A kind of low-nickel type medium chromium ferritic stainless steel and its manufacturing method

Abstract

The invention discloses low-nickel type medium-chromium ferrite stainless steel and a manufacturing method thereof. The low-nickel type medium-chromium ferrite stainless steel comprises, by weight, 0.7%-1.2% of Ni, 0.002%-0.012% of C, 0.002%-0.020% of N, 0.10%-0.50% of Si, 0.1%-0.50% of Mn, 17.00%-22.50% of Cr, 1.70%-2.50% of Mo, 0.15%-0.45% of Nb, 0.05%-0.25% of Ti, 0.005%-0.010% of O, and the balance Fe and inevitable impurities. The following relational expressions are met, wherein (C+N) is smaller than or equal than 0.030%, Nb / Ti is equal to 1.5-4, and (Nb+Ti) / (C+N) is equal to 12-22. The low-nickel type medium-chromium ferrite stainless steel obtained through the method has excellent low-temperature toughness and high strength; the ductile-brittle transition temperature is smaller than or equal to -40 DEG C, the yield strength is larger than or equal to 330MPa, and strength of extension is larger than or equal to 445MPa; and the metallographic structure is a pure ferrite equiaxed grain structure.

Description

technical field [0001] The invention belongs to the field of ferritic stainless steel, and in particular relates to a low-nickel type medium-chromium ferritic stainless steel with excellent low-temperature toughness and a manufacturing method thereof. Background technique [0002] Ferritic stainless steel has the characteristics of low cost risk (without or containing a small amount of Ni) and excellent corrosion resistance (especially resistance to stress corrosion, pitting, and crevice corrosion). Structure, water treatment system and other industries have a wide range of applications and broad development prospects. Countries such as Europe, America and Japan have begun to use a large number of ultra-pure ferritic stainless steel containing molybdenum, and the representative steel grade is SUS444. Traditional ferritic stainless steel has the disadvantages of high ductile-brittle transition temperature, low strength, and poor processability. The use of modern advanced sta...

AI Technical Summary

Problems solved by technology

However, compared with austenitic stainless steel, ferritic stainless steel has less movable slip system at low temperature, and is prone to cracks, and sharp cracks will expand rapidly and cause brittle cracks.

Specifically, ferritic stainless steel produced by conventional processes has poor low-temperature toughness, high ductile-brittle transition temperature, and even some ferritic stainless steels have a ductile-brittle transition temperature above 20°C. At the same time, ferritic stainless steel has low strength. This limits the application of ferritic stainless steel as structural parts

[0004] Chinese patent CN102643968 improves the low-temperature toughness of medium-chromium ferritic stainless steel from the aspect of technology. The specific method is to add a method of medium-temperature rolling in the range of 260-600°C, which can reduce the ductile-brittle transition temperature to 20-41°C, but The low temperature toughness value will not be very high, and its strength has not been greatly improved

Japanese patent JP2013209705 (A) stipulates that 0.01% to 0.30% of Ni, 0.02% to 1.2% of Al, 0.02% to 0.5% of V, and 0.001% to 0.3% of Co are added. Al acts as a deoxidizer, and the Al content is suitable When , the ductile-brittle transition temperature can be reduced, but increasing the ductile-brittle transition temperature will increase, and increasing the content will increase the difficulty of production and pouring. Co can strengthen the matrix, but it will cause a decrease in plasticity and impact toughness

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