EP2233596B1 - Cold worked steel object - Google Patents

Description

The invention relates to a cold work tool steel article, in particular tool with high compaction depth or high Durchvergütungsvermögen containing the alloying elements carbon, manganese, silicon, chromium, molybdenum, vanadium and tungsten, optionally the element niobium, as well as accompanying elements with a content of less than 0.4 Wt .-% and impurity elements and iron as the remainder.

In particular, the invention relates to a tool coated with hard material at a temperature of more than 500 ° C.

Cold work steels are alloys which, in the thermally tempered state, have a property profile with high hardness, high wear resistance and high material toughness, with good machinability and particular dimensional stability during hardening and tempering being important criteria. These cold work steels are used i.a. as tools in the stamping technique of plastic molding for fine cutting as die parts and the like.

Alloy technology, these cold work steel materials are mostly geared to the tooling and the main load criteria in the practical application.

From the EP 1 471 160 is known, for example, a powder metallurgically produced cold work steel, which is composed differently in comparison with high-alloy high-speed steels and to improve the material toughness and high compressive strength with favorable fatigue behavior, including up to 1.0 wt .-% C, up to 6.2 wt .-% Cr, to to 3.8 wt .-% Mo, up to 2.9 wt .-% V and up to 3.4 wt .-% W has.

For a high wear resistance and a high dimensional stability of tools, a hardness of preferably at least 60 HRC and a high carbide content with uniform distribution of the carbides in a high-strength matrix of the material are important. However, it should be a simple annealing technology for the parts be applicable, wherein a desired, deep hardening of the material under the quenching surface is required.

For tools or parts to which a particular hard material layer, such as a nitride, carbonitride or oxide carbide layer of the elements titanium, chromium, aluminum and the like, is applied at a coating temperature of about 500 ° C, further, the substrate, so the Cold work steel object, this temperature load over the required or necessary coating time withstand or experienced no significant decrease in the property values, in particular the hardness and toughness of the material.

Based on the requirements of a fully improved property profile of a cold work tool steel object, the invention has for its object to provide a thermally annealed material, which of conventional easily adjustable temperatures between 1030 and 1080 ° C with increased cooling to great depths in a converted martensitic structure, high material hardness and toughness on tempering and up to temperatures of over 500 ° C for treatment times of up to several hours is resistant to wear and has high wear resistance.

kleiner als 88 ist,This object is achieved in that the steel or the iron-based alloy has a respective concentration of the alloying elements of in% by weight. C = 1.1 to 1.7 Mn = 0.1 to 0.6 Si = 0.4 to 1.1 Cr = 5.6 to 7.0 Mo = 1.2 to 1.8 V = 3.5 to 3.9 W = 1.1 to 5.0 Nb = to 1.0 with the proviso that contains the value $${\mathrm{W}}_{\mathrm{Nb}}\mathrm{=}\frac{\left(\mathrm{Not\; a\; word}\mathrm{+}\mathrm{W}\mathrm{/}\mathrm{2}\right)\mathrm{+}\mathrm{V}}{\mathrm{Nb}}$$

is less than 88,

• Verdüsen einer Schmelze,
• Hochtemperaturverdichten des Pulvers, hergestellt und durch
• thermisches Vergüten gehärtet wird,

sodass der Gegenstand eine Härte von mindestens 60 HRC bei einer Materialzähigkeit, gemessen durch die Schlagarbeit nach SEP 1314, von größer 50 J aufweist.Contains residual iron with less than 0.4 wt .-% accompanying elements and impurity elements, and the article by:

• Atomizing a melt,
• High temperature compaction of the powder, manufactured and by
• thermal quenching is cured,

so that the article has a hardness of at least 60 HRC with a material toughness, measured by the impact work to SEP 1314, of greater than 50 J.

The advantages achieved by the invention are essentially given by the fact that the alloying elements in their respective intended concentration in the material, as was found, are adjusted on the basis of the interaction of the carbide formers with the carbon concentration such that at a high solidification rate achieved by powder metallurgical production the Formation of the carbide phases and the matrix solidification by atomic lattice strain yield high abrasion resistance and material strength with high tempering resistance and high material toughness.

The effective carbide-forming elements of the fifth and sixth groups in the Periodic System, depending on the concentration, in particular carbon activity and temperature, form carbides with different crystal structures and properties in the matrix. In other words: carbides of type MC, M ₄ C ₃ and M ₂₃ C ₆ having cubic crystal structure and hexagonal- or trigonal-structured carbides of the type M ₂ C with MC fractions and M ₇ C ₃ are formed according to the respective carbon activity corresponding to the respective carbon Concentration of the carbide-forming metal elements in interaction of the available, free carbon content, whereby a certain amount distribution of the carbide types is set in the matrix and in this by free, embedded alloy atoms, a material-strengthening lattice strain is achieved.

Thus, in order to achieve carbide formation and interaction of the elements in the form in which the desired material properties are achievable in the product, it is important to have in the steel at a carbon content of 1.1 to 1.7 a respective concentration of the carbide formers in wt Adjust% chromium to 5.6 to 7.0, molybdenum 1.2 to 1.8, vanadium 3.5 to 3.9, and tungsten 1.1 to 5.0. In this way, monocarbides, mixed carbides and a carbon and element concentration in the matrix are adjusted with regard to the desired material properties.

A cold work tool according to the invention can, as is familiar to the person skilled in the art, be produced only in the case of powder metallurgy production of the material with a microstructure which, if necessary, also gives the prerequisites for the task-specific material property profile in a hot forming process, wherein a hardness of greater than 60 HRC and a toughness with the extent of impact work of greater than 50 J represent the lower limits.

kleiner als 88, vorzugsweise kleiner als 39 ist. As a particularly advantageous according to the invention it is provided that the steel contains up to 1.0 wt .-% Nb with the proviso that the value $${\mathrm{W}}_{\mathrm{Nb}}\mathrm{=}\frac{\left(\mathrm{Not\; a\; word}\mathrm{+}\mathrm{W}\mathrm{/}\mathrm{2}\right)\mathrm{+}\mathrm{V}}{\mathrm{Nb}}$$

is less than 88, preferably less than 39.

This alloying technique works to fine-tune the carbide grain size and, as found, is due to the action of Nb on solidification of the homogeneous melt in the presence of carbon and other carbide-forming elements.

The elements vanadium as a strong monocarbide former as well as tungsten and molybdenum, which form M ₂ C and MC carbides, usually form larger mixed carbides. Niobium, on the other hand, has only a slight tendency to mixed carbide formation, ie it represents fine, homogeneously distributed monocarbides, which are highly effective as carbide nuclei and ultimately result in a small carbide grain size in the matrix.

If the concentration of at least one alloying element has the following values in% by weight: C = greater than 1.2, less than 1.6, preferably 1.35 to 1.55 Mn = greater than 0.2, less than 0.55, preferably 0.3 to 0.5 Si = greater than 0.45, less than 1.0, preferably 0.5 to 0.9 Cr = greater than 5.7, less than 6.9, preferably 5.8 to 6.5 Mo = greater than 1.3, less than 1.7, preferably 1.4 to 1.6 V = greater than 3.55, less than 3.9, preferably 3.6 to 3.8 W = greater than 1.9, less than 4.5, preferably 3.1 to 4.4 Nb = greater than 0.1, less than 0.9, preferably 0.4 to 0.75 the property profile of the cold work tool steel article can be improved. This applies in particular to the element tungsten interacting with niobium in the region of narrow carbon activities.

The narrower the range of the chromium concentration by an average value of about 6.2, the more advantageous, as emerged from the investigations, is a Structure formation in the remuneration, because on the one hand only low stability of the retained austenite is given and on the other hand there is great through-hardening capacity.

A cold work tool steel article having superior properties can be made most economically when it bears on the work surface a coating applied during annealing at a temperature of at least 500 ° C, optionally 550 ° C and higher.

In this way, at least one tempering treatment can be carried out simultaneously with a surface coating and an outstanding adhesion of the layer can be achieved. A scientific justification, why a simultaneous application of a coating and a tempering treatment of the cured article at more than 500 ° C causes a higher adhesion of the wear layer, is currently not given.

If, with advantage for a high property profile, the cold work tool article has a material hardness of greater than 62 HRC, in particular 63 to 65 HRC, measured at a material toughness SEP 1314 greater than 50 J, in particular greater than 55 J, is a extensive usability of the alloy at high loads.

If a hard coating is applied to a thermal coating subsequent to the article in an hour and longer at a temperature of about 500 ° C to 550 ° C, so there is no deterioration of the material properties.

In the following, the invention will be explained in more detail based on development results, which represent only one embodiment.

From the investigations, two steels with similar chemical compositions but different niobium contents were selected.

Some test results are given below and, if applicable compared. The composition of the alloys is shown in Tab. Tab. 1 alloy Alloy elements in% by weight C Si Mn Cr Not a word V W Nb Fe + impurities K490 1:47 0.82 12:34 6.28 1:57 3.86 4:09 12:01 rest K490-Sun 1:41 12:55 12:35 6:42 1:48 3.70 3:50 12:46 rest

In Table 2 of the alloys K490 and K490-So the mean values of six equal tests of impact energy A in [J] according to SEP 1314 and the measured hardness values in [HRC] of the materials are given, each of an austenitizing temperature T _A of 1080 ° C and tempered at four different temperatures three times two hours. Tab. 2 Tempering temperature [° C] K490 K490-Sun impact energy
A [J] hardness
[HRC] impact energy
A [J] hardness
[HRC] 520 66.1 65.3 72.5 65.4 540 71.0 64.8 78.5 64.4 560 70.0 63.0 77.5 63.9 580 82.2 58.9 87.0 58.5

Fig. 1 and Fig. 2 show the values of Tab. 1 in graphical representation.

Based on the values from Tab. 2 and the graphs in Fig. 1 and Fig. 2 the skilled person recognizes a high material toughness of the alloys of the cold work tool according to the invention when tempering to more than 60 HRC. This limit of hardness of 60 HRC, which is often made a delivery condition for many articles in practical use, has been found to be achieved with tempering at a temperature of up to 570 ° C with three times heating for a period of 2 hours become. This allows the application of coating processes for the application of hard material layers, which run for kinetic reasons at high temperatures of 540 ° C and higher, can achieve maximum adhesion to the substrate and so significantly improve the performance characteristics of cold work tool steel objects.

According to one embodiment of the invention can be further increased by adding Niobium (K490-So) in particular the toughness of the annealed material at substantially the same hardness.

This is due to a carbide grain refinement, as studies with high magnification of the microstructure show.

Fig. 3 shows, for example, the material K490 with fine structure, which was achieved by a PM-production.

The size of the carbide particles can, as Fig. 4 can be reduced by alloying in the given case 0.46 wt .-% Nb, which leads to an increase in the material toughness. Associated with this are a faster dissolution of carbides during austenitizing of the material and a martensitic transformation when extinguishing to greater depths of the object.

Fig. 5 and Fig. 5A show the formation and the composition of carbides, which were formed with a nucleating effect of NbC. As Fig. 5 As a result, the high brightness tungsten-molybdenum carbides are smaller and more accurately confined relative to the matrix. In contrast, the slightly brighter vanadium-tungsten-molybdenum niobium carbides shown have a broad transition to the matrix. Examination of the carbide composition shows how Fig. 5A shows the germination of NbC in carbide formation.

Claims (5)

1. A cold-worked steel object, in particular a tool with large quenching and tempering depth or good capability of through quenching and tempering, wherein the steel consists of, in % by weight: C = 1.1 to 1.7 Mn = 0.1 to 0.6 Si = 0.4 to 1.1 Cr = 5.6 to 7.0 Mo = 1.2 to 1.8 V = 3.5 to 3.9 W = 1.1 to 5.0 Nb = to 1.0, with the proviso that the value of $${\mathrm{W}}_{\mathrm{Nb}}\mathrm{=}\frac{\left(\mathrm{Mo}\mathrm{+}\mathrm{W}\mathrm{/}\mathrm{2}\right)\mathrm{+}\mathrm{V}}{\mathrm{Nb}}$$

   

   
   is below 88,
   and the balance iron with less than 0.4 % by weight of companion elements and impurity elements, and the object is produced by:

   atomizing of a melt, and

   high-temperature compressing of the powder, and is hardened by quenching and tempering,

   so that the object has a hardness of at least 60 HRC at a material toughness, measured by impact according to SEP 1314, of more than 50 J.
2. The cold-worked steel object according to claim 1 characterized in that the concentration of at least one alloy element has the following values in % by weight: C = more than 1.2, less than 1.6, preferably 1.35 to 1.55, Mn = more than 0.2, less than 0.55, preferably 0.3 to 0.5, Si = more than 0.45, less than 1.0, preferably 0.5 to 0.9, Cr = more than 5.7, less than 6.9, preferably 5.8 to 6.5, Mo = more than 1.3, less than 1.7, preferably 1.4 to 1.6, V = more than 3.66, less than 3.9, preferably 3.6 to 3.8, W = more than 1.9, less than 4.5, preferably 3.1 to 4.4, Nb = more than 0.1, less than 0.9 preferably 0.4 to 0.75.
3. The cold-worked steel object according to any one of the claims 1 or 2 characterized in that it carries a coating on the working surface that is applied at a temperature of at least 500 °C, optionally 550 °C and higher, during tempering.
4. The cold-worked steel object according to any of the claims 1 to 3 characterized in that the object has a material hardness of more than 62 HRC, in particular 63 to 65 HRC, at a material toughness, measured by impact according to SEP 1314, of more than 60 J, in particular of more than 65 J.
5. The cold-worked steel object according to any one of the claims 1 to 4 characterized In that the object has a hard material coating applied at a temperature of more than 500 °C.

Images