EP1445339A1 - Alloy and article with high heat resistance and high heat stability - Google Patents

Abstract

An alloy contains (in weight%) carbon (0.15-0.44), silicon (0.04-0.3), manganese (0.06-0.4), chromium (1.2-5), molybdenum (0.8-6.5), nickel (3.4-9.8), vanadium (0.2-0.8), cobalt (0.1-9.8), aluminum (1.4-3), copper (less than 1.3), niobium (less than 0.35) and remainder consist of iron and impurities. An independent claim is included for hot-forging steel component.

Description

The invention relates to an alloy for the production of articles with high Heat resistance and toughness.

In particular, the invention relates to a hot work tool steel article with high hardness, high heat resistance and high thermal stability.

In general, hot-work tool steels can be used as heat-treatable Iron-base alloys are called, whose increased mechanical Properties after the heat treatment, in particular their high strength and hardness up to temperatures of 500 ° C and above.

Complying with the increasing demands of technical development the general demand for hot working materials whose quality continues to increase improve and in particular their heat resistance at high thermal Stabiltiät to increase, as well as to increase the toughness.

Conventional hot working steels are carbonaceous iron-base alloys containing 0.3 to 0.4% by weight of carbon (C), the hardness of which is increased as required by quench hardening by martensite formation in the structure and tempering. An addition of alloying elements usually in wt .-%: Silicon (Si) to 1.5 Chrome (Cr) 2.5 to 5.5 Molybdenum (Mo) to 3.0 Vanadin (V) to 1.0 to the iron base material and an application of specially designed heat treatment processes makes it possible to produce from this an article which has high values for desired mechanical properties at a temperature of use up to about 500 ° C. By alloying tungsten (W) to 9 wt .-% and cobalt (Co) to 3.0 wt .-%, the use temperature can be slightly increased.

Essentially, the hot hardness of such steels is given by a Elimination mechanism that is considered by the specialist as a secondary hardening increase wherein finest chromium-molybdenum-tungsten-vanadium carbides in Martensite grid are formed.

Another in the nature of quench hardening different increase of Strength of a material can be achieved by precipitation hardening become. The prerequisite for precipitation hardening is one with the Temperature decreasing solubility of an alloy additive or of Alloy elements in the base metal.

In the case of precipitation hardening, an alloyed material becomes one for the time being Solution heat treatment followed by increased cooling subjected to an alloying addition or phase completely or partially dissolved and kept in supersaturated solution. One then heating to a temperature below the Solution annealing temperature causes a departure of the supersaturation of the (s) of the element (s) or the phase (s), which is a modification of Material properties, usually a material hardness increase causes.

Precipitation-hardenable iron base materials generally have alloy contents in% by weight of: Carbon (C) to 0.05 Manganese (Mn) to 2.0 Chrome (Cr) to 16.0 Molybdenum (Mo) to 6.0 Nickel (Ni) to 26.0 Vanadin (V) to 0.4 Kobait (Co) to 10.0 Titanium (Ti) to 3.0 Aluminum (Al) to 0.3

Both the iron-base alloys with a martensite formation in one Quench hardening, as well as those caused by excretion of elements and Phases have experienced a change in their mechanical properties Disadvantage in common that in the respective area of the alloy composition and / or by a heat treatment technology only each Individual properties, such as the hardness and strength or the Temperature resistance, improved, but with a drop of more Property values, such as material toughness, thermal stability and the like.

The aim of the invention is to provide an alloy which enables the Property profile to improve a total of a manufactured article. According to the object of the invention is a hot-work tool steel article at the same time high hardness and high toughness, high heat resistance and high to create thermal stability.

The object of the invention mentioned at the outset is with an alloy containing in% by weight: Carbon (C) 0.15 to 0.44 Silicon (Si) 0.04 to 0.3 Manganese (Mn) 0.06 to 0.4 Chrome (Cr) 1.2 to 5.0 Molybdenum (Mo) 0.8 to 6.5 Nickel (Ni) 3.4 to 9.8 Vanadin (V) 0.2 to 0.8 Cobalt (Co) 0.1 to 9.8 Aluminum (Al) 1.4 to 3.0 Copper (Cu) below 1.3 Niobium (Nb) below 0.35 Iron (Fe) rest as well as accompanying elements and production-related contamination.

The advantages resulting from the invention are essentially to be seen in the fact that a material was created by alloying measures, in which the quenching or Martensithärtung a precipitation hardening is superimposed. The activities of the alloying elements compared to the carbon and those in connection or phase formation are chosen so low that even at comparatively low Austenitisierungstemperaturen curing by ultrafine, secondary Karbideausscheidungen, especially chromium-molybdenum-vanadium carbides, and curing by a Elimination of intermetallic phases, in particular of Al Fe ₂ Ni occur simultaneously in the remuneration and a high hot hardness with high toughness of the material is achieved.

According to the invention, also a hardenability of large parts is improved possible because of alloying a corresponding thermal Conversion behavior of the material is set. Likewise are the Tempering resistance and thus the thermal stability of the tempered material high hardness significantly improved.

In an iron-based alloy according to the invention is a carbon content of provided at least 0.15 wt .-%, so that one for a desired Secondary hardening increase sufficient amount of carbide is excreted. higher Carbon concentrations as 0.44 wt .-% can with the provided carbide-forming elements form interfering primary toughening carbides, so that the content of carbon should be between 0.15 and 0.44 wt .-%.

The content of silicon must be an advantageous composition of a Desoxidation due to at least 0.04 wt .-%, on the other hand but not higher than 0.3 wt .-%, because higher silicon values the Material toughness adversely affect.

Manganese is in a concentration between 0.06 and 0.4 wt .-% provided in the steel according to the invention. Lower levels can cause brittleness in a thermoforming and higher contents disadvantages for the hardenability of the Cause material.

The contents of chromium, molybdenum and vanadium are important for a desired Secondary hardness formation of the material in the remuneration and should together to be viewed as. Chromium contents below 1.2 wt .-% have an adverse effect on the Cured by the material, those of more than 5.0 wt .-% worsen the thermal stability of the same, because thereby the activity of molybdenum is pushed back.

At molybdenum concentrations below 0.8 wt .-% is in the course of Heat treatment brought too little of this element into solution, causing too low secondary hardness values. About 6.5 wt .-% molybdenum in the steel can cause a too high carbide content, which reduces the toughness of the material and can bring economic disadvantages.

The strong carbide former vanadium is according to the invention with a minimum content of 0.2 wt .-% provided sufficient, stable secondary curing of the Ensure steel. Higher contents than 0.8% by weight of vanadium especially at carbon contents in the upper region of the intended Concentration margin, leading to the excretion of primary carbides, causing the toughness properties of the material are abruptly deteriorated.

Although the effect of niobium is similar to that of vanadium, it is remarkable through a formation of very stable carbides, so that the content of niobium should advantageously be less than 0.35 wt .-%.

To ensure a desired secondary hardness increase during tempering of the martensite of the alloy according to the invention thus has this in a Carbon concentration of 0.15 to 0.44 wt .-% contents in wt .-% of chromium from 1.2 to 5.0, molybdenum from 0.8 to 6.5 and to vanadium from 0.2 to 0.8.

The nickel concentration of the steel and its aluminum content are to be seen in terms of the precipitation kinetics of the phase of Al Fe ₂ Ni for hardness increase in a proposed heat treatment technology. At nickel contents below 3.4 wt .-% and at an aluminum concentration of less than 1.4 wt .-% precipitation hardening is pushed back, so the additive increase in hardness as a material during tempering low.

Higher contents than 9.8 wt% nickel shift the δ / α conversion lower temperatures, causing problems in the soft annealing of the Steel, a high processing hardness and the disturbance of the discharge kinetics can lead.

Contents above 3.0 wt .-% aluminum disadvantageously promote a high DELTA (δ) ferrite range in the conversion behavior, a nitride formation and lower the material toughness of the alloy.

According to the invention, therefore, the nickel content and the aluminum content of the steel in wt .-% in the ranges 3.4 to 9.8 nickel and 1.4 to 3.0 aluminum.

Copper can form unwanted, intermetallic phases and should be less Concentration of less than 1.3 wt .-% be contained in the steel.

In order to further improve the property profile of the alloy according to the invention, it may be provided that it has one or more of the elements with the following concentrations in% by weight: Carbon (C) 0.25 to 0.4, preferably 0.31 to 0.36 Silicon (Si) 0.1 to 0.25, preferably 0.15 to 0.19 Manganese (Mn) 0.15 to 0.3, preferably 0.2 to 0.29 Chrome (Cr) 1.9 to 2.9, preferably 2.2 to 2.8 Molybdenum (Mo) 1.2 to 4.5, preferably 2.1 to 2.9 Nickel (Ni) 5.0 to 7.6, preferably 5.6 to 7.1 Vanadin (V) 0.24 to 0.6, preferably 0.25 to 0.4 Cobalt (Co) 1.4 to 7.9, preferably 1.6 to 2.9 Aluminum (Al) 1.6 to 2.9, preferably 2.1 to 2.8

Due to these narrower content ranges of elements in the chemical Composition of the steel may be another property improvement of be achieved from it.

Of particular importance for overall high mechanical steel values, but especially for high toughness properties of the material is a limited amount of admixtures.

In an advantageous embodiment of the invention, an alloy is provided, comprising one or more of the concomitant and impurity elements with the following MAXIMUM concentrations in% by weight: Phosphorus (P) 0.02, preferably 0.005 Sulfur (S) 0,008, preferably 0,003 Copper (Cu) 0.15 preferably 0.06 Titanium (Ti) 0.01, preferably 0.005 Niobium (Nb) 0.001, preferably 0.0005 Nitrogen (N) 0,025, preferably 0,015 Oxygen (O) 0.009, preferably 0,002 Calcium (Ca) 0,003, preferably 0.001 Magnesium (Mg) 0,003, preferably 0.001 Tin (Sn) 0.01, preferably 0.005 Tantalum (Ta) 0.001, preferably 0.0005

To a particularly pronounced, the secondary hardening superimposed by carbides, To achieve precipitation hardenability of the alloy may be advantageous when the value nickel content refracted by aluminum content in each case in wt .-% between 1.8 and 4.2, preferably between 2.1 and 3.9. This will be a Overhang of a precipitate forming element avoided.

The stated object of the invention is according to an improved Property profiles solved with a hot work tool object, if one after produced by a fusion metallurgy or powder metallurgy process Starting material, in particular by hot forming and machining in the form which molded article after a curing Heat treatment secondary precipitated carbides, as well as intermetallic Has precipitates.

The total hardness of the material is advantageous by an overlay the secondary hardness increase by carbide precipitations and the Elimination hardening achieved. As a result, high material hardness values can be achieved Although the tempering technology is based on maintaining high material toughness is directed and compared with a hot work tool according to the state of Technique use lower hardening temperatures. This lower one Austenitizing temperature can also provide significant advantages in terms of a low distortion in a tempering treatment of complicated shaped parts to have.

However, if the hardening temperatures are set at a high level, so result in otherwise good material toughness extremely high hardness values of the steel object.

If in the structure of the hot-work tool object a relationship intermetallic precipitates broken by secondary precipitated Carbides in Vol .-% of less than 3.0, preferably 1.0 and smaller, however above 0.38, the toughness is particularly high at high hardness values and thermal stability up to 50 ° C and more to higher temperatures postponed.

A hot-work tool according to the invention, which has secondarily precipitated chromium-molybdenum-vanadium mixed carbides and essentially intermetallic phases of the Al Fe ₂ Ni type in the microstructure, has a particularly preferred property profile and can be economically produced in conventional hardening plants at comparatively low hardening temperatures ,

A pronounced thermal stability of the object can be achieved if the alloy has a ratio of chromium + molybdenum + vanadium broken by carbon, in each case in wt .-% of greater than 13, but less than 19 has.

On the basis of some investigation results and representations the Invention be exemplified in more detail.

From an alloy A according to the invention, from a conventional hot-work steel B and from a precipitation-hardening steel C (maraging steel), samples were produced, thermally tempered and their material properties were investigated. The alloys have the chemical compositions given in Tab. 1: element Alloy A Alloy B Alloy C C 0.32 0.38 0.13 Si 0.18 0.40 <0.05 Mn 0.25 0.33 <0.02 Cr 2.45 4.79 0.11 Not a word 2.43 2.78 5.26 Ni 6.46 0.18 18.01 V 0.28 0.62 0.02 Co 1.97 <0.05 8.71 al 2.46 0.016 0.13 Cu 0.06 0.07 0.08 Nb <0.005 <0005 <0005 Fe bal. bal. bal. P 0,008 0,015 <0.005 S 0.001 0.001 0.009 Ti <0.005 <0.005 0.79 N 0.0048 0.0068 0.0017 O 0.0022 0.0023 0.0007 Ca mg sn <0.005 <0.005 0.009 Ta

For the time being, a measurement of the thermal expansion α [10 ^-6 / K] as a function of the temperature at an initial hardness of the material of 50 to 52 HRC was carried out on the sample material. The values which can be taken from Table 2 show that the alloy according to the invention has a smaller expansion in comparison with a conventional hot-work steel B, which also indicates a better dimensional stability during a heat treatment. Temperature [° C] A B C 100 10.8 11.2 9 200 11.2 11.61 9.5 300 11.7 12 9.95 400 12.2 12.5 10.44 500 12.7 12.9 10.9

After hardening to about 55 HRC each of samples of the inventive alloy A and the conventional hot-work steel B, the hardness profile of the materials was determined as a function of the temperature. It is essential that the alloy A according to the invention required an austenitizing temperature of 990 ° C. in order to achieve this hardness, but that of 1050 ° C. was required for the conventional hot-rolled steel B, however. Depending on the temperature, as shown in Tab. 3A and Tab. 3B, increased in the range between 500 ° C and 600 ° C, the hardness of the inventively assembled sample A to values around 60 HRC, whereas in conventional hot-work steel B, a maximum hardness value of 56 HRC at 500 ° C. A
temperature Hardness In HRC 25 54 100 54 200 50 300 51 400 54 500 60 530 60 560 60 590 59 620 55 650 49 680 43 B
temperature Hardness In HRC 25 55 300 52 400 53 500 54 530 53 560 52 590 50 620 47 650 43

In a graphical representation in Fig. 1, the respective hardness profile in dependence of Temperature of the material A of the invention and the Hot work steel alloy B according to the prior art shown comparatively.

Starting from the same hardness, which however is achieved with an optionally advantageous lower austenitizing temperature, in the case of the alloy A according to the invention, a considerably greater increase in the hot hardness of the alloy A is produced by a superimposed precipitation mechanism in which Al Fe ₂ Ni precipitates are formed in the finest form in the microstructure Subject, whereby this is maintained even at higher temperatures.

Based on a hardening specification according to Vickers the investigation took place: the Softening behavior of the materials as a function of time at a temperature from 650 ° C.

A hardness determination on the test specimen at the test temperature was carried out after the Rebound hardness method (Shore hardness) is performed, for which return values So far only a conversion into Vickers hardness values is available.

Starting from approximately the same hardness at room temperature and that of 50 - 52 HRC, which for the alloys A, B and C with a composition according to Tab. 1 by different in the examination insert result sheet 1 was achieved, was carried out a Hardness test over time at 650 ° C.

In comparison with a conventional hot-work steel B and a Maraging steel C has the inventive alloy A at the same Initial hardness at 650 ° C, for a time of up to 1000 minutes, the highest Material hardness on. After this time, maraging steel C had a higher hardness at high thermal stability, whereas where the inventive Hot working steel A lost about 10% of its hardness up to about 2000 minutes. The thermal stability of conventional hot-work steel B was low; of the Increased hardness difference in comparison with the alloy A according to the invention steady for up to 1000 minutes.

Initial hardness: 50-52 HRC

Heat treatment: A Hardening tempering 990 ° C // 30 min // Oil quenching 640 ° C // 3x1 h // Air cooling B Hardening tempering 1050 ° C // 30 min // Oil quenching 550 ° C // 1h // Air cooling + 610 ° C // 2 h // Air cooling C Hardening tempering 820 ° C // 30 min // Oil quench 570 ° C // 3 h // Air cooling Erweichungsverhatten A (= considered alloy) B (conventional hot-side steels) C (maraging steel) Time [min] Hardness [HV] Time [min] Hardness [HV] Time [min] Hardness [HV] 2.89034 346.95705 2.89034 336.2518 2.89034 294.89709 4.06581 355.72974 4.08581 335.64438 4.08581 298.33194 5.77573 362.37786 5.77573 332.74216 5.77573 300.39692 8.16463 367.00547 8.16463 327.7911 8.16463 301.23444 11.54158 369.71665 11.54158 321.03717 11.54158 300.98688 16.31528 370.61546 16.31528 312.72632 16.31528 299.79666 23.06342 369.806 23.06342 303.10452 23.06342 297.80617 32.60264 367.39232 32.60264 292.41773 32.60264 295.1578 46.08737 363.47851 46.08737 280.91191 46.08737 291.99397 65.1495 358.16863 65.1495 268.83304 65.1495 288.45706 92.09588 351.56676 92.09588 256.42706 92.09588 284.68948 130.18751 343.77697 130.18751 243.93995 130.18751 280.83363 184.03416 334.90334 184.03416 231.61767 184.03416 277.0319 260.15225 325.04994 260.15225 219.70618 260.15225 273.4267 367.75342 314.32084 367.75342 208.45144 367.75342 270.16042 519.85933 302.82012 519.85933 198.09942 519.85933 267.37547 734.87754 290.65184 734.87754 188.89607 734.87754 265.21424 1038.8291 277.92009 1038.8291 181.08737 1038.8291 263.81913 1468.49759 264.72894 2075.8806 251.18246

Claims (8)

Alloy for the production of articles with high heat resistance and toughness containing in% by weight: Carbon (C) 0.15 to 0.44 Silicon (Si) 0.04 to 0.3 Manganese (Mn) 0.06 to 0.4 Chrome (Cr) 1.2 to 5.0 Molybdenum (Mo) 0.8 to 6.5 Nickel (Ni) 3.4 to 9.8 Vanadin (V) 0.2 to 0.8 Cobalt (Co) 0.1 to 9.8 Aluminum (Al) 1.4 to 3.0 Copper (Cu) below 1.3 Niobium (Nb) below 0.35 Iron (Fe) rest as well as accompanying elements and production-related contamination. An alloy according to claim 1 containing one or more of the following concentrations in% by weight: Carbon (C) 0.25 to 0.40, preferably 0.31 to 0.36 Silicon (Si) 0.10 to 0.25, preferably 0.15 to 0.19 Manganese (Mn) 0.15 to 0.30, preferably 0.20 to 0.29 Chrome (Cr) 1.9 to 2.9, preferably 2.2 to 2.8 Molybdenum (Mo) 1.2 to 4.5, preferably 2.1 to 2.9 Nickel (Ni) 5.0 to 7.6, preferably 5.6 to 7.1 Vanadin (V) 0.24 to 0.6, preferably 0.25 to 0.4 Cobalt (Co) 1.4 to 7.9, preferably 1.6 to 2.9 Aluminum (Al) 1.6 to 2.9, preferably 2.1 to 2.8 An alloy according to claim 1 or 2, comprising one or more of the companion and impurity elements having the following MAX concentrations in wt%: Phosphorus (P) 0.02, preferably 0.005 Sulfur (S) 0,008, preferably 0,003 Copper (Cu) 0.15 preferably 0.06 Titanium (Ti) 0.01, preferably 0.005 Niobium (Nb) 0.001, preferably 0.0005 Nitrogen (N) 0,025, preferably 0,015 Oxygen (O) 0.009, preferably 0,002 Calcium (Ca) 0.003, preferably 0.001 Magnesium (Mg) 0,003, preferably 0.001 Tin (Sn) 0.01, preferably 0.005 Tantalum (Ta) 0.001, preferably 0.0005 Alloy according to one of claims 1 to 3, wherein the value of nickel content broken by aluminum content in each case in wt .-% between 1.8 and 4.2, preferably between 2.1 and 3.9 Ni al = 1.8 to 4.2, preferably 2.1 to 3.9 Hot work tool steel with high hardness, high heat resistance and high thermal stability, one after a melt metallurgical or Prefabricated material produced by powder metallurgical process preferably with a in the ancillary claims characterized chemical composition, was shaped in particular by hot forming and machining, which molded article after a curing heat treatment in Structure secondary precipitated carbides, as well as intermetallic precipitations having. A hot-rolled steel article according to claim 5, having a ratio in the microstructure intermetallic precipitates broken by secondary precipitated Carbides in Vol .-% of less than 3.0, preferably 1.0 and smaller, however over 0.38, owns. Hot-rolled steel article according to claim 5 or 6, which has chromium-molybdenum-vanadium mixed carbides secondarily microstructured in the microstructure and essentially Al Fe ₂ Ni intermetallic phases in the microstructure. A hot work tool steel article according to any one of claims 5 to 7, which has in its chemical composition a ratio of chromium + molybdenum + vanadium broken by carbon each in wt% greater than 12 but less than 19. 12 < Cr + Mo + V C <19

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