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.

/pdf/effect-of-oxygen-content-upon-the-microstructural-and-ptxhfu13if.pdf

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

In the present article, an attempt was made to review the weldability of high nitrogen steels. In the last few years, a lot of work has been put into a better understanding and processing of this class of steels. Through our metallurgical knowledge, it is obvious that the nitrogen content in the weld zone is the essential factor. It is a major task to identify all parameters influencing nitrogen content in the weld metal.

Welding of High Nitrogen Steels

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

A B S T R A C T This study explores an innovative metal machining process by using bacteria. Acidithiobacillus ferrooxidans (At. ferrooxidans) was used to remove metal. The bacteria first carried out the oxidation of Fe 2+ to Fe 3+ . The produced Fe 3+ then oxidized the metals. The machining of copper, nickel and aluminum was experimentally investigated using both the cells and the culture supernatant of At. ferrooxidans. The material removal rates of these three metals were 2.0, 1.6, 0.55 and 5.5, 4.2 and 0.7 mg/h cm 2 by using cells and culture supernatant, respectively. Higher metal removal rate was achieved for copper by using the culture supernatant. A microbe-based fabrication of micropattern is thus feasible applying the current principle. 2012 CIRP.

Metal removal by Acidithiobacillus ferrooxidans through cells and extra-cellular culture supernatant in biomachining

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.

Sus 304 mig溶接金属中の酸素と破壊靱性に関する研究

Relationship between the microstructure and the fracture behavior of welds which were tested by Charpy impact on SUS329J1 (Fe-25Cr-5Ni-0.1N) stainless steel has been studied.Volume fraction of γ phase decreases at HAZ which has been heated over 1400K. At the region over 1600K, the morphology of γ also change to Widmanstatten and the Kurdjumov-Sachs relation exists between γ and α phase, so the phase boundary has good coherency.There is certain relationship between crack propagation and microstructure. When the Charpy test performed at room temperature, tearing or voids occur in α region, because the ductility and strength of γ phase are higher than ones of α. γ phase is deformed at the circumference of dimple and γ maintains the ductility of duplex steel.Consequently, the fracture toughness increases with increasing the γ volume fraction.At low temperature, cleavage fracture occurs in a phase, same time γ phase plays the part of a little obstacles to crack propagation. In Widmanstatten like γ, Charpy impact value slightly increases with increasing the volume fraction of γ phase. In band like γ, a separation of α-γ phase boundary occurs and the crack propagates zigzag manner, so the impact value increases more substantially than widmanstatten like γ in the case of crack propagation normal to the γ phase.

Sus 329 j1二相ステンレス鋼溶接部の破壊靱性に及ぼす金属組織の影響

Bacteria living in natural environments usually attack metals leaving unacceptable corrosion and causing critical deterioration. This negative phenomena is studied in this paper in a positive sense by means of control of these bacteria for the purpose of biomachining of metals. The main objective of this research is the achievement of a low cost machining process at normal temperature with less energy involvement and more involvement of bacteria in biomachining without straining them. The main focus in this paper is on the effect of Thiobacillus ferrooxidans, iron oxidizing bacteria and their ability to oxidize iron. It has been found that the extent of corrosion of carbon steel in the presence of Thiobacillus ferrooxidans was remarkably large. A tendency towards preferential corrosion offerrite was also observed. The results of our experiments show that biomachining using Thiobacillus ferrooxidans is possible by controlling the structure of steel.

Fundamental studies on biomachining of carbon steel by iron oxidizing bacteria

Microstructure and fracture toughness of 316L high nitrogen weld metal produced by high-pressure nitrogen arc welding

https://www.jstage.jst.go.jp/article/qjjws/24/3/24_3_253/_pdf

神谷修

Papers

Sus 304 mig溶接金属中の酸素と破壊靱性に関する研究

Sus 329 j1二相ステンレス鋼溶接部の破壊靱性に及ぼす金属組織の影響

Fundamental studies on biomachining of carbon steel by iron oxidizing bacteria

Microstructure and fracture toughness of 316L high nitrogen weld metal produced by high-pressure nitrogen arc welding

Sn-3.5Ag,Sn-0.7Cu鉛フリーはんだの表面変形度合による低サイクル疲労寿命の定義

神谷 修

Papers

Sus 304 mig溶接金属中の酸素と破壊靱性に関する研究

Sus 329 j1二相ステンレス鋼溶接部の破壊靱性に及ぼす金属組織の影響

Fundamental studies on biomachining of carbon steel by iron oxidizing bacteria

Microstructure and fracture toughness of 316L high nitrogen weld metal produced by high-pressure nitrogen arc welding

Sn-3.5Ag,Sn-0.7Cu鉛フリーはんだの表面変形度合による低サイクル疲労寿命の定義

神谷修