JP2879898B2 - Manufacturing method of high hardness flat thin and medium steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention corrects a shape defect such as bending and warping which occurs in a thin and medium steel sheet hardened by cold working or quenching or the like, and realizes a material stable and high quality. The present invention relates to a method for producing a steel plate having a flat hardness.

(Prior art) Hv generally used for large blades, leaf spring materials and tools
For hardened steel sheets of 300 or more, heat-treated steel sheets such as quenching and tempering of high carbon steel, steel sheets using work hardening by cold rolling of austenitic stainless steel such as SUS304 and SUS301, martensitic precipitation hardening type such as SUS630 Stainless steel or the like is used.

After the hot strip mill rolling,
A cut plate is used to obtain a predetermined hardness by heat treatment such as quenching or to obtain a required thickness by cold rolling or the like, and then heat-treated, and then flattened using a leveler or the like before use.

In addition, a work hardening type austenitic stainless steel sheet such as SUS301 is used as a cut plate as rolled, after being hardened by cold rolling to increase the hardness and then leveled by a leveler or the like.

However, it is difficult to roll and manufacture these steel sheets as completely flat sheets, and they are used with some bends and warpages left, or those that are cut out from thick ones and flattened. Have been.

On the other hand, a very powerful tension leveler for the purpose of mechanical correction has been developed and used, but it is still difficult to completely correct it.

Generally, the factors that govern the work hardening of austenitic stainless steel such as SUS301 and SUS304 by cold rolling are:
Masonro or microscopic distortion of the structure due to processing and working martensitic transformation of the austenitic structure.
It is known that in a component system, almost all of the structure is changed to martensite when the processing rate is increased. Austenitic stainless steel (SUS3
01 material), when heated from 480 ° C to 500 ° C, the hardness further increases, and the relationship between the heating temperature and the hardness increases, as shown in Fig. 1, the higher the cold rolling reduction, the higher the hardness. I do. For a 60% rolling reduction material, Hv is obtained by heating from 400 ° C to 480 ° C for about 1 hour.
Hv50 becomes harder from 20.

However, such a treatment does not change the bending and warpage of the steel sheet at all, but rather tends to increase the deformation, and does not correct the steel sheet. In addition, even if austenitic stainless steel sheet such as SUS301 that has been cold-rolled and hardened to about Hv480 is straightened using a powerful tension leveler, the warpage of a square plate of about 300 mm or more is stabilized to 0.2 mm or less. It is almost impossible.

On the other hand, even if a steel plate which appears to be a flat plate by such correction is given a heat cycle of heating from room temperature to 200 ° C., it starts to deform in one to several cycles and cannot maintain a stable plate shape. As shown by the curves and in FIG. 2, it can be seen that the warp of the SUS301 work hardened steel sheet subjected to the conventional leveler straightening treatment becomes 5 to 10 times larger than that of the original sheet in several thermal cycles. This mechanical correction is also
This means that the steel sheet is distorted, and the bending and warpage of the steel sheet may be increased depending on the use conditions.

(Problems to be Solved by the Invention) Accordingly, the present invention eliminates the above-mentioned problems, and furthermore, obtains a flat steel sheet which is stable in material while maintaining the original hardness of a thin and medium steel sheet by an inexpensive manufacturing method. It is an object.

(Means and Actions for Solving the Problems) The present invention relates to a method for producing a high-hardness flat thin medium-sized steel sheet having a hardness of room temperature of Hv 300 or more and having no material bending and warping, such as cold rolling. Austenitic stainless steel sheet with a thickness of 0.1 mm to 5.0 mm obtained by adding cold working or quenching and hardening the steel sheet to a hardness of Hv 300 or more.
Alternatively, one or more martensitic steel sheets or high carbon steel sheets are stacked on a flat surface plate and the pressure is 200 gr / cm.
^In the condition of ² or less, the hardness at room temperature does not decrease below Hv300.It does not cause steady creep of 600 ° C or less and does not cause transition creep. A method for producing a high-hardness flat medium-thin steel plate characterized by

 The present invention will be described in detail.

The present inventors have focused on self-plastic deformation due to the transition creep phenomenon of a material, repeated various creep test experiments, and found conditions that are very effective for flattening a steel sheet. In particular, by applying the transition creep phenomenon at high temperature or hot, the steel sheet bends and warps plastically with a slight pressing pressure, and it is flattened without hardening the hardness of the steel sheet given by cold working etc. It was found that a high-hardness thin and medium steel plate of stable material could be manufactured.

In order to flatten a steel sheet by such a method, a flat surface plate is required first. Place the steel plate requiring corrective over the platen, and more preferably pressed onto a light pressure enough to shed a flat pressing plate (1gr / cm ² from 200gr / cm ²⁾ thereof.

Of course, the present invention is based on the application of the warm or hot transition creep phenomenon, so that the straightened steel sheet bends and warps to some extent by its own weight without applying a special pressing pressure on the straightened steel sheet. Is corrected, but to reduce processing time,
It is desirable to apply pressure with the holding plate. in this case,
Naturally, the degree of straightening depends on the high temperature or hot creep characteristics of the material, but the higher the set temperature, the shorter the time required for straightening.

In general, some corrections can be seen from the transition creep properties even in heat treatment processes such as tempering and strain relief annealing, but with a general heat treatment time of several tens of minutes to several hours, it is not possible to make a flat steel sheet with a warpage of 0.2 mm or less .

However, the flattening treatment method using the transition creep phenomenon according to the present invention can produce a stable flat steel sheet having a hardness of about Hv480 because the heating temperature is low. Further, since the steel sheet manufactured by the method of the present invention is subjected to high-temperature soaking at a high temperature for a long time, a very stable structure is formed in terms of material, and the heat cycle from normal temperature to 200 ° C. shown in FIG. It can also be seen from the test given that no stability was given as shown in the curve.

The feature of the manufacturing method of the high hardness flat steel sheet according to the present invention is that the hardness of the as-rolled steel sheet is first hardened by work such as cold rolling to a hardness higher than the required hardness as a product, and then to the required hardness or less. The object of the present invention is to complete the straightening by giving a temperature and a heating time at which a warm transition creep at which the steel sheet hardness does not decrease is obtained. Therefore, when the heating temperature is increased, the time required for straightening becomes shorter, but the rate of decrease in hardness also increases, and when the rate of decrease in hardness is greater than the rate of straightening due to self-plastic deformation of the steel sheet, the steel sheet can be completely straightened. It must be noted that by the time the hardness falls below the required value and softens. Therefore, if a steel sheet whose hardness decreases at a high temperature at a relatively low rate is selected, the range of the higher temperature transition creep characteristics is used, and a certain degree of straightening effect is achieved before the steel sheet hardness decreases below the required hardness. And then a two-stage heating process in which the heating temperature is lowered and the treatment is carried out for a longer time can also be applied as an effective flattening process.

FIG. 3 shows an example of a high temperature transition creep curve according to heating temperature of a material obtained by cold rolling work hardening of a SUS301 stainless steel sheet. This transition creep occurs at an early stage, and it is known that the deformation becomes the cubic root of time with respect to the initial dimension of the material. After that, in general, steady-state creep, in which the amount of deformation for the initial dimension is an exponential function of time, transitions, but in relatively low temperature ranges, steady-state creep practically does not occur, and it stops at the stage of transitional creep It is known. Fig. 3
At temperatures below 600 ° C, the amount of plastic deformation with time gradually increases and becomes extremely small over the range of 50 hours or more. In such a temperature range, only transient creep occurs without steady creep. I understand. From the above, the temperature range is 600 ° C or less and the time is 5
The time may be 0 hours or more, but the amount of self-plastic deformation also depends on the working ratio, so that the rolling ratio, heating temperature and heating time that can satisfy the required hardness and flatness of the steel sheet are determined.

Applying the self-plastic deformation caused by high-temperature transition creep of the present invention to straighten and manufacture steel sheets without significantly lowering the hardness of the steel sheets is not limited to work-hardened stainless steel, and is not limited to work hardened stainless steel. This is also possible for steel plates.

(Example) Next, an example of producing a high-hardness flat thin steel sheet by correcting the bending and warpage of a cold-rolled work-hardened thin steel sheet according to the present invention is described below.
The explanation uses a SUS301 stainless steel plate with a thickness of 4 mm.

The steel sheet is cold-rolled with a reduction rate of 53% or more, and a cold-rolled coil with a width of 1000 mm hardened to a Vickers hardness of Hv500 (20 kg) or more is manufactured. About 10mm to 20mm per 1000mm
I made a cutting board 1100mm long. This is divided into 550mm
Even if it is long, it is a steel sheet that still has a warpage of 5 to 10 mm.

Thirty sheets were placed on a surface plate prepared in advance, and a flat thick plate of 10 kg was placed thereon as a holding plate. In this case to be straightened the top of the steel plate is 3gr / cm ^2, the bottom of the steel sheet is under light load of about 35gr / cm ^2.

In this state, put in a heating furnace and heat at 480 ° C for about 70 to 100 hours, and cool down the furnace to eliminate bending and warp, and produce extremely flat, high-hardness stainless steel sheet showing Hv480 (20Kg). We were able to.

Furthermore, if the soaking temperature is set at 500 ° C under the same conditions, a high hardness flat steel plate with a hardness of Hv460 (20Kg) can be produced. At a near-heating temperature of 530 ° C, a steel plate with a hardness of Hv420 (20Kg) can be made. Was completed.

FIG. 4 (a) shows the frequency distribution of the warpage of the stainless steel sheet manufactured in this manner as compared with that of a conventional thin steel sheet which has been leveled while being rolled, and the flattened steel sheet according to the present invention is as shown in FIG. It can be seen that the warpage was 0.25 mm or less, and the warpage of the conventional steel plate was corrected and stabilized from 1/10 to 1/40 or less.

Similarly, the present invention was applied to the production of hardened, flat and thin steel sheets of SUS301 having a thickness of 1 mm and 0.5 mm by applying the method of the present invention, and it was confirmed that the steel sheets were stable in terms of material quality.

Furthermore, the cold rolling rate of SUS304 stainless steel sheet is 60
%, And the as-rolled hardness is Hv410 (20Kg)
The steel sheet having a large bending and warpage of 0.5 mm thickness was subjected to a heat treatment at 450 ° C. for 72 hours by the method of the present invention to obtain a very flat steel sheet having a hardness of Hv380 (20 kg).

(Effect of the Invention) As described above, a deformed state such as bending and warping of a steel sheet hardened by cold rolling and quenching processing is flattened while maintaining the required hardness without greatly reducing the hardness. The method according to the present invention is very effective in producing a flat and stable steel sheet having a hardness of Hv 300 or more without bending and warping. In addition, in the method of the present invention, the hardness of the steel sheet to be straightened can be freely adjusted within the range of hardness from as-rolled to around Hv300 from hardness as-rolled by a process of adjusting the relationship between the as-rolled work hardening hardness and the processing soaking temperature. There are advantages that you can choose. Furthermore, long-time constant-temperature heating, which is the condition for self-plastic deformation of transition creep according to the present invention, can greatly improve the quality of the steel sheet material, as shown in FIG. This is clear from the fact that the difference between the mechanical test values in the (C direction) is very small.

[Brief description of the drawings]

Fig. 1 shows the change in cold rolling rate (%) of SUS301 stainless steel sheet and the hardness after rolling and according to the heating temperature during normal heat treatment. Fig. 2 shows the leveler of as-rolled SUS301 stainless steel sheet. Fig. 3 is a graph comparing the change with time of the warping deformation when a heat cycle is applied to a steel sheet passed through a steel sheet and a steel sheet manufactured by the manufacturing method according to the present invention. Diagram showing the relationship between the amount of plastic deformation,
FIG. 4 (a) is a comparison diagram of the frequency distribution of the amount of warpage between a flattened steel sheet manufactured by the method of the present invention and a conventional steel sheet which has been subjected to leveling after cold rolling, and FIG. FIG. 5 is a diagram showing warpage, and FIG. 5 is a comparison diagram of tensile strength and hardness variation distribution in the rolling direction of a high hardness flat steel sheet and a cold-rolled steel sheet produced by the production method of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) C21D 8/00-8/04 C21D 9/46-9/48 B21D 1/00

Claims (2)

(57) [Claims] 1. The steel sheet bends when the hardness at room temperature is Hv300 or more,
In the manufacturing method of high-hardness, flat, thin and medium-sized steel plates that are stable in material without warping, the thickness of the steel plates is reduced from 0.1mm to 5.0mm by applying cold working such as cold rolling to harden the steel plates to Hv300 or more.
Placed on top of one or a plurality of austenitic stainless steel sheet to a flat surface plate, in a state of pressure 200gr / cm ² or less, the hardness of the room temperature does not drop below Hv 300 600
Heating for more than 50 hours in a temperature range that causes transitional creep without causing steady creep below ℃, bending of the steel sheet,
A method for manufacturing a high-hardness, flat, thin, medium-sized steel plate, which comprises correcting warpage. 2. The steel sheet bends when the hardness at room temperature is Hv300 or more,
In the manufacturing method of high-hardness flat thin and medium-thick steel plates that are stable in material without warping, the steel plates are quenched to increase the hardness of the steel plates to Hv300.
One or more sheets of austenitic stainless steel sheet or high carbon steel sheet having a thickness of 0.1 mm to 5.0 mm hardened and hardened as described above are placed on a flat surface plate, and the pressing force is 200 gr / cm ²
Under the following conditions, the steel sheet should be heated for at least 50 hours in a temperature range that causes transitional creep without causing steady-state creep of 600 ° C or less where the hardness at room temperature does not drop below Hv300, and corrects bending and warping of the steel sheet. Manufacturing method of high hardness flat thin and medium steel plate.