EP2803736A1 - Acier au manganèse résistant à l'usure - Google Patents

Acier au manganèse résistant à l'usure Download PDF

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Publication number
EP2803736A1
EP2803736A1 EP20130167522 EP13167522A EP2803736A1 EP 2803736 A1 EP2803736 A1 EP 2803736A1 EP 20130167522 EP20130167522 EP 20130167522 EP 13167522 A EP13167522 A EP 13167522A EP 2803736 A1 EP2803736 A1 EP 2803736A1
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Prior art keywords
tungsten
cast
sample
steel
manganese
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German (de)
English (en)
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Johan EKENGÅRD
Niklas Ehrlin
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Sandvik Intellectual Property AB
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Sandvik Intellectual Property AB
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Priority to EP20130167522 priority Critical patent/EP2803736A1/fr
Priority to PCT/EP2014/054579 priority patent/WO2014183895A1/fr
Publication of EP2803736A1 publication Critical patent/EP2803736A1/fr
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    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a wear resistant manganese steel and its method of production.
  • a particular category of wear resistant steels are typically referred to as Hadfield, manganese or austenitic manganese steels. These materials are suitable for applications where a high toughness and a moderate abrasion resistance are required including for example use as wear parts for crushers that are subjected to strong abrasion and dynamic surface pressures due to the rock crushing action. Abrasion results when the rock material contacts the wear part and strips-off material from the wear part surface. Additionally, the surface of the wear part is subjected to significantly high surface pressures that cause wear part fatigue and breakage.
  • Manganese or Hadfield steel is typically characterised by having an amount of manganese usually above 11% by weight.
  • the ratio of carbon and manganese is typically adjusted such that the ratio by weight of manganese is typically of the order of 10-11 times the weight of carbon.
  • Such steels commonly comprise 0.8 to 1.25% carbon and 11 to 15% manganese by weight as their fundamental composition.
  • fully austenitic (carbide-free) Hadfield steel is typically too ductile for wear parts in modern crushers that are subject to extreme operating conditions. Accordingly, attempts have been made to improve the work hardening characteristic of manganese steels from the fundamental composition by using additional alloying components.
  • chromium, molybdenum, vanadium and tungsten are alloying elements that form strong carbides within the resulting alloy.
  • Hardened manganese alloys are disclosed in US 5,308 , 408 ; RU 2009116306 ; US 2009/123324 ; CN101736658 ; HU197775 ; CN1271028 ; CN101831590 and CN101638753 .
  • existing manganese steels exhibiting enhanced wear resistance are typically energy inefficient to produce, due largely to the very high processing temperatures involved (typically above 1000°C for extended holding times). There is therefore a need for a manganese steel that is energy efficient to produce and exhibits enhanced wear resistance and hardeners so as to find a particular application as a crusher wear part.
  • the objectives are achieved by providing a manganese steel alloy having a microstructure that provides a high hardness of the steel matrix whilst keeping the impact toughness at a desirable level.
  • This is achieved by forming highly dispersed carbides, and in particular tungsten carbides, within the austenite phase (the matrix of the alloy).
  • the solubility of tungsten and carbon in the grain boundaries and within the matrix of the material is achieved by introducing a powdered form of tungsten to the initial base charge steel melt.
  • the tungsten comprises a particle size of less than 200 ⁇ m, 150 ⁇ m, or more preferably less than 100 ⁇ m.
  • the present manganese steel comprises highly dispersed small tungsten carbides precipitated within i) the matrix and optionally ii) within the matrix and at the grain boundaries.
  • a high degree of dispersion is achieved as the small particulate size of the powdered tungsten is dispersed homogenously within the melt.
  • the tungsten may be added in a form of powder-pressed Fe and W (that may be referred to as ferrotungsten). Accordingly, wear parts formed from the present alloy and method do not exhibit segregated physical and mechanical properties to provide a highly wear resistant part whilst maintaining toughness and deformation hardening properties.
  • the present method of producing the manganese steel alloy advantageously comprises a heat treatment phase in which the cast alloy is heat treated at a temperature above a predetermined level.
  • undesirable phases such as a cementite phase of the alloy
  • optimising the heat treatment is important so as to not exceed a predetermined temperature threshold to maintain and not dissolve the phase comprising tungsten carbide.
  • the present method for producing an alloy is configured to establish an equilibrium in the alloy so as to achieve only two desired phases: an austenite phase and a phase comprising tungsten carbide.
  • the present method comprises quenching immediately after heat treatment to ensure these phases are retained and persist at room temperature. Accordingly, a wear part having significant wear resistance is provided.
  • the present alloy comprises uniformly dispersed carbide (preferably tungsten carbide) precipitates throughout the microstructure which, in turn, may be considered to increases the micro hardness of the matrix. Additionally, the carbide is precipitated homogeneously at the different grains such that the microscopic hardness of the alloy is optimised.
  • a method for producing a wear resistant manganese steel comprising: creating a steel melt having a chemical composition by weight: carbon: 0.4 to 2.0%; manganese: 10 to 22%; silicon: 0.2 to 1.0%; tungsten: 0.5 to 5%; chromium: less than or equal to 1.0%; wherein the balance comprises iron and impurities; wherein powdered tungsten or a powdered tungsten containing material is added to the steel melt.
  • the method comprises creating a steel melt having a chemical composition by weight: carbon: 0.4 to 2.0%; manganese: 10 to 16%; silicon: 0.2 to 1.0%; tungsten: 0.5 to 5%; chromium: less than or equal to 1.0%; wherein the balance comprises iron and impurities; wherein powdered tungsten or a powdered tungsten containing material is added to the steel melt.
  • the powdered tungsten is added in the form of ferro tungsten containing pressed powder of Fe and W.
  • briquettes of pressed Fe and W powder are added to the initial base charged melt so as to dissolve readily within the melt to provide homogenous dispersion of tungsten.
  • other forms of powdered tungsten may be suitable optionally in depressed composite form with other elements of the present alloy.
  • a particle size of the powdered tungsten is within the range 2 to 150 ⁇ m. More preferably, the particle size of the powdered tungsten in the range of 10 to 100 ⁇ m.
  • the powdered tungsten is added to the steel melt following an initial melting process of the various other starting materials of the present alloy. Alternatively, the powdered tungsten is added to the starting material components prior to the initial melting process to create the base melt.
  • the method further comprises casting the steel melt to produce a cast.
  • the method comprises heat treating the cast at a temperature between a liquidus temperature of the cast and a precipitation temperature of tungsten carbide within the manganese steel.
  • the method further comprises heat treating the cast at a temperature high enough to dissolve a cementite phase within the manganese steel and below a precipitation temperature of a tungsten carbide within the manganese steel.
  • the method comprises heat treating the cast at a temperature in the range 800 to 1400°C. More preferably, the heat treatment is within the temperature range 950 to 1200 °C; 1000 to 1200 °C and more preferably 1050 to 1150 °C. Preferably, the heat treatment at this elevated temperature represents a final heat treatment of the cast.
  • the method comprises heat treating the cast at the heating temperature for a holding time of 1 hour/25mm thickness of the cast.
  • the heating rate may comprise heating in the order of 100 °C/h.
  • the method further comprises quenching the heat treated cast directly from the heat treatment temperature.
  • the manganese steel comprises a chemical composition by weight: carbon: 1.1 to 1.4%; manganese: 11 to 14%; silicon: 0.4 to 0.8%; tungsten: 2.5 to 3.5%; chromium: less than or equal to 0.5%.
  • a wear resistant manganese steel having a chemical composition by weight: carbon: 0.4 to 2.0%; manganese: 10 to 22%; silicon: 0.2 to 1.0%; tungsten: 0.5 to 5%; chromium: less than or equal to 1.0%; wherein the steel comprises dispersed carbides within a matrix of the steel.
  • the chemical composition by weight comprises manganese at 10 to 16%.
  • the steel comprises dispersed carbide precipitates within an austenite matrix of the steel.
  • the carbides are tungsten carbides. Reference within the specification to 'dispersed' encompasses a generally uniform dispersion of the carbide precipitates within the resulting cast alloy so as to represent carbide islands within the austenite matrix. The carbides are therefore spatially separated from one another in a randomly arranged manner within the austenite grains of the alloy.
  • a method for producing a wear resistant manganese steel comprising: creating a steel melt having a chemical composition by weight: carbon: 0.4 to 2.0%; manganese: 10 to 16%; silicon: 0.2 to 1.0%; tungsten: 0.5 to 5%; chromium: less than or equal to 1.0%; wherein the balance comprises iron and impurities; casting the melt and then heat treating the cast at a temperature: between a liquidus temperature of the cast and a precipitation temperature of tungsten carbide within the manganese steel; at a temperature high enough to dissolve a cementite phase within the manganese steel and below a precipitation temperature of a tungsten carbide within the manganese steel and/or at a temperature in the range 800 to 1400°C; 950 to 1200 °C; 1000 to 1200 °C or 1050 to 1150 °C.
  • a crusher wear part configured to crush material within a crusher comprising manganese steel as claimed herein.
  • the main heat transfer mechanisms in a foundry and heat treatment plant are radiation, conduction and convection.
  • the atomic diffusion both in the melt and in the solid state is closely dependent on temperature, with higher diffusion rates at higher temperatures. Diffusion also is dependent on the rate of temperature change. Any solidification starts by the heat transfer from the melt, and when enough heat has been transferred, the melt starts to solidify at nucleation points, from where the grains start to grow. If the casting is done by pouring the melt into a mould, the nucleation and solidification usually starts at the mould-melt interface. The casting is kept in the mould until it is completely solidified, before it is removed and the casting continues to cool in ambient atmosphere.
  • the present casting is heat treated.
  • the present heat treatment is optimised by temperature, temperature rates and holding times.
  • the heat treatment is followed by a quenching step known to those skilled in the art and comprises submersion of the cast in water, oil or liquid salts with the purpose of attaining a high cooling rate to suppress undesired growth of the lower temperature phases.
  • the inventors have identified that using powdered tungsten (e.g., in the form of pressed Fe and W) followed by a characterised heat temperature and quenching process, an alloy is produced with highly dispersed carbides within the primary phase of the metal (austenite matrix).
  • pressed briquettes of W and Fe powder were used with a particulate size of the W and Fe being in the range 10 to 100 ⁇ m.
  • the specific composition of the briquettes may vary (according to the present example)
  • the objective W composition of the present alloy is between 2.5 to 3.5 wt.%. This concentration range is correlated to the maximum solubility of W in the austenitic matrix which is approximately 3.5 wt.% in the present alloy at and around the present heat treatment process.
  • the melt is prepared with an electric arc furnace which is loaded with scrap iron and alloying elements.
  • the temperature of a tap ready melt should be around 1550 °C, before it is poured into a preheated ladle.
  • the ladle is a bottom pour ladle and the temperature of the melt when in the ladle is around 1510° C.
  • the melt is poured in vacuum moulds of sand and the temperature of the melt is around 1465° C when casted. The cast material is removed from the mould shortly after it has solidified.
  • Heat treatment of the solidified cast is then undertaken at a predetermined temperature, heating rate and holding time.
  • the heating rate should be of the order of 100° C/h.
  • the holding temperature of approximately 1100° C should be kept for at least 1 hour/25 mm (1 hour/inch) casting thickness.
  • the subsequent quenching is to be performed in water down to room temperature.
  • a steel melt was prepared according to table 1.
  • iron scrap 190 kg
  • 44 kg of FeMn and 2 kg of FeSi This was melted and analysed and when the melt had a temperature of 1508° C, 9 kg of pressed briquettes of Fe and W powder was added and after 35 minutes the samples were casted.
  • No Cr was added in order to keep the Cr concentration low in the alloy, with the intention of not letting the formation of Cr carbides compete with the formation of tungsten carbide.
  • the moulds comprised furan sand.
  • the sample was casted as a step casting with three different thicknesses; 25, 50 and 100 mm ( Figure 1 ). The different thicknesses were obtained to give different cooling and heating rates at different sections of the casting to assess the microstructure of the material.
  • a holding temperature of approximately 950 to 980° C and a holding time of 1 h/25 mm was chosen initially in order to try and fully dissolve any carbides in the material.
  • the heating rate of 'laboratory oven' as used is much higher than the heat treatment oven used in typical production and has an average heating rate of about 13.5 °C/min.
  • the temperature was lowered to about 850°C in order to find the equilibrium where the only carbide forming is the tungsten carbide.
  • the holding time at 850°C was again 1 h/25 mm, before the material was quenched in water.
  • the casted step were cut and separated in its different thicknesses prior to the heat treatment.
  • Table 3 lists chosen elements of the present cast as prepared and described above expressed as wt.%.
  • Table 3 Composition of the cast tungsten alloyed manganese steel: Element Mn W c Si Cu Cr Ni V P S wt. % 13.5 3.5 1.4 0.6 0.22 0.1 0.1 0.028 0.05 0.008
  • a Mettler Toledo ML6001E was used to measure the density of the material. In the setup, the density is measured by weighing the sample first in air, then in water. A bigger piece of the cast tungsten manganese steel (1192.6 g) was used to measure the density of the material. The density of the cast material was assumed to be homogenous on the different thicknesses. Five measurements were made on the same sample and in order to homogenize the measurements, the samples were soaked in water prior to the first weighing, to get all of the measurements on wet material.
  • the M1 quality reference material came from a scrapped wear part (mantle) manufactured at a foundry in China.
  • the M1 piece was assumed to have been heat treated according to a standard heating rate 100° C/h and; a heating temperature of 1100° C at a holding time of 1h/25 mm.
  • Table 4 The composition of the used M1 reference material: Element Mn Cr c Si Cu P Ni V Mo S Wt.% 11.07 1.65 1.11 0.6 0.0617 0.0542 0.0379 0.0115 0.0109 0.0103
  • a small piece of the material preferably with the dimensions of 20 x 20 x 20 mm was cut. This was followed by an embedding in a thermosetting resin, done in a Struers LaboPress-3.
  • the produced pellet with the embedded metal sample was then polished in a pre-set polishing program including 5 different steps, all with different polish material. This was done with a Struers TegraPol-15.
  • the sample pellet was rinsed in ethanol and dried with a blow dryer.
  • the material was etched with 2 % nital (2 wt.% nitric acid, HNO 3 in alcohol, in the present case, ethanol).
  • the resin had to be removed to make the sample conducting again and to avoid charging the sample.
  • An XEDS analysis was performed in order to determine the elemental composition within the different phases in the samples.
  • the test undertaken was a standardized test used typically to determine the abrasive index, AI, of a rock material.
  • the metal barrel is 120 mm deep barrel with the diameter of 300 mm.
  • Inside the barrel is a holder to mount a piece of tool steel for testing (standard QRO 90 material) conventionally in the shape of a paddle.
  • standard QRO 90 material standard QRO 90 material
  • the barrel rotates with 72 rpm.
  • the holder with the paddle inside the barrel is rotating 9 times faster, 648 rpm, in the same direction as the outer barrel.
  • the barrel is filled with 400 ⁇ 1 grams of the rock material and run for 15 min.
  • the barrel is emptied of rock material and the rock product is collected, before filling it again with 400 ⁇ 1 grams and run for another 15 min.
  • samples called "thumbs” were prepared, with the intended geometry of 25 x 25 x 6.2 mm. A thickness of 6.2 mm was selected and in further testing by this method, the thickness can be selected as either 6 or 7 mm.
  • These samples were weighed and measured, before placed one by one, unattached within the barrel together with 400 ⁇ 1 grams of rock material.
  • the standardized steel (QRO 90) paddle was weighed and mounted in the holder in the barrel.
  • the wear resistance is related to the volume loss of the sample. Measurements have been made in order to determine the densities of the two materials, the M1 reference and the cast tungsten manganese steel which can be used to calculate a thought volume loss. A statistical test of significance was performed on the obtained data in order to evaluate if there is a material dependent difference in the wear of the tested materials. Brinell hardness tests were performed on the samples after the run in the stone barrel in order to determine if the stone barrel test had induced any deformation hardening of the material. The weight loss of the mounted paddle (QRO 90) was measured in order to facilitate the comparison of the wear between different runs.
  • the barrel was then closed and run for 15 minutes, before the rock material was emptied and replaced with 400 ⁇ 1 grams of unused rock material. Before filling the barrel again it was brushed to remove as much dust material as possible. Also the sample was brushed. The procedure was done 4 times, giving a total running time of 60 minutes, thru 1600 ⁇ 4 grams of rock material for each sample. The sample was then removed and washed first in water and then with 30 % HCl for about 10 seconds before it was rinsed with water again. Then the sample was dried and weighed again. The paddle was dismounted and washed in the same manner as the sample and it too was dried and weighed again. In order to minimize any possible corrosive wear, the rock material was kept dry.
  • the diameter of the residual impression, d, is measured and a hardness number can be calculated.
  • the test was made with a steel ball with the diameter of 10 mm.
  • 20 tests were done on material that had not been run in the stone barrel, so called unaffected material, 5 tests on the reference M1 material (work nr 47617), 5 tests on the thickest section (work nr 47602 - heat treated with v1) and 5 on the mid-section (work nr 47601 - heat treated with v1) of the cast tungsten manganese steel as well as 5 tests on a sample heat treated according to v2 (work nr 47635).
  • Micro hardness test is based on the same principle as the Brinell test, but performed with a much smaller indenter and with a load (F) of between 0.01 kg and 2 kg and denoted in Newtons.
  • F load
  • polished and etched samples were used.
  • the loads used in the test varied depending on the examined phase. On smaller phases, such as the different morphologies of the carbides in the samples, a smaller load was used in order to exclusively measure the intended area. The load was held for 30 seconds in every case.
  • the second method considered was to first perform a Brinell test on a machined and smooth surface, and follow this with micro hardness measurements both within the Brinell indentation and outside of it and hopefully a difference in hardness of the matrix inside the deformed area and outside, could be noted.
  • the purpose of these tests would not be to get a value on how much the material harden on deformation, but to examine both if the material has the ability to deformation harden and if the stone barrel induces any deformation hardening on the material.
  • a Charpy V impact test (to evaluate the brittleness of a material) with sample preparation, was ordered from Exova Materials Technology.
  • the calculated diagram ( Figure 2 ) with the correct composition of our test alloy using Thermo-CalcTM prediction model (a computational thermodynamics software that uses different database packages) is the best prediction available for the present complex alloy.
  • the 13 wt.% of Mn in the alloy will stabilize the austenite phase (2: FCC_A1#1) down to 600° C, before the bcc phase (1: BCC_A2) start to form.
  • the Fe-rich austenite show a maximum solubility of W at about 1.3 at.%, which is about 3.5 wt%. If the austenite phase in the present alloy is stable down to 600° C, this could mean that there will not be any precipitation of metallic W.
  • the other carbides presented in the Thermo-CalcTM are 4: M5C2 and 5: M7C3, both at temperatures below 550° C. These carbides could be Mn 5 C 2 , Mn 7 C 3 , and Cr 7 C 3 but the probable reason that they are present, as shown in figure 2 , is the fact that the calculation is done at full equilibrium and infinite time. In reality a very long holding time at about 550° C and below would have been required if these carbides should form. And since the material is quenched from temperatures well above, these phases can be disregarded.
  • the light microscope analysis was done at three different magnifications, 25, 100 and 500 times magnification.
  • the 500X magnification clearly reveals the lamellar structure around the carbide centre in both the heat treated v1 ( Figure 13 ) sample and the as-cast sample ( Figure 14 ).
  • the matrix in the two samples looks about the same when examined in the light optical microscope.
  • both samples that were heat treated with v2 Figure 15 , 16
  • the lamellar structure has dissolved into smaller point phases. These small phases are also spread in the matrix, but at a lower concentration.
  • the areas of the metallic carbide centre also look smaller after heat treatment v2.
  • the M1 quality ( Figure 17 ) show quite a different microstructure with small spheroidal shaped carbides and an overall smaller total area of visible carbides than by the samples heat treated with v2.
  • the concentration of C in the M1 is only 0.3 wt.% lower than the concentration within the tungsten alloyed manganese sample.
  • the SEM examination was mainly performed to make an X-ray Energy Dispersion Spectroscopy (XEDS) on the different areas and phases of the samples.
  • the SEM and XEDS were performed using a Hitachi S-3700N. Three different samples of the tungsten alloyed manganese steel were examined; one as-cast sample, one with heat treatment v1 and one with heat treatment v2.
  • the XEDS on the matrix of the as-cast sample show a composition as expected for Fe and Mn.
  • the high wt.% of C most likely comes from surface contamination or polishing residues and will probably be higher when performing an area scan as the area/volume ratio is slightly bigger than when performing a point analysis.
  • the wt.% of W is higher than the total added to the alloy. This could mean that the concentration of W in the matrix is not homogenous and is higher at the examined area, or it could be an uncertainty regarding the quantification as the signal detecting W is from the M-peak of W with a less intense signal.
  • the composition of the lamellar structure shows a higher concentration of both W and Mn than in the matrix. Also the wt.% of C is higher.
  • the lamellar structure is probably a mixture of the matrix and different carbides.
  • the carbides could be M6C (either as Fe 3 W 3 C, Fe 3 Mn 3 C or a combination of the both) but could also be a complex of Mn 7 C 3 and Fe 3 C together with either metallic W or WC.
  • point XEDS analyses were performed in order to more precisely determine the composition of the different carbides.
  • an interesting phase is shown.
  • the composition has a stoichiometric relationship between W and C that could indicate WC and the shape of the phase is triangular, also an evidence that point towards WC.
  • the Fe and Mn signal is probably from the matrix beneath the carbide.
  • the area show a higher concentration of C, Mn and W compared to the matrix in Figure 23 .
  • concentrations of Mn and W is lower in the dissolved area than in the lamellar structure of the sample heat treated with v1, which could indicate that the total volume of carbides in the area is lower in the dissolved lamellar phase.
  • a visual inspection also leads to the probable conclusion that this phase is in fact matrix material, with small carbides spread in the phase.
  • a point analysis on the thought matrix at the dissolved lamellar area ( Figure 25 ) show that the composition in fact is very close to the matrix of the sample, which supports the above conclusion regarding the dissolved area.
  • the carbide centre mainly has the same composition as the examined area in Figure 26 . As revealed in the light optical microscope, the phase is usually located in the centre of a dissolved lamellar structure and usually also along grain boundaries.
  • the concentration of W in these phases are typically between 25-30 wt.% or 64-69 wt.%.
  • the examined phase also show a triangular like structure that can be found in alloys containing WC.
  • the signals from Fe and Mn could either come from the underlying matrix or the fact that the phase is a carbide complex of the identified elements (i.e. M6C carbide). It should be mentioned that some of the structures examined showed a concentration of W up to about 45 wt.% or 70 wt.% which could indicate that the phase also contain metallic W or an undissolved particle of the Fe-W powder.
  • Both series of the tungsten manganese steel that were heat treated with v1 have a higher expected mean of the volume loss than the reference material (work nr 47601).
  • the series with the tungsten manganese steel that were heat treated with v2 have the same expected mean of the volume loss as the reference material.
  • the expected mean of the volume loss can be the same for work nr 47635 and work nr 47602.
  • the three different phases that where measured with the micro hardness tester was defined as pictured in Figure 28 .
  • the magnification is 400 times, compared to the magnification of 500 times.
  • Samples that were heat treated with heat treatment v2 had almost no lamellar structure as it had dissolved and the carbide metallic centre had decreased in size.
  • the M1 reference had carbides that were too small to measure.
  • HV 1 is the force of 9.89 N giving the load of 1 kg
  • HV 0.1 is 0.99 N
  • HV 0.05 corresponds to 0.49 N.
  • the carbides were too small to measure, why only the matrix of this sample was measured.
  • the sample nr 4477 and nr 47617 were cut from the M1; the sample nr 4462 and 4462b were cut from the cast tungsten manganese test alloy, where 4462 was heat treated with heat treatment v1 and 4462b was as-cast without any heat treatment.
  • the sample nr 4495 was cut from the tungsten manganese test alloy with sample nr 47602 that was heat treated according to heat treatment v2. Due to the surprisingly high hardness of the matrix in sample 4495, a second test run was performed after the tester was calibrated again to verify the result. The results are shown in figures 30 to 32 .
  • sample nr 4477 the M1 reference, had carbides too small to measure.
  • the sample nr 4477 does not have any lamellar structure between the carbide centre and the matrix that is detectable and measurable with this method.
  • the structure between the carbide centre and the matrix in sample nr 4495 is no longer lamellar and looks like a dissolved lamellar structure, and this was the phase that was examined.
  • the Charpy test performed by Exova AB gave an average value of the absorbed energy for the tungsten alloyed manganese steel (heat treatment v2) of 35 J.
  • the reference M1 material gave an average value of 110 J.
  • the tungsten alloyed material show a much lower ductility than the M1 material.
  • the heat treatment v2 made the material more ductile as expected since the grain boundary carbides had decreased in volume, than by heat treatment v1. This manifested in a lower Brinell hardness and a better result from the stone barrel test.
  • heat treatment v2 there is a metallic/carbide phase in the grain boundaries that is not completely dissolved and most likely still makes the material more brittle than the M1 quality.
  • the phases are not present in the M1 quality, although the difference in carbon concentration is not that large.
  • These metallic/carbide phases are probably a mixture of metallic W and complex carbides such as M6C, which is indicated by the XEDS analysis. If the concentration of W was to be lowered in the alloy and/or a higher holding temperature provided, these phases could be decreased.
  • micro hardness (within the matrix) assessment on the sample heat treated according to v3 it was observed that the sample remained ductile and did not exhibit higher brittleness than the referenced material.
  • the micro hardness (matrix) was found to be approximately 268 HV and a macro hardness of approximately 230 HB. This is to be contrasted with a micro hardness for v1 of around 230 HV; a macro hardness for v1 of approximately 230 HB; a micro hardness for v2 being approximately 370 HV and a macro hardness for v2 being approximately 203 HB.
  • the v3 heat treated sample did not show improvement in mechanical properties based on the above hardness measurements as compared with the reference material.
  • the v3 heat treated sample provided a ductile material with finely dispersed carbides within the grains.
  • an objective of the present invention is to provide small carbides dispersed within the grains that act as dislocation 'lock up' that will enable fast deformation hardening. These carbide precipitates are most likely tungsten carbide in the form of WC (with a hardness of up to 2400 HV) or a carbide with a high concentration of W such as M6C (with a hardness of approximately 1400 HV) and hence reportedly being a harder carbide than a Cr carbide.
  • the fact that the carbides, as confirmed by figure 33 are evenly dispersed within the matrix will accordingly improve the abrasive wear resistance of the resulting material.

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WO2024041687A1 (fr) 2022-08-23 2024-02-29 Schaeffler Technologies AG & Co. KG Actionneur électromécanique
DE102023117976A1 (de) 2022-08-23 2024-02-29 Schaeffler Technologies AG & Co. KG Elektromechanischer Aktuator

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2024041687A1 (fr) 2022-08-23 2024-02-29 Schaeffler Technologies AG & Co. KG Actionneur électromécanique
DE102023117976A1 (de) 2022-08-23 2024-02-29 Schaeffler Technologies AG & Co. KG Elektromechanischer Aktuator

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