Effect of microstructural banding in steel

Tensile and notch-impact properties in wrought steel containing 0.25 pct C and 1.5 pct Mn, with and without elongated inclusions and processed so as to be severely banded or virtually free of microstructural banding, are compared. A short-time, high-temperature normalizing treatment removed the banded condition. Both banding and elongated inclusions cause anisotropy in tensile ductility and impact energy. Elimination of banding is effective in reducing anisotropy in clean steel, but results in only modest improvement in steel containing numerous elongated inclusions. Eliminating microstructural banding alters austenite transformation to only a small extent but improves subsequent machining and cold forming by replacing martensite concentrated in bands with randomly dispersed small volumes of martensite in steel incompletely transformed to ferrite and pearlite or to bainite. This paper is based on an invited talk presented at a symposium on Homogenization of Alloys, sponsored by the IMD Heat Treatment Committee, and held on May 11, 1970, at the spring meeting of The Metallurgical Society of AIME, in Las Vegas, Nev.     

高强高韧低合金锰钢的研制

采用多元合金化思路设计了一种新型低合金高强度高韧性锰钢.研究了该钢的静态CCT曲线、显微组织、断口形貌以及热处理工艺对钢的力学性能的影响.结果表明:该钢中过冷奥氏体的稳定性高,具有高淬透性及高回火稳定性,经890～930℃淬火及200～230℃回火后获得回火板条马氏体组织,使该钢具有高的强韧性(抗拉强度R_m≥1500MPa,冲击韧性A_kv≥85J)匹配;钢中适当提高锰含量,符合我国资源情况,具有较高的性价比.     

The effect of microstructural banding on failure initiation of HY-100 steel

Microstructural banding of a hot-rolled HY-100 steel plate was accentuated by cooling slowly from the austenite region, which resulted in alternating layers of soft, equiaxed ferrite, and hard “granular ferrite.” The segregation of substitutional alloying elements such as Ni and Cr was identified as the main cause for the microstructural banding. Such banding induces anisotropic flow behavior at large strains, with deformation constrained by “pancake-shaped” bands of the hard granular ferrite. Tensile tests of circumferentially notched HY-100 specimens were performed in order to explore the stress dependence of failure in the slow-cooled as well as the quenched and tempered conditions. The failure behavior of the slow-cooled, microstructurally banded material exhibited a pronounced susceptibility to a void-sheet mode of failure. However, the absence of carbides within the equiaxed ferrite delays void coalescence and material failure to higher strains than in a quenched and tempered microstructure, despite the increased susceptibility to shear localization.     

The effect of microstructural banding on failure initiation of HY-100 steel

Microstructural banding of a hot-rolled HY-100 steel plate was accentuated by cooling slowly from the austenite region, which resulted in alternating layers of soft, equiaxed ferrite, and hard “granular ferrite.” The segregation of substitutional alloying elements such as Ni and Cr was identified as the main cause for the microstructural banding. Such banding induces anisotropic flow behavior at large strains, with deformation constrained by “pancake-shaped” bands of the hard granular ferrite. Tensile tests of circumferentially notched HY-100 specimens were performed in order to explore the stress dependence of failure in the slow-cooled as well as the quenched and tempered conditions. The failure behavior of the slow-cooled, microstructurally banded material exhibited a pronounced susceptibility to a void-sheet mode of failure. However, the absence of carbides within the equiaxed ferrite delays void coalescence and material failure to higher strains than in a quenched and tempered microstructure, despite the increased susceptibility to shear localization.     

400mm特厚低合金结构钢Q345E的研发

通过合理的钢种成分设计,模铸、钢锭加热和3 800mm轧机轧制及热处理工艺设计,采用晶粒细化、固溶强化、析出强化等手段,研发了厚度400mm的特厚板Q345E。钢板的屈服强度控制在305～350MPa,平均为335MPa;抗拉强度控制在470～555MPa,平均达到530MPa;伸长率控制在23%～28%,平均达到26%;-40℃纵向冲击功控制在109～287J,平均达到了198J,实现了强度和韧性的良好匹配,并具有较高的内部质量。     

High-strength low-alloy powder steel with a composite structure

The influence of carbon, nanodisperse Ni-Cu alloy, and ZrO₂ nanoparticles on the sintering and properties of sprayed iron powder is investigated. The mechanical properties of the new steel with a composite structure exceed by a factor of 2-3 those for the steel of the same composition produced from a mixture of ordinary powder.     

低合金钢中总化合氮的测定

介绍了低合金钢中总化合氮的测定方法。首先利用 5 g/L的柠檬酸和 5.0g/L氯化钾水溶液进行电解 ,然后溶解电解残渣 ,再蒸馏滴定 ,测定电解残渣中的总化合氮。该方法易于操作 ,实用性强 ,精密度和准确度都达到要求 ,为提高钢材性能研究提供了依据。     

In-situ microstructural evolutions of 5Mn steel at elevated temperature in a transmission electron microscope

The microstructural evolutions of 5 Mn steel during various heat treatments have been investigated by in-situ transmission electron microscopy(TEM).The specimen of 5 Mn steel was prepared using focused ion beam(FIB)milling,which allowed the selection of specific morphology of interest prior to the in-situ observation.The complete austenization at 800°C was verified at the atomic scale by minimizing thermal expansion and sample drift in a heating holder based on micro-electro-mechanical-systems.During annealing at 650°C,the formation of reverted austenite was dynamically observed,while the morphologies of austenite laths of 5 Mn steel after in-situ heating were quite similar to that after ex-situ intercritical annealing.During annealing at 500°C,the morphological evolution of cementite and associated Mn diffusion were investigated.It was demonstrated that a combination of FIB sampling and high temperature in-situ TEM enables us to probe the morphological evolution and elemental diffusion of specific areas of interest in steel at high spatial resolution.     

Effective rough rolling of low-alloy steel

The behavior of surface defects in continuous-cast slabs is investigated during rough rolling. A model of the change in defect shape is developed, and recommendations are made regarding the prevention of crack motion toward the strip axis.     

Microstructure development in high-strength low-alloy steel welds

The reliability of steel welds becomes more critical issue with increasing steel strength,because brittle phases are more likely to form in the weld metals and heat-affected zone(HAZ) and thereby the toughness and ductility of the welds are degraded.Therefore,refinement of microstructure and minimization of the brittle phases are necessary to improve the reliability of the high-strength steel welds.In this presentation,microstructure formation that controls the toughness of weld metals and HAZ in high-strength low-alloy(HSLA) steel welds is reviewed and possible routes to the improvement of the weld microstructure and weld toughness are discussed.     

Microstructure in low-carbon low-alloy high-strength pipe steel

The microstructure of a broad range of low-carbon low-alloy high-strength pipe steels produced by thermomechanical treatment is studied by transmission electron microscopy. Such steels consist of a mixture of various types of ferrite matrix with high-carbon phases and structural components. The classification of the structures is refined, with separate consideration of the components forming the low-carbon ferrite matrix and the high-carbon components that appear as isolated regions and also as layers and inclusions in bainitic ferrite. A deformational dilatometer is used to determine the temperatures ranges in which the various phases and structural components are formed.     

原位观察TiN粒子对低合金高强度钢模拟焊接热影响区粗晶区晶粒细化作用

采用高温激光共聚焦显微镜原位观察和电子背散射衍射技术研究TiN粒子在低合金高强度钢模拟大线能量焊接热循环过程中晶粒细化效果.研究发现合理的Ti和N含量能形成大量细小弥散分布的纳米级TiN粒子,在焊接热循环过程中有效钉扎热影响区粗晶区奥氏体晶界,抑制晶粒粗化.同时,TiN附着在Al₂O₃表面析出,在冷却过程中有效促进针状铁素体形核,得到有效晶粒尺寸非常细小的由少量针状铁素体和大量贝氏体构成的复合组织.     

低合金高强钢中非金属夹杂物的改性

借助热力学软件Thermo-Calc和ASPEX自动扫描电镜等分析手段,研究了低合金高强钢精炼过程渣-钢反应和钙处理对夹杂物改性行为的影响.通过提高炉渣碱度和w(CaO)/w(Al₂O₃)值以及降低炉渣氧化性等措施,钙处理前钢中Al₂O₃夹杂物转变为靠近1600℃液相区的CaO-MgO-Al₂O₃复合夹杂物和少量的MgO·Al₂O₃尖晶石.在渣-钢反应对Al₂O₃部分变性的基础上,钙线喂入量每炉由优化前的800 m减少到300 m仍能达到夹杂物改性的目的.     

The formation of austenite in a low-alloy steel

Austenite formation from different microstructural conditions has been studied in an Fe-lV-0.2C steel. The starting microstructures of ferrite, bainite, and martensite, and the morphology of austenite formation have been examined in detail by light microscopy and transmission electron microscopy. Retained austenite in quenched martensitic areas has been used to establish the crystallographic relationships during austenite nucleation, and to indicate the behavior of the initial vanadium carbide dispersion present in the ferrite starting microstructure. Limited measurements were also made of the kinetics of austenitization. Formerly Research Student, Department of Metallurgy and Materials Science, University of Cambridge. Formerly of Royal Society, Warren Research Fellow, Department of Metallurgy and Materials Science, University of Cambridge.     

Tempering behaviour of a dual-phase low-alloy steel

The tempering behaviour of a dual phase steel of 0.08% C, 1.21% Mn, 1.00% Si, 0.42% Cr, and 0.41% Mo composition with two different martensite contents of 30 and 52%. (obtained by intercritical treatments at 820 and 860°C, respectively) has been studied. The ultimate tensile strength decreased and percentage elongation increased continuously with increasing tempering temperature up to 600°C for both intercritical treatments. The yield strength has, however, increased up to 300°C, beyond which it decreased for the steel with 30% martensite. In contrast it remained almost constant for 52% martensite up to 300°C, beyond which it decreased. The martensite of dual-phase steel for both the intercritical treatments has undergone microstructural changes on tempering that are akin to those of fully martensitic low carbon steels. The SEM fractographs from the as-quenched specimens indicate that the tensile specimens failed by microvoid coalescence with the martensite areas appearing facetted and featureless while those for 600°C tempered condition by the formation of equiaxed dimples.     

Predicting the ferrite grain size in low-alloy steel

Mathematical models are proposed for calculating the onset temperature of ferrite transformation and the ferrite grain size as a function of the cooling conditions and the initial austenite grain size. The models are calibrated on the basis of experimental data for steels with ferrite-pearlite microstructure. The models are integrated in HSMM software, with considerable gain in computational power when considering the mechanical properties of steel rolled on the 2000 mill at OAO Severstal??.