Hot rolled steel is manufactured by taking hot, molten steel, pouring it into large ingots and rolling the steel as it cools to improve the metal's performance characteristics. As the steel is rolled, the material is strengthened because of increased structural density. After the metal is rolled, it can be shaped into coils that are easy to transport across the country via trucks or rail, or stamped into usable plate steel. Hot rolled steel sheets are weldable and available in many grades and alloys. They remain bendable without becoming brittle, and can be used for both drawn and manufactured parts.
The Manufacturing Process
Hot rolled steel differs form cold rolled steel in that it is rolled and formed while still in a molten state. Iron ore is melted and purified in large ladles. Then alloy metals, such as carbon, magnesium, tungsten, etc. are mixed in the molten solution to improve the end use characteristics. The molten steel is poured into rough shapes which look like long bars. The metal is then transported to devices which look like massive rolling pins. The metal is processed multiple times between the rollers, and as it cools shaped into coils and sheets. Each time the material is rolled, the grain structure improves, and the steel becomes more resilient.
Tensile Yield Stress
The tensile yield is a measure of the pressure at which the material will permanently deform and lose its shape. Steel has a limited elasticity and will stretch and compress under minor stress without permanently losing its shape. This is one of the properties that makes hot rolled steel so useful. However, there is a point at which the material permanently deforms and will not "snap back" into its original shape. The tensile strength of hot rolled steel sheets is approximately 66,700 PSI. Under this load, hot rolled steel sheet will permanently deform.
Ultimate Tensile Strength
Tensile strength is a measure of the pressure at which a single piece of the material will suffer a break and shear or snap into multiple pieces. This ultimate yield strength is important to engineers when designing applications which undergo dynamic stresses, such as the plating on an oceangoing ship. As the ship cuts its way through the water, the ship's plating will encounter different amounts of stress depending on the weather conditions, the speed of the ship and the weight of the ship's cargo. The ultimate yield tensile strength of hot rolled steel sheets is 75,400 and 95,000 PSI.
Elongation at Break
The property of "elongation at break" refers to the point at which the hot rolled steel sheets will suffer a permanent break. Steel is elastic and will snap back into shape under minor loads. However, if the steel is subjected to increasing mounts of force, in the next phase steel will elongate and deform, but not break. If the stress increases from this point, the steel will eventually break. Hot rolled steel sheets will elongate to between 15 per cent to 19 per cent of the original length and then break into multiple pieces.