All steels have some carbon content (basically iron & carbon together make steel) and increasing the carbon content will result in a higher tensile strength steel alloy. But that can only be done up to a point. Higher carbon content - while increasing hardness - will also produce a more brittle, less ductile (bendable) steel.
What has the greatest effect on the tensile strength of steel is what happens during the manufacturing process. High tensile steel is subjected to much higher pressure when it is rolled at the mill.
That's about all I know about steel.