JP2015007278A - Method for producing die steel for plastic molding and die for plastic molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a die steel for plastic molding which suppresses the occurrence of segregation without performing diffusion treatment, satisfies mechanical characteristics and suppresses the occurrence of the emboss due to segregation during embossing using as a die material.SOLUTION: There is provided a method for producing a die steel for plastic molding which is a method for producing a steel containing 0.10 to 0.55% of C, 0.05 to 1.0% of Si, 0.10 to 1.50% of Mn, 0.001 to 0.040% of P, 0.040% or less of S, 0.5% or less of Cu and 0.003 to 0.050% of Al and further containing 10 to 100 ppm of Bi and the balance being Fe and impurities, wherein steel ingots having an average diameter of 1800 mm or less and a weight of 45 tons or less are cast by an ordinary casting method using a casting mold having a polygonal cross section.

Description

  The present invention relates to a method of manufacturing a mold steel for plastic molding suitable for embossing. Moreover, it is related with the metal mold for plastic molding which used the steel ingot manufactured with the manufacturing method as a raw material.

  An example of a plastic product molding method is an injection molding method using a mold. When molding, a pattern is formed on the surface of the mold by applying a texture to the surface of the molded product, so that a pattern such as leather, satin, wood, or cloth can be transferred and applied as a design pattern.

  However, if there is a large amount of micro-segregation or macro-segregation (hereinafter collectively referred to as “segregation”) in the ingot that is the material of the mold, it was formed on the surface of the mold when subjected to graining. Unevenness (hereinafter also referred to as “spot unevenness”) occurs in the pattern, and the pattern does not become the intended one.

  As a technique for suppressing the occurrence of grain unevenness during graining on the mold surface, Patent Document 1 discloses that the Si content of steel is 0.35 wt% or less, the Cr content is 3.0 wt% or less, and the Mo content is Is described as a steel with 1.0% by weight or less.

  In addition, in Patent Document 2, in order to suppress the deterioration of the texture processing of the mold, the formation of a band-like structure with the steel Si content of less than 0.50 mass% and the Mn content of 1.5 mass% or less In addition, a steel is described in which the P, S, Cr, and Al contents are suppressed to a predetermined value or less, and the wrinkle workability is reduced. Furthermore, it is described that numerical values calculated from the contents of C, Si, Mn, P, S, Mo, Cr, and Ni are used as a measure of the influence of these elements on the embossing processability.

JP 2001-294773 A Japanese Patent No. 4223442

  Microsegregation and macrosegregation inevitably occur in steel ingots produced by the ordinary ingot-making method. Microsegregation occurs when molten steel enriched in alloy elements generated between dendritic arms (hereinafter referred to as “concentrated molten steel”) solidifies, and macrosegregation occurs when the concentrated molten steel at the final solidification position of the steel ingot is It is generated by solidifying as it is.

  In particular, macro segregation has a larger scale as the distance from the initial solidification position to the final solidification position of the steel ingot is longer and the solidification time of the steel ingot is longer. The solidification time in the ordinary ingot casting method is greatly affected by the weight and size of the steel ingot, and the solidification time becomes longer and the macrosegregation increases as the weight and cross-sectional area of the steel ingot increase.

  For this reason, the larger the weight or size of the steel ingot, the greater the segregation that occurs in the plastic molding die steel, and the plastic molding die manufactured using this steel ingot is likely to have unevenness during embossing. However, Patent Documents 1 and 2 do not pay attention to either the weight or the cross-sectional area of the steel ingot.

  As a method of reducing these segregation that inevitably occurs, a method of reducing the alloy element itself that causes segregation, or a forging process of a steel ingot that is a subsequent process of the ingot process by diffusion treatment of the segregated alloy element And the like.

  However, there is a possibility that the method of reducing the alloy elements cannot satisfy the mechanical characteristics required for the plastic mold. In addition, the method of performing diffusion treatment of alloy elements is not practical because it requires new equipment investment and excessive energy consumption.

  The present invention has been made in view of these problems, and provides a method for producing a mold steel for plastic molding capable of preventing the occurrence of grain unevenness during graining in consideration of the weight, shape and dimensions of a steel ingot. Objective.

  The present inventor first examined a method for reducing segregation in a steel ingot produced by the ordinary ingot-making method by adding an alloy element. If segregation can be reduced by the addition of alloy elements, the conventional diffusion treatment can be shortened or omitted, which is preferable from the viewpoint of energy saving. In addition, no new capital investment for the diffusion treatment is required.

  Bi was considered as an alloy element to be added. Since Bi is an element that reduces the interfacial energy at the solid-liquid interface of steel, it is thought that inclusion of this makes it possible to refine the dendrite structure of the steel ingot and reduce segregation.

  Next, a test conducted for confirming the effect of Bi will be described. Bi was added to molten steel of a steel type generally used for plastic molds, and a unidirectional solidification test was performed. The produced steel ingot was made into a columnar shape with a diameter of 15 mm and a length of 50 mm, and the Bi content was 15 mass ppm, 30 mass ppm and 40 mass ppm, and those containing no Bi were also produced.

  FIG. 1 is a graph showing the relationship between the Bi content and the primary arm spacing of dendrites. The structure of each steel ingot was observed, and the primary arm interval d of the dendrite was measured. The primary arm interval of the steel ingot not containing Bi was d0, and in the same figure, the horizontal axis was Bi content and the vertical axis was d / d0. From the figure, it can be seen that the higher the Bi content, the smaller the primary arm interval d, and even a small amount of Bi is effective in reducing the dendrite arm interval.

  Since the dendrite arm interval is made finer, the concentrated molten steel generated between the dendrite arms is reduced, so that microsegregation is also reduced. Further, by reducing individual microsegregation, the concentration of alloy elements in the molten steel discharged to the unsolidified portion of the steel ingot is reduced as compared with the case where microsegregation is not reduced. Therefore, macro segregation occurring at the final solidification position is also reduced.

  The inventor used a steel ingot whose segregation was reduced by adding a small amount of Bi as a material, and produced a material for a plastic molding die having the same size as the actual product. Then, the relationship between the occurrence of grain unevenness in the plastic molding material and the weight, shape and dimensions of the steel ingot was examined. As a result, as demonstrated in the examples described later, it has been found that there are conditions for suppressing the occurrence of grain unevenness during graining.

  This invention is made | formed based on this knowledge, and the summary exists in the manufacturing method of the following mold steel for plastic molding.

  In mass%, C: 0.10 to 0.55%, Si: 0.05 to 1.0%, Mn: 0.10 to 1.50%, P: 0.040% or less, S: 0.040 %, Cu: 0.5% or less, and Al: 0.003 to 0.050%, Bi is further contained in an amount of 10 to 100 ppm by mass, and the balance is Fe and impurities. A mold for producing plastics, characterized by casting a steel ingot having an average diameter of 1800 mm or less and a weight of 45 t or less by a normal ingot method using a mold having a polygonal cross section. A method for producing steel molds.

  In this method, the steel ingot is replaced with a part of Fe, Ni: 2.0% or less, Cr: 2.0% or less, Mo: 0.6% or less, and V: 0.2% or less It is good also as what contains 1 type, or 2 or more types.

  The gist of the present invention resides in a plastic molding die characterized by using a steel ingot produced by the above-described method for producing a plastic molding die steel as a raw material.

  In the following description, “mass%” and “mass ppm” for the component composition of steel are also simply expressed as “%” and “ppm”, respectively.

  According to the method for producing a mold steel for plastic molding of the present invention, the occurrence of microsegregation and macrosegregation is suppressed without performing diffusion treatment, and a steel ingot suitable for embossing can be produced. The plastic molding die manufactured from this steel ingot satisfies the required mechanical properties and suppresses the occurrence of grain unevenness due to segregation during the graining of the surface.

It is a figure which shows the relationship between Bi content rate and the primary arm space | interval of a dendrite. It is a figure which shows the incidence rate of the grain unevenness in the test piece of each comparative example and each example of the present invention.

  Below, the reason which prescribed | regulated the manufacturing method of the metal mold steel for plastic molding of this invention as mentioned above, and its preferable aspect are demonstrated.

1. 1. Range of component composition of mold steel for plastic molding and reasons for limitation 1-1. Essential element C: 0.10 to 0.55%
C is an element effective for increasing the strength of steel. However, if the C content is less than 0.10%, the strength of the steel is not sufficient. On the other hand, if the C content exceeds 0.55%, the toughness, weldability and machinability of the steel will be reduced. Therefore, the C content is set to 0.10 to 0.55%. Preferably, it is 0.15 to 0.45%.

Si: 0.05-1.0%
Si is an element that is used for deoxidation of steel and improves hardenability and machinability. However, when the Si content is less than 0.05%, sufficient deoxidation cannot be performed, and addition of other elements such as Al and Ti is necessary. On the other hand, if the Si content is too high, segregation is promoted, and if it exceeds 1.0%, it is not possible to suppress the occurrence of irregularities during the embossing of the mold. Therefore, the Si content is set to 0.05 to 1.0%. Preferably, it is 0.15 to 0.30%.

Mn: 0.10 to 1.50%
Mn is an element effective for improving the hot workability and hardenability of steel. However, if the Mn content is less than 0.10%, these effects cannot be obtained. On the other hand, when the Mn content exceeds 1.50%, segregation increases, and the occurrence of grain unevenness during the grain machining of the mold cannot be suppressed. Therefore, the Mn content is set to 0.10 to 1.50%. Preferably, it is 0.90 to 1.35%.

P: 0.001 to 0.040%
Since P is an element that impairs the toughness of steel, it is preferable that the content is as low as possible. Then, as a range manufactured with a normal industrial refining method, P content rate shall be 0.001-0.040%.

S: 0.040% or less S is an element effective for improving the machinability of steel. However, S is detrimental to the toughness of steel, and weld cracks are likely to occur. Therefore, the S content is set to 0.040% or less. Preferably, it is 0.015-0.040%.

Cu: 0.5% or less Cu is an element that improves the corrosion resistance of steel. However, if the Cu content is excessive, it segregates at the grain boundaries of the steel and causes embrittlement of the steel. Considering these points, the Cu content is set to 0.5% or less. Preferably, it is 0.01 to 0.20%.

Al: 0.003 to 0.050%
Al is an element that promotes deoxidation of molten steel. However, if the Al content is excessive, non-metallic inclusions are formed, causing pinholes. Therefore, the Al content is set to 0.003 to 0.050%. Preferably, it is 0.003 to 0.020%.

Bi: 10 to 100 ppm
As shown in FIG. 1, Bi is an element effective for miniaturizing the dendrite arm interval of steel even in a small amount. However, when the Bi content exceeds 100 ppm, hot embrittlement of the steel occurs. Therefore, Bi content rate shall be 10-100 ppm. The Bi content is preferably 10 to 30 ppm.

  The balance other than the above components is Fe and impurities.

1-2. Optional Additive Element Instead of a part of Fe, one or more of the following optional additive elements may be contained.

Ni: 2.0% or less Ni is an element that improves the hardenability of the steel while reducing the machinability. Ni is more expensive than the above essential elements. Considering these points, when Ni is contained, the content is made 2.0% or less. More preferably, it is 0.01 to 0.70%.

Cr: 2.0% or less Cr is an element effective for improving the hardenability of steel. However, if the Cr content exceeds 2.0%, the machinability of the steel is impaired. Therefore, when Cr is contained, the content is made 2.0% or less. More preferably, it is 0.20 to 1.30%. In order to ensure hardenability, the total content of Cr and Mn is preferably 0.5% or more.

Mo: 0.6% or less Mo is an element effective in improving the hardenability of steel and preventing temper embrittlement. However, Mo is a strong segregation element. Considering these points, when Mo is contained, the content is made 0.6% or less. More preferably, it is 0.01 to 0.40%.

V: 0.2% or less V is an element used for refining steel crystal grains. V is more expensive than the above essential elements. Considering these points, when V is contained, it is set to 0.2% or less. More preferably, it is 0.03 to 0.07%.

2. Manufacturing method of mold steel for plastic molding of the present invention The manufacturing method of mold steel for plastic molding of the present invention has the above-mentioned component composition by an average ingot method using a mold having a polygonal cross section, and has an average diameter of This is a method of casting an ingot having a weight of 1800 mm or less and a weight of 45 t or less. The weight of the steel ingot is preferably 17 t or more, and the average diameter is preferably 1100 mm or more. The shape of the cross section of the mold is preferably a polygon having rotational symmetry. In addition, octagons to 24 polygons having rotational symmetry and the same length of each side are more preferable.

  By this method, a steel ingot in which the occurrence of microsegregation and macrosegregation is suppressed without requiring diffusion treatment can be produced. The plastic molding die manufactured from this steel ingot satisfies the mechanical characteristics, and suppresses the occurrence of grain unevenness due to segregation during the graining of the surface.

  In order to confirm the effect of the method for producing the mold steel for plastic molding of the present invention, a test for producing a steel ingot of the same size as the actual product and a material for the mold for plastic molding was conducted, and the result was evaluated. did.

1. Test Method A steel ingot was produced by the ordinary ingot-making method under the conditions shown in Table 1. In comparative examples, C: 0.10 to 0.55%, Si: 0.05 to 1.0%, Mn: 0.10 to 1.50%, P: 0.010 to 0.040%, S: 0.040% or less, Ni: 2.0% or less, Cr: 2.0% or less, Mo: 0.6% or less, V: 0.2% or less, Cu: 0.5% or less, and Al: 0. A molten steel containing 003 to 0.050% and refined so that the balance is composed of Fe and impurities and having a Bi content of 0 (below the detection limit) was used. This is a steel type widely used in plastic molds. In the examples of the present invention, a part of Fe was Bi, the Bi content was in the range shown in Table 1, and the molten steel having the same component composition as that of the comparative example was used. Even if Bi in an amount specified in the present invention is added, the compositional balance of other elements is not changed, and therefore mechanical properties required for a plastic molding die are not affected.

  Table 1 also shows the cross-sectional shape of the mold used for producing the steel ingot, the range of the weight and average diameter of the produced steel ingot, and the number of produced steel ingots. The average diameter is the average value of the diameter of the circumscribed circle and the diameter of the inscribed circle in the cross section of each steel ingot from the upper end to the lower end of the ingot. In the same table, the “octagon” and “24-gon” in the shape of the cross section of the mold mean octagons and 24-gons having rotational symmetry and the lengths of each side being equal.

  Since the degree of segregation occurring in the steel ingot fluctuates due to the influence of the forging process, the forging conditions are the same for all the steel ingots. Specifically, the produced steel ingot was heated to 1260 ° C. and forged so as to be a regular quadrangular column having a cross section of 1000 mm in length and 1000 mm in width. The forging end temperature was 1000 ° C. The obtained forged material was subjected to normalization at 900 ° C. for 20 hours and then tempered at 600 ° C. for 30 hours. After completion of tempering, the part corresponding to the hot metal and dish part of the steel ingot of the material after forging was cut off and used as a material for a plastic molding die.

  In the plastic molding material thus produced, a plate material having a thickness of 20 mm was cut horizontally from the vicinity of each upper end, and test pieces each having a length of 100 mm and a width of 100 mm were cut out one by one from the center. In order to simulate embossing with a plastic molding die, a textured pattern was applied by embossing that corroded the surface of the cut-out test piece, and each test piece was visually examined for occurrence of wrinkle unevenness.

2. Test Results FIG. 2 is a diagram showing the occurrence rate of grain unevenness in the test pieces of each comparative example and each invention example. Table 1 shows the number of test pieces in which the unevenness occurred and the occurrence rate of the uneven unevenness, together with the test conditions, for each comparative example and each inventive example.

  From Comparative Examples 2 and 3, when Bi is not contained, if the weight and average diameter of the steel ingot are the same, the occurrence of grain unevenness is suppressed when the number of polygons constituting the cross section is larger. I understand that.

  Moreover, from Comparative Examples 1-4, when Bi is not contained, if the shape of a cross section is the same, it will be understood that the occurrence of grain unevenness is more remarkable when the weight and average diameter of the steel ingot are larger. This corresponds to the fact that in the ordinary ingot forming method, the larger the weight and average diameter of the steel ingot, the greater the scale of segregation.

  From Examples 2 and 3 of the present invention, when Bi is contained, if the weight and average diameter of the steel ingot are the same, even if the polygon constituting the cross section is a 24 or 8 polygon, the occurrence of grain unevenness is completely achieved. It turns out that it is suppressed. From this result, it is considered that even when the number of polygons constituting the cross section of the mold is larger than 24, the effect of suppressing the occurrence of graininess is not impaired.

  In addition, it can be seen from Example 1 of the present invention that when the steel ingot has a weight of 45 t and an average diameter of 1800 mm and contains Bi, the influence of segregation can be eliminated and the occurrence of graininess is completely suppressed. . In consideration of this result and the ordinary ingot forming method, the larger the weight and average diameter of the steel ingot, the larger the scale of segregation. The steel ingot has a weight of less than 45 t and an average diameter of less than 1800 mm. Similarly, when Bi is contained, it is considered that the effect of segregation can be eliminated and the occurrence of graininess can be suppressed. The results of Examples 2 to 4 of the present invention agree with this.

  According to the method for producing a mold steel for plastic molding of the present invention, the occurrence of microsegregation and macrosegregation is suppressed without performing diffusion treatment, and a steel ingot suitable for embossing can be produced. The plastic molding die manufactured from this steel ingot satisfies the required mechanical properties and suppresses the occurrence of grain unevenness due to segregation during the graining of the surface.

Claims (3)

In mass%, C: 0.10 to 0.55%, Si: 0.05 to 1.0%, Mn: 0.10 to 1.50%, P: 0.001 to 0.040%, S: Plastic containing 0.040% or less, Cu: 0.5% or less, and Al: 0.003 to 0.050%, further containing Bi at 10 to 100 mass ppm or less, and the balance being Fe and impurities A method for producing mold steel for molding,
A method for producing a mold steel for plastic molding, characterized by casting a steel ingot having an average diameter of 1800 mm or less and a weight of 45 t or less by an ordinary ingot forming method using a mold having a polygonal cross section.   The steel ingot is replaced with a part of Fe, any one of Ni: 2.0% or less, Cr: 2.0% or less, Mo: 0.6% or less and V: 0.2% or less or The method for producing a mold steel for plastic molding according to claim 1, comprising two or more kinds.   A plastic molding die characterized by using a steel ingot produced by the method for producing a plastic molding die steel according to claim 1 or 2 as a raw material.

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