41OS不锈钢带表面"砂金"缺陷成因及机理分析

系统地分析了不锈钢分公司41OS冷轧成品带钢部分出现表面"砂金"缺陷(表面点状发亮花纹)的成因及其形成机理.对带铜表面"砂金"缺陷进行了表面形貌观察和成分分析以及金相观察,结合国外类似经验,指出产生该缺陷的成因--晶间腐蚀.在系统阐述了不锈钢敏化及晶间腐蚀理论的基础上,详细分析了41OS产生晶间腐蚀的过程及原因,并简要探讨了大生产中控制该缺陷的可行措施.     

SUS430铁素体不锈钢砂金缺陷研究

结合生产实际对SUS430铁素体不锈钢砂金缺陷产生原因进行了追溯与分析。结果表明:卷板在罩式炉退火过程中因局部温度过高造成外圈敏化,使其在酸洗过程中极易发生晶间腐蚀,是后续发生砂金缺陷的重要原因。针对该问题,制定了一系列生产过程改进方案,将砂金缺陷等级控制在客户可以接受的范围内。     

Nb、Ti对低铬铁素体不锈钢腐蚀性能的影响

采用点腐蚀试验、电化学腐蚀试验和晶间腐蚀试验对409L,409M,410L,410S四种低铬铁素体不锈钢的耐腐蚀能力进行评定,并使用扫描电镜对试验用不锈钢的表面腐蚀情况进行形貌观察及成分分析,结果表明:由于Nb和Ti稳定化元素的添加,409型低铬不锈钢可获得较低的腐蚀速率,而无添加Nb和Ti稳定化元素的410型铁素体不锈钢具有较高的腐蚀速率;由于含镍钛夹杂物TiS、Ti(CN)和Nb(CN)的存在,409型不锈钢主要发生点蚀和晶间腐蚀等局部腐蚀;而无稳定化元素的410型不锈钢试样表面更易发生全面腐蚀。     

410S重卷中产生挫伤的原因分析与对策

针对不锈钢事业部1 780 mm生产线生产的410S不锈钢在平整机组重卷时经常产生挫伤缺陷的质量问题,从工艺、设备、原料和测量等方面分析了挫伤缺陷产生的原因.结合1 780 mm平整机组自身的特点,对开卷机的接卷操作方式、开卷张力参数、张力单元中张力辊的投用方式和开卷机油缸工作压力等进行调整,并应用于生产实际,有效控制410S不锈钢表面挫伤缺陷.     

410S热轧带钢氧化皮结构对酸洗效果的影响

热轧带钢氧化皮结构是影响其酸洗效果的重要因素。以410S铁素体不锈钢为研究对象,研究其热轧带钢表面氧化皮的结构和组成物相,分析其对酸洗效果的影响。     

热轧410S铁素体不锈钢表面缺陷形成原因分析

采用扫描电镜(SEM)结合能谱分析仪(EDS)对410S铁素体不锈钢表面翘皮缺陷的形貌、成分进行观察分析。结果表明,410S铁素体不锈钢表面翘皮缺陷,本质上是外层以富铁的氧化物为主,内层以铁-铬尖晶石相为主、含少量Fe2Si O4的氧化铁皮结构,它导致除鳞不彻底,轧制时铁素体不锈钢基体软,残留的氧化铁皮被压入钢板表层,硬度大的颗粒状氧化物割裂氧化层与基体,导致形成表面翘皮缺陷。     

430铁素体不锈钢冷轧带钢表面黑带缺陷分析

采用扫描电子显微镜(SEM)及能谱分析(EDS)等方法对冷轧带钢表面黑带缺陷和连铸板坯表层碳化物的形貌、尺寸及分布进行了分析研究。结果表明：430不锈钢带钢表面黑带缺陷部位较正常区域有更高的碳含量,且出现贫铬元素,为明显的晶间腐蚀缺陷。分别使用A型和B型保护渣的430不锈钢铸坯边部和中部表层均存在颗粒状碳化物,碳化物区域深度不同,呈不连续的分布。因此,由于结晶器液面波动或保护渣熔速过慢导致熔渣层补充不足,富碳层与钢液和铸坯表面接触,造成铸坯表面覆碳,在后续轧制过程形成黑带缺陷。     

带钢表面“起皮”原因分析及对策

通过金相观察、电镜和能谱分析，对带钢表面“起皮”原因进行分析，并介绍相应措施以减少和消除该缺陷。“起皮”的主要原因是夹杂物的存在降低了材料的塑性，在深加工过程中表面变形较大而产生。     

不锈钢带连续退火针压缺陷的研究

针压是不锈钢冷轧薄带钢在连续退火酸洗机组生产过程中经常出现的表面缺陷。现场实测及针压缺陷的显微分析结果表明：在连续退火过程中,炉辊与不锈钢带表面存在相对滑动时,辊子表面积累的颗粒状异物是形成针压缺陷的主要原因。为了减少颗粒状异物和改善表面接触状态,现场试验分析发现冷却段3%辊是产生带钢表面针压缺陷的主要部件,改变冷却段3#辊的材质和辊子形状可降低针压缺陷的发生率,采取相应措施使得针压缺陷得到了明显改善。     

热轧带麻面缺陷分析与控制

对唐钢不锈钢公司1580生产线热轧带钢表面麻点状缺陷进行了分析。结合产线特点,从改善轧辊氧化膜剥落和产生三次氧化铁皮的条件入手,制定了详细的改进措施,有效地控制了热轧带钢表面麻点缺陷,满足了用户使用要求。     

邢钢低碳400系铁素体不锈钢AOD控氮工艺实践

在低碳400系不锈钢中,氮能恶化晶间腐蚀、低温冲击韧性、缺口敏感性和焊接等性能。因此,在低耗、高效前提下降低其氮含量成为AOD冶炼中的重要课题。结合生产试验,通过探讨回归分析法在其吹氩脱氮工艺控制中的应用,结合脱氮的热力学计算对AOD生产实践数据的分析,由拟合方程确定的AOD冶炼410S不锈钢和低碳430不锈钢时氮氩切换点为吹氮450m³时切换氩气,410S不锈钢正常冶炼时一般吹氩量控制在1550m³,低碳430不锈钢AOD吹氩量一般控制在2050m³时可以将AOD终点氮含量控制在0.009 0%以下,并降低氩气消耗。     

硅对含强氧化性离子沸腾硝酸中奥氏体不锈钢耐蚀性的影响

 超低碳Cr Ni奥氏体不锈钢在含强氧化性离子的硝酸溶液中会发生过钝化腐蚀和晶间腐蚀,而高硅不锈钢在强氧化性浓硝酸中具有优良的耐蚀性。笔者以高纯级000Cr25Ni20和00Cr14Ni14Si4钢作为对比材料,发现在纯稀硝酸中000Cr25Ni20钢具有更优良的耐蚀性,在不同含量的40%沸腾硝酸溶液中,00Cr14Ni14Si4钢可有效抑制过钝化腐蚀,而且不发生晶间腐蚀。     

晶粒尺寸对Cr-Ni奥氏体不锈钢在硝酸中晶间腐蚀敏感性的影响

通过在含400 mg/L Cr6++40%硝酸溶液中浸没试验和电化学试验,发现随晶粒尺寸的减小,Cr-Ni奥氏体不锈钢晶间腐蚀敏感性随之增加,但当晶粒尺寸小于临界晶粒尺寸时,晶间腐蚀敏感性开始降低。过钝化电位数值与晶粒尺寸无直接关系,与材料本身特性有关,极化后的表面腐蚀形貌与浸没试验结果相一致。     

TMCP工艺轧制桥梁用不锈钢复合板的组织与性能

为了获得桥梁用不锈钢复合板良好的综合性能,采用控轧控冷(thermal mechanical control process,简称TMCP)工艺轧制了桥梁用不锈钢复合板316L+Q370qD,利用金相、扫描、拉伸、冲击、弯曲、剪切和晶间腐蚀等手段研究了该复合板的组织与性能。结果表明,316L+Q370qD桥梁用不锈钢复合板的界面实现了完全冶金结合,未发现孔洞、裂纹等缺陷以及大颗粒的析出物及氧化物夹杂等;复合板的屈服强度为421~446MPa,伸长率为24.0%~28.0%,-20℃纵向冲击吸收能量平均值为200J,180°内、外弯曲合格,平均剪切强度为412 MPa,复合板的各项力学性能均满足GB/T 8165—2008《不锈钢复合钢板和钢带》标准要求。按照GB/T 4334—2008方法 E进行晶间腐蚀试验,复层不锈钢316L未出现晶间腐蚀现象,具有良好的耐晶间腐蚀性能。     

Effect of cold work on stress corrosion cracking behavior of types 304 and 316 stainless steels

The influence of cold work (prestraining) in the range 2.3 to 56 pct on stress corrosion cracking (SCC) properties of types 304 and 316 stainless steels in boiling MgCl2 solution at 154 °C was investigated using a constant load method. In both materials, SCC initiation was in transgranular mode. Transition in stress corrosion cracking mode from transgranular to intergranular, as the crack proceeds, was observed at all cold work levels in 316 stainless steel and at cold work levels of 26 pct and 56 pct in 304 stainless steel. Both prestraining and increase in the initial applied stress facilitated the transition in crack morphology to intergranular mode. Increased tendency to intergranular SCC at high applied stresses and in cold worked specimens appears to be mechanistically analogous.     

Effect of cold work on stress corrosion cracking behavior of types 304 and 316 stainless steels

The influence of cold work (prestraining) in the range 2.3 to 56 pct on stress corrosion cracking (SCC) properties of types 304 and 316 stainless steels in boiling MgCl2 solution at 154 °C was investigated using a constant load method. In both materials, SCC initiation was in transgranular mode. Transition in stress corrosion cracking mode from transgranular to intergranular, as the crack proceeds, was observed at all cold work levels in 316 stainless steel and at cold work levels of 26 pct and 56 pct in 304 stainless steel. Both prestraining and increase in the initial applied stress facilitated the transition in crack morphology to intergranular mode. Increased tendency to intergranular SCC at high applied stresses and in cold worked specimens appears to be mechanistically analogous.     

430铁素体不锈钢晶间腐蚀敏感性评测方法及影响因素

采用双环-电化学(DL-EPR)法评价了热轧和退火430铁素体不锈钢(/%:0.038C、16.83Cr)的晶间腐蚀敏感性。确定了一种适合的试验参数,试验溶液为0.05 mol/L H₂SO₄+0.001 mol/L KSCN+0.01 mol/LNa₂SO₄,扫描速率为正扫5.0 mV/s,反扫1.67 mV/s,当Ra值(反扫电流Ir/正扫电流Ia)越高,晶间腐蚀敏感性越严重。试验结果表明,热轧后的430铁素体不锈钢存在明显的晶间腐蚀敏感性,空冷试样的舶值比水冷的高;经过750～850℃10 min退火处理能够有效减轻和消除热轧430铁素体不锈钢晶间腐蚀敏感性。     

Sensitization Behaviour of Manganese‐Alloyed Austenitic Stainless Steels

Manganese is an essential alloying element in advanced austenitic stainless steels with specific properties such as high resistance to harsh corrosive environments, high strength or low material costs. These materials are often used for welded constructions which have to be highly corrosion resistant. Hence it has to be ensured that the heat input during welding does not initiate the precipitation of chromium carbide resulting in a susceptibility to intergranular corrosion. This leads to the question whether the sensitization behaviour of manganese‐alloyed austenitic stainless steels is comparable to that of the well‐known conventional chromium nickel austenites. In the present work the effect of heat‐input on the susceptibility of the CrNi‐steel 1.4301 and the CrNiMn‐steel 1.4376 to intergranular corrosion (IGC) was considered. Investigations were carried out by corrosion testing in the so‐called Strauss‐Test to elucidate the effect of the annealing temperatures on the microstructure. Furthermore, the influence of heat treatment on the mechanical properties was evaluated by tensile testing. As a result, it could be demonstrated that manganese‐alloyed austenitic stainless steels like grade 1.4376 exhibit a sensitization behaviour very similar to the conventional austenitic steel grades. The same kinds of tests on intergranular corrosion resistance can be applied for both types of materials.     

Pitting Corrosion Behavior of Stainless Steel 304 in Carbon Dioxide Environments

The pitting corrosion behavior of stainless steel (SS) 304 in aqueous CO2-H2S-CI-environment was investigated by potentiodynamic cyclic anodic polarization and electron probemicroanalysis (EPMA). The experimental results show that the pitting corrosion susceptivityof SS 304 increases with the increase of temperature. Chlorine ion is the prerequisite for pittingcorrosion of SS 304 in H2S-CO2 environments. There is a linear relatiotxship between the pittingcorrosion potential (Eb-100) and chlorine ion concentration, and Eb-00 becomes noble with in-creasing pH value of the solution with or without H2S. pH value has little effect on the protec-tion potential with the presence of Hz S. H2S increases strongly the pitting corrosion susceptivi-ty and deteriorates the pitting corrosion resistance of SS 304 in CO2 environments. The obser-vations by EPMA show that SS 304 in CO2-saturated NaCI solution (3%) with H2S sufferspitting corrosion accompanied with intergranular corrosion.     

The 80-year history of duplex stainless steel

80 years has passed since duplex stainless steels were first produced and now they have developed into an integral series with the efforts on R & D and development of technology.In the recent decade, duplex stainless steels have been accepted by more and more customers and increasingly used. The first duplex grade produced in Sweden was 453E(26Cr-5Ni) in the 1930s,and then developed into 329.These two grades were characterized by high carbon content and called the first generation of duplex stainless steels.At that time,it was very difficult to add nitrogen into the steels and maintain the phase equilibrium,thus influencing the application properties,for example,intergranular corrosion post welding. One method to solve this problem is to alter the chemical composition,like adding nitrogen,etc.And that came to reality with the development of AOD and metallurgical theory of stainless steels.New series of duplex grades,called the second and third generations duplex,have successively emerged since the 1980s. These grades are characterized by high amounts of alloying elements,like chromium,molybdenum and nitrogen.Furthermore,super duplex stainless grades,like S32750,S32760 and S32707,were developed for various harsh service environments with their outstanding corrosion resistance and workability.These grades possess corrosion resistance corresponding to super austenitic grades,or close to nickel-base alloys, and are used in ocean-engineering,sea water desalination and oil industries,etc. And the application of duplex stainless steel is expending into other industries.For instance,453E is used in the pulp & paper industry.2205(S32205),a medium-alloyed grade,has become the most typical one in the duplex stainless steel family and widely used in many industries like pulp & paper,chemical and oil.New applications are emerging with better understanding of the duplex grades. Modern duplex stainless steels features most the corrosion resistance and strength,making them most cost-efficient in more and more projects. In this paper,the history of duplex stainless steels is recalled and reviewed from R&D,production to application,and latest grades like S82441 are also introduced.