Method for temperature-treating a manganese steel intermediate product, and steel intermediate product which has been temperature-treated in a corresponding manner

Abstract

A method for temperature-treating a manganese steel intermediate product whose alloy includes: a manganese content, which lies in the following manganese range: 3 wt. %≤Mn≤12 wt. %, a fraction of one or more alloying elements of the group: silicon (Si), aluminum (Al), nickel (Ni), chromium (Cr), molybdenum (Mo), phosphorus (P), sulfur (S), nitrogen (N), copper (Cu), boron (B), cobalt (Co), tungsten (W), an optional carbon content (C) of less than 1 wt. %, an optional content of one or more microalloying elements, wherein the total content of the micro-alloying elements is less than 0.45 wt. %; and as a remainder an iron content (Fe) and unavoidable impurities.

1 : Method for temperature-treating a manganese steel intermediate product whose alloy comprises:
 a manganese content (Mn), which lies in the following manganese range (MnB): 3 wt. %≤Mn≤12 wt. %,   a content of one or more alloying elements of the group: silicon (Si), aluminum (Al), nickel (Ni), chromium (Cr), molybdenum (Mo), phosphorus (P), sulfur (S), nitrogen (N), copper (Cu), boron (B), tungsten (W), cobalt (Co),   an optional carbon content (C) of less than 1 wt. %,   an optional content of one or more microalloying elements, wherein the total content of the micro-alloying elements is less than 0.45 wt. %; and   as a remainder an iron content (Fe) and unavoidable impurities, wherein the temperature-treating of the steel intermediate product comprises a first temperature treatment process (S. 1 ) and a subsequent second temperature treatment process (S. 2 ), characterized in that   the first temperature treatment process (S. 1 ) is a high-temperature process in which the steel intermediate product is subjected during a first holding period (Δ 1 ) to a first annealing temperature (T 1 ) lying above a critical temperature limit (T KG ), which is defined as follows: T KG =(856−S K *manganese content) degrees Celsius, wherein S K  is a slope value, and wherein said slope value S K =7.83±10%, preferably S K =7.83,   the second temperature treatment process (S. 2 ) is an annealing process in which the steel intermediate product is subjected to a second annealing temperature (T 2 ) which is lower than the first annealing temperature (T 1 ).   
     
     
         2 : Method according to  claim 1 , characterized in that the first annealing temperature (T 1 ) in said manganese range (MnB) has a dependence defined as follows: T 1 ≈(866−S K *manganese content) degrees Celsius. 
     
     
         3 : Method according to  claim 1 , characterized in that the first holding period (Δ 1 ) is at least 10 seconds and preferably between 10 seconds and 6000 minutes. 
     
     
         4 : Method according to  claim 1 , characterized in that the second annealing temperature (T 2 ) is in the range between the temperatures A 1  and Δ 3 , wherein A 1  is the start temperature of austenitization and A 3  is the start temperature of full austenitization. 
     
     
         5 : Method according to  claim 1 , characterized in that the second annealing temperature (T 2 ) is in the range of 630° C. to 675° C. 
     
     
         6 : Method according to  claim 1 , characterized in that within the scope of the second temperature treatment process (S. 2 ), the second annealing temperature (T 2 ) is held during a second holding period (Δ 2 ) of at least 10 seconds. 
     
     
         7 : Method according to  claim 1 , characterized in that the second temperature treatment process (S. 2 ), including a heating process (E 2 ) of the steel intermediate product, the holding (H 2 ) of the second annealing temperature (T 2 ) and a cooling process (A 2 ) of the steel intermediate product, takes less than 6000 minutes and preferably less than 5000 minutes. 
     
     
         8 : Method according to  claim 1 , characterized in that the content of the one or more alloying elements is in the following range:
 silicon (Si) ≤3 wt. %, and preferably ≤2 wt. %,   aluminum (Al) ≤8 wt. %, and preferably ≤6 wt. %,   nickel (Ni) ≤2 wt. %, and preferably ≤1 wt. %,   chromium (Cr) ≤2 wt. %, and preferably ≤0.5 wt. %,   molybdenum (Mo) ≤0.5 wt. %, and preferably ≤0.25 wt. %,   phosphorus (P) ≤0.05 wt. %, and preferably ≤0.025 wt. %,   sulfur (S) ≤0.03 wt. %, and preferably ≤0.01 wt. %,   nitrogen (N) ≤0.05 wt. %, and preferably ≤0.025 wt. %,   copper (Cu) ≤1 wt. %, and preferably ≤0.5 wt. %,   boron (B) ≤0.005 wt. %, and preferably ≤0.0035 wt. %,   tungsten (W) ≤1 wt. %, and preferably ≤0.5 wt. %,   cobalt (Co) ≤2 wt. %, and preferably ≤1 wt. %.   
     
     
         9 : Method according to  claim 1 , characterized in that the micro-alloying elements are elements of the group: titanium (Ti), niobium (Nb), vanadium (V). 
     
     
         10 : Method according to  claim 1 , characterized in that the first temperature treatment process (S. 1 ) concerns a process which is carried out in a continuous strip plant or in a discontinuously operating plant. 
     
     
         11 : Method according to  claim 1 , characterized in that the second temperature treatment process (S. 2 ) is a process which is carried out in a continuous strip plant or in a discontinuously operating plant, wherein the steel intermediate product in this plant is exposed in the annealing process to a protective gas atmosphere. 
     
     
         12 : Method according to  claim 11 , characterized in that a hood-type annealing device is used as a discontinuously operating plant. 
     
     
         13 : Method according to  claim 1 , characterized in that the steel intermediate product is subjected to a skin-pass rolling process in a step which is downstream of the second temperature treatment process (S. 2 ), wherein this skin-pass rolling process is primarily directed to condition the surface of the steel intermediate product. 
     
     
         14 : Method according to  claim 1 , characterized in that the first temperature treatment process (S. 1 ) is carried out during a hot rolling process, wherein said hot rolling process is carried out with a rolling end temperature which lies in the range above the critical temperature limit (T KG ). 
     
     
         15 : Steel intermediate product which has been heat-treated according to a method of  claim 1 , characterized in that it has a Lüders strain (A L ) which is less than 3% and preferably less than 1%. 
     
     
         16 : Steel intermediate product according to  claim 15 , characterized in that a Lüders strain (A L ) of less than 3% on the steel intermediate product is measurable before the steel intermediate product was subjected to a subsequent skin-pass rolling process. 
     
     
         17 : Steel intermediate product according to  claim 15 , characterized in that, due to a reduced Lüders strain (A L ), in comparison to the reduction of Lüders strain with skin-pass rolling, it has a greater useful technical elongation.