均热温度对不同成分980 MPa级高强钢组织和性能的影响

采用Gleeble-3500热模拟试验机对两种不同成分的1.4 mm厚冷硬带钢进行退火热模拟试验,并利用万能拉伸试验机、光学显微镜、扫描电镜、EDS对所得热模拟退火试样进行力学性能和组织分析。结果表明,其他退火参数相同,低C高Mn成分前提下,添加合金元素Cr、Mo及高Si含量的C-Mn-Si(高)+Cr+Mo钢和不添加合金元素Cr、Mo且低Si含量的C-Mn-Si(低)钢经760、780 ℃均热退火可得到力学性能满足要求的980 MPa级双相钢。不同均热温度下,C-Mn-Si(高)+Cr+Mo钢组织均为铁素体、岛状马氏体和少量贝氏体,区别在于均热温度高的铁素体晶粒细小且数量较多,呈凹凸不平形貌,马氏体含量少一些,贝氏体呈针状或团簇状;C-Mn-Si(低)钢组织则由铁素体、马氏体、少量的贝氏体和残留奥氏体组成,区别在于均热温度高,铁素体晶粒细化,轧制特征不明显,马氏体含量少,贝氏体呈粒状且量较少。残留奥氏体呈亮白色条状,这种亮白色的特征主要是因为Mn的局部富集。两种试验钢组织差异本质上是Cr、Mo和Si 3种合金元素的含量差异影响过冷奥氏体稳定性引起的。

Effect of soaking temperature on microstructure and properties of 980 MPa grade high strength steel with different chemical composition

Continuous-annealing process was simulated to treat 1.4 mm chilled steel strips with different chemical composition by Using Gleeble-3500 thermal simulation machine, and the mechanical properties and microstructure of the simulating annealed specimens were analyzed by means of universal tensile testing machine, optical microscope, scanning electron microscope and EDS. The results show that other annealing parameters are the same, under the premise of low C and high Mn composition, the C-Mn-Si(high)+Cr+Mo steel with alloying elements Cr, Mo and high Si content and the C-Mn-Si(low) steel without alloying elements Cr, Mo and with low Si content can obtain 980 MPa grade dual-phase steel with mechanical properties meeting requirements when annealed at soaking temperature of 760 ℃ and 780 ℃. The microstructure of the C-Mn-Si(high)+Cr+Mo steel is composed of ferrite, island-like martensite and a small amount of bainite at different soaking temperatures. The difference is that the ferrite at high soaking temperature has small grain size and a large amount, uneven morphology, and the martensite content is relatively less, and the bainite is needle-like or cluster-like. The microstructure of the C-Mn-Si(low) steel is composed of ferrite, martensite and a small amount of bainite and retained autensite. The difference lies in the refinement of ferrite grain at high soaking temperature, not obvious rolling characteristics, less martensite content, and less granular bainite. The retained autensite is bright white stripes, which is mainly caused by local enrichment of Mn. In essence, the difference of microstructure between the C-Mn-Si(high)+Cr+Mo steel and C-Mn-Si(low) steel is caused by the different content of alloying elements Cr, Mo and Si, which affects the stability of undercooled austenite.