Dual-phase steel and manufacturing method therefor

Abstract

Disclosed in the present invention is dual-phase steel, comprising, in addition to 90% or more of Fe and inevitable impurities, the following components in percentages by mass: C: 0.09-0.11%, Si: 0.1-0.3%, Mn: 1.4-1.6%, Al: 0.01-0.03%, Nb: 0.01-0.03%, Ti: 0.01-0.03%, and B: 0.0020-0.0030%. In the present invention, by rationally controlling the chemical components of steel, dual-phase steel with both low cost and high mechanical properties is obtained. Further disclosed in the present invention is a manufacturing method for the dual-phase steel.

1 . A dual-phase steel, comprising, in addition to at least 90% of Fe and unavoidable impurities, the following components in mass percentage: C: 0.09%-0.11%, Si: 0.1%-0.3%, Mn: 1.4%-1.6%, Al: 0.01%-0.03%, Nb: 0.01%-0.03%, Ti: 0.01%-0.03%, and B: 0.0020%-0.0030%. 
     
     
         2 . The dual-phase steel of  claim 1 , comprising the following components in mass percentage: C: 0.09%-0.11%, Si: 0.1%-0.3%, Mn: 1.4%-1.6%, Al: 0.01%-0.03%, Nb: 0.01%-0.03%, Ti: 0.01%-0.03%, and B: 0.0020%-0.0030%, and a balance of Fe and unavoidable impurities. 
     
     
         3 . The dual-phase steel of  claim 1 , wherein the dual-phase steel is free of Mo and Cr. 
     
     
         4 . The dual-phase steel of  claim 1 , wherein the dual-phase steel has a hardenability factor Y Q  that satisfies: 1.9≤Y Q ≤2.1, wherein Y Q =Mn+200×B, wherein Mn and B each represent a numerical value before a percentage sign of a mass percentage content of a corresponding element. 
     
     
         5 . The dual-phase steel of  claim 1 , wherein the contents of impurity elements in mass percentage satisfy: P≤0.015%, S≤0.003%, and N≤0.005%. 
     
     
         6 . The dual-phase steel of  claim 1 , wherein the dual-phase steel has a microstructure comprising martensite and ferrite. 
     
     
         7 . The dual-phase steel of  claim 6 , wherein martensite and ferrite each have an average grain size of 5 μm or less. 
     
     
         8 . The dual-phase steel of  claim 1 , wherein the dual-phase steel is a 80 kg-grade dual-phase steel having the following performances: a yield strength of ≥420 MPa; a tensile strength of ≥800 MPa; and an A 50 -gauge-length elongation at break of ≥18%. 
     
     
         9 . The dual-phase steel of  claim 1 , wherein the dual-phase steel has a yield strength of ≥450 MPa, a tensile strength of ≥820 MPa, and an A 50 -gauge-length elongation at break of ≥20%, and the dual-phase steel is able to withstand a force of 83-90 kilograms per square centimeter. 
     
     
         10 . A method for manufacturing the dual-phase steel of  claim 1 , wherein the method includes the following steps:
 1. Smelting and continuously casting molten steel to obtain a continuously cast product;   2. hot rolling the continuously cast product;   3. Cold rolling;   4. Annealing;   5. Tempering; and   6. temper rolling to obtain the dual-phase steel.   
     
     
         11 . The method of  claim 10 , wherein in the step of annealing, an annealing soaking temperature is 825-855° C.; an annealing time is 40-200 s; then, the temperature is reduced to a rapid cooling start temperature of 735-760° C. at a rate of 3-5° C./s, followed by rapid cooling at a rate of 40-100° C./s, with a rapid cooling end temperature being 220-260° C. 
     
     
         12 . The method of  claim 10 , wherein in the step of hot rolling, the continuously cast product is first heated to 1160-1190° C., held for 150 minutes or longer, then hot rolled with a rolling-end temperature being 850-890° C., then rapidly cooled at a rate of 30-80° C./s after the rolling; then coiled at a coiling temperature of 500-540° C., and then air-cooled after the coiling. 
     
     
         13 . The method of  claim 10 , wherein in the step of cold rolling, a cold rolling reduction ratio is 50-70%. 
     
     
         14 . The method of  claim 10 , wherein in the step of tempering, a tempering temperature is 220-260° C., and a tempering time is 100-400 s. 
     
     
         15 . The method of  claim 10 , wherein in the step of temper rolling, a temper rolling reduction ratio is ≤0.3%. 
     
     
         16 . The dual-phase steel of  claim 1 , wherein the dual-phase steel has a microstructure consisting of martensite and ferrite. 
     
     
         17 . The dual-phase steel of  claim 6 , wherein the martensite has a volume percentage content of 55% or higher and 85% or lower. 
     
     
         18 . The dual-phase steel of  claim 17 , wherein the martensite has a volume percentage content of 58-80%. 
     
     
         19 . The dual-phase steel of  claim 7 , wherein the martensite and ferrite each have a grain size of 5 μm or less. 
     
     
         20 . The method of  claim 11 , wherein the annealing soaking temperature is 830-840° C.