Steel, carburized steel component, and carburized steel component production method

Abstract

Steel according to one embodiment of the present invention includes prescribed ranges of chemical components, has a quenching index Ceq of more than 7.5 but less than 44.0, has an AlN precipitation index IAlN of more than 0.00030 but less than 0.00110, and has a metal structure that includes 85-100 area% of ferrite. The average distance between sulfides that have an equivalent circular diameter ofat least 1 [mu]m but less than 2 [mu]m that are observed in a cross-section that is parallel to the rolling direction of the steel is less than 30.0 [mu]m. The density of the sulfides that have an equivalent circular diameter of at least 1 [mu]m but less than 2 [mu]m that are observed in the cross-section that is parallel to the rolling direction of the steel is 300 / mm<2> or higher.

Description

Technical field

[0001] The invention relates to a method for manufacturing steel, carburized steel parts and carburized steel parts.

[0002] This application claims priority based on Japanese Patent Application No. 2015-232118 for which it applied to Japan on November 27, 2015, and uses the content here. Background technique

[0003] Generally, Mn, Cr, Mo, Ni, etc. are added in combination in steel used in mechanical structural parts. By applying mechanical processing such as forging and cutting to the carburizing steel that has such a chemical composition and manufactured through processes such as casting, forging, and rolling, and then performing heat treatment such as carburization, a hardened layer with a surface layer, namely, carburizing can be obtained. The carbon layer and the base material that is not affected by the carburizing treatment, namely the carburized steel parts of the steel part.

[0004] Among the costs of manufacturing the carburized steel parts, the costs r...

Examples

Embodiment 1

[0179] Steels a to aa having the chemical compositions shown in Table 1A and Table 1B were melted in a 270-ton converter, and continuous casting was performed using a continuous casting machine to produce a 220×220 mm square slab. Here, the superheat of the molten steel in the tundish is set to 30°C, and the casting speed is set to 1.0 m / min.

[0180] In the continuous casting of the cast slab, the average cooling rate in the temperature range from the liquidus temperature to the solidus temperature at a depth of 15 mm from the surface of the cast slab was performed by changing the cooling water volume of the mold control. By operating in this way, casting slabs a to aa having the chemical compositions shown in Table 1A and Table 1B were continuously cast. For the slab o, the slab p, and the slab q, the primary arm spacing of the dendrites within a range of 15 mm from the surface layer reached 600 μm or more. In other cast slabs, the dendrite primary arm interval within a range...

Embodiment 2

[0242] Except for the average cooling rate in the temperature range from the liquidus temperature to the solidus temperature (hereinafter referred to as the "average cooling rate") at a depth of 15 mm from the surface of the cast slab, it is comparable to steel a and steel Under the same manufacturing conditions as g, steel for carburization having the same chemical composition as steel a and steel g was produced, and various evaluations were performed on these steel for carburization by the same method as steel a and steel g. The average cooling rate was set to the value shown in Table 3.

[0243] [table 3]

[0244]

[0245] As shown in Table 3, test numbers 1 and 7 in which the average cooling rate is within the range of 100 to 500°C have the hardness, ultimate compressibility, and clearance surface wear before carburization because the sulfide is appropriately finely dispersed. The amount and chip weight are within the acceptable range, and the carburized layer thickness, carbu...

Technical field

[0001] The invention relates to a method for manufacturing steel, carburized steel parts and carburized steel parts.

[0002] This application claims priority based on Japanese Patent Application No. 2015-232118 for which it applied to Japan on November 27, 2015, and uses the content here. Background technique

[0003] Generally, Mn, Cr, Mo, Ni, etc. are added in combination in steel used in mechanical structural parts. By applying mechanical processing such as forging and cutting to the carburizing steel that has such a chemical composition and manufactured through processes such as casting, forging, and rolling, and then performing heat treatment such as carburization, a hardened layer with a surface layer, namely, carburizing can be obtained. The carbon layer and the base material that is not affected by the carburizing treatment, namely the carburized steel parts of the steel part.

[0004] Among the costs of manufacturing the carburized steel parts, the costs r...

Examples

Embodiment 1

[0179] Steels a to aa having the chemical compositions shown in Table 1A and Table 1B were melted in a 270-ton converter, and continuous casting was performed using a continuous casting machine to produce a 220×220 mm square slab. Here, the superheat of the molten steel in the tundish is set to 30°C, and the casting speed is set to 1.0 m / min.

[0180] In the continuous casting of the cast slab, the average cooling rate in the temperature range from the liquidus temperature to the solidus temperature at a depth of 15 mm from the surface of the cast slab was performed by changing the cooling water volume of the mold control. By operating in this way, casting slabs a to aa having the chemical compositions shown in Table 1A and Table 1B were continuously cast. For the slab o, the slab p, and the slab q, the primary arm spacing of the dendrites within a range of 15 mm from the surface layer reached 600 μm or more. In other cast slabs, the dendrite primary arm interval within a range...

Embodiment 2

[0242] Except for the average cooling rate in the temperature range from the liquidus temperature to the solidus temperature (hereinafter referred to as the "average cooling rate") at a depth of 15 mm from the surface of the cast slab, it is comparable to steel a and steel Under the same manufacturing conditions as g, steel for carburization having the same chemical composition as steel a and steel g was produced, and various evaluations were performed on these steel for carburization by the same method as steel a and steel g. The average cooling rate was set to the value shown in Table 3.

[0243] [table 3]

[0244]

[0245] As shown in Table 3, test numbers 1 and 7 in which the average cooling rate is within the range of 100 to 500°C have the hardness, ultimate compressibility, and clearance surface wear before carburization because the sulfide is appropriately finely dispersed. The amount and chip weight are within the acceptable range, and the carburized layer thickness, carbu...

Images