Patent Application
20250075301
This application claims the benefit of Chinese Patent Application No. 202311090925.5 filed on Aug. 28, 2023. The entire disclosure of the application referenced above is incorporated herein by reference.
The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The present disclosure relates to tools for die casting, and more particularly to tool steel and surface treated tool steel for die casting of metals.
Tools including dies made of tool steel are used when die casting molten metals. Lubricant is typically applied to surfaces of the dies that contact the molten metal. The lubricant is used between cycles to reduce die temperature and avoid molten metal such as aluminum sticking to the die during die casting. The lubricant requires time to spray onto the surfaces of the die, which reduces productivity. In addition, the lubricant has both adverse economic and environmental effects.
The dies are typically water cooled. When the molten metal is poured into a die cavity, the die typically experiences large thermal gradients which cause thermal fatigue of the die.
A tool steel for a die for casting metal comprises iron (Fe); carbon (C) in a range from 0.001 wt % to 0.1 wt %; copper (Cu) in a range from 0.2 wt % to 2.0 wt %; nickel (Ni) in a range from 3 wt % to 10 wt %; aluminum (Al) in a range from 0.5 wt % to 3 wt %; manganese (Mn) in a range from 0.2 wt % to 1.5 wt %; chromium (Cr) in a range from 0 to 1.5 wt %; molybdenum (Mo) in a range from 0 to 1.5 wt %; tungsten (W) in a range from 0 to 1.5 wt %; and niobium (Nb) in a range from 0 to 0.2 wt %. A transition layer on the steel substrate, having a thickness in a range from 0.1 μm to 3 μm, and metal of the transition layer including Ni in a range from 5 to 20 wt % copper in a range from 1 to 5 wt %. One of an oxide layer and an oxide/nitride layer on the transition layer and having a thickness in a range from 1 μm to 10 μm.
In other features, a ratio of Ni:Al is greater than or equal to 2. The chromium (Cr) is in a range from 0.01 wt % to 1.5 wt %. The molybdenum (Mo) is in a range from 0.01 wt % to 1.5 wt %. The tungsten (W) in a range from 0.01 wt % to 1.5 wt %. The niobium (Nb) is in a range from 0.01 wt % to 0.2 wt %.
In other features, a microstructure of the tool steel after austenitization is a mixture of martensite, bainite and ferrite and nanoprecipitation having a size less than 20 nm and a density greater than 1024/m3 and austenite less than 5% in volume. After quenching from austenitization, a hardness of the tool steel is less than 30 HRC.
In other features, after hardening and oxidizing, the hardness of the tool steel is greater than or equal to 42 HRC. After tempering and oxy-nitriding, the hardness of the tool steel is greater than or equal to 49 HRC. After tempering and surface treatment, thermal conductivity is greater than 35 W/mK.
A method for surface treating tool steel includes providing tool steel comprising iron (Fe), carbon (C) in a range from 0.001 wt % to 0.1 wt %, copper (Cu) in a range from 0.2 wt % to 2 wt %, nickel (Ni) in a range from 3 wt % to 10 wt %, aluminum (Al) in a range from 0.5 wt % to 3 wt %, manganese (Mn) in a range from 0.2 wt % to 1.5 wt %, chromium (Cr) in a range from 0 to 1.5 wt %, molybdenum (Mo) in a range from 0 to 1.5 wt %, tungsten (W) in a range from 0 to 1.5 wt %, and niobium (Nb) in a range from 0 to 0.2 wt %; austenitizing the tool steel at a first temperature in a range from 900° C. to 950° C. for a first period in a range from 0.5 h to 24 h; creating a geometry of a die using the tool steel; and one of: oxidizing the tool steel at a second temperature in a range from 380° C. to 600° C. for a second period in a range from 0.1 h to 40 h; oxy-nitriding the tool steel at a third temperature in a range from 380° C. to 600° C. for a third period in a range from 0.1 h to 48 h; oxidizing the tool steel after hardening at a fourth temperature in a range from 380° C. to 600° C. for a fourth period in a range from 0.1 h to 20 h; and oxy-nitriding the tool steel after hardening at a fifth temperature in a range from 380° C. to 600° C. for a fifth period in a range from 0.1 h to 24 h.
In other features, the method includes using the die to cast one of aluminum and aluminum alloy. The tool steel is oxidized, the second temperature is in a range from 450° C. to 550° C., and the second period is in a range from 2 h to 30 h. In other features, the tool steel is nitrided and oxidized, the third temperature is in a range from 450° C. to 550° C., and the third period is in a range from 2 h to 36 h.
In other features, the tool steel is oxidized, the fourth temperature is in a range from 450° C. to 550° C., and the fourth period is in a range from 1 h to 10 h. The tool steel is nitrided and oxidized, the fifth temperature is in a range from 450° C. to 550° C., and the fifth period is in a range from 1 h to 12 h.
In other features, after one of the oxidizing and the oxidizing and hardening, the tool steel includes an oxide layer having a thickness in a range from 1 μm to 10 μm, and a transition layer having a thickness in a range from 0.1 μm to 3 μm and metal of the transition layer including Ni in a range from 5 to 20 wt % and Cu in a range from 1 to 5 wt.
In other features, after one of the oxy-nitriding and the oxy-nitriding and hardening, the tool steel includes an nitride layer having a thickness in a range from 30 μm to 100 μm; an oxide layer having a thickness in a range from 1 μm to 10 μm; and a transition layer having a thickness in a range from 0.1 μm to 3 μm and metal of the transition layer including Ni in a range from 5 to 20 wt % and Cu in a range from 1 to 5 wt %.
Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims, and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
In the drawings, reference numbers may be reused to identify similar and/or identical elements.
The present disclosure relates to a tool including one or more dies made of tool steel and a surface treatment for the tool steel used for creating the dies. The tool is used to cast components that are made of light metal such as aluminum or aluminum alloy. The tool steel includes a higher concentration of nickel (Ni), aluminum (Al) and copper (Cu) (to improve hardness of tool steel and cohesiveness of the iron oxide layer), and a lower level of carbon (C) (to improve thermal conductivity).
In some examples, the surface treatment includes oxidizing (or oxy-nitriding) the tool steel to form an oxide layer or an oxy-nitride layer. During the oxidizing (oxy-nitriding) process, a transition layer (including metal having higher concentrations of Ni and Cu than the tool steel) forms below the oxide layer. The surface treatment reduces sticking of the casting metal to the dies and increases wear resistance of the dies.
The tool according to the present disclosure can be used to cast light metal components without the need for die lubricants (or optionally with significantly less lubricant). For example, a typical cycle time for conventionally casting a component is about 10-20 s for spraying and blowing when die lubricant is used and a total cycle time of about 40-90 s. For example, a typical cycle time for a casting is less than 0-10 s for spraying and blowing. In some cases, spraying/blowing can be eliminated. In some cases, shorter spraying/blowing can be used. Die lubrication is optional and does not influence the cycle time. Cycle time can be over 40 s in cases of larger castings. In this example, eliminating or reducing the need for die lubricant between casting cycles reduces the cycle time by about 5-30%. As a result, there is less process cost, less environmental pollution due to the die lubricant, and the tool life is longer due to the avoidance of thermal fatigue related to quench.
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After adding the molten metal to the cavity 58, a piston 64 moves through the cavity 58 to force the molten metal into the die cavity 44 as can be seen in
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Ni and Cu are less prone to react with oxygen than iron during oxidizing or oxy-nitriding. In other words, during oxidizing, the atmosphere reacts with an outer surface of the tool steel (i.e., forming oxides with Fe and/or other active elements such as Al and Cr). Ni and Cu do not form oxides and are being expelled from the surface oxides into the steel substrate 162. Additionally, due to the diffusion coefficient of Ni and Cu in iron is low, the Ni and Cu does not diffuse rapidly into the core and their concentrations become much higher at the interface of the core and the oxide layer. As a result, a transition layer 166 (in which a large island of iron oxides are interspersed in a matrix of Ni+Cu rich metal) is formed. As a result, a tight mechanical oxide-metal bond forms between the layer 160 and the steel substrate 162.
During oxy-nitriding, the atmosphere reacts with an outer surface of the tool steel (i.e., forming oxides/nitrides with Fe and/or other active elements such as Al and Cr). The transition layer 166 (that is Ni- and Cu-enriched) forms between the layer 160 and the nitrogen diffusion layer/zone 164. The molten metal contacts the die surface and promotes diffusion of oxygen atoms in molten metal (e.g., Al) into steel substrate. Energy required to expel Ni+Cu metal in the transition layer into core reduces the driving force for internal oxidation, slows down the internal oxidation and leads to fewer voids and better coherence.
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The tool steel according to the present disclosure has a composition as follows: carbon (C) in a range from 0.001 wt % to 0.1 wt %, copper (Cu) in a range from 0.2 wt % to 2 wt %, nickel (Ni) in a range from 3 wt % to 10 wt %, aluminum (Al) in a range from 0.5 wt % to 3 wt %, manganese (Mn) in a range from 0.2 wt % to 1.5 wt %, chromium (Cr) in a range from 0 to 1.5 wt %, molybdenum (Mo) in a range from 0 to 1.5 wt %, tungsten (W) in a range from 0 to 1.5 wt %, niobium (Nb) in a range from 0 to 0.2 wt %, and the balance comprising iron (Fe) and other components.
In some examples, a ratio of Ni:Al is greater than or equal to 2 to ensure full precipitation of Al and reduce interstitial Al that cause lattice distortion and reduces thermal conductivity.
In some examples, chromium (Cr) is in a range from 0.01 wt % to 1.5 wt %. In some examples, molybdenum (Mo) is in a range from 0.01 wt % to 1.5 wt %. In some examples, tungsten (W) is in a range from 0.01 wt % to 1.5 wt %. In some examples, (Nb) is in a range from 0.01 wt % to 0.2 wt %.
In some examples, the microstructure of the tool steel is a mixture of martensite, bainite and ferrite and nanoprecipitation having a size less than 20 nm and a density greater than 1024/m3. with unavoidable austenite (less than 5% in volume).
In some examples, the layer 160 has a thickness in a range from 1.0 μm and 10 μm. In some examples, the transition layer 166 has a thickness in a range from 0.1 μm and 3 μm. Metal of the transition layer 166 includes Ni in a range from 5 wt % to 20 wt % and copper in a range from 1 wt % to 5 wt %. In some examples, after oxy-nitriding, the nitrogen diffusion layer/zone 164 has a thickness in a range of 30 μm and 100 μm.
After austenitizing, hardness of the tool steel is less than 30 HRC. After hardening and oxidizing, hardness of the tool steel is greater than or equal to 42 HRC. After hardening and oxy-nitriding, hardness of the nitrogen diffusion layer/zone is greater than or equal to 49 HRC. Thermal conductivity after surface treatment is greater than 35 W/mK.
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In some examples, ageing is combined with oxidizing or oxy-nitriding so that the efficiency of die manufacturing can be improved and cost reduced. Austenitizing (or called solution treatment for this material) dissolves Ni, Al, Cu into the steel matrix, which reduces the hardness of the steel. Then, the ageing treatment induces Ni (Fe, Al) and Cu nanoprecipitation and improves hardness. In this disclosure, the temperature/time range of ageing and oxidizing/oxy-nitriding is largely overlapping so that the process time is not lengthened substantially. Optionally, another ageing treatment can be conducted before or after oxidizing or oxy-nitriding to obtain desired hardness (usually harder is better)).
The method for making a die according to the present disclosure reduces processing steps by integrating surface treatment with heat treatment and reduces time for integrating surface treatment due to quick oxidizing or oxy-nitriding. As a result, the cost and production lead time for creating the dies is reduced.
If oxidizing is performed after austenitizing, the die is oxidized at a second temperature in a second temperature range from 380° C. to 600° C. for a second predetermined period in a range from 0.1 h to 40 h. In some examples, the second temperature range is from 450° C. to 550° C. In some examples, the second predetermined period is in a range from 2 h to 30 h. The die is then cooled to room temperature.
If oxy-nitriding is performed after austenitizing, the die is oxy-nitrided at a second temperature in a second temperature range from 380° C. to 600° C. for a second predetermined period in a range from 0.1 h to 48 h. In some examples, the second temperature range is from 450° C. to 550° C. In some examples, the second predetermined period is in a range from 2 h to 36 h. The die is then cooled to room temperature.
If oxidizing is performed after austenitizing and hardening, the die is oxidized at a third temperature in a third temperature range from 380° C. to 600° C. for a third predetermined period in a range from 0.1 h to 20 h. In some examples, the third temperature range is from 450° C. to 550° C. In some examples, the third predetermined period is in a range from 1 h to 10 h. The die is then cooled to room temperature.
If oxy-nitriding is performed after austenitizing and hardening, the die is oxy-nitrided at a third temperature in a third temperature range from 380° C. to 600° C. for a third predetermined period in a range from 0.1 h to 24 h. In some examples, the third temperature range is from 450° C. to 550° C. In some examples, the third predetermined period is in a range from 1 h to 12 h. The die is then cooled to room temperature.
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The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.
Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023110909255 | Aug 2023 | CN | national |
