8 Methods to Heat Treat 17-4 PH Stainless Steel

17-4 PH grade of stainless steel is a metallic material which possesses several characteristics making it a preferred choice in high temperature applications. Major properties that make this alloy famous include exceptional formability, weldability and corrosion resistance. Apart from that, this material has the tendency to modify its properties through different heat treatment processes. This article focuses on eight different methods to heat treat 17-4 PH stainless steel that are responsible for modifying its properties according to your application needs and requirement.

Understanding 17-4 PH Stainless Steel

Understanding the material characteristics is crucial before getting familiar with the process of heat treating that material. These are discussed below one by one:

Figure 1: 17-4 grade SS

Precipitation Hardening Mechanism

The purpose of this process to increase the mechanical properties of 17-4 PH SS especially the strength and hardness. To acquire that, the material undergoes two major steps:

Solution Treatment: The alloy is heated to about 1025°C with one-hour soaking time followed by rapid water or air quenching ensuring a homogeneous and uniform distribution of elements within the material.

Aging: This process includes the reheating of alloy between 480 - 620°C with specified soaking period which leads to the formation of copper-rich precipitates that hinders the dislocations serving the purpose of enhanced mechanical properties within the material.

Chemical Composition

Table 1: Chemical Composition 17-4 SS

Is 17-7 PH Stainless Steel Magnetic?

17-7 PH stainless steel is magnetic in nature. This certain property is achieved when this material undergoes heat treatment process that helps in the formation of martensitic structure. Eventually, making itself available for applications that demand magnetic properties.

Density

The approximate density for 17-4 PH SS is 7.75 g/cm³ making itself available for applications requiring durability and high strength.

17-4 PH Hardness

It strictly depends on the specified heat treatment through which the material undergoes. However, it has a hardness value that lies between 28-44 HRC.

Yield Strength

The alloy has a yield strength of 1030 MPa when it is solution treated. Moreover, there is an abrupt change when it undergoes precipitation hardening.

17 4 PH Stainless Steel Mechanical Properties

Below is the table illustrating on the mechanical properties of 17-4 PH SS:

Table 2: Mechanical Properties Of 17-4 PH SS

17-4 Stainless Steel Machinability

The alloy has a good machining ability when solution treated but it usually decreases when the material undergoes precipitation hardening. Despite that, the machining performance could be maintained using advance machining techniques.

17-4 PH stainless steel equivalent

The alloy constitutes of properties like hardness, strength along with corrosion resistance making it a great choice for demanding applications. Yet under certain conditions, the equivalent material for this alloy is mentioned below：

• AMS 5643
• DIN 1.4542
• AISI 630
• EN 1.4542 / X5CrNiCuNb16-4
• ASTM A564
• JIS SUS630

17-4 Heat Treat Chart

Table 3: 17-4 Heat treat chart

How to Heat Treat 17 4 Ph Stainless Steel

Advantages and Disadvantages of 17-4 PH Stainless Steel

Below are the major pros and cons of 17-4 PH stainless steel：

Condition A (Annealed): The Foundation for Further Heat Treatment

Purpose of Annealing

It is the first step for the material component for heat treating and processes. This step comprises of great importance in removing internal stresses resulting in a soften alloy for easy machining and handling. It gives a fine grain microstructure that homogenizes the material properties leading to precise machining and forming with great accuracy.

Process Steps

Following steps are involved in annealing:

1. Heating of the alloy is done at elevated temperature that usually lies between 1040-1065°C. This step makes sure to dissolve the alloying elements into a solid solution leading to homogenized microstructure.
2. The material is further soaked for 30-60 minutes for even distribution of elements.
3. The third and final steps is slow cooling of the alloy component either inside the furnace or at room temperature.

Resulting Properties

This process leads to enhance several properties achieving a condition A material characteristic:

• Improved Ductility
• Enhanced Machinability
• Lower Strength and Hardness
• Uniform Microstructure

Condition H900: Achieving Maximum Strength and Hardness

Purpose of H900 Treatment

In this process, the alloy component goes through H900 heat treatment which allows copper-rich precipitates to form withing the microstructure that will serve the purpose of stopping the dislocation movements. As a result, 17-4 PH stainless steel has maximum mechanical properties in term of strength and hardness making itself available for applications that demand high tensile and yield properties.

Process Steps

Following steps are involved in H900 treatment:

1. Heating of the alloy is done at elevated temperature that is usually 482°C. This step ensures copper-rich precipitates formation without comprising the alloy structure.
2. The material is further soaked for 4 hr. duration leading to even distribution of precipitates.
3. The third and final step is controlled air cooling to preserve these precipitates of the alloy component and stabilize properties.

Resulting Properties

This treatment apparently increases several mechanical properties of the alloy component that are mentioned below:

• Increased Tensile Strength to 1450 MPa
• Enhanced Yield Strength to 1400 MPa
• Higher Hardness
• Slight Decrease in Ductility

Condition H1150: Balancing Strength and Toughness

Purpose of H1150 Treatment

The alloy component that undergoes through this treatment constitutes a balance of both strength and toughness. The H1150 heat treatment is applicable for applications that demand strengthening qualities with substantial amount of impact resistance. Hence, the material which is exposed to this special treatment can exhibit impact and cyclic loading while maintaining its mechanical integrity.

Process Steps

Following steps are involved in H1150 treatment:

1. Heating of the alloy is done at elevated temperature that is usually 621°C. This step ensures precipitates formation.
2. The material is further soaked for 4 hr. duration at this temperature leading to optimized precipitates formation.
3. The third and final step is controlled air cooling (at room temperature) to stabilize these precipitates of the alloy component and maintain mechanical properties.

Resulting Properties

This treatment influences several mechanical properties of the alloy component that are mentioned below:

High Tensile Strength (1210 MPa) a little lower than H900 treatment

• Enhanced Yield Strength (1070 MPa)
• Improved Toughness
• Balanced Performance

Condition H1025: Optimizing Corrosion Resistance

Purpose of H1025 Treatment

This treatment is done to enhance corrosion resistance of 17-4 PH SS along with other strengthening properties. The alloy component that undergoes through H1025 treatment ensures to withstand highly corrosive environment. This process is of great importance especially in marine, chemical and other aerospace applications.

Process Steps

Following steps are involved in H1025 treatment:

1. Heating of the alloy is done at elevated temperature that is usually 552°C. This step ensures copper-rich precipitates formation.
2. The material is further soaked for 4 hr. at 552°C leading to optimized precipitates formation.
3. The third and final step is controlled air cooling (at room temperature) to stabilize these precipitates of the alloy component and maintain mechanical properties.

Resulting Properties

This treatment influences following properties:

• High Tensile Strength and Yield Strength
• Improved Corrosion Resistance

Condition H1075: Enhancing Toughness and Ductility

Purpose of H1075 Treatment

This heat treatment is used to modify toughness and ductility within 17-4 PH stainless steel component. The process is introduced to tailor application that demands high impact resistance and formability. The alloy component exposed to this treatment are capable to tackle dynamic forces and deformation.

Process Steps

Following steps are involved in H1075 treatment:

1. Heating of the alloy is done at elevated temperature that is usually 579°C. This step ensures a blend of toughness and strengthening properties.
2. The material is held for 4 hr. at 579°C leading to optimized precipitates formation.
3. The third and final step is controlled air cooling (at room temperature) to stabilize the respective properties.

Resulting Properties

This treatment influences following properties:

• Increased Toughness
• Enhanced Ductility
• Good Strength
• Balance of Properties

Condition H1100: Achieving High Strength with Moderate Toughness

Purpose of H1100 Treatment

The H1100 treatment process serves its purpose by providing high strengthening properties with moderate toughness to 17-4 PH stainless steel alloy component. Materials gone through this process are designed to bear substantial load-bearing capacity and deformation. This condition is suited for applications that demand high mechanical performance and are less prone to severe impact conditions.

Process Steps

Following steps are involved in H1075 treatment:

1. Heating of the alloy is done at elevated temperature that is usually 593°C.
2. The material is held for 4 hr. at 593°C for necessary changes to acquire the desired properties.
3. The third and final step is controlled air cooling (at room temperature) to retain the respective properties.

Resulting Properties

This treatment influences following properties:

• High Tensile Strength
• Moderate Yield Strength
• Decent Toughness
• Versatile Performance

Condition H1125 & H925: Maximizing Toughness and Customizing Properties

Purpose of H1125 and H925 Treatments

• The purpose of H1125 is to enhance toughness up to maximum level to tailor impact forces and high stresses. Ultimately, this property will resist the material component cracking under aggressive conditions.
• H925treatment provides balanced properties that includes hardness, strength and toughness. Components gone through this treatment opens gate for wide range of engineering applications.

Process Steps

Resulting Properties

This treatment influences following properties:

H1125

• Exceptional Toughness
• Improved Ductility
• Strength

H925

• Balanced Strength and Hardness
• Intermediate Toughness
• Versatility

What are the Risks of Improper Heat Treatment of 17-4 PH?

The risk of irregular and improper heat treatment of the material component can lead to significant change in the microstructure with properties that are undesirable. The potential risks are mentioned below:

• Under-Aging
• Over-Aging
• Distortion
• Cracking

What is the Best Way to Prevent Rust on 17-4 PH Stainless Steel?

Following are the best ways to prevent this alloy from rust:

• Proper Heat Treatment
• Surface Protection
• Passivation
• Environmental Control
• Regular Inspection and Maintenance
• Proper Design and Fabrication
• Use High-Quality Stainless Steel

Choosing the Right Heat Treatment: Matching Properties to Applications

Below is the table that gives you a detailed analysis of properties achieved via certain heat treatment. By interpreting accurately, you can easily choose which treatment on 17-4 PH SS is considered best for your application

Table 4: Properties achieved under certain Heat Treatments

FAQ

17-7 PH Stainless Steel vs 304

17-7 PH comprise of 17% Cr, 7% Ni offer good corrosion and remarkable fatigue life. In contrast, 304 with 18% Cr and 8% Ni assist in enhanced ductility and welding characteristics.

17-7 PH Stainless Steel vs 316

17-7 PH comprise of 17% Cr, 7% Ni offer good corrosion and remarkable fatigue life while 316 with 16% Cr, 10% Ni, and 2% Mb is suitable for chloride rich environment.

13-8 PH vs 15-5 PH vs 17-4 PH Stainless Steel

• 13-8 PH with 13% Cr and 8% Ni provide good strength and toughness.
• 15-5 PH with 15% Cr and 5% Ni provide a blend of strength and toughness.
• 17-4 PH SS with 17% Cr and 4% Ni offer strength with good corrosion resistance.