Effects of low-temperature transformation and transformation-induced plasticity on weld residual stresses: Numerical study and neutron diffraction measurement

Influence of filler metals and welding techniques on the structure–property relationships of Inconel 718 and AISI 316L dissimilar weldments

Review: Low transformation temperature weld filler for tensile residual stress reduction

There have been considerable efforts to create welding consumables which on solid state phase transformation partly compensate for the stresses which develop when a constrained weld cools to ambient temperatures. All of these efforts have focused on structural steels which are ferritic. In the present work, alloy design methods have been used to create a stainless steel welding consumable which solidifies as δ ferrite, transforms almost entirely into austenite which then undergoes martensitic transformation at a low temperature of about 220°C. At the same time, the carbon concentration has been kept to a minimum to avoid phenomena such as sensitisation. The measured mechanical properties, especially toughness, seem to be significantly better than commercially available martensitic stainless steel welding consumables, and it has been demonstrated that the use of the new alloy reduces distortion in the final joint.

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Stainless steel weld metal designed to mitigate residual stresses

Weld filler alloys that exploit transformation plasticity through low austenite to martensite transformation temperatures offer an effective method of reducing residual stresses in strong steel wel ...

Effect of interpass temperature on residual stresses in multipass welds produced using low transformation temperature filler alloy

A low transformation temperature (LTT) welding consumable has been developed to prevent cold cracking in high strength steel welded joints without preheating In the LTT welded joint, the residual tensile stress is reduced by martensitic expansion of weld metal formed by the LTT consumable In the weld cracking tests, cold cracking in the LTT weld metal is successfully prevented under high restraint conditions, but cold cracking occurs at very low joint restraint strength in case the weld metal is fully martensitic Chemical compositions of the consumable are designed to retain austenite in martensite in the newly developed weld metal to absorb the diffusible hydrogen into the austenite to prevent cold cracking In the newly developed LTT weld metal, cold cracking is almost fully suppressed without preheating under every joint restraint condition

Development of new low transformation temperature welding consumable to prevent cold cracking in high strength steel welds

There has been growing interest in high strength steel with a tensile strength higher than 800 MPa, which would be ideal for weight reduction and better performance of steel structures. However, there are two major problems in the application of high strength steel to structures. One is that the fatigue strength of welded joints is far lower than that of the base metal, and the other is that the weld metal and the heat-affected zone (HAZ) are likely to have cold cracking. These problems must be solved before high strength steel can be widely used in steel structures. As a solution to the problem of cold cracking, a reduced preheating type of high strength steel has recently been developed in which cold cracking in the HAZ is reduced by reduction of alloy components (lower Ceq, Pcm) without loss of strength. However, since the resistance to cold cracking of the weld metal has not been improved, preheating of the weld metal is still necessary, and the problem remains toward its wider use. Recently, Ohta et al. developed a low transformation-temperature welding consumable, in which compressive residual stress is induced by transformation expansion of martensitic transformation of weld metal at a low temperature near room temperature, and demonstrated that this consumable improves the fatigue strength of welded joints. We considered that the reduction of tensile residual stress in the low transformation-temperature welding consumable might also be effective in decreasing the cold cracking and that this consumable would be useful in manufacturing high performance welded joints with improved fatigue strength and cold-cracking resistance. In the present study, we examined the effects of low temperature-transformation weld materials on the prevention of cold cracking in high strength steel. Firstly, the y-shaped weld cracking tests demonstrated that reduction of residual tensile stress induced by martensitic transformation expansion of weld metal was effective in reducing cold cracking. Secondly, the effects of the degree of joint constraint on cold cracking in low transformation-temperature weld materials were examined by the y-shaped and H-shaped weld cracking tests. The cracking ratio was high at low degrees of joint constraint and low at high degrees of joint constraint. Two causes were considered: one was that the reduction of tensile residual stress by transformation expansion is higher at a higher degree of joint constraint, and the other was that the weld metal of martensitic structure alone is sensitive to cold cracking. According to the above investigation, we attempted to develop a weld material with high resistance to cold cracking at different degrees of constraint. To maintain the effects of reduction of tensile residual stress by transformation expansion to reduce the amount of diffusible hydrogen and the sensitivity of cracking, which are other causes of cracking, we designed and developed a 2-microstructure phase weld metal (martensite + retained austenite) by modifying the low temperature-transformation weld material to obtain a lower Ms point. We examined the effects of the degree of joint constraint on cold cracking, and confirmed that the cracking rate of the modified rod was almost 0% at all degrees of constraint, and its resistance to cold cracking was high.

Development of New Low Transformation-Temperature Welding Consumable to Prevent Cold Cracking in High Strength Steel Welds

(57) [Summary] (Modifications required) [Problem] To propose a fillet welding method for high-strength thick-walled steel materials capable of obtaining a sufficient throat thickness without generating welding defects even with a heat input of 200 kJ / cm or less. . [Solution] Tensile strength of 590 MPa class or more, sheet thickness 45 mm In the welding method of forming a T-joint between the grooved web material and the flange material by two-electrode downward submerged welding, as a welding material, a sintering flux containing iron powder: 20 to 40 wt%, and C content Use a welding wire whose amount satisfies the following equation. 0.36 × C pl + 0.34 × C w ≦ 0.10 where C pl is the C content of steel (wt%), C w is the C content of wire (wt%) The leading electrode has a current of 1400 A or less and a voltage of ( 0.0 05 x Leading electrode current (A) +23)-(0.005 x Leading electrode current) (A) +32) V, the voltage of the trailing electrode is (0.005 × current of the trailing electrode) (A) +25) to (0.005 x leading electrode current (A) +40) V, partial penetration welding under the conditions that the welding speed is 21 / min or more and the heat input is 200 kJ / cm or less.

Fillet welding method of high strength thick plate steel

In order to improve fatigue strength in welded joints, low transformation-temperature welding wire has been developed in which residual tensile stress can be reduced. In application of the low transformation-temperature welding wire, the prevention of cold cracking without preheating in high strength steel welded joints is expected and examined from the control of residual tensile stress. However, it is expected that residual stress distribution in a welded joint can be suggested by numerical analysis, because the residual stress cannot be measured simply and non-distractively. In this report, martensite transformation behaviour such as Ms point, transformation expansion, and so on is measured firstly by the Formaster test. And temperature dependence of several mechanical properties was measured in full-austenite and full-martensite microstructures, and temperature dependence of mechanical properties was estimated in dual phase microstructure of austenite and martensite. By these data, numerical analysis ...

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Analysis of martensite transformation behaviour in welded joints of low transformation-temperature materials

PROBLEM TO BE SOLVED: To provide a welding method of a thick steel plate which is suitable for pipe making welding of large diameter steel pipes such as UOE steel pipe with a thickness of ≥30 mm and spiral steel pipe. SOLUTION: In welding a steel material with a thickness of ≥30 mm or more from both sides, an electrode for gas shielded arc welding is arranged, as multi-electrode welding as necessary, in the front in the welding direction of the first electrode in multi-electrode submerged arc welding for hybrid welding. In the hybrid welding, the multi-electrode submerged arc welding is performed with a heat input to satisfy an expression (1) while, desirably, the gas shielded arc welding is performed with a heat input to satisfy an expression (2). If the gas shielded arc welding is multi-electrode welding, the wire diameter to be applied for the first electrode is ≥1.4 mm, with a current density set at ≥500 A/mm 2 . Provided that 0.18t-3≤Q S ≤0.35t-5.5 (1), where t is the thickness (mm) of the steel material and Q S is a welding heat input (KJ/mm) of multi-electrode submerged arc welding, and that Q G ≤0.17t-1.5 (2), where t is the thickness (mm) of the steel material and Q G is a welding heat input (KJ/mm) of gas shielded arc welding. COPYRIGHT: (C)2011,JPO&INPIT

Naoya Hayakawa

Papers

Development of new low transformation temperature welding consumable to prevent cold cracking in high strength steel welds

Development of New Low Transformation-Temperature Welding Consumable to Prevent Cold Cracking in High Strength Steel Welds

Fillet welding method of high strength thick plate steel

Analysis of martensite transformation behaviour in welded joints of low transformation-temperature materials

Welding method of thick steel plate