The Effect of Tempering Temperature on the Microstructure and Properties of Q500qENH Steel
The Q500qENH pilot test was carried out by a Φ350 mm four/two roll hot rolling experimental machine.The test steel plate was tempered between 400 and 750 ℃,and the properties of the rolled and tempered was performed further by using scanning electron microscopy,optical microscopy,and transmission electron microscopy.The results indicate that the bainite ferrite has good toughness and high strength because of the high-density dislocations in the rolled micro-structure.As the tempering temperature increases,the acicular ferrite in the matrix organization becomes polygonal.When the tempering temperature is 650 ℃,small Nb(C,N)and ε-Cu particles appear on the acicular ferrite.When the tempering temperature is 750 ℃,the quantity of Nb(C,N)andε-Cu decreases and their size becomes coarser.When the tempering temperature is between 400 and 500 ℃,the strength and impact toughness are slightly higher than those of TMCP state,and the yield strength ratio is lower than 0.86.When the tempering temperature is between 500 and 650 ℃,the toughness and yield strength ratio both increase significantly,and the yield strength ratio reaches the maximum value of 0.88 at the tempering temperature of 650 ℃.When the tempering temperature is between 700 and 750 ℃,the strength decreases rapidly,and the toughness deteriorates when tempering temperature reaches 750 ℃.
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