EP1382704B1 - Cold work steel with high wear resistance - Google Patents

Description

The invention relates to a cold work tool with high wear resistance for powder metallurgically produced workpieces and tools with high toughness and Strength.

Parts and tools for cold work applications will become more and more important Technology developments ever higher and at the same time universal Exposed to stress. Independent of direction, high characteristic features can achieve the material, a powder metallurgical production the same can be selected, with one on this production method with the shortest Solidification times of the powder grains oriented chemical composition of Alloy allows a further increase in the quality of the steel object.

Cold work steels with high resistance to wear have a structure in their structure a matrix embedded high hard phase content, in particular carbides, which the substantiate high abrasion resistance. In terms of high toughness and hardness of the material, however, are the carbide formation and the matrix property, in particular their increased strength of importance.

A cold work steel alloy for the powder metallurgical production of parts, especially tools with high toughness and hardness, as well as resistance to Wear and fatigue is described in the Austrian patent application no. Called 587/2001. Such a chemically composed material can quite high mechanical property values provide quality assurance. Indeed are often at a full through hardening of large workpieces especially at deep hardening temperatures a grain boundary assignment with chromium-containing Mixed carbides are found, whereby the toughness potential of the alloy is not is fully exploitable. In many cases, an increased Material toughness of the product and a simpler Heat treatment technology for this desired.

Based on this prior art, the invention is based on the object a cold work tool steel with high wear resistance for powder metallurgy produced workpieces and tools with high toughness and strength too create, which even with simple thermal compensation and / or lesser Hardening temperature reaches a desired level of properties.

This object is achieved in a generic steel containing the alloying elements in wt .-%: carbon (C) 2.21 to 2.64 silicon (Si) 0.08 to 1.1 manganese (Mn) 0.05 to 1.1 chrome (Cr) 3.71 to 4.69 molybdenum (Not a word) 3.1 to 4.4 nickel (Ni) 0.14 to 0.3 vanadium (V) 8.45 to 9.5 tungsten (W) 0.5 to 1.5 cobalt (Co) 1.1 to 4.9 as well as the accompanying elements sulfur (S) to 0.3 niobium (Nb) to 0.1 nitrogen (N) to 0.1 aluminum (Al) to 0.06 titanium (Ti) to 0.01 the pollution elements phosphorus (P) max 0.029 oxygen (O) max 0.03 and the base element iron (Fe) as rest solved.

The advantages achieved by the invention are to be seen in particular in that it by alloying measures or by using the Interaction of the activities controlling the structural transformation and the carbide - forming elements has succeeded, on the one hand the through - hardenability of the Material to increase and on the other hand to achieve a solid solution hardening, even at low curing temperatures a pre-eutectic Carbide precipitation, especially at the grain boundaries is reduced.

In the sense of high wear resistance with improved toughness and in particular superior flexural strength are the carbide-forming elements of 5. Group of the periodic table interact with those of group 6 to see. It was found that with niobium contents of 0.1% by weight and smaller in the case of Vanadium according to the invention contain globulitic monocarbides and mixed carbides with tungsten and molybdenum in the specified concentration ranges of these Form elements, wherein the approximately spherical monocarbides of substantially Vanadin secure a high wear resistance of the material. highly stable Tungsten and molybdenum monocarbides can not arise due to activity, on the other hand, tungsten- and molybdenum-rich vanadium-containing mixed carbides become formable. These mixed carbides are used in the thermal treatment of Matrix curing, have the advantage of a lower precipitation temperature and are also easier to solidify during austenitizing. This in the Substantially also niobfreien carbide configurations, whereby by a leicher Solution of mixed carbides very high bending strength and impact resistance in the tempered material are closely related to kinetics of reaction low chromium concentration together.

Chromium can on the one hand, individually, at least three carbide formations with form different carbon concentrations and is slightly more metallic than metallic Component introduced by substitution in mixed carbides, the chromium content influenced, but on the other hand also significantly the hardness behavior as Acid acceptance, through hardenability, secondary hardness formation of the material. in principle increasing Chomgehalte retard the structural transformation when hardening or increase the Einhärteiefe and thus act in particular with nickel and manganese similar. On the other hand, cobalt contents in the alloy increase the diffusion coefficient for Carbon, which on the one hand can lead to lower hardness depths, on the other hand Cobalt suppresses to a high degree a pre-effective carbide precipitation, in particular at the grain boundaries, whereby substantial improvements of Toughness of the quenched material can be achieved.

With regard to the desired property level of cold work steel, which is formed deep within the workpiece even at low hardening temperatures the elements are chorm, manganese, nickel and cobalt in the invention Set concentration limits, with the preferred content ranges a Increase of mechanical material values and quality assurance of the material cause.

As mentioned earlier, the monocarbide formation as well as the activities of the vanadium, molybdenum and tungsten elements are important in terms of mixed carbide presentation and matrix cure for superior performance of the cold work tool of the present invention. It has been found that in the narrow concentration limits of the elements at a ratio according to the formula: V Mo + W = 1.5 to 2.2 superior mechanical properties of the steel article can be achieved with a compensation with relatively low curing temperatures, for example, 1030 ° C to 1050 ° C, with an increased hardening depth is given in inner fine grain structure.

Both with regard to an increase in the wear resistance and to further increase the toughness and hardness of the cold work tool according to the invention, it is advantageous if one or more than one element has the following concentrations in% by weight: carbon (C) = 2.3 to 2.6, preferably 2.4 to 2.55 silicon (Si) = 0.3 to 0.8, preferably 0.42 to 0.68 manganese (Mn) = 0.15 to 0.8, preferably 0.3 to 0.55 chrome (Cr) = From 3.85 to 4.58, preferably from 4.0 to 4.45 molybdenum (Mo) = From 3.31 to 4.18, preferably from 3.55 to 3.98 nickel (Ni) = 0.16 to 0.25 vanadium (V) = 8.61 to 9.34, preferably 8.81 to 9.2 tungsten (W) = 0.7 to 1.3, preferably 0.75 to 1.25 cobalt (Co) = 1.4 to 3.82, preferably 1.61 to 2.42

Furthermore, it has proved to be favorable, in particular for achieving increased material toughness, if one or more than one accompanying element has the following concentration values in% by weight: sulfur (S) to 0.03, preferably to 0.025 niobium (Nb) to 0.01, preferably to 0.006 nitrogen (N) to 0.09, preferably to 0.08 aluminum (Al) to 0.05, preferably to 0.04 and / or more than one impurity element has the following concentration values in% by weight: phosphorus (P) max 0.025 oxygen (O) max 0.009

For a powder metallurgically produced cold work tool steel article with a chemical composition according to any of the aforementioned materials, it is in In view of highest toughness and strength of the material, even when using usual standard hardening temperatures for the remuneration, so even with easier Heat treatment, important that a high degree of purity of the steel accordingly a K0 value of less than or equal to 3.0 according to DIN 50602 is given. Higher K0 values can lead to an increased deterioration in the performance characteristics of the Lead object.

Based on results from comparative investigations, the invention be explained in more detail.

Tab. 1 eine Darstellung der chemischen Zusammensetzung des erfindungsgemäßen Kaltarbeitsstahles und der Vergleichslegierungen

Tab. 2 die erhaltenen Meßwerte an Biegebruchfestigkeit, Schlagbiegearbeit und Verschleißwiderstand der vergüteten Stähle

Fig. 1 Meßanordnung zur Ermittlung der Biegebruchfestigkeit

Fig. 2 Probeform für die Prüfung der Schlagbiegearbeit

Fig. 3 Schema der Vorrichtung zur Messung der Verschleißwiderstandes

Fig. 4 vergleichende Balkendarstellung der Biegebruchfestigkeit der Stahllegierungen

Fig. 5 Darstellung der Schlagbiegearbeit

Fig. 6 Gegenüberstellung des Verschleißwiderstandes der jeweiligen Kaltarbeitsstähle

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Tab. 1 is a representation of the chemical composition of the cold work tool according to the invention and the comparative alloys

Tab. 2 the obtained measured values of bending strength, impact bending and wear resistance of the tempered steels

Fig. 1 measuring arrangement for determining the bending strength

Fig. 2 Probeform for testing the impact bending work

Fig. 3 Scheme of the device for measuring the wear resistance

Fig. 4 Comparative bar graph of the bending strength of the steel alloys

Fig. 5 representation of the impact bending work

Fig. 6 Comparison of the wear resistance of the respective cold work steels

Tab. 1 shows the chemical composition of a cold work steel alloy according to the invention with the designation Leg. K and those of comparative alloys described by Leg. A to Leg. J, can be seen.

Tab. 2 shows the test results, namely the bending strength, the impact bending work and the wear resistance, with the deformed specimens being tempered to the same hardness of 61 HRC.

The flexural strength of the cold work steel alloys was determined on round samples (R _D = 5.0 mm) in a device shown in Fig. 1 . The pre-load F _r was 200 N, the speed to full pre-load was 2 mm / min and the test speed was 5 mm / min.

The investigations of the impact bending work of the material was carried out on samples having a shape according to FIG. 2 .

From Fig. 3 , the device used for determining the wear resistance of the materials is shown schematically.

Fig. 1 shows in a bar graph the superior bending strength of the leg according to the invention. K, wherein the prior art corresponding comparison materials A to J each have high bending fracture values.

In a comparison of the impact bending work according to FIG. 5 , also in bar graph, the superior toughness of the material according to the invention can be seen.

If the wear resistance values of the differentially assembled cold work tool steels are compared, again in the case of bar graphs, in FIG. 6, the alloy according to the invention is in the range of the best materials for this type of stress.

It can be seen from the results of the investigations that the cold work steel composed according to the invention has an outstanding property level with regard to toughness and strength and has a comparable wear resistance in comparison with the best alloys of the prior art.

Claims (7)

1. Cold work steel having high wear resistance for powder metallurgically-manufactured work pieces and tools of high toughness and strength, containing the following alloying elements in wt.%: Carbon (C) 2.21 to 2.64 Silicon (Si) 0.08 to 1.1 Manganese (Mn) 0.05 to 1.1 Chromium (Cr) 3.71 to 4.69 Molybdenum (Mo) 3.1 to 4.4 Nickel (Ni) 0.14 to 0.3 Vanadium (V) 8.45 to 9.5 Tungsten (W) 0.5 to 1.5 Cobalt (Co) 1.1 to 4.9, as well as the accompanying elements Sulfur (S) to 0.3 Niobium (Nb) to 0.1 Nitrogen (N) to 0.1 Aluminium (Al) to 0.06 Titanium (Ti) to 0.01, the contaminating elements Phosphorus (P) max. 0.029 Oxygen (O) max. 0.03 and the basic element Iron (Fe) as the remainder.
2. Cold work steel according to Claim 1, with the proviso that the ratio of vanadium to molybdenum plus tungsten is 1.5 to 2.2: VMo + W    = 1,5 bis 2,2
3. Cold work steel according to Claim 1 or 2, with the proviso that the ratio of chromium plus manganese plus nickel to cobalt is 2.05 to 2.95: Cr + Mn + NiCo    = 2,05 to 2,95
4. Cold work steel according to any one of Claims 1 to 3, in which one or more than one element has the following concentration values in wt.%: Carbon (C) = 2.3 to 2.6, preferably 2.4 to 2.55 Silicon (Si) = 0.3 to 0.8, preferably 0.42 to 0.68 Manganese (Mn) = 0.15 to 0.8, preferably 0.3 to 0.55 Chromium (Cr) = 3.85 to 4.58, preferably 4.0 to 4.45 Molybdenum (Mo) = 3.31 to 4.18, preferably 3.55 to 3.98 Nickel (Ni) = 0.16 to 0.25 Vanadium (V) = 8.61 to 9.34, preferably 8.81 to 9.2 Tungsten (W) = 0.7 to 1.3, preferably 0.75 to 1.25 Cobalt (Co) = 1.4 to 3.82, preferably 1.61 to 2.42
5. Cold work steel according to any one of Claims 1 to 4, in which one or more than one accompanying element has the following concentration values in wt.%: Sulfur (S) to 0.3, preferably to 0.025 Niobium (Nb) to 0.1, preferably to 0.006 Nitrogen (N) to 0.09, preferably to 0.08 Aluminium (Al) to 0.05, preferably to 0.04
6. Cold work steel according to any one of Claims 1 to 5, in which one or more than one contaminating element has the following concentration values in wt.%: Phosphorus (P) max. 0.025 Oxygen (O) max. 0.009
7. A powder metallurgically-manufactured cold-work steel article having a chemical composition according to any one of the preceding claims and a degree of purity corresponding to a K0 value of less than/equal to 3.0 according to DIN 50602.

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