[0001] The present disclosure relates to a high-chromium white iron alloy.

BACKGROUND

[0002] High-chromium white iron alloys are generally known. However, a problem is often the rather large carbide crystals formed within the alloy, which may also not be evenly dispersed, increasing the brittleness of the alloy product.

SUMMARY

[0003] It is an objective of the present invention to provide an improved white iron alloy.

[0004] According to an aspect of the present invention, there is provided a high- chromium white iron alloy comprising rare-earth (RE) element. The alloy comprises RE of 0.01-0.6 wt%, Cr of 26-30 wt%, C of 2.5-4 wt%, Si of 0.2-2 wt%, Mn of 0.5-1 wt%, Mo of 0.2-0.5 wt%, Ni of 0.01-0.6 wt%, at most 1 wt% of impurities, and a balance of Fe.

[0005] According to another aspect of the present invention, there is provided a method of preparing a high-chromium white iron alloy comprising RE element. The method comprises adding an RE powder to a metal melt whereby a white iron alloy melt comprising RE is formed. The alloy melt comprises RE of 0.01-0.6 wt%, Cr of 26-30 wt%, C of 2.5-4 wt%, Si of 0.2-2 wt%, Mn of 0.5-1 wt%, Mo of o.2-0.5 wt%, Ni of 0.01- 0.6 wt%, at most 1 wt% of impurities, and a balance of Fe.

[0006] According to another aspect of the present invention, there is provided a white iron product made from an embodiment of the alloy, or alloy melt, of the present disclosure, wherein the white iron product is or comprises any of a dispersing disc, a grinding disc, a refiner disc, an abrasion resistant plate, a mixing blade, a mixing arm or a cutting blade, preferably a dispersing disc, a grinding disc or a refiner disc, most preferably a dispersing disc.

[0007] The at most 1 wt% of impurities typically comprises a plurality of compounds other than those specified herein as part of the alloy or alloy melt, such as copper (Cu) resulting from using scrap metal as an iron source. Each of said compounds of impurity, e.g. Cu, is typically present in an amount of less than 0.5 wt%, less than 0.2 wt%, less than 0.1 wt% or less than 0.05 wt% of the alloy or alloy melt.

[0008] It has now been found by the inventors that the inclusion of RE in an amount within the range of 0.01-0.6 wt% in the alloy results in finer and more well dispersed carbide crystal structures. The carbide crystals are more rounded and thus prevent crack formation in the alloy product. The high chromium content of the present invention results mainly in M ₇ C ₃ carbides (where M is metal, here typically Fe or Cr) being formed, e.g. Fe ₇ C ₃ and/or Cr ₇ C ₃ carbide formation, especially Cr ₇ C ₃ carbide formation. Thus, an effect of the RE used in accordance with the present invention is more rounded carbide crystal structures, where the carbide is mainly comprised of M ₇ C ₃ carbides.

[0009] Different chromium carbides are formed at different chromium contents of an alloy. In steel alloys with up to about 13 wt% Cr, Cr substitutes Fe in the carbide phase cementite (M ₃ C, where M is metal, typically Fe or Cr). At higher Cr content, another carbide phase (M ₇ C ₃ ) is formed with Cr, i.e. Cr ₇ C ₃ . Cr ₇ C ₃ has a more compact structure than cementite and thus a higher hardness and impact strength.

[0010] For embodiments of the present invention, the Cr ₇ C ₃ carbides are desired and the properties of the inventive alloy are improved by the rounding of the Cr ₇ C ₃ carbides provided by the presence of RE. However, when the Cr content is further increased, e.g. above the range of 26-30 wt% and especially above about 35 wt%, the carbide phase may be too dominant in the alloy, making it brittle. Further, for even higher Cr content, especially above 40 wt% Cr, the undesirable carbide phase Cr ₂₃ C ₆ , which is softer and more brittle than Cr ₇ C ₃ , is formed. Since the Cr content in the alloy may typically not be completely homogenous during forming thereof, parts having a Cr content of 40 wt% or more maybe formed also where the overall Cr content is lower, such as above 30 wt%.

[0011] Thus, it has now been found that a Cr content within the range of 26-30 wt%, in combination with an RE content within the range of 0.01-0.6 wt%, results in an alloy comprising the desired carbide Cr ₇ C ₃ in a suitable amount and with the Cr ₇ C ₃ carbides being rounded by the RE present, preventing the formation of cracks. Also, compared with an even higher Cr content, the alloy is harder and stronger, with reduced risk of brittleness resulting from too much carbide phase and/or from presence of undesired Cr ₂₃ C6 carbides. [0012] It is to be noted that any feature of any of the aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any of the other aspects. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0013] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein.

DETAILED DESCRIPTION

[0014] Embodiments will now be described more fully hereinafter. However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0015] In some embodiments, the amount of RE in the alloy, product or alloy melt is within the range of 0.05-0.6 wt% or o.1-0.5 wt%, preferably within the range of o.2-0.4 wt% which maybe a preferred range in some embodiments.

[0016] In some embodiments, the amount of chromium (Cr) in the alloy, product or alloy melt is within the range of 27-29 wt%, which may be a preferred range in some embodiments.

[0017] In some embodiments, the amount of carbon (C) in the alloy, product or alloy melt is within the range of 2.5-3.2 wt%, which maybe a preferred range in some embodiments.

[0018] In some embodiments, the amount of silicon (Si) in the alloy, product or alloy melt is within the range of 0.3-1 wt%, which may be a preferred range in some embodiments.

[0019] In some embodiments, the amount of manganese (Mn) in the alloy, product or alloy melt is within the range of 0.8-1 wt%, which may be a preferred range in some embodiments.

[0020] In some embodiments, the amount of molybdenum (Mo) in the alloy, product or alloy melt is within the range of o.4-0.5 wt%, which may be a preferred range in some embodiments. [0021] In some embodiments, the amount of nickel (Ni) in the alloy, product or alloy melt is within the range of 0.2-04 wt%, which maybe a preferred range in some embodiments.

[0022] There is typically a small amount of inevitable impurities in the alloy, product or alloy melt, e.g. if the iron (Fe) is from scrap metal. The amount of impurities is preferably at most 1 wt%. The at most 1 wt% of impurities typically comprises a plurality of compounds other than those specifically specified herein as part of the alloy or alloy melt, e.g. copper (Cu) resulting from using scrap metal as an iron source. Each of said compounds comprised in the at most 1 wt% of impurities, e.g. Cu, is typically present in an amount of less than 0.5 wt% or less than 0.2 wt%, preferably less than 0.1 wt% or less than 0.05 wt% of the alloy or alloy melt.

[0023] In some embodiments, the RE comprises or consists of cerium (Ce), lanthanum (La) and/or yttrium (Y), preferably Ce (which is easily obtainable).

[0024] The balance of the alloy, product or alloy melt is Fe. In some embodiments, the alloy, product or alloy melt comprises Fe within the range of 60-70 wt%.

[0025] RE powder is added to the metal melt to produce the alloy melt of the present disclosure. The RE powder may have a particle size distribution between 0.2 and 7 mm. The RE powder may have an RE content within the range of 25-40 wt%. The RE powder may comprise or consist of so called mischmetal.

[0026] The alloy melt may be used for casting a product, to obtain a white iron product. The casting is preferably by line forming, shell forming, hand forming or by 3D-printed moulds or cores. Line forming may be preferred, but shell forming has been seen to give primary austenite formation which maybe desirable in some embodiments.

[0027] In some embodiments, the white iron product is or comprises any of a dispersing disc, a grinding disc, a refiner disc, an abrasion resistant plate, a mixing blade, a mixing arm or a cutting blade, preferably a dispersing disc, a grinding disc or a refiner disc, most preferably a dispersing disc.

[0028] The present disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.