There are many materials in this world, classified into four groups: metals, ceramics, polymers, and composites. Out of these, metals are most commonly used for manufacturing applications. Steel, an alloy made of iron and carbon, has been one of the most widely used materials worldwide since the beginning of the industrial revolution. 

There are many different grades of steel designed for specific applications. When chromium is added to steel, we get stainless steel. 

In this article, we will discuss one specific martensitic stainless steel – 17-4PH. 

Understanding 17-4 PH Stainless Steel.

The numbers in this steel’s name indicate the amount of chromium and nickel present, whereas the alphabets denote the treatment process it went through.

This steel grade contains 17% chromium and 4% nickel. The ‘PH’ here stands for precipitation hardening – a heat treatment process this material goes through. 17-4PH stainless steel is also known as type 630 stainless steel in the industry. 

This steel contains iron, nickel, chromium, and copper. It also contains manganese, silicon, and phosphorus in small amounts.

SS 17-4PH also contains 3-5% copper, which makes it different from type 304 and 430 steels. The addition of copper improves the precipitation hardening process. Copper also improves the resistance of steel to corrosion in acidic or marine environments. 

How Is 17-4PH Steel Made?

17-4PH steel is formed by a heat treatment process called precipitation hardening. This process happens at a low temperature and uses alloying materials to form precipitates for strengthening. However, there are other steps that you carry out before precipitation hardening:

• Melt your raw materials, which include iron, nickel, chromium, copper, and other alloying additions, using an electric arc furnace. 
• Pour the molten material into molds to form ingots. 
• Hot-roll your ingots to form slabs or other shapes, such as plates.
• Anneal your formed bars or plates to remove inbuilt stresses. This process improves the steel’s flexibility and toughness. 
• Perform precipitation hardening for 17-4PH stainless steel at around 620 degrees celsius for many hours. This process helps form a fine distribution of alloying elements present in the steel matrix, including nickel and copper, helping increase the strength and ductility of the steel. 
• Finally, you can perform different finishing processes, such as cutting, polishing, or coating, to prepare your steel for different applications. 

What Is the Microstructure of 17-4PH Stainless Steel?

17-4PH steel is martensitic in nature. It has a fine grain and uniform structure. This steel also has a uniform distribution of precipitates of alloying elements such as copper and nickel in a martensitic steel matrix. Such a microstructure gives it enhanced strength, hardness, and corrosion resistance. 

Properties of 17-4PH Stainless Steel.

17-4PH stainless steel has a wide range of desirable properties that allow it to be used in high-end applications, like medical devices and the nuclear power industry, amongst others. 

1. High Strength.

This alloy has a high tensile strength of 1275 MPa and a hardness of 350 around the Brinnel hardness scale. These values are much higher than those for 304 and 316 stainless steel. 

1. High Corrosion Resistance. 

SS 17-4PH has high corrosion resistance in acidic, marine, and high-temperature environments. It has good corrosion resistance because of copper, nickel, and chromium. The addition of molybdenum can further improve this property. 

This steel is also stable against corrosion caused by high-temperature. 

1. Good Weldability 

This steel type can be welded using techniques like Tungsten Inert Gas Welding (TIG) and Plasma Arc Welding. However, there is a risk of cracking steel samples with welding. It is important that the welding is carried out using low heat to prevent cracking. 

1. Good Magnetic Properties 

SS 17-4PH is magnetic in the annealed condition. This is because large amounts of ferrite and martensite are present in the microstructure of the steel after annealing. The ferrite phase is primarily responsible for giving steel its magnetic properties. 

1. High Toughness

17-4PH stainless steel has a very high toughness and yield strength of 1170 MPa, which is much higher than the yield strength values for 304 and 316 stainless steel. This means that 17-4PH stainless steel does not fracture easily. 

Applications of SS 17-4PH.

17-4PH stainless steel has many different properties, making it possible for us to use this steel in different industries. Uses of 17-4PH stainless steel include:

1. Nuclear Power Generation 

17-4PH stainless steel is used for making dry casks for nuclear power generation. These are used to store the used fuel from the power generation process. 

As this alloy has good weldability, you can butt-weld the steel cask to prevent fuel from leaking. 

1. Turbine Blades. 

Turbine blades experience high heat and pressure and must be able to remain functional under these conditions. So, 17-4PH stainless steel is suitable for making turbine blades as it has high resistance to heat. 

This steel does not lose its strength even at high temperatures, which is important for turbine blades. 

1. Oil and Gas Industry 

17-4PH stainless steel is used in the oil and gas industry to make pipes deep below sea level. This is because it can bear the high pressure experienced at depths. 

This alloy is also suitable for oil and gas pipelines because it resists corrosion in acidic, hydrogen, and sulfide-containing environments. 

1. Pulp and Paper Industry 

SS 17-4PH is used in the paper industry to make equipment like bulk digesters for pulp products. As this equipment is at a high risk of rust, using 17-4PH is an intelligent decision to protect it from corrosion. 

1. Food Manufacturing. 

This material is used for making food processing equipment because it shows good resistance to corrosion. It is also easy to clean, making it easier for us to keep our equipment neat and clean. 

1. Marine Industry 

1SS 7-4PH is used for making pumps, propellers, and other equipment used in the marine industry because it shows high corrosion resistance in salt water. 

1. Defense Equipment

Type 17-4PH can be used for making parts for firearms and missile aircraft. This type of steel has high strength compared to other steels and shows good corrosion resistance in different environments, making it suitable for use in defense equipment. 

1. Medical Devices

17-4PH steel is used for making medical devices such as surgical instruments and implants because it has high corrosion resistance. This steel also shows good biocompatibility with the human body and has good strength making it suitable for implants. 

Limitations of 17-4PH  Stainless Steel 

There are some disadvantages associated with every material, and SS 17-4PH is no exception.

1. High Cost. 

17-4PH stainless steel is a relatively expensive material. This is because of its high amounts of alloying elements, such as chromium, nickel, and copper. 

1. Limited Availability

17-4PH stainless steel is difficult to find in markets. The limited availability is because the manufacturing process for 17-4PH stainless requires many steps, including precipitation hardening. You may need help sourcing this type of steel as it is less easily available than other steels like 304 and 314.

1. Welding Conditions Require Control 

17-4PH stainless steel can be welded using traditional techniques such as TIG. However, this type of steel can easily crack during the welding process. You must control welding conditions such as angle and heat to prevent this. 

You will need to hire professional welders, which is an additional cost in manufacturing processes. 

1. Stress Corrosion Cracking 

SS 17-4PH is highly resistant to many forms of corrosion except stress corrosion cracking. So, you can not use it in an environment with high stress and chloride concentration, or it will crack. 

1. Varying Magnetic Properties 

This type of steel can act magnetic and non-magnetic depending on the heat treatment it has undergone. If 17-4PH stainless steel is only annealed, it will contain ferrite to show magnetic properties. However, ferrite will not be present if the steel is precipitation-hardened, so the steel will not be magnetic. 

Using this steel in magnetic or non-magnetic applications is difficult since it depends on the heat treatment the steel has undergone. 

Endnote

17-4PH stainless steel is a martensitic steel formed by precipitation hardening. It has a wide range of desirable properties due to high amounts of nickel, chromium, and copper.

SS 17-4PH is used in many industries, such as nuclear power industries, for making turbine blades and even medical devices like implants. You can also use it in the marine industry as it shows excellent corrosion resistance in seawater environments.

Good weldability and stability make this steel suitable for manufacturing different equipment parts. 

However, you will have to carry out the welding process carefully. Finding someone who manufactures the steel you require for your industry is sometimes difficult. If that’s the case for you, please contact us so we can help!