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.     

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.     

Longitudinal surface cracks of thin slabs

Based on the production practice of medium carbon thin slabs in the CSP plant,the reasons and influencing factors for the formation of longitudinal cracks were investigated,and some industrial measures were taken to eliminate the cracks.The results show that the efficient solutions to reduce longitudinal cracks are improving the performance of the mold powder,stabilizing the mold heat flux,and maintaining a proper taper of the mold during casting.Proper pouring temperature and secondary cooling also play...     

Effects of Ti addition on low carbon hot strips produced by CSP process

Large quantity of fine Ti（C,N） particles, 15-30 nm in size, were observed in low carbon hot strips added to a small amount of Ti and produced by CSP process. The results showed that the precipitation of Ti（C,N） mostly took place during soaking and hot rolling, which is significantly different from that in the conventional production. These fine Ti carbonitride particles could be very effective on the austenite grain refinement by hindering grain growth of recrystallized austenite. Their precipitation behavior was discussed and compared with that of the steels produced in the conventional production.     

Microstructure and of mechanics microwave boriding

Microwave boriding layer microstructure of carbon steels and its diffusion mechanics were studied. The results show that the existence of microwave field in the boriding can＇t change the growth mechanics of boriding layer. Compared with conventional boriding, if the treatment temperature and time remain constantly, the descend rate of the boriding layer thickness with the increase of carbon content of steel is smaller. The diffusion activation energy ofT8 steel is 2.6× 10^5 J/mol between the temperature of 750 ℃ and 900 ℃ in microwave field, which is in the same order of conventional boriding.     

稀土微合金低镍奥氏体不锈钢定向凝固组织的研究

采用电磁感应定向生长炉制备稀土微合金低镍奥氏体不锈钢定向凝固组织,系统地研究凝固速度和稀土元素Ce对不锈钢凝固时界面形态以及枝晶间距的影响。研究发现,在特定温度梯度下,随着凝固速度的增加,定向凝固的固液界面由胞状晶转变为树枝晶。凝固速度和稀土元素Ce的增加使得定向凝固组织的枝晶形貌逐渐细化,枝晶间距减小。     

薄板坯和常规板坯生产冷轧产品的质量比较

作为生产冷轧产品的原料,薄板坯热卷与常规板坯热卷相比,薄板坯热卷在纵裂纹缺陷、屈服强度和屈强比等方面控制更加困难.论述薄板坯热卷原料纵裂纹缺陷和机械性能对生产冷轧产品的衍生影响,比较同一罩式退火条件下,分别以薄板坯连铸连轧工艺和常规板坯工艺生产的IF钢热卷作为原料冷轧IF钢的性能,两者屈服强度相差30MPa左右.     

成型工艺对PBRBSC素坯及烧结体性能的影响

研究了不同成型工艺对PBRBSC的素坯结构及烧结体显微组织的影响。研究发现，用原位凝固工艺获得的素坯比用干压和注浆成型的素坯孔径分布更加均匀，具有单峰性，孔洞形状规则。干压和注浆成型的烧结体中有大块残C与残余Si，而原位凝固工艺的烧结体无大块残余Si和C，它们都弥散分布在基体中。     

CSP工艺衔接区温度行为分析

分析了CSP工艺衔接区温度的行为和坯料在入炉前的温度,指出此区域内影响坯料温度的因素、温度变化状况和冷却特点;研究了加热段的加热行为、加热特点、模型选择和保温要求;提出了CSP衔接区坯料的冷却方式,并给出了相应的模型.     

Influence of austenitizing temperature on apparent morphologies of as-quenched microstructures of steels

1 INTRODUCTIONZackey et al[1]found that high austenitizingtemperatures can suppress plate martensite forma-tion,and canincrease the amount of lath martens-ite in structural steels ,and further suggested thatthe toughness of steels may bei mproved by raisingthe quenching temperature . Up to now, many re-searchers have studied the influence of hardeningtechnologies on martensitic morphologies andproperties , and have drawn the same conclusionthat the amount of lath martensite may be in-creas…     

Metallurgical quality of CSP thin slabs

The casting structure, chemical composition segregation, dendrite arm space, inclusiona and during the CSP (compact strip production) rolling process were investigated. The results show that the CSP thin slab has a feature of uniform fine grains, more columnar crystals, less central porosity and segregation etc. There is no great difference in macrostructure between the CSP thin slab and conventional slab; however, the fine dendrite structure of the CSP slab is more uniform. Moreover, the central porosity and segregation are obviously improved after the first pass; and the dendrite is bent along the rolling direction rather than broken into pieces.Small inclusions with the diameter less than 10 p.m in the CSP slab are dominantly consisted of aluminates formed by A1 deoxidation and Ca treatment and not floating out of the melt. The large size inclusions found in the continuous casting slab are very few.     

Effects of Mn on Microstructures and Properties of Hot Rolled Low Carbon Bainitic Steels

Two kinds of Mn-Si-Mo low carbon steels were designed to study the effects of Mn on the microstructures and properties of hot rolled low carbon bainitic steels.To reduce the production cost,a very low Mo content of 0.13%was added in both steels.After hot rolling,the mechanical properties of samples were tested.Microstructure was observed and analyzed by optical microscope and transmission electron microscope.The results show that the strength of tested steels increases with the increase in Mn content,while the elongation decreases.When Mn content increases,the bainite microstructure increases.The results can provide a theoretical basis for composition design and industrial production of low cost low carbon bainitic steels.     

铸态锰钢中的碳化物

对铸态锰钢中的碳化物作了研究，铸态锰钢中有两类碳化物：一类是凝固时生成的弥散分布在基体上的团球状碳化物，另一类是在塑性变形时，在应变马氏体形成以前，优先 析出的呈弥散分布的细小颗粒，这两类碳化物一起构成了铸态锰钢组织中的第二相硬质点，这些硬质点和细化的奥氏体晶粒的界面都是位错运动的障碍，造成了位错密度的提高，进而提高了铸态锰钢的加工硬化能力和抗磨性能。     

热穿-热轧法生产的新型贝氏体中空渗碳钢的组织和性能

用热穿-热轧法制备了新型贝氏体中空钢．研究了热处理对新型贝氏体钢和渗碳处理对中空钢组织和性能的影响．结果表明：新型贝氏体钢正火＋低温回火热处理后的组织为贝氏体铁素体和奥氏体,淬火＋低温回火后的组织由马氏体、贝氏体和奥氏体组成;正火或淬火＋低温回火后,新型贝氏体中空钢具有良好的强韧性．正火＋低温回火后,中空钢的组织为贝氏体铁素体和残余奥氏体组织．新型贝氏体中空钢渗碳后空冷,渗层的组织为高碳马氏体和残余奥氏体组织,非渗层为贝氏体铁素体和残余奥氏体组织,实体中空钢具有较好的强韧性和渗碳效果．     

对硼铬共渗组织形态的研究

采用粉末法对B-Cr共渗的组织形态及共渗介质对层深的影响做了较全面的研究。其结果表明,碳钢的硼铬共渗组织可分为五种形态,其中A型、D型组织兼有单元渗B、渗Cr的优点,具有较大的应用价值;B-Cr共渗时,B对Cr的扩散有促进作用,而Cr对B的扩散有阻碍作用。     

对镀钴渗硼复合处理组织形态的研究

在低碳钢上分别电刷镀Co,Ni,Fe,然后渗硼处理。通过金相及扫描电镜分析,探讨了镀渗复合处理的组织形态,镀层对渗层的影响以及镀层与渗层的最佳组合。     

Effect of cooling parameters on the microstructure and properties of Mobearing and Cr-bearing steels

To develop low-cost low carbon bainitic steel,Mo-bearing and Cr-bearing steels were melted in a vacuum induction furnace and were researched by thermal simulation and hot rolling at the laboratory.As the cooling rate increases from 0.2 to 50℃/s,the transformation temperatures of two steels lie between 650 and 400℃,and the final microstructures of them change from quasi-polygonal ferrite and granular bainite to lath bainite.Compared with cooling in air or by interrupted cooling,Mo-bearing and Cr-bearing steel plates cooled by sprayed water boast higher strength and superior toughness,for large-size islands are responsible for the poor mechanical properties.Compared to Mo,Cr is effective to isolate the bainitic reaction in low carbon steel,and the bainitic microstructure can also be obtained in Cr-bearing steel cooled at a wide range of cooling rate.     

Study on temper-rapid cooling process of low carbon steel produced by CSP

On the basis of the effect of carbon precipitation on the microstructure and properties of steel products below At temperature, a new thermal treatment method （temper-rapid cooling process） was studied. By the temper-rapid cooling process, the yield strengths of the high strength low carbon （HSLC） steel ZJ330 and SPA-H produced using the compact strip production （CSP） process increased from 340 to about 410 MPa and from 410 to about 450 MPa, respectively. The results indirectly indicated that there existed nanoscaled iron-carbon precipitates that have obvious precipitation effect on low carbon steel produced by CSP. The prospect of application is discussed.     

Nano-scaled iron-carbon precipitates in HSLC and HSLA steels

This paper studies the composition, quantity and particle size distribution of nano-scaled precipitates with size less than 20 nm in high strength low carbon (HSLC) steel and their effects on mechanical properties of HSLC steel by means of mass balance calculation of nano-scaled precipitates measured by chemical phase analysis plus SAXS method, high-resolution TEM analysis and thermodynamics calculation, as well as temper rapid cooling treatment of ZJ330. It is found that there existed a large quantity of nano-scaled iron-carbon precipitates with size less than 18 nm in low carbon steel produced by CSP and they are mainly Fe-O-C and Fe-Ti-O-C precipitates formed below temperature A1. These precipitates have ob- vious precipitation strengthening effect on HSLC steel and this may be regarded as one of the main reasons why HSLC steel has higher strength. There also existed a lot of iron-carbon precipitates with size less than 36 nm in HSLA steels.     

贝氏体钢的组织结构和性能

研究了不同含碳量的贝氏体钢的组织和性能，由于钢中含碳量的差别，在铸态和空冷条件下得到不同形态和数量的贝氏体。在低碳范围得到全部贝氏体组织。随碳量增加，贝氏体量减少，形态发生变化，同时，马氏体量增多．在合适成分，空冷可得到近于半贝氏体和半马氏体组织，这种钢具有优良的综合力学性能和高耐磨性，它比目前现场使用的几种典型耐磨材料有更高的耐磨性能．