The Investigation on Welding Processes for SUS316LN Tubes Used in Superconducting Magnetic System of EAST

The force flow cooled superconducting cable-in-conduit conductor （CICC） is used in both of EAST toroidal field （TF） and poloidal field （PF） coils. The conductor consists of multi-stage NbTi superconducting cable and 1.5 mm thick square jacket. The cable is pulled through in a thin wall circular jacket and then compacted to square cross-section conductor. The jacket material is SUS316LN austenitic stainless steel seamless tubes （about 10 m each）, which is assembled by butt-welding up to 600 m. The results of the welding procedure investigation and quality assurance procedures carrying out are described in this paper.

316L不锈钢多孔结构的选区激光烧结成型工艺研究

研究了一种新型的制备金属多孔结构技术—选区激光烧结,着重说明该技术的基本原理和工艺过程,并利用此制备技术对316L不锈钢粉末进行了激光烧结制备多孔材料的实验研究。利用SEM分析了316L不锈钢多孔试样的微观孔隙特征,并测定其孔隙率。结果表明,在较高的扫描速率下可获得孔径分布均匀、孔隙贯通性良好的多孔结构;随扫描速率逐渐提高,试样孔隙率和弹性模量呈上升趋势。

Enhancement Mechanism of Cerium in 316LN Austenitic Stainless Steel During Creep at 700 ℃

Effect of cerium(Ce)on creep strength and microstructure of 316LN austenitic stainless steel(316LN steel)at 700℃/150 MPa was investigated by scanning electron microscopy(SEM),scanning transmission electron microscopy(STEM)and thermodynamic calculations.Addition of 0.032 wt%Ce to 316LN steel results in a prominent increase in creep life from 313 to 556 h.Ce enriches in titanium nitride nanoparticles,increases slightly the activity and diffusion coefficient of Mo,and facilitates the formation of fine and dense intragranular Laves phase precipitates.Thus the creep strength is remarkably enhanced by Ce addition in 316LN steel through the intragranular Laves phase precipitation strengthening.It reveals a new insight into the improvement effect of rare earth(RE)elements such as Ce on creep strength of austenitic stainless steels,which inspired the design of RE-microalloying heat-resistant steels.

Prediction of Critical Conditions for Dynamic Recrystallization in 316LN Austenitic Steel

Hot compression experiments conducted on a Gleeble-3500thermo-mechanical simulator and metallographic observation tests were employed to study the critical conditions of dynamic recrystallization（DRX）of 316 LN austenitic stainless steel.The true stress-true strain curves of 316 LN were obtained at deformation temperatures ranging from 900℃to 1 200℃and strain rates ranging from 0.001s-1 to 10s-1.Based on the above tests,the critical conditions of DRX were determined and compared with those obtained from work-hardening theory and the Cingara-McQueen flow stress model.Furthermore,the microstructure was observed to validate the calculated results.The ratio of critical strain to peak strain（εc/εp）for 316 LN was determined,and the quantitative relationship between the critical strain and the deformation parameters of 316 LN was elucidated.The results demonstrated that the onset of DRX corresponds to the constant normalized strain hardening rate（Γ）,namely,the critical strain hardening rateΓcfor316LN is equal to 0.65.

Effects of process parameters on fragment and refinement of millimeter- grade coarse grains for 316LN steel during hot cogging

The heterogeneous mixed-grain microstructure is a common defect for the heavy forging of 316LN austenitie stainless steel. Isothermal compression experiments were performed on a Gleeble-3500 thermo-mechanical simulator to investigate the effect of process parameters on the fragment and re- finement of millimeter-grade coarse grains （MCGs） during hot cogging. The experimental results in- dicate that the stress of MCG specimens is much larger than that of fine grain （FG） ones at 1150 ℃, while the stress difference between MCG and FG samples became smaller at 1200 ℃. Moreover, the MCGs can be well fragmented and refined under the condition of temperature of 1200 ℃, strain rate of 0.01 s-1 , and reduction rate of 50%. Meanwhile, numerical simulations were conducted to study the influences of temperature, strain and strain rate on microstructure evolution. The results of ex- periments and simulations comprehensively demonstrate that the MCG results in the increase of de- formation resistance and incompatibility of deformation, and it can be fragmented and refined at 1200 ℃ so that the plastic deformation energy decreases remarkably with the increase of temperature from 1 150 to 1200 ℃.

Ductile Fracture Prediction of 316LN Stainless Steel in Hot Deformation Process

A ductile fracture criterion of 316LN stainless steel, combined with the plastic deformation capacity of ma- terial and the stress state dependent damages, was proposed to predict ductile fracture during hot deformation. To the end, tensile tests at high temperatures were first performed to investigate the fracture behavior of 316LN stain- less steel. The experimental results show the variation of the critical fracture strain as a function of temperature and strain rate. Second, the criterion was calibrated by using the upsetting tests and the corresponding numerical simula- tions. Finally, the proposed fracture criterion was validated by the designed tests and the corresponding finite ele- ment （FE） simulation. The results show that the criterion can successfully predict the onset of ductile fracture at ele- vated temperatures.

核级不锈钢焊接接头钝化膜耐蚀性能和半导体特性研究

采用电化学阻抗谱(EIS)、场发射扫描电子显微镜(SEM)、Auger扫描能谱仪(AES)以及容抗测试技术(M-S曲线),研究了316LN/316L不锈钢焊接接头在模拟压水堆一回路高温高压水中形成的钝化膜的耐蚀性能和半导体特性。结果表明,焊缝区、热影响区和母材区形成的钝化膜的耐蚀性能不同,热影响区钝化膜开路电位及电化学阻抗等均低于其他区域,说明热影响区钝化膜的耐蚀性能最差,这主要与钝化膜的致密程度、厚度及Cr氧化物的含量有关。M-S曲线表明,母材区钝化膜平带电位为-0.7V,较其他区域(-0.4V)负移,表明有BO-3等阴离子在钝化膜表面吸附,加之具有较低的施主和受主浓度,可排斥侵蚀离子的腐蚀,使之较其他区域有更强的耐蚀性能。

HPMA作用下CaCO_3结垢特性及其对传热的影响

以水解聚马来酸酐(HPMA)对碳酸钙(CaCO_3)结晶垢的影响为研究对象,在Re=2 850和流量为20L/h的条件下,研究了316L不锈钢管在CaCO_3质量浓度分别为400 mg/L、600 mg/L、800mg/L、1 000mg/L和1 200 mg/L及添加比(m(HPMA)/m(CaCO_3))分别为1.6/100、2.4/100、3.2/100、4.0/100和4.8/100时的结垢特性及其对传热的影响,并利用扫描电镜(SEM)考察了在羧酸基阻垢剂(HPMA)作用下CaCO_3污垢的晶型变化。实验结果表明:在HPMA作用下CaCO_3污垢及其热阻随时间呈线性增长;污垢和热阻的增长速率受溶液浓度及HPMA添加比的影响,存在临界阈值效应;在羧酸基阻垢剂(HPMA)作用下CaCO_3污垢的晶型扭曲明显。