Surface-treated tool steel for metal die casting

Abstract

The invention relates to a surface-treated tool steel for metal die casting. The tool steel contains iron (Fe); 0.001% to 0.1% by weight of carbon (C); from 0.2 wt% to 2.0 wt% of copper (Cu); 3% to 10% by weight of nickel (Ni); 0.5 wt% to 3 wt% of aluminum (Al); from 0.2 wt% to 1.5 wt% of manganese (Mn); 0 to 1.5 wt% chromium (Cr); from 0 to 1.5 wt% molybdenum (Mo); 0 to 1.5% by weight of tungsten (W); and from 0 to 0.2 wt% niobium (Nb). And the transition layer is arranged on the steel base material. The metal of the transition layer includes 5 to 20% by weight of Ni and 1 to 5% by weight of copper. One of an oxide layer and an oxide / nitride layer is disposed on the transition layer.

Description

Technical Field

[0001] The present disclosure relates to tools for die casting, and more particularly to tool steels and surface treated tool steels for metal die casting. Background Art

[0002] The information provided in this section is for the purpose of generally presenting the background of the present disclosure. The work of the presently named inventors, to the extent described in this section, and aspects of the specification that may not constitute prior art at the time of filing are neither expressly nor impliedly admitted to be prior art to the present disclosure.

[0003] The present disclosure relates to tools for die casting, and more particularly to tool steels and surface treated tool steels for metal die casting.

[0004] When die casting molten metal, a tool including a mold made of tool steel is used. Lubricants are usually applied to the surface of the mold that contacts the molten metal. Lubricants are used between cycles to reduce the mold temperature and prevent molten metal such as aluminum from sticking to the mold during the die casting process. Lubricants require time to spray onto the mold surface, which reduces productivity. In addition, the lubricants have adverse economic and environmental impacts.

[0005] The mold is usually water-cooled. When the molten metal is poured into the mold cavity, the mold usually experiences a large thermal gradient, which causes thermal fatigue of the mold. Summary of the invention

[0006] Tool steel for a mold for casting metal contains iron (Fe); 0.001 wt% to 0.1 wt% carbon (C); 0.2 wt% to 2.0 wt% copper (Cu); 3 wt% to 10 wt% nickel (Ni); 0.5 wt% to 3 wt% aluminum (Al); 0.2 wt% to 1.5 wt% manganese (Mn); 0 to 1.5 wt% chromium (Cr); 0 to 1.5 wt% molybdenum (Mo); 0 to 1.5 wt% tungsten (W); and 0 to 0.2 wt% niobium (Nb). The transition layer on the steel substrate has a thickness of 0.1 μm to 3 μm, and the metal of the transition layer contains 5 to 20 wt% Ni and 1 to 5 wt% copper. One of the oxide layer and the oxide / nitride layer is on the transition layer and has a thickness of 1 μm to 10 μm.

[0007] In other features, the ratio of Ni:Al is greater than or equal to 2. Chromium (Cr) is 0.01 wt% to 1.5 wt%. Molybdenum (Mo) is 0.01 wt% to 1.5 wt%. Tungsten (W) is 0.01 wt% to 1.5 wt%. Niobium (Nb) is 0.01 wt% to 0.2 wt%.

[0008] In other features, the microstructure of the tool steel after austenitization is martensite, bainite and ferrite with particles having a size less than 20 nm and particles greater than 10 nm. 24 / m 3 In other features, a microstructure of the tool steel after austenitization is a mixture of martensite, bainite and ferrite and nanoprecipitation having asize less than 20nm and a density greater than 10 24 / m 3 and austenite less than 5% in volume). After quenching by austenitization, the hardness of the tool steel is less than 30HRC.

[0009] In other features, the hardness of the tool steel after hardening and oxidation 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, the thermal conductivity is greater than 35 W / mK.

[0010] The method for surface treating tool steel includes providing a tool steel comprising iron (Fe), 0.001 wt % to 0.1 wt % carbon (C), 0.2 wt % to 2 wt % copper (Cu), 3 wt % to 10 wt % nickel (Ni), 0.5 wt % to 3 wt % aluminum (Al), 0.2 wt % to 1.5 wt % manganese (Mn), 0 to 1.5 wt % chromium (Cr), 0 to 1.5 wt % molybdenum (Mo), 0 to 1.5 wt % tungsten (W) and 0 to 0.2 wt % niobium (Nb); treating the tool steel with austenitic stainless steel at a first temperature of 900° C. to 950° C. The invention relates to a method of manufacturing a mold tool steel having a first period of time of 0.5 to 24 hours of bodying; using the tool steel to produce a mold geometry; and one of the following: oxidizing the tool steel at a second temperature of 380°C to 600°C for a second period of time of 0.1 to 40 hours; oxy-nitriding the tool steel at a third temperature of 380°C to 600°C for a third period of time of 0.1 to 48 hours; oxidizing the hardened tool steel at a fourth temperature of 380°C to 600°C for a fourth period of time of 0.1 to 20 hours; and oxy-nitriding the hardened tool steel at a fifth temperature of 380°C to 600°C for a fifth period of time of 0.1 to 24 hours.

[0011] In other features, the method includes casting one of aluminum and an aluminum alloy using the mold. The tool steel is oxidized, the second temperature is 450° C. to 550° C., and the second time period is 2 hours to 30 hours. In other features, the tool steel is nitrided and oxidized, the third temperature is 450° C. to 550° C., and the third time period is 2 hours to 36 hours.

[0012] In other features, the tool steel is oxidized, the fourth temperature is 450°C to 550°C, and the fourth time period is 1 hour to 10 hours. The tool steel is nitrided and oxidized, the fifth temperature is 450°C to 550°C, and the fifth time period is 1 hour to 12 hours.

[0013] In other features, after one of oxidation and oxidation and hardening, the tool steel includes an oxide layer having a thickness of 1 μm to 10 μm, and a transition layer having a thickness of 0.1 μm to 3 μm, and the metal of the transition layer includes 5 to 20 wt % Ni and 1 to 5 wt % Cu.

[0014] In other features, after one of oxy-nitriding and oxy-nitriding and hardening, the tool steel includes a nitride layer having a thickness of 30 μm to 100 μm; an oxide layer having a thickness of 1 μm to 10 μm; and a transition layer having a thickness of 0.1 μm to 3 μm, and the metal of the transition layer includes 5 to 20 wt % Ni and 1 to 5 wt % Cu.

[0015] The present disclosure includes the following aspects:

[0016] 1. Tool steel for molds for casting metals, comprising:

[0017] a steel substrate comprising iron (Fe), 0.001 wt% to 0.1 wt% carbon (C), 0.2 wt% to 2.0 wt% copper (Cu), 3 wt% to 10 wt% nickel (Ni), 0.5 wt% to 3 wt% aluminum (Al), 0.2 wt% to 1.5 wt% manganese (Mn), 0 to 1.5 wt% chromium (Cr), 0 to 1.5 wt% molybdenum (Mo), 0 to 1.5 wt% tungsten (W), and 0 to 0.2 wt% niobium (Nb);

[0018] A transition layer having a thickness of 0.1 μm to 3 μm, and the metal of the transition layer comprises 5 to 20 wt % Ni and 1 to 5 wt % copper; and

[0019] One of an oxide layer and an oxide / nitride layer having a thickness of 1 μm to 10 μm.

[0020] 2. The tool steel of aspect 1, wherein the ratio of Ni:Al is greater than or equal to 2.

[0021] 3. The tool steel of aspect 1, wherein the chromium (Cr) is 0.01 wt % to 1.5 wt %.

[0022] 4. The tool steel of aspect 1, wherein the molybdenum (Mo) is 0.01 wt % to 1.5 wt %.

[0023] 5. The tool steel according to aspect 1, wherein the tungsten (W) is 0.01 wt % to 1.5 wt %.

[0024] 6. The tool steel of aspect 1, wherein the niobium (Nb) is 0.01 wt % to 0.2 wt %.

[0025] 7. The tool steel of aspect 1, wherein the microstructure of the tool steel after austenitization is martensite, bainite and ferrite with a size of less than 20 nm and a size of greater than 10 24 / m 3 A mixture of a density of and less than 5 volume % of austenite nanoprecipitates.

[0026] 8. The tool steel of aspect 1, wherein after quenching by austenitizing, the hardness of the tool steel is less than 30 HRC.

[0027] 9. The tool steel of aspect 8, wherein one of the following is satisfied:

[0028] The hardness of the tool steel after hardening and oxidation is greater than or equal to 42 HRC; and

[0029] After tempering and oxy-nitriding, the hardness of the tool steel is greater than or equal to 49 HRC.

[0030] 10. The tool steel of aspect 1, wherein after tempering and surface treatment, the thermal conductivity is greater than 35 W / mK.

[0031] 11. The tool steel of aspect 1, wherein the tool steel includes one of the nitride layers having a thickness of 30 μm to 100 μm.

[0032] 12. A method for surface treating tool steel comprising:

[0033] A tool steel is provided, the tool steel comprising:

[0034] iron (Fe), 0.001 wt% to 0.1 wt% carbon (C), 0.2 wt% to 2 wt% copper (Cu), 3 wt% to 10 wt% nickel (Ni), 0.5 wt% to 3 wt% aluminum (Al), 0.2 wt% to 1.5 wt% manganese (Mn), 0 to 1.5 wt% chromium (Cr), 0 to 1.5 wt% molybdenum (Mo), 0 to 1.5 wt% tungsten (W), and 0 to 0.2 wt% niobium (Nb);

[0035] austenitizing the tool steel at a first temperature of 900° C. to 950° C. for a first period of 0.5 to 24 hours;

[0036] using said tool steel to produce a die geometry; and

[0037] One of the following:

[0038] oxidizing the tool steel at a second temperature of 380° C. to 600° C. for a second period of 0.1 hour to 40 hours;

[0039] oxy-nitriding the tool steel at a third temperature of 380° C. to 600° C. for a third period of 0.1 hour to 48 hours;

[0040] Oxidizing the hardened tool steel at a fourth temperature of 380° C. to 600° C. for a fourth period of 0.1 hour to 20 hours; and

[0041] The oxy-nitriding hardened tool steel is subjected to a fifth period of time of 0.1 hour to 24 hours at a fifth temperature of 380° C. to 600° C.

[0042] 13. The method of aspect 12, further comprising using the mold to cast one of aluminum and an aluminum alloy.

[0043] 14. The method of aspect 12, wherein the tool steel is oxidized, the second temperature is 450° C. to 550° C., and the second period of time is 2 hours to 30 hours.

[0044] 15. The method of aspect 12, wherein the tool steel is nitrided and oxidized, the third temperature is 450° C. to 550° C., and the third period of time is 2 hours to 36 hours.

[0045] 16. The method of aspect 12, wherein the tool steel is oxidized, the fourth temperature is 450° C. to 550° C., and the fourth period of time is 1 hour to 10 hours.

[0046] 17. The method of aspect 12, wherein the tool steel is nitrided and oxidized, the fifth temperature is 450° C. to 550° C., and the fifth period of time is 1 hour to 12 hours.

[0047] 18. The method of aspect 12, wherein after one of oxidation and oxidation and hardening, the tool steel comprises:

[0048] An oxide layer having a thickness of 1 μm to 10 μm, and

[0049] The transition layer has a thickness of 0.1 μm to 3 μm, and the metal of the transition layer includes 5 to 20 wt % Ni and 1 to 5 wt % Cu.

[0050] 19. The method of aspect 12, wherein after one of oxy-nitriding and oxy-nitriding and hardening, the tool steel comprises:

[0051] a nitride layer having a thickness of 30 μm to 100 μm;

[0052] an oxide layer having a thickness of 1 μm to 10 μm; and

[0053] The transition layer has a thickness of 0.1 μm to 3 μm, and the metal of the transition layer includes 5 to 20 wt % Ni and 1 to 5 wt % Cu.

[0054] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings.The detailed description and specific examples are intended for illustrative purposes only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0056] Figures 1A to 1E is a side cross-sectional view of an example of a tool including a mold made of a conventional tool steel such as H13 in a casting process for a light metal such as aluminum;

[0057] Figure 2A is a side cross-sectional view of an example of a tool including a die made of a tool steel having a surface treatment according to the present disclosure;

[0058] Figure 2B and 2C is a side cross-sectional view showing an example of surface treatments including oxidation and oxy-nitriding, respectively, of a tool steel according to the present disclosure;

[0059] Figure 3A and 3B are enlarged views showing H13 tool steel and tool steel having a surface treatment according to the present disclosure, respectively;

[0060] Figure 4 is a graph showing thermal conductivity of H13 tool steel and tool steel having a surface treatment according to the present invention;

[0061] Figure 5 is a side cross-sectional view of a mold including one or more cooling channels during heating by molten metal;

[0062] Figure 6 is a graph showing an example of tool steel temperature as a function of time during austenitizing, geometry forming, hardening, and oxidation (or oxy-nitriding) according to the present disclosure;

[0063] Fig. 7Ais a cross-sectional view showing the cohesion of the surface layer after oxidation (or oxy-nitridation) of a tool steel having a surface treatment according to the present disclosure; and

[0064] Figure 7B is a cross-sectional view showing the cohesion of the surface layer of a hardened tool steel having a surface treatment according to the present disclosure after immersion in molten aluminum.

[0065] Among the drawings, reference numerals may be repeated to identify similar and / or identical elements. DETAILED DESCRIPTION

[0066] The present disclosure relates to a tool comprising one or more molds made of tool steel and a surface treatment of the tool steel used to produce the mold. The tool is used to cast parts made of light metals such as aluminum or aluminum alloys. The tool steel contains relatively high concentrations of nickel (Ni), aluminum (Al) and copper (Cu) (to improve the hardness of the tool steel and the cohesion of the iron oxide layer), and relatively low levels of carbon (C) (to improve thermal conductivity).

[0067] In some examples, the surface treatment includes oxidizing (or oxy-nitriding) the tool steel to form an oxide layer or an oxynitride layer. During the oxidation (oxy-nitriding) process, a transition layer (metal containing Ni and Cu at a higher concentration than the tool steel) is formed under the oxide layer. The surface treatment reduces the adhesion of the cast metal to the mold and improves the wear resistance of the mold.

[0068] Tools according to the present disclosure can be used for casting light metal parts without mold lubricants (or optionally using significantly less lubricants). For example, when using mold lubricants, the typical cycle time of conventional casting parts is about 10-20 seconds for spraying and blowing, and the total cycle time is about 40-90 seconds. For example, the typical cycle time of casting is less than 0-10 seconds for spraying and blowing. In some cases, spraying / blowing can be eliminated. In some cases, shorter spraying / blowing can be adopted. Mold lubrication is optional and does not affect the cycle time. In the case of larger castings, the cycle time can exceed 40 seconds. In this example, eliminating or reducing the need for mold lubricants between casting cycles reduces the cycle time by about 5-30%. As a result, the process cost is lower, the environmental pollution caused by mold lubricants is less, and the tool life is longer due to avoiding thermal fatigue associated with quenching.

[0069] Now refer to Figures 1A to 1E, shows an example of a tool 30, which includes a first mold portion 42A, a second mold portion 42B, and a mold filling portion 51 defining a cavity 58. The first mold portion 42A and the second mold portion 42B define a mold cavity 44 and a gate 48 in fluid communication with the cavity 58. An ingot 56 is used to pour molten metal 60 through an opening 54 into the cavity 58 of the mold filling portion 51. The tool 30 includes a core pin 68 to eject the casting.

[0070] like Figure 1B and 1C As can be seen in FIG. 5 , after the molten metal is added to the cavity 58, the piston 64 moves through the cavity 58 to force the molten metal into the die cavity 44. The piston 64 fills the die cavity 44 with the molten metal and applies pressure. The molten metal cools and solidifies, and as shown in FIG. Figure 1D As shown in FIG. 1 , the casting 70 can be ejected by moving the first mold section 42A and the second mold section 42B apart. Figure 1E In the embodiment of the present invention, the spray system 80 sprays air and / or lubricant onto the surface of the tool 30 and blows water away from the surface.

[0071] Now refer to Figures 2A to 2B , the mold 150 is made of a tool steel 152 having a surface treatment 156 according to the present disclosure. As will be further described below, the tool steel 152 contains higher levels of nickel (Ni), aluminum (Al) and copper (Cu), and lower levels of carbon (C) than conventional tool steels used for light metal casting. The mold 150 also includes a surface treatment 156 that involves oxidation (or oxy-nitriding) to reduce adhesion to the casting and improve the wear resistance of the mold 150.

[0072] Now refer to Figure 2B , showing a surface treatment 156 after austenitizing, hardening and oxidation. The tool steel 152 includes a steel substrate 162, a transition layer 166 including iron oxide and a metal including nickel (Ni) and copper (Cu), and an oxide layer 160.

[0073] Now refer to Figure 2C , showing the surface treatment 156 after austenitizing, hardening and oxy-nitriding. The tool steel 152 includes a steel substrate 162, a nitrogen diffusion layer / region 164, a transition layer 166, and an oxide layer 160.

[0074] Ni and Cu are less reactive with oxygen than iron during oxidation or oxy-nitridation. In other words, during oxidation, the atmosphere reacts with the outer surface of the tool steel (i.e., forms oxides with Fe and / or other active elements such as Al and Cr). Ni and Cu do not form oxides, and are expelled from the surface oxides into the steel substrate 162. In addition, due to the low diffusion coefficients of Ni and Cu in iron, Ni and Cu do 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 is formed (in which large iron oxide islands are interspersed in a matrix of Ni+Cu rich metal). As a result, a tight mechanical oxide-metal bond is formed between the layer 160 and the steel substrate 162.

[0075] During the oxynitriding process, the atmosphere reacts with the outer surface of the tool steel (i.e., forming oxides / nitrides with Fe and / or other active elements such as Al and Cr). A transition layer 166 (i.e., rich in Ni and Cu) is formed between the layer 160 and the nitrogen diffusion layer / region 164. The molten metal contacts the mold surface and promotes the diffusion of oxygen atoms in the molten metal (e.g., Al) into the steel substrate. The energy required to expel the Ni+Cu metal in the transition layer into the core reduces the driving force for internal oxidation, slowing internal oxidation and resulting in fewer voids and better cohesion.

[0076] Now refer to Figure 3A and 3B , respectively, show the difference between a conventional tool steel such as H13 and a tool steel with a surface treatment according to the present disclosure. Conventional tool steels such as H13 are medium carbon steels with a carbon content of about 0.4%. Strengthening is based on martensite with a high defect density and a certain content of carbides. However, due to these defects, thermal conductivity is reduced.

[0077] exist Figure 3B The tool steel according to the present disclosure has a carbon content of 0.001 wt. % to 0.1 wt. %. Strengthening is based on Ni (Fe, Al) and Cu nanoprecipitations. The tool steel according to the present disclosure has a much lower microstructural defect density and higher thermal conductivity.

[0078] Now refer to Figure 4 , the thermal conductivity of the tool steel according to the present disclosure (at 182) is about 40% higher than the thermal conductivity of the H13 tool steel (at 180) at all production temperatures. Both have the same hardness.

[0079] Now refer to Figure 5, the mold 190 typically includes one or more cooling channels 194 for receiving coolant. When molten metal such as aluminum contacts the mold surface, there is a large temperature gradient (heat from the molten metal is shown at 196). Since the mold is made of tool steel with an ultra-low carbon chemical composition, the mold has a high thermal conductivity. The high thermal conductivity allows heat to spread more evenly throughout the mold, and thus the mold has an overall lower surface temperature. The lower surface temperature inhibits the reaction between the tool steel and the molten metal (e.g., Al) to avoid the metal sticking / welding to the tool steel.

[0080] The tool steel according to the present disclosure has the following composition: 0.001 wt% to 0.1 wt% of carbon (C), 0.2 wt% to 2 wt% of copper (Cu), 3 wt% to 10 wt% of nickel (Ni), 0.5 wt% to 3 wt% of aluminum (Al), 0.2 wt% to 1.5 wt% of manganese (Mn), 0 to 1.5 wt% of chromium (Cr), 0 to 1.5 wt% of molybdenum (Mo), 0 to 1.5 wt% of tungsten (W), 0 to 0.2 wt% of niobium (Nb), and the balance includes iron (Fe) and other components.

[0081] In some examples, the ratio of Ni:Al is greater than or equal to 2 to ensure complete precipitation of Al and reduce interstitial Al that causes lattice distortion and reduces thermal conductivity.

[0082] In some examples, chromium (Cr) is 0.01 wt % to 1.5 wt %. In some examples, molybdenum (Mo) is 0.01 wt % to 1.5 wt %. In some examples, tungsten (W) is 0.01 wt % to 1.5 wt %. In some examples, (Nb) is 0.01 wt % to 0.2 wt %.

[0083] In some examples, the microstructure of the tool steel is martensite, bainite and ferrite with particles having a size less than 20 nm and particles greater than 10 nm. 24 / m 3 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 10 24 / m 3.with unavoidable austenite(less than5%in volume)).

[0084] In some examples, the layer 160 has a thickness of 1.0 μm to 10 μm. In some examples, the transition layer 166 has a thickness of 0.1 μm to 3 μm. The metal of the transition layer 166 includes 5 wt % to 20 wt % Ni and 1 wt % to 5 wt % copper. In some examples, after oxy-nitridation, the nitrogen diffusion layer / region 164 has a thickness of 30 μm to 100 μm.

[0085] After austenitizing, the hardness of the tool steel is less than 30HRC. After hardening and oxidation, the hardness of the tool steel is greater than or equal to 42HRC. After hardening and oxy-nitriding, the hardness of the nitrogen diffusion layer / area is greater than or equal to 49HRC. The thermal conductivity after surface treatment is greater than 35W / mK.

[0086] Now refer to Figure 6 , the tool steel is austenitized at 320 at a temperature of 900° C. to 950° C. for a first predetermined period of 0.5 hour to 24 hours (e.g., after forging or rolling). After austenitizing, the geometry of the die is produced at 330 using any suitable method. After the geometry of the die is produced at 330, the die is oxidized or oxynitrided at 340 at a temperature of 380° C. to 600° C. while hardening for a second predetermined period of 0.1 hour to 48 hours. Oxidation or oxy-nitriding treatment may also be performed alone after austenitizing and hardening at a temperature of 400° C. to 600° C. for a third predetermined period of 0.1 hour to 30 hours. Oxidation is performed by exposing the tool steel to an atmosphere containing oxygen. Nitriding is performed by exposing the tool steel to an atmosphere containing nitrogen.

[0087] In some examples, aging is combined with oxidation or oxy-nitriding, which can improve the efficiency of mold manufacturing and reduce costs. Austenitization (or solution treatment of such materials) dissolves Ni, Al, and Cu into the steel matrix, which reduces the hardness of the steel. Subsequently, aging treatment causes Ni (Fe, Al) and Cu nanoprecipitation and improves hardness. In the present disclosure, the temperature / time ranges of aging and oxidation / oxy-nitriding overlap to a large extent, thereby substantially not extending the process time. Optionally, another aging treatment may be performed before or after oxidation or oxy-nitriding to obtain the desired hardness (usually the harder the better).

[0088] The method for manufacturing a mold according to the present disclosure reduces the processing steps by integrating surface treatment with heat treatment, and reduces the time for integrating surface treatment due to rapid oxidation or oxy-nitridation. As a result, the cost and production lead time for producing the mold are reduced.

[0089] If oxidation is performed after austenitizing, the mold is oxidized at a second temperature in a second temperature range of 380° C. to 600° C. for a second predetermined period of time of 0.1 to 40 hours. In some examples, the second temperature range is 450° C. to 550° C. In some examples, the second predetermined period of time is 2 to 30 hours. The mold is then cooled to room temperature.

[0090] If oxy-nitriding is performed after austenitizing, the mold is oxy-nitrided at a second temperature in a second temperature range of 380° C. to 600° C. for a second predetermined period of time of 0.1 to 48 hours. In some examples, the second temperature range is 450° C. to 550° C. In some examples, the second predetermined period of time is 2 to 36 hours. The mold is then cooled to room temperature.

[0091] If oxidation is performed after austenitizing and hardening, the mold is oxidized at a third temperature in a third temperature range of 380° C. to 600° C. for a third predetermined period of time of 0.1 to 20 hours. In some examples, the third temperature range is 450° C. to 550° C. In some examples, the third predetermined period of time is 1 to 10 hours. The mold is then cooled to room temperature.

[0092] If oxy-nitriding is performed after austenitizing and hardening, the mold is oxy-nitrided at a third temperature in a third temperature range of 380° C. to 600° C. for a third predetermined period of time of 0.1 to 24 hours. In some examples, the third temperature range is 450° C. to 550° C. In some examples, the third predetermined period of time is 1 to 12 hours. The mold is then cooled to room temperature.

[0093] Now refer to Fig. 7A , showing a transition layer with interpenetration of oxide and metal after surface treatment according to the present disclosure. There are concentrations of iron oxide and Ni+Cu metal in this thin layer. Figure 7B As can be seen in the figure, after molten Al immersion, the cohesion of the surface oxide layer is shown, and fewer and smaller voids are formed due to the transition layer chemistry of the tool mold (e.g., higher levels of Ni and Cu) suppressing internal oxidation.

[0094] The foregoing description is merely illustrative, and is by no means intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in various forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be so limited, because after studying the drawings, the specification and the appended claims, other modifications will become apparent. It should be understood that, without changing the principles of the present disclosure, one or more steps in the method can be performed in different orders (or simultaneously). In addition, although each embodiment is described above as having certain features, any one or more of those features described in any embodiment of the present invention can be implemented in any of other embodiments and / or combined with the features of any of other embodiments, even if the combination is not explicitly described. In other words, the embodiments described are not mutually exclusive, and the replacement of one or more embodiments with each other remains within the scope of the present disclosure.

[0095] Various terms are used to describe the spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.), including "connected," "engaged," "coupled," "adjacent," "immediately adjacent," "on top," "above," "below," and "disposed." Unless explicitly described as "directly," when the relationship between a first and a second element is described in the above disclosure, the relationship can be a direct relationship in which there are no other intervening elements between the first and second elements, but can also be an indirect relationship in which there are one or more intervening elements (spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be interpreted to mean a logical (A or B or C) using a non-exclusive logical "or," and should not be interpreted to mean "at least one of A, at least one of B, and at least one of C."

Claims

1. Tool steel for surface treatment of a mold for casting metal, comprising: a steel substrate comprising iron (Fe), 0.001 wt% to 0.1 wt% carbon (C), 0.2 wt% to 2.0 wt% copper (Cu), 3 wt% to 10 wt% nickel (Ni), 0.5 wt% to 3 wt% aluminum (Al), 0.2 wt% to 1.5 wt% manganese (Mn), 0 to 1.5 wt% chromium (Cr), 0 to 1.5 wt% molybdenum (Mo), 0 to 1.5 wt% tungsten (W), and 0 to 0.2 wt% niobium (Nb); A transition layer on the steel substrate having a thickness of 0.1 μm to 3 μm, and the metal of the transition layer comprises 5 to 20 wt % Ni and 1 to 5 wt % copper; and One of an oxide layer and an oxide / nitride layer on the transition layer has a thickness of 1 μm to 10 μm.

2. The surface treated tool steel of claim 1, wherein the ratio of Ni:Al is greater than or equal to 2.

3. The surface treated tool steel of claim 1, wherein the chromium (Cr) is 0.01 wt% to 1.5 wt%.

4. The surface treated tool steel of claim 1, wherein the molybdenum (Mo) is 0.01 wt% to 1.5 wt%.

5. The surface treated tool steel of claim 1, wherein the tungsten (W) is 0.01 wt% to 1.5 wt%.

6. The surface treated tool steel of claim 1, wherein the niobium (Nb) is 0.01 wt% to 0.2 wt%.

7. The surface treated tool steel of claim 1, wherein the microstructure of the tool steel after austenitization is martensite, bainite and ferrite with a size of less than 20 nm and a size of greater than 10 nm. 24 / m 3 A mixture of a density of and less than 5 volume % of austenite nanoprecipitates.

8. The surface treated tool steel of claim 1, wherein the hardness of the tool steel after quenching by austenitizing is less than 30 HRC.

9. The surface treated tool steel of claim 8, wherein one of the following is satisfied: The hardness of the tool steel after hardening and oxidation is greater than or equal to 42 HRC; and After tempering and oxy-nitriding, the hardness of the tool steel is greater than or equal to 49 HRC.

10. The surface treated tool steel of claim 1, wherein after tempering and surface treatment, the thermal conductivity is greater than 35 W / mK.

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