DH36高强度船板钢生产优化

对敬业中厚板公司高强度船板DH36力学性能不合原因进行分析,发现主要原因是钢板中心存在微裂纹,微裂纹产生的原因在于心部条状MnS、碳氮化物夹杂的聚集以及马氏体、贝氏体硬性组织的出现。通过合理设计化学成分,改进炼钢、轧钢等工艺,使钢板力学性能得到大幅提高,并顺利通过九国船级社的认证。     

Q345B钢板拉伸性能不合格原因分析

利用光学显微镜、扫描电镜及能谱仪对Q345B钢板拉伸性能不合格的原因进行了分析。结果表明:试样中心的白点缺陷、微裂纹和硫化物夹杂,是引起该批次Q345B钢板拉伸性能不合格的主要原因;偏析带上的魏氏组织也会对钢板的延伸性能产生不利影响。最后针对钢板拉伸性能不合格原因提出了工艺改进措施。     

中厚钢板超声波探伤不合格原因分析

针对中厚钢板超声波探伤出现的两类典型缺陷,通过低倍检验和金相检验等手段,并结合实际探伤过程中缺陷的分布位置对探伤不合格的原因进行了分析。结果表明:点状密集型缺陷主要与连铸坯的中心偏析有关,侧边条型缺陷则主要来源于连铸坯的三角区裂纹或靠近三角区的中心裂纹,钢板体部的条型缺陷则是由连铸坯的中间裂纹造成的。     

Q345R钢板探伤不合格原因分析

采用光学显微镜、扫描电镜和能谱仪对探伤不合格的Q345R钢板进行显微组织、夹杂物及拉伸断口形貌的观察与分析,探讨了引起Q345R钢板探伤不合格的原因。结果表明:引起Q345R钢板探伤不合格的主要原因是钢板中存在硫化锰夹杂物偏聚、裂纹及中心疏松等,并提出相应的改进措施,以提高钢板的探伤合格率。     

Q355B钢板拉伸断口分层原因及改善措施

采用宏观观察、化学成分分析、拉伸试验、热酸蚀检验、金相检验、扫描电镜及能谱分析等方法,分析了Q355B钢板拉伸断口出现分层的原因.结果表明:Q355B钢板拉伸断口出现分层的主要原因是连铸坯厚度中心处存在缩孔、疏松、偏析和夹杂物缺陷,导致钢板产生中心裂纹,在拉伸试验过程中,裂纹处产生应力集中,随着变形量的不断增加,裂纹不...     

Q345R钢板断后伸长率不合格原因分析

采用光学显微镜、扫描电镜和能谱仪对断后伸长率不合格的Q345R钢板的显微组织、断口形貌以及夹杂物进行观察和分析,分析了导致Q345R钢板断后伸长率不合格的原因。结果表明:引起Q345R钢板断后伸长率不合格的主要原因是严重的带状组织,尤其是较宽的贝氏体硬组织带、魏氏组织等;硫化物夹杂的存在对钢板的断后伸长率有一定的影响,但不是主要原因。     

某宽厚钢板等离子切割开裂原因

在某宽厚板的等离子切割工序中,其板厚1/2处产生中心裂纹。采用宏观观察、化学成分分析、金相检验、扫描电镜及能谱分析、硬度测试等方法分析该钢板开裂的原因。结果表明：在钢板1/2厚度处存在明显的偏析带,基体和偏析带的显微组织分别为回火马氏体和淬火马氏体,在偏析带中分布有长条状夹杂物,裂纹从夹杂物处萌生并扩展;等离子切割后的淬硬层硬度较大,具有很大的淬硬倾向,在热应力和组织应力的作用下,钢板最终开裂。     

中厚板轧材探伤不合的原理分析与措施

因铸坯内部质量原因造成轧材探伤不合的原因主要有四个,分别是氢致裂纹,铸坯内部的中心偏析与裂纹,铸坯内部的夹杂物和铸坯内部的带状组织发达。本文针对中厚板生产中出现的轧材分层问题展开分析,从连铸坯的内部质量缺陷和轧钢的压下量等方面分析轧材分层产生的原因及预防措施。     

Q460C钢板力学性能不合格原因分析

利用光学显微镜和扫描电子显微镜分析了某厂生产的多个批次Q460C钢板力学性能低于GB/T 1591-2008技术要求的原因.结果表明:钢板中心偏析造成的贝氏体组织、微裂纹、MnS以及铌和钛复合夹杂物的存在是导致该Q460C钢板力学性能不合格的主要原因;另轧制工艺控制不当造成的魏氏体组织也会降低钢板的力学性能.     

连铸10CrNi3MoV钢裂纹尖端张开位移(CTOD)试验研究

对电炉模铸及不同批转炉连铸 10CrNi3MoV钢进行了CTOD试验研究 ,并探讨了CTOD特征值与钢板中心偏析关系。结果表明 ,模铸钢板抵抗裂纹早期扩展的能力高于连铸板 ,但连铸板抵抗裂纹失稳扩展能力并不低于模铸板 ;钢板中心偏析使CTOD特征值降低 ;控制碳含量在较低水平 ,或碳含量达上限 (0 .11%C)时采取减轻偏析的有效措施 ,可使连铸 10CrNi3MoV钢具有较高的断裂韧性     

A Study to Establish Correlation Between Intercolumnar Cracks in Slabs and Off-Center Defects in Hot-Rolled Products

Delamination and cracking related to segregations are mostly observed at the centerline of hot-rolled products. The delamination is related to heavy concentration of manganese sulfide inclusions originating from centerline segregation in slabs. In multiple cases, similar delamination or cracking is observed at locations away from the mid thickness plane of hot-rolled products during forming operations at customer end. This leads to rejection of materials. Metallographic investigation reveals segregation line with plenty of manganese sulfide stringers at the off-center location similar to observations in cases of centerline defects. Centerline segregation is a well-understood phenomenon, but the presence of off-center segregation line in hot-rolled products has not been systematically studied before. Several literatures report intercolumnar cracks in slabs to be filled with segregations. Also, they occur away from the centerline of continuously cast slabs. A laboratory-based experimental study was conducted using a slab suspected by S-printing to contain intercolumnar cracks. The aim of this study was to evaluate the effect of intercolumnar cracks on internal quality of rolled products. This paper reports the finding of this study that established a strong correlation between intercolumnar cracks in slabs and off-center cracking in hot-rolled products.     

45Mn2钢管的"亮线"缺陷分析

在车削加工45Mn2钢管时,发现管壁中存在类似裂纹状的有金属光泽的"亮线"线务,通过宏观和微观形貌分析、力学性能测试、压扁试验和腐蚀试验等方法分析了钢管"亮线"的形成原因.结果表明:"亮线"的微观形貌由贝氏体组织构成,是异于钢管基体的成分偏析带,来源于连铸坯;这种"亮线"是一种不允许存在的缺陷,建议炼钢厂采取措施,提高...     

Banded microstructure in a low-alloyed eutectoid steel

The possible influence of banded microstructure on the fracture performance of a high-carbon steel is investigated using electron microscopy and X-ray diffraction techniques. The banded microstructure was found to be alternating layers of bainite and tempered martensite/retained austenite. Transformation of bainite was promoted by a combined effect of segregation of alloying elements, non-uniform thermal gradient across the steel, and the insufficient austenitisation. The transformation of bainite along the prior austenite grain boundaries (PAGBs) introduces a non-uniform strain distribution at bainite/martensite interface and a higher stress concentration, which may eventually lead to the failure of the heavy section in a brittle intergranular manner. Results provide insights to the importance of understanding the bainitic transformation in such eutectoid steel systems.     

Finite element prediction of crack formation induced by quenching in a forged valve

Quenching treatment is commonly used to improve the mechanical properties of steel components. However, in these components, quench cracks are often observed as a result of improper material choice and thermal treatment process. Prediction of quench cracks is important to reduce production cost and to prevent in-service component failure; however, a generally accepted criterion for their formation has to be still established. In this study, finite element prediction of crack formation induced by quenching in a forged valve used in the offshore oil drilling field, is performed by means of the commercial finite element software Abaqus®. Microstructures (austenite, martensite, bainite, pearlite and ferrite) which can be formed during the thermal treatment are taken into account. The simulation results, compared with the effects of the quenching on the actual component, indicate that this type of simulation can effectively predict the quench cracks formation in 3D components.     

Caustic stress corrosion cracking of a spheroidal graphite cast iron: characterisation of ex-service component

Abstract

This paper discusses observations of features suggesting grain boundary embrittlement ahead of stress corrosion crack tips in ex-service cast iron components exposed to strong caustic environments during Bayers process for alumina processing. The cracks and the neighbouring areas in the ex-service specimens were examined using conventional metallography, SEM, the extraction replica technique in the TEM and Auger electron spectroscopy. In all cases, the cracking was initiated at the surface of the steel exposed to the corrosive environment and it appeared that crack nucleation may have been aided by local stress concentrations and/or zones of local residual stress concentration. The fracture mode was almost exclusively intergranular and the crack path followed ferrite grain boundaries. There was clear evidence of a local zone of grain boundary embrittlement extending ahead of the tip of the major cracks examined. The phenomenon was established by investigating the fresh fracture surfaces produced by extending pre-existing cracks under impact loading at liquid nitrogen temperature. Auger electron spectroscopy of the fresh intergranular fracture surface failed to reveal any evidence of local elemental grain boundary segregation that might account for the observed embrittlement. In the absence of evidence of any other embrittling species on the exposed intergranular facets, there arises the possibility of hydrogen being involved in the embrittlement. The paper discusses hydrogen assisted intergranular cracking, as observed in the case of similar materials, to be the possible mechanism.     

Cracking Failure of Hardfacing Layer of Repaired Backup-Roller in Rolling Mill

A worn backup-roller in rolling mill was repaired by hardfacing technology. The routine flaw detection after machining revealed that randomly distributed circumferential short cracks occurred on the surface of repaired roller. Sectional observation throughout hardfacing region showed that intensively distributed transverse short cracks were also present inside the outer layer of hardfacing region. Detailed metallographic analysis and fractographic investigation indicate that the transverse short cracks are crystallization cracks, caused by hot-cracking. General excessive element of P in the outer layer and the segregation of impurity elements P, S within the interdendritic space and at the grain boundary are metallurgical factors responsible for hot-cracking. Occurrence of the bending load on the roller, resulting from the great self-weight of roller, is mechanical factor leading to forming transverse crystallization cracks.     

Mechanism of Fe-Mn-Al alloy steel ingot failure from MgO-C refractory corrosion

Fe-Mn-Al alloy steel was melted in a mass production tonnage arc furnace equipped with ladle refining facilities. The ingots were cracked and torn apart on hot rolling. Blue flames erupted from the cracks and became red. A white powder was observed adjacent to the cracks in ingots. The white powder was identified as magnesia. Concentrations of Mg and Ca were high in the centre of the ingot, implying the segregation of impurities. Quantitative elemental analysis and microstructural investigation revealed Mg, Si, Ca and S containing impurities and Cr, Mo and Si carbides were segregated within grain boundaries. The segregation was the main cause of ingot cracking. The 1600°C static cup test for carbon containing MgO-C refractories exhibited the reduction reaction, which raised the Mg concentration up to 0.017 wt% in Fe-Mn-Al alloy steel, whereas the pure MgO refractory cup test showed inertness to Fe-Mn-Al alloy.     

非调质钢曲轴感应淬火裂纹失效分析

目的分析非调质钢曲轴感应淬火时出现裂纹的原因。方法首先统计了裂纹的分布规律,并确定了裂纹源位置,之后通过金相检验、低倍检验,从锻打工艺、材料偏析等角度对裂纹进行了原因分析。结果产生在分模面位置的裂纹,是因产品结构造成该区域材料在锻打过程中发生流速不均,当材料的框型偏析位置在锻造挤压下流动到此处时,偏析的材料产生了微细空洞,该微细空洞在后续感应淬火时成为裂纹源而引起开裂。结论该裂纹的产生与材料框型偏析有直接关系。研究对控制非调质钢曲轴生产中的裂纹缺陷,提高曲轴生产质量,具有重要应用价值。     

变形温度对贝氏体钢组织性能的影响

为合理制定Si-Mn-MO系无碳化物贝氏体钢的生产工艺,利用GLEEBLE-3800热模拟试验机,在真空条件下开展了变形温度对贝氏体钢组织性能影响的热模拟试验.利用光学显微镜、透射电镜等设备,采用力学性能测试、微观组织观察等技术分析手段,对热模拟试样进行了组织观察和硬度检测分析,绘制了Si-Mn-MO系无碳化物贝氏体钢不同变形温度的动态CCT曲线,得出了变形温度对其组织和硬度的影响规律.结果表明,变形温度越低,无碳化物贝氏体钢的相变温度越低,组织越细小,先析铁素体越易析出,越有利于提高贝氏体钢的强硬性和韧塑性.