JPH0621320B2 - High toughness high carbon thin steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is excellent in impact resistance and wear resistance after heat treatment,
Moreover, it has good manufacturability and workability,
The present invention relates to a high toughness and high carbon thin steel sheet suitable for band saws, needles, washers, springs and the like.

<Prior art and its problems> In general, round saws for cutting grass, round saws for sawing, various cutlery, etc. are high carbon cold-rolled thin steel sheets such as SK4M and SK5M specified in JIS G3311, and carbon amounts such as SKS5M and SKS51M. It is usually manufactured by using a cold-rolled thin steel sheet of alloy steel, which is often used, as a raw material, forming it, hardening it by heat treatment such as quenching and tempering, and then subjecting it to sharpening and straightening.

Here, the material steel plate for each product is soft and easy to process before forming, and a desired strength can be obtained only by a heat treatment performed after forming, and sufficient impact resistance when used as a product. Since it is required to exhibit wear resistance as well as the above, a material with a high carbon content as described above is selected as a material, and in general, it is soft when a thin steel sheet is shipped from a steel manufacturer. Spheroidizing annealing is performed. Then, the raw material thin steel plate after shipping is formed into a desired shape by the user and subjected to heat treatment such as quenching and tempering to give necessary characteristics, but in this case,
Since the tempering temperature has a great effect on the impact resistance and wear resistance of the product, various tempering temperatures of "as-quenched" or "up to 650 ° C" are carefully selected depending on the form and situation of use. (Usually 180-450 ° C
The degree is applied well).

However, the quenching / tempering type high carbon thin steel sheet specified in JIS has insufficient impact resistance in spite of careful selection of heat treatment conditions. For example, when it is applied to a circular saw for mowing, stone roller etc. It was difficult to completely prevent the brittle fracture from being caused by the contact impact.

Therefore, the applicant first added a predetermined amount of Mo to the high carbon steel having a high Mn content in relation to the P content, and heat-treat this under predetermined conditions to obtain impact resistance / resistance. A method for producing a steel material having excellent wear resistance has been proposed (JP-A-62-139811).

However, the Mo-added high carbon steel material previously proposed by the applicant has excellent wear resistance and impact resistance, and exhibits excellent performance when used as a blade product such as a circular saw for cutting grass. However, as a result of examination from various viewpoints after that, rolling cracks are likely to occur due to a slight difficulty in rollability when a steel manufacturer manufactures a thin plate material. We have come to recognize that it may become an unfavorable factor even when considering further workability improvement measures.

<Matters Underlying the Basis of Completion of the Invention> From the above viewpoints, the present inventors have sufficient wear resistance and impact resistance as a material for a circular saw for cutting grass, and have a good workability. As a result of research to provide a thin steel sheet that is good and does not cause inconveniences such as cracks even in the rolling process and the forming process into the final product, the following findings were obtained.

(a) It is presumed that the addition of 0.2% or more (hereinafter,% representing the composition ratio is% by weight) of Ni to high-carbon steel is because the deformation resistance of the ferrite matrix phase is reduced. Processability is improved, cracks can be suppressed from occurring during the rolling process into thin plates, and the processing when manufacturing final products from thin plate materials is facilitated.

(b) Moreover, even in the high carbon steel containing Ni, Mn
If the content of S and S is controlled to a sufficiently low value, the effect of improving the impact resistance can be achieved by adding Mo without adversely affecting the wear resistance and workability. It is possible to easily form a thin steel sheet with good formability without causing trouble such as cracking by hot rolling and cold rolling, and to ensure excellent wear resistance and impact resistance by heat treatment. To be.

(c) In the above proposal (JP-A-62-139811), not only sufficient impact resistance cannot be obtained even by adding Ni to high carbon steel, but also Ni is brittle. It is said to cause the change. However, this is because when a high Ni content steel contains a large amount of Mn and Mo, it becomes too hard and the toughness deteriorates. Therefore, the Mn and S contents were reduced to below a specific value. In this case, it is possible to obtain a remarkable effect of improving the toughness by adding Mo without actually reducing the wear resistance to an inconvenient level.

Here, S is present in the steel as MnS and becomes a starting point of cracking, so it is necessary to reduce it. However, in the case of steel with high hardness and addition of Mo, the effect of MnS is particularly It must be large and reduced as much as possible.

(d) When a specific amount of Ca is contained in the above-mentioned "high carbon / high Ni steel in which Mo is added to control the Mn and S contents," S in the steel is Ca.
Since it is fixed as S, the formation of MnS is suppressed, the brittleness tendency due to MnS is suppressed, and the toughness of steel is further improved.

(e) On the other hand, addition of a predetermined amount of Cr to the steel is effective in improving the corrosion resistance and is also preferable in terms of preventing graphitization, which leads to the addition of properties more suitable as a material for round saws, blades and the like.

<Means for Solving the Problems> The present invention has been completed based on the above-mentioned findings, and states that “a thin steel sheet manufactured by rolling is made of C: 0.70 to 1.10%, Si: 0.70% or less, Mn. : 0.05 to 0.50%, P: 0.03% or less, S: 0.004% or less, Ni: 0.2% to less than 2.0% Mo: 0.10 to 0.30%, Acid-soluble Al: 0.08% or less, or further Cr : 0.50% or less, Ca: 0.02% or less 1 type or 2 types are included, and the balance is substantially Fe.
It is characterized by imparting excellent wear resistance and toughness (impact resistance) as well as good workability by constituting the component composition consisting of.

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

(a) C In order to obtain the desired hardness and wear resistance in the C steel sheet, the C content must be 0.70% or more. On the other hand, if the C content exceeds 1.10%, the steel becomes significantly brittle and Since the rolling manufacturing becomes difficult, the C content is set to 0.70 to 1.10%.

(b) Si Although active addition is not particularly required, if the content of Si exceeds 0.70%, the steel sheet tends to become hard and brittle, so the Si content was set to 0.70% or less.

(c) Mn In the wear-resistant steel sheet, Mn is generally added in a large amount, but it is necessary to reduce Mn in the steel sheet of the present invention containing Ni and Mo. When the Mn content of the steel sheet of the present invention exceeds 0.50%, the steel sheet is likely to be hardened by heat treatment and becomes too hard, resulting in a decrease in toughness. On the other hand, if the Mn content is less than 0.05%, the amount of solid solution S increases and embrittlement occurs during hot working,
Since the manufacturability of steel sheets is impaired, the Mn content is
It was defined as 0.05 to 0.50%.

(d) In the steel sheet containing P Mo, it is needless to say that the lower the P content is, the better the toughness is, although the usual level is acceptable. When the P content exceeds 0.03%, P segregates at the grain boundaries, and grain boundary embrittlement easily occurs. Therefore, the P content is set to 0.03% or less.

(e) S Even in ordinary steel, it is better that S is low, but particularly in steel materials such as the steel sheet of the present invention having high strength and high wear resistance, the presence of MnS has a significant effect on deterioration of toughness. In the steel sheet according to the present invention, unless the S content is suppressed to 0.004 or less after reducing the Mn content, MnS becomes coarse and impairs toughness, so the S content is set to 0.004% or less. It was

Various methods for suppressing the S content to 0.004% or less are known, but means for adding Ca alone or Ca-
It is preferable to employ a means for performing Si injection treatment.

In this method, Ca is added in the molten steel stage, and S is removed as CaS. In this case, the above desulfurization causes Ca in the steel.
However, there is a method of setting S ≦ 0.004 and a method of fixing S in steel as CaS while leaving Ca, but any method may be used.

(f) Ni Ni is a component that is positively added because it has the effect of improving the workability of steel. If the content is less than 0.2%, the desired workability cannot be ensured.

That is, by adding 0.2% or more of Ni, it becomes possible for a steel maker to perform rolling when producing a thin plate.
If the content is less than 2%, cracks and the like are likely to occur during rolling, making it difficult to perform stable work. In addition, ensuring a Ni content of 0.2% or more in the steel sheet also facilitates the processing when the user processes the steel sheet. As described above, this is presumed to reduce the deformation resistance of the ferrite matrix phase.

On the other hand, even if Ni is contained in an amount of 2.0% or more, not only the workability improvement effect is saturated and the steel plate cost increases, but also the hardness after heat treatment increases and the impact resistance deteriorates. The amount was set to 0.2% or more and less than 2.0%.

(g) Mo Mo is an important component, and the addition of Mo has the effect of maintaining high toughness and high wear resistance after heat treatment without degrading the workability of the steel sheet before heat treatment (before quenching and tempering). Brought out.

Generally, when steel is tempered at a temperature of around 300 ° C. after quenching, so-called “low temperature temper embrittlement” occurs 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 temper embrittlement" is remarkably reduced particularly in the case of a thick sample, and therefore "tempering near 300 ° C" is sometimes used. However, in that case, deterioration in toughness still poses a problem depending on the usage conditions. Even against such brittleness,
The addition of Mo is very effective.

And, in the steel sheet according to the present invention, the Mo content is 0.10%
If the amount is less than 0.1%, the above effect cannot be obtained. On the other hand, if the amount exceeds 0.30%, the effect will be saturated, so the Mo content was set to 0.10 to 0.30%.

(h) Acid-soluble Al Al is a component added as necessary as a deoxidizer, but if the content of acid-soluble Al exceeds 0.08%, not only will the cost increase, but it will also cause hardening of the steel sheet. So there is no advantage. As described above, the content of acid-soluble Al is allowed up to 0.08%, so that the content was set to 0.08% or less.

(i) Cr Cr is a component added as necessary because it has the action of improving the corrosion resistance of steel and the action of preventing graphitization. But 0.
If the content exceeds 50%, the material is hardened and becomes brittle, so the Cr content was set to 0.50% or less.

(j) Ca Ca is a component added as required as a desulfurizing element, but if it exceeds 0.02%, it becomes a large inclusion and deteriorates toughness, so the Ca content is 0.20% or less. I decided.

Now, the thin steel sheet according to the present invention is manufactured by melting the steel containing the above components and the balance being substantially Fe, and extending it to a desired plate thickness by hot rolling and cold rolling. . During this, annealing for softening may be performed. In any case, finally, annealing is carried out to improve the workability, but 700 to 880 ° C. is suitable for this final annealing.

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

Next, the effects of the present invention will be described by comparing the examples with the comparative examples.

<Example> Example 1 First, after melting steel of each component composition as shown in Table 1, it was hot rolled to form a hot rolled sheet having a thickness of 3.0 mm and then softened by annealing. Cold rolled to 1.35 mm thickness. In the rolling process, the steel sheets A, B and D finished rolling without any trouble, but it was confirmed that the steel sheet C having a high Mn content tends to cause rolling cracks.

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

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

Then, samples are taken from these annealed plates and the temperature is 850 ° C.
After heating, it was oil-quenched and then tempered at various temperatures. The tempering time was 15 minutes.

The hardness of each sample after the above heat treatment was measured, a Charpy V-notch test piece was prepared, and an impact test at 0 ° C. was performed to determine the impact absorption energy. The results were summarized by the tempering temperature and shown in FIG. Shown in.

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

That is, the wear resistance of the steel sheet is roughly determined by the C content and hardness, and at the C content level of the test steel sheet, hardness of H _R C45 or higher is required depending on the application. And
Generally, hardness decreases as the tempering temperature rises, so to obtain high hardness (high wear resistance), low temperature (40
Tempering below 0 ° C is required. From such a viewpoint, the comparative steel sheet B having a high S content has a drawback that the absorbed energy in the high temperature tempering is large, but the absorbed energy in the low temperature tempering is small. Further, the comparative steel sheet C having a high Mn content and a high S content, and the comparative steel sheet D having a high S content and no Mo added have a small absorbed energy under any tempering condition.

On the other hand, it is clear that the steel sheet A of the present invention exhibits absorbed energy of 3.5 kg · m or more at any tempering temperature and is excellent in impact resistance.

Example 2 A disk was punched out from a 1.35 mm-thick high carbon cold-rolled steel sheet (composition composition as shown in Table 1) before quenching produced in Example 1 and further kept at 870 ° C. for 40 minutes and then oil-cooled. Quenching, tempering treatment at 380 ° C. for 150 minutes, and further shaping were performed to prepare a circular saw 1 (thickness: 1.35 mm thick, diameter: 230 mmφ) as shown in FIG.

Next, the circular saw 1 was rotated at 4000 rpm, and the steel ingot 3 was struck by the blade of the circular saw 1 for 15 seconds by releasing the clasp 2 during rotation as shown in FIG. The "blade chipping" situation of the circular saw 1 was investigated.

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

The results shown in Table 2 also show that only the circular saw made of the steel sheet A of the present invention having a low Mn content and S content and having a predetermined amount of Mo added does not cause "blade chipping" and It can be confirmed that the impact resistance is good.

Example 3 Steels having the respective component compositions shown in Table 3 were melted and hot-rolled,
Cold rolling and annealing were sequentially performed to manufacture a thin steel plate having a thickness of 1.5 mm.

These steel sheets, hardness after annealing (H _{R B),} and which quenching and tempering treatment (treatment conditions third is as shown in Table) was followed hardness (H _R C) and Charpy impact test absorbed energy (At 0 ° C) was measured, and the result was the third
It is also shown in the table.

As is apparent from the results shown in Table 3, satisfying thin steel sheet E~P of the present invention are all after annealing the hardness (H _R
B) even though is a softer low, whereas the heat treatment (quenching and tempering) after hardness is high (H _R C ≧ 45), yet the impact absorbed energy is high (3.5 kg · m or higher), It can be seen that since the comparative steel sheet Q has a low C content, the hardness after heat treatment is low, and desired wear resistance cannot be obtained.

Further, it can be confirmed that the comparative steel sheet R having a large P content and the comparative steel sheet S having a large Ni content also have low impact absorption energy and poor impact resistance.

<Summary of Effects> As described above, according to the present invention, it is possible to realize a high toughness high carbon thin steel sheet that is easy to manufacture and process and has excellent wear resistance and impact resistance. A very useful effect in the industry such that it can be applied to materials such as circular saws for mowing, circular saws for woodworking, saw blades, various blades, needles, washers and springs to further improve the performance of these products. Is brought about.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing “changes in hardness and impact absorbed energy depending on tempering temperature” of thin steel sheets manufactured in Examples. FIG. 2 is a conceptual diagram illustrating a blade chipping test method for the circular saw manufactured in the example. In the drawing, 1 ... Circular saw, 2 ... Fastener, 3 ... Steel ingot.

Continuation of the front page (56) Reference JP 62-202022 (JP, A) JP 63-7351 (JP, A) JP 62-139811 (JP, A)

Claims (4)

[Claims] 1. By weight ratio, C: 0.70 to 1.10%, Si: 0.70% or less, Mn: 0.05 to 0.50%, P: 0.03% or less, S: 0.004% or less, Ni: 0.2% or more and less than 2.0%, High toughness high carbon thin steel sheet with Mo: 0.10 to 0.30%, acid-soluble Al: 0.08% or less, and the balance being essentially Fe. 2. By weight ratio, C: 0.70 to 1.10%, Si: 0.70% or less, Mn: 0.05 to 0.50%, P: 0.03% or less, S: 0.004% or less, Ni: 0.2% or more and less than 2.0%, High toughness high carbon thin steel sheet with Mo: 0.10 to 0.30%, acid-soluble Al: 0.08% or less, Cr: 0.50% or less, and the balance of the balance being essentially Fe. 3. By weight ratio, C: 0.70 to 1.10%, Si: 0.70% or less, Mn: 0.05 to 0.50%, P: 0.03% or less, S: 0.004% or less, Ni: 0.2% or more and less than 2.0%, High toughness high carbon thin steel sheet with Mo: 0.10 to 0.30%, acid-soluble Al: 0.08% or less, Ca: 0.02% or less, and the balance of the balance being essentially Fe. 4. By weight ratio, C: 0.70 to 1.10%, Si: 0.70% or less, Mn: 0.05 to 0.50%, P: 0.03% or less, S: 0.004% or less, Ni: 0.2% or more and less than 2.0%, Mo: 0.10 to 0.30%, acid-soluble Al: 0.08% or less, Cr: 0.50% or less, Ca: 0.02% or less, and a high toughness high carbon thin steel sheet whose balance is essentially Fe.