Method for heat-treating uppermost surface of spheroidal graphite cast iron and spheroidal graphite cast iron heat-treated by the same

Patent metadata

Field	Value
Publication number	US-2020216923-A1
Application number	US-201916662633-A
Country	US
Kind code	A1
Filing date	Oct 24, 2019
Priority date	Jan 7, 2019
Publication date	Jul 9, 2020
Grant date	—

Abstract

Disclosed are a method for heat-treating a surface of a spheroidal graphite cast iron, particularly, heat-treating an uppermost surface of spheroidal graphite cast iron, and spheroidal graphite cast iron heat-treated by the same. The method may include first heat treating for forming ferrite and second heat treating for oxy-nitriding. The spheroidal graphite cast iron heat-treated includes an oxidation layer and a compound layer having a thickness of about 15 to 30 μm, which may be uniform. The method of the heat-treating may decrease the pearlite fraction in the uppermost surface of spheroidal graphite cast iron and increase the ferrite fraction by forming ferrite, thereby forming a compound layer having a thickness of about 15 to 30 μm during an oxy-nitriding heat treatment.

First claim

What is claimed is:

1 . A method for heat-treating a surface of spheroidal graphite cast iron, comprising:
first heat treating the spheroidal graphite cast iron for forming ferrite; and second heat treating for oxy-nitriding the spheroidal graphite cast iron.

2 . The method of claim 1 , wherein the first heat treating comprises: heating the spheroidal graphite cast iron to a first heating temperature of about 940 to 1,060° C.; and maintaining the first heating temperature, wherein a total time for the first heat treating time is about 80 to 100 minutes.

3 . The method of claim 2 , wherein the first heat treatment step further comprises: air-cooling the spheroidal graphite cast iron for about 110 to 130 minutes.

4 . The method of claim 1 , wherein the second heat treating comprises:
nitrocarburizing by introducing a gas; oxidizing the spheroidal graphite cast iron; and cooling; wherein the nitrocarburizing is performed at a second heat treating temperature of about 550° C. to 570° C. for about 720 minutes to 1,200 minutes.

5 . The method of claim 4 , wherein the cooling is furnace cooling.

6 . A spheroidal graphite cast iron comprising:
an oxidation layer; and a compound layer, wherein the compound layer has a thickness of about 15 to 30 μm.

7 . The spheroidal graphite cast iron of claim 6 , wherein the thickness of the compound layer is uniform.

8 . The spheroidal graphite cast iron of claim 6 , wherein an uppermost surface of the spheroidal graphite cast iron comprises ferrite fraction in about 60 to 80%.

9 . The spheroidal graphite cast iron of claim 8 , wherein the compound layer comprises:
a pore layer; and a nitride compound layer comprising a gamma prime phase and an epsilon phase.

10 . The spheroidal graphite cast iron of claim 9 , wherein the nitride compound layer consists of the gamma prime phase and the epsilon phase.

11 . The spheroidal graphite cast iron of claim 9 , wherein the nitride compound layer comprises the epsilon phase in about 80% or greater.

12 . The spheroidal graphite cast iron of claim 9 , wherein the compound layer has the hardness of about HV 600 to 1000.

13 . The spheroidal graphite cast iron of claim 9 , wherein the compound layer comprises the pore layer in a fraction of about 25 to 35%.

14 . The spheroidal graphite cast iron of claim 10 , wherein the compound layer comprises the pore layer in a fraction of about 25 to 35%.

15 . The spheroidal graphite cast iron of claim 9 , wherein the compound layer comprises the oxidation layer, the pore layer, the gamma prime phase and the epsilon phase from the uppermost surface of the spheroidal graphite cast iron.

16 . The spheroidal graphite cast iron of claim 6 , the cast iron comprises the oxidation layer and the compound layer from an uppermost surface of the cast iron.

17 . A vehicle part comprising a spheroidal graphite case iron of claim 6 .

18 . A vehicle comprising a vehicle part of claim 17 .

Assignees

• Hyundai Motor Co Ltd
• Kia Motors Corp

Inventors

• Kwon Eun-Soo
• Lee Hyung-Gook
• Sim Yong-Bo

Classifications

• C23C8/30

  Carbo-nitriding · CPC title

• C23C8/18

  Oxidising of ferrous surfaces · CPC title

• C22C37/04

  containing spheroidal graphite · CPC title

• C21D8/0257

  with diffusion of elements, e.g. decarburising, nitriding · CPC title

• C21D1/78 Primary

  Combined heat-treatments not provided for above · CPC title