Acoustic emission detection of 316L stainless steel welded joints during intergranular corrosion

This study analyzes acoustic emission (AE) signals during the intergranular corrosion (IGC) process of 316L stainless steel welded joints under different welding currents in boiling nitric acid. IGC generates several AE signals with high AE activity. The AE technique could hardly distinguish IGC in stainless steel welded joints with different welding heat inputs. However, AE signals can effectively distinguish IGC characteristics in different corrosion stages. The IGC resistance of a heat-affected zone is lower than that of a weld zone. The initiation and rapid corrosion stages can be distinguished using AE results and microstructural analysis. Moreover, energy count rate and amplitude are considered to be ideal parameters for characterizing different IGC processes. Two types of signals are detected in the rapid corrosion stage. It can be concluded that grain boundary corrosion and grain separation are the AE sources of type 1 and type 2, respectively.     

Effects of H content on the tensile properties and fracture behavior of SA508-III steel

SA508-Ⅲ steel was charged with different hydrogen (H) contents using a high-pressure thermal charging method to study the effects of H content on the tensile properties and evaluate the H embrittlement behavior of the steel. The results indicate that the ultimate tensile strength remains nearly unchanged with the addition of H. In contrast, the yielding strength slightly increases, and the elongation significantly decreases with increasing H content, especially at concentrations exceeding 5.6×10-6. On the basis of fractographic analysis, it is clear that the addition of H changes the fracture mode from microvoid coalescence to a mixture of river patterns and dimples. Carbides are strong traps for H; thus, the H atoms easily migrate in the form of Cottrell atmosphere toward the carbides following moving dislocations during tensile deformation. In addition, stress-induced H atoms accumulate at the interface between carbides and the matrix after necking under three-dimensional stress, which weakens the interfacial bonding force. Consequently, when the local H concentration reaches a critical value, microcracks occur at the interface, resulting in fracture.     

一种新型结构材料S280

 S280 是一种超高强度不锈钢, 采用低碳马氏体相变强化和时效强化叠加, 靠析出强化获得所需的强度。使用状态下的基体组织为低碳板条马氏体, 主要强化相为Fe₂Mo 等, 抗拉强度σ_b为1920～1930 MPa, 断裂韧度K_IC为95～100 MPa √m, 具有比300M 和AerMet100 更好的耐腐蚀性能, 主要用于抗腐蚀性能要求高的超高强度构件。     

BaO-CaO基精炼渣对含铬铁水的氧化脱磷

在氩气保护气氛的MoSi2炉内,进行了BaO-CaO基精炼渣对不同初始碳含量的含铬铁水氧化脱磷实验研究.实验结果发现,含铬铁水的初始碳质量分数在3%-4%时,脱磷效果最好,在1 500℃时,脱磷率可达60%以上;氧化脱磷温度对脱磷率影响显著,随着温度的升高,脱磷率显著下降,脱磷温度宜控制在1 500-1 550℃;含铬铁水几乎没有铬损,初始碳含量较高的炉次出现了增铬现象.     

硅烷偶联剂对不锈钢表面膜基结合强度的影响

运用拉伸法研究了硅烷偶联剂对316L不锈钢高分子涂层的结合强度的影响,并对硅烷偶联剂的含量、预处理时间及pH值等工艺条件进行了优化。采用ATRIR,XPS等技术表征了偶联剂提高膜基结合强度的机理。结果表明：硅烷偶联剂能够显著提高不锈钢与高分子涂层之间的结合强度,最佳的工艺条件为：偶联剂含量W=0．05,处理时间为10s,溶液的pH值为6。作用机理是：偶联剂一端与金属生成了Si-O-Me键。另一端与高分子相互缠绕形成了复杂的互穿网络结构。     

轧制退火316奥氏体不锈钢的晶界特征分布

利用EBSD技术对不同形变量冷轧并退火处理的316奥氏体不锈钢的晶界特征分布进行了研究．结果发现,小变形轧制经退火处理后,试样晶粒尺寸明显长大的同时∑3^n（n=1,2,3）晶界（也称特殊晶界）比例不断提高．晶粒取向分析表明,合金中高斯（Goss）、黄铜（Brass）、铜型（Cop—per）和立方（Cube）取向（包括其几何变体）的择优长大是特殊晶界比例提高的重要原因．     

碳纳米管在不锈钢衬底上生长电化学应用

将不锈钢衬底进行适当的预处理,采用等离子体增强化学气相沉积(PECVD)的方法,在适当的工艺条件下,利用甲烷与氢气的混和气体,在不锈钢衬底上生长出多壁碳纳米管(MWCNT).将生长有碳纳米管(CNT)的不锈钢片作为基体电极,通过共价修饰法,制备出壳聚糖(CS)与碳纳米管复合膜的化学修饰电极,用来检测亚硝酸盐.对NO2-在电极表面的阳极溶出伏安特性进行研究,结果表明:使用CS/CNT修饰电极检测亚硝酸盐,在0.1 mol/L,pH=6.0的KCl底液中,对NO2-具有良好的选择性与吸附性,峰电流与NO2-的浓度在2.0×10-6~1.0×10-3mol/L范围内呈良好的线性关系,检测限可达3.0×10-7mol/L,具有很好的应用前景.     

410S铁素体不锈钢的静态再结晶行为

通过不同温度-时间的再结晶实验,研究热轧态铁素体不锈钢410S的再结晶行为.结果表明,对于竹节状铁素体+马氏体(质量分数约30%)的410S热轧态变形组织,为防止马氏体的再度出现以及加快再结晶过程的综合考虑,其最佳再结晶退火温度为780~800℃.在此温度下所发生的再结晶,均有一个2~5 h的孕育期,当再结晶体积分数达到50%时,结晶速度达到最大.与试样内部相比,热轧态410S板材的再结晶晶粒更易于在表面形成.经过再结晶的410S硬度从初始的86.5 HRB下降到66.5 HRB,硬度降低25%.     

熔模铸造双相不锈钢铸件缺陷分析及解决措施

针对铸件容易产生的充型不完整和产生气孔的缺陷,采用熔模铸造法试制双相不锈钢铸件.结果表明,通过控制金属液出炉温度和模壳温度并在铸件凝固时强化冷却,能防止上述缺陷的产生.应用试制工艺生产的铸件外观质量良好.     

压力对铍/铜/HR-1不锈钢热静压组织结构的影响

在800℃下,分别在20、30、40、50MPa压力下对铍/铜/HR-1不锈钢进行真空热静压扩散连接。利用光学金相、显微硬度计、扫描电镜(SEM)、俄歇电子能谱(AES)和X射线衍射仪(XRD)分析了接头扩散区的微区成分和组织结构;探讨了扩散区成分,组织结构与压力的关系。研究表明:压力的作用将使试样产生动态形变再结晶和扩散性蠕变,也能影响扩散焊区的扩散宽度、晶粒大小和金属间化合物数量;单轴向压力作用下,基材或扩散焊区出现织构;降低铍/铜/HR-l不锈钢接头性能的主要因素是金属间化合物优先沿晶界生成,适当降低压力或缩短热压时间可减少金属间化合物的形成,改善连接性能。