Classification
Alloy steels differ from carbon steels in that they contain a high proportion of other alloying elements. The following are regarded as the minimum levels:
| Element | % | Element | % | Element | % |
| Aluminium | 0.3 | Lead | 0.1 | Silicon | 2.0 |
| Chromium | 0.5 | Manganese and silica | 2.0 | Sulphur and phosphorus | 0.2 |
| Cobalt | 0.3 | Molybdenum | 0.1 | Tungsten | 0.3 |
| Copper | 0.4 | Nickel | 0.5 | Vanadium | 0.1 |
Alloy steels are classified according to increasing proportion of alloying elements and also phase change during heating and cooling as follows:
low alloy steels
medium alloy steels
high alloy steels
and according to the number of alloying elements as follows:
ternary - one element
quarternary - two elements
complex - more than two elements
General description
Low alloy steels
These generally have less than 1.8% nickel, less than 6% chromium, and less than 0.65% molybdenum. The tensile strength range is from 450-620 N mm-’ up to 85O-1000 N mm-2
Medium alloy steels
These have alloying elements ranging from 5-12%. They do not lend themselves to classification. They include: nickel steels used for structural work, axles, shafts, etc.; nickel-molybdenum steels capable of being case-hardened, which are used for cams, camshafts, rolling bearing races, etc.; and nickelchromemolybdenum steels of high strength which have good fatigue resistance.
High alloy steels
These have more than 12% alloying elements. A chromium content of 13-18% (stainless steel) gives good corrosion resistance; high wear resistance is obtained with austenitic steel containing over 11% manganese. Some types have good heat resistance and high strength.
Labels: engineering materials