Low Alloy High Strength Plate

High-strength low-alloy steel plate (HSLA plate) is a type of alloy steel plate that provides better mechanical properties or greater resistance to corrosion than carbon steel. HSLA steel plates vary from other steels in that they are not made to meet a specific chemical composition but rather have specific mechanical properties. They have a carbon content between 0.05 and 0.25% to retain formability and weldability. Other alloying elements include up to 2.0% manganese and small quantities of copper, nickel, niobium, nitrogen, vanadium, chromium, molybdenum, titanium, calcium, rare-earth elements, or zirconium. Copper, titanium, vanadium, and niobium are added for strengthening purposes. These elements are intended to alter the microstructure of carbon steels, which is usually a ferrite-pearlite aggregate, to produce a very fine dispersion of alloy carbides in an almost pure ferrite matrix. This eliminates the toughness-reducing effect of a pearlitic volume fraction yet maintains and increases the material's strength by refining the grain size, which in the case of ferrite increases yield strength by 50% for every halving of the mean grain diameter. Precipitation strengthening plays a minor role, too. Their yield strengths can be anywhere between 250–590 megapascals (36,000–86,000 psi). Because of their higher strength and toughness HSLA steel plates usually require 25 to 30% more power to form, as compared to carbon steel plates.

Copper, silicon, nickel, chromium, and phosphorus are added to increase corrosion resistance. Zirconium, calcium, and rare-earth elements are added for sulfide-inclusion shape control which increases formability. These are needed because most HSLA steels have directionally sensitive properties. Formability and impact strength can vary significantly when tested longitudinally and transversely to the grain. Bends that are parallel to the longitudinal grain are more likely to crack around the outer edge because it experiences tensile loads. This directional characteristic is substantially reduced in HSLA steels that have been treated for sulfide shape control.

HSLA steel plates are used in cars, trucks, cranes, bridges, roller coasters, and other structures that are designed to handle large amounts of stress or need a good strength-to-weight ratio. HSLA steel cross-sections and structures are usually 20 to 30% lighter than carbon steel with the same strength.

HSLA steel plates are also more resistant to rust than most carbon steels because of their lack of pearlite – the fine layers of ferrite (almost pure iron) and cementite in pearlite. HSLA steels usually have densities of around 7800 kg/m3.

The Society of Automotive Engineers (SAE) maintains standards for HSLA steel grades because they are often used in automotive applications.

China Standard:
In China, common production standards for Low Alloy High Strength Plate include
GB/T 1591-2018: High strength low alloy structural steels.
This standard applies to low-alloy high-strength structural steel plates, steel strips, section steel, steel bars, etc. for general structures and engineering. Its chemical composition is also suitable for steel billets.
GB/T 3274-2017: Hot-rolled plates、sheets and strips of carbon structural steels and high strength low alloy structural steels.
This standard applies to hot-rolled steel sheets and strips of carbon structural and low-alloy structural steels with a thickness not greater than 400mm.

American standard:
In the United States, common production standards for Low Alloy High Strength Plate include
ASTM A572/A572M-18: Standard Specification for High Strength Low Alloy Steels for Building Construction
ASTM A709/A709M-18: Standard Specification for Structural Steel for Bridges
ASTM A514/A514M-18: Standard Specification for High Strength Alloy Steel Plates

British Standards:
In the UK, common production standards for Low Alloy High Strength Plate include
BS EN 10025-2: Standard for Technical Delivery Conditions of Structural Steel
BS EN 10025-6: Standard for Technical Delivery Conditions for Hot Rolled Products, including High Strength Low Alloy Steels
BS EN 10149-2: Standard for technical delivery conditions for cold-rolled hot-rolled steel plates and strips

Japanese Standards:
In Japan, common production standards for Low Alloy High Strength Plate include
JIS G3101: Standard for general-purpose hot-rolled weldable structural steel
JIS G3106: Standard for Hot Rolled Weldable High Strength Steel Sheets and Strips
JIS G3114: Standard for Hot Rolled Atmospheric Corrosion Resistant Structural Steels

The following specific specification standards are the Chinese national standards.
GB/T 1591-2018
Thickness: 3 mm to 150 mm
Width: 900 mm-4800 mm
Length: 3000 mm-25000 mm
Weight: 1.5 ton - 25 ton
Allowable deviations: The standard document provides specific requirements on size, shape, quality, and allowable deviations, such as straightness, edge condition, surface quality, etc. These requirements will vary depending on the grade and specification.

GB/T 3274-2017
Thickness：6mm-200mm
Width: 1500mm-4700mm
Length: 3000mm-27000mm
Weight: The weight of the steel plate varies according to size and thickness. The common weight range is usually between 1.5 tons and 20 tons, depending on the size and thickness of the steel plate
Allowable deviations: The allowable dimensional and shape deviations are specified in the standard documents. The specific allowable deviation limits will vary depending on the grade, thickness, and size of the steel plate. 

Generally speaking, the allowable dimensional deviation includes length deviation, width deviation, and thickness deviation, while the shape deviation includes the curvature and straight edge of the steel plate, etc.