An Integrated Study on the Evolution of Inclusions in EH36 Shipbuilding Steel with Mg Addition: From Casting to Welding

Inclusion evolution behaviors, in terms of composition, size, and number density, and associated influence on the microstructures of the as-cast slabs, rolled plates, and simulated welded samples of plain EH36 and EH36-Mg shipbuilding steels have been systematically investigated. The results indicate that the inclusions in the as-cast plain EH36 are almost Al-Ca-S-O-(Mn) complex oxides with sizes ranging from 1.0 to 2.0 μm. After Mg addition, a large amount of individually fine MnS precipitates and Mg-containing Ti-Al-Mg-O-(Mn-S) complex inclusions are generated, which significantly refine the microstructure and are conducive to the nucleation of acicular ferrite in the rolled and welded sample. Moreover, after rolling and welding thermal simulation, the number of individual MnS decreases gradually due to its precipitation on the surface of Ti-Al-Mg-O oxides.     

Profiling Microstructure Evolution Roadmap in Heat-Affected Zones of EH36 Shipbuilding Steel Under Controlled Thermal Simulation

Metallurgical and Materials Transactions A - Microstructural evolution roadmap in heat-affected zones of EH36 shipbuilding steel has been investigated at different welding heat inputs. Quantified...     

EH36船板钢大线能量焊接连续冷却转变行为研究

利用Gleeble3800热模拟试验机,对EH36船板大线能量焊接模拟热影响区连续冷却转变行为和不同冷却速度下模拟焊接热影响区的相变组织进行了研究。结果表明,当冷速足够大时,在440℃发生马氏体转变,相变组织均为马氏体;随着冷速逐渐下降,相变组织由以马氏体和贝氏体为主变为铁素体和贝氏体。冷却速度在2~5℃/s范围内,焊接热影响区具有优良的性能。根据SH-CCT曲线选择的焊接工艺合理,大线能量焊接热影响区性能满足船级社规范要求。     

Detailing Microstructural Evolution Roadmap in the Weld Metal of EH420 Shipbuilding Steel Subjected to Varied Reheating Inputs

Metallurgical and Materials Transactions A - Microstructural evolution roadmap in the weld metal of EH420 shipbuilding steel subjected to various reheating inputs has been investigated. As...     

EH36钢120 t BOF-LF-RH-CC流程精炼过程中夹杂物演变研究

对采用“120tBOF-LF-RH-260mm板坯CC”工艺流程生产的EH36钢,在精炼过程中的夹杂物演变规律进行了研究。通过现场各工序取样检测,结合夹杂物形成热力学计算,分析了夹杂物种类和尺寸的变化。研究表明,在“LF→RH→中间包”的精炼过程中,钢中夹杂物数量密度呈逐渐降低趋势,而其中直径>5μm的大颗粒夹杂物数量密度则逐渐增加。大颗粒夹杂物种类为MnO-SiO₂系氧化物和CaO-Al₂O₃系钙铝酸盐,如3CaO·Al₂O₃,12CaO·Al₂O₃和CaO·Al₂O₃。在精炼过程中,当钢中Ca含量较低时,形成CaO·6Al₂O₃和CaO·2Al₂O₃,随着钢中Ca含量的升高,主要形成12CaO·7Al₂O₃和3CaO·Al₂O₃。     

Unravelling Microstructure Evolution and Grain Boundary Misorientation in Coarse-Grained Heat-Affected Zone of EH420 Shipbuilding Steel Subject to Varied Welding Heat Inputs

Microstructure evolution and grain boundary misorientation in coarse-grained heat-affected zone of EH420 shipbuilding steel have been investigated at different welding heat inputs. As heat input increases, main constituents transform from lath bainites to granular bainites, and to acicular ferrites as a result of reduced cooling rate. Corresponding fraction of high angle grain boundaries decreases from 28.24 to 20.04 pct as heat input is raised from 50 to 150 kJ/cm but reverses to 29.04 pct at 200 kJ/cm.     

Microstructure Evolution in Heat-Affected Zone of Shipbuilding Steel Plates with Mg Deoxidation Containing Different Nb Contents

This study is to comprehensively clarify the effect of Nb addition on the particles, austenite grain growth, microstructure evolution, and toughness in the heat-affected zone after high heat input welding at 400 kJ cm⁻¹ for shipbuilding steel plates with Mg deoxidation containing 0.002 and 0.016 wt pct Nb. The Nb addition enhances the dissolution of small particles (< 20 nm) and the coarsening of large particles (> 20 nm) during welding period of T > 1300 °C, because the stability of (Ti, Nb)(C, N) particles is reduced caused by the weaker bonding of Ti–C, Nb–N, and Nb–C. With the temperature above 1300 °C during welding, the austenite grain growth rate increases with Nb addition because the particle pinning force reduces by the small-sized particle dissolution and large-size particle coarsening. Nb addition hinders the ferrite transformation with the transformation temperature decreasing from 700–535 °C to 670–520 °C, due to the increased PAG size. Thus, with Nb addition, the microstructures change from high-temperature fine polygonal ferrite in small prior austenite grains (PAGs) to low-temperature coarse intragranular bainite ferrite in large PAGs, reducing the high-angled grain boundary density from 1.3 to 0.5 μm⁻¹ and increasing the effective grain size from 10.4 to 17.6 μm. Thus, the toughness at − 40 °C decreases from 127 to 58 J.

     

Transient Inclusion Evolution During Modification of Alumina Inclusions by Calcium in Liquid Steel: Part II. Results and Discussion

The formation of intermediate reaction products after calcium addition to aluminum-killed steel was studied. Steel samples were taken from laboratory and industrial heats before and at various times after calcium treatment. Inclusions were characterized by automated and manual scanning electron microscopy and X-ray microanalysis of polished cross sections and inclusions extracted by dissolution of the steel. Industrial and laboratory melts containing more than 40 parts per million (by mass) of dissolved sulfur showed calcium sulfide as the main reaction product after calcium injection, with calcium aluminates appearing later. It is proposed that the calcium aluminates are formed by reaction between the calcium sulfide and the alumina. A laboratory heat containing 7 parts per million of sulfur showed calcium oxide as the main initial calcium reaction product. A simple mechanism is proposed for the modification of alumina inclusions by calcium, considering transient CaO and CaS formation.     

镁处理易切削钢硫合金化后夹杂物演变行为研究

为开发含镁硫系易切削钢,采用高温模拟实验及热力学计算相结合的方法研究了夹杂物演变.探究了硫合金化对钢液中不同镁系夹杂物的影响及作用机理.实验结果显示,硫合金化会导致钢液中镁系夹杂物沿着MgO(s)→2MgO·SiO2(s)→MgO-SiO2-MnO(1)的路径转变.热力学计算结果表明,随着钢液中硫含量的增加,[Mg]-...     

Change in Properties of Pipe Steel with Two-Phase Structure During Low-Temperature Heating and Subsequent Plastic Deformation

Metallurgist - Results are given for evaluation of the effect of longitudinal deformation on the change of the mechanical properties and steel properties with a two-phase pipe metal structure...     

Transient Inclusion Evolution During Modification of Alumina Inclusions by Calcium in Liquid Steel: Part I. Background,Experimental Techniques and Analysis Methods

In aluminum-killed steels, modification of solid alumina inclusions is often carried out by calcium treatment, converting the alumina to liquid calcium aluminates. When calcium treatment is performed, calcium can either react with sulfur in the melt or with solid alumina. Calcium sulfide inclusions are solid at steel casting temperatures and thus would be detrimental to castability if they remained in the steel after calcium treatment. The aim was to study the transient evolution of inclusions after calcium treatment, testing the hypothesis that calcium sulfide may form as an intermediate reaction product, which can subsequently react with alumina to form modified calcium aluminates. The first part gives the project background and describes the experimental and quantification techniques adopted, including the effect of sampler size in laboratory melts. Results of the formation of intermediate calcium reaction products in laboratory and industrial heats are presented in the second part.     

<Emphasis Type="Italic">In Situ</Emphasis> Observation of the Nucleation and Growth of Ferrite Laths in the Heat-Affected Zone of EH36-Mg Shipbuilding Steel Subjected to Different Heat Inputs

The nucleation and growth behaviors of ferrite laths in the heat-affected zone (HAZ) of EH36-Mg shipbuilding steel with different heat inputs were observed in situ by high-temperature confocal scanning laser microscope (CSLM). It was found that ferrite laths prefer to nucleate on the surface of inclusions instead of grain boundaries under the heat input of 120 kJ/cm, while FSPs are easier to form in 210 kJ/cm due to a significantly reduced cooling rate.