17-4 Stainless Steel: Deep Dive Into a High-Performance Alloy

In the world of stainless steel alloys, there are plenty of grades to choose from. But few offer the practical and versatile balance of strength, corrosion resistance, and hardness that 17-4 stainless steel offers. This precipitation-hardened stainless steel is used across industries, from aerospace and industrial to medical and more. 

Read on to learn all about 17-4 stainless steel metals, how they’re made, 17-4 stainless steels’ properties, and most common uses.

What is 17-4 Stainless Steel?

17-4 stainless steel, also known as SAE Type 630 stainless steel, is named for its chemical makeup. It’s an alloy that comprises approximately 17% chromium (although it can range from 15 to 17.5%) and 4% nickel (actually ranging from 3-5%). It also contains between 3% and 5% copper and may contain other materials like columbium, manganese, and silicon. 

17-4 Stainless Steel and Precipitation Hardening

17-4 stainless steel is the most common type of martensitic stainless steel. The term martensitic refers to the crystalline structure of the steel. Its atoms have undergone a treatment process that aligns them in a tetragonal unit, resulting in a very hard material. 

Martensitic steel alloys are strengthened through heat treatments. In the case of 17-4 stainless, the material is hardened through a process known as precipitation hardening (PH):

• Solutionizing: First, the metal is heated to a high temperature until all its elements are dissolved into a uniform solution. 
• Quenching: Then, the steel alloy is rapidly cooled, a process known as quenching. During quenching, the materials’ particles remain held in this uniform solution. 
• Aging: At this point, the material is aged. It’s heated to a moderately high temperature, then held there for an extended period of time. During aging, various elements in the metal form small particles called precipitates on its surface. This increases the yield strength and tensile strength of the material. 

Mechanical Properties of 17-4 Stainless Steel

These stainless steels, like 17-4 PH SOL, are strong, hard, and corrosion-resistant metals. 17-4 stainless steel properties include: 

• Tensile strength: Tensile strength refers to the stress a material can withstand before fracturing. Depending on the treatment the metal undergoes, 17-4 stainless steel’s strength can range from 1,000 MPa to 1,300 MPa or higher.  
• Yield strength: Yield strength refers to stress a material can withstand without deforming. Again, it can vary according to the stainless steel’s treatment, but in terms of yield, 17-4 stainless steel’s strength is typically 1,000 MPa or higher. 
• Hardness: Hardness is measured using a scale known as the Rockwell C scale. The higher the number, the harder the material. 17-4 stainless steel can be hardened to 44 Rc. 
• Corrosion resistance: 17-4 stainless steel is very corrosion-resistant when heat treated. 
• Machinability: 17-4 stainless steel has greater machinability than other types of stainless, like austenitic 304 stainless. 
• Weldability: This stainless steel also offers better weldability than other stainless steels, but it can be prone to some cracking. 
• Magnetic: Because it’s a martensitic steel alloy, 17-4 stainless steel is magnetic. 

Common Industries and Applications 

Its mechanical properties make this type of stainless steel a very practical and versatile material that’s used across a range of industries. 17-4 stainless steel is used for: 

• Aerospace: This steel alloy has high strength and good corrosion resistance, making it a great aerospace metal for high-stress aerospace components like turbine blades, fasteners, and other structural components. 
• Industrial: Corrosion resistance and good weldability also benefit the industrial industry, particularly in when interacting with highly corrosive products in chemical processing. This industrial metal is also commonly used to make molds, dies, and other manufacturing tools. 
• Medical devices: As a biocompatible material, 17-4 stainless is an excellent medical grade metal. It’s commonly used in the medical industry to make surgical instruments and implants. 

Fry Steel: Your 17-4 Stainless Steel Supplier

For a wide selection of 17-4 stainless steel and other steel materials, choose Fry Steel. With over 76 years of experience in the metal supply industry, we’re a reliable supplier with a reputation that speaks for itself. We’re independently ISO/AS certified and hold our suppliers to the same high standards. Contact us today to get started. 

17-4 Stainless Steel: FAQ 

Why is it called 17-4 stainless steel? 

17-4 stainless steel is named for its chemical makeup of approximately 17% chromium and 4% nickel. Chromium is the primary component in any stainless steel alloy, but not all contain nickel. By adding nickel, this stainless steel’s corrosion resistance, toughness, and ductility are all improved. 

How does 17-4 stainless steel compare to other types of stainless steel? 

17-4 stainless steel tends to be much stronger and harder than other types of stainless steel, like 316. This makes it a better choice for high stress environments like the aerospace and industrial industries. That said, it’s less resistant to corrosion, so it doesn’t behave as well in highly corrosive applications. 

How is 17-4 stainless steel strengthened? 

While some cold-working is possible with 17-4 stainless steel, it’s typically strengthened through a process known as precipitation hardening. During this process, the stainless steel is heated to a high heat, then rapidly cooled, then held at a moderate heat for an extended period of time. In doing so, hard particles called precipitates form, increasing its strength. 

What forms is 17-4 stainless steel available in? 

17-4 stainless is available in long bar. At Fry Steel, we carry over 126 sizes and conditions of 17-4 stainless, including round, flat, square, and hex cross-fittings.