# US 12,760,395 B2 · Black heart malleable cast iron and method for producing same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,760,395 B2 - Document ID: US12760395B2 - Status: Granted - Kind: B2 - Application number: 17/909,346 - Filed: 2021-03-05 - Published: 2023-03-23 - Granted: 2026-10-13 - Earliest claimed: 2020-03-06 - Assignees: Kuwana Metals, Ltd. - Applicants: Kuwana Metals, Ltd. - Inventors: Ryo Goto - Web page: https://patentgrep.com/patent/US12760395B2 ## CPC - C22C 37/10: containing aluminium or silicon - C21D 5/14: Graphitising - C22C 33/08: Making cast-iron alloys - C21D 2211/005: Ferrite - C21D 2211/006: Graphite - C22C: ALLOYS (treatment of alloys C21D, C22F) - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) ## Abstract The black heart malleable cast iron according to the present embodiment comprises a matrix of ferrite and lump graphite included in the matrix, the black heart malleable cast iron comprising 50 ppm or more and 100 ppm or less of boron, and 65 ppm or more and 200 ppm or less of nitrogen in a mass ratio, wherein a grain size of the matrix is 8.0 or more and 10.0 or less in terms of grain size number, numerically determined by comparison between a metallographic photograph and a standard grain size chart. ## Claims ### Claim 1 A black heart malleable cast iron comprising a matrix of ferrite and lump graphite included in the matrix, the black heart malleable cast iron comprising 50 ppm or more and 100 ppm or less of boron, and 65 ppm or more and 200 ppm or less of nitrogen in a mass ratio, wherein the black heart malleable cast iron excludes bismuth, the black heart malleable cast iron excludes aluminum, when the content of boron is B (ppm) and the content of nitrogen is N (ppm) in a mass ratio, the values of B and N satisfy the following formula (1), and a grain size of the matrix is 8.0 or more and 10.0 or less in terms of grain size number, numerically determined by comparison between a metallographic photograph and a standard grain size chart; N ≥ 1. 3 ⁢ B - 10. ( 1 ) ### Claim 2 (depends on 1) The black heart malleable cast iron according to claim 1, further comprising titanium, wherein when the content of titanium is Ti (ppm), the content of boron is B (ppm) and the content of nitrogen is N (ppm) in a mass ratio, the values of Ti, B and N satisfy the following formula (2): N ≥ 1. 3 ⁢ B + 0 . 3 ⁢ T ⁢ i - 10. ( 2 ) ### Claim 3 (depends on 2) The black heart malleable cast iron according to claim 2, further comprising 2.0% or more and 3.4% or less of carbon, and 0.5% or more and 2.0% or less of silicon in a mass ratio, the balance being iron and inevitable impurities. ### Claim 4 (depends on 1) The black heart malleable cast iron according to claim 1, wherein the lump graphite is present while being dispersed at positions of crystal grain boundaries of the matrix. ### Claim 5 (depends on 1) The black heart malleable cast iron according to claim 1, wherein an average particle diameter of the lump graphite is 10 micrometers or more and 40 micrometers or less. ### Claim 6 (depends on 1) The black heart malleable cast iron according to claim 1, wherein the number of particles of the lump graphite per square millimeter of a cross-sectional area thereof is 200 or more and 1,200 or less. ### Claim 7 (depends on 1) The black heart malleable cast iron according to claim 1, further comprising 2.0% or more and 3.4% or less of carbon, and 0.5% or more and 2.0% or less of silicon in a mass ratio, the balance being iron and inevitable impurities. ### Claim 8 (depends on 7) The black heart malleable cast iron according to claim 7, further comprising more than 0% and 1.0% or less of manganese in a mass ratio. ### Claim 9 (depends on 1) The black heart malleable cast iron according to claim 1, further comprising more than 0% and 1.0% or less of manganese in a mass ratio. ### Claim 10 (depends on 1) A method for producing the black heart malleable cast iron of claim 1, which comprises the steps of: adjusting the composition of a molten metal obtained by melting raw materials, obtaining a cast iron comprising 2.0% or more and 3.4% or less of carbon, 0.5% or more and 2.0% or less of silicon, 50 ppm or more and 100 ppm or less of boron, and 65 ppm or more and 200 ppm or less of nitrogen in a mass ratio, the balance being iron and inevitable impurities, by casting using the molten metal with the composition adjusted, the cast iron wherein when the content of boron is B (ppm) and the content of nitrogen is N (ppm) in a mass ratio, the values of B and N satisfy the following formula (1), and graphitizing the cast iron at a temperature exceeding 680° C.; N ≥ 1. 3 ⁢ B - 10. ( 1 ) ### Claim 11 (depends on 10) The method for producing a black heart malleable cast iron according to claim 10, wherein a time for graphitizing the cast iron at the temperature exceeding 680° C. in the step of graphitizing the cast iron is 1 hour or more and 6 hours or less in total. ### Claim 12 (depends on 10) The method for producing a black heart malleable cast iron according to claim 10, wherein the step of adjusting the composition of the molten metal includes the step of: adding a second molten metal after adding a nitrogen-containing compound to a first molten metal. ### Claim 13 (depends on 10) The method for producing a black heart malleable cast iron according to claim 10, wherein the step of adjusting the composition of the molten metal includes the step of: adding at least one of ferroboron and manganese nitride to the molten metal before casting to adjust the composition. ### Claim 14 (depends on 9, 10) The method for producing a black heart malleable cast iron according to claim 10, wherein at least one of a cast iron or a black heart malleable cast iron produced by using the method for producing a black heart malleable cast iron according to claim 9 is included in raw materials. ### Claim 15 (depends on 10) The method for producing a black heart malleable cast iron according to claim 10, further comprising titanium, wherein when the content of titanium is Ti (ppm), the content of boron is B (ppm) and the content of nitrogen is N (ppm) in a mass ratio, the values of Ti, B and N satisfy the following formula (2): N ≥ 1. 3 ⁢ B + 0 . 3 ⁢ T ⁢ i - 10. ( 2 ) ### Claim 16 A black heart malleable cast iron comprising a matrix of ferrite and lump graphite included in the matrix, the black heart malleable cast iron comprising 50 ppm or more and 100 ppm or less of boron, and 156 ppm or more and 200 ppm or less of nitrogen in a mass ratio, wherein when the content of boron is B (ppm) and the content of nitrogen is N (ppm) in a mass ratio, the values of B and N satisfy the following formula (1), and a grain size of the matrix is 8.0 or more and 10.0 or less in terms of grain size number, numerically determined by comparison between a metallographic photograph and a standard grain size chart; N ≥ 1 . 3 ⁢ B - 10. ( 1 )