A relatively new class of material, ULCB steels have been developed over the last twenty years or so with an aim to producing materials with all-purpose high strength and toughness.
By comparing cooling behavior in CCT diagrams between HSLA-80 and a ULCB steel it is possible to make some interesting conclusions related to the micro structure of the materials and the challenges associated with classification using optical microscopy.
Monthly Archives: May 2013
Rail Steels: Part Two
Grade 700 rails that used to be the main product for railroads some 60 years ago, may be considered as the starting point for the development which since took place. The Grade 700, with about 0.5% C, has a microstructure of about 30% ferrite and 70% pearlite within the rail head, which is the relevant location for comparison.
The first step to raise strength, and consequently wear resistance, was to increase the carbon content to achieve a 100% pearlitic microstructure. This way Grade 900 rails were developed.
Rail Steels: Part One
Modern railway systems are subjected to intense use, with fast trains and increasing axle loads. Rails have to be more wear resistant and achieve higher standards of straightness and flatness in order to avoid the surface and internal defects which may lead eventually to failure. The shape of the manufactured rail depends to a large extent on the uniformity of thermo mechanical processing; the most advanced mills are computer controlled with continuous feed-back from the product during manufacture.
Application of Fracture Mechanics
Fracture mechanics is a useful method of characterizing fracture toughness, fatigue crack growth, or stress-corrosion crack growth behavior in terms of structural design parameters familiar to the engineer, namely stress and flaw size. Fracture mechanics is based on a stress analysis and does not depend on the use of service experience to translate laboratory results into practical design information (as with the Charpy V-notch test, for example).
Precipitation Hardening of Aluminum Alloys
Precipitation hardening, or age hardening, provides one of the most widely used mechanisms for the strengthening of metal alloys. The strongest aluminum alloys (2xxx, 6xxx and 7xxx) are produced by age hardening.
In order for an alloy system to be able to be precipitation-strengthened, there must be a terminal solid solution that has a decreasing solid solubility as the temperature decreases. The precipitation-hardening process involves three basic steps: solution treatment, quenching and aging.