露点对连续退火0.2%C-1.5%Si-2.5%Mn高强钢选择性氧化及脱碳的影响  

Effect of Dew Point on Selective Oxidation and Decarburization of 0.2%C-1.5%Si-2.5%Mn High Strength Steel Sheet During Continuous Annealing

作　　者：金鑫焱[1,2] 储双杰 彭俊[1] 胡广魁[1] JIN Xinyan;CHU Shuangjie;PENG Jun;HU Guangkui(Baoshan Iron and Steel Co.,Ltd.,Shanghai 201999,China;State Key Laboratory of Development and Application Technology of Automotive Steels,Baosteel,Shanghai 201999,China)

机构地区：[1]宝山钢铁股份有限公司,上海201999 [2]汽车用钢开发与应用技术国家重点实验室(宝钢),上海201999

出　　处：《金属学报》2023年第10期1324-1334,共11页Acta Metallurgica Sinica

摘　　要：以成分为0.2%C-1.5%Si-2.5%Mn(质量分数)的先进高强钢为研究对象,采用连续退火模拟实验研究了露点对钢板表面Si、Mn选择性氧化以及次表层脱碳的影响。使用辉光放电发射光谱(GD-OES)分析了退火试样表面元素深度分布,使用SEM、OM观察了试样截面内氧化层及脱碳层深度,使用TEM观察了FIB制备的截面试样上Si、Mn内外氧化层的微观结构。结果表明,提高连续退火加热段和均热段的气氛露点可以促使Si、Mn由外氧化转变成内氧化,但露点过高会引起钢板次表层发生明显的脱碳,形成次表层显微硬度显著降低的铁素体层。当露点提高到临界值后,继续提高露点对进一步减少外氧化的效果有限,但是内氧化层和脱碳层的厚度会继续显著增加,因此在退火时需要选择兼顾外氧化和脱碳层控制的合适的露点范围。The use of advanced high strength steel(AHSS)sheets has been acknowledged as an important solution for vehicle weight reduction,and thus,carbon dioxide emission reduction.The development of third-generation AHSS has become one of the steel industry􀆳s most prominent concerns in recent years.However,the selective oxidation of alloy components such as silicon and manganese makes obtaining high-quality hot-dipped galvanized steel sheets extremely difficult.To determine an optimal process window for controlling the surface microstructure of AHSS,the effect of dew point on selective oxidation of silicon and manganese,and decarburization in a 0.2%C-1.5%Si-2.5%Mn(mass fraction)steel sheet was studied by performing continuous annealing simulation experiments.Glow discharge optical emission spectrometry(GD-OES)was used to determine the depth profiles of alloy elements,and SEM and OM were used to determine the depths of internal oxidation and decarburization zones in the subsurface.The surface and internal oxides􀆳precise microstructures were studied using TEM on a FIB-prepared cross-sectional specimen.The increasing dew point of the atmosphere through the heating and soaking section portion of continuous annealing results in the transformation of external oxidation of silicon and manganese to internal oxidation.When the steel was annealed in an environment with a dew point of-40oC,a continuous silicon,manganese external oxidation layer with an average thickness of 40-50 nm covered the surface.When the dew point was elevated to+10oC,a subsurface oxidation layer approximately 5-μm thick formed.Due to the substantially lower oxygen pressure required for the Si/SiO2 equilibrium,the internal oxides exhibited a core-shell structure consisting of a Si-rich oxide core and a surrounding Mn-Si mixed oxide shell.A higher dew point results in the formation of an obvious decarburization layer in the subsurface,which is visible as a layer of ferrite grains with significantly decreased microhardness.When the dew point was increased

关 键 词：高强钢 露点 选择性氧化 脱碳 连续退火 

分 类 号：TG156.2[金属学及工艺—热处理]