Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/12—Both compacting and sintering
  • B22F3/14—Both compacting and sintering simultaneously
  • B22F3/15—Hot isostatic pressing
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
  • C22C33/0285—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5% with Cr, Co, or Ni having a minimum content higher than 5%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon

Definitions

• This invention refers to a method for producing a high speed steel with the composition according to the preamble of claim 1 .
• ion-implantation Ion beam modification of metals, G. Dearnley, Nuclear Instruments and Methods in Physics Research B50 1990 p358-367.
• ion-implantation Ion beam modification of metals, G. Dearnley, Nuclear Instruments and Methods in Physics Research B50 1990 p358-367.
• a problem with ion-implantation is the Gaussian distribution of ions, which causes depth varying material characteristics. Ion-implantation also implies a limited useful thickness of the modified layer; therefore it is not suited for use in the aforementioned applications.
• US Patent No. 5989491 to Isamoto et al. discloses a method that uses oxide dispersion strengthening for a powder metallurgy alloy.
• the inventors behind this patent noted that fine dispersion of particles of an oxide in an oxide dispersion strengthened heat resisting powder metallurgy alloy enhanced creep rupture strength in addition to fundamental heat resisting properties inherent to heat resisting alloys.
• the alloy disclosed in US5989491 is not suitable for mechanical applications involving wear such as those aforementioned, since the wear resistance of the end product will not be affected by the addition of fine particles of an oxide.
• JP2003253396A, and JP1008252A are cumbersome to produce with standard casting techniques.
• JP57085952A discloses an alloy with a composition corresponding to the composition according to the preamble of claim 1 of the present invention. It must be assumed that the document in question also discloses casting as the method of producing the alloy. It must be assumed that the steel disclosed therein has a microstructure that results in poor strength of the material and therefore makes it less usable as a wear part.
• the object of this invention is to present a method by means of which the above mentioned problems associated with manufacturing of high speed steel comprising of rare earth element yttrium (Y) for applications that involve wear at elevated temperatures, are reduced or solved.
• Y rare earth element
• the present invention also aims at providing a manufacturing method which increases the ability of high speed steel to withstand wear at elevated temperatures.
• the present invention is based on the insight of the problems of segregation and coarse carbide structures associated with casting and the addition of yttrium into
• the steel is in solid state, i.e. non-molten state.
• the temperature during said step of elevated temperature is within the range of from 950-1200 'C, wherein lower temperatures may be required for alloys with relatively high content of C and low content of alloying elements such as Mo, W, Co, Y, etc and wherein higher temperatures within said range is required for alloys with relatively low content of C and high content of said further alloying elements. If the temperature is too low, the final result will be a porous material, and if the temperature is too high, the material might start to melt, which should be avoided.
• the pressure during the consolidation step is dependent on the temperature, which is chosen for each respective steel composition.
• a relatively low temperature may be compensated for by means of a higher pressure.
• the pressure should be in the range of from 800-1500 bar. In general, higher content of alloying elements will require a higher pressure for a specific chosen temperature.
• the body of consolidated powder that now has a very low porosity level or no porosity at all, is then subjected to soft annealing.
• the soft annealing is performed in order to facilitate subsequent machining of the alloy.
• the maximum temperature of the soft annealing step is the temperature of the foregoing consolidation step, while the minimum temperature is the temperature at which the steel undergoes softening and carbides in the steel spheroidize and the martensite transforms to ferrite. In any case, the temperature must not be so high that it results in severe coarsening of the carbide grain size.
• the selected soft annealing temperature will depend on the composition of the alloy.
• the body may thereafter be subjected to machining if necessary and thereafter heat treated with a hardening (austenizing) step at a temperature in the range of from 950-1200 ° C, depending on the specific composition of the steel that is hardened. After hardening, there will be some remaining austenite in the steel, the main part of the steel now being
• the technical effect of the method of the present invention as disclosed hereinabove or hereinafter is that the rare earth element yttrium is evenly distributed in the powder. If the high speed steel according to the inventive concept would have been produced by a conventional casting method, the highly reactive element yttrium would segregate and not be evenly distributed. An even distribution of yttrium in the high speed steel base-matrix causes an oxide scale that is formed to adhere effectively to the high speed steel. The added yttrium also changes the growth kinetics of the oxide scale so that the scale quickly grows to a saturation thickness. The growth rate of the oxide scale is drastically reduced above this saturation thickness.
• the beneficial technical effect on the wear resistance, at elevated temperatures, due to the fine dispersion of yttrium in the base-matrix of the high speed steel is unexpectedly good.
• This technical effect is beyond what a person skilled in the art would expect from an addition of yttrium using a powder metallurgy method.
• the gain in technical effect is so high that it, unexpectedly, compensates for the higher costs related to the use of powder metallurgy as the method of producing this steel, making the steel very useful in any application in which it is subjected to severe wear conditions.
• the steel will have a mean carbide particle size which is much lower than that of a corresponding material made using casting method.
• the steel should have a mean carbide particle size of ⁇ 3 ⁇ , something it will have if the method of the invention is being used for the production thereof.
• the steel will also have an isotropic microstructure, which is also advantageous for its wear properties.
• the present invention teaches that the consolidation step and the subsequent heat treating steps shall be performed such that the steel obtains a mean carbide particle size which is ⁇ 3 ⁇ and an isotropic microstructure.
• the provision of the powder mixture comprises the step of argon-atomisation of molten metal comprising said elements into said powder.
• the amount of nitrides is minimized compared to using nitrogen-atomisation wherein the use of nitrogen gas causes the nitrides to form.
• the yttrium content of the high speed steel is within the range 0.20 to 1 .0 weight%. It is preferred that the yttrium content of the high speed steel is more than 0.40 weight%, and less than 0.70 weight% more preferably less than 0.60 weight%.
• the chromium (Cr) content is in the range of from 3.0-6.0 weight%. This interval causes good hardenability as well as the necessary forming of carbides. However, too much chromium causes formation of residual austenite and increased risk for over-tempering; therefore the upper limit of Cr must not be exceeded. According to one embodiment, the Cr content is within the range of from 4.0-5.0 weight%.
• the molybdenum (Mo) content is in the range of from 4.5-5.5 weight%. This interval causes secondary hardening by precipitation of carbides that will increase the hot hardness and wear resistance of the high speed steel.
• the tungsten (W) content is in the range of from 6.0-7.0 weight%. This interval causes secondary hardening by precipitation of carbides that will increase the hot hardness and wear resistance of the high speed steel.
• Mo and W have similar effects on this kind of steel and that they are therefore to a large extent replaceable with each other.
• Mo+0.5W 2-10 weight%.
• Mo+0.5W 5-8.5 weight%. It should be pointed out that the elements having a lower limit of 0 weight% are optional.
• the vanadium (V) content is in the range of from 3.0-5.0 weight%. This interval causes secondary hardening by precipitation of carbides that will increase the hot hardness and wear resistance of the high speed steel. However, too much vanadium causes the high speed steel to become brittle and therefore, the upper limit must not be exceeded. According to a preferred embodiment the V content is in the range of from 3.0-3.5 weight%.
• the cobalt (Co) content of said high speed steel is in the range of from 8.0-9.0 weight%.
• the alloying of high speed steel with cobalt improves the tempering resistance and hot hardness, both of which are of great importance for the high speed steel to be used in a high temperature wear application.
• the amount of cobalt also has an effect on the hardness of the high speed steel by affecting the amount of retained austenite, causing said retained austenite to easily be converted to martensite during tempering.
• the selected interval for cobalt is a suitable interval for a high speed steel of this composition wherein the upper level is more an economic compromise than a scientific constraint.
• the cobalt content is 0% or at an impurity level.
• Powder metallurgical high speed steel produced by the inventive method possesses properties, such as very good resistance to high temperature wear even in
• Figure 1 is a schematic figure of a "pin on disc” test equipment
• Figure 2 shows a cross section of a typical groove obtained from a "pin on disc” evaluation, perpendicular to the longitudinal direction
• Figure 3 is a diagram showing the groove depth at room temperature and 650 Q C for the alloys A, B and C in the "pin on disc” experiment
• Figure 4 is a diagram showing the volume loss per meter at 650 Q C for the alloys A, B and C in the "pin on disc” experiment
• Figure 5 shows the hardness in HRC for alloy A, B and C.
• the industrial production of semi-finished products, components and cutting tools based on powder metallurgical high speed steel started 35 years ago.
• the first powder metallurgical production of high speed steel was based on hot isostatic pressing (HIP) and consolidation of atomized powders.
• the HIP step was normally followed by hot forging of the hipped billets. This method of production is still the dominating powder metallurgical method to produce high speed steel.
• the original objective for research and development on powder metallurgical processing of high speed steel was to improve its functional properties and performance in demanding applications.
• the main advantages from the powder metallurgical manufacturing process are no segregation and uniform and isotropic microstructure.
• the well known problems with coarse and severe carbide segregation in conventional cast steel and forged steel are thus avoided in powder metallurgical high speed steel.
• the powder metallurgical manufacturing method of a high speed steel with sufficient amount of carbon and carbide forming elements results in a disperse distribution of carbides that to a large extent solves the problem of low strength and toughness associated with conventionally produced high speed steel.
• the present invention refers to a method for producing a high speed steel.
• the elements having a lower limit of 0 % are optional.
• the provision of the powder mixture comprises the step of argon gas-atomisation of molten metal comprising said elements into said powder.
• the argon gas-atomisation of the molten high speed steel causes high speed steel particles of a maximum size of 160 ⁇ to be formed.
• a body is formed from said powder. This forming may, for example, comprise pouring said powder into a capsule.
• the capsule is then evacuated, e.g. by being subjected to a negative pressure of below 0.004 mbar for 24 hours in order to evacuate said capsule.
• the capsule is then sealed in order to maintain said negative pressure in the capsule.
• the consolidation of the powder is achieved by subjecting the capsule to an elevated temperature, e.g. about 1 150°C, and an elevated pressure, e.g. about 1000 bar, for a long period of time, e.g. two hours. This last consolidation step is called hot isostatic pressing, HIP.
• Table 1 shows the elements of the high speed steel used in the experiment. Smelts were produced with the elements in table 1 , and from these smelts powders were produced by means of gas atomisation using argon. The powders of alloy B and C in table 1 have a particle size of ⁇ 160 ⁇ , while the powder of alloy A has a particle size of ⁇ 500 ⁇ .
• the yttrium content of the high speed steel is more than 0.4 weight%, and less than 0.7 weight%, more preferably less than 0.6 weight%, more preferably 0.4 to 0.6 weight%, such as 0.4 to 0.5 weight%, such as 0.4, 0.41 , 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49 and 0.5.

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• 2011
  • 2011-09-19 EP EP11181771A patent/EP2570507A1/en not_active Withdrawn
• 2012
  • 2012-09-19 JP JP2014530277A patent/JP2014530294A/ja not_active Withdrawn
  • 2012-09-19 EP EP12759474.5A patent/EP2758558A1/en not_active Withdrawn
  • 2012-09-19 WO PCT/EP2012/068428 patent/WO2013041558A1/en active Application Filing
  • 2012-09-19 CN CN201280045555.7A patent/CN103814145A/zh active Pending
  • 2012-09-19 US US14/345,413 patent/US20140356218A1/en not_active Abandoned

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