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.
Nanoperm Alloys
Although a relatively recent discovery, nanocrystalline materials are a well studied group of materials which have some specific magnetic applications whilst exhibiting some useful property characteristics also.
Due to a very fine distribution of crystalline grains within the amorphous matrix nanocrystalline alloys display excellent soft magnetic properties.
Fatigue Properties: Part Two
A fatigue fracture will have two distinct regions; One being smooth or burnished as a result of the rubbing of the bottom and top of the crack. The second is granular, due to the rapid failure of the material.
Striations are thought to be steps in crack propagation, were the distance depends on the stress range. Beachmarks on the other hand may contain thousands of striations.
Hydrogen in Steels
The control of hydrogen content in steels is an important task of steelmakers because of its generally detrimental effects on processing characteristics and service performance of steel products. Just a few parts per million of hydrogen dissolved in steel can cause hairline cracks (flakes), hydrogen embrittlement, hydrogen blistering and loss of tensile ductility, particularly in large steel castings ingots, blooms and slabs.
Fatigue Properties: Part One
Fatigue cracking is one of the primary damage mechanisms of structural components. Fatigue cracking results from cyclic stresses that are below the ultimate tensile stress, or even the yield stress of the material.
The fatigue life of a component can be expressed as the number of loading cycles required to initiate a fatigue crack and to propagate the crack to its critical size.
High Carbon Steels
Generally, the high carbon steels contain from 0.60 to 1.00% C with manganese contents ranging from 0.30 to 0.90%.
The pearlite has a very fine structure, which makes the steel very hard. Unfortunately this also makes the steel quite brittle and much less ductile than mild steel.
Strain Ageing of Steel: Part Two
Strain ageing can have a serious detrimental effect on low carbon structural steels and so two material examples are examined to see how different pre-strain and ageing conditions affect material mechanical properties.
A carbon steel (40% martensite) and a microalloyed steel (20% martensite) were both treated under the same parameters and then the UTS and stress strain curves were evaluated to gain some valuable conclusions.