surface-of-a-railroad-rail

Railway steel or some called rail steel is used for making railroad tracks. Railroad tracks are bearing heavy loads and subject to wear and fatigue. So the grade of railway steel must meet the demands of train speed and load. Proper chemical composition of railway steel enables the rails to have enough hardness and wear resistance, also anti-fatigue property. Generally, the content of carbon is no more than 0.82%, and manganese is no more than 1.7%.

The composition and properties of railway steel

CountryType of Rail steelC  %Si  %Mn  %S  %P  %V  %MpaHB
JapanJISE600.63~0.750.15~0.300.70~1.10≤0.030≤0.025 ≥800≥235
AmericaAREA0.72~0.820.10~0.600.60~1.25≤0.037≤0.035 ≥960≥300
EuropeUIC900A0.60~0.800.10~0.500.80~1.30≤0.040≤0.040 ≥880260~300
ChinaU71Mn0.65~0.750.10~0.500.80~1.30≤0.030≤0.030 ≥880260~300
ChinaU75V0.70~0.780.50~0.700.750.80~1.05≤0.030≤0.0300.04-0.08≥980280~320

The developing trend of railway steel is hyper purity and hyper high strength. To meet the requirements, researchers across the world keep making progress in optimizing the performance of railway steel. Japan has developed the hypereutectoid pearlite rail steel, the UK has discovered the martensite rail steel. The bainite rail steel of Europe and America are becoming key points in researching and developing new high strength railway steel.

Hypereutectoid pearlite rail steel

As we all know, the wear resistance of the rail steel can be improved by adding alloying elements or through heat treatment. To get high-quality railway steel to some extent is to get more fine pearlite microstructure. Studies on pearlite steel show that by increasing the density of the cementite phase of the pearlite sheets, the wear resistance of the rail steel can be improved. Through the experimental study of the composition of eutectoid and hypereutectoid rail steel, researchers concluded that the performance of the hypereutectoid rail steel can be optimized by increasing the accumulation of ferrite.

the-lamellar-structure-of-peralite-rail-steel
the-lamellar-structure-of-peralite-rail-steel

Anti-cracking rail steel

In the 1990s, Japan’s NKK, American Railways and Burlington Northern jointly developed heat-treated steel rails called “Anti-cracking”. By adjusting the cooling rate during heat treatment, the surface and the top angle of the rail are treated with different hardness. Under the action of impact load, the tread with softer hardness will produce more wear. By increasing the wear rate at the center of the top surface of the rail, that is, the tread surface, the harmful fatigue cracks in this part can be naturally “worn” without expanding or expensive sanding. Since 1990, this kind of rail has been under the test in Burlington Northern and the results were satisfactory.

Martensite rail steel

Martensite rail steel is discovered by the staff of the British Iron and Steel Research Center in recent years. The railhead hardness of this new type of steel is as high as 445HB. Although the wear resistance of this low-carbon martensitic steel is almost the same as that of heat-treated steel, its toughness is much higher than that of heat-treated steel rails.

Bainite rail steel

Bainite rail steel has high hardness, tensile strength, high wear resistance. Especially the toughness of bainite rail steel is 2-5 times that of pearlite rail steels. Due to so many advantages, It is being developed in various countries around the world. At present, bainite steel is mainly studied from three perspectives.

  1. From the perspective of further improving the wear resistance. The bainite rail steel developed by German used on the 300-meter radius curve of the northern Norway mining line shows that its wear resistance life is 8 times that of traditional hot-rolled rails. The strength grade of the bainite rail steel has reached 1400 Mpa.
  2. France and Japan have aimed at improving the fatigue wear resistance (strength grade greater than 1100MPa) tested on the railroad has also achieved good results. 
  3. From the perspective of prolonging the service time of railway switch, more than 1000 sets of railroad frog (made of bainite steel) have been working great in the UK.  American is undergoing the process of testing.
microstructure-of-bainite-rail-steel-for-railroad-frog
microstructure-of-bainite-rail-steel-for-railroad-frog

The chemical composition and mechanical properties of bainite steel made in German, USA and UK

CountryC %Si  %Mn  %Cr  %Mo  %V  %B  %Mpa
German0.401.500.71.100.800.10>1300
USA0.261.842.01.940.440.003>1531
UK0.101.02.000.5Ni3.00.003>1000

The blooming of high-speed rails can not happen without the fine treatment of railway steel. It is a focal point for the developing of the heavy-haul railway. As the study of railway steel goes deeper, the railway system will be pushing forward much further and better.

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