Surface-treated tool steel for die casting of metal

Abstract

A tool steel 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 is arranged on the steel substrate. Metal of the transition layer includes 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 is arranged on the transition layer.

What is claimed is: 
     
         1 . A surface treated tool steel for a die for casting metal, comprising:
 a steel substrate 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 2.0 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 %; and   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.   
     
     
         2 . The surface treated tool steel of  claim 1 , wherein a 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 in a range from 0.01 wt % to 1.5 wt %. 
     
     
         4 . The surface treated tool steel of  claim 1 , wherein the molybdenum (Mo) is in a range from 0.01 wt % to 1.5 wt %. 
     
     
         5 . The surface treated tool steel of  claim 1 , wherein the tungsten (W) in a range from 0.01 wt % to 1.5 wt %. 
     
     
         6 . The surface treated tool steel of  claim 1  wherein the niobium (Nb) is in a range from 0.01 wt % to 0.2 wt %. 
     
     
         7 . The surface treated tool steel of  claim 1 , wherein 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 10 24 /m 3  and austenite less than 5% in volume. 
     
     
         8 . The surface treated tool steel of  claim 1 , wherein after quenching from austenitization, a hardness of the tool steel is less than 30 HRC. 
     
     
         9 . The surface treated tool steel of  claim 8 , wherein one of:
 after hardening and oxidizing, the hardness of the tool steel 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, thermal conductivity is greater than 35 W/mK. 
     
     
         11 . The surface treated tool steel of  claim 1 , wherein the tool steel includes one of a nitride layer having a thickness in a range from 30 μm to 100 μm. 
     
     
         12 . A method for surface treating tool steel, comprising:
 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. 
   
     
     
         13 . The method of  claim 12 , further comprising using the die to cast one of aluminum and aluminum alloy. 
     
     
         14 . The method of  claim 12 , wherein 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. 
     
     
         15 . The method of  claim 12 , wherein 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. 
     
     
         16 . The method of  claim 12 , wherein 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. 
     
     
         17 . The method of  claim 12 , wherein 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. 
     
     
         18 . The method of  claim 12 , wherein, 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.   
     
     
         19 . The method of  claim 12 , wherein, after one of the oxy-nitriding and the oxy-nitriding and hardening, the tool steel includes:
 a 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 %.