Tungsten inert gas (TIG) and metal inert gas (MIG) welding are the most popular gas-shielded arc-welding processes used in many industrial fields. MIG welding is a high-efficiency process compared to TIG welding. However, improvements are needed to reduce spatter and improve weld metal toughness. Although pure argon shielding gas is desirable for weld metal toughness, MIG arcs are unstable in pure Ar to the extent that executing welding is difficult. We have found that MIG arcs become stable even using pure argon by simply using a hybrid TIG and MIG system. This process has the possibility of becoming a new welding process giving high quality and efficiency. In this study, we investigate the influence of the balance of current between the TIG and MIG arcs, which is most important in determining arc stability and arc penetration. We have confirmed the suitable range of conditions both experimentally and through numerical simulation and have applied this process for butt and fillet joints. We show that the welding time can be reduced to 17 ~ 44 % of the time required using a conventional TIG process.

Study for TIG–MIG hybrid welding process

Although hot isostatic pressing (HIP) has been shown to demonstrate significant advances over more conventional manufacture routes, it is important to appreciate and quantify the detrimental effects of oxygen involvement during the HIP manufacture process on the microstructural and material properties of the resulting component. This paper quantifies the effects of oxygen content on the microstructure and Charpy impact properties of HIP’d austenitic stainless steel, through combination of detailed metallographic examination and mechanical testing on HIP’d Type 316L steel containing different concentrations (100 to 190 ppm) of oxygen. Micron-scale pores were visible in the microstructure of the HIP’d materials postmetallographic preparation, which result from the removal of nonmetallic oxide inclusions during metallographic preparation. The area fraction of the resulting pores is shown to correlate with the oxygen concentration which influences the Charpy impact toughness over the temperature range of 77 K to 573 K (−196 °C to 300 °C), and demonstrates the influence of oxygen involved during the HIP manufacture process on Charpy toughness. The same test procedures and microstructural analyses were performed on commercially available forged 316L. This showed comparatively fewer inclusions and exhibited higher Charpy impact toughness over the tested temperature range.

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Effect of Oxygen Content Upon the Microstructural and Mechanical Properties of Type 316L Austenitic Stainless Steel Manufactured by Hot Isostatic Pressing

With near-net shape technology becoming a more desirable route toward component manufacture due to its ability to reduce machining time and associated costs, it is important to demonstrate that components fabricated via Hot Isostatic Pressing (HIP) are able to perform to similar standards as those set by equivalent forged materials. This paper describes the results of a series of Charpy tests from HIP’d and forged 304L and 316L austenitic stainless steel, and assesses the differences in toughness values observed. The pre-test and post-test microstructures were examined to develop an understanding of the underlying reasons for the differences observed. The as-received microstructure of HIP’d material was found to contain micro-pores, which was not observed in the forged material. In tested specimens, martensite was detectable within close proximity to the fracture surface of Charpy specimens tested at 77 K (−196 °C), and not detected in locations remote from the fracture surface, nor was martensite observed in specimens tested at ambient temperatures. The results suggest that the observed changes in the Charpy toughness are most likely to arise due to differences in as-received microstructures of HIP’d vs forged stainless steel.

/pdf/a-microstructural-study-on-the-observed-differences-in-1oan31o1gp.pdf

A Microstructural Study on the Observed Differences in Charpy Impact Behavior Between Hot Isostatically Pressed and Forged 304L and 316L Austenitic Stainless Steel

The effect of δ ferrite morphology and grain boundary property on the low temperature toughness of austenitic stainless steel SUS304L weld metal has been studied The types of δ ferrite were classified into three categories : vermicular, lacy, and globular When Charpy test were performed at low temperature, brittle fracture easily occurred in a vermicular type δ ferrite because the longitudinal direction of this δ perallel to [100]δ, that is a cleavage plainOn the other hand, brittle fracture scarcely occurred in both a globular type and a lacy type δ ferrite, because the the stress concentration must be low at globular type δ and the Kurdjumov-Sachs (K-S) relationship holds between lacy type δ and γ phase Grain boundary holding the K-S are coherence to grains and hardly cause the decohesionThe present data indicate that changing the δ ferrite morphology from a vermicular type to lacy type prevents the cleavage fracture and increases the fracture toughness at low temperature

Effects of delta ferrite morphology on low‐temperature fracture toughness of austenitic stainless steel weld metal

Development of novel MIG welding process with duplex current feeding

In the gas shield arc welding with SUS304 austenitic stainless steel base metal and, JISY308L type electrod, the effect of the welding condition on the oxygen content and microstructure of weld metal has been investigated. Next, the effect of the oxygen on the mechanical properties, mainly on the fracture toughness, were studied. The main results are summarized as follows;1) The oxygen content of weld metal is increased with dicreasing the welding current (from 200A to 400A) and with increasing the arc voltage (from 20V to 30V). At the constant welding atmosphere, there is a linear correlation between the oxygen content and a parameter of A/V which is established by the authors, where A is welding current and V is arc voltage. The oxygen content decreases with increasing the parametre A/V.2) The most of the oxygen exists in the γ region as the spherical oxide of Mn-Silicate. The number of oxide per unit volumu is related to the welding heat input. The number decreases with increasing the heat input.3) Charpy impact values and Jin values decrease with increasing the oxide volume fraction.4) The relationship between Charpy impact value and oxide volume fraction is represented by linear line on the log-log cordinate. At the constant oxide voulme fraction, the distribution (number and size) of oxide has little effect to Charpy impact value.

藤田春彦

Papers

Sus 304 mig溶接金属中の酸素と破壊靱性に関する研究

藤田 春彦

Papers

Sus 304 mig溶接金属中の酸素と破壊靱性に関する研究

藤田春彦