【作者】 王琦；

【导师】 李阳；

【作者基本信息】 东北大学 ， 钢铁冶金， 2020， 硕士

【摘要】 440C不锈轴承钢是一种马氏体型钢,含碳量为1.0%,含铬量为16%～18%。440C钢适用范围广,可以用来制造能够抗冲击、耐腐蚀的轴承,如轧机轴承、铁路轴承、海洋石油钻机轴承、船舶发动机轴承等。但是,采用传统冶炼工艺生产出来的440C钢仍然存在着诸多问题。例如钢中氧质量分数偏高;钢内存在有大量网状碳化物,在经过锻造后,碳化物偏聚现象严重;440C钢作为一种不锈轴承钢,具有一定的耐腐蚀能力,但是轴承钢作为精密基础部件的原材料需要更强的耐腐蚀能力,来保证生产出来的轴承拥有优秀的疲劳寿命。大量的研究结果表明,对钢液进行镁处理,能有效净化钢液、细化组织、改善钢内碳化物分布。本实验在加压的条件下,以质量分数5%的镍镁合金作为金属镁加入钢液的载体,减少镁与钢液反应面积,减弱镁与钢液反应的剧烈程度,从而达到提高镁收得率的目的。在实验室条件下共制备了4炉440C钢,各炉次中镁质量分数分别为:≤0.0005%、0.0029%、0.0081%、0.0160%。并且随着钢中镁质量分数的提高,钢中的氧、硫、氮质量分数不断降低,其中氧质量分数从0.0013%降低到0.0003%,硫质量分数从0.0032%降低到0.0018%,氮质量分数从0.0088%降低到0.0049%。与此同时,随着镁加入量的提升,镁的收得率也在不断升高。夹杂物及显微组织分析表明,镁元素可以变质钢中夹杂物,细化晶粒。在不添加镁时,钢中的夹杂物主要有MnS和Al2O3;当镁质量分数为0.0029%时,钢中MnS夹杂中开始出现镁元素,变为Mn-S-Mg夹杂,还出现了MnS包裹的Mg-O-S复合夹杂;当镁含量提高到0.0081%,钢中开始出现单相的尺寸细小的MgO夹杂与Mg-O-S复合夹杂;当镁质量分数达到0.0160%时,钢中的夹杂物类型未发生明显变化。随着镁质量分数的增加,单位面积内夹杂物的数量减少,夹杂物的平均当量直径也随之减小;铸态钢中等轴比升高,二次枝晶间距减小,回火状态下钢的晶粒度从13.0级升高到了 14.9级。力学性能实验的结果表明,随着镁质量分数的增加,440C钢的强度、韧性都有不同程度的上升。加入镁元素后,440C钢的晶粒得到了细化,并且钢中的碳化物与夹杂物情况都得到了改善,很好的提升了440C的机械性能。均匀腐蚀实验表明,随着镁质量分数的升高,440C钢耐均匀腐蚀能力得到一定提高,均匀腐蚀速率从不加镁的0.000757 g·cm-2h-1下降到了0.000664 g·cm-2h-1。点蚀实验表明,随着镁质量分数的升高,钢中夹杂物与碳化物尺寸减小,减少了点蚀发生的机会。使得440C钢的点蚀电位提升到足以抵抗海水的腐蚀,可以提高440C钢在海水中的寿命。更多还原

【Abstract】 440C stainless bearing steel is a martensitic steel with a carbon content of 1.0%and a chromium content of 16%to 18%.440C steel has a wide range of applications and can be used to manufacture bearings that are resistant to impact and corrosion,such as rolling mill bearings,railway bearings,offshore oil rig bearings,and marine engine bearings.However,there are still many problems with the 440C steel produced by traditional smelting process.For example,there is a large amount of reticulated carbide in steel.After forging,the phenomenon of carbide segregation is serious;440C steel has a certain corrosion resistance as a stainless bearing steel,but bearing steel is used as a raw material for precision basic components.A stronger corrosion resistance is required to ensure that the produced bearings have excellent fatigue life.A large number of research results show that magnesium treatment of molten steel can effectively purify molten steel,refine microstructure and improve carbide distribution in steel.In this experiment,under the condition of pressure,the nickel-magnesium alloy with a mass fraction of 5%is added as the carrier of magnesium to the molten steel,which reduces the reaction area between magnesium and molten steel,and weakens the reaction degree of magnesium and molten steel,so as to improve the yield of magnesium.A total of 4 furnaces of 440C steel were smelted under laboratory conditions,and the magnesium contents in each furnace were:≤0.0005%,0.0029%,0.0081%,and 0.0160%,respectively.And with the increase of magnesium content in steel,the content of oxygen,sulfur and nitrogen in steel decreased continuously,and the oxygen content decreased from 0.0013%to 0.0003%,the sulfur content decreased from 0.0032%to 0.0018%,and the nitrogen content decreased from 0.0088%to 0.0049%.At the same time,with the increase in the amount of magnesium added,the yield of magnesium is also rising.Inclusions and microstructure analysis show that magnesium can modify inclusions in steel and refine grains.When no magnesium is added,the inclusions in the steel are mainly MnS and Al2O3;When the magnesium content is 0.0029%,magnesium appears in the MnS inclusions in the steel,and becomes Mn-S-Mg inclusions.Mg-O-S composite inclusions also appear in the MnS;when the magnesium content is increased to 0.0081%,a single-phase small MgO inclusion and Mg-O-S composite inclusions begin to appear in the steel;when the magnesium content reaches 0.0160%,the inclusion type in the steel does not change significantly.With the increase of magnesium content,the number of inclusions per unit area decreases,and the average equivalent diameter of inclusions decreases.The as-cast ratio of the as-cast steel increased,the secondary dendrite spacing decreased,and the grain size of the steel increased from 13.03 to 14.89 in the tempered state.The results of mechanical properties experiments show that the strength and toughness of 440C steel increase with different degrees with the increase of magnesium content.With the addition of magnesium,the grains of 440C steel have been refined,and the conditions of carbides and inclusions in the steel have been improved,which has greatly improved the mechanical properties of 440C.The uniform corrosion experiment showed that the uniform corrosion resistance of 440C steel was improved with the increase of magnesium content.The uniform corrosion rate decreased from 0.000757 g·cm-2h-1 without magnesium to 0.000664 g·cm-2h-1.Pitting experiment showed that with the increase of magnesium content,the size of inclusions and carbides in steel decreases,reducing the chance of pitting.The pitting potential of 440C steel is increased enough to resist the corrosion of seawater,which can improve the life of 440C steel in seawater.更多还原