Stainless steel is produced in a large number of grades that have austenitic, ferritic or martensitic structures. 17-4 is a martensitic grade that can be precipitation hardened, (leading to the 17-4 PH designation). It’s often investment cast and is a good choice for parts requiring high strength and excellent corrosion-resistance. For anyone looking to have parts made in 17-4, this blog explains what’s involved.

Properties of 17-4 Stainless Steel

Most stainless steels are known by their official designation, such as 304 or 420. The official designation for 17-4 is 630, but engineers everywhere know it by its composition – 17% chromium and 4% nickel.

Chromium is responsible for the corrosion-resistance that stainless is known for. 17% is particularly high though, and this gives 17-4 higher resistance than other grades. 304 grade stainless is very similar (18% Cr vs. 17% and 8% Ni vs. 4%), but 17-4 has a significantly higher yield strength.

As a martensitic stainless steel, 17-4 can be precipitation hardened to further increase strength. It is magnetic, (most grades are not), but as with all types of stainless, it has a very high melting point.

Applications for 17-4

Corrosion resistance makes 17-4 a good choice for applications with exposure to chemicals or harsh weather. Valve bodies and manifolds for the chemical processing industry are often made from 17-4 for this reason. The oil and gas industry use 17-4 for its combination of strength and corrosion resistance. Applications include tooling and related devices.

17-4 finds many applications in aerospace. Here its strength helps minimize mass while corrosion resistance ensures longevity. Landing gear components, hinges, attachment points for control surfaces, and brackets of many types are examples of parts made from this alloy.

Investment Casting of 17-4 Stainless

Investment casting uses an expendable mold formed by a ceramic shell. First, a wax pattern replicating the part to be cast is molded. Cores are incorporated into the pattern as needed to create cavities in the final part. One or more patterns are joined to a central wax sprue and the whole assembly is coated with a ceramic slurry. Once this has dried the wax is melted out to leave a cavity for the metal.

17-4 melts at around 2,600 °F (1,427 °C) so is heated above this for pouring. Preheating the shell mold lessens thermal shock and slows the metal solidification rate.

When poured, 17-4 exhibits good fluidity and flows readily to fill thin sections. However, shrinkage during solidification can cause cracking, so particular care must be taken around areas with changes in section.

Reasons to Investment Cast 17-4 Stainless

The main advantages of investment casting over other casting processes are:

• Superior ability to reproduce fine detail
• Able to form thin walls
• Good surface finish
• No draft angles

All these advantages are realized when investment casting parts in 17-4 stainless.

Heat Treatment

17-4 is a precipitation-hardening grade of stainless. This refers to a heat treatment process where the metal soaks at an elevated temperature to ensure all the alloying constituents are fully dissolved. Rapid cooling followed by heating to a lower temperature than that used initially then leaves particles of copper distributed throughout the structure.

The benefit of this process is that the finely dispersed particles limit how dislocations can move through the crystal structure. This reduces plasticity, which increases hardness and strength. A further advantage is improved machinability.

Your Partner for Investment Cast Stainless Steel

For parts needing high strength and excellent corrosion-resistance, 17-4 stainless steel is often the first choice. Investment casting parts in this alloy minimizes part mass and reduces secondary machining requirements.

Impro is a leader in investment casting and has experience with all widely used grades of stainless steel. If you need metal parts that are lightweight, high-strength, and corrosion-resistant, we can help. Contact us to learn more.