereinafter, carbon steel with Mn: 1.5% by weight or less, or the above basic components, Cr: 2.0% by weight or less, Mo + 1.0% by weight or less, W: 1.0% by weight or less, V: 0.5 % by weight or less, Ti: 0.5% by weight or less, others Si, Mn.

Ni, Zr, Nb, Ta, Cu, P, S, Pb.

It can be applied to alloy steels containing one or more of Ca, REM, etc., as appropriate, and steels with restricted upper limits of O, S, P, etc.

In this case, if the C content in the steel is less than 0.4% by weight, the amount of ferrite produced will increase, which is undesirable, and if it is too large, network-like carbides will be formed, so it is more preferably 1.3% by weight or less. shall be.

When hot rolling such steel, it is more desirable that the rolling end temperature is equal to or higher than the austenite transformation point (Ar3 transformation point). In this case, if the end-of-rolling temperature is too high, the amount of ferrite produced will increase, which is undesirable.On the other hand, if the end-of-rolling temperature is too low, a large amount of bainite will precipitate, which is undesirable. Therefore, the end temperature during hot rolling is preferably determined in consideration of the formation of ferrite and bainite.

More preferably, the temperature is 750 to 850°C.

After this hot rolling, as shown in FIG. 1(a), the rolled material is once cooled and then reheated, or following the above hot rolling, it is rolled to a predetermined thickness.

Patenting is applied by plate width or wire diameter. or,
As shown in FIG. 1(b), after the hot rolling, annealing and cold rolling are performed, and then patenting is applied to a predetermined plate thickness, plate width, or wire diameter.

Alternatively, as shown in FIG. 1(c), after the above-mentioned hot rolling, the steps of annealing, cold rolling, low temperature annealing, and cold rolling are repeated once or twice or more, and then a predetermined plate thickness is obtained. Patenting is done by width or wire diameter.

Incidentally, the annealing in the pre-patenting step does not necessarily have to be spheroidizing annealing, and it is sufficient as long as cold rolling after annealing can be performed well. Therefore, it is only necessary to select annealing and low-temperature annealing conditions that take cold rolling into consideration.
No harsh conditions are required. Of course, it is more preferable to perform spheroidizing annealing, but it is sufficient to select conditions that do not interfere with the subsequent cold rolling, taking into account annealing efficiency, cost, etc.

Patenting, which is carried out after this process,
By keeping the rolled material at a constant temperature, a constant fine lamellar pearlite can be obtained. In this case, for maintaining the constant temperature, conventionally known means such as boiling water, lead bath, salt bath, etc. can be used, and in some cases, air patenting etc. can also be used.

The upper limit of the constant temperature during patenting should be determined by taking into account the temperature at which ferrite precipitates, and the lower limit by taking into account the temperature at which bainite precipitates, and more preferably 400 to 650°C. is good. The grain size of the structure obtained after this constant temperature treatment can be appropriately adjusted by selecting the treatment temperature described above, thereby obtaining the desired carbide grain size.

After the above patenting, as shown in Fig. 81, low temperature annealing is performed, but in this case, the heated austenite transformation point (
It is more desirable to carry out the process at a temperature below (Ac, transformation point).

At this time, the grain size of the structure can be changed by adjusting the low-temperature annealing temperature and time, so it is preferable to determine the low-temperature annealing conditions depending on the use of the steel material, such as a copper strip, steel bar, or steel wire.

After this low-temperature annealing, a slight cold rolling, that is, a skin pass may be performed. When performing this skin pass,
It is preferable to set the rolling ratio to about 5 to 20%. The reason is,
This is because if the rolling rate is too small, the effect of the skin pass will be small, and if it is too large, work hardening will occur and the workability (punching, bending, etc.) in the next process will be poor.

The carbide structure of the steel material obtained after such a series of treatments is fine and uniform, and it is possible to improve the structure of the product itself using this steel material, as well as to improve the shearing process of this steel material. It has the excellent feature of being able to increase the life of tools used in the process, as well as creating a good shearing surface.For example, it has good workability when processing into springs, cutlery, etc. At the same time, it has the advantage that fluctuations in quenching hardness can be minimized.

Examples of the present invention will be described below along with comparative examples.

A total of four types of carbon steel (No.
1, 2) and alloy steels (No. 3, 4) are melted and ingot-formed, and then each steel ingot is hot-rolled to a plate thickness of 4+.
A rolled material with a diameter of 1 nm was obtained. At this time, the rolling end temperature was set to aoo'c as shown in the table. Next, according to the process shown in FIG. 1(a), part of the rolled material is cooled and then reheated, and the other part is continuously rolled by adjusting the temperature after hot rolling. After holding at 850°C for 2-3 minutes in a type heating furnace, 450°C, 550°C, 5o
A patenting treatment was carried out by passing for 2 minutes in a continuous lead bath furnace maintained at a temperature of .degree.

In addition, the remaining part of the hot rolled material was annealed at 720°C for 2 hours as shown in the table according to the process shown in FIG. 1(b), and then cold rolled at the rolling rate shown in the table. After that, each was heated at 850°C in a continuous heating furnace for 2 to 30 minutes.
After holding for 3 minutes, 450'C! , 550℃, 65
A patenting treatment was carried out by passing for 2 minutes in a continuous lead bath furnace maintained at a temperature of 0°C.

Subsequently, as shown in the same table, the copper strip after patenting was partially annealed at a low temperature of 720°C for 2 hours, and the other part was annealed at a low temperature of 720°C for 10 hours.

The average grain size of the carbide structure of each of the steel materials thus obtained and its dispersion were investigated, and the results were also shown in Table 1. Further, when the structure of each steel material was investigated, the results illustrated in FIGS. 3 and 4 were obtained.

The remainder of the hot-rolled material with a thickness of 4 nm obtained in the above example was subjected to spheroidizing annealing under the conditions shown in Table 2 according to the process shown in FIG. Cold rolling was performed at the rolling rate shown in Table 2 to obtain a cold rolled material with a plate thickness of 2 mm, followed by low temperature annealing under the conditions shown in Table 2.

Then, when the average value of the grain size of the carbide structure of each of the steel materials obtained in this manner and its dispersion were investigated, the results were also shown in Table 2.

As is clear from the results shown in Table 1, Table S2, and Figures 83 and 4, the carbide structure of the steel obtained by this invention is considerably finer than that of conventional spheroidizing annealing. Moreover, it was recognized that the particle size was uniform with little variation.

Although the above Examples and Comparative Examples have been explained using copper strips as an example, even when S steel or steel wires are used, the carbide structure of the steel material according to the present invention is considerably finer and more uniform than that of conventional ones. It was recognized that it was a thing.

As explained above, according to the present invention, it is possible to obtain steel materials such as steel strips, steel bars, steel wires, etc., which have small variations in composition and structure and have an extremely fine and uniform carbide structure. It is easy to manufacture steel materials, so it has excellent productivity, and there is no bending of copper strips, steel bars, &r4 wires, etc. when used as coil materials for spheroidizing annealing as in the past, so there is no need to straighten them. Depending on the dimensions, etc., it is not always necessary to perform cold rolling, and this can bring about a significant effect in that steel products of excellent quality can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the manufacturing process of steel materials in an embodiment of this invention, FIG. 2 is an explanatory diagram showing the manufacturing process of steel materials in a comparative example, and FIGS. 3 and 4 are explanatory diagrams showing the manufacturing process of steel materials in an embodiment of this invention. It is a micrograph (400 times) of the microstructure of the steel material. Patent applicant: Daido Steel Co., Ltd. Patent attorney Yutaka Oshio Figure 1 (a) (b) (C) Figure 2

Claims (1)

[Claims] (1) Carbon steel or alloy steel with a C content of 0.4% by weight or more is hot-rolled, patented, and then low-temperature annealed to produce a steel material with a fine uniform carbide structure. Production method.