Rail Steels: Part Two

The further strengthening of pearlitic steel rails to 1100–1200 MPa tensile strength is based on increased pearlite refinement. As shown in Figure 2, the properties of rail steels are influenced by the spacing between cementite lamellae. The yield strength and tensile strength increase as the interlamellar spacing decreases while the elongation decreases with a reduction in the interlamellar spacing.

Figure 2: Effect of pearlite refinement on the properties of rail steel.

The continuous cooling transformation (CTT) diagram of Grade 900 steel shows two possibilities for achieving pearlite refinement. Firstly, as shown in Figure 3, the field of austenite to pearlite transformation may be moved to the right, e.g. through additions of chromium and other alloying elements, so that air cooling of the rail head transforms the austenite into fine pearlite with narrow interlamellar spacing. This type is the high strength and highly wear resistant alloy Grade 1100-1200, which cools at still air after rolling.

Figure 3: CCT diagram showing the effect of alloying to achieve pearlite refinement.

The second possibility is that the cooling speed of the rail head may be accelerated to move the austenite to pearlite transformation of the Grade 900 steel to the left in order to achieve a microstructure of fine pearlite; generating a 1100-1200MPa tensile strength with the same steel composition as shown in Figure 4.

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This type is a head-hardened rail. The heat treatment and accelerated cooling (slack quenching) of the rail head may be performed after reheating (offline) or using the still austenitic microstructure directly after rolling (in-line).

Figure 4: CCT diagram showing the effect of cooling rate on pearlite refinement.

The changes in pearlite transformation temperature in these two types of rails caused by changes in the cooling rate from the austenite region are schematically shown on the CCT diagram, Figure 5. To set the pearlite transformation temperature at about 600°C, slack quenching (cooling rate: 4-6°C/s) is required for the carbon steel rail, while natural air cooling (cooling rate: ~0.7°C/s) after hot rolling is sufficient for the alloy steel rail due to the high hardenability from alloying. These treatments could give the rails more than 1100MPa tensile strength.

Rail Steels: Microstructures and Properties of Pearlitic Rail Steels

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.

Microstructures and Properties of Pearlitic Rail Steels

Pearlite is an important feature of the microstructure because it possesses good wear resistance, hence making carbon an essential alloying element in rail steels. However, it is not only the amount of pearlite that is important but also its morphology, which means the shape and the distance between the cementite lamellae. The finer the structure of pearlite, the higher is its strength whilst still retaining reasonable toughness. Therefore the development of pearlitic rail steels has been focused on the refinement of pearlite.

Pearlite comprises a mixture of relatively soft ferrite and a hard, brittle iron carbide called cementite, taking the form of roughly parallel plates. It achieves a good resistance to wear because of the hard carbide and some degree of toughness as a result of the ferrite’s ability to flow in an elastic/plastic manner. Figure 1 shows the microstructure of a pearlitic railway rail steel. The cementite is white and the ferrite is black. The interlamellar spacing is about 0.3 microns.

Figure 1: Microstructures of pearlitic rail steels

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.

Due to the rather slow cooling of the rail head on the cooling bed after rolling, the pearlite structure is relatively coarse. 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.

The wear resistant rails of Grade 900 have a coarse pearlitic microstructure with sufficient ductility and toughness for general applications. Welding techniques were developed to replace fishplate connections and Grade 900 became the standard rail instead of Grade 700 for main lines. Nowadays Grade 700 rails are only used for tracks where low axle loads are applied, e.g. for trams. In some places like narrow curves and mountainous regions, but mainly for heavy haul ore and coal transportation, strengths greater than that exhibited by Grade 900 rails are needed; an increase in tensile strength of about 200 MPa doubles the wear resistance of the rails and consequently their service life.

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For sale: U Beam Support, steel mining support

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Mining support:

Material: 20mnk Q275

Detail parameter:

18U: height: 99mm thickness:10mm thory:18.96kg/m 

25U: height:110mm thickness:17mm Theoretic Weight :24.76kg/m

29U height:124mm thicness:16mm TheoreticWeight :29kg/m

36U height:138mm thicness:17mm TheoreticWeight :36kg/m

Mine support steel main characteristics: under pressure, support time, easy to install is not easy to deformation, etc.

Rail Steels: Properties of Quality

So what makes rail steel superior to other steels? The simplest answer is its unique composition.

As we mentioned above, the rails are subject to heavy contact cyclic loading that accompanies increased car size and loading, to 100 and 125 ton capacity, increased train size, and increased train speeds used to transport bulk products over the last several decades. These increasing demands require manufacturing and metallurgical approaches that offset wear and other types of failure that limit rail life.

An early type of rail failure was associated with entrapped hydrogen that produced shatter crack or flakes in heavy rail sections, but that difficulty has been effectively controlled cooling and by vacuum degassing of liquid steel.

Typically, rail steels are produced in large BOS vessels and are vacuum degassed prior to being continuously cast into large blooms. Vacuum degassing, coupled with ladle trimming facilities, permits very tight control over chemical composition. After casting, the blooms are placed in insulated boxes, whilst still at a temperature of about 600°C, and are cooled at a rate of 1°C per hour for a period of three to five days. This treatment, coupled with prior vacuum degassing, reduces the hydrogen level in the finished rail to about 0.5 ppm, thereby reducing substantially the susceptibility to hydrogen cracking.

The blooms are then reheated and rolled directly to the finished rail profile. The rail produced by steel rail manufacturer from each bloom is hot sawn to specific lengths prior to passage through a rotary stamping machine en route to the cooling areas.

Depending upon the properties required, the rails are either cooled normally in air or subjected to enhanced cooling for the development of high strength. On cooling to room temperature, the rails are passed through a roller-straightener machine which subjects the section to a number of severe bending reversals and emerge with a very high degree of straightness. Finally, the rails pass through a series of ultrasonic, eddy current and laser inspection stations which monitor non-metallic inclusions, external defects and the flatness of the running surface.

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.

Up until the 1970s, railway rails for passenger and freight trains were regarded as relatively simple undemanding products and the specifications had changed very little for decades. However, investments in railway systems, the advent of high-speed passenger trains and the requirement for longer life track imposed a demand for high quality rails, greater strength and tighter geometric tolerances. Therefore there have been major innovations in the past 20 years in terms of the method of manufacture, degree of inspection and range of products.

Rail steel is extremely tough. As figure 2, rail steel resists breakage even after the yield point is exceeded. In addition, rail steel has satisfactory amount of ductility and after re-heating, can be used to complete most forming operations.

Their average yield point is greater than 60,000 PSI, while actual tensile strength normally ranges from 100,000 PSI to 130,000 PSI. This high yield point means rail steel provides ample stiffness, enduring heaviest demands with little deformation.

Even after years of service and high stress, there is no difference between the grain structure of a used rail and a new rail. Age, traffic and weather do not change its basic properties. All stresses are relieved through heating prior to being re-rolled. This re-rolling, in accordance with ASTM-A-499, decreases the rails’ grain size, and that means improved resiliency. The additional working of the steel actually makes it better than when it was a rail!

Wood Vs. Steel Support Beams - B

Durability

Steel support is very durable and is more likely to survive natural disasters like hurricanes, earthquakes, and fire. Steel also does not rot, mold, or dry out. It is not subject to infestation and will not shrink or warp in different weather conditions. Steel supports, walls, and frames stay straight and flat through construction and during its lifetime better than wood.

Construction

Steel beam support can be pre-engineered or prefabricated, meaning the construction is done beforehand. This can save time and money and is generally an easier way to construct a building. This is done by constructing certain parts, bodies, or pieces in a factory before they are shipped to a construction site.

Environment

Both steel roof support and wood have claims to being green, or environmentally-friendly. Wood grows naturally so the energy needed to process it is little. Iron on the other hand must be dug from the ground and then processed in large factories. This can create large amounts of greenhouse gases and pollution. However, while wood is a renewable resource, it is dependent on the time it takes to grow a tree and whether or not enough trees are growing. Steel is not a renewable resource, but it easier to recycle than wood. In fact, a great deal of steel in the United States is recycled.

Wood Vs. Steel Support Beams - A

Wood has traditionally been the building material for most support beams in home construction. However, with steel proving itself as an excellent building material in large buildings, it is slowly replacing wood construction in conventional homes as well. This is due to many factors, from price and availability, strength and durability, and the elimination of misconceptions. Although wood remains important in home construction, steel support provides many advantages. Steel buildings can even be pre-engineered to speed construction and efficiency.

Price
Fortunately, wood and lumber is a renewable resource. Unfortunately, the rate of its needs versus how fast it is replanted is much higher. This means lumber prices can fluctuate. Steel mining support , on the other hand, is readily available in large quantities. It is also recyclable. Steel prices, although historically higher than wood, is now on par with wood. The pricing of steel is usually consistent.

Strength
Steel support beams have very high load strength and can handle stress much better than wood. Aside from being one of the strongest building materials available for home construction, it is a manufactured metal, meaning its strength isn’t dependant on things like knots, twists, or defects that may be found in wood.

How Much Does a Steel I Beam Cost?

A steel I beam is a great structural alternative to lolly columns or other support methods. Steel is one of the strongest building materials known to man. Steel is mostly comprised of iron, 98%. The other 2% is a hardening agent, usually carbon. It is the carbon that makes it super strong and rust resistant.

Steel I-Beam Costs
You can find a steel I-beam from your local steel supplier. If you need just one length of I-beam you may be able to have them cut you a 6’ or 8’ length from a scrap piece they have left over from a large shipment. This will cost anywhere from $.90 to $1.25 per pound.That means you can purchase a 125 to 150 pound beam (roughly 6 feet in length) for a cost of $112.50 to $187.50.

How much does it cost to install a steel I beam?
You will first need to hire an engineer to come in and do some calculations and give a written sign-off on your project. He will calculate the proper length and mass of the I beam to meet code. It will cost $400 to $600 to hire an engineer for this job.
You may look at Residential Steel Beam Column Load and Span Tables to get an idea of what size I beam you need. The engineer will certainly be using these to size up you project. You will then need to hire a contractor to install the steel beam support

Things to Consider

I-Beams are only good at supporting weight in one direction. The web, or main vertical section of the beam is what provides the strength for this. If there is going to be a lot of twisting or bending as a result of horizontal pressure then an I beam will not work. Ask a professional. Tutorial on I beams and how they are used.