다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The ability to map plastic deformation around high strain gradient microstructural features is central in studying phenomena such as fatigue and stress corrosion cracking. A method for the visualization of plastic deformation in electron back-scattered diffraction (EBSD) data has been developed and is described in this article. This technique is based on mapping the intragrain misorientation in polycrystalline metals. The algorithm maps the scalar misorientation between a local minimum misorientation reference pixel and every other pixel within an individual grain. A map around the corner of a Vickers indentation in 304 stainless steel was used as a test case. Several algorithms for EBSD mapping were then applied to the deformation distributions around air fatigue and stress corrosion cracks in 304 stainless steel. Using this technique, clear visualization of a deformation zone around high strain gradient microstructural features (crack tips, indentations, etc.) is possible with standard EBSD data.

Misorientation mapping for visualization of plastic deformation via electron back-scattered diffraction.

The trend in welding on a world basis is discussed and the close cooperation between science and industry to develop new welding processes and solve existing problems is emphasised. Possible future development in welding is outlined, and some of the newer welding processes are briefly discussed.

Welding in the world

Effect of Ti variation on microstructure evolution and mechanical properties of low carbon medium Mn heavy plate steel

Deep penetration fiber laser-arc hybrid welding of thick HSLA steel

On the determining role of acicular ferrite in V-N microalloyed steel in increasing strength-toughness combination

In this study, the high-cycle fatigue behavior of low-C medium-Mn high strength steel was studied at stress ratio R (σmin/σmax) = − 1 and 0.1. Excellent fatigue performance with push-pull fatigue limit strength (σ−1) and pull-pull fatigue limit strength (σ0.1) after 107 cycles of 450 MPa and 683 MPa was obtained. The fatigue ratio (σ−1/Rm, σ0.1/Rm) was 0.54 and 0.82, respectively. Two types of failure modes were observed, surface-induced failure mode and internal inclusion-induced failure mode. The retained austenite (RA) transformation ratio of fracture surface increased from ~ 30% to ~ 63% with increase in maximum stress (σmax) from 470 MPa to 550 MPa. The higher mechanical driving force contributed to the total driving force for martensite transformation, and higher damage accumulation in terms of cyclic plasticity. The high density of high misorientation boundaries between tempered martensite effectively prevented the propagation of fatigue crack, and enhanced the fatigue strength. The experimental steel with excellent fatigue property was mainly attributed to the transformation-induced plasticity (TRIP) effect of metastable RA in the small plastic deformation zone, which relaxed the local stress concentration, absorbed the strain energy, delayed the crack initiation and suppressed its propagation.

High-cycle fatigue behavior of low-C medium-Mn high strength steel with austenite-martensite submicron-sized lath-like structure

Intercritically reheat-coarse grained heat-affected zone (ICCGHAZ), as a brittle zone in double-pass welding, its toughness is affected by the peak temperature of the secondary thermal cycle. To elucidate the effect of secondary peak temperature on the microstructure and impact toughness of ICCGHAZ in laser-arc hybrid welded X100 pipeline steel joints, thermal simulation studies were carried out. The experimental results indicated that the microstructure of ICCGHAZ consisted of tempered martensite and products of secondary thermal cycle along the prior austenite grain boundaries. The products of secondary thermal cycle were necklace-type M-A constituent, necklace-type lath martensite and granular bainite + acicular ferrite at 740 °C, 790 °C and 840 °C, respectively. Based on experimental observations, transformation mechanism of ICCGHAZ at different secondary peak temperatures was proposed. The higher half zone(790℃∼Ac3) in ICCGHAZ of the laser-arc hybrid welded joint has a higher impact energy than the base metal. Consequently, microhardness difference between the products of secondary thermal cycle and matrix was reduced such that the stress concentration and crack nucleation rate was decreased during impact. The lattice orientation was more dispersed and fraction of high angle grain boundaries was increased at 840 °C, which suppressed crack propagation. The method of pipeline steel by laser-arc hybrid welding can effectively reduce the width of low toughness zone in ICCGHAZ and increase the impact energy of the welded joints.

Effect of secondary peak temperature on microstructure and toughness in ICCGHAZ of laser-arc hybrid welded X100 pipeline steel joints

Press-hardened steels (PHS) with a 1.5-mm-thick coated Al–Si layer is welded using an IPG YLS6000 continuous fiber laser in the air atmosphere. An SU5000 scanning electron microscope (SEM) and an Oxford EDS X-Max20 energy spectrometer are used to characterize the microstructure, which consists of delta (δ)-ferrite and lath martensite. It is similar to that of the welding performed in the Ar atmosphere, but the content of δ-ferrite is less. The reason is the formation of Al2O3 inclusions in the molten pool, which reacts with oxygen from the air ambient and the Al from the molten Al–Si coating of PHS. The oxygen content is measured with an ONH-3000 analyzer. An HV-1000 microhardness tester and DNS-100 universal material test equipment are performed to test the hardness and tensile strength. Similar hardness and strength of welded joints are achieved welding in the air atmosphere compared to that of the Ar atmosphere. Fracture was initialed in the fusion line of overlapping zone and propagated along the interface of two plates and fusion line due to the Al segregation.

A Study on Microstructure and Properties of PHS Fiber Laser Welded Joints Obtained in Air Atmospheres

Study on the mechanism of heat input on the grain boundary distribution and impact toughness in CGHAZ of X100 pipeline steel from the aspect of variant

Qi Xiaonan

Papers

On the determining role of acicular ferrite in V-N microalloyed steel in increasing strength-toughness combination

High-cycle fatigue behavior of low-C medium-Mn high strength steel with austenite-martensite submicron-sized lath-like structure

Effect of secondary peak temperature on microstructure and toughness in ICCGHAZ of laser-arc hybrid welded X100 pipeline steel joints

A Study on Microstructure and Properties of PHS Fiber Laser Welded Joints Obtained in Air Atmospheres

Study on the mechanism of heat input on the grain boundary distribution and impact toughness in CGHAZ of X100 pipeline steel from the aspect of variant