Alloying Element Partition and Growth Kinetics of Proeutectoid Ferrite in Hot-Deformed Fe-0.1C-3Mn-1.5Si Austenite

Alloying element partition and growth kinetics of proeutectoid ferrite in deformed austenite were studied in an Fe-0.1C-3Mn-1.5Si alloy. Very small ferrite particles, less than several microns in size, were formed within the austenite matrix, presumably at twin boundaries as well as at austenite grain boundaries. Scanning transmission electron microscopy–energy-dispersive X-ray (STEM-EDX) analysis revealed that Mn was depleted and Si was enriched in the particles formed at temperatures higher than 943 K (670 °C). These were compared with the calculation of local equilibrium in quaternary alloys, in which the difference in diffusivity between two substitutional alloying elements was assumed to be small compared to the difference from the carbon diffusivity in austenite. Although the growth kinetics were considerably faster than calculated under volume diffusion control, a fine dispersion of ferrite particles was readily obtained in the partition regime due to sluggish growth engendered by diffusion of Mn and Si.     

强磁场下保温时间对Fe 0.76%C钢先共析 铁素体组织形貌的影响

 借助于光学显微镜研究了磁场（12 T）对Fe 0.76%C合金在807 ℃奥氏体化保温不同时间(10 min、30 min、60 min)后以2 ℃/min的冷速冷却后,先共析铁素体显微组织的形貌变化。结果表明：在相同奥氏体化保温时间下,经强磁场热处理样品的先共析铁素体的面积分数和晶粒数量明显高于无磁场热处理样品。这可归结为强磁场降低了先共析铁素体形核所需的驱动力。随着奥氏体化保温时间的延长先共析铁素体晶粒沿着强磁场方向伸长的趋势明显变弱。这主要是由于奥氏体晶粒随着奥氏体化保温时间的延长逐渐增大,导致铁素体晶核之间的距离增大,从而造成奥氏体中的Fe原子向先共析铁素体晶粒扩散的距离增大所致。     

Forming Limit Curve (FLC) and Fracture Mechanism of Newly Developed Low‐Carbon Low‐Silicon TRIP Steel

The Forming‐Limited Diagram (FLD) of intercritically annealed 0.11C‐1.65Mn‐0.62Si TRIP‐assisted steel was investigated. The high FLD₀ value of this new low carbon TRIP steel was indicative of a superior formability. The micro‐structural changes during deformation and fracture were studied in detail. The polygonal ferrite phase was found to plastically deform first and deformed most at larger strains. Fracture was initiated by micro‐voids nucleated at ferrite grain boundaries, within ferrite grains or at the interface between ferrite and the harder phases. Cracks were formed after micro‐voids grew, coalesced, and expanded in one direction. When crack tips reached the bainite phase or the martensite/austenite constituent, the cracks propagated along the boundary of these phases. Cracks reaching retained austenite islands caused stress‐induced martensite transformation at the crack tip. The direction of motion of the cracks also changed in this case.     

Selective Oxidation and Sub‐Surface Phase Transformation of TWIP Steel during Continuous Annealing

The selective oxidation of Twinning Induced Plasticity (TWIP) steel during annealing at 800 °C in a N₂ + 10%H₂ gas atmosphere with a dew point of ?17 °C and ?3 °C was investigated by means of high resolution transmission electron microscopy of cross‐sectional samples. The annealing resulted in the selective oxidation of Mn and Si and the austenite‐to‐ferrite phase transformation of the sub‐surface region. In the low dew point atmosphere, the annealing resulted in the formation of a MnO layer at the surface. Crystalline c –xMnO · SiO₂ (x ≥ 2) particles and amorphous a –xMnO · SiO₂ (x < 0.9) particles were found at the interface between the MnO layer and the steel matrix. In a narrow zone of the sub‐surface, the Mn depletion resulted in the transformation of the initial austenite. In the high dew point atmosphere, a thicker MnO layer was formed on the surface and no mixed manganese‐silicon oxides particles were observed at the MnO/steel matrix interface. In the sub‐surface, Mn was significantly depleted in the range of 2–3 µm below the surface and the initial austenite in this zone was transformed to ferrite. MnO particles were found at the grain boundaries and in the interior of grains.     

Kinetic Transition During Ferrite Growth Induced by Interfacial Solute Segregation in an Fe–C–Mn–Si Alloy

The kinetic transition of partitionless proeutectoid ferrite transformation from austenite, experimentally reported earlier in an Fe–C–Mn–Si alloy, is simulated incorporating interfacial segregation of carbon and alloy elements. The time-dependent diffusion equations of solutes are solved within the α/γ interface to evaluate the transient effects of solute accumulation on the migration of interface. The carbon concentration at the interface in the matrix decreased faster and the interface migration ceased, or the so-called stasis occurred, when the carbon concentration gradient in the immediate front of the interface turned to null or reversed. This can happen earlier than the partitionless-to-partitioned growth transition predicted from conventional theory in the absence of interfacial segregation, depending upon austenite grain size, i.e., the extent of soft impingement of carbon diffusion fields in the matrix in which a large carbon supersaturation remained. The subsequent transformation may be resumed accompanying the bulk partitioning of Mn (and probably Si) and/or nucleation of new ferrite crystals.

     

Hot corrosion of Fe-Cr-Ni-AI-Si alloys in molten carbonate

The change in weight of five newly developed steel alloys containing Fe, 10–11.3 % Cr, 15–18.27 % Ni, 4.98–5.76 % Mn, 4.18–5.52 % Al and 0.36–1.5 % Si together with Inconel 690 and stainless steel 304 has been investigated in Na₂CO₃ + K₂CO₃ eutectic mixture at 800°C under atmospheric pressure and under isothermal and cyclic conditions. The scales formed were examined with optical and scanning electron microscopy and were analysed by energy dispersive X-ray diffraction techniques. It has been shown that the corrosion resistance of the alloys is far better than that of stainless steel 304, but slightly less than that of Inconel 690. The relatively high contents of Si and Al gave alloy 5 its highest corrosion resistance. About 0.2 % N were found to refine the grains without the danger of depleting the grain boundaries from Al and Cr. The results have been explained in the light of the alkaline conditions prevailing in the carbonate melt.     

双辊连铸304不锈钢2.0 mm薄带中铁素体的形态与分布

采用化学侵蚀、彩色金相显示和电子探针(EPMA)分析研究了304奥氏体不锈钢(%:0.08C、1.37Mn、0.62Si、17.77Cr、9.09Ni)2.0 mm连铸薄带内残留铁素体的形态和分布。结果表明,在薄带表层铁素体呈棒状,其间距≤20μm;在薄带柱状树枝晶区,铁素体位于一次枝晶臂和二次枝晶臂中心,铁素体二次枝晶间距≤10μm;在中心等轴晶区,残留铁素体形貌和分布与等轴晶区半固态形成机理有关。先凝固的固相颗粒内部铁素体为弯曲树枝状和网状形貌,固相颗粒间隙铁素体呈岛状形貌。     

AOD精炼高氮奥氏体不锈钢1Cr22Mn15N的工艺实践

用 20 t AOD精炼成分(%)为1.84C ,2.18Mn ,24.88Cr的粗炼钢水 ,经吹O2 、N2 ,加电解锰、硅铁、铝块以及NCr合金成分微调 ,冶炼出(%) 0.12C ,0.42Si,14.96Mn ,0.026P ,0.001S ,22.57Cr,0.56N的高氮奥氏体不锈钢 1Cr22Mn15N。精炼钢水浇铸成590kg锭 ,初轧轧成 135mm × 157mm坯 ,再经连轧成Φ8～12mm的棒材。成品材固溶处理后的屈服强度为565～585MPa ,抗拉强度920～955 MPa ,延伸率为54.5 %～56.5% ,具有优良的耐腐蚀性能     

电渣重熔Mn18Cr18N钢铸态热塑性与组织的关系

研究了电渣重熔Ｍｎ１８Ｃｒ１８Ｎ钢的高温热塑性及其与组织的关系。结果表明，Ｍｎ１８Ｃｒ１８Ｎ钢热塑性曲线具有高温脆性区、高温塑性区和二次脆性区。Ｍｎ１８Ｃｒ１８Ｎ钢在高温脆性区塑性变差的原因是由于奥氏体晶界成为位错晶界；在高温塑性区塑性良好是由于奥氏体晶粒发生大量的孪生变形；在二次脆性区塑性变差是由于铸态组织的成分偏析导致晶界局部析出薄膜状铁素体。     

Preparation and printability of high performance 15Cr13MoY alloy steel powder for direct laser deposition

ABSTRACT

A novel 15Cr13MoY alloy steel powder used for direct laser deposition was produced using the vacuum induction gas atomisation (VIGA) method. The characteristics and laser printability of the 15Cr13MoY alloy steel powder were studied. The flowability of the spherical powder was 18.98?s/50?g^?1, and apparent density was 4.75?g?cm^?3. The fabricated 15Cr13MoY alloy steel samples composed of ferrite and bainite were prepared by DLD. The phases primarily consisted of a Fe–Cr–Mn solid solution M₇C₃, M₂₃C₆ and Y₂O₃. At the optimum laser power of 2200W, the average microhardness of 15Cr13MoY alloy steel sample was 350 HV, the tensile strength was 897?MPa, the yield strength was 704?MPa, the average elongation was 14.5%, and the product of strength and plasticity was 13.0?GPa%. The 15Cr13MoY alloy steel powder produced usingthe VIGA method had good powder characteristics and printability for fabricating the components produced by DLD.     

微合金化控轧控冷钢筋纵向金相组织研究

 对微合金化控轧控冷钢筋的纵向金相组织进行了研究,并分析了不同成分试验钢纵向“条带”组织的差异及形成原因。研究结果表明：偏析元素（P、Si、Mn等）在轧制过程中沿轧制方向呈条状分布,是20MnSi、20MnSiV钢产生带状组织的原因。铌及其碳氮化物的溶质拖曳和“钉扎”作用,使20MnSiNb钢的奥氏体未再结晶轧制温度提高到1050℃,在冷却过程中,先共析铁素体在形变奥氏体晶界和内部变形带均匀析出,随后沿形变奥氏体晶界（在先共析铁素体与奥氏体的界面上）生成珠光体带,最后在形变奥氏体晶粒内部形成贝氏体条。研究条件下优势形核点的排序为：形变奥氏体晶界和形变奥氏体晶内变形带、偏析元素和夹杂、再结晶奥氏体晶界。     

超级双相不锈钢S32760凝固过程Thermo-Calc热力学软件的应用

利用Thermo-Calc热力学计算软件得到S32760（022Cr25Ni7Mo3WCuN）超级双相不锈钢凝固过程中的相图,确定了S32760双相钢是FA （铁素体-奥氏体）凝固模式,通过改变奥氏体和铁素体的形成元素的含量,确定在不同的化学成分下的热加工性能、Cr₂N和σ相析出温度,得到S32760双相钢热加工温度区间随着奥氏体形成元素C、N、Ni、Mn含量的增加而变大,随着铁素体形成元素Si、Cr、Mo含量的增加而减小,而W对热加工性能没有影响。根据热力学计算,确定了最优的化学成分（/%:0.022C,0.30Si,0.80Mn,25.60Cr,6.20Ni,0.54Cu,3.50Mo,0.54W,0.27N）,S32760双相钢最佳热塑性温度为1195℃, Cr₂N相的析出温度为1050℃, σ相析出温度为1020℃,热加工区间为145℃,并且通过了后续的现场实践验证。     

On the Eutectoid Reaction in a Quaternary Fe-C-Mn-Al Alloy: Austenite → Ferrite + Kappa-Carbide + M23C6 Carbide

Lamellae of ferrite, kappa-carbide, and M₂₃C₆ carbide are involved in a eutectoid reaction of an Fe-C-Mn-Al alloy after isothermal holding at temperatures below 923 K (650 °C). These lamellar phases are product phases from the decomposition of austenite during the eutectoid reaction of the quaternary alloy, i.e., austenite → ferrite + kappa-carbide + M₂₃C₆ carbide. Since the Al concentration in the steel is higher than that of the eutectoid composition, proeutectoid ferrite and kappa-carbide appear in the austenite prior to the eutectoid reaction to reduce the Al content of the retained austenite. The retained austenite decomposes into ferrite, kappa-carbide, and M₂₃C₆ carbide during the eutectoid reaction.     

直接热轧法制备Cu-P-Cr-Ni-Mo双相耐候钢

 在商用09CuPCrNi耐候钢化学成分的基础上,通过调整合金元素含量,研制出了可直接热轧双相化的Cu-P-Cr-Ni-Mo耐候钢。该钢种变形奥氏体的CCT曲线具有较宽的铁素体析出区,可作为热轧“可行的速度窗口”;铁素体析出区与贝氏体转变区之间存在约80℃的奥氏体亚稳区,可作为热轧“可行的卷取范围”;贝氏体转变区的右侧端部封口,可避免在卷取过程中发生贝氏体转变。根据Cu-P-Cr-Ni-Mo耐候钢的变形奥氏体的CCT曲线,制定了5种热轧双相化工艺,并采用Gleeble-3500热模拟机进行了轧制模拟,制备出了Cu-P-Cr-Ni-Mo热轧双相耐候钢。不同工艺下获得的双相耐候钢组织均为铁素体基体及其上呈岛状分布的马氏体,马氏体体积分数为17%~28%。     

The kinetics of ferrite nucleation at austenite grain edges in Fe-C and Fe-C-X alloys

Nucleation kinetics of proeutectoid ferrite allotriomorphs at the edges of austenite grains in Fe-C and Fe-C-X alloys, where X is successively Mn, Ni, Co, and Si, have been measured using a modification of the techniques previously developed to study nucleation at grain faces. Analysis of these data with classical heterogeneous nucleation theory has shown that ferrite nuclei formed at grain edges have low energy interphase boundaries. An equivalent conclusion was reached during our previous studies of ferrite nucleation at austenite grain faces. The influence of alloying elements on nucleation rates was also found to follow a pattern similar to that demonstrated for grain face nucleation. Formerly Graduate Student with the Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University,     

热轧材冷拉过程65钢硬线断裂分析

65钢(/%:0.62～0.。70C、0.18～0.28Si、0.55～O.75Mn)硬线盘条的生产流程为120 t转炉-LF-170mm×170 mm连铸-高速线材轧制。采用光学和扫描电子显微镜分析了65钢φ6.5 mm热轧盘条在冷拉至φ1.85mm过程中断裂的原因。实验结果表明,断口宏观特征为笔尖状,盘条横截面组织均匀性较差;裂纹起源于心部粗大的先共析铁素体和粗片状渗碳体,断裂的主要原因是索氏体化率低,存在大块先共析铁素体和中心碳偏析。     

奥氏体不锈钢凝固组织中残留铁素体特征研究

 采用化学侵蚀、彩色金相和电子探针（EPMA）等方法对AISI304奥氏体不锈钢连铸方坯凝固组织及其残留铁素体的形貌、化学组成等特征进行了分析,并采用DICTRA软件对铁素体向奥氏体的扩散转变进行了模拟研究,结果表明AISI304不锈钢铸坯表层树枝晶区的二次枝晶间距为12~20μm,富Cr贫Ni的残留铁素体呈骨骼状分布;铸坯中心等轴晶区的残留铁素体为蠕虫状分布,中心等轴晶区的残留铁素体富Cr贫Ni的同时富Si贫Mn,且其富Cr贫Ni的程度比柱状晶区的残留铁素体轻。钢液成分和先析铁素体向奥氏体扩散转变时间、距离是影响残留铁素体化学组成的主要因素。     

Volume Fractions of Proeutectoid Ferrite/Pearlite and Their Dependence on Prior Austenite Grain Size in Hypoeutectoid Fe-Mn-C Alloys

It has been generally believed that pearlite transformation in hypoeutectoid steels starts when the average carbon concentration in untransformed austenite reaches the A_cm line after the formation of proeutectoid ferrite. To test this concept experimentally, volume fractions of proeutectoid ferrite/pearlite and carbon contents in the austenite being transformed into pearlite were measured for the Fe-2Mn-0.3C alloy isothermally transformed in the temperature range 848 K to 898 K (575 °C to 625 °C). It was found that lamellar pearlite can form even when the average carbon content in untransformed austenite is much lower than the A_cm line. This peculiar observation is probably due to the two-dimensional diffusion of carbon, i.e., parallel to and normal to the austenite/pearlite interface, which enables lamellar cementite to grow continuously by supplying carbon atoms to its growth front. This results in proeutectoid ferrite fractions with respect to pearlite being much lower than those predicted by the lever rule. With decreasing prior austenite grain size, proeutectoid ferrite fractions with respect to pearlite were found to increase, but the thickness of proeutectoid ferrite was constant within the range of grain size investigated. This is due to the existence of the critical α/γ interface velocity only below which pearlite (actually cementite) can be nucleated at the migrating α/γ interface. Furthermore, the upper limit temperatures for pearlite formation in the Fe-1Mn-0.33C and Fe-2Mn-0.3C alloys were found to be well between the PLE/NPLE and PE A_e1 temperatures.     

Enhanced carbon solubility in solvent for SiC rapid solution growth:Thermodynamic evaluation of Cr-Ce-Si-C system

The carbon dissolution in solvent plays a key role in the process of solution growth route for SiC single crystal,which could determine the growth rate and quality of the products.However,the carbon dissolving ability of binary alloy solvent still needs to be improved.Here,we demonstrate the improved carbon dissolution and enlarged carbon supersaturation in Cr-Ce-Si ternary solvent,showing great potential for SiC solution growth.The phase relations of Cr-Ce-Si-C system were determined by using C...     

奥氏体化温度对30Cr3SiMnNiWMo钢组织性能的影响

试验研究了860～980℃奥氏体化处理对30Cr3SiMnNiWMo钢(%:0.28C、0.74Mn、1.04Si、2.70Cr、1.15Ni、0.45Mo、1.04W、0.07V、0.05Al)组织以及260℃回火后钢的力学性能的影响。结果表明,30Cr3SiMnNiWMo钢860～920℃淬火组织中存在大量M6C碳化物,对回火钢的韧性不利;950℃淬火后,钢中M6C碳化物基本溶解,原奥氏体晶粒开始长大,回火后钢的强度降低;30Cr3SiMnNiWMo钢经920℃1h油淬+260℃2h回火可以获得具有少量残余奥氏体和未溶碳化物的板条马氏体组织,并具有优良的强韧性(Rm=1680 MPa, Rp0.2=1330 MPa,A=13%, Z=58.5%, AKU=85 J) 。