Phase Transformation of Nb in Carburized Zone of 25Cr35NiNb+MA Alloy After Service

Abstract25Cr35NiNb+MA alloy is widely used in ethylene pyrolysis furnace tube, the highest service temperature can be 1100°C, and has high resistance to creep and carburization. Ethylene pyrolysis furnace tube will suffer carburizing during service, which lead to phase transformation. Phase transformation of 25Cr35NiNb+MA heat-resistant ethylene pyrolysis furnace tube was investigated after service and the Nb transition during service was discussed. The phase transformation of ethylene pyrolysis furnace tube was characterized with field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectrum (EDS). Results reveal that the microstructure of as-cast 25Cr35NiNb+MA alloy contains NbC carbides on the dendrite boundaries. During service at high temperature, the NbC carbides transform to blocky G-phase (Ni16Nb6Si7) between M23C6 and matrix. As the carburizing process occurs, the blocky G-phase (Ni16Nb6Si7) gradually transforms to granular NbC, and distribute at the center of chromium carbide. The granular NbC will improve resistance of creep

Meta-Analysis of Smoking and the Risk of Gastric Cancer among the Chinese Population

OBJECTIVE To reevaluate the eff ect of tobacco smoking on the risk of developing gastric cancer among the Chinese population. METHODS Thirty articles from the literature both in Chinese and English from January, 1988 to present were identified and from which adjusted odd ratios (ORs) or relative risks (RRs) were combined by meta-analysis. Generalized least squares (GLS) for trend estimation of summarized dose-response data was carried out. All the analyses were performed using software of STATA version 10.0.RESULTS Comparing current smokers with subjects who have never smoked, the summary effect values on gastric cancer with a 95% confidence interval (CI) were 1.67 (1.43 1.96) for case-control studies and 1.52 (1.17-1.96) for cohort studies, respectively. The combined effect values with a 95%CI for the comparison of smoking quantity of current smokers with the referent group were 1.41 (1.15-1.72) for case-control studies and 1.24 (1.02-1.52) for cohort studies, respectively. The combined eff ect values with a 95%CI for the comparison of accumulative years smoked of current smokers with the referent group were 1.07 (0.89-1.28) for case-control studies and 1.28 (0.95-1.74) for cohort studies, respectively. Dose-response meta-analysis showed that the gastric cancer risk will increase 50% (OR = 1.50, 95%CI: 1.34-1.67) with each 20 cigaret e per day increment and increase 14% (OR = 1.14, 95%CI: 1.10-1.18) with each 10 year increment of smoking. CONCLUSION The gastric cancer risk among the Chinese population is significantly associated with tobacco smoking and the smoking quantity per day. Smoking cessation should be more strongly advocated