CN111118390A

CN111118390A - High-strength nodular cast iron with good weldability and machinability

Info

Publication number: CN111118390A
Application number: CN201910499116.7A
Authority: CN
Inventors: H·李; J·杨; D·J·威尔逊; D·A·杰勒德; D·M·锡尼
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2018-10-30
Filing date: 2019-06-10
Publication date: 2020-05-08
Also published as: US20200131606A1; DE102019115680A1

Abstract

The invention provides a high-strength ductile iron with good weldability and machinability. A ductile iron alloy and automotive components such as differential components and transaxle components are provided. The ductile iron alloy may comprise iron, about 3.1-3.3 wt.% carbon, about 2.7-4.3 wt.% silicon, about 0.15-0.40 wt.% manganese, about 0-0.10 wt.% magnesium, about 0-0.2 wt.% nickel, about 0-0.4 wt.% copper, about 0-0.30 wt.% chromium, about 0-0.03 wt.% phosphorus, and about 0-0.02 wt.% sulfur. The ductile iron alloy may have an ultimate tensile strength of at least 620MPa in the as-cast condition. The alloy has good weldability, can be welded with steel parts without substantial preheating or postweld heat treatment for weldments with high hardness and high toughness, and has good machinability to facilitate comprehensive machining operations.

Description

High-strength nodular cast iron with good weldability and machinability

Technical Field

The present disclosure relates generally to ferrous alloys and, more particularly, to ferrous alloys that are spherical and have the strength required for weldability and machinability, and components made therefrom, such as differential and transaxle components.

Background

The welded front wheel drive differential carrier reduces both weight and cost compared to conventional bolted joints. However, conventional high strength ductile iron, such as SAE D5506 and D7003, have poor weldability to steel and poor machinability due to a high percentage of pearlite in the matrix (e.g., about 70% -100%). High concentrations of pearlite typically result in low weldability, low machinability and low fracture toughness. On the other hand, for ductile iron, the more pearlite phase, the higher the strength. Many automotive components often require high strength.

The low toughness of the weld Heat Affected Zone (HAZ) in ductile iron makes the weld susceptible to weld cracking. For example, since pearlite in D7003 is bulky, welding is very difficult without complicated welding processes such as those including preheating and post-weld heat treatment.

Disclosure of Invention

The present disclosure provides a novel high strength ductile iron alloy having desirable weldability and machinability. For example, the novel ductile iron alloy may have an ultimate tensile strength of at least 620MPa and an elongation of at least 6%. The high strength ductile iron alloy may have a ferrite/pearlite matrix with no more than 35% pearlite phase. By using the novel ductile iron alloy, toughness and fatigue strength of a weld Heat Affected Zone (HAZ) are enhanced, and machining costs can be reduced.

In one example (which may be combined with or separate from other examples and features provided herein), there is provided a ductile iron alloy comprising: iron, about 3.1 wt.% to about 3.3 wt.% carbon, about 2.7 wt.% to about 4.3 wt.% silicon, and about 0.15 wt.% to about 0.40 wt.% manganese.

In another example (which may be combined with or separate from other examples provided herein), there is provided a ductile iron alloy consisting essentially of: about 3.1 to about 3.3 weight percent carbon, about 2.7 to about 4.3 weight percent silicon, about 0.15 to about 0.40 weight percent manganese, 0 to about 0.10 weight percent magnesium, 0 to about 0.2 weight percent nickel, 0 to about 0.4 weight percent copper, 0 to about 0.30 weight percent chromium, 0 to 0.03 weight percent phosphorus, 0 to 0.02 weight percent sulfur, and the balance iron.

Additional features may optionally be provided, including but not limited to the following: wherein the silicon is provided in an amount of about 3.5 wt.% to about 4.1 wt.%; wherein the iron is provided in an amount of at least 86.55 wt.%; the ductile iron alloy further comprises magnesium in an amount not exceeding 0.10 wt%; the ductile iron alloy further comprises nickel in an amount not exceeding 0.2 wt%; the ductile iron alloy further comprises copper in an amount not exceeding 0.4 wt%; the ductile iron alloy further comprises chromium in an amount not exceeding 0.30 wt%; the ductile iron alloy further comprises sulfur in an amount not exceeding 0.02 wt%; the ductile iron alloy further comprises phosphorus in an amount not exceeding 0.03 wt%; wherein the ductile iron alloy has an ultimate tensile strength greater than 620MPa in the as-cast condition; the ductile iron alloy has an elongation of greater than 6%; wherein the ductile iron alloy is substantially free of cobalt and molybdenum; wherein the iron is present in a ferrite microstructure of 65% to 85% and a pearlite microstructure of 15% to 35%; and wherein the iron surrounds the plurality of graphite nodules.

Additional features may be included, including but not limited to the following: an automobile part formed of any one modification of a ductile iron alloy; and the automotive component is a differential component or a drive axle component.

The above features and advantages and other features and advantages of the present disclosure will become apparent from the following detailed description of the many aspects of the present disclosure when taken in conjunction with the accompanying drawings and the appended claims.

Drawings

The drawings are provided for illustrative purposes only and are not intended to limit the present disclosure or the appended claims.

FIG. 1 is an enlarged view of a ductile iron alloy showing its microstructure according to the principles of the present disclosure; and is

FIG. 2 is a perspective view of a differential assembly having components formed from a ductile iron alloy according to the principles of the present disclosure.

Detailed Description

Ductile iron alloys having the desired strength, weldability and machinability are provided. These ductile iron alloys are particularly useful for cast automotive parts that are subjected to large loads, fatigue, and extensive machining operations, as well as being welded to another part. These automotive parts can be realized as an as-cast, which saves additional steps and costs. For example, components formed from the disclosed ductile iron alloys may be laser welded to steel without preheating or post-weld heat treatment. The hardness/brittleness of the heat affected zone may be lower than that of conventional ferrous alloys, resulting in improved fracture toughness and fatigue characteristics of the weld zone.

The ductile iron alloys disclosed herein comprise iron, carbon, silicon, manganese, and the ductile iron alloys may further comprise phosphorus, sulfur, nickel, copper, chromium, and magnesium.

The ductile iron alloy disclosed herein may comprise iron and about 3.1 wt% to about 3.3 wt% (or just 3.1 wt% -3.3 wt%) carbon by weight, about 3.5 wt% to about 4.1 wt% (or just 3.5 wt% -4.1 wt%) silicon by weight, about 0.15 wt% to about 0.40 wt% (or just 0.15 wt% -0.40 wt%) manganese by weight. In some cases, the silicon can be provided in an amount as low as about 2.7 wt% or up to about 4.3 wt%, and the equivalent weight of the carbon remains about 4.2 wt% to about 4.4 wt%.

The iron can be provided in an amount of at least 86.55 wt.%. The ductile iron alloy may further comprise one or more of the following: magnesium in an amount of no more than 0.10 wt.%; nickel in an amount of no more than 0.2 wt.%; copper in an amount of no more than 0.4 wt.%; chromium in an amount of not more than 0.30 wt.%; phosphorus in an amount of no more than 0.03 wt%; and sulfur in an amount not exceeding 0.02 wt%. For example, table 1 shows a first example of a ductile iron alloy that includes iron, carbon, silicon, manganese, and may further include phosphorus, sulfur, magnesium, nickel, copper, and chromium. The iron can be provided in an amount of at least 86.55 wt.%.

Table 1: first example of novel spheroidal graphite cast iron alloy

In another example, table 2 shows an example of a ductile iron alloy that includes iron, carbon, silicon, manganese, and may further include phosphorus, sulfur, magnesium, nickel, copper, and chromium. In this second example, silicon has a smaller range of possible energies, in weight percent. As previously mentioned, the iron can be provided in an amount of at least 86.55 wt.%.

Table 2: second example of novel spheroidal graphite cast iron alloy

As with table 1, it should be understood that the novel ductile iron alloy may have any combination of the elements listed in table 2 above, and need not contain all of them.

Referring now to fig. 1, a ductile iron alloy 10 is shown, the ductile iron alloy 10 may have a microstructure formed from compositions such as those shown in table 1. There are a plurality of graphite nodules 12 and iron 14 surrounding the graphite nodules 12. Of the iron 14 surrounding the graphite nodules 12, 65% -85% of the iron has a ferrite microstructure 16 and only 15% -35% of the iron has a pearlite microstructure 18. In one example, the iron 14 may be set to be about 20% pearlite and about 80% ferrite. Generally, the pearlite microstructure 18 surrounds the ferrite microstructure 16, and the ferrite microstructure 16 is disposed directly adjacent to the graphite nodules 12. The ferrite microstructure 16 appears lighter than the pearlite microstructure 18 in fig. 1, according to conventional etching procedures for metallographic characterization.

The ductile iron alloy 10 may have an ultimate tensile strength of, for example, at least 620MPa in the as-cast condition. In some examples, the as-cast ductile iron alloy may have an ultimate tensile strength in the range of about 620MPa to about 700 MPa. Thus, the ductile iron alloy 10 has sufficient strength for use in high-load automotive parts, such as differential and transaxle parts, but is also weldable and machinable. The ductile iron alloy 10 may have an elongation of, for example, at least 6%.

The ductile iron alloys described herein may be used to manufacture automotive components, which in some cases may be cast automotive propulsion system components. Accordingly, it is within the contemplation of the inventors herein to extend the disclosure to automotive components, including, but not limited to, differential components, transaxle components for both front and rear axles, and the like. For example, referring to fig. 2, a differential assembly 200 is shown, the differential assembly 200 may have components made of any of the variations of the ductile iron alloys described herein, and the differential assembly 200 may be cast. For example, the differential assembly 200 has a differential carrier 202 that may be formed from variations of the ductile iron alloys described herein. Thus, differential carrier 202 may be effectively welded to adjacent components via

welds

204, 206. More specifically, differential carrier 202 may be welded to outer ring gear 208 by axial weld 204 to further connect to the transmission assembly. Alternatively, the components may be arranged such that the weld 204 may be a radial weld. Additionally, differential carrier 202 may be welded to another component, such as cover 210, for example, by radial weld 206. In this example, outer ring gear 208 and cover 210 are formed of steel, and differential carrier 202, which is formed of the ductile iron alloys disclosed herein, forms a good weld with these steel components.

Differential carrier 202 may

house side gears

212, 214 connected to

half shafts

216, 218 and

differential pinions

220, 222 connected to shaft 224. Any of the components of the differential assembly 200 may be formed from any of the variations of the ductile iron alloys disclosed herein. Thus, the components of differential assembly 200 (such as differential carrier 202) are machinable, weldable, and strong enough to be used in automotive applications. The ductile iron alloy of the present invention is also useful in oil and gas industrial parts as well as general industrial parts.

Further, while the above examples are described separately, those skilled in the art will appreciate that, having the benefit of this disclosure, the amounts of elements described herein may be mixed and matched with various examples within the scope of the appended claims. It should also be understood that any of the above concepts may be used alone or in combination with any or all of the other above concepts.

Claims

1. A ductile iron alloy comprising:

iron;

about 3.1 wt% to about 3.3 wt% carbon;

about 2.7 wt% to about 4.3 wt% silicon; and

about 0.15 wt% to about 0.40 wt% manganese.

2. The ductile iron alloy according to claim 1, wherein said silicon is provided in an amount of about 3.5 to about 4.1 wt.%.

3. The ductile iron alloy according to any of the preceding claims, wherein said iron is provided in an amount of at least 86.55 wt.%.

4. The ductile iron alloy according to any of the preceding claims, further comprising:

magnesium in an amount of no more than 0.10 wt.%;

nickel in an amount of no more than 0.2 wt.%;

copper in an amount of no more than 0.4 wt.%; and

chromium in an amount of not more than 0.30% by weight.

5. The ductile iron alloy according to any of the preceding claims, further comprising:

sulfur in an amount not exceeding 0.02 wt%; and

phosphorus in an amount not exceeding 0.03 wt%.

6. The ductile iron alloy according to any of the preceding claims, wherein said ductile iron alloy has an ultimate tensile strength in the as-cast condition of more than 620MPa, and wherein said ductile iron alloy has an elongation of more than 6%.

7. The ductile iron alloy according to any of the preceding claims, wherein said ductile iron alloy is substantially free of cobalt and molybdenum.

8. The ductile iron alloy according to any of the preceding claims, wherein said iron is present in a ferrite microstructure of 65-85% and a pearlite microstructure of 15-35%, wherein said iron surrounds a plurality of graphite nodules.

9. An automotive part formed from the ductile iron alloy according to any one of the preceding claims.

10. The automotive part of claim 9, wherein the automotive part is one of a differential part and a drive axle part.