JPH0318403A - Production of steel sheet for precision blanking - Google Patents

Abstract

PURPOSE:To improve combined formability and hardenability by a short-time heating by specifying the limitation of chemical components and the regulation of hot rolling conditions at the time of producing a steel sheet for precision blanking. CONSTITUTION:The chemical compsn. component of a billet is constituted, by weight, of 0.10 to 0.19% C, <=0.50% Si, 0.70 to 1.50% Mn, 0.05 to 0.80% Cr, 0.0005 to 0.005% Bi, and <=0.08% Al, and the balance Fe and unavoidable impurities. This billet is hot rolled under the temp. control of 800 to 950 deg.C austenite area region and 500 to 690 deg.C coiling temp. As a result, the steel sheet for precision blanking which has the characteristics of low yield strength and high (n) value of a low strain area so as to have the excellent combined formability combined with coining, bulging, etc., and with which the homogeneously hardened structure is obtd. in the short-time heating is produced in this way.

Description

[Detailed Description of the Invention] The present invention... *Related to a method for manufacturing steel sheets for precision punching (hereinafter sometimes abbreviated as FB) with excellent composite formability and short-time rapid heating hardenability. Recent FB processing includes coining and overhang. It is developing into a complex kimono process that includes paring, etc. Also, depending on the part, after some processing. Dielectric heating. It is necessary to perform a short-time heat treatment such as induction hardening to minimize dimensional changes in parts and improve wear resistance.

In view of this background, an object of the present invention is to provide an inexpensive material that has excellent composite shapeability and short-time heat hardenability. For this purpose, mechanical properties. In addition to the fact that the material (hot rolled material) is soft and has excellent ductility. From the viewpoint of improving the n value in the low strain region, improving the impact properties, and lowering the yield ratio. Regarding the short-time heating characteristics, we selected and balanced the chemistry and regulated the hot rolling conditions from the viewpoint of improving hardenability and facilitating austenite formation.

Thus, in the present invention, C: 0.10 to 0.19% by weight,
Si: 0.50% or less, Mn: 0.70
~1.50%, Cr:0.05~0.80%,
B: 0.0005-0.005% and Al0.0
8% or less. In some cases, a steel billet containing Ti: 0.05% or less, with the remainder consisting of Fe and unavoidable impurities, is heated to an austenite region temperature, and then heated to a finishing temperature of 800 to 950°C and rolled in a hot rolling process. Temperature taken;
Provided is a method for producing m-plates for precision punching, which are characterized by hot rolling under temperature control of 530 to 690°C and are excellent in composite forming processability and short-time rapid heating hardenability. The technical reasons for limiting chemical precepts and regulating hot rolling conditions in the present invention will be explained. C is. If it exceeds 0.19%, the steel becomes hard and FB properties and FB composite shapeability are inhibited. Also, C is 0. lO
%, there is a tendency that sufficient surface hardness cannot be obtained by short-time heat quenching such as induction hardening. Si tends to increase the AC, point of m and inhibit the austenitization of steel during short-time heating such as high-frequency heating. In addition, although St is effective in increasing hardenability, it is not as effective as Mn, and its effect of increasing the strength of the base metal is strong.
This is disadvantageous from a gender perspective. Therefore. Upper limit 0.50%
regulated.

On the one hand, Mn lowers the AC2 point of the steel, so it is advantageous in making the steel austenitizing, and on the other hand, it is an effective element that improves the hardenability. Therefore, it is necessary to add 0.70% or more. However, if it exceeds 1.50%, the increase in base metal strength becomes excessive. Tensile strength is often 50k
exceeding g/m-. Since processability and FB properties may be inhibited, the upper limit was set at 1.50%. Cr is. Compared to Sl and Mn, it is an effective element that improves hardenability without significantly increasing the strength of the base metal.
In the present invention, Cr is added with the intention of having a synergistic effect of improving hardenability with Mn. Within the above Mn content range, 0.05% or more of Cr is required to achieve a significant synergistic effect, but if the Cr content exceeds 0.80%, FB properties and workability deteriorate. Because it is more likely to occur. The upper limit is 0.80
%.

B is. In the present invention, it is an extremely important element from the viewpoint of hardenability of the material heated for a short time. however. The content is o. ooooo
If the amount is less than s%, the effect will not be exhibited, and if the amount is less than o. o
Even if the oso% is exceeded, the effect is saturated and there is a disadvantage that the cleanliness of the rope is adversely affected. Al is added as a deoxidizing agent for steel, and the amount of Al needs to be 0.08% or less. An excessive amount of Al exceeding this has the disadvantage of impairing the cleanliness of S.

Ti is added to prevent reduction in addition yield due to oxidation and nitridation of B. Therefore, Ti may not be added, but
Hardenability is more stable when Ti is added. However, Ti is 0.
If it exceeds 0.5%, the effect of precipitation strengthening will be large and will impair FB properties, especially mold life, so an upper limit was set.

In manufacturing the steel plate of the present invention. The above-mentioned steel slab is heated to an austenite region temperature of 1100 to 1350°C according to a conventional method, and then subjected to hot rolling. As for the hot rolling conditions, the finishing temperature must be in the range of 800 to 950°C, and the coiling temperature must be in the range of 530 to 690'C.

Figure 1 shows the invention! (ME) and comparative steel (Steel A) were subjected to the hot rolling conditions shown in Table 2. Impact values and low strain region n values of hot rolled materials. and is a graph showing the relationship between the distance between barlite groups (see Table 2) and hot rolling conditions (coiling temperature). According to the figure, the impact value and n value in the low strain range are higher for the invention steel than for the comparative steel, and the -t-temperature is within the range of 550 to 690°C specified by the present invention. By doing so, a clear difference appears. The reason why the invented steel has an excellent impact value is that the carbonitrides produced by boron addition are Fe. One reason may be that it becomes a nucleus for C generation and exhibits a fine pearlite distribution.

In addition, the reason why the n-value in the low strain range is excellent is thought to be because nitrogen is fixed by boron addition, which improves the strain propagation ability. From the perspective of FB. Particularly high impact value. From the standpoint of composite formability, it is desirable that the n value in the low distortion region be high. In addition, the yield strength of both materials must also be low. like this.
The outstanding properties of the invented steel are. As provided by the present invention. This cannot be achieved unless the finishing temperature is in the range of 800 to 950°C.

When the finishing temperature is 800°C or lower, processing distortion from hot rolling tends to remain. Yield strength increases. This results in a decrease in the n value in the low distortion region. Also, the finishing temperature was set to 950.
If the temperature is above ℃. This is because hot rolling tends to cause surface decarburization and poor surface texture.

on the other hand. From the viewpoint of short-time rapid hardenability. It is desirable that the distance between pearlite groups is small. When the distance between barlite groups is small, carbon is easily dissolved in the heliostenite during short-term heating, and homogeneous austenite is easily obtained. According to Fig. 1, the distance between pearlite groups generally tends to be larger when coiling at high temperatures than when coiling at low temperatures, but in the steel of the present invention, even if the coiling temperature is set high, the distance between pearlite groups The distance between them is difficult to increase. In Figure 2. Samples with different distances between pearlite groups, that is,
For w4H heated to 1230℃. Finishing temperature 840
'C and the finishing temperature is the same as that of the sample with a barite group distance of 9.8 μ obtained by hot rolling at a coiling temperature of 690 °C < 840
℃ and a sample with a distance between pearlite groups of 15.4μ obtained by hot rolling at a coiling temperature of 730℃, 100k
The hardness distribution (relationship between depth from the end face and hardness) when Hz induction hardening (hardening of the rotating end face) is performed. According to the hot rolling conditions of the present invention, the distance between pearlite groups is small, the homogeneous austenite depth and 90% martensite depth are large under the same heating conditions, and the variation in hardness is small.

Thus, according to the present invention, it is possible to have excellent composite formability in which coining, overhanging, etc. are combined. It has the characteristics of low yield strength and high n-value in the low strain range. Moreover, a steel plate for precision punching can be produced which can obtain a homogeneous quenched structure by heating for a short time.

Next, the present invention will be further explained by giving specific examples.

Table 1 shows the chemical properties of the test steel. 50IIl+Il(
Plate thickness) X6Q+m (width) X 150w++i (length)
After heating a small piece of steel to a temperature of 1230℃, it was rolled using a small hot rolling mill. 50mm (original thickness) → 32mm → 20.8m
m→14.6n+m→10. 6. Rolled to Omm-7.0mm and ground. 'Omm. The rolling temperature is
1150℃, 1100℃. 1060℃, 1020
℃ and the finishing temperatures shown in Table 2. 2nd after rolling
It was wound at the winding temperature shown in Table 3 and Table 3, kept in a salt bath at the same temperature for 1 hour, and then slowly cooled.

In Tables 2 and 3. The mechanical properties and induction hardening (950°C) properties of the hot-rolled material are shown. Experiment numbers 1 to 10 in Table 2 have already been explained with reference to Figures t and 2. In experiment numbers 11 and 12 in Table 3, the sample 1lI A
(S15C, comparative steel) and B (S20C, comparative steel) were subjected to normal hot rolling conditions, but the resulting hot rolled materials had poor induction hardenability and a 90% martensite depth of 0.
．． It was less than 3 mm. The hot-rolled material of Experiment No. 13 obtained by subjecting test steel C (SCR420) to normal hot-rolling conditions was as follows. Although it showed good high-frequency short-time heating characteristics, the tensile strength exceeded 50 kg/m- and the yield strength substantially exceeded 30 kg/m+w'', causing problems in FB properties, especially mold life. The value is also low.In experiment number 14, the sample steel D used was low carbon (0.07%).
Since the hot-rolled material was made of boron steel, it is soft and has good workability and formability, but its induction hardenability is insufficient. Experiment numbers 15 and 16 are examples of the present invention, and the obtained hot-rolled materials had a tensile strength of 50 kg/am" or less, a yield strength of 30 kg/ms" or less, and a low strain range n{10.20 or more. ．． The workability was good, and the induction hardening properties were also good. Regarding experiment number 17, the winding temperature is low, so the low strain region n
The value is low and the desired characteristics are not obtained.

In experiment number 18. This was because the carbon content of the sample steel G used was excessive. The tensile strength of the hot-rolled material exceeded 50 kg/mm2, and good shapeability was not obtained.

In experiment number 19, the Siil of the sample EH used was high.
The austenitization of the hot-rolled material during short-term heating was slow, and sufficient surface hardness could not be obtained.

[Brief explanation of the drawing]

Figure 1 is. This is a graph showing the relationship between various properties of hot-rolled material and hot-rolling conditions. And the second figure is. This is a graph showing the induction hardening characteristics of hot-rolled materials with different distances between pearlite groups.

Claims (2)

[Claims] (1) C: 0.10-0.19%, Si: 0.5 by weight
0% or less, Mn: 0.70-1.50%, Cr: 0.0
A steel billet containing 0.0005% to 0.80% B, 0.0005% to 0.005% B, and 0.08% or less Al, with the balance consisting of Fe and unavoidable impurities is heated to an austenite range temperature and hot-treated. Finishing temperature in rolling process: 800-950
C. and coiling temperature: A method for producing a steel plate for precision punching, characterized by hot rolling the same under temperature control of 530 to 690 C. (2) C: 0.10-0.19%, Si: 0.5 by weight
0% or less, Mn: 0.70-1.50%, Cr: 0.0
5-0.80%, B: 0.0005-0.005%, A
Contains l: 0.08% or less, Ti: 0.05% or less,
A steel billet, the balance of which is Fe and unavoidable impurities, is heated to an austenite range temperature and subjected to a hot rolling process at a finishing temperature of 800 to 950°C and a coiling temperature of 530 to 690°C.
A method of manufacturing a steel plate for precision punching, which is characterized by hot rolling the steel plate under temperature control of ℃.