DE19508947A1 - New wear resistant iron@-molybdenum@-tungsten@ alloy - Google Patents

Abstract

Novel wear- and temper-resistant, high hot strength alloy has the compsn. (by wt.) 10-35% Mo and/or 20-50% W; 0.6-6% C; 5-25% V, Ti, Zr, Nb and/or Ta; 0-20% Cr; 0-12% Co; 0-8% Ni; 0-5% Si; 0-5% Al; 0-5% Mn; 0-5% Cu; 0-2% B; 0-0.5% N; balance at least 30% Fe and impurities, with the provisos that (a) the total Mo+W concn. has a minimum value increasing linearly from 10% to 20% with increasing W content and a max. value increasing linearly from 35% to 50% with increasing W content; (b) the ratio of C atoms to total number of V, Ti, Zr, Nb and/or Ta atoms is 0.5-2; and (c) the total Cr, Co, Ni, Si, Al, Mn, Cu, B and N concn. is max. 25%. Also claimed are prodn. processes for the above alloy in which the alloy is produced by melting or powder metallurgy and then either rapidly cooled or nitrided to increase wear resistance and strength.

Description

The invention relates to a wear-resistant, tempering resistant dige and heat-resistant alloy based on iron. Of the invention further relates to a method of manufacture development of such an alloy in which the alloy initially from the melt or on powder metallurgical Ways is generated.

Especially in the field of hot work tools Increase in heat resistance and wear resistance of materials, as this means that the quality of the products produced by the tools increased and the pro production costs can be reduced.

Leave the traditional martensitic hot work steels despite further development in this regard, only be expected limited improvements. The wear resistance can be done by storing hard materials in a con tional steel matrix, such as. B. in high-speed steels and hot-work steel-carbide composite materials the. However, the use of these materials is high Temperature due to the low heat resistant matrix limits puts.

The high-temperature steels, alloys and high-melting Metals such as austenitic steels, nickel and Ko balt alloys as well as molybdenum and tungsten alloys have a high heat resistance, but only a low one Strength at low temperatures and also have a low ver due to the lack of hard material storage wear resistance. High-temperature alloys are the more expensive than conventional hot work tool steels and also difficult to edit.

From DE 32 07 161 A1 a hard alloy is knows that is editable first and then by a heat treatment can be hardened. This well-known  Hard material alloy consists of a metal carbide component and the rest of a steel alloy with the alloy elements ten C, W and Co. This hard alloy stands out due to high wear resistance, temper resistance and heat resistance.

Disadvantages of the known hard alloy are particularly especially the costly high cobalt content and the powder metallurgical processes limited manufacturing poss options.

It is therefore an object of the present invention to le Provision of the type mentioned at the outset is simple and inexpensive to manufacture and at the same time high values regarding wear resistance, an resistance and heat resistance.

This problem is solved by an alloy of the beginning mentioned type, consisting of (in% by weight):

• a) 10% to 35% Mo or 20% to 50% W or Mo and W, whereby for the total concentration of Mo and W an with increasing increasing proportion of W linearly increasing from 10% to 20% Minimum value and a linearly increasing with increasing proportion of W 35% to 50% increasing maximum applies
• b) 0.6% to 6% C,
• c) 5% to 25% V or alternatively 5% to 25%
• aa) Ti or Zr or Nb or Ta or
• bb) any mixture of V in terms of its proportions, Ti, Zr, Nb and Ta,

where the ratio of the number of carbon atoms to the Ge total number of Va, Ti, Zr, Nb and / or Ta atoms min is at least 0.5 and at most 2,

• d) 0% to 20% Cr,
  0% to 12% Co
  0% to 8% Ni,
  0% to 5% Si,
  0% to 5% Al,
  0% to 5% Mn,
  0% to 5% Cu,
  0% to 2% B and
  0% to 0.5% N,
  wherein the total concentration of Cr, Co, Ni, Si, Al, Mn, Cu, B and N is at most 25%, and
• f) as the remainder from impurities caused by production and at least 30% Fe.

Molybdenum mainly increases temper resistance and Heat resistance through mixed crystal hardening and formation of carbides or of intermetallic phases. also becomes the thermal conductivity by the supply of the molybdenum increases and the thermal expansion of the alloy decreases. This reduces both the hot crack sensitivity under tem temperature change stress as well as the risk of overheating on the surface due to heat build-up, e.g. B. with direct con clocks with a hot workpiece. It also has molybdenum a friction-reducing effect.

Tungsten is very similar to molybdenum Lich, why the tungsten partially or up to the molybdenum specified maximum concentration can completely replace.

The carbide formers Mo, V, Ti, Zr, Nb, and / or Ta as well Form Cr on the one hand by direct excretion from the Melt primary carbides and in the solid state, e.g. B. at a later heat treatment, secondary carbides. While the Pri färkarbide in particular the wear resistance verbes The secondary carbides mainly contribute to an Fe increase in stability.

The alloy according to the invention can advantageously also be composed in such a way that it contains:
15% to 30% Mo or 20% to 40% W or Mo and W, whereby for the total concentration of Mo and W a minimum value that increases linearly with increasing W content from 15% to 20% and one that increases linearly with increasing W content 30% to 40% of increasing maximum value applies.

Furthermore, the alloy according to the invention can be put together in this way be set that include:

• a) 5% to 15% V or alternatively 5% to 15%
• aa) Ti or Zr or Nb or Ta or
• bb) any mixture of V in terms of its proportions, Ti, Zr, Nb and Ta.
• b) 1% to 4% C, the ratio of the number of C atoms to the total number of Va, Ti, Nb, Zr and / or Ta atoms is at least 0.5 and at most 1.5.

With a content of approx. 10% vanadium and at the same time ratio of the number of carbon atoms to the number of V atoms of about 1, the alloy has an almost eutectic structure and stands out next to the other posi tive properties also characterized by high toughness. Due to a narrow melting interval, the Le Alloys with this composition, especially for the pouring or melting manufacturing process.

The alloy according to the invention can be made in the usual way the melt, e.g. B. by casting, or on powder metallurgy generated path.

The alloy of the invention can thus by all common processes are manufactured, which is why simple The way, quantity and distribution of the individual structures components through a suitable selection of alloys setting can be adjusted in fine steps. A ge desired property profile with regard to heat resistance, ver wear resistance and toughness can be predetermined. The heat resistance can be increased by increasing the Mo or W component and the wear resistance due to an increase of the metal carbide portion increased and a high toughness by selecting a eutectic composition be enough.  

Since their manufacture is not based on certain processes, e.g. B. powder metallurgical type, is limited, the Alloy according to the invention excellent for the production of Surface layers on a base body of a different composition application using different application methods.

Such a surface layer can e.g. B. with the help of La ser, electron or plasma rays are generated. Here are the for the desired composition of the surface Alloy materials required on the surface of the main body. Simultaneously with the application of the alloy substances (one-step process) or this surface closes (two-stage process) with the laser, electron or plasma beam locally so far heated that the alloys located there in egg a melt pool or also by diffusion processes can produce the desired surface layer.

It is in the formation of the surface layer between egg a pure coating process and an alloy process drive to distinguish. In the former, the surfaces layer by the applied alloy materials testifies. I.e. the composition of the basic body Alloy materials applied to the surface correspond to Layer composition. In contrast, in the alloying process becomes the basic body within a certain, the upper surface-forming layer with the applied alloy fabrics alloyed until the layer has the desired combination setting.

The application of the alloy substances to the surface of the Basic body is possible in different ways. So the alloying elements in elemental form as pul can be applied mixed. Alternatively, the metals to be supplied in part when applied in Karbi be bound. All alloy materials to be fed or even part of it can be in the form of a pre-alloy tion are applied, such a master alloy  can in turn have metal carbides. This master alloy can be either as a powder or in the form of wire, Tape or foils on the surface of the base body be brought.

Furthermore, it is also possible to add the alloying materials elementary form or in alloy form with or without Metal carbides by thermal spraying on the surface to apply the base body.

In addition to the laser, electron or Plasma welding can also be used for cladding Generation of a surface layer on a base body to serve. For this purpose, a welding electrode is made from a Vorle used for the surface layer has the desired composition.

A production method of the ge is preferred named type in which the alloy immediately after its Generation is rapidly cooled.

A high cooling rate creates a fine solidification structure and one of alloying elements and carbon supersaturated metal matrix that has a low initial hardness having. The latter has the advantage that those from the Legie parts are easy to machine. Tools produced in this way then either reach in situ when used at high temperatures or through a separate heat treatment a high hardness.

In the above surface coating processes the surface of the base body is only briefly in each case heated locally. As a rule, the Mass of the base body compared to the melted Mass is low, cool with these coating processes the surface layers immediately after their creation regularly without special measures at high speed  off. The surface layers thus have the most favorable fine solidification structure with high toughness.

The alloy according to the invention can also be produced in this way be that the alloy after cooling to increase wear resistance and strength for 1 to 6 hours a temperature of 500 ° C to 800 ° C is outsourced.

The increase in strength occurs during the outsourcing to special through the formation of retired secondary carbides. Such outsourcing is to be used if the alloy according to the invention at low temperatures is used. When used at high temperatures there is no need for outsourcing, since the hardening effect then during operation at high temperatures.

The alloy according to the invention can preferably also be produced in this way be made that the alloy 2 to 4 hours in the Tem temperature range from 600 ° C to 700 ° C.

Furthermore, the alloy according to the invention can be used in this way provides that to increase wear resistance the alloy is nitrided.

This causes the formation of nitrite on the surface whose hardness increases. The nitriding process can be carried out immediately after rapid cooling of the alloy according to the invention or to further increase hardness after outsourcing be applied.

Finally, a method of the type mentioned at the beginning also be carried out so that the alloy according to its Er generation to increase wear resistance and strength is nitrided.

The following is an example of the alloy according to the invention and are shown on the basis of diagrams Properties of this alloy clarified.  

Show it
Diagram 1 The Vickers hardness of the alloy according to the invention in a specific composition and
Diagrams 2-4 show the isothermal heat hardness curve of laser-alloyed surface layers with a specific composition of the alloy according to the invention in comparison with a conventional tempered hot-work steel at different temperatures.

On a base made of tempered hot-work steel (Material No. 1.2365) was using a 5kW CO₂ laser creates a surface layer by laser beam alloying, which is generated by the laser beam on the base body Mo-VC powder mixture was fed into the molten bath.

An analysis of the surface layer showed a concentration of (in weight percent) for the added alloying substances:
Mo: 20 ± 1%
V: 10 ± 1%
C: 2.4%,
where the C content was calculated from the V content. The latter was possible because C was only supplied in the form of VC.

Furthermore, for the originating from the basic body Element Cr analyzed for a content of approx. 2.5%.

Diagram 1 shows the Vickers hardness of the above surface layer at room temperature depending on the Tempering temperature. The duration of the occasion treatment was each because two hours.  

The maximum hardness was for the composition mentioned of 800 HV at a tempering temperature of 650 ° C. After tempering at 800 ° C the hardness is still approximately 650 HV. With further surface layers with a higher one Mo content of 25% was used with otherwise unchanged V, C and Cr content hardening of 870 HV (tempering temperature 650 ° C) and 790 HV (tempering temperature 800 ° C) reached. By a re reduction of the V content to 5% and the C content to 1.2% could in other surface layers with a Mo content of 25% a maximum hardness of 950 HV (tempering temperature 650 ° C) and hardness at a tempering temperature of 800 ° C of 820 HV can be achieved.

Diagrams 2-4 show the isothermal warm hardness curve the exemplary surface layer compared to the con conventional tempered hot-work steel of the base body at temperatures of 600 ° C, 700 ° C and 800 ° C. In the slide gram is the warm hardness of the materials to be compared depending on the holding time at the respective tempe applied. The squares give the warmth values of the base material and the circles the hot hardness values of the surface layer with the Zu according to the invention composition. Be at a temperature of 800 ° C Differences in hardness between the materials to be compared lien of up to 300 HV reached.

Furthermore, the wear resistance of the alloy with the composition according to the above example before and after a two-hour tempering treatment at 650 ° C measured. For this purpose, a pen from the one considered here Alloy with a SiC disc with grain size 240 an average speed of 1.6 m / s and a load of 6.5 N over a glide path of 951 m with water as Ground lubricant. Before starting, the ver wear approx. 0.55 g / cm², after tempering approx. 0.35 g / cm².

By increasing the V-share to 15% and with it going to 3.6% while maintaining the  Mo and Cr contents could adhere to wear tempering can be reduced to approx. 0.25 g / cm².

The tempered hot-work steel forming the basic body (Material No. 1.2365) showed under the same grinding machine conditions a wear of 1.6 g / cm².

Claims (10)

1. Wear-resistant, temper-resistant and heat-resistant alloy consisting of (in% by weight):

• a) 10% to 35% Mo or 20% to 50% W or Mo and W, whereby for the total concentration of Mo and W a minimum value increasing linearly with increasing W content from 10% to 20% and one with increasing W- Proportion linearly increasing from 35% to 50% maximum value applies
• b) 0.6% to 6% C,
• c) 5% to 25% V or alternatively 5% to 25%
• aa) Ti or Zr or Nb or Ta or
• bb) any mixture of V, Ti, Zr, Nb and Ta in their proportions,

where the ratio of the number of C atoms to the total number of Va, Ti, Zr, Nb and / or Ta atoms is at least 0.5 and at most 2,

• d) 0% to 20% Cr,
  0% to 12% Co
  0% to 8% Ni,
  0% to 5% Si,
  0% to 5% Al,
  0% to 5% Mn,
  0% to 5% Cu,
  0% to 2% B and
  0% to 0.5% N,

the total concentration of Cr, Co, Ni, Si, Al, Mn, Cu, B and N is at most 25%,

• f) the rest of production-related impurities and at least 30% Fe.

2. Alloy according to claim 1, characterized in that it contains:
15% to 30% Mo or 20% to 40% W or Mo and W, whereby for the total concentration of Mo and W a minimum value that increases linearly with increasing W content from 15% to 20% and one that increases linearly with increasing W content 30% to 40% of increasing maximum value applies. 3. Alloy according to claim 1 or 2, characterized in that it contains:

• a) 5% to 15% V or alternatively 5% to 15%
• aa) Ti or Zr or Nb or Ta or
• bb) any mixture of V, Ti, Zr, Nb and Ta in their proportions.
• b) 1% to 4% C, the ratio of the number of C atoms to the total number of Va, Ti, Nb, Zr and / or Ta atoms being at least 0.5 and at most 1.5 be .

4. Process for producing a wear-resistant, temper-resistant and heat-resistant alloy with the A composition according to any one of claims 1 to 3, in which the alloy first from the melt or on powder metallurgical way is generated, characterized thereby records that the alloy immediately after its Generation is rapidly cooled.   5. The method according to claim 4, characterized characterized in that the alloy after cooling to Increased wear resistance and strength 1 to 6 Hours at a temperature of 500 ° C to 800 ° C is outsourced. 6. The method according to claim 5, characterized characterized in that the alloy 2 to 4 hours in Temperature range from 600 ° C to 700 ° C is outsourced. 7. The method according to any one of claims 4 to 6, characterized in that to increase the Wear resistance the alloy is nitrided. 8. Process for producing a wear-resistant, temper-resistant and heat-resistant alloy with the A composition according to any one of claims 1 to 3, in which the alloy first from the melt or on powder metallurgical way is generated, characterized thereby records that the alloy after its production for Increased wear resistance and strength nitrided becomes.