Electro-galvanized super-strength dual-phase steel resistant to delayed cracking, and manufacturing method therefor

Abstract

Disclosed is an electro-galvanized super-strength dual-phase steel resistant to delayed cracking. A matrix structure thereof is ferrite+tempered martensite and the steel contains the following chemical elements in the following mass percentages: C:0.07-0.1%, Si: 0.05-0.3%, Mn: 2.0-2.6%, Cr: 0.2-0.6%, Mo: 0.1-0.25%, Al: 0.02-0.05%, Nb: 0.02-0.04%, and V: 0.06-0.2%. Also disclosed is a method for manufacturing the electro-galvanized super-strength dual-phase steel resistant to delayed cracking, the method comprising the steps of: smelting and continuous casting, hot rolling, cold rolling, annealing, tempering, leveling and electroplating. The electro-galvanized super-strength dual-phase steel resistant to delayed cracking according to the present invention not only has better mechanical properties, but also has excellent delayed cracking resistance and low initial hydrogen content.

1 . An electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking, wherein the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking has a matrix structure of ferrite+tempered martensite, and comprises the following chemical elements in mass percentages, in addition to Fe:
 C: 0.07-0.1%, Si: 0.05-0.3%, Mn: 2.0-2.6%, Cr: 0.2-0.6%, Mo: 0.1-0.25%, Al: 0.02-0.05%, Nb: 0.02-0.04%, V: 0.06-0.2%.   
     
     
         2 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 1 , wherein the chemical elements have the following mass percentages:
 C: 0.07-0.1%, Si: 0.05-0.3%, Mn: 2.0-2.6%, Cr: 0.2-0.6%, Mo: 0.1-0.25%, Al: 0.02-0.05%, Nb: 0.02-0.04%, V: 0.06-0.2%, and a balance of Fe and other unavoidable impurities.   
     
     
         3 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 1  or  2 , wherein it further comprises 0.0015-0.003% of element B. 
     
     
         4 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 2 , wherein the unavoidable impurities include elements P, S and N, and contents thereof are controlled to be at least one of the following: P≤0.012%, S≤0.003%, N≤0.005%. 
     
     
         5 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 1 , wherein a phase proportion of the tempered martensite is >50%. 
     
     
         6 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 1 , wherein dispersive fine carbide particles are precipitated in the matrix structure, wherein the carbide particles include MoC, VC, Nb(C, N), and wherein the carbide particles are all distributed in the matrix structure in a coherent form. 
     
     
         7 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 6 , wherein the carbide particles have a size of 60 nm. 
     
     
         8 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 1 , wherein the tempered martensite further comprises coherently distributed ε carbide. 
     
     
         9 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 1 , wherein its properties meet at least one of the following: yield strength ≥550 MPa, tensile strength ≥980 MPa, elongation after fracture ≥12%, initial hydrogen content ≤3 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength. 
     
     
         10 . A manufacturing method for the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 1 , wherein the method comprises the following steps:
 (1) Smelting and continuous casting;   (2) Hot rolling;   (3) Cold rolling;   (4) Annealing: heating to an annealing soaking temperature of 780-820° C. at a heating rate of 3-10° C./s, an annealing time being 40-200 s; and then rapidly cooling at a rate of 30-80° C./s, a starting temperature of the rapid cooling being 650-730° C.;   (5) Tempering: tempering temperature: 200-280° C.; tempering time: 100-400 s;   (6) Temper rolling;   (7) Electroplating.   
     
     
         11 . The manufacturing method according to  claim 10 , wherein in the step (1), a drawing speed in the continuous casting is controlled at 0.9-1.5 m/min during the continuous casting process. 
     
     
         12 . The manufacturing method according to  claim 10 , wherein in step (2), a cast slab is controlled to be soaked at a temperature of 1200-1260° C.; then rolled with a finishing rolling temperature being controlled at 840-900° C.; then cooled at a rate of 20-70° C./s after rolling; then coiled at a coiling temperature of 580-630° C.; and then subjected to heat preservation treatment after coiling. 
     
     
         13 . The manufacturing method according to  claim 10 , wherein in step (3), a cold rolling reduction rate is controlled at 45-65%. 
     
     
         14 . The manufacturing method according to  claim 10 , wherein in step (6), a temper rolling reduction rate is controlled at ≤0.3%. 
     
     
         15 . The manufacturing method according to  claim 10 , wherein in step (2), a cast slab is controlled to be soaked at a temperature of 1210-1245° C.; in step (4), heating at a heating rate of 3-10° C./s is performed to achieve an annealing soaking temperature of 790-810° C., the annealing time being 40-160 s, and then rapid cooling is performed at a rate of 35-80° C./s, a starting temperature of the rapid cooling being 650-730° C.; in step (5), the tempering temperature is 210-270° C., and the tempering time is 120-300 s. 
     
     
         16 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 2 , wherein it further comprises 0.0015-0.003% of element B. 
     
     
         17 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 2 , wherein a phase proportion of the tempered martensite is >50%; and/or dispersive fine carbide particles are precipitated in the matrix structure, wherein the carbide particles include MoC, VC, Nb(C, N), and wherein the carbide particles are all distributed in the matrix structure in a coherent form; and/or the tempered martensite further comprises coherently distributed ε carbide. 
     
     
         18 . The electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to  claim 2 , wherein its properties meet at least one of the following: yield strength ≥550 MPa, tensile strength ≥980 MPa, elongation after fracture ≥12%, initial hydrogen content ≤3 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength. 
     
     
         19 . The manufacturing method according to  claim 10 , wherein the chemical elements have the following mass percentages: C: 0.07-0.1%, Si: 0.05-0.3%, Mn: 2.0-2.6%, Cr: 0.2-0.6%, Mo: 0.1-0.25%, Al: 0.02-0.05%, Nb: 0.02-0.04%, V: 0.06-0.2%, optional B: 0.0015-0.003%, and a balance of Fe and other unavoidable impurities. 
     
     
         20 . The manufacturing method according to  claim 10 , wherein a phase proportion of the tempered martensite is >50%; and/or dispersive fine carbide particles are precipitated in the matrix structure, wherein the carbide particles include MoC, VC, Nb(C, N), and wherein the carbide particles are all distributed in the matrix structure in a coherent form; and/or the tempered martensite further comprises coherently distributed c carbide.