GB2116585A

GB2116585A - Cast iron alloys

Info

Publication number: GB2116585A
Application number: GB08304633A
Authority: GB
Inventors: Guiseppe Fazzina; Alessandro Sandionigi
Original assignee: AE ITALY SpA
Current assignee: AE ITALY SpA
Priority date: 1982-02-27
Filing date: 1983-02-18
Publication date: 1983-09-28
Also published as: GB8304633D0

Abstract

A grey or mottled cast iron alloy includes 0.01% to 0.03% boron by weight. The boron increases the wear resistance of the cast iron and makes it especially suitable for the manufacture of cylinder liners for internal combustion engines or compressors. The boron is introduced in the form of borax which is placed in the casting ladle encased in a mild steel box.

Description

SPECIFICATION Cast iron alloys The invention relates to cast iron alloys, to methods for their production and to cylinder liners for internal combustion engines or compressors made of such alloys or by such methods.

Grey and mottled cast irons have the advantage of being cheap to produce and readily cast and machined and are thus suitable for the manufacture of items such as cylinder liners for internal combustion engines or compressors.

They have the disadvantage, however, that their abrasion resistance is not good and this is plainly a disadvantage in cylinder liners because in use they are in rubbing contact with the associated piston.

It is an object of this invention to overcome this disadvantage.

According to a first apsect of the invention, there is provided a grey or mottled cast iron alloy including by weight from 0.01% to 0.03% boron for improving the abrasion resistance of the cast iron.

According to a second aspect of the invention, there is provided a method of manufacture of a grey or mottled cast iron alloy comprising adding to molten cast iron an amount of boron from 0.01% to 0.03% by weight and then cooling.

According to a third aspect of the invention, there is provided a grey or mottled cast iron alloy when made by the method of the second aspect of the invention.

The invention also includes within its scope a cylinder liner for an internal combustion engine or a compressor when made of the alloy according to the first or third aspects of the invention or by the method according to the second aspect of the invention.

The following is a more detailed description of one embodiment of the inv'ention, by way of example.

A grey cast iron alloy is prepared by taking borax (Na2 B4 07.1 OH2 ) and subjecting the borax to a vitrification process to make the borax as anhydrous as possible. An amount of borax is then selected which, on a stoichoimetric determination, should give a required final percentage of boron in the grey cast iron alloy of between 0.01% and 0.03%.

The required amount of anhydrous borax is then placed in a mild steel box which is in turn placed at the base of a casting ladle. Grey cast iron is then added to the casting ladle and the constituents melted. After melting, a deoxidisation of the molten metal is performed to remove oxygen and the temperature stabilized at a casting temperature of between 14400 and 14600.

The molten metal is then cast, for example, in a centrifugal casting apparatus. This should be performed within 8 minutes of pouring. The metal may, for example, be cast as a cylinder liner for an internal combustion engine or a compressor. The castings are then removed and finish machined as necessary.

Examination of the finished metal reveals that the boron is present in two forms. First, as soluble boron with the matrix structure and, secondly, as a complex carbide of Fe-C-B structure which spreads over the intercyrstalline edges. The soluble boron has been found to be present in an amount from 0.01% to 0.01 5% by weight.

Grey cast iron alloys have been produced with the following boron compositions: Total boron Boron in Solution (% by weight) (% by weight) 1. 0.01 0.005 2. 0.02 0.01 3. 0.03 0.015 The average mechanical properties of such alloys are as follow: Hardness: 230-270 (BHN) Tensile Strength: at least 390 N/mmZ Resistance to Bending Stress: at least 195 N/mm2 The grey cast iron alloy so produced has been found to have good resistance to stress, corrosion and wear particularly when used for a cylinder liner. It thus provides the liner with improved wear resistance. It is at present believed that this is due to the fact that the soluble boron increases the compactness of the matrix and that the complex Fe-C-B carbide controls grain growth.

It has been found that if the boron content is lower than 0.01% by weight and boron does not achieve its maximum beneficial effect on the alloy and if the content is much above 0.03% the alloy becomes difficult to machine.

Mottled cast iron may be used in place of grey cast iron.

Claims

1. A grey or mottled cast iron alloy including by weight from 0.01% to 0.03% boron for improving the abrasion resistance of the cast iron.

2. An alloy according to claim 1 wherein the boron is present in the form of a complex carbide of the Fe-C-B type and is also present in the form of soluble boron.

3. An alloy according to claim 2 wherein the soluble boron is present in an amount from 0.005% to 0.015% by weight.

4. A grey or mottled cast iron substantially as herinbefore described.

5. A method of manufacture of a grey or mottled cast iron alloy comprising melting a cast iron and then adding to the molten cast iron an amount of boron from 0.01% to 0.03% by weight and then cooling the molten alloy.

6. A method according to claim 5 and comprising adding the boron by placing the required quantity of boron in a metal box and then placing the boron-containing metal box with the cast iron.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cast iron alloys The invention relates to cast iron alloys, to methods for their production and to cylinder liners for internal combustion engines or compressors made of such alloys or by such methods. Grey and mottled cast irons have the advantage of being cheap to produce and readily cast and machined and are thus suitable for the manufacture of items such as cylinder liners for internal combustion engines or compressors. They have the disadvantage, however, that their abrasion resistance is not good and this is plainly a disadvantage in cylinder liners because in use they are in rubbing contact with the associated piston. It is an object of this invention to overcome this disadvantage. According to a first apsect of the invention, there is provided a grey or mottled cast iron alloy including by weight from 0.01% to 0.03% boron for improving the abrasion resistance of the cast iron. According to a second aspect of the invention, there is provided a method of manufacture of a grey or mottled cast iron alloy comprising adding to molten cast iron an amount of boron from 0.01% to 0.03% by weight and then cooling. According to a third aspect of the invention, there is provided a grey or mottled cast iron alloy when made by the method of the second aspect of the invention. The invention also includes within its scope a cylinder liner for an internal combustion engine or a compressor when made of the alloy according to the first or third aspects of the invention or by the method according to the second aspect of the invention. The following is a more detailed description of one embodiment of the inv'ention, by way of example. A grey cast iron alloy is prepared by taking borax (Na2 B4 07.1 OH2 ) and subjecting the borax to a vitrification process to make the borax as anhydrous as possible. An amount of borax is then selected which, on a stoichoimetric determination, should give a required final percentage of boron in the grey cast iron alloy of between 0.01% and 0.03%. The required amount of anhydrous borax is then placed in a mild steel box which is in turn placed at the base of a casting ladle. Grey cast iron is then added to the casting ladle and the constituents melted. After melting, a deoxidisation of the molten metal is performed to remove oxygen and the temperature stabilized at a casting temperature of between 14400 and 14600. The molten metal is then cast, for example, in a centrifugal casting apparatus. This should be performed within 8 minutes of pouring. The metal may, for example, be cast as a cylinder liner for an internal combustion engine or a compressor. The castings are then removed and finish machined as necessary. Examination of the finished metal reveals that the boron is present in two forms. First, as soluble boron with the matrix structure and, secondly, as a complex carbide of Fe-C-B structure which spreads over the intercyrstalline edges. The soluble boron has been found to be present in an amount from 0.01% to 0.01 5% by weight. Grey cast iron alloys have been produced with the following boron compositions: Total boron Boron in Solution (% by weight) (% by weight) 1. 0.01 0.005 2. 0.02 0.01 3. 0.03 0.015 The average mechanical properties of such alloys are as follow: Hardness: 230-270 (BHN) Tensile Strength: at least 390 N/mmZ Resistance to Bending Stress: at least 195 N/mm2 The grey cast iron alloy so produced has been found to have good resistance to stress, corrosion and wear particularly when used for a cylinder liner. It thus provides the liner with improved wear resistance. It is at present believed that this is due to the fact that the soluble boron increases the compactness of the matrix and that the complex Fe-C-B carbide controls grain growth. It has been found that if the boron content is lower than 0.01% by weight and boron does not achieve its maximum beneficial effect on the alloy and if the content is much above 0.03% the alloy becomes difficult to machine. Mottled cast iron may be used in place of grey cast iron. Claims

4. A grey or mottled cast iron substantially as herinbefore described.

7. A method according to claim 6 wherein the metal box is of mild steel.

8. A method according to any one of claims 5 to 7 wherein the boron is added in the form of an hydros borax.

9. A grey or mottled cast iron alloy when made by the method of any one of claims 5 to 8.

10. A method of manufacture of a cast iron alloy substantially as herein described.

11. A cylinder liner for an engine or a compressor and made of a cast iron alloy according to any one of claims 1 to 4 or by the method of any one of claims 5 to 10.