Study On The Refining Process Of High Clean Spring Steel In Huaigang

The refining process of high clean spring steel in Huaigang is studied in this paper.Devices like the direct reading spectrometer,X-fluorescence spectrometer, hydrogen measuring meter,oxygen and nitrogen analyzer,metallurgical microscope, scanning electron microscope and X-ray energy spectrometer are used accordingly to analyze steel samples taken from the converter at tapping,tundish and billets and slag samples taken from LF and RH during the refining.The changes of total oxygen, sulfur,nitrogen and hydrogen in steel and their affecting factors during the refining out of the converter are studied by analyzing the data,meanwhile a systematic analysis is performed on the amount,distribution,appearance,source and affecting factors of non metallic inclusions in spring steel.The conclusion is as follows:1.Oxygen content is reduced obviously from the beginning of LF to the end of LF,it is reduced by 3.72ppm.Average content of oxygen is reduced by 2.57ppm from the beginning of RH to the end of RH.There is a oxygen increment of 0.59ppm from the end of RH to tundish.Oxygen content is decreased by 2.45ppm from tundish to billet.Oxygen content in final billet is controlled at 7.62ppm.2.It is helpful to reduce the amount of total oxygen in liquid spring steel by increasing the content of aluminum in steel.Production experience indicates it is suitable to control Al content in steel liquid within 0.02～0.030%.It can reduce oxygent content without affecting operation of CCM.3.Extending RH refining time,adopting refining slag with high basicity(R＞4) and high Al₂O₃ content(around 20%) and lowering the content of FeO and MnO in slag(FeO+MnO＜0.5%),all above-mentioned measures are benefiting to reduce total oxygen content in spring steel liquid.4.Most sulfur can be removed from liquid steel after LF refining.At the end of the process,the average sulfur content in the molten steel was from 0.001%to 0.005%and the desulfurization rate range from 70%to 97%.The average rate of desulfurization was about 90%. 5.Nitrogen in liquid steel is increased remarkably during LF refining.Nitrogen removal mainly happens at the phase of RH refining.The content of nitrogen in steel can be controlled at 20～30ppm after RH treatment.6.Hydrogen in steel can be removed effectively in the vacuum condition during RH refining.It is favorable to remove hydrogen if the treatment time for hydrogen removal is extended and stirring with argon is adopted.The content of hydrogen in steel is about 1ppm after RH treatment.7.Most large sized inclusions in liquid steel are removed and their amount is reduced remarkably after the refining from LF to RH.Main inclusions in steel during LF process are sulfides and composite oxides whose most grain sizes are below 15μm; Those in steel during RH process are composite oxides whose most grain sizes are below 10μm;Those in steel during tundish are Al₂O₃,sulfides and composite oxides whose most grain sizes are below 15μm and those in wires and rods are composite oxides whose most grain sizes are below 10μm.