JPH01198447A - High toughness and high carbon thin steel plate - Google Patents

Abstract

PURPOSE:To facilitate the manufacturing and working of the title thin plate and to provide it with high toughness and excellent impact resistance and wear resistance by specifying the contents of Si, Mn, P, S, Ni, Mo and Al in a high carbon steel. CONSTITUTION:The compsn. of the thin steel plate is constituted of, by weight, 0.70-1.10% C, <=0.70% Si, 0.05-0.50% Mn, <=0.03% P, <=0.004% S, 0.2-2.0% Ni, 0.10-0.30% Mo and <=0.08% acid soluble Al, constituted, at need, of <=0.50% Cr and <=0.02% Ca and the balance consisting substantially of Fe. The high carbon thin steel plate contg. the above compsn. has high toughness, has excellent impact resistance and wear resistance after a heat treatment and furthermore has good manufacturability and workability. The thin steel plate is therefore suitable for edged tools, circular saws, band saws, bands, washers, springs, etc.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention has excellent impact resistance and abrasion resistance after heat treatment,
Moreover, it has good manufacturability and processability, so it can be used for cutting tools, circular saws, etc.
The present invention relates to a high-toughness, high-carbon thin steel sheet suitable for use in band saws, needles, washers, springs, etc.

<Prior art and its problems> In general, circular saws for mowing grass, circular saws for lumbering, various types of cutlery, etc. are SK4M specified in JIS G3311.

High carbon cold rolled thin steel sheets such as SK5M and SKS5M.

It is usually manufactured using a cold-rolled thin alloy steel plate with a high carbon content, such as SKS51M, which is formed, hardened through heat treatment such as quenching and tempering, and then subjected to blade sharpening, straightening, etc. be.

Here, the material steel plates for each of the above products are soft and easy to process before forming, can only obtain the desired strength through heat treatment after forming, and have sufficient impact resistance when used as a product. Therefore, materials with high carbon content as mentioned above are selected, and generally, when shipping thin steel sheets from steel manufacturers, they are made to be soft. Spheroidizing annealing is performed. After shipping, the raw material thin steel sheet is formed into the desired shape by the user, and heat treated by quenching and tempering to impart the necessary properties.
The impact resistance and abrasion resistance of the product are particularly affected by the tempering temperature, so the various tempering temperatures from "as quenched" to "up to 650℃" are carefully selected depending on the form and conditions of use. (usually 180-450℃)
well applied).

However, despite the careful selection of heat treatment conditions, the hardened and tempered high carbon thin steel sheets specified by JIS have insufficient impact resistance, and when applied to circular saws for mowing grass, for example, It has been difficult to completely prevent brittle fracture from occurring when contact impacts such as these occur.

For this reason, the applicant first added a predetermined amount of Mo to high carbon steel with a high Mn content in relation to the P content, and then heat-treated it under predetermined conditions to improve impact resistance and resistance. Proposed a method for manufacturing steel materials with excellent wear resistance
No. 9811).

However, the MO-added high carbon steel material previously proposed by the present applicant has excellent wear resistance and impact resistance, and exhibits excellent performance when used as a cutter product such as a circular saw for mowing grass. However, as a result of subsequent consideration from various perspectives,
When manufacturing thin sheet materials at steel manufacturers, rolling cracks are likely to occur due to some difficulty in rolling properties, and this is also an unfavorable factor when considering further workability improvement measures during forming processing performed by users. I have come to realize that there is a possibility that

<Findings that served as the basis for the completion of the invention> Therefore, from the above-mentioned viewpoints, the present inventors have developed a material that has enough wear resistance and impact resistance to be used as a material for circular saws for mowing, etc., and also has workability. We conducted research to provide a thin steel sheet that is in good condition and does not cause problems such as cracking during the rolling process or forming process into final products, and we were able to obtain the following knowledge.

(a) It is presumed that this is because the deformation resistance of the ferrite matrix decreases when 0.2% or more (hereinafter, % representing the component ratio is expressed as weight %) of Ni is added to high carbon steel. The workability of the steel is improved, the occurrence of cracks can be suppressed during the rolling process into thin sheets, and the processing when manufacturing final products from thin sheets is also facilitated.

佽）Maybe, even in this Ni-added high carbon steel,
As long as h and S content are controlled to sufficiently low values, the addition of Mo can significantly improve impact resistance without adversely affecting wear resistance or workability, and the resulting steel usually A thin steel sheet that can be easily formed into a thin steel sheet with good formability without causing problems such as cracking through hot rolling and cold rolling, and which also ensures excellent wear resistance and impact resistance through heat treatment. To be.

(e) In addition, the above-mentioned light proposal (Japanese Patent Laid-Open No. 1398-1988
No. 11) states that even if N1 is added to high carbon steel, sufficient impact resistance cannot be obtained, and the presence of Ni causes embrittlement. However, this is because if a steel with a high Ni content contains a large amount of Mn and Mo, it becomes too hard and the toughness decreases, so reducing the content of Mn and S to below a specific value appears. In some cases, it is possible to obtain a remarkable toughness improvement effect by adding No without reducing the wear resistance to an extent that is actually disadvantageous.

Here, S exists in steel as nS and needs to be reduced because it becomes the starting point of cracks, but in the case of steel that has high hardness and Mo added, the influence of MnS is It is particularly large and must be reduced as much as possible.

(d) When a specific amount of Ca is contained in high carbon/high N1f4J with Mo added by controlling the in and S content, the S in the steel is fixed as CaS, so the formation of MnS is suppressed. , the embrittlement tendency caused by MnS is suppressed, and the toughness of the steel is further improved.

(el) On the other hand, addition of a predetermined amount of Cr to the steel is effective in improving corrosion resistance and is also preferable in terms of preventing graphitization, leading to imparting properties more suitable as a material for circular saws, cutlery, etc.

Means for Solving the Problems> The present invention was completed based on the above findings, and provides the following: [A thin steel plate manufactured by rolling, C: 0.70 to 1.10%, Si: 0 .70% or less.

Mn: 0.05-0.50%, P: 0.
03% or less.

S: 0.004% or less, Ni: 0.2~
2.0%.

Mo: 0.10-0.30%, acid-soluble Al:
Contains 0.08% or less, or further contains Cr: 0.50% or less.

Ca: Contains 0.02% or less of one or two types, and the remainder is substantially F.
It is characterized by having excellent abrasion resistance and toughness (impact resistance) as well as good workability by having a component composition consisting of e.

Here, the reason why the composition of the thin steel sheet according to the present invention is numerically limited as described above will be explained.

(a) C In order to obtain the desired hardness and wear resistance of the steel plate, the C content must be 0.70% or more;
If the C content exceeds 0.70 to 1%, the steel becomes extremely brittle and it becomes difficult to roll and manufacture thin steel sheets.
．． It was set at 10%.

(b) Si It is not particularly necessary to actively add Si, but if it is added in excess of 0.70%, the steel plate tends to become hard and brittle, so the Si content was set at 0.70% or less. .

(C) Mn Generally, a large amount of Mn is added to wear-resistant steel sheets, but Mn needs to be reduced in steel sheets of the present invention containing Ni and Mo. In the steel sheet of the present invention, Mn is 0.
If the content exceeds 50%, it tends to be hardened by heat treatment, becoming too hard and causing a decrease in toughness.

On the other hand, if the Mn content is less than 0.05%, solid solution S will increase, causing embrittlement during hot working and impairing the manufacturability of the steel sheet. 05~0.
It was set at 50%.

(d) P In a steel plate containing Mo, a normal level of P content is sufficient, but it goes without saying that the lower the P content, the better in terms of toughness. If the P content exceeds 0.03%, P segregates at the grain boundaries and tends to cause grain boundary embrittlement, so the P content should be set to 0.03%.
It was set at 0.3% or less.

(e) S The lower the S value in ordinary steel, the better, but especially in steel materials with high strength and high wear resistance, such as the steel plate of the present invention, I'ln
The presence of S has a significant effect on toughness deterioration, and in the steel sheet according to the present invention, unless the Mn content is reduced and the S content is suppressed to 0.004% or less, MnS becomes coarse. The S content is 0.00 because it impairs toughness.
It has been set at 4% or less.

Although various methods are known for suppressing the S content to 0.004% or less, it is preferable to employ a method of adding Ca alone or a method of performing Ca-3t injection treatment.

In this method, Ca is added at the stage of molten steel, and S is replaced by Ca.
It is removed as S. In this case, there is a method in which no Ca remains in the steel by the desulfurization and S≦0.004, and a method in which Ca is left and the S in the steel is fixed as CaS.
Either is fine.

<n Ni Ni is a component that is actively added because it has the effect of improving the workability of steel, and if its content is less than 0.2%, desired workability cannot be ensured.

That is, by adding 0.2% or more of Ni, it becomes possible for steel manufacturers to roll thin plates when producing them, but
．． If the content is less than 2%, cracks are likely to occur during rolling, making it difficult to perform stable operations. Furthermore, ensuring a Ni content of 0.2% or more in the steel plate also facilitates the processing of the steel plate by the user.

As mentioned above, this is presumed to be because the deformation resistance of the ferrite matrix is reduced.

On the other hand, even if Ni is added in excess of 2.0%, the effect of improving workability will be saturated while only increasing the cost of the steel sheet, so the Ni content was set at 0.2 to 2.0%.

(g) N.

Mo is an important component, and the addition of Mo creates an effect that maintains high toughness and high wear resistance after heat treatment without deteriorating the workability of the steel sheet before heat treatment (before quenching and tempering).

Generally, when steel is tempered at a temperature of around 300° C. after quenching, it undergoes so-called "low-temperature tempering embrittlement" and becomes extremely brittle.

However, in order to obtain desired hardness and wear resistance, tempering at the above temperature may be necessary. In fact, the above-mentioned "low-temperature tempering embrittlement" is particularly noticeable in the case of thick samples, and is reduced in thin plates, so "tempering at around 300° C." is sometimes employed. However, in that case, a decrease in toughness may still be a problem depending on the usage conditions. Addition of Mo is very effective against such embrittlement as well.

In the steel plate according to the present invention, the Mo content is 0.
If it is less than 10%, the above effect cannot be obtained; on the other hand, if it is 0.30
The Mo content was set at 0.10 to 0.30% since the effect would be saturated even if it was added in an amount exceeding 0.10% to 0.30%.

(h) Acid-soluble AI M is a component added as needed as a deoxidizing agent, but if the content of acid-soluble M exceeds 0.08%, not only will the cost increase, but the hardening of the steel plate will also occur. There is no advantage as it brings As described above, since the content of acid-soluble M is allowed up to 0.08%, the content was determined to be 0.08% or less.

(1) Cr Cr is a component that is added as necessary because it has the effect of improving the corrosion resistance of steel and preventing graphitization. but,
If the Cr content exceeds 0.50%, it becomes hard and brittle, so the Cr content was set at 0.50% or less.

0) Ca Ca is a component that is added as a desulfurization element as necessary, but if it is contained in an amount exceeding 0.02%, it becomes large inclusions and deteriorates toughness, so the Ca content is set to 0.02%. 2
It was set as 0% or less.

Now, the thin steel plate according to the present invention is manufactured by melting steel containing the above-mentioned components and the remainder being substantially Fe, and rolling it to a desired thickness by hot rolling and cold rolling. . During this time, annealing may be performed for softening. In any case,
Finally, annealing is performed to improve workability, and the appropriate temperature for this final annealing is 700 to 880°C.

The thin steel sheet manufactured as described above is usually processed by the user and then heat treated to obtain desired hardness and performance.

Next, the effects of the present invention will be explained using examples and comparing with comparative examples.

<Examples> - Example 1 First, steel having each component composition as shown in Table 1 was melted, and then hot rolled to 3. It was made into a hot-rolled sheet with a thickness of 1.5 mm, then softened by annealing, and then cold-rolled to a thickness of 1.35 cm. In addition, in the above rolling process, steel plates A, B,
Although the rolling of D was completed without any problems, it was confirmed that steel plate C with a high Mn content had a tendency to develop rolling cracks.

Next, this cold rolled sheet was subjected to batch annealing "held at 720° C. for 16 hours".

The hardness of the steel plate after annealing is also shown in Table 1.

Next, samples were taken from these annealed plates and heated to 850°C.
After heating, quenching with oil cooling was performed, and further tempering treatment was performed at various temperatures. Note that the tempering time was 15 minutes.

In addition to measuring the hardness of each sample after the above heat treatment, Charpy V-notch specimens were prepared and subjected to an impact test at 0°C to determine the impact absorption energy.The results are summarized by tempering temperature and are shown in Figure 1. Shown below.

The following can be seen from the results shown in FIG.

That is, the wear resistance of a steel plate is roughly determined by the C content and hardness, and the C content level of the test steel plate is required to have a hardness of 81045 or more, although it depends on the application. and,
In general, hardness decreases as the tempering temperature increases, so in order to obtain high hardness (high wear resistance), it is necessary to
00°C or lower) is required. From this point of view, comparative steel sheet B with a high S content has a drawback that the absorbed energy is large in high-temperature tempering, but the absorbed energy is small in low-temperature tempering. In addition, the comparative steel sheet C1, which has a high Mn content and S content, and the comparative steel sheet, which has a high S content and does not contain Mo, have small absorbed energy under any tempering conditions.

On the other hand, the steel sheet A of the present invention exhibits absorbed energy of 3.5 kg-m or more at any tempering temperature, and is clearly superior in impact resistance.

Example 2 A disk was punched out from the 1.351 m thick high carbon cold-rolled steel sheet (composition is as shown in Table 1) before quenching produced in Example 1, further held at 870°C for 40 minutes, and then cooled in oil. After quenching and tempering at 380°C for 150 minutes, it was further molded into a round li! as shown in Figure 2. 1 (thickness = 1.35 m, diameter: 230 mmφ) was prepared.

Next, rotate this circular saw 1 at 400 rpm, and
As shown in the figure, by releasing the clasp 2 during rotation, the steel ingot 3 collided with the blade of the circular saw 1, and was left there for 15 seconds to investigate the "blade chipping" situation of the circular saw 1.

The results are shown in Table 2 along with the hardness of the circular saw.

From the results shown in Table 2, only the circular saw made of the steel sheet A of the present invention with low Mn content and S content (in addition, a predetermined amount of MO addition) did not cause "blade chipping". It can be confirmed that the impact resistance is good.

Table 2 Example 3 Steel having each component composition shown in Table 3 was melted, hot rolled,
A thin steel plate having a thickness of 1.5 mm was manufactured by sequentially performing cold rolling and annealing.

Hardness (HRB) after annealing for these thin steel plates.

The hardness (HIC) and Charpy impact test absorbed energy (at 20°C) were measured after quenching and tempering (processing conditions are as shown in Table 3).The results are shown in Table 3. It is also shown in .

As is clear from the results shown in Table 3, all of the thin steel sheets E-0 that meet the conditions of the present invention have a hardness (H
Although the IB) is low and soft, the hardness after heat treatment (quenching/tempering) is high (HRC ≥ 45) and the impact absorption energy is high (3.5 kg-m or more). It can be seen that the steel plate P has a low hardness after heat treatment because of its low C content, and the desired wear resistance cannot be obtained.

Furthermore, it can be confirmed that the comparative steel sheet Q, which has a high P content, has a small impact absorption energy and is inferior in impact resistance.

Summary of Effects> As explained above, according to the present invention, it is possible to realize a high-toughness, high-carbon thin steel plate that is easy to manufacture and process and has excellent wear resistance and impact resistance. Circular saw for mowing grass, circular saw for woodworking, band saw.

It can be applied to materials such as various cutlery, needles, washers, springs, etc. to further improve the performance of these products, resulting in extremely useful effects industrially.

[Brief explanation of the drawing]

FIG. 1 is a graph showing "changes in hardness and impact absorption energy depending on tempering temperature" of the thin steel sheets manufactured in Examples. FIG. 2 is a conceptual diagram illustrating a method for testing the cutting edge of a circular saw manufactured in an example. In the drawings: 1... circular saw, 2... fastener. 3... Steel ingot.

Claims (4)

[Claims] (1) Weight percentage: C: 0.70-1.10%, Si: 0.70% or less, M
n: 0.05-0.50%, P: 0.03% or less, S:
0.004% or less, Ni: 0.2-2.0%, Mo: 0
．． 10 to 0.30%, acid-soluble Al: 0.08% or less,
A high-toughness, high-carbon thin steel plate, the remainder of which is essentially Fe. (2) Weight percentage: C: 0.70-1.10%, Si: 0.70% or less, M
n: 0.05-0.50%, P: 0.03% or less, S:
0.004% or less, Ni: 0.2-2.0%, Mo: 0
．． 10-0.30%, acid-soluble Al: 0.08% or less, C
r: 0.50% or less, a high-toughness high-carbon thin steel plate in which the remainder substantially consists of Fe. (3) Weight percentage: C: 0.70 to 1.10%, Si: 0.70% or less, M
n: 0.05-0.50%, P: 0.03% or less, S:
0.004% or less, Ni: 0.2-2.0%, Mo: 0
．． 10-0.30%, acid-soluble Al: 0.08% or less, C
a: High-toughness high-carbon thin steel plate containing 0.02% or less and the remainder substantially consisting of Fe. (4) Weight percentage: C: 0.70 to 1.10%, Si: 0.70% or less, M
n: 0.05-0.50%, P: 0.03% or less, S:
0.004% or less, Ni: 0.2-2.0%, Mo: 0
．． 10-0.30%, acid-soluble Al: 0.08% or less, C
A high-toughness, high-carbon thin steel plate having r: 0.50% or less, Ca: 0.02% or less, and the remainder substantially consisting of Fe.