EP1251187A1 - Tool steel for plastic material molds - Google Patents

Abstract

Use of tool steel in the manufacture of molds for plastic parts is new. The steel contains (wt.%): <??>(1) carbon (0.25-0.3); <??>(2) silicon (0.04-0.2); <??>(3) manganese (1.2-2.0); <??>(4) chromium (1.0-2.0); <??>(5) nickel (0.9-1.5); <??>(6) molybdenum (0.3-0.8); <??>(7) vanadium ( ≤ 0.2); and <??>(8) aluminum and a balance of iron (0.01-0.03). <??>Preferred Features: The steel contains 0.9-1.2 wt.% nickel, 0.04-0.15 wt.% silicon, 1.2-1.6 wt.% manganese, 0.4-0.6 wt.% molybdenum, 0.05-0.15 wt.% vanadium and 0.008-0.15 wt.% sulfur. The steel is pre-hardened using water or a polymer.

Description

The invention relates to the manufacture and use of a pre-tempered tool steel for producing molds for plastic parts, in particular for dies with large dimensions.

Plastic molds for spraying or pressing plastic parts always exist from two halves, a die and the core part. The surface quality of the plastic part is essentially determined by the quality of the matrix material.

• gleichmäßig hohe Härte zur Vermeidung von mechanischen Beschädigungen und plastischen Verformungen durch Verkratzen, Verschleiß bei der Kunststoffverarbeitung, Deformation beim Zusammenfahren der Formhälften, Verbiegen und Rißbildung unter Betriebsbedingungen
• gleichmäßige Vergütungsgefügestruktur und hoher Reinheitsgrad zur Sicherstellung einer guten Maschinenbearbeitbarkeit und guter Polier- und fotochemischer Narbeigenschaften.

Requirements for the matrix material are:

• uniformly high hardness to avoid mechanical damage and plastic deformation due to scratching, wear in plastics processing, deformation when the mold halves collapse, bending and cracking under operating conditions
• uniform tempered microstructure and high purity to ensure good machinability and good polishing and photochemical scar properties.

Here, the working hardness of the mold steel of about 30-40 HRC is already by tempering the rolled or forged blank at steel manufacturers adjusted (pre-tempered plastic mold steel).

Molds for plastics processing are today predominantly made of steels Material number. 1.2311 and 1.2738 and made from AISI P 20 (Chemical Analyzes see Table 1).

For special applications such as the processing of wear-promoting, reinforced plastics or hydrochloric acid releasing substances such as PVC In addition, special high-hardness (50 - 60 HRC) or corrosion-resistant Chromium-alloyed tool steel alloys used.

When using conventional pre-tempered plastic molds a particular problem in the limited hardenability of the steels. The requirement after uniform hardness in the entire volume of the steel mold required Through-hardening to the core of the steel block, regardless of its dimensions.

The hardenability of the usually oil-hardened and annealed to about 30 HRC Standard steels AISI P2O, 1.2311 and 1.2738 are shown in Figure 1. It goes at the same time the maximum dimension for the use of the respective steel, up to which there is still no significant decrease in hardness in the core, compared to the Edge hardness occurs.

The trend of the plastic industry to ever larger parts requires ever larger Shapes and correspondingly large steel blocks with dimensions of over 1000 mm thickness. For these dimensions, block weights of> 50 tons are today common.

The inevitable use of large forging blocks Weights of over 80 to increase segregation-related inhomogeneities that be further increased by increasing alloying levels and in plastic molds can lead to quality problems (mechanical processing, polishing, Scar).

For example, EP 0 709 481 B1 describes a steel for the type in question Application proposed that has certain levels of boron, the hardenability to increase, with aluminum and titanium to shield the borer Nitrogen must be added. The use of boron for improvement However, the hardenability leads to non-reproducible at larger diameters Results, i. undefined hardening, especially in the core area.

In EP 0431 557 B1 is a tool steel for use in Plastic mold described in terms of good weldability Sulfur content of 0.025 to 0.10 weight percent should have. Furthermore, should the tool steel of an additional condition BH = 326.0 + 847.3 (C%) + 18.3 (Si%) 8.8 (Mn%) - 12.5 (Cr%) ≤ 460, which is a carbon content under all circumstances of the highest 0.208 weight percent. Such a lower one Although carbon content is beneficial for weldability, it is available Achieving the required hardening of the tool steel after pre-tempering opposite.

The object of the invention is a tool steel for plastic molds to create, even with large diameters high core hardness without qualitative Disadvantages enabled.

C = 0,25 - 0,30

Si = 0,04 - 0,20

Mn = 1,2 - 2,0

Cr = 1,0 - 2,0

Ni = 0,9 - 1,5

Mo = 0,3 - 0,8

V ≤ 0,2

Al = 0,01 - 0,03

wobei der Rest aus Eisen und unvermeidlichen Verunreinigungen besteht.According to the invention, the object is achieved by a tool steel having the following composition (in weight percent):

C = 0.25-0.30

Si = 0.04-0.20

Mn = 1.2-2.0

Cr = 1.0 - 2.0

Ni = 0.9-1.5

Mo = 0.3 - 0.8

V ≤ 0.2

Al = 0.01-0.03

the remainder being iron and unavoidable impurities.

The tool steel according to the invention is used to avoid qualitative disadvantages deliberately made without the addition of boron, with the necessary hardness through the targeted set nickel content is achieved. Surprisingly, it has become namely shown that the missing or only in the context of inevitable impurities Boron present at carefully adjusted nickel content not Disadvantages in the achievable hardness values, but the steel at the same time especially for larger workpiece diameters better reproducible results in terms of its hardenability with less tendency to embrittlement shows. Similarly, no titanium is needed to shield the boron from nitrogen to be admitted.

Thus, the tool steel according to the invention is ideal for use in plastic molds suitable, especially for larger diameters of the workpiece over 400 mm up to 1300 mm and above.

By the inventively provided weight fraction of molybdenum between 0.3% and 0.8%, preferably between 0.4% and 0.6% is further improved Starting resistance reached, so that at an exemplary workpiece diameter of 1000 mm and an exemplary Mo content of 0.5 percent by weight to reach 30 HRC, a tempering temperature of about 620 ° C is advantageous, while known mold steels with tempering temperatures significantly below 600 ° C be tempered.

The mold steel according to the invention is without Spannungsrißgefahr in water or Polymer curable, has only low segregations and a high degree of purity and is very high due to the higher tempering temperature after the heat treatment homogeneous and low in residual stress.

To improve weldability, a sulfur content of up to 0.15 Weight percent be provided, but usually one is to ensure a high degree of purity, the sulfur content as well as to keep phosphorus content as low as possible, for example S ≤ 0.005% and / or P ≤ 0.02%.

In Table 1 and Figure 1 is an example within the scope of the invention Composition of manufactured mold steel compared to commercially available steels. This carbon was lowered so far that Seigerungen minimized and water hardenability is given at the same time (C max 0.30%). The silicon content was used to minimize the block segregations to an average value lowered from 0.1%, as well as the chromium content of 2.0 to 1.25%. The hardening-promoting alloy content has largely remained unchanged of Mn (about 1.50%), while the steel 1.2738 also corresponding content to Ni (about 1.10%) in conjunction with the other contents of the said surprisingly good overall properties.

Because of the non-reproducible in large dimensions hardenability Effect and at the same time embrittling properties was added to boron deliberately omitted, the addition of titanium can therefore also be omitted.

The improved temper resistance is set by higher additions of molybdenum (0.5% instead of about 0.20% at 1.2738) and vanadium (0.1% versus no vanadium at 1.2738). For large dimensions over 1000 mm, the tempering temperatures for about 30 HRC change as follows: Mold steel 1.2738 after oil hardening 595 ° C Inventive mold steel 620 ° C.

To ensure a high degree of purity, the content of sulfur on about 0.002% limited.

The comparison of the hardenability of the mold steel according to the invention with Standard steel available on the market is shown in Figure 1. After that is suitable Steel for pre-tempered dimensions up to 1300 mm without any disadvantages.

Claims (9)

Tool steel for producing molds for plastic parts, characterized by the following composition (in percent by weight): C = 0.25-0.30 Si = 0.04-0.20 Mn = 1.2-2.0 Cr = 1.0 - 2.0 Ni = 0.9-1.5 Mo = 0.3 - 0.8 V ≤ 0.2 Al = 0.01-0.03 the remainder being iron and unavoidable impurities. Tool steel according to claim 1, characterized by a content of Ni between 0.9 and 1.2 weight percent. Tool steel according to claim 1 or 2, characterized by a content of Si between 0.04 and 0.15 weight percent. Tool steel according to one of the preceding claims, characterized by content of Mn between 1.2 and 1.6 weight percent, a content of Mo between 0.4 and 0.6 weight percent and a content of V between 0.05 and 0.15 weight percent. Tool steel according to one of the preceding Ansprüchem characterized by a content of S between 0.008 and 0.15 weight percent. Tool steel according to one of the preceding claims, characterized in that it is pre-treated with water or polymer and has a maximum hardness of up to 40 HRC. Tool steel according to one of the preceding claims, characterized in that it is tempered after curing at a tempering temperature of about 620 ° C for about 30 HRC. Tool steel according to one of the preceding claims, characterized in that it is pre-tempered with a diameter of at least 400 mm. Tool steel according to claim 8, characterized in that it is pre-tempered with a diameter of over 1000 mm.

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