EP0395623A1 - Maraging steel - Google Patents

Abstract

Maraging steel, in particular for the production of plastic moulds, which consists of 0.06 - 0.2% by weight of carbon 0.15 - 0.8% by weight of silicon 1.4 - 3.6% by weight of manganese 0.12 - 0.4% by weight of sulphur 0 - 0.9% by weight of chromium 2.8 - 3.4% by weight of nickel 0.03 - 0.15% by weight of vanadium 0.1 - 4.0% by weight of copper 0.1 - 4.0% by weight of aluminium 0.9 - 4.1% by weight of aluminium + copper 0.03 - 0.12% by weight of niobium 0.01 - 0.1% by weight of zirconium 0 - 0.1% by weight of calcium 0.01 - 0.1% by weight of titanium 0 - 1.0% by weight of molybdenum 0 - 1.0% by weight of tungsten 0 - 1.5% by weight of Mo + W W DIVIDED 2 the remainder being iron and impurities resulting from the production.

Description

The invention relates to a martensitic steel, in particular for the production of plastic molds, and the use thereof.

Martensite-hardenable steels with 18% Ni, 8% Co, 5% Mo and up to 1% Ti, in which part of the nickel content can be replaced by manganese, have a high tensile strength, but are due to their high cobalt and Molybdenum levels expensive. Cobalt- and molybdenum-free steels with a content of 12% Mn, 5% Ni and 4% Ti can be hardened, but these steels have a difficult formation of martensite and therefore have too high levels of residual austenite for practical use as a material for plastic molds the high titanium concentrations lead to uneconomically long outsourcing times.

For the production of plastic molds, mainly plastic mold steel DIN material no. 1.2311 or a sulfur-containing variant DIN material no. 1.2312 are used. These steels can be tempered by the producer to a tensile strength of 900 to a maximum of 1100 N / mm² and processed in this state into molds or tools in order to avoid dimensional changes or surface impairments during the heat treatment of finished coated tools.

auf.On the one hand, this is becoming increasingly difficult due to the Machinability of the material limits its strength, on the other hand, high tool wear occurs when machining raw bodies with higher strength values, eg 1050 N / mm $\genfrac{}{}{0ex}{}{\text{2nd}}{\text{,}}$

on.

The object of the invention was therefore to specify a steel which is particularly suitable for the production of plastic molds and which steel in the tempered state has a strength of at least 1050 N / mm² and a hardness of at least 38 HRC with improved isotropy of the mechanical values, slightly cutting is editable and can be polished accordingly and can be used in this state without thermal aftertreatment. To achieve this object, a steel with a composition according to claim 1 is proposed according to the invention.

The conventional martensitic-hardenable steels are only of limited use because of their high alloy content and the associated costs, because of the complex manufacturing technology for the plastic molds and / or because of the poor machinability due to machining with high tool wear. The steel according to the invention or the steel to be used according to the invention is an iron-based alloy with the components specified in claim 1. With regard to a synergistic effect, the steel contains the alloying elements in a concentration corresponding to the invention in order to achieve good machinability with little tool wear even in the hardened state exhibiting high tensile strength and hardness of the material, while at the same time the isotropy of the mechanical values, the polishability or achievable surface quality and the service life of the plastic molds are improved. Large plastic molds can also be produced as a result, since no thermal post-treatment or outsourcing of the machined mold, which can cause distortion, is required.

keinen unerwünschten Zähigkeitsverlsut des Materials zu bewirken, sind Gehalte an Kupfer + Aluminium von 0,9 bis 4,1 % vorzusehen. Die besten Ergebnisse wurden bei der erfindungsgemäßen Legierung mit Gehalten von 1,8 bis 2,2 % Mangan, 3,4 bis 3,6 % Nickel, 0,4 bis 2,4 % Kupfer, 0,1 bis 2,1 % Aluminium gefunden, wenn der Wert von Kupfer und Aluminium zwischen 1,5 und 2,5 % lag. Chrom als die Austenitbildung hinderndes Element soll eine Konzentration von 0,9 %, vorzugsweise 0,5 %, nicht übersteigen, weil bei hoheren Gehalten die Ausscheidungsvorgänge der erfindungsgemäßen Legierun­gen nachteilig beeinflußt werden. Auch Molybdän und Wolfram, insbesondere kombiniert, wirken ab Konzentrationen von 1,0 % bzw. 1,5 % ungünstig, obwohl diese Elemente in hoheren Gehalten in üblichen martensitaushärtbaren Stählen als festigkeits-und härte­steigernde Komponenten oftmals erforderlich sind.In the alloy according to the invention there is a carbon content in the Range of at least 0.06% and at most 0.2%, preferably 0.08% to 0.18%, in particular 0.1% to 0.15%, important for achieving the corresponding matrix strength and hardness. Levels below 0.06% C reduce the attainable strength, contents above 0.2% C lead to embrittlement of the material. Silicon concentrations below 0.15% lead to a poor degree of purity and those above 0.8% cause a decrease in the toughness of the material despite an increase in hardness. Manganese has a stabilizing effect on austenite, but in particular it forms sulfide, so that with appropriate manganese and sulfur concentrations, the machining properties of the material are improved by inclusions of sulfide. With sulfur contents of 0.12% to 0.4%, a manganese concentration of 1.4% to 3.6% is given for sulfide excretion with the appropriate morphology and a desired degree of austenite stabilization, the most favorable values being 0.15 to 0. 25% sulfur and 1.8 to 2.2% manganese were found. After hot forming, sulphides or sulphide inclusions can lead to a line structure of the material and to an anisotropy of the mechanical properties, and can also cause crater wear of the tool during machining. With zirconium and titanium contents of 0.01 to 0.1%, preferably from 0.02 to 0.06%, in particular from 0.03 to 0.05%, the sulfide morphology is favorably influenced, so that this results in improved machining properties of the material Increased isotropy of its mechanical properties and a reduction in tool wear during machining can be achieved. Calcium contents of up to 0.01%, in particular in a range from 0.002 to 0.006%, cause molding of alumina spinel inclusions and a favorable sulfide morphology in the melt composed according to the invention. This inclusion modification further improves the isotropy of the mechanical properties and the machinability of the material; in particular, there is a substantial reduction in wear or an increase in the service life of the cutting tools. Vanadium contents from 0.03 to 0.15%, in particular from 0.05 to 0.1%, provide one Increase in secondary hardness during heat treatment and cause grain refinement and associated high material toughness. Niobium is similar to vanadium, but the grain-refining effect is more pronounced due to the high carbon activity of the niobium, with concentrations from 0.03 to 0.12% improved and contents from 0.05 to 0.08% with the best results. The steel according to the invention is further alloyed with carbon, manganese, nickel, copper and aluminum, which elements are dissolved in the austenite when heated to a temperature of over 800 ° C. and kept in solution by rapid cooling to room temperature. Reheating or aging at temperatures around 500 ° C leads to the alloy elements separating from the martensite or to the formation of intermetallic phases or compounds which cause an increase in the hardness of the material. With manganese contents from 1.4 to 3.6% and nickel contents from 2.8 to 4.3%, copper concentrations from 0.1 to 4.0% and aluminum concentrations from 0.1 to 4.0% increase strength and hardness. However, in the case of a desired increase in hardness and strength to at least 38 HRC, in particular 40 HRC, or at least 1100 N / mm 2, in particular 1200 N / mm $\genfrac{}{}{0ex}{}{\text{2nd}}{\text{,}}$

In order not to cause undesired loss of toughness of the material, copper + aluminum contents of 0.9 to 4.1% should be provided. The best results were obtained with the alloy according to the invention with contents of 1.8 to 2.2% manganese, 3.4 to 3.6% nickel, 0.4 to 2.4% copper, 0.1 to 2.1% aluminum found when the value of copper and aluminum was between 1.5 and 2.5%. Chromium as the element preventing austenite formation should not exceed a concentration of 0.9%, preferably 0.5%, because at higher contents the precipitation processes of the alloys according to the invention are adversely affected. Molybdenum and tungsten, in particular in combination, also have an unfavorable effect from concentrations of 1.0% and 1.5%, although these elements are often required in higher contents in conventional martensitic steel as strength and hardness-increasing components.

The invention is explained in more detail below on the basis of exemplary embodiments.

Example 1:

A steel A with a composition according to Table 1 was precipitation hardened to a strength of 1271 N / mm² and a hardness of 40 HRC. Machining was carried out by turning (dry cutting) with the following parameters:
Cutting material: WSP SB20 SPUN 12 03 08
Cutting speed V = 180 m / min
Cutting depth: a = 2.0 mm
Feed: s = 0.220 mm / rev

bearbeitet, wobei die Verschleißmarkenbreite der Werkzeuge 0,26 mm bzw. 0,24 mm betrug. Im Vergleich mit Werkstoff Nr. 1.2312 waren bei Untersuchungen der mechanischen Eigenschaften und der erreichten Oberflächenqualität beim Polieren die erhaltenen Werte der Legierung A wesentlich verbessert.After a cutting time of 20 minutes, the tool showed a wear mark width of VB = 0.15 mm. In the same test with the same parameters, the steels were tested according to DIN material no. 1.2311 and material no. 1.2312 with a strength of 1250 N / m $\genfrac{}{}{0ex}{}{\text{2nd}}{\text{m}}$

machined, the wear mark width of the tools was 0.26 mm and 0.24 mm. Compared to material no. 1.2312, the results of alloy A obtained were significantly improved when the mechanical properties and the surface quality achieved during polishing were examined.

Example 2:

und eine Härte von über 40 HRC ausscheidungsgehärtet. Wiederum ist im Vergleich mit Stählen gemäß Werkstoff Nr. 1.2311 und Werkstoff Nr. 1.2312 erfolgte ein Fräsen von Proben mit hartmetallbestückten Schlagzahnfräsern bei folgenden Bedingungen:
Schnittgeschwindigkeit: V = 118 m /min
Vorschub: s = 0,24 mm/Zahn
Schnittiefe: a = 2,0 mmA steel B with the alloy concentrations according to Table 1 was tested for a strength of 1264 N / m $\genfrac{}{}{0ex}{}{\text{2nd}}{\text{m}}$

and a precipitation hardened hardness of over 40 HRC. Again, compared to steels according to material no. 1.2311 and material no. 1.2312, samples were milled with carbide-tipped impact milling cutters under the following conditions:
Cutting speed: V = 118 m / min
Feed: s = 0.24 mm / tooth
Cutting depth: a = 2.0 mm

The wear mark width V of the tools with a machined volume of 350 cm³ was 0.23 mm for steel B, 0.35 mm for material no. 1.2311 and 0.33 mm for material no. 1.2312.

Example 3:

Die Schnittgeschwindigkeit betrug jeweils 48 m/min, der Vorschub S = 0,125 mm/U. Die Bohr­leistung bzw. der Bohrweg war in Stahl C 3171 mm , wogegen im werkstoff Nr. 1.2311 2018 mm und im Werkstoff Nr. 1.2312 2163 mm erreicht wurden, was eine ca. 47% höhere Bohrleistung beim erfin­dungsgemäßen Stahl C bedeutet. Tabelle 1 Chemische Zusammensetzung Stahl C Mn S Cr Ni V Nb Cu Al Zr Ti Co Si Mo A 0,14 2,19 o,25 o,22 3,52 0,09 0,06 2,05 0,42 0,03 0,04 0,003 0,63 0,28 B 0,11 1,97 0,18 0,51 3,43 0,1 0,04 1,23 1,o3 0,07 0,03 - 0,28 0,40 C 0,08 1,62 0,16 0,43 3,69 0,07 0,08 0,79 1,34 0,04 0,06 0,005 0,31 - Werkstoff Nr.1.2311 0,41 1,45 0,008 1,92 0,63 - - 0,18 0,001 - - - 0,32 0,23 Werkstoff Nr. 1.2312 0,39 1,52 0,09 1,87 0,28 - - 0,21 0,002 - - - 0,28 0,19 Comparative tests were carried out on deep-hole drilling with carbide-tipped single-lip drills (diameter 10 mm) on a steel C according to Table 1 with a strength of 1280 N / mm² (40.5 HRC) and the materials no. 1.2311 or no. 1.2312 with a strength of 1040 or 1080 N / mm $\genfrac{}{}{0ex}{}{\text{2nd}}{\text{.}}$

The cutting speed was 48 m / min, the feed S = 0.125 mm / rev. The drilling capacity or the drilling path was in steel C 3171 mm, whereas in material no. 1.2311 2018 mm and in material no. 1.2312 2163 mm were achieved, which means an approx. 47% higher drilling capacity for steel C according to the invention. Table 1 Chemical composition stole C. Mn S Cr Ni V Nb Cu Al Zr Ti Co Si Mon A 0.14 2.19 o, 25 o, 22 3.52 0.09 0.06 2.05 0.42 0.03 0.04 0.003 0.63 0.28 B 0.11 1.97 0.18 0.51 3.43 0.1 0.04 1.23 1, o3 0.07 0.03 - 0.28 0.40 C. 0.08 1.62 0.16 0.43 3.69 0.07 0.08 0.79 1.34 0.04 0.06 0.005 0.31 - Material No.1.2311 0.41 1.45 0.008 1.92 0.63 - - 0.18 0.001 - - - 0.32 0.23 Material no.1.2312 0.39 1.52 0.09 1.87 0.28 - - 0.21 0.002 - - - 0.28 0.19

Claims (5)

1. Martensite-hardenable steel, in particular for the production of plastic molds, which consists of in% by weight
Carbon 0.06-0.2
Silicon 0.15-0.8
Manganese 1.4-3.6
Sulfur 0.12 - 0.4
Chromium 0 - 0.9
Nickel 2.8 - 4.3
Vanadium 0.03-0.15
Copper 0.1 - 4.0
Aluminum 0.1 - 4.0
Aluminum + copper 0.9 - 4.1
Niobium 0.03 - 0.12
Zircon 0.01-0.1
Calcium 0-0.01
Titanium 0.01-0.1
Molybdenum 0-1.0
Tungsten 0-1.0
Mon + $\frac{\text{W}}{\text{2nd}}$

0 - 1.5
Rest of iron and manufacturing-related impurities. 2. Martensite hardenable steel according to claim 1, which consists of in wt .-%
Carbon 0.08-0.18
Silicon 0.25-0.40
Manganese 1.6-2.8
Sulfur 0.15 - 0.3
Chromium 0 - 0.5
Nickel 3.3 - 3.7
Vanadium 0.05-0.1
Copper 0.3-3.0
Aluminum 0.1 - 2.8
Aluminum + copper 1.0 - 3.1
Niobium 0.04-0.09
Zircon 0.02 - 0.06
Titanium 0.02 - 0.06
Calcium 0 - 0.008
Molybdenum 0-0.8
Tungsten 0-0.8
Molybdenum + $\frac{\text{W}}{\text{2nd}}$

0-1.0
Rest of iron and manufacturing-related impurities. 3. Martensite hardenable steel according to claim 1, which consists of in wt .-%
Carbon 0.10 - 0.15
Silicon 0.25-0.35
Manganese 1.8-2.2
Sulfur 0.15-0.25
Chromium 0 - 0.5
Nickel 3.4-3.6
Vanadium 0.05-0.1
Copper 0.4-2.4
Aluminum 0.1 - 2.1
Aluminum + copper 1.5 - 2.5
Niobium 0.05-0.08
Zircon 0.03-0.05
Titan 0.03-0.05
Calcium 0.002 - 0.006
Molybdenum 0-0.8
Tungsten 0-0.8
Molybdenum + $\frac{\text{W}}{\text{2nd}}$

0-1.0
Rest of iron and manufacturing-related impurities. 4. Martensite-hardenable steel, in particular for the production of plastic molds, which additionally in% by weight
0.12-0.4, preferably 0.15-0.30, in particular 0.15-0.25 sulfur
0.01-0.1, preferably 0.02-0.06, in particular 0.05-0.08 zircon,
0.01-0.1, preferably 0.02-0.06, in particular 0.05-0.08 titanium,
0.001-0.01 calcium. 5. Use of a martensit-hardenable steel according to claim 1 or 2 or 3 as a material for the production of plastic molds.