15-7PH不锈钢电渣重熔过程夹杂物的行为

Behavior of inclusions during electroslag process of 15-7PH stainless steel

为了明晰15-7PH沉淀硬化不锈钢中夹杂物的行为,进一步提高其洁净度,采用超高功率电弧炉初炼→AOD(Argon Oxygen Decarburization)脱碳→LF(Ladle Furnace)精炼→模铸工艺制备了自耗电极,并用带压摆控制的气体保护电渣重熔炉进行重熔。采用HORIBA氧氮氢气体分析仪检测了电渣重熔前后氧、氮等含量的变化;ASPEX扫描电镜分析了夹杂物的尺寸、数目、化学成分、形貌等。结果表明,电渣重熔后15-7PH不锈钢中氧、氮含量有轻微的下降,但夹杂物的组成变化不大,主要由氮化物夹杂物(氮化铝+氮化钛)、氮化物-氧化物复合夹杂物、氧化物夹杂物、硫化物-氧/氮化物夹杂物组成,其中氮化物夹杂物尺寸最大、数量最多,明显高于其他夹杂物。电渣重熔对夹杂物的数量、尺寸有明显影响。重熔后夹杂数量大幅增加,氮化物尤为明显,但大颗粒夹杂物明显减少。氮化物夹杂物大量存在的主要原因在于钢中存在较高的Al,Ti,N等元素,而电渣过程由于熔渣吸附、部分夹杂物溶解,使大颗粒夹杂物减少,重熔过程的快速冷却抑制了夹杂物长大,最终结果是夹杂物尺寸更细小,但数量增加。

In order to clarify the behavior of inclusions in 15-7PH stainless steel and further improve its cleanliness,the consumable electrodes were prepared by UHP electric arc furnace→AOD decarburization→LF refining→mold casting process,and remelted by gas shielded electroslag remelting furnace with voltage swing control.The changes of oxygen and nitrogen before and after electroslag remelting were analyzed by HORIBA gas analyzer.The size,number,chemical composition and morphology of inclusions were analyzed by ASPEX SEM.It was found that the content of oxygen and nitrogen in 15-7PH stainless steel decreased slightly after electroslag remelting,and there was little change in the composition of inclusions,which were mainly composed of nitride inclusions(AlN,TiN),nitride/oxide composite inclusions,oxide inclusions and sulfide-oxygen/nitride inclusions.Among them,nitride inclusions had the largest size and quantity,which were significantly higher than other inclusions,and were worthy of special attention.Electroslag remelting had an obvious effect on the number and size of inclusions.After remelting,the number of inclusions increased greatly,especially nitrides.However,large inclusions were significantly reduced.The main reason for the large amount of nitride inclusions was the high content of Al,Ti,N in the steel.During the electroslag process,due to the adsorption of slag and the dissolution of some nitrides,the large inclusions were reduced,and the rapid cooling in the remelting process inhibited the growth of inclusions which led to the small size but increased of the number of inclusions in the electroslag ingot.