Through thermal expansion and metallographic-hardness method,the effect of cooling rate on the continuous cooling transformation of 65 steel without boron and with 0.001 5％ (by mass,the same below) boron was studied.The results showed that during continuous cooling,the microstructure was ferrite and pearlite with the cooling rate ranging from 0.1 ℃/s to 5 ℃/s;when the cooling rate increased between 5 ℃/s and 15 ℃/s,the microstructure was pearlite;in the range from 15 ℃/s to 35 ℃/s,the microstructure was mainly lath martensite and a small amount of ferrite.With the increase of cooling rate,the hardness of 65 steel without boron and with 0.001 5％ boron increased gradually.Under the same cooling rate,compared with the steel without boron,that with 0.001 5％ boron obtained smaller ferrite grain size,pearlite interlamellar spacing and higher hardness.In order to obtain the sorbite with excellent drawing property,the cooling rate for 65 steel without boron should be controlled between 5 ℃/s and 10 ℃/s,and that with 0.001 5％ boron should be controlled between 10 ℃/s and 15 ℃/s.%利用热膨胀法和金相-硬度法,研究了冷却速率(0.1～35℃/s)对不合硼和含0.001 5％硼(质量分数,下同)的65钢过冷奥氏体连续冷却转变的影响.结果表明,65钢在连续冷却过程中,当冷速为0.1～5℃/s时,组织为铁素体加珠光体;冷速为5～15℃/s时,主要是珠光体;冷速为15～35℃/s时,主要是板条马氏体加少量珠光体.随着冷却速度的增加,不合硼和含0.001 5％硼的65钢硬度值均逐渐增大.在相同冷速下,相比不含硼的65钢,含().001 5％硼的65钢铁素体晶粒和珠光体片层间距更小、总体硬度更高.为获得具有优异拉拔性能的索氏体,对于不合硼65钢,其冷速应控制在5～10℃/s,对于含0.001 5％硼65钢,其冷速应控制在10～15℃/s.
展开▼
