17-4PH Stainless Steel

17-4 Precipitation Hardening also known as Type 630 is a chromium-copper precipitation hardening stainless steel used for applications requiring high strength and a moderate level of corrosion resistance. High strength is maintained to approximately 600 degrees Fahrenheit (316 degrees Celsius).

General Properties

Alloy 17-4 PH is a precipitation hardening martensitic stainless steel with Cu and Nb/Cb additions. The grade combines high strength, hardness (up to 572°F / 300°C), and corrosion resistance.

Mechanical properties can be optimized with heat treatment. Very high yield strength up to 1100-1300 MPa (160-190 ksi) can be achieved.

The grade should not be used at temperatures above 572°F (300°C) or at very low temperatures. It has adequate resistance to atmospheric corrosion or in diluted acids or salts where its corrosion resistance is equivalent to Alloy 304 or 430.

Corrosion Resistance

Alloy 17-4 PH withstands corrosive attacks better than any of the standard hardenable stainless steels and is comparable to Alloy 304 in most media.

If there are potential risks of stress corrosion cracking, the higher aging temperatures then must be selected over 1022°F (550°C), preferably 1094°F (590°C). 1022°F (550°C) is the optimum tempering temperature in chloride media.

1094°F (590°C) is the optimum tempering temperature in H2S media.

The alloy is subject to crevice or pitting attack if exposed to stagnant seawater for any length of time.

It is corrosion resistant in some chemical, petroleum, paper, dairy and food processing industries (equivalent to 304L grade).

If you would like to know more about 17-4PH stainless steel then click 17-4PH Technical Data.

Introduction

Grade 630 stainless steels are martensitic stainless steels that are precipitation hardened to achieve excellent mechanical properties. These steel achieve high strength and hardness following heat treatment. The heat and corrosion resistance of grade 630 are similar to that of grade 304 steels. This grades is also commonly referred to as grade 17-4PH.

One of the key benefits of this grade is that it is available in solution treated conditions, at which they can be easily machined and age-hardened to attain high strength. The age treatment of grade 630 is carried out at low temperatures, to avoid significant distortion. Therefore, this grade is used for applications such as the manufacture of long shafts that do not require re-straightening after heat treatment.

Key Properties

The properties mentioned below pertain to commonly available grade 630 bar products in ASTM A564. The specifications may not be similar to other forms such as forgings and plates.

Composition

The compositional ranges of grade 630 stainless steels are displayed below:

Table 1. Composition ranges for grade 630 stainless steels

Mechanical Properties

The table below outlines the mechanical properties of grade 630 stainless steels:

Table 2. Mechanical properties of grade 630 stainless steels

Physical Properties

The physical properties of grade 630 stainless steels are given in the following table:

Table 3. Typical physical properties of grade 630 stainless steels

Grade Specification Comparison

The typical grade specifications of 630 stainless steels are tabulated below:

able 4. Grade specifications for grade 630 stainless steels

Table 5. Possible alternative grades to 630 stainless steels

Corrosion Resistance

Grade 630 stainless steels have good corrosion resistance in many environments. They exhibit improved resistance against stress corrosion cracking, if aged at 550°C or more. However, grade 630 steels are less resistant to solution treated Condition A, and hence these steels, even with considerable hardness, should not be used in this condition.

Heat Resistance

Grade 630 stainless steels have good resistance to oxidation. However, long-time exposure of grade 630 to temperatures of 370 to 480°C should be avoided, to prevent loss of toughness at ambient temperature. These grades should not be used at temperatures above age-hardening temperature, to avoid reduction of hardness and mechanical properties of the metal.

Heat Treatment

Solution treatment (Condition A) - Grade 630 stainless steels are heated at 1040°C for 0.5 h, then air-cooled to 30°C. Small sections of these grades can be oil quenched.

Hardening - Grade 630 stainless steels are age-hardened at low temperatures to achieve the required mechanical properties. During the process, superficial discoloration occurs followed by shrinkage at 0.10% for condition H1150, and 0.05% for condition H900.

The table below shows the typical mechanical properties of grade 630 steels after solution treatment and age hardening:

Table 6. Typical mechanical properties of grade 630 steels achieved after solution treating

Welding

Grade 630 stainless steels can be welded using all conventional methods, and they do not require pre-heating. Care should be taken in designing and welding of high strength steels to prevent weldment stresses.

Machining

Grade 630 stainless steels can be machined in their solution-treated condition. They have machining rates similar to that of grade 304 steels.

Applications

Some of the major applications of grade 630 stainless steels include:

• Engine components
• High strength and boat propeller shafts
• Plastic moulding dies
• Valves and gears