Steel, an alloy of carbon mixed with iron, is one of the most common industrial metals used throughout the world. Steel is rated for many kinds of strength; tensile strength is a measure used by structural engineers to determine how much force it takes to stretch something until its cross sectional area narrows. If you've ever pulled taffy until it narrows, you've performed the basic tensile strength test. High-tensile steel has a number of mechanical properties, and there are more than one steel alloys marketed and sold as high tensile. Tensile strength is measured in force per square meter, or Pascals in the metric system. In the British Imperial system, it's measured in pounds per square inch, or PSI.
Mechanical Definition: What Qualifies as High Tensile Strenght?
High-tensile steels start at a yield strength (where the first deformation occurs) at 50,000 PSI. Unlike mild steel grades, high-tensile steel isn't identified by its material composition, but rather by its mechanical properties. As tensile strength is selected for, a wider range of alloying compounds, such as molybdenum and chromium, is needed. Extreme high-end high-tensile steel can have yield strengths as high as 80,000 PSI or more. Most high-tensile steels have a density of 7,800kg per cubic meter.
Chemical Properties: Corrosion Resistance and Weight Savings
Many of the same alloying materials that produce high-tensile strength steels are also the same alloying agents that make for improved corrosion resistance, in particular chrome and molybdenum. This makes for a very light weight steel -- often called "chrome-moly" in the automobile industry, and the broad category of high-tensile-strength steels are also known as high-strength, low-alloy (HSLA) steels.
Specific High Tensile Steel Grades
Standard steelmaking grades that encompass high-tensile steels start with grade 950X, and proceed to 980X; the last two digits represent the number of thousands of PSIs needed to cause a deformation of the steel. The X at the end of the steel's rating is an indicator of a low-alloy steel.