Casting/mould interfacial heat transfer during solidification in graphite,steel and graphite lined steel moulds

Heat flow between the casting and the mould during solidification of three commercially pure metals, in graphite, steel and graphite lined steel moulds, was assessed using an inverse modelling technique. The analysis yielded the interfacial heat flux (q), heat transfer coefficient (h) and the surface temperatures of the casting and the mould during solidification of the casting. The peak heat flux was incorporated as a dimensionless number and modeled as a function of the thermal diffusivities of the casting and the mould materials. Heat flux transients were normalised with respect to the peak heat flux and modeled as a function of time. The heat flux model proposed was used to estimate the heat flux transients during solidification in graphite lined copper composite moulds.     

薄板坯连铸低碳冷轧用钢保护渣的研究与开发

介绍了唐钢薄板坯连铸低碳冷轧用钢保护渣的研究开发过程.通过漏斗形结晶器与保护渣性能匹配的关系研究、保护渣组成和物性研究、多次生产试验和性能优化,最终开发出满足工艺要求的国产低碳钢保护渣,保证了低碳冷轧用钢的稳定生产.     

保护渣碱度对薄板坯结晶器平均热流量的影响

在钢的连铸过程中,钢水在结晶器内的凝固对铸坯的产量和质量均有很大影响,几乎所有的铸坯表面缺陷均形成于结晶器内。近年来,随着连铸拉速的增加及对铸坯表面质量要求的提高,有关结晶器冷却、传热对钢水的初始凝固及表面纵裂纹影响的研究成为连铸科学研究的重点。结晶器壁热流不均是纵裂纹产生的有利环境,保护渣控制传热为常用的措施。薄板坯浇铸时由于拉速高,为获得表面无缺陷铸坯,对保护渣控制传热的要求更高,同时也需协调保护渣的润滑功能。通过生产试验,研究比较3种碱度保护渣（CaO/SiO2分别为1.06、1.26和1.48）对薄板坯结晶器平均热流量的影响,发现与低碱度保护渣相比,使用高碱度保护渣时,结晶器热流量最低,有利于实现弱冷却,形成均匀凝固坯壳,在一定拉速条件下浇铸裂纹敏感钢种时有助于获得良好表面质量的铸坯。     

薄带铸轧产品特性及应用进展

薄带铸轧工艺是将快速凝固与轧制变形融为一体的短流程、近终型生产工艺,具有流程短、工序少、能耗低、排放少的优势。通过对薄带铸轧产品进行组织分析及力学性能研究,结果表明,在薄带铸轧的快速凝固、快速冷却、小压下量轧制条件下,产品组织与传统热连轧工艺产品在晶粒形态、晶粒尺寸上具有显著区别。薄带铸轧产品性能波动小、各向同性好、利于焊接、尺寸公差精确、表面质量好,易于生产高强度薄规格产品,在轻量化及“以热代冷”趋势下具有广阔的应用空间。     

铸钢件冒口离开热节工艺设计

改变传统的铸钢件工艺设计时冒口必须放在热节上的方法，采用竖浇、倾斜浇注、安放冷铁、厚壁处远离浇口等方法，将冒口放在钢液最后充型处而非热节处，减小了接触热节，使厚壁处先充型先凝固、薄壁处后充型后凝固，形成从厚壁到薄壁的温度梯度和凝固顺序即动态凝固顺序，从而减小了冒口，提高了工艺出品率。文中通过典型的生产实例阐明了这一工艺设计的思想和方法，取得了较好的经济效益。     

电磁铸造铝合金大板坯的变形研究

设计了电磁铸造模拟试验装置,研究了电磁铸造大板坯工艺参数,如浇注温度、冷却水量、喷水孔距等对板坯变形的影响,探索板坯的变形与其凝固阶段温度场的关系及其控制方法。实验结果表明：合理调整影响板坯凝固进程的电磁铸造工艺参数,能够有效地减小变形,提高板坯平直度。     

汽车门板用450mm特厚模具钢1.2311钢板的试制

南阳汉冶特钢有限公司采用转炉洁净钢冶炼技术、水冷铜板结晶锭模技术、高温低速大压下轧制技术以及先进的热处理工艺,成功研发出450mm厚汽车门板用模具钢1.2311特厚板。通过水冷模浇铸凝固、缓冷回火扩氢、JMatPro软件模拟该钢种静态CCT曲线制定合理的热处理冷却工艺,保证了该钢种优良的可切削性及镜面研磨性能,硬度指标均匀且稳定。     

SS400薄板坯表面纵裂的控制

结合邯钢CSP生产实践,研究了钢水成分、结晶器铜板表面质量、结晶器热流控制等对SS400薄板坯表面纵裂的影响及裂纹形成的机理.研究表明:SS400钢种的碳含量远离包晶区,结晶器宽面热流控制在2.05×106W/m,渣膜结晶率控制在40%,稳定拉速,可有效地减少铸坯表面纵裂.     

EVOLVEMENT MECHANISM OF SURFACE OSCILLA- TION MARKS ON ROUND BILLET DURING SOFT–CONTACT ELECTROMAGNETIC CONTINUOUS CASTING

在实验室立式连铸机上对碳素结构钢Q235B进行了电磁软接触连铸实验,测量了结晶器内磁场分布和Sn--Pb--Bi合金熔体弯月面形状. 结果表明,采用电磁软接触连铸技术, 可以显著改善铸坯表面质量; 当电源功率达到最佳值时, 振痕完全受到抑制, 铸坯表面光洁; 但当电源功率过大时,铸坯表面出现波浪形振痕. 分析认为, 铸坯表面质量得到改善是高频电磁场的Lorentz力效应和Joule热效应共同作用的结果;当电源功率过大时, 分瓣结晶器 内的磁场分布不均匀,沿结晶器周向呈波浪形分布, 加之钢水液面波动也更加剧烈,因此在铸坯表面产生波浪形振痕.     

Effect of section thickness and modification on thermal analysis parameters of A357 alloy

Abstract

Thermal analysis technique relies on the cooling curve obtained when the sample is cooled in a sampling cup. This may not represent the cooling behaviour of the real casting. The microstructure developed during solidification depends not only on the nucleation and modification potential of the melt but also on the thermal gradient imposed during solidification by the mould. The factors affecting the thermal gradient are the mould material and casting section thickness. In the present investigation the effect of modification melt treatment, cooling rate and casting section thickness on the thermal analysis parameters of A357 alloy was studied. It is found that the dimensionless heat flux parameter is high for small section thickness castings. The metal/mould interfacial heat flux is high in a copper mould. Thermal analysis parameters of A357 alloy are found to be affected significantly by the combined action of modification, chilling and section thickness.     

Enhanced cooling for solidification of aluminium alloys in permanent moulds using advanced heat pipe solutions

Abstract

In order to obtain sound cast components with good properties, a number of measures must be taken to make parts defect free. It is well recognised by the casting industry that it is essential to control cooling rates of permanent mould castings in order to speed up solidification and control the solidification pattern. Each of the traditional controlled cooling techniques (air or water cooling passages and chill inserts) presents certain disadvantages and none offers optimum thermal management. A new cooling method for permanent moulds is proposed. This new technique is based on heat pipe technology that was developed specifically for the cooling of permanent moulds in the casting of light metals where high heat fluxes are normally encountered. The influence of the conductivity of mould coatings on casting solidification and dendrite arm spacing with heat pipe cooling was investigated. Typical experimental results are also presented.     

3D Numerical Simulation on Thermal Flow Coupling Field of Stainless Steel During Twin-Roll Casting

The surface crack and lateral crack of the AISI 304 stainless steel thin strip produced by twin-roll casting were observed. The temperature at the center of outlet during twin-roll-casting process was determined by infrared thermometer. In order to avoid the surface cracks of the casting strip, the thermal flow coupling field of AISI 304 stainless steel during twin-roll-casting process was simulated by a 3D fluid-structure coupling model. According to the simulation result, the effect of the casting speed on thermal flow field was analyzed and the process parameters were optimized. Moreover, by studying heat flux curves, the heat transfer mechanism between molten pool and roll was analyzed. The results show that, with the increase of the casting speed, the temperature of the molten pool increases and the solidification point moves toward the outlet. Meanwhile, the whirlpool above gets larger. Based on the solidification front position, the optimized process parameters are 1500 °C and 0.37 m/s. The heat transfer mechanism between molten pool and roll contains direct contacting heat transfer and air gap heat transfer.     

薄板坯连铸结晶器技术及钢种开发的几个问题分析(续)

薄板坯连铸结晶器是薄板坯连铸技术的核心，通过对薄板坯连铸结晶器内钢水的流动、传热以及凝固壳的收缩和变形行为的研究，分析了连铸坯几种典型裂纹缺陷的形成原因；并结合实验室和生产实践，对薄板坯连铸连轧生产冷轧基料用B微合金化钢、电工钢、V-N微合金高强度钢等的工艺特性以及钢材性能进行了分析。文章分二次发表，本次是上海金属2006—1期文章的续栽，内容是关于薄板坯连铸连轧典型品种的开发以及薄板坯连铸连轧技术的发展与展望。     

本钢FTSC生产SPA-H工艺技术研究

采用薄板坯连铸机（FTSC）生产SPA-H,通过化学成分控制、温度制度调整、结晶器保护渣选择和连铸二冷水调试等,解决了FTSC铸坯纵裂问题,表面质量和内部质量合格,FTSC铸坯板材性能优于常规铸坯轧材,FTSC已能批量生产SPA-H。     

薄板坯连铸结晶器技术及钢种开发的几个问题分析

薄板坯连铸结晶器是薄板坯连铸技术的核心，通过对薄板坯连铸结晶器内钢水的流动、传热以及凝固壳的收缩和变形行为的研究，分析了连铸坯几种典型裂纹缺陷的形成原因；并结合实验室和生产实践，对薄板坯连铸连轧生产冷轧基料用B微合金化钢、电工钢、V—N微合金高强度钢等的工艺特性以及钢材性能进行了分析。文章分二次发表，本次发表的内容是关于薄板坯连铸结晶器的相关技术及板坯典型裂纹的分析。     

Solidification microstructure of M2 high speed steel by different casting technologies

The present work investigated the solidification microstructure of AISI M2 high speed steel manufactured by different casting technologies,namely iron mould casting and continuous casting.The results revealed that the as-cast structure of the steel was composed of the iron matrix and the M2C eutectic carbide networks,which were greatly refined in the ingot made by continuous casting process,compared with that by the iron mould casting process.M2C eutectic carbides presented variation in their morphologies and growth characteristics in the ingots by both casting methods.In the ingot by iron mould casting,they have a plate-like morphology and grow anisotropically.However,in the ingot made by continuous casting,the carbides evolved into the fiber-like shape that exhibited little characteristics of anisotropic growth.It was noticed that the fiber-like M2C was much easier to decompose and spheroidize after heated,as a result,the carbides refined remarkably,compared with the case of plate-like carbides in the iron mould casting ingot.     

Hot rolling of AISI 304 tailored strips produced by twin roll strip casting

A process for the production of steel strips with an optimized cross section by means of twin-roll strip casting has recently been developed at the Institute of Metal Forming and offers considerable technical and commercial potentials. This production concept is based on the use of profiled casting rolls which continuously transfer the profile geometry to the solidified strip. In order to reduce the internal porosity and improve the surface finish the cast strip was hot rolled using profiled rolls. Offline and inline rolling experiments were performed to prove the effectiveness of this combined forming process. This paper describes the design of a proper rolling tool and the effect of this forming step on the final profile geometry, surface quality, internal porosity and mechanical properties of the strip. The experiments showed that a rolling step with 15 % thickness reduction already allows the global internal porosity to be reduced by 48 % and the strip surface roughness to reach a minimum value of R_a = 2.3 µm. The tensile strength is improved after the hot rolling operation and the obtained values are within the 500–700 MPa range specified by the norm EN 10088-3 for the stainless steel AISI 304. The prescribed ultimate elongation of 45 % is also reached.     

薄板坯的跑偏机制分析及控制实践

通钢FTSC（flexible thin slab casting）薄板坯连铸机自2005年投产以来,发生多次连铸坯运行到加热炉内时跑偏问题。2016年11月连续3个浇次发生连铸坯跑偏撞到加热炉炉墙无法出炉,生产被迫中断,从加热炉共剔出连铸坯1 000多t,严重影响了通钢薄板坯连铸连轧产线的生产。针对通钢现有的条件和跑偏产生的机制,通过对结晶器两个窄面热流偏差、二冷水喷水状态、夹持辊状态、扇形段状态等进行优化调整,最终解决了连铸坯的跑偏问题。     

包钢CSP热轧卷板纵裂缺陷分析与控制

为了研究薄板厂CSP产线热轧卷板纵裂缺陷产生原因,对连铸工艺及设备各运行参数进行了调查分析。结果表明,连铸机振动台振动精度差、结晶器铜板结垢是导致热轧卷纵裂缺陷的主要原因。采取调整振动参数、提升振动台对中精度以及控制铜板结垢等措施后,热轧卷板表面纵裂纹缺陷显著降低,纵裂率由最高的1.15%降至0.10%以下。针对CSP铸机,在保证结晶器铜板导热良好的前提下,需严格控制结晶器振动台四连杆机构的关节轴承间隙在0.02 mm以内,振动台台面标高偏差在0.05 mm之内。结晶器振动在水平方向的位移量在0.1 mm以内为宜。     

本钢FTSC生产SPA—H钢的工艺技术研究

采用薄板坯连铸机（FTSC）生产SPA—H钢,通过化学成分控制、温度制度调整、结晶器保护渣选择和连铸二冷水调试等,解决了FTSC铸坯纵裂问题,表面质量和内部质量合格,FTSC铸坯板材性能优于常规铸坯轧材,FTSC已能批量生产SPA—H钢。