Stainless Steel - Grade 630

Chemical Formula

Fe, <0.07% C, 15-17.5% Cr, 3.0-5.0% Ni, <1.0% Mn, <1% Si, <0.040% P, <0.03% S, 3.0-5.0% Cu, 0.15-0.45% Nb+Ta

Topics Covered

Introduction
Key Properties
    Composition
    Mechanical Properties
    Physical Properties
    Grade Specification Comparison
    Possible Alternative Grades
Corrosion Resistance
Heat Resistance
Heat Treatment
Welding
Machining
Applications

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

*These values are specified for ASTM A564 and they apply only to certain size ranges. The specification should be consulted for the complete details of these properties.
Condition 900 is aged at 900°F (482°C), Condition 1150 is aged at 1150°F (621°C).
Solution treatment is at 927°C and cooled as required.

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:

Table 4. Grade specifications for grade 630 stainless steels

Possible Alternative Grades

The following table lists the possible alternative grades to 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