EP1300482B1 - Hot-work tool-steel article - Google Patents

Abstract

Heat-deviating steel object is made from a composition containing (in wt.%): 0.451-0.598 carbon, 0.11-0.29 silicon, 0.11-0.39 manganese, 4.21-4.98 chromium, 2.81-3.29 molybdenum, 0.41-0.69 vanadium and a balance of iron and impurities. The object has a hardness of at least 58 HRC at an impact bending force of at least 170 J and a notched bar impact work of at least 11 J. <??>Preferred Features: The ratio of the concentration of vanadium to carbon is 0.82-1.38. The ratio of chromium + molybdenum + vanadium is 15.2 to 18.4.

Description

The invention relates to a hot-work tool steel article, in particular tool for forming metals and alloys at elevated temperatures. For Components, especially tools that are stressed at elevated temperature, for example, extrusion dies, forging tools, die casting dies, Press punches, mandrels and the like. Materials are required, the load corresponding mechanical material properties at temperatures of optionally 550 ° C and above and possess these properties during maintained a long service life.

According to the prior art, however, the highest hardness of the material and Toughness, minimal plastic deformation under extreme conditions, high Wear resistance, tempering resistance and good fatigue properties of hot-working steel in the temperature range above 550 ° C not in the desired extent simultaneously by alloying measures to be reached. So there are given thermal and mechanical Stresses of an object whose chemical composition and To select heat treatment so that the profile of the achievable Material properties as close as possible to requirements, often shorter Service life of the object or tool must be tolerated.

Materials science has long been confronted with the problem that Long-term use properties at elevated temperature of objects To improve hot working steel and to find an alloy with which at thermal quenching a high material toughness can be achieved at high hardness can, so that thereby the risk of breakage even with sudden stress of a Part and the plastic deformation and wear are minimized. there are also the tempering resistance and the thermal conductivity of the material too consider.

The expert is known that a tempering resistance or an unchanged Maintaining the mechanical properties of a thermally tempered Steel article is effected at elevated temperature by special carbides, the at carbon concentrations in the range of 0.5 wt.% and at chromium levels from 3 to 5 wt .-% Cr of the alloy can be formed, wherein molybdenum-tungsten and Vanadin content whose warm stability further increased. The usual Hot work steels essentially have contents in wt .-% of 0.35 to 0.665 C, 2.0 to 7.0 Cr, 1.5 to 8.0 Mo and / or 1.5 to 18.0 W and 0.4 to 2.0 V, wherein Vanadium by higher molybdenum or especially higher Tungsten concentrations can be replaced.

To a high hardenability of the hot work tool steel with good tempering resistance and Wear resistance even with a compensation of items with large To reach diameter is excited according to EP-0249855, a Steel composition of essentially in wt% C = 0.42 to 0.5, Mn = 0.35 to 0.6, Si = 0.8 to 1.2, Cr = 5.8 to 6.2, Mo = 1.85 to 1.95, V = 0.7 to 0.9 use. In comparison with a steel after AISI Type H 13 at the above alloy composition, an improvement in toughness, hardness, Strength and wear resistance achieved. A remuneration on a hardness greater than 58 HRC, however, causes coarse grain formation of the texture and adverse Viscous dissipation.

To the mechanical high temperature properties, especially at cyclic Strain, to improve, is also the use of a cobalt-containing hot-work steel produced by powder metallurgy (US Pat. No. 6,015,446) been proposed.

From AT 403 058 (EP-A-733719) is known for tools for chipless thermoforming of metals and alloys a hot-work tool with increased To use aluminum contents. This steel is quite for higher Working temperatures suitable, but has a hardness values of about 58 HRC Tendency to embrittlement.

As a material for hot working tools that have a thermal conductivity of over 35 Must have w / m k, according to EP-0632139 an alloy consisting in Substantially in wt% C = 0.3 to 0.5, Si <0.9, Mn <1.0, Cr = 2.0 to 4.0, Mo = 3.5 to 7.0, 0.3 to 1.5 V and / or Ti and / or Nb, Al = 0.005 to 0.1 suggested, thereby reducing the load on the tool surface and a flatter temperature gradient in the tool to avoid Thermal shock and voltage cracks to achieve.

EP-0939140 discloses a hot work tool consisting essentially of in weight% C = 0.25 to 0.79, Cr = 1.10 to 7.95, Mo = 0.56 to 3.49, V = 0.26 to 1.48, Fe = remainder. To improve the properties of the deformed material At high temperatures are in the above alloy, the impurity and Begieitelemente limited. With this measure can after a remuneration of the material to a hardness less than HRC = 56 high values for the Heat resistance, hot toughness and hot shearing resistance However, there was a strong spread of the respective mechanical Properties at high temperature with a compensation to a hardness of Item of greater than 58 HRC.

A powder metallurgically produced hot-work steel, which is characterized by a content of Carbides of type MC is characterized by 1.5 to 2.5 vol .-%, is from the WO 00/26427 become known. Above a material hardness of 58 to 59 HRC, at which increasingly tools are to be provided for cold work, both act higher as well as lower MC contents than 2.5 to 1.5 vol .-% disadvantageous to the Impact toughness.

Furthermore, EP 0 869 196 A2 has disclosed a cold work tool steel, for its production, a steel with a composition range of (in% by weight) C = 0.5 to 0.8, Si <1.0, Mn = 0.25 to 1.50, Cr = 4.0 to 8.0, Mo = 1.0 to 5.0, V = 0.2 to 1.0, niobium = 0.2 to 2.0, optional nickel up to 2.5 and optionally tungsten to 2.5, balance iron and manufacturing impurities, is used. Based on the knowledge and the resulting resulting technical solutions of the metallurgical experts is the Invention the task is based on the shortcomings in the given state of the art and to create a hot-work tool steel object that at high Material hardening and the like strength properties simultaneously Ensures toughness values at a significantly elevated level and at good thermal conductivity improved resistance to wear at elevated Temperatures and an effective extension of the life of the part at reinforced, possibly jerky stresses.

This object is achieved by a hot-rolled steel article according to claim 1. The in Claim 1 specified impact work SBP is in accordance with STEEL EISEN test sheets (SEP) 1314 determined, the determination of the notch impact work has to DIN EN 10045. The advantages achieved by the invention are essentially to be seen in that by alloy technology or by a balanced concentration of carbon and carbide-forming elements in steel Solid solution hardening with low carbide content is possible. It can Curing to values greater than 58 according to the lighter carbon solubility HRC of lower Austenitisierungstemperaturen, for example, from 1080 ° C or lower, which promotes the fine granularity of the material and advantageous in the With regard to high material toughness. In other words, it was found that by certain concentrations within narrow limits of carbon and of the special carbide and monocarbide forming elements during thermal quenching promoted a desired Mischkristallhärtbarkeit and carbide hardening or a hardness-increasing precipitation of coarser carbides at the expense of matrix hardness be largely suppressed.

It is important according to the invention, due to the interactions of the elements, better represented, the activities of the reacting elements, these to each other vote. A carbon content of at least 0.451 wt% is important to the minimum activity of carbon for a strain of the lattice of the Matrix crystals and a carbide formation tendency in the proposed chromium-molybdenum and vanadium concentrations, but higher Carbon contents of the alloy as 0.598 wt .-% one the wear resistance although promoting, but the hardness and toughness of the object adversely have an influencing effect. The chromium content is synergistic in the narrow To set limits between 4,21 and 4,98% by weight. Higher Cr concentrations 4.98 wt.%, the tempering resistance of the hot work tool steel may lower Temperatures, however, cause lower chromium levels than 4.21 Wt .-% a reduced tendency to special carbide formation. The by their content certain activity of molybdenum and vanadium over carbon is im With regard to the matrix curing in the remuneration of particular importance. It it was found that Mo has a kind of masking effect for V and in At least 2.81% by weight of a VC monocarbide precipitate and thus delaying a matrix depletion. On the other hand, with molybdenum contents above 3.29 wt .-% of the affinity for carbon so large that a solution of the same at austenitization of the object is greatly delayed or reduced can. For a corresponding development of the secondary hardness when starting the Hot work tool steel article is a minimum content of 0.41 wt .-% V higher contents than 0.69 wt .-% V increase the tendency to Mono carbide formation, which was also found in terms of a reduction the heat conduction of the steel may be detrimental. Silicon in concentrations between 0.11 and 0.29 wt.% is important for efficient deoxidation of the Liquid steel. Higher Si contents than 0.29 wt% deteriorate the Material toughness at the intended application temperatures. Manganese is for Setting of sulfur required. When using the modern Desulphurization is possible, the manganese content with at least 0.11 % By weight to be kept low. Higher manganese concentrations than 0.39 wt .-% can in particular with other grain boundary active elements the toughness of the Steel deteriorate.

From the above, it can be seen that an inventive synergetic choice of the respective concentrations of carbon, silicon, Manganese, chromium, molybdenum and vanadium are the prerequisites Hot work steel article with high hardness of 58 HRC and higher with at the same time to provide superior toughness through thermal quenching.

Advantageously, the choice of the contents of carbon and vanadium is made so that the ratio: concentration of V broken by that of C equals 0.82 to 1.38. By this ratio within narrow limits becomes Kinetic kinetically pushed back the monocarbide in favor of the matrix content and the mixed crystal curability is preferred.

An increase in hardness with increase in the tempering resistance, an improvement in the Hot wear resistance and service life of a hot work tool steel article can be achieved if the ratio of the concentrations of Chromium + molybdenum + vanadium broken by the carbon content between 15.2 and 18.4.

Completely surprising, because molybdenum and tungsten in terms of their inclination For carbide formation as interchangeable, it was found that tungsten Tendency to primary carbide formation promotes and in particular segregations and optionally promotes grain growth, with a Seigerungsabbau by Annealing of hot-work steel by tungsten is substantially reduced. According to the invention, therefore, the tungsten content of Hot-work tool steel article less than 0.1% by weight.

The hot-work steel article preferably has a share in the Solidification in the melt formed carbides of less than 0.45 vol .-%. On the one hand, this results in a depletion of the mixed crystals with respect to the Prevents carbon and to achieve a further increase in hardness, On the other hand, it has been found that increasing the thermal conductivity of the Hot working steel material achieved. An improvement in thermal conductivity By reducing the carbide content in the material is still scientifically not secured, but could at an interface kinetics and / or on the Properties of the carbides are based.

In a further embodiment of the invention, a reduction of Contamination and / or accompanying elements advantageous for improved Performance characteristics of the hot work steel object at elevated To provide temperatures. The this-respect provided individual and Collection concentrations of the elements are in the characterizing part of Anspmches 5 and claim 7 specified.

It has proven to be advantageous to use the nitrogen content of the alloy 0.025 wt .-% to limit, because nitrogen with the carbide-forming Elements cr. Mo and V forms stable nitrides, making remuneration-technical Disadvantages can arise.

A hot work tool steel article having a particularly high performance profile may be produced when at one temperature of 500 ° C one or both of the mechanical steels value (s) is equal to or greater than:
Bending work: SBP 180 J
Longitudinal impact: Charpy-U 14 J
and the hardness at RT is 59 HRC and higher.

The decisive advantages of a fine-grained structure with regard to a high Material toughness with high hardness values can at the alloy composed according to the invention, when the Hardening temperature for thermal quenching for adjusting the mechanical Properties lower than 1080 ° C, especially 1050 ° C, plus / minus 10 ° C. is.

In the following the invention will be explained in more detail by means of examples. Table 1 gives the chemical compositions of some of the materials investigated in the development work. Chemical composition wt% alloy C Si Mn Cr V Not a word Co A 00:39 00:23 00:32 4.27 00:52 2.90 B 00:52 00:25 00:25 4:45 0.68 3.21 C 00:43 00:28 00:24 4:48 00:58 4:36 D 00:40 00:28 00:24 4:37 0.80 4:39 e 00:48 00:30 00:26 4:48 00:56 3.10 F 00:52 00:17 00:16 4:38 00:54 4:57 G 00:53 00:29 00:26 4:51 0.84 4:56 1.2367 00:38 00:35 00:32 5:07 0.67 2.83 ~1.2885 00:38 00:28 00:37 2.95 0.67 2.83 2.9

The materials designated in Table 1 with alloys B and E have a Composition according to the invention, with 1.2367 and 1.2885 are samples with The material numbers are marked according to DIN steel iron list, the latter Sample with respect to the carbon content outside the prescribed Borders lies.

In order to be able to compare the mechanical properties of the materials with the different alloy compositions, an attempt was made to compensate the respective sample material to a hardness of 58 to 59 HRC. Specifically, this was done by measures indicated in Table 2, wherein oil was used as the quenching medium. stole hardening start Achieved hardness temperature Time temperature Time number A 1100 ° C 30 min 560 ° C 60min 3x 56 B 1060 ° C 30 min 560 ° C 60min 3x 59 C 1100 ° C 30 min 530 ° C 60min 3x 59 D 1100 ° C 30 min 560 ° C 60min 3x 56 e 1060 ° C 30 min 560 ° C 60min 3x 58 F 1060 ° C 30 min 550 ° C 60min 3x 58 G 1060 ° C 30 min 550 ° C 60min 3x 59 1.2367 1100 ° C 30 min 550 ° C / 120min + 560 ° C / 120min 56 ~1.2885 1100 ° C 30 min 550 ° C / 120min + 560 ° C / 120min 56

The materials according to DIN material numbers 1.2367 and 1.2885 were also by special measures not to a hardness of over 56 HRC to remunerate.

The values of the alloy (B, E) according to the invention and comparative materials obtained from mechanical material testing are shown numerically in Table 3. Steel / hardness Bending work A [J] RT Impact testing (ISO-U) KU [J] RT Impact energy (ISO-U) KU [J] 500 ° C A / 56HRc 147.8 9.6 - B / 57HRc 175.0 11.3 15.8 C / 59HRc 84.8 6.8 - D / 56HRc 133.5 8.3 - E / 58HRc 185.0 11.8 16.3 F / 58HRc 80.8 8.0 - G / 59HRc 91.0 6.9 - 1.2367 / 56HRc 116.8 11.5 16.8 ~1.2885 / 56HRc 17.8 5.3 12.3

For a vivid comparison, those obtained during the testing were Property values graphically as a bar graph in FIGS. 1, 2, and 3 shown.

According to FIG. 1 and FIG. 2, the alloy A is opposite to the invention Alloys lowered hardness as well as impact resistance and notched impact values because apparently due to the low carbon content is not sufficient Matrix strength has been achieved. On the other hand, the material of alloy C has one high hardness, but a very low toughness, indicating a low Carbon content in conjunction with a high molybdenum concentration, so on a matrix depletion, indicates. The same applies to a lesser extent for the Alloy D, where apparently the increased vanadium content is the high molybdenum content with respect to toughness but showing low hardness efficiency. At a quite good hardening assumption in the tempering treatment shows the material of Alloy F the full effect of high molybdenum levels in terms of sinking the toughness properties, in particular the impact resistance. same for essentially also for the work piece made of the alloy G. The steel with the Material number. 1. 2367 is only suitable for low hardness values and has Due to the increased chromium content, a low starting resistance; at a quite high impact energy, however, is a relatively small Impact resistance given at RT of the material. For the one improved Starting resistance material No. 1.2885 became extremely low Property level determined.

A comparison of notch impact strength (ISO-U) at 500 ° C of Materials according to the invention of alloy B and E and materials with the Material No. 1.2367 and 1.2885 Fig. 3. The low hardness according to DIN Standard materials promotes toughness; unexpectedly low KU values were reported for the Steel determined with the material no. 1.2885.

The comparison of the test results of the impact resistance at RT, the Impact energy (ISO-U) at RT and notched impact strength (ISO-U) at 500 ° C the examined materials can be taken that the invention composite materials after tempering a high hardness of greater than or equal to 58 HRC, an exceedingly high level of mechanical Possess properties, with the annealing advantageously low curing temperatures are applicable.

Claims (8)

1. Hot-work tool-steel article, particularly tool for transforming metals and alloys at an elevated temperature, which is formed of an alloy of a composition, in percent per weight, of carbon (C) 0.451 to 0.598 silicon (Si) 0.11 to 0.29 manganese (Mn) 0.11 to 0.39 chromium (Cr) 4.21 to 4.98 molybdenum (Mo) 2.81 to 3.29 vanadium (V) 0.41 to 0.69 optionally tungsten (W) less than 0.1 optionally nitrogen (N) up to 0.025 optionally nickel (Ni) up to 0.15 in maximum optionally cobalt (Co) up to 0.1 in maximum optionally copper (Cu) up to 0.1 in maximum wherein a sum concentration of (Ni + Co + Cu) amounts to 0.25 in maximum, iron (Fe) as well as inevitable impurities form the balance, and the hardness in annealed condition is greater than or equal to 58 HRC, at a impact flexure energy SMP of greater than or equal to 170 J, and notched-bar impact energy in longitudinal direction Charpy-U of the material is greater than or equal to 11 J.
2. Hot-work tool-steel article according to claim 1, characterised in that the ratio of concentration of V divided by that of C is 0.82 to 1.38. VC = 0.82 to 1.38
3. Hot-work tool-steel article according to claim 1 or 2, characterised in that the ratio of the concentrations of (Cr + Mo + V) divided by that of C of the alloy is 15.2 to 18.4. Cr+Mo+V C = 15.2 to 18.4
4. Hot-work tool-steel article according to any of claims 1 to 3, characterised in that the proportion of carbides, which have formed in the melt during solidification, is less than 0.45 % by volume.
5. Hot-work tool-steel article according to any of claims 1 to 4, characterised in that one or a plurality of impurity or metalloid elements of the alloy are in individual and/or sum concentrations, in percent per weight, which show a maximum value of sulphur (S) = 0.005 phosphorus (P) = 0.007 (S + P) = 0.010 aluminium (Al) = 0.02 magnesium (Mg) = 0.001 calcium (Ca) = 0.001 (Al + Mg + Ca) = 0.02
6. Hot-work tool-steel article according to any of claims 1 to 5, characterised in that at a temperature of 500°C, one or both value(s) of the mechanical steel properties is (are) equal or higher than:

   Impact flexure energy: SBP 180 J

   notched-bar impact energy in longitudinal direction: Charpy-U 14 J

   and hardness is 59 HRC or more.
7. Hot-work tool-steel article according to any of claims 1 to 6, characterised in that one or a plurality of impurity or metalloid elements of the alloy are in individual and/or sum concentrations, in percent per weight, which show a maximum value of arsenic (As) = 0.005 bismuth (Bi) = 0.003 tin (Sn) = 0.005 zinc (Zn) = 0.002 antimony (Sb) = 0.002 boron (B) = 0.002 (As+Bi+Sn+Zn+Sb+B) = 0.009
8. Hot-work tool-steel article according to any of claims 1 to 7, characterised in that the annealing temperature for thermally annealing to set the mechanical properties is lower than 1080°C, particularly 1050°C plus/minus 10°C.

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