Overview

Haynes 188 is a cobalt-based superalloy with excellent high temperature strength, oxidation resistance and corrosion resistance. It is a solution-strengthened and age-strengthened alloy consisting of 14% tungsten solution-strengthened and M6C and M23C6 carbide precipitation strengthened. This alloy combines excellent high temperature strength with excellent oxidation resistance, is suitable for long-term exposure in environments up to 2000°F (1095°C), and has excellent resistance to sulphate deposition thermal corrosion environments.

Haynes 188 also has good forming, welding process performance and good constraint welding performance. It can be manufactured and formed by conventional methods and has been used for casting parts. At the same time, the alloy has the characteristics of high melting point, high thermal expansion coefficient and high thermal conductivity.

Limiting Chemical Composition, %

Nickel...................................................................................................................................................................................20.00-24.00

Chromium............................................................................................................................................................................20.00-24.00

Tungsten..............................................................................................................................................................................13.00-16.00

Cobalt...................................................................................................................................................................................30.93-46.73

Iron...........................................................................................................................................................................................3.00 max.

Lanthanum...............................................................................................................................................................................0.02-0.12

Manganese..............................................................................................................................................................................1.25 max.

Carbon......................................................................................................................................................................................0.05-0.15

Silicon.......................................................................................................................................................................................0.20-0.50

Boron......................................................................................................................................................................................0.015 max.

Sulphur...................................................................................................................................................................................0.015 max.

Phosphorus..............................................................................................................................................................................0.02 max.

Physical properties

Mechanical Properties

Heat-Treatment

The heat treatment of Haynes 188 alloy is very important for its properties. In order to maximize the properties of the alloy, specific heat treatment procedures are usually followed. The following are general heat treatment recommendations:

Solution treatment: This is the initial step of the heat treatment and aims to make the alloy fully austenitic. The temperature is usually set between 1800°F (982°C) and 2000°F (1093°C), depending on the thickness of the alloy being treated. This temperature should be maintained for a length of time sufficient to ensure uniform heating of the alloy, but not longer than necessary to avoid overheating of the alloy. The goal of solution treatment is to maximize the dissolution and uniform distribution of carbides.

Two-step aging treatment: The first step is medium temperature aging, usually between 1300°F (704°C) and 1500°F (816°C). The purpose of this step is to precipitate part of the carbide and prepare for subsequent low temperature aging. This stage takes about 8 hours, but the exact time may vary depending on the alloy thickness and the desired microstructure.

Low temperature aging: During this stage, the alloy is heated to approximately 1000°F (538°C). The aim of this step is to further strengthen the alloy to achieve the best mechanical properties by completely precipitating the carbide. Low temperature aging usually takes much longer, possibly from a few days to a few weeks, depending on the thickness of the alloy and the desired microstructure.

Stabilization treatment: In some cases, stabilization treatment may be required to prevent grain boundary corrosion. This step involves heating the alloy to about 1800°F (982°C) and then cooling it quickly. This can fix the carbide on the grain boundary and prevent its migration in subsequent use.

Cooling: After aging treatment, the alloy should be slowly cooled to room temperature. The slow cooling rate helps to minimize harmful transformations in the microstructure.

Please note that specific heat treatment parameters such as temperature, time and cooling rate should be adjusted according to the specific alloy composition, application and equipment used. In practice, it is recommended to work with a materials scientist or metallurgist with expertise and experience to ensure the best results.

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