JPS62286626A - Press forming method for steel plate - Google Patents

Abstract

PURPOSE:To easily enable a pressing even with less forming pressure by press- forming a steel plate at the specific temp. after annealing it with recrystallization at the specific temp. CONSTITUTION:A steel plate is subjected to a recrystallization annealing at >=650 deg.C and formed at the temp. of >=400 deg.C by a press machine. In the case of the press-forming at >=400 deg.C, the deformation of the steel plate becomes easy due to its yielding point being reduced, is enabled with less steps and the press forming is easily enabled with the die having smaller stiffness. In this case, a rapid cooling is performed by the contact with the die simultaneously with the forming and since the solid solution carbon, etc. freezed in the iron grid is finely deposited while its being left in the atmosphere of after forming and it becomes of high stiffness.

Description

[Detailed description of the invention] 3. Detailed description of the invention (Industrial application field) The present invention relates to a method of press forming a steel plate.

(Prior Art) Steel sheets have a wide range of uses, including automobile parts and electrical products. The parts are press-formed using a press mold, and steel plates are generally press-formed at room temperature.

The yield point of a steel plate is generally 14 to 20 Kgf/mm', and in order to form it, a mold with strong rigidity (ie, n-thickness) is required. In recent years, press parts have also been formed into complex shapes; for example, deep drawing, stretch forming, composite forming thereof, etc. are being performed. Molding of complex shapes is impossible in one stage of press molding, so several stages of press molding are performed to finally create a complex molded part6. In order to do this, the material of the steel sheet must have a quality that can withstand this forming.For example, A1 killed steel, Nb killed steel, Ti killed steel, and more recently, Ti-Nbtm, which has a composite addition of Ti and Nb, etc. is appearing. Therefore, materials of general grade, drawing grade, deep drawing grade, etc. are prepared and used depending on the degree of forming of the press-formed product.

In such a conventional press molding method, the press process is performed in multiple stages, and the cost of the mold becomes high.

Moreover, the use of high-quality materials increases the cost, which is not preferable.

(Problems to be Solved by the Invention) The present invention is an extremely advantageous press forming process in which the press process can be performed in a small number of stages (one stage) and can be formed without using high-grade materials. The present invention provides a method.

(Means for solving the problem) In the conventional press forming method, the steel plate material is formed at room temperature or in a warm state, and this requires several 8F press forming processes and the use of high-quality materials. It is something that exists. The object of the present invention is to provide an extremely advantageous press forming method that solves all of the conventional problems by press forming a steel plate while it is hot, rather than forming it while the steel plate is at room temperature.

Press forming in a high temperature state, which is a component of the present invention, is carried out in 4
The temperature is preferably 00°C or higher. The reason for press forming at 400°C or higher is that, as shown in Figure 1, the yield point of the steel plate is lowered, making it easier to deform the steel plate, which can be done with fewer stages, and with a less rigid mold. The reason is that press molding can be easily performed.

At this time, it is rapidly cooled by contact with the mold at the same time as the molding, and the solid solution carbon etc. frozen in the iron lattice are finely precipitated while being left at room temperature after molding, resulting in high rigidity. More preferably, after heating to Ac1 point (720 ° C.) or higher and then pressing at Ar1 transformation point or higher, austenite changes to martensite, for example, due to rapid cooling.
The rigidity of the panel can be significantly increased because it transforms into a microstructure such as (ferrite + pearlite) or *III (ferrite + pearlite). In particular, in steel types to which 5 to 100 ppm of poron is added, the strength of the panel is significantly improved due to the quench hardening of poron. It is not necessary to add more than 100 ppm of poron because the effect is saturated. 400℃
Press forming with less than
As mentioned above, not only cannot press molding be performed easily, but also non-uniform deformation such as serrations may occur, which is not preferable.

Furthermore, since the present invention press-forms a steel plate at a high temperature, it is necessary to cool the press-forming machine. For example, cooling water can be passed into the press mold for cooling. It is advantageous for manufacturers of materials such as steel to supply cold-rolled materials as they are to a press manufacturer, and the press manufacturer performs recrystallization heat treatment before pressing.

Or, conversely, cold rolling is performed at a steel manufacturer, and then the coil remains or! After forming the iJJ plate, the steel plate may be passed through a continuous annealing furnace to be heated, and after recrystallization annealing, a press may be installed on the exit side and press forming may be performed while the steel plate is in a high temperature state.

In the present invention, there is a problem that the press-formed product is oxidized because it is press-formed in a high-temperature IE. Press molding may be performed without consideration, and the press molded product may be pickled in a post-process.

However, if the press molding is carried out in an inert atmosphere to avoid forming an oxide film, the molded product will have fewer pill defects in the mold and will be free from defects. In particular, it is easy to install the press machine on the outlet side of the continuous annealing furnace because the atmosphere is the same as that of the reducing scum in the furnace.

Next, regarding the material used in the present invention, there are basically no particular limitations on the steel type of the material. The reason for this is that in the past, pressing was performed at room temperature, which resulted in the use of low-order Al killed steel, low-order rimmed steel, hardened steel, or ultra-low carbon steel, which had a low yield point. However, in the present invention, pressing is performed at a high temperature where the yield point is significantly lowered, so it is possible to use medium carbon steel with an even higher carbon content. However, if the carbon content is too high, the rolling pressure will increase during cold rolling, so it is preferable that C<0.015$.

In addition, in the steel manufacturing stage, slabs may be manufactured and used by a continuous casting machine, or steel slabs may be manufactured and used by a mold. However, high formability is imparted to the steel plate by heat treating the steel plate to a temperature of 400° C. or higher during press forming.

Next, examples of the present invention will be shown.

(Example) A material having the components shown in Table 1 was cold rolled to a thickness of 0.
8) Wind the coil into a coil of 1111914 mm, then shear the coil into a 1000 mw long cut plate, heat the cut plate in a batch heat treatment furnace, press-form it into a front fender part, and process it in a continuous annealing furnace. The cut plate was heated and the same part was press-molded using a press machine installed on the exit side. The atmosphere during pressing was partially HNX dregs (N2 =
951. N2 = 5%) (7) Pressing was performed in reducing residue.

Table 2 shows the heat treatment conditions and press molding results.

□ Examples D, E, and F are examples in which press molding was performed on Arl fish gear and the strength of the molded panel was increased by transformation reinforcement due to the microstructure. Add B.

In example E, as in the examples 0 and above, where the increase in strength is particularly remarkable, according to the present invention, the forming pressure is extremely low compared to conventional cold pressing, and even parts that are difficult to press can be pressed well. It turns out that it can be done.

As described above, the present invention requires less forming pressure, but at the same time, the process up to press forming of the steel plate can be largely omitted, and the mold for press forming can be small. It also has the following effects.

(Effects of the Invention) According to the present invention, when pressing difficult-to-press parts, pressing can be easily performed without using high-grade steel plates, and furthermore, press forming can be performed with less molding pressure, and the effects are as follows: It is extremely large.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the relationship between the yield point of a steel plate and the temperature of the steel plate.

Claims (1)

[Claims] 1) After recrystallizing a steel plate at 650°C or higher in a continuous annealing furnace,
A method for press forming a steel plate, characterized in that press forming is performed at a temperature of 400° C. or higher using a press machine provided on the exit side. 2) A method for press forming a steel plate, which comprises heating the steel plate to a temperature of Ac_1 point (720°C) or higher in a continuous annealing furnace, and then press-forming the steel plate at a temperature of Ar_1 point or higher using a press machine installed on the exit side.