High Strength Dual-Phase TRIP Steel and Method for Making Same

Abstract

A high strength dual-phase TRIP steel includes 8-12 wt. % Mn, 0.4-0.6 wt. % C, 1-3 wt. % Al, 0.5-1 wt. % V, and a balance of Fe. A method for making the high strength dual-phase TRIP steel is also provided.

What is claimed is: 
     
         1 . A high strength dual-phase TRIP steel, comprising: 8-12 wt. % Mn, 0.4-0.6 wt. % C, 1-3 wt. % Al, 0.5-1 wt. % V, and a balance of Fe. 
     
     
         2 . The high strength dual-phase TRIP steel of  claim 1 , wherein the high strength dual-phase TRIP steel comprises 10 wt. % Mn, 0.47 wt. % C, 2 wt. % Al, 0.7 wt. % V, and a balance of Fe. 
     
     
         3 . The high strength dual-phase TRIP steel of  claim 1 , wherein the high strength dual-phase TRIP steel consists of ferrite and retained austenite phases. 
     
     
         4 . The high strength dual-phase TRIP steel of  claim 3 , wherein the high strength dual-phase TRIP steel consists of two types of retained austenite and fine-grained ferrite. 
     
     
         5 . The high strength dual-phase TRIP steel of  claim 4 , wherein one type of the retained austenite is fine-grained austenite with a grain size that is smaller than 1 μm, the other type is the large-grained austenite with a size larger than 10 μm. 
     
     
         6 . The high strength dual-phase TRIP steel of  claim 3 , wherein a volume fraction of austenite contained in the high strength dual-phase TRIP steel before a tensile test is 70-90%, a volume fraction of ferrite contained in the high strength dual-phase TRIP steel before the tensile test is 10-30%. 
     
     
         7 . The high strength dual-phase TRIP steel of  claim 6 , wherein the volume fraction of austenite contained in the high strength dual-phase TRIP steel before the tensile test is 80.8%, the volume fraction of ferrite contained in the high strength dual-phase TRIP steel before the tensile test is 19.2%. 
     
     
         8 . The high strength dual-phase TRIP steel of  claim 6 , wherein a volume fraction of the fine-grained austenite contained in the retained austenite is 60-80%, a volume fraction of the large-grained austenite contained in the retained austenite is 20-40%. 
     
     
         9 . The high strength dual-phase TRIP steel of  claim 8 , wherein the volume fraction of the fine-grained austenite contained in the retained austenite is 67%, the volume fraction of the large-grained austenite contained in the retained austenite is 33%. 
     
     
         10 . The high strength dual-phase TRIP steel of  claim 6 , wherein after the high strength dual-phase TRIP steel is deformed, the volume fraction of austenite drops to 30-60%, the volume fraction of martensite increases to 30-60% and the volume fraction of the ferrite remains still. 
     
     
         11 . The high strength dual-phase TRIP steel of  claim 10 , wherein the volume fraction of austenite drops to 52.7%, the volume fraction of martensite increases to 28.1% and the volume fraction of the ferrite remains 19.8%. 
     
     
         12 . The high strength dual-phase TRIP steel of  claim 1 , wherein the high strength dual-phase TRIP steel includes vanadium carbide precipitations with a size of about 20-30 nm. 
     
     
         13 . A method for making the high strength dual-phase TRIP steel, comprising:
 providing ingots, the ingots comprising 8-12 wt. % Mn, 0.4-0.6 wt. % C, 1-3 wt. % Al, 0.5-1 wt. % V, and a balance of Fe;   hot rolling the ingots to produce a plurality of thick steel sheets with a thickness of 3-6 mm, then the steel sheets being treated by an air cooling process;   warm rolling the steel sheets at a temperature of about 150-200° C. with a thicknesses reduction of about 15-44%;   cold rolling the steel sheets at a room temperature with the thicknesses reduction of about 7%;   annealing the steel sheets at the temperature of about 625-660° C. for 10-300 min to form the high strength dual-phase TRIP steel.   
     
     
         14 . The method for making the high strength dual-phase TRIP steel of  claim 13 , wherein during the hot rolling process, a starting hot rolling temperature is 1100-1300° C., and a finishing hot rolling temperature is 800-1000° C., the thickness of each steel sheet is 3-6 mm. 
     
     
         15 . The method for making the high strength dual-phase TRIP steel of  claim 13 , wherein the steel sheets are finally water quenched to the room temperature after the anneal process. 
     
     
         16 . The method for making the high strength dual-phase TRIP steel of  claim 13 , wherein the high strength dual-phase TRIP steel comprises 8-12 wt. % Mn, 0.4-0.6 wt. % C, 1-3 wt. % Al, 0.5-1 wt. % V, and a balance of Fe. 
     
     
         17 . The method for making the high strength dual-phase TRIP steel of  claim 16 , wherein the high strength dual-phase TRIP steel comprises 10 wt. % Mn, 0.47 wt. % C, 2 wt. % Al, 0.7 wt. % V, and a balance of Fe. 
     
     
         18 . The method for making the high strength dual-phase TRIP steel of  claim 13 , wherein the high strength dual-phase TRIP steel consists of ferrite and retained austenite phases, the retained austenite phase consists of fine-grained austenite with a grain size that is smaller than 1 μm, and large-grained austenite with a size larger than 10 μm. 
     
     
         19 . The method for making the high strength dual-phase TRIP steel of  claim 18 , wherein a volume fraction of austenite contained in the high strength dual-phase TRIP steel before a tensile test is 70-90%, a volume fraction of ferrite contained in the high strength dual-phase TRIP steel before the tensile test is 10-30%, a volume fraction of the fine-grained austenite contained in the retained austenite is 60-80%, a volume fraction of the large-grained austenite contained in the retained austenite is 20-40%. 
     
     
         20 . The method for making the high strength dual-phase TRIP steel of  claim 13 , wherein the high strength dual-phase TRIP steel includes vanadium carbide precipitations with a size of 20-30 nm.