HOT-WORKING DIE STEEL, HEAT TREATMENT METHOD AND HOT-WORKING MOLD
The present invention relates to a hot working tool steel, a heat treatment method thereof, and a hot working tool. The hot working tool steel has a chemical composition, in weight percent, of: Ni: 4.5-12%, Al: 0.8-2.1% and Al:Ni=0.075-0.234, Cu: 0.4-1.99%, Mn: 0.001-1%, C: 0.0001-0.1%, with the balance being Fe and unavoidable impurities. The heat treatment method includes a hardening step, wherein: when 0.4%≤Cu<0.8%, the hot working tool steel is heated to a temperature in the range of 560-650° C.; when 0.8%≤Cu<1.5%, the hot working tool steel is heated to a temperature in the range of 470-580° C.; and when 1.5%≤Cu≤1.99%, the hot working tool steel is heated to a temperature in the range of 450-520° C.; and held for 1-240 hours, preferably 4-24 hours, and then cooled to room temperature.
1 . A hot working tool steel, wherein the chemical composition, in weight percent, is: Ni: 4.5-12%, Al: 0.8-2.1% and Al:Ni=0.075-0.234, Cu: 0.4-1.99%, Mn: 0.001-1%, C: 0.0001-0.1%, and the balance is Fe and unavoidable impurities.
2 . The hot working tool steel according to claim 1 , wherein 0.075≤Al:Ni<0.18.
3 . The hot working tool steel according to claim 1 , wherein 0.18≤Al:Ni≤0.234.
4 . The hot working tool steel according to claim 3 , wherein 0.18≤Al:Ni≤0.22 and Ni: 5-9%.
5 . The hot working tool steel according to claim 1 , wherein 0.5<Cu:Al<1 and/or Cu: 0.4-1.5%.
6 . The hot working tool steel according to claim 5 , wherein 0.6≤Cu:Al≤0.9 and/or Cu: 0.4-1.2%.
7 . The hot working tool steel according to claim 1 , wherein C: 0.0001-0.05%.
8 . A method for heat treating the hot working tool steel according to claim 1 , comprising a hardening step, the hardening step including: when 0.4≤Cu<0.8%, heating the hot working tool steel to a temperature in the range of 560-650° C.; when 0.8≤Cu<1.5%, heating the hot working tool steel to a temperature in the range of 470-580° C.; and when 1.5≤Cu≤1.99%, heating the hot working tool steel to a temperature in the range of 450-520° C., and holding for 1-240 hours, and then cooling to room temperature.
9 . The heat treatment method according to claim 8 , comprising: when 0.4%≤Cu<0.8%, heating the hot working tool steel to a temperature in the range of 560-620° C.; when 0.8%≤Cu<1.5%, heating the hot working tool steel to a temperature in the range of 480-580° C.; and when 1.5%≤Cu≤1.99%, heating the hot working tool steel to a temperature in the range of 450-500° C. and holding for 4-24 hours, and then cooling to room temperature.
10 . The heat treatment method according to claim 8 , further comprising: prior to the hardening step, a solution treatment step, the solution treatment step including: heating the hot working tool steel to a temperature in the range of 850-950° C. and holding for 0.5-240 hours, and then cooling to room temperature.
11 . The heat treatment method according to claim 10 , further comprising: prior to the solution treatment step, a forging step, the forging step including: heating the hot working tool steel to a temperature in the range of 900-1150° C. for forging, and then cooling to room temperature.
12 . The heat treatment method according to claim 11 , wherein the cooling in the forging step is first slowly cooled to below 600° C. at a rate of ≤60° C./h, and then air cooled to room temperature.
13 . The heat treatment method according to claim 8 , wherein the heat-treated hot working tool steel has the following properties: hardness ≥36 HRC, room temperature thermal conductivity: 34-50 W/mK, notched impact energy ≥200 J, and the Al dissolved in the matrix ≤0.05%.
14 . A hot working tool made of the hot working tool steel obtained by the heat treatment method according to claim 1 , wherein the hot working tool can be used as a hot stamping die for steel plates, an aluminum alloy die casting die, or a hot extrusion drawing die.
15 . The heat treatment method according to claim 9 , further comprising: prior to the hardening step, a solution treatment step, the solution treatment step including: heating the hot working tool steel to a temperature in the range of 850-950° C. and holding for 0.5-240 hours, and then cooling to room temperature.
16 . The heat treatment method according to claim 9 , wherein the heat-treated hot working tool steel has the following properties: hardness ≥36 HRC, room temperature thermal conductivity: 34-50 W/mK, notched impact energy ≥200 J, and the Al dissolved in the matrix ≤0.05%.
17 . The heat treatment method according to claim 10 , wherein the cooling in the solution treatment step is first slowly cooled to below 600° C. at a rate of ≤60° C./h, and then air cooled to room temperature.