JP6020963B2 - Manufacturing method of high-speed tool steel material with excellent hot workability - Google Patents

Description

  The present invention relates to a method for producing a high-speed tool steel material excellent in hot workability and used for various cutting tools, cutting tools, dies, and the like.

  Conventionally, it is known that Ca added to high-speed tool steel has an effect of increasing the absolute amount of MC type carbide in the structure and making it finer. And the high-speed tool steel which reduced S with respect to the high-speed tool steel with which Ca was added, and also reduced N increases the effect by said Ca, As a result, when it was set as a product It is excellent in suppressing chipping and chipping and is effective in improving the life (Patent Document 1). And Ca added to high-speed tool steel acts also as an element which refines | miniaturizes a solidification structure | tissue, and improves hot workability (patent document 2).

  Usually, the above products made of high-speed tool steel are obtained by casting molten steel adjusted to a predetermined composition to form a material such as a steel ingot or slab, or by sintering powder obtained by casting the molten steel. The material is subjected to hot working, and then subjected to various processing and heat treatments to finish the final shape and characteristics. In the case of the high-speed tool steel material to which Ca is added, the component composition of the molten steel before casting has been adjusted in a vacuum induction furnace (Patent Documents 1 and 2). Or in order to reduce S amount, the slag refining by a ladle was applied (patent document 3).

JP-A 64-008252 JP-A-11-006042 Japanese Patent Laid-Open No. 04-111962

  It is possible to adjust the component composition of the high-speed tool steels of Patent Documents 1 to 3 by vacuum melting. However, when the amount of S in the material is reduced to a very small amount, it is necessary to prepare a high-grade raw material with a low amount of S as a matter of course, leading to an increase in manufacturing cost. Ca is an element having a relatively low boiling point (high vapor pressure). Therefore, if component adjustment is performed using vacuum melting in an actual operation with a large amount of molten steel, it is necessary to add Ca under a vacuum with a boiling action, and there is a problem that the amount of Ca added in the molten steel is not stable. . In addition, when Ca is added simultaneously with desulfurization in slag refining for desulfurization, Ca added to the molten steel combines with S to form sulfides. Even if a fixed amount of Ca is contained, the above-described effect expressed by Ca alone is weakened.

  The problem of the present invention is that, for example, in a method for producing a high-speed tool steel material having a component composition such as Patent Documents 1 to 3, S and N in the material can be reduced to a low content, and a target amount of Ca is added. By being able to do it, it is providing the manufacturing method of the high-speed tool steel raw material which can maintain the outstanding hot workability stably.

  This inventor examined the optimization of the timing of desulfurization, denitrification, and Ca addition in a melt | dissolution process about the manufacturing method of the high speed tool steel raw material which has component composition of patent documents 1-3. As a result, for example, slag refining that can efficiently remove S in the molten steel is applied to subsequent processes such as vacuum refining, and S and N are sufficiently reduced before Ca is added to the molten steel. In actual operation with a large amount of dissolution at one time, it was found that a target amount of Ca can be added, and the material after casting can produce a high-speed tool steel material in which the formation of Ca sulfide is suppressed. The invention has been reached.

That is, the present invention
A first step of preparing molten steel having a component composition of high-speed tool steel;
A second step of refining the prepared molten steel with slag to reduce S in the molten steel to 0.004% by mass or less;
A third step of adding Ca to the slag refined molten steel to adjust Ca in the molten steel to 0.005 to 0.015 mass%;
A fourth step of casting the molten steel to which the Ca is added;
It is a manufacturing method of the high-speed tool steel raw material excellent in hot workability characterized by consisting of.

The molten steel prepared in the first step is mass%,
C: 0.5-2.2%
Cr: 3.0-7.0%,
According to one or two of W and Mo (W + 2Mo): 5.0 to 30.0%,
V: 0.6-5.0%
It is preferable that it is a component composition of the high-speed tool steel containing.

  Moreover, it is preferable that the molten steel prepared at a 1st process is what was vacuum refined. Alternatively, the addition of Ca to the molten steel in the third step is preferably performed by penetrating the slag covering the upper surface of the molten steel after finishing the slag refining and introducing a Ca source into the deep part of the molten steel. . In this case, the input Ca source is preferably a CaSi alloy. In the molten steel before casting in the fourth step, N is preferably reduced to 0.01% by mass or less.

And the obtained high speed tool steel material is mass%,
C: 0.5-2.2%
Si: 0.1 to 1.0%,
Mn: 0.1 to 1.0%,
S: 0.004% or less,
Cr: 3.0-7.0%,
According to one or two of W and Mo (W + 2Mo): 5.0 to 30.0%,
V: 0.6-5.0%
Al: 0.3% or less (including 0%),
Ca: 0.005 to 0.015%,
N: 0.01% or less,
O: 0.004% or less,
The balance is preferably composed of Fe and inevitable impurities. The high-speed tool steel material may further include Co: 10.0% or less.

  According to the present invention, a high-speed tool steel material having a component composition such as Patent Documents 1 to 3 having excellent hot workability can be manufactured efficiently and with good reproducibility. This is a technique useful for extending the life of the final product made from the material.

High-speed tool steel material No. It is a drawing substitute photograph which shows the external appearance of a steel piece when hot-working 1 (invention example). High-speed tool steel material No. It is a drawing substitute photograph which shows the external appearance of the steel piece when 3 (comparative example) is hot worked.

  The feature of the present invention is that the S and N in the steel can be removed to a low level by reviewing the manufacturing method of the high-speed tool steel material excellent in hot workability proposed in Patent Documents 1 to 3 and the like. , Ca clarifies the process in which the target amount can be added, and thereby the hot workability of the material can be stably maintained. Below, each component of this invention is demonstrated.

[Composition composition of high-speed tool steel material]
First, the component composition (mass%) of a high-speed tool steel material that is preferable for achieving excellent hot workability will be described. And the manufacturing method of this invention mentioned later is optimal when manufacturing the high-speed tool steel raw material of such a component composition.

・ C: 0.5-2.2%
C is an element that combines with Cr, W, Mo, and V to form carbides, imparts quenching and tempering hardness, and improves wear resistance. However, when too much, toughness falls. Therefore, it is preferably 0.5 to 2.2% after balancing with the Cr, W, Mo, and V amounts described later. More preferably, it is 1.0% or more and / or 1.5% or less. More preferably, it is 1.3% or less.

・ Si: 0.1-1.0%
Si is usually used as a deoxidizer in the dissolution process. However, if the amount is too large, the toughness decreases, so 0.1 to 1.0% is preferable. More preferably, it is 0.6% or less.

Mn: 0.1 to 1.0%
Mn is used as a deoxidizer in the same manner as Si. However, if the amount is too large, the retained austenite increases in the structure after quenching and tempering, and the toughness is reduced, so 0.1 to 1.0% is preferable. More preferably, it is 0.2% or more and / or 0.5% or less.

-S: 0.004% or less When S is too much, in addition to inhibiting hot workability itself, it combines with Ca described later added by the present invention, whereby the heat exerted by Ca alone is exhibited. The improvement effect such as inter-workability is also hindered. Therefore, S is an element to be reduced and is preferably regulated to 0.004% or less. More preferably, it is 0.002% or less, and still more preferably 0.001% or less.

・ Cr: 3.0-7.0%
Cr is an element effective for imparting hardenability, wear resistance, oxidation resistance, and the like. However, if the amount is too large, the toughness, high-temperature strength, and temper softening properties are reduced. Therefore, 3.0 to 7.0% is preferable. More preferably, it is 3.5% or more and / or 5.0% or less.

-By 1 or 2 types of W and Mo (W + 2Mo): 5.0 to 30.0%
W and Mo combine with C to form a special carbide and impart wear resistance and seizure resistance. Moreover, the secondary hardening action at the time of tempering is large, and the high-temperature strength is also improved. However, when too much, hot workability will be inhibited. Therefore, in the relational expression of (W + 2Mo), it is preferable that one or two of these be 5.0 to 30.0%. More preferably, it is 10.0% or more and / or 25.0% or less. More preferably, it is 15.0% or more and / or 22.0% or less.

・ V: 0.6-5.0%
V combines with C to form a hard carbide, which contributes to improved wear resistance. However, when too much, toughness falls. Therefore, it is preferable to set it as 0.6 to 5.0%. More preferably, it is 1.0% or more and / or 4.0% or less. 3.5% or less is more preferable.

・ Ca: 0.005 to 0.015%
Ca develops dendrite crystals in the solidification process during casting and makes the cast structure uniform and fine, and thus has the effect of improving the hot workability of the material. Moreover, since the absolute amount of MC type carbide is increased and it is made finer, chipping and chipping in a product are suppressed. However, if it is too much, Ca oxide becomes inclusions and remains in the material, and the cleanliness of the high-speed tool steel material is lowered. Therefore, Ca to be added is preferably 0.005 to 0.015%. More preferably, it is 0.006% or more and / or 0.01% or less.

N: 0.01% or less N is unavoidably present in the material. And when too much, MC type carbide in a raw material will coarsen and the effect by said Ca addition will be inhibited greatly. Therefore, N in the material is preferably regulated to 0.01% or less. More preferably, it is important to regulate the amount to 0.005% or less, and further preferably to 0.002% or less.

  The solid solubility of N in steel increases as the Cr content increases. And, in the case of the high speed tool steel of Cr amount according to the present invention, if it is an actual operation with a large amount of molten steel, the amount of N in the raw material after casting easily exceeds several hundred ppm even without intention of addition. End up. Therefore, for the method for producing a high-speed tool steel material of the present invention, a melting method for extremely reducing the N amount within the above-mentioned regulation value is important. And this extremely reduced amount of N can be achieved stably and efficiently by the production method of the present invention described later.

O: 0.004% or less O is an element that inevitably exists in steel and forms an oxide. If too much, the oxides formed in the material will reduce the quality of the product. Moreover, in the high-speed tool steel according to the present invention to which Ca is added, by combining with Ca, the above effect of Ca is also inhibited. Therefore, the upper limit of O in the material is preferably regulated to 0.004%. More preferably, it is 0.002% or less. The extremely reduced amount of O in the material can be achieved stably and efficiently by the production method of the present invention described later.

  In addition, the high-speed tool steel material manufactured by the manufacturing method of the present invention may include 10.0% or less Co and 0.3% or less Al. Co is dissolved in the base to improve the strength and heat resistance of the product. Al, like Ca described above, makes the cast structure uniform and fine, and makes the MC type carbide fine, thereby improving the hot workability of the material and the life of the product. A preferable Al content for obtaining this effect is 0.02% or more. More preferably, it is 0.06% or more and / or 0.25% or less.

[About manufacturing method of high-speed tool steel material]
The component composition of the high-speed tool steel material containing 0.005 to 0.015% Ca and having S controlled to 0.004% or less, preferably N to 0.01% or less, is excellent. It is preferable for achieving high hot workability. And the manufacturing method of this invention is for manufacturing the high-speed tool steel raw material of such a component composition. Hereinafter, the 1st-4th process which comprises the manufacturing method of this invention is demonstrated.

-<1st process> It is the process of preparing the molten steel which has a component composition of high-speed tool steel.
In the present invention, the content of at least main elements constituting the high-speed tool steel is adjusted before the second step (slag refining) for desulfurization and the third step of adding Ca, which will be described later. The main elements at this time are, for example, C, Cr, W, Mo, V, and the like. And these content is the mass%, and it is preferable to set it as the following.
C: 0.5-2.2%
Cr: 3.0-7.0%,
According to one or two of W and Mo (W + 2Mo): 5.0 to 30.0%,
V: 0.6-5.0%

  Moreover, it is preferable that the molten steel prepared at a 1st process is what was vacuum refined. As described above, it is preferable for the present invention to reduce N and O in the high-speed tool steel material. In particular, N greatly reduces the effect of the addition of Ca of the present invention, and therefore it is preferable to reduce it to 0.01% or less at the time of the molten steel before casting. And the component composition of high-speed tool steel is adjusted by preparing raw materials in the iron source before melting, or by introducing the raw materials into the molten molten steel. If it contains impurities, this is one factor that increases N and O in the material. Therefore, the molten steel before the second step is subjected to vacuum refining with excellent degassing effect in which deoxygenation and denitrification proceed by reaction between C and O in the molten steel and boiling accompanying this reaction. It is preferable to keep it.

-<2nd process> The molten steel prepared at the 1st process is slag refined, and S in molten steel is reduced to 0.004% or less.
Even if the molten steel prepared in the first step is reduced in N and O, if S is high, when Ca is added to this, most of Ca is combined with S and sulfided. Form things. As a result, even if the material after casting contains 0.005 to 0.015% of Ca which is the target amount of the present invention, if it is present by forming the above sulfides, it is expressed by Ca alone. The effect of the present invention is not sufficiently exhibited. Therefore, in order for the Ca contained in the raw material after casting not to form the sulfide, it is necessary to positively and sufficiently reduce the S amount before final adjustment of the Ca amount in the melting step. It is valid. And this invention reduces S in a molten steel to 0.004% or less by applying the 2nd process which is slag refining further with respect to the molten steel prepared at the 1st process. Is the final adjustment.

  In the desulfurization by slag refining, S in molten steel is combined with a desulfurizing agent to form a sulfide, which is taken into the slag and removed. As the desulfurizing agent, conventionally known Ca, Mg, rare earth elements and the like can be used. When Ca is used as the desulfurization agent, the remaining Ca amount may be supplemented with respect to the Ca amount remaining as a result of the desulfurization reaction in the third step to be described later in which the final adjustment amount of Ca is added. The slag can be selected from conventionally known steelmaking slags. The structure of the slag can contain Ca and Mg that function as the desulfurizing agent in the form of CaO and MgO.

-<3rd process> Ca is added to the molten steel which refined slag in the 2nd process, and reduced S to 0.004 mass% or less, and adjusts Ca in molten steel to 0.005-0.015 mass%. .
If S in the molten steel is reduced to 0.004% or less in the second step, even if Ca is added thereto, most of them can be prevented from forming sulfides. And if this process order is followed and the molten steel which added 0.005-0.015% Ca is cast, the outstanding hot workability will be achieved for the raw material after casting.

  And it is preferable to add Ca to the molten steel in the third step by penetrating the slag covering the upper surface of the molten steel after finishing the slag refining and introducing a Ca source into the deep part of the molten steel. Slag refining is usually performed under atmospheric pressure on the molten steel in the ladle. Therefore, when the slag refining for reducing the amount of S is completed, if the Ca source is continuously introduced through the slag and the deep portion of the molten steel, the existing slag covers the upper surface of the molten steel and the Ca Since evaporation can be suppressed, the Ca addition yield is improved. Further, if the Ca source at this time is introduced into the molten steel in the form of a compound such as a CaSi alloy, evaporation immediately after the addition can be further suppressed, and the Ca addition yield is further improved. And since the slag refining apparatus used at the 2nd process can be used and the stirring apparatus in it can be utilized, it can improve the addition yield of Ca, without requiring special input equipment.

-<4th process> The molten steel which added Ca at the 3rd process is cast.
By casting the molten steel with the component composition adjusted as described above, a high-speed tool steel material is obtained. The casting method may be any method other than the ordinary ingot method using an ingot case, such as a continuous casting method or a remelting method performed once on a steel ingot after casting. The powder obtained by the atomizing method may be solidified by sintering or the like. Then, the material after casting is usually subjected to hot working such as forging and rolling. However, if the material is obtained by the present invention, cracks and the like at this time can be suppressed. The material after the hot working is subjected to further hot working, cold working, machining, and heat treatment as necessary to finish various products.

[Invention Examples 1 and 2]
Vacuum refining was performed on 25 t of molten steel adjusted to a predetermined component composition to prepare molten steel A (first step). Molten steel A of Invention Example 1 had a component composition containing 0.23% Co with no additive. Molten steel A of Invention Example 2 was adjusted to a component composition containing 4.97% by adding Co. Then, these molten steel A, to implement the slag refining using CaO-CaF ₂ slag, to obtain molten steel B (second step). Next, a feeder is inserted through the slag into the deep part of the molten steel B that has been subjected to slag refining, and then a CaSi alloy is introduced into the molten steel to obtain a molten steel C to which Ca is added (third step). . The input amount of the CaSi alloy is an amount (hereinafter simply referred to as “calculated amount”) in which the Ca content in the molten steel is 100 ppm in calculation when the Ca component yield is 10%. And the molten steel C was cast and the high-speed tool steel raw material was manufactured (4th process). Table 1 shows the component compositions of molten steels A and B and molten steel C (raw material after casting) for inventive examples 1 and 2.
[Comparative Example 3]
With respect to the manufacturing method of the present invention, high-speed tool steel material was manufactured by casting molten steel added with Ca to molten steel A subjected to vacuum refining without performing slag refining. Ca was added by adding a CaSi alloy, and was added to molten steel in a vacuum environment after predetermined vacuum refining was completed. The input amount of the CaSi alloy is a calculated amount at which the Ca content in the molten steel becomes 100 ppm. Table 1 shows the component composition of the high-speed tool steel material after casting.
[Comparative Example 4]
In the manufacturing method of the present invention, Ca was added to molten steel A subjected to vacuum refining, and then slag refining was performed and cast to manufacture a high-speed tool steel material. Ca was added by adding a CaSi alloy, and was added to molten steel in a vacuum environment after predetermined vacuum refining was completed. The input amount of the CaSi alloy is a calculated amount at which the Ca content in the molten steel becomes 100 ppm. CaO—CaF ₂ slag was used for slag refining. Table 1 shows the component composition of the raw material after casting.

  From the results in Table 1, No. obtained by the production method of the present invention. The high-speed tool steel materials 1 and 2 had an actual Ca content of 87 to 99 ppm with respect to the target Ca content of 100 ppm, and Ca was added with a good yield. And the amount of S was reduced to the level of 2 ppm and the amount of N was reduced to 50 ppm. On the other hand, no. In the high-speed tool steel material of No. 3, the Ca content was only 2 ppm, the yield was poor, and the S content was a high level of 45 ppm. In addition, No. in which Ca was added before slag refining. Also in the high-speed tool steel material of No. 4, the S content was a low level of 5 ppm, but the Ca content was a low content of 14 ppm.

  The high-speed tool steel material obtained in Example 1 was heated to 1160 ° C., and hot working was performed to plastically process to a steel piece having a cross-sectional dimension of 135 × 135 mm square. And the surface of the steel piece after hot processing was observed visually. As a result, no. The surface of the steel slab obtained by hot-working the high-speed tool steel materials 1 and 2 was smooth, and no significant cracks were observed (a drawing substitute photo showing the appearance of the No. 1 steel slab is shown in FIG. 1). . In contrast, no. 3 was confirmed to have a remarkable crack that could not be removed by grinding (a photo substituted for a drawing showing the appearance is shown in FIG. 2). No. No. 4 steel slab has no. No. 3 steel slab, but no. Compared with the steel pieces of 1 and 2, the remarkable crack was confirmed.

Claims (7)

A first step of preparing molten steel having a component composition of high-speed tool steel;
A second step of refining the prepared molten steel with slag to reduce S in the molten steel to 0.004% by mass or less;
A third step of adding Ca to the slag refined molten steel to adjust Ca in the molten steel to 0.005 to 0.015 mass%;
A fourth step of casting the molten steel to which the Ca is added;
Tona is, the molten steel prior to casting in the fourth step, N is hot method for producing superior high-speed tool steel material in workability characterized that you have been reduced to less than 0.01 wt%. The molten steel prepared in the first step is mass%,
C: 0.5-2.2%
Cr: 3.0-7.0%,
According to one or two of W and Mo (W + 2Mo): 5.0 to 30.0%,
V: 0.6-5.0%
The method for producing a high-speed tool steel material excellent in hot workability according to claim 1, wherein the composition is a component composition of high-speed tool steel including The method for producing a high-speed tool steel material excellent in hot workability according to claim 1, wherein the molten steel prepared in the first step is vacuum refined. The addition of Ca to the molten steel in the third step is performed by penetrating the slag covering the upper surface of the molten steel after finishing the slag refining and introducing a Ca source into the deep part of the molten steel. Item 4. A method for producing a high-speed tool steel material excellent in hot workability according to any one of Items 1 to 3. The method for producing a high-speed tool steel material excellent in hot workability according to claim 4, wherein the Ca source to be input is a CaSi alloy. The obtained high-speed tool steel material is mass%,
C: 0.5-2.2%
Si: 0.1 to 1.0%,
Mn: 0.1 to 1.0%,
S: 0.004% or less,
Cr: 3.0-7.0%,
According to one or two of W and Mo (W + 2Mo): 5.0 to 30.0%,
V: 0.6-5.0%
Al: 0.3% or less (including 0%),
Ca: 0.005 to 0.015%,
N: 0.01% or less,
O: 0.004% or less,
The method for producing a high-speed tool steel material excellent in hot workability according to any one of claims 1 to 5 , wherein the balance Fe and unavoidable impurities are included. The obtained high-speed tool steel material is mass%,
Co: 10.0% or less,
The manufacturing method of the high-speed tool steel raw material excellent in hot workability of Claim 6 characterized by the above-mentioned.