Nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting

The shape, type, content, and dimension of nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting were studied using scanning electron microscopy （SEM）. The results show that the inclusions are mainly spherical Al2O3 and complex oxides composed of MnO, Al2O3 , and SiO2. The percentage of fine oxides smaller than 3 μm reaches up to 51.8%. The theoretical calculations show that fine oxides have precipitated during solidification. Therefore, it is concluded that during twin-roll strip casting, because of high cooling rate, the size of inclusions precipitated during solidification decreases, and the amount increases.     

Microstructure and strengthening parameters of ultra—thin hot strip of low carbon steel

The microstructure and precipitation mechanism of ultra-thin hot strip produced by CSP technology were analyzed by electron back scattered diffraction(EBSD),H-800 transmission electron microscope(TEM) and thermodynamics theory.The EBSD results show that the finishing hot rolling microstructures are mixture of recrystallized and deformed austenite.After phase transformation,ferrite grains embody subastructures and dislocations that led ultra-thin hot strip high strength and relatively low elongation rate.TEM observations show that there are a lot of fine and dispersive precipitates in microstructures.Most of aluminium nitrides are in grains.While coexisted precipitates of MnS along grain boundaries,Coexisted precipitates compose cation-vacancy type oxides such as Al2O3 in the core,while MnS at the fringe of surface.At the same time,reasons for microstructure refinement and strengthening effect were invstigated.     

Microstructure evolution and precipitation behavior of low carbon steel hot strips produced by CSP

The microstructures of low carbon steel before, during and after rolling deformation of each stand were observed using optical microscope. The result showed that the microstructures were very fine after six passes rolling deformation. The effect of the first stand reduction on microstructure refinement was very distinct. During the rolling process, with the increase of the accumulated strain, the microstructures would further refine, and the density of dislocation would increase at the same time. In continuous casting thin slabs and each finishing stand, lots of observed precipitates were mainly A12O3 and MnS along the grain boundaries or in grains,which played an important role in the mechanical properties of the hot strips of low carbon steel produced by CSP (compact strip production) technology.     

Grain refinement of low carbon steel produced by CSP process

In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM,TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to ～125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm,respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process.The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystalliza-tion at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.     

锆英粉涂料涂层结构研究

通过研究锆英粉(其中有少量铝矾土)涂料层的断面结构,发现在高温条件下,锆英粉能分解出少量ZrO2微粉和SiO2;钢液表面的FeO能渗透到涂层中,与SiO2和水玻璃等形成铁橄榄石相;锆英粉能被水玻璃缓慢溶解,但其颗粒仍然能保持完整状态;SiO2、FeO、Al2O3、Na2O等生成了大量低熔点的玻璃相,填充其颗粒间空隙,形成致密层,能防止钢液渗透;涂层中的铝矾土在水玻璃的作用下,其颗粒状态消失,形成铝酸铁钠新相.     

Morphology, chemical compositions and size distribution of rare earth oxides in pure iron

The pure iron was melted and deoxidized by metallic A1 and rare earth elements La, Ce and Y respectively at 1600℃ in a vertical resistance furnace. The morphology, chemical composition and size distribution of the inclusions in deoxidized liquid iron have been investigated by using of SEM and image-analysis techniques. The investigated results show that the deoxidation products in molten iron are complex inclusions of rare earth oxide or A12O3 combined with FeO finely distributed. The proper holding time and rapid cooling rate can make inclusions finer. La, Y and A1 are more effective than Ce for obtaining finely distributed inclusions.     

微碳钢铁素体区热轧试验研究

在连铸连轧生产线采用铁素体轧制技术制备微碳钢热轧薄板,并对所制备薄板的组织、性能及织构进行分析。结果表明：铁素体轧制微碳钢热轧薄板的组织为完全再结晶铁素体,平均晶粒尺寸50 m左右。相对于常规奥氏体轧制,铁素体轧制薄板的屈服强度和抗拉强度分别下降了21%和6%,延伸率略有下降。热轧薄板的塑性应变比值为0.4,明显低于常规奥氏体轧制。薄板中存在较强的{001}织构是导致值较低的主要原因。     

含BaO,Na2O渣系渣钢间硫平衡研究

在钼丝炉上进行了含BaO,Na2O精炼渣系渣钢间流平衡实验。研究 结果表明,在传统精炼渣系中加入BaO,能够提高渣系的硫容量,Na2O对渣系的硫容量也有很大的影响,但稳定性不好。     

Wcomet直接还原法渣铁分离影响因素研究

研究还原温度、渣相配料碱度和渣中CaF2、K2O、P2O5、S、FeO的含量等因素对2CaO·SiO2形成及其相变的影响规律。结果表明,在快速升温条件下,温度高于1300℃后2CaO·SiO2才大量生成;CaF2、S和FeO对2CaO·SiO2相变不产生影响,但K2O和P2O5对2CaO·SiO2相变具有明显抑制作用;渣相二元碱度R〈1．8时渣的自然粉化效果明显变差。     

保护渣组分对部分稳定氧化锆原料高温稳定性的影响

选择CaO稳定氧化锆、CaO—Y2O3复合稳定氧化锆、Y2O3稳定氧化锆和MgO稳定氧化锆原料为研究对象,借助x射线衍射仪和扫描电子显微镜分析Al2O3、SiO2、Fe3O4、MnO2及3种不同组分的结晶器保护渣对这些原料高温稳定性的影响。结果表明,部分稳定氧化锆原料的高温稳定性主要取决于其稳定剂与渣组分的反应程度;高碱度渣有利于保持部分稳定氧化锆原料的稳定性。     

Al 脱氧弹簧钢钙处理过程中铝酸钙硫化物析出热力学分析

通过钢液与夹杂物间的热力学平衡计算,对Al脱氧弹簧钢钙处理过程中铝酸钙硫化物的析出行为进行热力学分析,探讨[Al]、[Ca]、[S]浓度和钢液温度对Al2O3夹杂物变性行为的影响。结果表明,1600℃钢液温度下,w[Al]＝0．03％时,Al2O3生成为低熔点12CaO ·7Al2O3时的 w[Ca]＞0．0034％,其值随钢液温度降低而减小,随铝含量增大而增大。CaS析出时的临界钙含量随钢液温度降低而显著减小,当w [S ]＜0．005％时,w[Ca]随w[S]变化而显著变化。要使钢中夹杂物控制在低熔点12CaO ·7Al2O3区域,需控制w [S]＜0．0037％,该值随钢液温度的降低或铝含量的增大而减小。     

Nature of large （Ti, Nb）（C, N） particles precipitated during the solidification of Ti, Nb HSLA steel

To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.     

不锈钢板坯连铸凝固特性的研究

分析了 2种不锈钢凝固时的结晶特性 ,模拟计算了连铸过程中不同拉速和不同二冷配水下铸坯温度场的变化 ,并分析了铸坯温度场的变化与铸坯质量的关系 总结出提高铸坯质量的二冷配水原则 ,为制定不同拉速下的二冷配水制度提供了科学依据     

Formation of Ca3SiO5 prepared by electric and microwave burning

A new method of sintering Ca3SiO5 by the combination of conventional and microwave heating methods was studied. The influence of transitional metal oxides such as Fe2O3, Cr2O3, MnO2, and V2O5 used as the additive of microwave absorption on the microwave-promoted burning of Ca3SiO5 was investigated. The experimental results indicate that the new burning technique is capa-ble of promoting the sintering of Ca3SiO5. At 1200-1300°C in an electric furnace, Ca3SiO5 can be obtained only when the sample is heated in a microwave for 110-240 s, and the free lime content is below 40wt%. Based on the experiments, Fe2O3, Cr2O3, MnO2, and V2O5 can enhance microwave sintering. Amongst them, Cr2O3 is the most effective. The characteristic of the X-ray diffraction peaks of Ca3SiO5 is similar to those of standard Ca3SiO5, but the peaks are wider.     

氧环境扫描电镜对氧化物的荷电补偿

在(5×10~(-3))～(2×10~(-2))Pa的氧环境扫描电镜(SEM)中观察到由入射电子束辐照引起的Al_2O_3、SiO_2等氧化物荷电现象得以减轻。氧化物受激氧解吸,使样品表面的氧空位成为荷电势阱而产生荷电。通过氧气氛中提供的氧离子对表面缺陷的修复作用,使氧化物的荷电现象得到补偿。氧环境扫描电子显微分析方法是针对氧化物类绝缘材料荷电的一种简便的、自动调节的荷电补偿方法。Al_2O_3的俄歇电子能谱证明,在6×10~(-6)Pa的氧压下可以完全消除Al_2O_3的表面荷电。     

低硅烧结矿的矿物组成分析

为研究二氧化硅对烧结矿的矿物组成的影响,采用EPMA面分析的方法对两种低硅烧结矿进行了分析。结果表明,与传统烧结矿相比,低硅烧结矿里的氧化铁量增加,铁酸钙量减少。在低硅烧结矿里没有氧化铝集中于铁酸钙里的趋势,各矿物组成里,随着二氧化硅含量的增加,MgO含量减少,而CaO含量却增加。     

Precipitation characteristic of high strength steels microalloyed with titanium produced by compact strip production

Transmission electron microscopy (TEM) and physics-chemical phase analysis were employed to investigate the precipitates in high strength steels microalloyed with Ti produced by compact strip production (CSP). It was seen that precipitates in Ti microalloyed steels mainly included TiN, Ti4C2S2, and TiC. The size of TiN particles varied from 50 to 500 nm, and they could precipitate during or before soaking. The Ti4C2S2 with the size of 40-100 nm might precipitate before rolling, and the TiC particles with the size of 5-50 nm precipitated heterogeneously. High Ti content would lead to the presence of bigger TiC particles that precipitated in austenite, and by contrast, TiC particles that precipitated in ferrite and the transformation of austenite to ferrite was smaller. They were less than 30 nm and mainly responsible for precipitate strengthening. It should be noted that the TiC particles in higher Ti content were generally smaller than those in the steel with a lower Ti content.     

Study on M／A islands in pipeline steel X70

The free structure of M/A islands in pipeline steel X70 has been studied by transmission electron microscope (TEM). It is shown that the M/A islands are about 1-2 μm in size and distribute at the grain boundary of irregular massive ferrite or acicular ferrite in the microstructure of the steel undergoing TMCP (thermo-mechanical controlled processing). The analysis of diffraction contrast shows that the M/A islands consist of retained austenite and some martensite lamellae different in size and orientation. The microtwinning and midrib exist in the lamella of lenticular martensite, which exhibit the typical character of high-carbon martensite. The influences of TMCP parameters on M/A islands have been studied carefully. With the increase of the cooling speed, the amount of M/A islands decrease slightly and the morphology of M/A islands changes to thin dispersive short bars from thick irregular long strips.     

700MPa级超低碳高强度贝氏体厚钢板的晶粒细化机制研究

根据超低碳微合金化的成分设计意图,采用控制轧制和控制冷却工艺得到细化的贝氏体组织,利用光学显微镜、FE-SEM和TEM对各类微观组织和析出物进行了研究和分析。结果表明,700MPa级超低碳贝氏体厚钢板为细小均匀的粒状贝氏体和少量针状铁素体与多边形铁素体的复合组织,其屈服强度不小于580MPa,抗拉强度不小于700MPa,低温冲击韧性为-20℃,Akv不小于150J。钢板具有强度高、韧性好和焊接性能良好的特点,其强度和韧性的良好匹配主要是由于在粒状贝氏体相变前形成了少量的针状铁素体分割奥氏体晶粒,从而细化了最终的复合组织。     

LD-BAr-CC工艺生产低碳铝镇静钢纯净度研究

研究武汉钢铁股份有限公司炼钢总厂四分厂LD-BAr-CC工艺条件下生产的低碳铝镇静钢的纯净度,分析各工艺阶段钢中显微夹杂、大型夹杂以及全氧、氮含量的变化情况。结果表明,在该厂现行工艺条件下,采用吹氩工艺可明显降低钢中夹杂物含量和全氧含量,全氧含量从精炼前的109.30×10-6降至30.75×10-6。各工序中钢的显微夹杂物主要为Al2O3和SiO2,这是脱氧产物和钢液二次氧化产物在钢中的残留物;大型夹杂物主要是Al2O3、SiO2以及硅铝酸盐等复合夹杂,与浮渣的卷入有很大关系。