Black Heart Malleable Cast-Iron and Method for Manufacturing Same

Patent metadata

Field	Value
Publication number	US-2020080173-A1
Application number	US-201816496894-A
Country	US
Kind code	A1
Filing date	Mar 12, 2018
Priority date	Mar 27, 2017
Publication date	Mar 12, 2020
Grant date	—

Abstract

Provided is a black heart malleable cast iron and a method for manufacturing the same which can significantly shorten the time required for graphitization, as compared with the prior art. The black heart malleable cast iron includes a matrix of ferrite and lump graphite included in the matrix, and includes at least one selected from the group consisting of (i) 0.0050% by mass or more and 0.15% by mass or less of bismuth and 0.020% by mass or more of manganese, and (ii) 0.0050% by mass or more and 1.0% by mass or less of aluminum and 0.0050% by mass or more of nitrogen. In addition, the 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 of the matrix and a standard grain size chart.

First 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 at least one selected from the group consisting of:
(i) 0.0050% by mass or more and 0.15% by mass or less of bismuth and 0.020% by mass or more of manganese; and (ii) 0.0050% by mass or more and 1.0% by mass or less of aluminum and 0.0050% by mass or more of nitrogen, 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 of the matrix and a standard grain size chart.

2 . 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.

3 . The black heart malleable cast iron according to claim 1 , wherein an average particle diameter of particles of the lump graphite is 10 micrometers or more and 40 micrometers or less.

4 . 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.

5 . The black heart malleable cast iron according to claim 1 , further comprising 2.0% by mass or more and 3.4% by mass or less of carbon, and 0.5% by mass or more and 2.0% by mass or less of silicon, the balance being iron and inevitable impurities.

6 . The black heart malleable cast iron according to claim 5 , wherein the carbon content is 2.5% by mass or more and 3.2% by mass or less, and silicon content is 1.0% by mass or more and 1.7% by mass or less.

7 . The black heart malleable cast iron according to claim 5 , further comprising more than 0% by mass and 0.010% by mass or less of boron.

8 . A method for manufacturing a black heart malleable cast iron, which comprises the steps of:
casting a casting material to produce a cast metal comprising 2.0% by mass or more and 3.4% by mass or less of carbon, 0.5% by mass or more and 2.0% by mass or less of silicon, and at least one selected from the group consisting of: (i) 0.0050% by mass or more and 0.15% by mass or less of bismuth, and 0.020% by mass or more of manganese, and (ii) 0.0050% by mass or more and 1.0% by mass or less of aluminum and 0.0050% by mass or more of nitrogen, the balance being iron and inevitable impurities; preheating a resultant cast metal at a temperature of 275° C. or higher and 425° C. or lower; and graphitizing the cast metal at a temperature exceeding 680° C. after the preheating.

9 . The method for manufacturing a black heart malleable cast iron according to claim 8 , wherein the cast metal further comprises more than 0% by mass and 0.010% by mass or less of boron.

10 . The method for manufacturing a black heart malleable cast iron according to claim 8 , wherein a time for preheating the cast metal at the temperature of 275° C. or higher and 425° C. or lower in the preheating step is 30 minutes or more and 5 hours or less.

11 . The method for manufacturing a black heart malleable cast iron according to claim 8 , wherein a total time for graphitizing the cast metal at the temperature exceeding 680° C. in the graphitizing step is one hour or more and 6 hours or less.

12 . The method for manufacturing a black heart malleable cast iron according to claim 8 , wherein the graphitization step includes first stage graphitization that includes heating the cast metal at a temperature exceeding 900° C., and second stage graphitization in which a start temperature is 720° C. or higher and 800° C. or lower, and a completion temperature is 680° C. or higher and 720° C. or lower.

13 . The black heart malleable cast iron according to claim 2 , wherein an average particle diameter of particles of the lump graphite is 10 micrometers or more and 40 micrometers or less.

14 . The black heart malleable cast iron according to claim 2 , 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.

15 . The black heart malleable cast iron according to claim 3 , 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.

16 . The black heart malleable cast iron according to claim 13 , 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.

17 . The method for manufacturing a black heart malleable cast iron according to claim 10 , wherein a total time for graphitizing the cast metal at the temperature exceeding 680° C. in the graphitizing step is one hour or more and 6 hours or less.

18 . The method for manufacturing a black heart malleable cast iron according to claim 10 , wherein the graphitization step includes first stage graphitization that includes heating the cast metal at a temperature exceeding 900° C., and second stage graphitization in which a start temperature is 720° C. or higher and 800° C. or lower, and a completion temperature is 680° C. or higher and 720° C. or lower.

19 . The method for manufacturing a black heart malleable cast iron according to claim 11 , wherein the graphitization step includes first stage graphitization that includes heating the cast metal at a temperature exceeding 900° C., and second stage graphitization in which a start temperature is 720° C. or higher and 800° C. or lower, and a completion temperature is 680° C. or higher and 720° C. or lower.

20 . The method for manufacturing a black heart malleable cast iron according to claim 17 , wherein the graphitization step includes first stage graphitization that includes heating the cast metal at a temperature exceeding 900° C., and second stage graphitization in which a start temperature is 720° C. or higher and 800° C. or lower, and a completion temperature is 680° C. or higher and 720° C. or lower.

Assignees

• Hitachi Metals Ltd

Inventors

• Goto Ryo
• Fukaya Takayuki
• Matsui Hiroshi
• Matsuura Kenta

Classifications

• C21D2211/005

  Ferrite · CPC title

• C21D5/14

  Graphitising · CPC title

• C22C33/08

  Making cast-iron alloys · CPC title

• C22C37/10 Primary

  containing aluminium or silicon · CPC title

• C22C37/00

  Cast-iron alloys · CPC title