A633GrC is a high strength low alloy structural steel plate covered by ASTM A633/A633M, the specification for normalized high strength low alloy structural steel. The plate is supplied in the normalized condition, which refines the grain structure and provides the notch toughness that the grade is specified for. It is intended for welded, riveted or bolted construction, and the C grade within the specification is one of a series of grades whose notch toughness requirements extend to progressively lower temperatures.
The ASTM A633 specification contains five grades, designated A, B, C, D and E. Each grade carries the same broad strength level but a different minimum impact test temperature, so the grade letter is selected from the lowest ambient temperature at which the structure must operate rather than from strength considerations.
Chemical Composition and Mechanical Properties
Chemistry is balanced for weldability and toughness, with carbon held low relative to ordinary structural plate, manganese as the main strengthener and small additions of alloying elements to provide the required properties in the normalized condition. Sulfur and phosphorus are restricted, and the specification requires the steel to be killed and fine grained, which is central to low temperature toughness.
| Property | Requirement for Grade C |
|---|---|
| Minimum yield strength | 345 MPa |
| Tensile strength range | Approximately 485 to 620 MPa |
| Elongation | At least 18 % in the specified test direction |
| Impact test | Charpy V notch test at the low temperature specified for the grade |
The specification requires the material to be normalized, and it provides for tension testing and, for the low temperature grades, impact testing of each heat or of each test lot as defined by the standard. The grade designations are often written with the Gr abbreviation, so A633GrA, A633GrC, A633GrD and A633GrE designate the same series as A633 Grade A through Grade E.
Delivery Condition and Inspection
Plate is delivered normalized, with surface quality and dimensional tolerances governed by the general requirements of the specification and by the referenced dimensional standard for hot rolled plate. Where the application is safety related, ultrasonic testing can be specified for internal soundness. Order documentation normally covers chemical composition, tensile results and impact results at the specified test temperature, and the test temperature itself should always appear on the mill certificate so that it can be checked against the design minimum service temperature.
Fabrication and Welding Notes
The grade is designed for welding and can be joined by the common arc processes with low hydrogen consumables under a qualified procedure. Preheat requirements depend on thickness, carbon equivalent and restraint; because the steel is normalized rather than quenched and tempered, post weld heat treatment for stress relief is generally well tolerated. Cold forming and rolling are straightforward at this strength level, and thermal cutting is followed by dressing of the cut edge. Where the plate will be bent to a tight radius, the direction of rolling should be considered, since transverse ductility is lower than longitudinal.
Applications
Typical uses include mining and earthmoving machinery such as drilling rigs, electric shovels, wheel loaders, hydraulic excavators, bulldozers and haul truck bodies, together with cranes, coal mine hydraulic supports, general construction plant, storage structures and fabricated frames for cold climate service. The combination of moderate strength, good weldability and low temperature toughness explains its long standing use in heavy equipment.
Frequently Asked Questions
Q: Which standard covers A633GrC plate?
A: ASTM A633/A633M, the specification for normalized high strength low alloy structural steel, which defines the chemistry, the normalized condition and the notch toughness requirement.
Q: How many grades are in ASTM A633?
A: Five, designated A, B, C, D and E. They share a similar strength level and differ mainly in the temperature at which impact toughness is verified.
Q: Why is the plate normalized?
A: Normalising refines the grain structure, which improves notch toughness and gives uniform properties, both of which matter in low temperature structural service.
Q: What is the minimum yield strength of Grade C?
A: 345 MPa, with a tensile strength of roughly 485 to 620 MPa depending on thickness.
Q: Can A633GrC be welded in cold weather?
A: Yes, with a qualified procedure. Preheat requirements become more important as thickness, restraint and carbon equivalent increase, and the joint should be protected from rapid cooling.
