ASTM A844/A844M-1993
This ASTM A844/A844M-1993 standard specifies the requirements for Grade 9% Nickel Steel plates used in pressure vessels. It applies to plates made by direct quenching and tempering process.
Grade 9% Nickel Steel is an age-hardening nickel-iron-chromium alloy. Nickel increases the strength and hardness of the steel with increasing temperatures. Chromium provides stable austenite at higher temperatures and resistive capacity against oxidation and corrosion.
In order to produce plates of Grade 9% Nickel Steel, two main processes are needed—initially the steel is cast, extruded, or rolled in the form of bars, to be later processed as plate by direct quenching followed by tempering. Direct quenching is a process used to increase hardness and strength of the steel greatly, by rapidly cooling it from a higher temperature.
This standard prescribes the requirements for the chemical composition of Grade 9% Nickel Steel and monitoring requirements for production and post-production operations for the plate manufacturing. It also covers the mechanical properties of the plate, including ultimate tensile, yield strength, elongation in 2-in. gauge length, Brinell Hardness, Charpy V-Notch, and ASTM Grain Size.
The basic element required in Grade 9% Nickel Steel is nickel. According to this standard, the maximum allowable content should not exceed 9%, while chromium should be within 1-2%, and carbon should be between 0.005-0.20%. Apart from these, sulfur and phosphorus may also be present in small amounts.
In order to be able to meet the maximum allowable chemical composition, the steel must be carefully monitored through various pre-process inspections. Also, post-process testing must be conducted to confirm final strength and hardness properties of the plate.
The mechanical properties to be obtained in the finished product shall comply with the standard, as they vary depending on shape, size, and strength levels. These include ultimate tensile and yield strength, elongation in 2-in. gauge length, Brinell Hardness, Charpy V-Notch and ASTM Grain Size. The tests must be conducted at room temperature after the plate is fully cooled and hardened.
All the test results should meet the quality requirements of the product, and any material which does not meet the minimum requirements should be rejected and separated from the product.
In order to ensure the quality and safety of the product, the manufacturer must ensure that the production, inspection, testing and delivery of the product are in accordance with the standards requirements.
The main purpose of this standard is to ensure that Grade 9% Nickel Steel plates produced provide, good quality and safety, and meet the needs of the industry, so that they can be suitably used in pressure vessels. Adherence to this standard provides assurance of quality and safety so that manufacturers and users could rest assured that their products meet the required specifications.
