Air-cooled bainite steel

Properties and applications of five bainite steels  

      Low carbon granular bainitic steel

     Professor Hongsheng Fang has proved that good combination of strength with toughness can be obtained by controlling the size, quantity and distribute of the M/A islands in granular bainite microstructure.

     A kind of granular bainitic steel was developed and became a new kind of non-modified steel. After the process of "forging or rolling-aircooling-medium temperature temperin" this type of steel can substitute for medium carbon alloy modified steel and can be used in modified articles such as auto front axles, bogies and connecting rods.

     This kind of granular bainitic steel without quenching has been used to manufacture sucker rods for many oil fields in a large amount. The following properties can be obtained:σ0.2⃿-850MPa,σb⃿-1100MPa,δ5⃿,ψ⃿ and αkuⅿJ/cm2.

     Low carbon air-cooled bainitic steel can be steadily used as bainite-type non-modified steel.

      Grain boundary allotriomorphic ferrite/granular bainite dual phase steel( FGBA/Bg)

     On condition that the supplementary refinement, controlled rolling technique, heat treatment and precious alloying elements are not used, air-cooled low carbon FGBA/Bg steel plates with thickness of 12mm, 16mm, 20mm can be successfully manufactured in steel plate production line and they have the following properties:σb⃿MPa,σ0.2⃿MPa,δ5⃿,αku value of 60J at 20‿and αku value of 27J at -40᾿br>
     This product has been tested and used in many units and the results indicate that it has advantages such as high strength and toughness, good wear resistance and excellent welding property, thus it has a bright prospect in large amount and wild area construction machinery. Besides being used in medium and heavy steel plate, this kind of steel also can be used in large gauge and high strength ribbed bars, bainite-type non-modified sucker rod, standard parts, plastic mould and so on.

      Medium and medium high carbon lower bainite/martensite dual phase steel

     The lower bainite/martensite microstructure can be obtained from medium carbon bainitic steels containing manganese by aircooling. The strength and toughness of this kind of steel is inferior to that of single martensitic steel when tempered at low temperature, but after tempering at 440₿it exhibits superior strength and toughness compare with tempered martensite with identical hardness.

     This kind of steel is applicable to most kinds of modified articles or surface induction heating hardening articles such as axle, cam shaft and crank shaft, etc. This kind of air-cooled bainitic steel has been successfully developed, for example, the spring steel, which is used to make leaf spring and spiral spring.

      Carbide-free bainite/martensite (CFB/M) dual phase steel

     The carbide-free bainite/martensite microstructure with ultra-fine structure can be obtained in aircooled condition when silicon is added to the bainitic steels containing manganese. The former austenite grains are divided and the martensite is refined by carbide-free bainite plates, and thus the strength and toughness of steel are improved.

     Up to now, low carbon CFB/M dual phase steel has been used to produce ultra-high strength structural articles such as high strength bolt, railway frog, high strength steel plate and seamless tube, etc. Medium carbon CFB/M dual phase steel can be used for making different kinds of spring, and medium-high carbon CFB/M dual phase steel can be used for making wear-resistant articles and grinding ball, etc.

      Low and medium bainitic cast steel

     Since bainitic steel is a kind of high hardness and toughness steel, air-cooled bainitic steel containing manganese has been used to manufacture various wear-resistant articles, such as grinding balls, casting tubes and other mining articles. On the basis of previous achievement in theoretical study and application, Professor Hongsheng Fang and his research team have developed several novel high silicon content bainitic cast steels and RE and titanium modified bainitic steels. The results show that the high silicon content and RE/Ti modification are effective for improving hardness and toughness of bainitic cast steels. These methods have been used in wear-resistant bainitic cast steels production successfully.

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