JP2006520431A5 - - Google Patents

Description

Intercritical annealing makes it possible to re-dissolve most of the carbide phase formed during winding after recrystallization. The phenomenon that the carbide phase austenitizes and dissolves after recrystallization occurs, releasing the trapped carbon during recrystallization as soon as the preserved and recrystallized ferrite crystal texture grows. It becomes possible. Therefore, as in the case of winding at a low temperature, solid solution-like carbon does not have a side effect on the crystal texture, but martensite is formed and it is only altered by isotropic characteristics.

Quenching with water makes it possible to form a large proportion of carbide phase compared to the analysis results considered. By lowering the maintenance temperature to a lower value in the critical region, or also by slow cooling prior to quenching, the formation of fractions of martensite phase can be reduced.

Claims (21)

A method for producing a cold-rolled ferritic / martensitic duplex steel strip, the chemical composition of which is in weight percent:
0.010% ≦ C ≦ 0.100%
0.050% ≦ Mn ≦ 1.0%
0.010% ≦ Cr ≦ 1.0%
0.010% ≦ Si ≦ 0.50%
0.001% ≦ P ≦ 0.20%
0.010% ≦ Al ≦ 0.10%
N ≦ 0.010%
A slab containing slab is hot-rolled, and the remainder is iron and impurities generated by refining, and the manufacturing method includes the following steps:
Winding the steel strip obtained at a temperature comprised between 550 ° C. and 850 ° C. at a high temperature, and
-Cold rolling the steel strip at a reduction rate comprised between 60% and 90%, and
-Annealing the steel strip continuously in the critical region, and-lowering the temperature of the steel strip to room temperature by one or more steps, cooling rate comprised between 600 ° C and room temperature is 100 ° C / S to 1500 ° C./s,
-And in some cases, subjecting the steel strip to tempering at a temperature below 300 ° C;
An annealing and cooling operation is performed so that the steel strip is finally formed to contain 1% to 15% martensite. The chemical composition is further weight percent:
0.020% ≦ C ≦ 0.060%
0.300% ≦ Mn ≦ 0.500%
0.010% ≦ Cr ≦ 1.0%
0.010% ≦ Si ≦ 0.50%
0.010% ≦ P ≦ 0.100%
0.010% ≦ Al ≦ 0.10%
N ≦ 0.010%
The method for producing a steel strip according to claim 1, characterized in that the remainder includes impurities from iron and refining. The method of manufacturing a steel strip according to any one of claims 1 and 2, wherein the steel strip is hot-rolled at a temperature exceeding 850 ° C. The steel strip production method according to any one of claims 1 to 3, wherein the steel strip is wound at a high temperature at a temperature comprised between 550 ° C and 750 ° C. The steel strip manufacturing method according to any one of claims 1 to 4, wherein the steel strip is cold-rolled at a reduction ratio included between 70% and 80%. The steel strip according to any one of claims 1 to 5, wherein the continuous annealing of the cold-rolled steel strip includes a step of increasing the temperature and a step of maintaining the steel strip at a predetermined temperature. Production method. The method of manufacturing a steel strip according to claim 6, wherein the maintenance temperature is included between Ac1 and 900 ° C. The method for producing a steel strip according to claim 7, wherein the maintenance temperature is between 750 ° C and 850 ° C. The process of lowering the temperature to room temperature includes the first gradual cooling included between the maintenance temperature and 600 ° C., where the cooling rate is less than 50 ° C./s, and between 100 ° C./s and 1500 ° C./s. The method for manufacturing a steel strip according to any one of claims 1 to 8, further comprising second cooling performed at a higher speed to room temperature. The method for producing a steel strip according to claim 9, wherein the second cooling is performed by quenching with water. The steel strip according to any one of claims 1 to 8, wherein the cooling is performed at a cooling rate comprised between 100 ° C / s and 1500 ° C / s in a single operation. Production method. The method for producing a steel strip according to claim 11, wherein the cooling is performed by quenching with water. Cold rolled ferritic / martensitic duplex steel strip, the chemical composition of which is by weight:
0.010% ≦ C ≦ 0.100%
0.050% ≦ Mn ≦ 1.0%
0.010% ≦ Cr ≦ 1.0%
0.010% ≦ Si ≦ 0.50%
0.001% ≦ P ≦ 0.20%
0.010% ≦ Al ≦ 0.10%
N ≦ 0.010%
The steel strip is characterized by including iron and impurities generated by refining, the steel strip further containing 1% to 15% martensite and exhibiting an average anisotropy coefficient r exceeding 1.1. . In addition to chemical composition,
0.020% ≦ C ≦ 0.060%
0.300% ≦ Mn ≦ 0.500%
0.010% ≦ Cr ≦ 1.0%
0.010% ≦ Si ≦ 0.50%
0.010% ≦ P ≦ 0.100%
0.010% ≦ Al ≦ 0.10%
N ≦ 0.010%
The steel strip according to claim 13, characterized in that the remainder is iron and impurities produced by refining. The steel strip according to claim 13 or 14, wherein the steel strip exhibits a tensile strength Rm exceeding 450 MPa. The steel strip according to claim 15, wherein the steel strip exhibits a tensile strength Rm exceeding 500 MPa. The steel strip according to claim 16, further exhibiting a tensile strength Rm exceeding 600 MPa. The steel strip according to any one of claims 13 to 17, wherein the steel strip exhibits an average anisotropy coefficient r exceeding 1.3. The steel strip according to any one of claims 13 to 18 , further comprising 1% to 10% martensite. The steel strip according to claim 19 , further comprising 5% to 8% martensite. 21. Use of a steel strip according to any one of claims 13 to 20 for producing a member for an automobile made by deep drawing.