TW201341537A - Method for producing high speed tool steel material with excellent hot workability - Google Patents

Abstract

A method for producing high speed tool steel material with excellent hot workability is provided, which may decrease S and N to lower content, and may add target quantity of Ca. The method for producing high speed tool steel material includes: a first step of preparing a molten steel having a component composition of a high speed tool steel; a second step of slag refining the prepared molten steel to decrese S in the molten steel to 0.004 mass% or less; a third step of adding Ca to the slag refined molten steel and adjusting Ca in the molten steel to 0.005 to 0.015 mass%; and a forth step of casting the molten steel added Ca. It is preferred that the molten steel prepared in the first step is obtained by vacuum refining. Moreover, it is preferred that in the molten steel before casting in the forth step, N is decreased to 0.01 mass% or less.

Description

Method for manufacturing high speed tool steel material with excellent hot workability

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

Previously, 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 the MC type carbide fine. Further, with respect to the high-speed tool steel to which Ca is added, the high-speed tool steel having a reduced S and further reduced N is improved by the effect of the above-described Ca, and as a result, it is excellent in cracking or chipping at the time of forming the product. It is effective for improving the life (Patent Document 1). In addition, Ca added to the high-speed tool steel also functions as an element that refines the solidified structure, thereby improving hot workability (Patent Document 2).

In general, as the above-described product of the high-speed tool steel, a material which has been adjusted to a predetermined composition and formed into a steel block or a steel sheet is cast, or a powder obtained by casting the molten steel is sintered to form a material, and the material is formed. Thermal processing, after various processing and heat treatment, is finished into the final shape and characteristics. In the case of the high-speed tool steel material to which Ca is added, the composition of the molten steel before casting is adjusted in a vacuum induction furnace (Patent Document 1 and Patent Document 2). Or, in order to reduce the amount of S, slag refining by means of a ladle is applied (Patent Document 3).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 64-008252

[Patent Document 2] Japanese Patent Laid-Open No. 11-006042

[Patent Document 3] Japanese Patent Laid-Open No. Hei 04-111962

The composition of the high-speed tool steel of Patent Documents 1 to 3 can be adjusted by vacuum melting. However, in the case where the amount of S of the material is reduced to an extremely small amount, it is necessary to prepare an advanced raw material having an S amount which is originally low, resulting in an increase in manufacturing cost. Further, Ca is an element having a relatively low boiling point (high vapor pressure). Therefore, when the component is adjusted by vacuum melting in the actual operation in which the amount of molten steel is large, it is necessary to add Ca under a vacuum having a boiling action, and there is a problem that the amount of Ca added to the molten steel is unstable. . Further, in the slag refining for the purpose of desulfurization, if Ca is to be added simultaneously with desulfurization, Ca added to the molten steel is bonded to S to form a sulfide, and as a result, even the material after casting is obtained. Containing a predetermined amount of Ca, the above effects exhibited by the Ca monomer are also weak.

An object of the present invention is to provide a method for producing a high-speed tool steel material, which is a method for producing a high-speed tool steel material having a composition of Patent Document 1 to Patent Document 3, for example, in the material. S or N is lowered to a low content, and a target amount of Ca is added, whereby excellent hot workability can be stably maintained.

The inventors of the present invention have studied the optimization of the timing of desulfurization, denitrification, and Ca addition in the melting step in the method for producing a high-speed tool steel material having the composition of Patent Document 1 to Patent Document 3. Result Now, in the following procedure, for example, in a subsequent step of vacuum refining or the like, the slag refining which can efficiently remove S in the molten steel is applied, and after S or N is sufficiently lowered, Ca is added to the molten steel. In this way, the target amount of Ca can be added even in the actual operation in which the amount of melting is large once, and the material after casting can produce high-speed tool steel material in which the formation of sulfide of Ca is suppressed, thereby completing the present. invention.

That is, the present invention is a method for producing a high-speed tool steel material excellent in hot workability, comprising: a first step of preparing a molten steel having a composition of high-speed tool steel; and a second step of preparing The molten steel is subjected to slag refining, and S in the molten steel is reduced to 0.004% by mass or less; in the third step, Ca is added to the molten steel refined by slag, and Ca in the molten steel is adjusted to 0.005 Mass %~0.015% by mass; and Step 4, casting the above-mentioned molten steel to which Ca is added.

Preferably, the molten steel prepared in the first step has the following compositional composition of the high-speed tool steel, that is, in mass%, C: 0.5% to 2.2%, and Cr: 3.0% to 7.0%, based on W and One or two types of Mo (W+2Mo): 5.0% to 30.0%, and V: 0.6% to 5.0%.

Further, the molten steel prepared in the first step is preferably vacuum-refined. Alternatively, it is preferable that the addition of Ca to the molten steel in the third step is to penetrate the slag covering the upper surface of the molten steel after the slag refining, and to the depth of the molten steel. The Ministry of Energy is put into the Ca source. In this case, it is preferable that the Ca source to be charged is a CaSi alloy. It is preferable that in the molten steel before casting in the fourth step, N is reduced to 0.01% by mass or less.

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

According to the present invention, a high-speed tool steel material having a composition of components such as Patent Document 1 to Patent Document 3, which is excellent in hot workability, can be produced efficiently and reproducibly. As a result, it is useful for the longevity of the final product produced from the material.

The present invention is characterized in that a method for producing a high-speed tool steel material excellent in hot workability proposed in Patent Documents 1 to 3 and the like is re-examined, whereby S or N in steel can be removed to a low level. At the level of the level, the step of adding the target amount of Ca is clarified, so that the hot workability of the material can be stably maintained. Hereinafter, each constituent element of the present invention will be described.

[About the composition of high-speed tool steel materials]

First, the component composition (% by mass) of the high-speed tool steel material which is preferable for achieving excellent hot workability will be described. Further, the production method of the present invention to be described later is preferable in the case of producing a high-speed tool steel material having such a component composition.

. C: 0.5%~2.2%

C is an element which bonds with Cr, W, Mo, and V to form a carbide, imparts quenching and tempering hardness, and improves wear resistance. However, if C is excessive, the toughness is lowered. Therefore, when a balance is made with the amount of Cr, the amount of W, the amount of Mo, and the amount of V to be described later, C is preferably 0.5% to 2.2%. More preferably, it is 1.0% or more and/or 1.5% or less. Further, it is preferably 1.3% or less.

. Si: 0.1%~1.0%

Si is usually used as an oxygen scavenger in the melting step. However, if too much Si is used, the toughness is lowered, so Si is preferably from 0.1% to 1.0%. More preferably, it is 0.6% or less.

. Mn: 0.1% to 1.0%

Mn is used as an oxygen scavenger similarly to Si. However, if Mn is too In many cases, the amount of residual austenite in the microstructure after quenching and tempering increases, so that the toughness is lowered, so Mn is preferably 0.1% to 1.0%. More preferably, it is 0.2% or more and/or 0.5% or less.

. S: 0.004% or less

When S is excessively large, the hot workability is inhibited by itself, and the Ca bond which will be described later added to the present invention also hinders the effect of improving the hot workability and the like of the Ca monomer. Therefore, S is an element which should be lowered, and is preferably limited to 0.004% or less. More preferably, it is 0.002% or less, further preferably 0.001% or less.

. Cr: 3.0%~7.0%

Cr is an element effective for imparting hardenability, abrasion resistance, oxidation resistance, and the like. However, if Cr is excessive, the toughness, high-temperature strength, and temper softening characteristics are lowered. Thus, Cr is preferably from 3.0% to 7.0%. More preferably, it is 3.5% or more and/or 5.0% or less.

. One or two types of W and Mo (W+2Mo): 5.0% to 30.0%

W and Mo are bonded to C to form a special carbide, which imparts abrasion resistance or burn-resistance. Moreover, the secondary hardening action at the time of tempering is large, and the high temperature strength is also improved. However, if there are too many W and Mo, hot workability will be impeded. Therefore, in the relational expression of (W+2Mo), it is preferred that one or two of W and Mo be 5.0% to 30.0%. More preferably, it is 10.0% or more and/or 25.0% or less. Further, it is preferably 15.0% or more and/or 22.0% or less.

. V: 0.6%~5.0%

V and C bond to form a hard carbide and contribute to wear resistance improve. However, if V is excessive, the toughness is lowered. Thus, V is preferably from 0.6% to 5.0%. More preferably, it is 1.0% or more and/or 4.0% or less. Further, it is preferably 3.5% or less.

. Ca: 0.005%~0.015%

Ca develops dendrite crystallization during solidification during casting, and makes the cast structure uniform and fine, thereby having an effect of improving the hot workability of the material. Further, since the absolute amount of the MC-type carbide is increased and the MC-type carbide is made fine, cracking or chipping at the time of forming the product is suppressed. However, if the amount of Ca is too large, the oxide of Ca remains as inclusions and remains in the material, thereby reducing the cleanliness of the high-speed tool steel material. Thus, the added Ca is preferably from 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 inevitably exists in the material. Further, if N is too large, the MC-type carbide in the material is coarsened, and the effect of the above-described Ca addition is greatly hindered. Therefore, N in the material is preferably limited to 0.01% or less. It is more important that the limit is 0.005% or less, and further preferably 0.002% or less.

The solid solubility of N in the steel increases as the Cr content increases. Further, in the case of the high-speed tool steel of the Cr amount of the present invention, if the amount of the molten steel is large, the amount of N in the material after casting tends to exceed several hundred ppm even if there is no intention of addition. Therefore, it is important for the method of manufacturing the high-speed tool steel material of the present invention to reduce the amount of N to within the above-described limit value. Moreover, this is greatly reduced The amount of N can be stably and efficiently achieved by the production method of the present invention to be described later.

. O: 0.004% or less

O is inevitably present in steel and is an element forming an oxide. If O is too much, the oxide formed in the material will degrade the quality of the product. Further, in the high-speed tool steel of the present invention to which Ca is added, O is also inhibited by Ca bonding, which also hinders the above-described effects of Ca. Therefore, it is preferable to limit the upper limit of O in the material to 0.004%. More preferably, it is 0.002% or less. Further, the amount of O which is extremely reduced in the material can be stably and efficiently achieved by the production method of the present invention to be described later.

Further, the high-speed tool steel material produced by the production method of the present invention may contain 10.0% or less of Co or 0.3% or less of Al. Co is solid-solved in the matrix to increase the strength or heat resistance of the article. Similarly to the Ca described above, Al makes the cast structure uniform and fine, and makes the MC-type carbide fine, thereby improving the hot workability of the material or the life of the product. In order to obtain this effect, a preferred Al content is 0.02% or more. More preferably, it is 0.06% or more and/or 0.25% or less.

[About the manufacturing method of high speed tool steel material]

The component composition of the high-speed tool steel material containing 0.005% to 0.015% of Ca and S is limited to 0.004% or less, preferably N is limited to 0.01% or less, is preferable in order to achieve excellent hot workability. Composition. Moreover, the manufacturing method of the present invention is used to manufacture high speed tool steel materials of such composition. Hereinafter, the first to fourth steps constituting the manufacturing method of the present invention will be described.

. <First Step> A step of preparing a molten steel having a composition of high-speed tool steel.

In the present invention, the adjustment of the content of at least the main element constituting the high-speed tool steel is performed in advance before the second step (slag refining) for performing desulfurization described later and the third step of adding Ca. The main elements at this time are, for example, C, Cr, W, Mo, V, and the like. Further, the content of the main elements is preferably 5% by mass, C: 0.5% to 2.2%, Cr: 3.0% to 7.0%, and one or two types of W and Mo (W+2Mo). ): 5.0% to 30.0%, and V: 0.6% to 5.0%.

Further, the molten steel prepared in the first step is preferably vacuum-refined. For the purposes of the present invention, as described above, it is preferred to reduce N or O in the high speed tool steel material. In particular, N greatly hinders the effect of the Ca addition of the present invention, and therefore it is preferable to reduce N to 0.01% or less in advance at the time of the molten steel before casting. Moreover, the composition of the high-speed tool steel is adjusted in the iron source before the melting, or the raw material is added to the molten steel for adjustment, and if the iron source or raw material contains a lot of impurities, One of the main reasons for increasing N or O in the material. Therefore, in the molten steel before the second step, it is preferred that the degassing effect of deoxidation and denitrification is performed in advance by the reaction of C and O in the molten steel or the boiling of the reaction. Vacuum refining.

. <Step 2> Melting the molten steel prepared in the first step The slag is refined and the S in the molten steel is reduced to below 0.004%.

Even if the molten steel prepared in the first step is a molten steel having a reduced N or O, if S is high, after Ca is added to the molten steel, most of Ca is bonded to S to form a sulfide. . As a result, even if the material after casting contains 0.005% to 0.015% of Ca in the target amount of the present invention, if the Ca is present as the sulfide, the effect of the present invention represented by the Ca monomer cannot be sufficiently exhibited. Therefore, in order to prevent the above-described sulfide from being formed in the Ca contained in the material after casting, it is effective to actively and sufficiently reduce the amount of S in the melting step before finally adjusting the amount of Ca. Further, in the present invention, the molten steel prepared in the first step is further applied as the second step of the slag refining, whereby the S in the molten steel is first lowered to 0.004% or less, and then the amount of Ca is finally adjusted.

The desulfurization caused by slag refining is such that S in the molten steel is bonded to the desulfurizing agent to form a sulfide, and the sulfide is mixed into the slag for removal. Further, Ca or Mg, a rare earth element or the like which has been previously known can be used for the desulfurizing agent. When Ca is used for the desulfurizing agent, in the third step described later, in which the final adjusted amount of Ca is added, the amount of Ca remaining may be added to the amount of Ca remaining in the result of the desulfurization reaction. The slag may be selected from previously known slag for steel making. In the configuration of the slag, Ca or Mg which functions as the above-described desulfurizing agent may be contained in the form of CaO or MgO.

. <Third Step> In the second step, Ca is added to the molten steel in which S is reduced to 0.004% by mass or less, and Ca is added to the molten steel to adjust the Ca in the molten steel to 0.005 mass% to 0.015 mass%.

When the S in the molten steel is previously lowered to 0.004% or less in the second step, even if Ca is added to the molten steel, most of the Ca can be suppressed from forming a sulfide. Further, when molten steel having 0.005% to 0.015% of Ca added is sequentially cast through this step, the material after casting achieves excellent hot workability.

Further, in the third step, it is preferable to add Ca to the molten steel, and it is preferable to pass through the slag covering the upper surface of the molten steel after completion of the slag refining, and to carry out the Ca source to the deep portion of the molten steel. The molten steel in the melting drum is usually subjected to slag refining under atmospheric pressure. Therefore, when the slag refining for reducing the amount of S is completed, and then the slag is passed through and the Ca source is introduced into the deep portion of the molten steel, the slag present covers the upper surface of the molten steel to suppress the evaporation of Ca. Thereby, the addition rate of Ca is increased. In addition, when the Ca source at this time is put into the molten steel in the form of a compound such as a CaSi alloy, the evaporation immediately after the introduction can be further suppressed, and the addition yield of Ca is further improved. Further, the slag refining device used in the second step can be used, and the stirring device therein can be effectively utilized, so that no special equipment is required, and the addition yield of Ca can be improved.

. <Fourth step> Cast steel in which Ca was added in the third step was cast.

Casting The molten steel of the composition is adjusted according to the above, thereby obtaining a high-speed tool steel material. As for the casting method, in addition to the ordinary agglomeration method using an ingot case, a continuous casting method or a remelting method for a steel block after temporary casting may be used, and the method is not limited. . The powder obtained by the atomization method can also be cured by sintering or the like. Moreover, usually, the material after casting is subjected to heat such as forging or rolling. The processing can suppress cracks and the like at this time as long as the material obtained in the present invention is used. The material that has finished the hot working can be further processed into various products by performing hot working or cold working, machining, and heat treatment as needed.

[Example 1] [Invention Example 1 and Inventive Example 2]

Vacuum refining is performed on a 25 t molten steel adjusted to a predetermined composition to prepare molten steel A (first step). The molten steel A of the first example of the present invention is a component composition containing 0.23% of Co which is not added. In the molten steel A of the second example of the present invention, Co was added to adjust the composition to a composition containing 4.97% of Co. Next, the molten steel A is subjected to slag refining using CaO-CaF ₂ slag to obtain molten steel B (second step). Then, the deep penetration slag of the molten steel B in which the slag refining is completed is inserted into a feeder, and a CaSi alloy is introduced into the molten steel from here to obtain a molten steel C to which Ca is added (third step). . The input amount of the CaSi alloy is such that when the yield of the Ca component is 10%, the Ca content in the molten steel is calculated to be 100 ppm (hereinafter simply referred to as "calculated amount"). Moreover, the molten steel C is cast to produce a high speed tool steel material (step 4). In the first example of the present invention and the second example of the present invention, the chemical compositions of the molten steel A, the molten steel B, and the molten steel C (material after casting) are shown in Table 1, respectively.

[Comparative Example 3]

With respect to the production method of the present invention, in the molten steel A subjected to vacuum refining, in the case where slag refining is not performed, molten steel obtained by adding Ca is cast, thereby producing a high-speed tool steel material. The addition of Ca is carried out by the input of the CaSi alloy, and is put into the prescribed vacuum refining junction. In the molten steel in the vacuum environment after the bundle. The input amount of the CaSi alloy is a calculated amount of Ca content in the molten steel of 100 ppm. The composition of the high-speed tool steel material after casting is shown in Table 1.

[Comparative Example 4]

With respect to the production method of the present invention, after Ca is added to the molten steel A subjected to vacuum refining, slag refining is performed and casting is performed to produce a high-speed tool steel material. The addition of Ca is carried out by the input of the CaSi alloy, and is introduced into the molten steel in a vacuum environment after the completion of the predetermined vacuum refining. The input amount of the CaSi alloy is a calculated amount of Ca content in the molten steel of 100 ppm. CaO-CaF ₂ based slag is used in slag refining. The composition of the material after casting is shown in Table 1.

According to the results of Table 1, the high-speed tool steel material of No. 1, No. 2 obtained by the manufacturing method of the present invention has an actual Ca amount of 87 ppm to 99 ppm with respect to the target Ca amount of 100 ppm, thereby Ca is added with good yield. Moreover, the amount of S is reduced to a level of 2 ppm, and the amount of N is lowered to a level of 50 ppm. On the other hand, in the high-speed tool steel material of No. 3 in which slag refining was omitted, the amount of Ca was only 2 ppm, and the yield was poor, and the amount of S was a high level of 45 ppm. Further, in the high-speed tool steel material of No. 4 in which Ca was added before the slag refining, the S amount was a low level of 5 ppm, and the Ca amount was also a low content of 14 ppm.

[Example 2]

The high speed tool steel material obtained in Example 1 was heated to 1160 ° C and subjected to hot working to be hot worked into a steel sheet having a section size of 135 mm × 135 mm square. Further, the surface of the hot-worked steel sheet was visually observed. As a result, the surface of the steel sheet obtained by hot working the high-speed tool steel material of No. 1 and No. 2 by the manufacturing method of the present invention was smooth, and it was confirmed that there was no significant crack (the steel sheet of No. 1 was shown). A photograph of the appearance of the substitute is shown in Fig. 1). On the other hand, in the steel sheet of No. 3, it was confirmed that the crack was not removed even if it was polished (the photograph of the substitute for the appearance is shown in Fig. 2). In the steel sheet of No. 4, although the crack of the steel sheet of No. 3 was not confirmed, it was confirmed that the steel sheet was significantly cracked compared with the steel sheets of No. 1 and No. 2.

Fig. 1 is a schematic photograph showing the appearance of a steel sheet when hot working of high-speed tool steel material No. 1 (invention example) manufactured in the example.

Fig. 2 is a schematic photograph showing the appearance of a steel sheet when the high speed tool steel material No. 3 (comparative example) manufactured in the example is subjected to hot working.

Claims (8)

A method for producing a high-speed tool steel material excellent in hot workability, comprising: a first step of preparing a molten steel having a composition of a high-speed tool steel; and a second step of melting the prepared molten steel Refining the slag and reducing the S in the molten steel to 0.004% by mass or less; in the third step, Ca is added to the molten steel refined by the slag, and the Ca in the molten steel is adjusted to 0.005 mass% to 0.015 mass% And the fourth step of casting the above-mentioned molten steel to which Ca is added. The method for producing a high-speed tool steel material having excellent hot workability according to the first aspect of the invention, wherein the molten steel prepared in the first step has the following composition of a high-speed tool steel, that is, The mass % meter includes: C: 0.5% to 2.2%, Cr: 3.0% to 7.0%, and one or two types of W and Mo (W+2Mo): 5.0% to 30.0%, and V: 0.6%~ 5.0%. The method for producing a high-speed tool steel material having excellent hot workability according to the first aspect of the invention, wherein the molten steel prepared in the first step is vacuum-refined. The method for producing high-speed tool steel material having excellent hot workability according to the first aspect of the invention, wherein the addition of Ca to the molten steel in the third step is continuous The slag on the upper surface of the molten steel after the completion of the slag refining is applied to the deep portion of the molten steel to carry out the Ca source. A method for producing a high-speed tool steel material having excellent hot workability as described in claim 4, wherein the Ca source to be charged is a CaSi alloy. The method for producing a high-speed tool steel material having excellent hot workability according to the first aspect of the invention, wherein in the molten steel before casting in the fourth step, N is reduced to 0.01% by mass or less. The method for producing a high-speed tool steel material excellent in hot workability according to any one of claims 1 to 6, wherein the high-speed tool steel material obtained by mass% includes: C: 0.5 %~2.2%, Si: 0.1%~1.0%, Mn: 0.1%~1.0%, S: 0.004% or less, Cr: 3.0%~7.0%, based on one or two kinds of W and Mo (W+2Mo ): 5.0%~30.0%, V: 0.6%~5.0%, Al: 0.3% or less (including 0%), Ca: 0.005%~0.015%, N: 0.01% or less, and O: 0.004% or less, And the remainder is Fe and unavoidable impurities. A method for producing a high-speed tool steel material having excellent hot workability as described in claim 7, wherein the high-speed tool steel material obtained is in a mass%, and further includes Co: 10.0% or less.