CN107475491B - Heat treatment process of ferritic stainless steel - Google Patents

Abstract

In order to solve the above problems, the present invention provides a heat treatment process for ferritic stainless steel, wherein the heat-treated ferritic stainless steel meets the requirements of hardness and elongation, and the heat treatment process comprises two annealing operations, and comprises the following specific steps: (1) annealing the material to be annealed at 900 ℃ for 2 hours, and then air-cooling to room temperature; (2) the material cooled to room temperature was annealed at 850 ℃ for 2 hours and then air-cooled to room temperature.

Description

Heat treatment process of ferritic stainless steel

Technical Field

The invention relates to the field of stainless steel heat treatment process, in particular to a heat treatment process of ferritic stainless steel.

Background

The ferritic stainless steel is the important stainless steel in five major stainless steel series, and the yield and consumption at home and abroad are only second to the austenitic stainless steel in recent years. Besides good stainless property and overall corrosion performance, the ferritic stainless steel has excellent pitting corrosion resistance, crevice corrosion resistance and chloride corrosion resistance, the thermal conductivity coefficient of the ferritic stainless steel is 130-150% of that of the austenitic steel, the expansion coefficient of the ferritic stainless steel is 60-70% of that of the austenitic steel, good heat resistance is shown, the ferritic stainless steel contains no nickel and a small amount of nickel, and the ferritic stainless steel is called nickel-saving steel, so the production cost is greatly lower than that of the austenitic steel. Despite the many advantages of ferritic stainless steels, investment casting ferritic stainless steels has been produced in very small quantities, mainly limited, and significantly different from casting austenitic stainless steels, in that cast ferritic stainless steels have the following disadvantages:

1. the material has low mechanical property, particularly poor toughness and plasticity, and the casting is easy to crack to generate waste products;

2. annealing is the only heat treatment process for producing ferritic stainless steel, and the grain size is much larger than that of austenitic stainless steel after solution heat treatment, and the material brittleness is large.

Disclosure of Invention

In order to solve the above problems, the present invention provides a heat treatment process of a ferritic stainless steel, which satisfies hardness and elongation requirements after heat treatment.

The technical scheme is as follows: the heat treatment process of the ferritic stainless steel is characterized by comprising two annealing operations, and comprises the following specific steps:

(1) annealing the material to be annealed at 900 ℃ for 2 hours, and then air-cooling to room temperature;

(2) the material cooled to room temperature was annealed at 850 ℃ for 2 hours and then air-cooled to room temperature.

After the process is adopted, carbides are thoroughly eliminated through two times of annealing, namely, the hardness is reduced, the toughness is increased, air cooling can quickly pass through a brittle phase region at 475 ℃ during cooling, and finally the hardness and the elongation of the obtained ferritic stainless steel meet the requirements.

Drawings

FIG. 1 is a schematic diagram of the composition and performance requirements of a 1.4740W ferritic stainless steel

FIG. 2 is a gold phase diagram without heat treatment;

FIG. 3 is a phase diagram of gold after annealing at 850 deg.C;

FIG. 4 is a phase diagram of gold after annealing at 900 deg.C;

FIG. 5 is a diagram of a gold phase after two anneals.

Detailed Description

A heat treatment process of ferritic stainless steel comprises two annealing operations, and comprises the following specific steps:

(1) annealing the material to be annealed at 900 ℃ for 2 hours, and then air-cooling to room temperature;

(2) the material cooled to room temperature was annealed at 850 ℃ for 2 hours and then air-cooled to room temperature.

A new exhaust pipe product is made of 1.4740W ferrite stainless steel, and the components and performance requirements are shown in figure 1.

The similar material 1.4740 is corresponding to the material standard EN 10295, and is required to be annealed, and the heat treatment temperature is 800-850 ℃ and is less than or equal to HB 300. As-cast mechanical properties: the bulk hardness HB421, tensile strength of the test bar 681MPa, yield 586, elongation 0%, and metallographic phase thereof are shown in FIG. 2.

If the annealing temperature is 850 ℃ alone, the temperature is kept for 2 hours, and then air cooling is carried out, wherein the mechanical properties are as follows: the hardness HB385, the tensile strength 852MPa, the yield 666MPa and the elongation 0.5 percent, the metallographic phase is shown in figure 3, the carbide part is scattered in the metallographic phase, the hardness can not meet the requirement, and the elongation basically does not exist in the tensile test bar.

If the annealing temperature is 900 ℃ alone, the temperature is kept for 2 hours, and then air cooling is carried out, wherein the mechanical properties are as follows: the hardness is HB336, the tensile strength is 824MPa, the yield is 677MPa, the elongation is 0%, the metallographic phase is shown in figure 4, most of carbide is scattered in the metallographic phase, the hardness still cannot meet the requirement, and the elongation does not exist in the tensile process of the test bar.

If two times of annealing are adopted, annealing the material to be annealed at 900 ℃ for 2 hours, and then air-cooling to room temperature; the material cooled to room temperature was then annealed at 850 ℃ for 2 hours and finally air-cooled to room temperature. Mechanical properties: the hardness HB258, the tensile strength 776MPa, the yield 635MPa and the elongation percentage are 1.8%, the metallographic phase is shown in figure 5, and the carbide is basically scattered and spheroidized in the metallographic phase.

The ferritic stainless steel can be annealed twice or even for multiple times to completely eliminate carbides (reduce hardness and increase toughness), and attention needs to be paid to cooling to room temperature in the annealing heat treatment and then carrying out the next heat treatment.

Claims (1)

1. The heat treatment process of the ferritic stainless steel is characterized by comprising two annealing operations, and comprises the following specific steps:

(1) annealing the material to be annealed at 900 ℃ for 2 hours, and then air-cooling to room temperature;

(2) the material cooled to room temperature was annealed at 850 ℃ for 2 hours and then air-cooled to room temperature.

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