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Ferrous Metals

Metals containing primarily iron are classified as "ferrous metals". They range from pure iron through exotic high alloy steels. Many stock parts are made from cast iron, defined as metallic iron in which more than 2 percent carbon is dissolved. One preferred variation- ductile or nodular iron- has all its carbon contained in the form of tiny spherical graphite nodules uniformly dispersed throughout the metal's matrix. This makes the material more ductile ( deformable rather then brittle) and eases casting and machining.         Even the best iron has only limited tensile strength. Increasing ductility, hardness, malleability and fatigue resistance requires removing most carbon and at the end, alloying iron with other elements, creating "steel", an iron with less than 2 percent carbon.     The most basic form is carbon steel, which contains up to 1.7 percent carbon and minimal additional alloying elements. Carbon steels are designated by a four digit number. The first two digits indicate the basic type and the last two digits indicate the approximate midpoint of the carbon content. Stock forged rods and cranks are usually made from 1045 or 1053 steel. The "10" ID's these alloys as nonresulfurized carbon steel with some manganese (popularly called medium carbon or mild steel); "45" or "53" means the steel contains about 0.45 or .053 percent carbon, respectively.      Alloy steels are where things really get crazy. Over time, as manufacturing techniques improve and chemical knowledge grew, metallurgists developed whole families of alloy steel custom tailored to make metals stronger, lighter, more durable, more ductile, springer and /or harder. Alloy steels are also identified by a four digit number, but now the first two digits indicate the major alloying element or elements, with the last two digits again indicating the approximate midpoint of the carbon range. The alloy steel series and the major alloying elements most often used to make forged or billet auto engine parts are:

41xx

Chromium 0.50, 0.80 or 0.95 percent; plus molybdenum 0.12, 0.20 or 0.30 percent

43xx

Nickel 1.83 percent, plus chromium 0.50 or 0.80 percent, plus molybdenum 0.53 percent

Chromium 0.80, 0.88, 0.95 or 1.00 percent

51xx

Within these major categories, these are the most common alloy steels used for auto parts:

The best known chrome moly steel, it's a great high strength / high stress alloy in thin sections (sheet or tube). But 4130 possesses poor deep heat treating characteristics and doesn't like varying cross sections, which make it a bad choice for machined or forged parts.

4130

A deep hardening chrome moly steel, it forges well and has good impact resistance, fatigue strength and general all around toughness.

4140

A nickel chrome moly deep hardening steel, this alloy is used to make premium rods and cranks. 4340 has fantastic tensile strength, toughness and fatigue resistance. Modified 4340 alloys with vanadium and more silicon cant his already great alloy even tougher and more fatigue resistant.

4340

This chromium alloy increases tensile strength, hardness, toughness and wear resistance over carbon steel but is more affordable than the 4000 series alloys.

5140