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| Influence of quenching way on microstructure and mechanical properties of high strength flat bulb steel at tempering process |
| LIANG Feng-rui，CHAI Feng，SU Hang，SHI Zhong-ran |
| （Division of Engineering Steel， Central Iron and Steel Research Institute， Beijing 100081， China） |
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Abstract Using OM， EBSD and other test techniques，the difference of microstructure and properties of high strength bulb flat steel after induction-heat quenching and furnace-heat quenching was studied， and the tempering microstructure and properties of the quenched samples were also analyzed after tempering 3 h at different temperatures （600， 630， 650， 670， 680， 690 ℃）. The results show that microstructure of the two kinds of quenching methods are martensite and a small amount of bainite， and the microstructure of induction heating quenched sample is slightly thinner than that of furnace-heating， and the strength is slightly higher. The results of EBSD show that the martensite blocks in the two quenching modes are both large angle grain boundaries and the laths are small angle grain boundaries. The average effective grain size （MED2°） of bulb head and flat for the induction heating quenching is 2.815 μm， and for the furnace-heating is 3.015 μm. For tempering microstructures with different quenching methods， the higher tempering temperature is beneficial to the disappearance of lath interface， which is conducive to the growth and spheroidization of precipitates at the interface between lath and original austenite grain boundaries； The higher the tempering temperature， the decrease of the strength and the increase of the ductility and toughness. For batch production， the induction heat treatment is preferred to obtain the flat ball steel products with good strength and toughness and uniform properties； For small batch production， in practice， the proper quenching and tempering standard can be selected according to the performance requirements， and the furnace-heating could be used to heat treatment of the ball flat steel.
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Received: 29 March 2018
Published: 29 June 2018
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2018, Vol. 37 
