磷元素在钢中的晶界偏聚

磷元素在钢中的晶界偏聚可以分为两类,即平衡偏聚和非平衡偏聚.介绍了这两类偏聚现象以及偏聚理论.以磷对晶界结合力、晶界扩散和晶界能的影响机理为基础,分析了磷元素对钢力学性能的影响和磷在钢中发生晶界偏聚的原因.     

合金元素对Cr-Mo钢第二类回火脆性影响研究综述

 对于一些长期在中温条件下服役的Cr-Mo钢(2.25Cr1Mo),由于钢中P、S等有害杂质元素在服役过程中不断向晶界偏聚,降低了晶界结合力,致使该类钢出现第二类回火脆性这一关键问题。为了探寻降低这类Cr-Mo钢第二类回火脆性倾向的有效方法,提高材料安全服役可靠性,从溶质元素偏聚机制出发,总结分析了合金元素晶界偏聚及改善钢第二类回火脆性的内在本质,重点归纳了几种常见元素的晶界偏聚行为及其对钢回火脆性的影响,同时还客观分析了理论计算和试验研究在阐释合金元素对晶界脆性影响存在差异的主要原因,期望能为中温用钢长期服役过程中存在的回火脆性提供一些有效控制方法,也为合金元素晶界偏聚行为的研究提供一些参考。     

钢中残余元素及其对钢性能的影响

简要地论 钢中残余元素的行为及其对钢性能的影响,主要内容有钢中残余元素的来源,残余元素在铸锭过程中的凝固偏析和偏处理时的晶界偏析,残余元素在热加工过程中表面热脆现象中的作用,残余元素在钢的第二类回火脆性现象中的作用,残余元素对钢材耐蚀性能,应变时效行为的影响,以及抑制晶粒长大的作用等,最后提出了纯净钢 我国钢铁工业面临的重大项目。     

10MnCuPTi耐大气腐蚀钢的韧性研究

Ｐ是耐大气腐蚀钢中的重要元素之一,但是Ｐ在钢中极易偏聚在晶界,导致钢的韧性下降,本文利用俄歇电子能谱分析研究了热轧状态下Ｐ的行为,并通过金相和扫描电镜观察分析了１０ＭｎＣｕＰＴｉ钢在热轧和正火后的显微组织,实验结果表明,钢中Ｐ有少量偏聚,但并未对钢的韧性产生影响,而较大的铁素体晶粒及沿晶分布的连续网状游离渗碳体是导致韧性下降的直接原因,采取适当的热轧工艺及轧后正火处理可以消除界渗碳体,改善韧性。     

不锈钢热塑性降低的非平衡偏聚机理

Mintz于1997年报道了一个有趣的试验现象:随着拉伸应变速率的增加,奥氏体钢韧性降低,铁素体钢韧性反而提高。其机制未得到解释。通过计算试验钢中P原子的非平衡晶界偏聚临界时间,结果发现奥氏体钢拉伸前热过程的等效时间短于其临界时间,而铁素体钢的等效时间长于其临界时间。由于奥氏体钢和铁素体钢分别在850和800℃等效时间最接近临界时间,韧性最低,即试验钢的热塑性降低都是由于非平衡晶界偏聚的临界时间造成的。应变速率降低,弹性应力作用时间增加。晶界偏聚量改变,热塑性降低的程度也随之改变。即热塑性降低的程度随应变速率的改变是由应力引起的非平衡晶界偏聚决定。     

低熔点元素铋对钢脆化行为的影响

 为了探明钢中低熔点元素铋在切削加工和高温变形生产过程中的“两面性”作用,借助切削加工试验、高温热塑性试验及微观组织结构分析,研究了不同温度范围内铋对钢脆化行为的影响。结果表明,在切削加工过程中,低熔点元素铋对钢的脆化作用,使铋易切削钢易于形成对切削加工有利的“C形”脆性屑,从而获得优良的可切削加工性能,该脆化行为主要与钢中铋的液态金属脆化作用有关,显著降低钢在铋熔点温度附近的塑性。在高温变形温度区间,低熔点元素铋对钢脆化行为的影响,主要与奥氏体晶界上铋膜的偏聚有关,脆化晶界,显著降低钢在1 000 ℃及以下试验温度时的热塑性。     

10MnCuPTi耐大气腐蚀钢的韧性研究

P是耐大气腐蚀钢中的重要元素之一 ,但是 P在钢中极易偏聚在晶界 ,导致钢的韧性下降 .本文利用俄歇电子能谱分析研究了热轧状态下 P的行为 ,并通过金相和扫描电镜观察分析了1 0 Mn Cu PTi钢在热轧和正火后的显微组织 .实验结果表明 ,钢中 P有少量偏聚 ,但并未对钢的韧性产生影响 ,而较大的铁素体晶粒及沿晶分布的连续网状游离渗碳体是导致韧性下降的直接原因 ;采取适当的热轧工艺及轧后正火处理可以消除晶界渗碳体 ,改善韧性 .     

NiCrMoV钢中铌和锡的非平衡晶界共偏聚

 结合偏聚理论的最新进展,对R.D.K.Misra等认为Ni和Sn的晶界偏聚动力学曲线相互平行,而且2种元素可同时达到一个晶界浓度极大值的实验结果重新进行了分析。分析结果证实,Ni和Sn在恒温过程中发生的是一非平衡晶界共偏聚现象,Ni的非平衡偏聚是由Sn的非平衡偏聚引起的。     

Gleeble模拟热轧工艺对磷非平衡晶界偏聚的影响

 采用Gleeble 3500热模拟试验机研究了轧制和卷取温度下磷元素晶界偏聚与热轧板高温热塑性的关联机制。研究结果表明,含磷钢中磷元素晶界偏聚符合空位-磷原子复合体非平衡共偏聚理论,800 ℃以上轧制温度对磷元素晶界偏聚引起的钢板脆性影响较小,而在500～650 ℃温度范围存在磷元素偏聚导致的热塑性低谷区,且在该温度区施加1%拉伸预应变将加剧磷元素晶界偏聚和钢板脆性。因此,本试验成分含磷钢热轧生产中卷取温度设定应避免550 ℃塑性低谷。     

NiCrMoV钢中铬和氮的非平衡晶界共偏聚

 在非平衡晶界共偏聚理论基础上,分析了NiCrMoV钢中铬和氮在700~900 K下的共偏聚动力学。结果表明,氮在时效过程中出现的非平衡偏聚特征是铬非平衡偏聚诱发的结果;铬、氮二者的晶界共偏聚行为属非平衡共偏聚。分析结果为非平衡晶界共偏聚理论提供了证据。     

Results of Research into the Segregation Behaviour of Manganese,Silicon and Chromium in Continuous Casting

For different steel grades the segregation factors of several alloying elements, both for crystal and for centre segregation, have been determined using electron probe microanalysis (EPMA). With this method two‐dimensional quantitative concentration images for several elements are assigned. The segregation factors depend on the chemical composition of a steel grade, in particular on its carbon content. Within a category of steel grades, the segregation factor will increase with increasing carbon content. For the first time, a large number of tests were performed on 53 slab samples from different steel grades to establish the segregation factors. The effects of the slab thickness, soft reduction and carbon content on crystal and centre segregation have been investigated. The results are essential for modelling the segregation phenomena occurring at solidification.     

Influencing Factors on Center Segregation in Continuously Cast Pipeline Steel Slabs

The factors which influence center segregation of continuously cast slabs are obtained through analyzing the database of macrostructrue. It indicates that center segregation becomes severer with the increasing content of carbon, phosphorus and sulfur; Center segregation will be reduced obviously if the content of manganese is higher than 1.5% and the ratio of Mn/S is higher than 300; High degree of superheat , high casting speed and increasing width of slabs will increase the degree of center segregation. Since center segregation below class B has little effect on the property of steel, hence, in order to low the ratio of center segregation of class B-1.0 down to 10%, several control strategies are presented as follows: the contents of carbon, phosphorus and sulfur must be focalized in lower range of steel grade demanded, but manganese upper operating range control. The referenced contents of the elements in molten steel are required like this: [C]<0.07%,[P]<0.01%,[S]<0.005%,[Mn]>1.5%,[Mn]/[S]>300; The degree of superheat should be lower than 24℃ and the casting speed should be defined to 1.0-1.1 m·min-1. At the same time, proper secondary cooling system of water distribution should be developed and the precision of continuous caster should be also improved.     

Segregation of C and P in Steel Droplets Solidified in Drop Tube

The properties of steels can be improved by adding appropriate amount of alloying elements.However,the quality and properties of steels may be affected due to the segregation of the alloying elements.Rapid solidification was regarded to be an effective method to reduce or eliminate the segregation of alloying elements.While in this paper,the segregation of C and P was also observed in rapid solidified carbon steel droplets (in silicon oil) by drop tube processing.The distributions of alloying elements in 0.2m drop tube samples were similar to those in 50m drop tube samples.While in both 0.2m and 50m drop tube,the segregation of C and P was quite different when the contents of the samples were varied,the segregation profiles were discussed in detail.The microstructures of 50m droplet samples were a little finer than those of 0.2m droplet samples.The solidification speed was approximately the same from the surface to the center of each sample.In high-C samples,the microstructure was also corresponding to the distribution of C.     

H13钢带状偏析演化规律研究

 针对H13钢中普遍存在的带状偏析现象,利用金相显微镜及SEM研究了H13钢不同状态带状偏析的演化规律。研究结果表明,H13钢退火态的带状偏析由枝晶偏析的热变形引起,表现为碳化物的球化程度、颗粒大小及分布的不均匀;退火组织的不均匀性直接影响H13淬火、回火态的组织均匀性,且退火组织中金属元素分布的不均匀及偏析带中存在的一次液析共晶碳化物一直保留到钢的回火状态,影响了H13钢的等向性;良好的退火组织是制造高品质H13热作模具钢的关键因素。     

Theoretical model for determining optimum soft reduction zone of continuous casting steel

Abstract

A theoretical model for determining the optimum soft reduction zone of continuous casting steel was developed. According to the theoretical analysis of the solute segregation behaviour in the mushy zone with the soft reduction by one pair of pinch rolls, there is an optimum soft reduction position for each element of steel, and all optimum soft reduction positions of different solute elements should be included in order to eliminate the centreline segregation effectively. The theoretical analysis shows that the carbon content has a great effect on the optimum soft reduction zone, and the cooling rate could affect both the optimum soft reduction positions of the segregation prone elements (P, S) and the optimum soft reduction zone of continuous casting steel. Plant trials of steel SWRH82B with soft reduction were carried out to validate the theoretical model, and the results show that the solute element segregation in the centreline of the strand has been improved with the optimum soft reduction zone.     

汽车悬架系统用55SiCr弹簧钢丝带状组织

 为了研究中心偏析对弹簧钢组织性能的影响,通过金相显微镜、扫描电镜、电子探针等手段研究了55SiCr弹簧钢的元素偏析行为、带状组织及力学性能。结果表明,带状组织由合金元素偏析引起,其内部锰、铬和硅质量分数为非偏析带2倍以上,合金元素偏析引起带状组织,弹簧钢拉伸试样中裂纹起源于偏析带状组织,并沿垂直于带状组织方向扩展导致最终断裂,带状偏析是影响高强度弹簧钢力学性能的主要因素。     

高速钢碳化物偏析的研究现状

高速钢因其硬度高、红硬性好、耐磨性好等特点被广泛应用于大型装备制造的加工工具。然而在大截面的高速钢生产过程中，易产生碳化物偏析等问题，影响材料的力学性能和使用寿命。通过对模铸、连铸、电渣重熔、粉末冶金方法的比较与分析，探究影响碳化物偏析的因素，研究改善碳化物偏析的方法。研究表明，通过添加孕育剂、微合金元素、机械搅拌、电磁搅拌可以改善碳化物偏析；此外，通过对比分析发现，使用电渣重熔法生产高速钢可以经济有效地控制碳化物偏析，电渣重熔法已成为生产高速钢的主要方法。     

10CrNiCu钢连铸坯中心偏析的原位分析

采用金属原位分析(OPA)方法研究了连铸10CrNiCu钢中心偏析的状况及其对材料性能的影响.分析表明,采用二冷电磁搅拌后,铸坯中大部分元素的最大偏析度均有不同程度的降低,C、Cr、Ni、Si等主要元素的最大正偏析降低了50%以上.该工作也表明,OPA技术对指导连铸工艺优化、提高产品质量是十分有效的方法和监测工具.     

PMO凝固均质化技术在20CrMnTi齿轮钢上的应用

 为了解决20CrMnTi齿轮钢在生产过程中铸坯柱状晶发达及铸坯元素分布不均匀等缺陷,运用上海大学研发并已在连铸生产中取得理想效果的脉冲磁致振荡(pulsed magneto oscillation,简称PMO)凝固均质化技术对连铸20CrMnTi齿轮钢矩形坯进行均质化处理。结果表明,经PMO处理的20CrMnTi齿轮钢铸坯中心等轴晶率增加1倍左右,中心碳偏析指数从1.22降为1.04。金属原位分析仪元素面扫描检测发现,PMO处理铸坯的各元素分布更加均匀,连铸坯宏观偏析得到有效控制。该技术为今后提高连铸坯内部质量提供了一种新方法。