HAZ Toughness Research Articles

Ｔｉオキサイド系溶接低温用高張力鋼板の開発

Ｔｉオキサイド系溶接低温用高張力鋼板の開発

Low temperature fracture toughness in coarse-grained weld HAZ of steels for low temperature service

Low temperature fracture toughness in coarse-grained weld HAZ of steels for low temperature service

Welding Metallurgy of Structural Steels

composition requirements for improved cold cracking susceptibility and HAZ toughness, along with the importance of low CE to both properties. TMCP operating mechanisms are then described together with conditions for optimizing their effects on the weldability of structural steels with lowtemperature toughness consistent with Arctic marine environments, tensile strengths > 500 Mpa, and thicknesses of 50 to 100 mm. Recent results at NKK with 63-mm plates are shown in Table I. The stable, accurate control required for producing TMCP steels can be adequately met by present levels of technology, but drawbacks of the process may include a heavy penalty in rolling efficiency. In his paper "A Viewpoint on the Weldability of Modern Structural Steels," P.R. Kirkwood of the British Gas Corporation discussed the controversy which has led to the belief that modern structural steels, particularly the lower sulfur steels, are more difficult to weld than their counterparts of the early 70's. Extensive investigations at British Gas did not appear to support the contention that the newer steels are more difficult to weld, but the inquiry did suggest that the British Standard weldability prediction method becomes increasingly inCritical CTOD Value at woC (mm)***

高張力鋼多層盛溶接熱影響部の靭性の推定 ＩＩＩ 多層盛溶接熱影響部の組織分布と靭性に関する研究

The method for predicting the toughness of multi-pass weld HAZ by simple thermal cycle simulation was investigated on the basis of the distribution of toughness which had been discussed in the previous report.The main results obtained were as follows.(1) It was confirmed that the toughness of single-pass weld HAZ could be predicted by single thermal cycle simulated specimen with the same cooling rate. It was difficult to predict the toughness of multi-pass weld HAZ by single thermal cycle simulated specimens.(2) Double thermal cycle simulation test (Peak temperature: 1350°C-650°C) was effective for the prediction of the toughness of multi-pass weld HAZ. That is, tempering thermal cycle (Peak temperature: 650°C) was essential for the simulation test.(3) Average toughness calculated by using value of the toughness and area fraction of each microstructure distributed in HAZ almost agreed with the measured toughness of multi-pass weld HAZ.

多層盛溶接熱影響部の組織分布と靭性に関する研究 ＩＶ 溶接熱影響部における低焼入性域の生成の要因

多層盛溶接熱影響部の組織分布と靭性に関する研究 ＩＶ 溶接熱影響部における低焼入性域の生成の要因

Fracture Toughness Testing of Maraging Steel Weldments

Evaluation of fracture toughness of 18 Ni M250 grade maraging steel weldments has been made by resorting to 'R' curve method as per ASTM E561 standard. Fracture toughness of HAZ was found to be higher than that of weld-metal. Most of the weldments passed the minimum specified value.

Weldability of low C-Nb-Ti-B steel for line pipe.

To reduce PCM value for prevention of cold cracking in girth welding and for sour environment service, low carbon steel is required. Strengthening of low carbon steel necessitates microstructural change from ferrite-pearlite to low temperature transformation products. Microalloying technique and dynamic accelerated cooling process after controlled rolling were applicable to develop low PCM high grade line pipe steel. Lowering nitrogen content is very preferable to make boron effective.From the metallurgical studies of microalloying, low G-Nb-Ti-B steel was developed.The HAZ toughness was improved by adding small amount of titanium. The risk of hot cracking was decreased by lowering carbon content. The hardenability of new type steel was considered by the effective boron contents. The P*CM formula was newly developed. The strength can be obtained with extremely low PCM level in boron treated new type steels, resulting low hardness in the HAZ.

Improvement of notch toughness and soundness in longitudinal seam weld of line pipe.

Multiple-electrode submerged arc welding process with three or four electrode is used for the production of longitudinally welded pipe. Increased welding speed is limited by the properties of flux against weld defects such as undercutting and slag inclusion and the toughness of weld metal deteriorated by impurity gas contamination.A flux with a solidification temperature of 950 to 1050°C and with a viscosity of 2.5 to 4.5 poise at 1400°C can minimize slag inclusion and undercutting. Welding of heavy wall thickness UOE pipes with a heat input above 100kJ/cm requires a flux with a high melting point and high viscosity.In order to obtain good notch toughness of weld metal at low temperature service, it is necessary to control the nitrogen content foreffective utilization of titanium and boron in weld metal. Optimum range of titanium to get high notch toughness is shifted by nitrogen content in weld metal.HAZ notch toughness of high strength line pipe is affected strongly by carbon and boron contents in base metal. Excellent notch toughness of HAZ was obtained by decreasing the carbon content in base metal below 0.05wt%.

多層盛溶接熱影響部の組織分布とじん性に関する研究 ＩＩ 高張力鋼多層盛溶接熱影響部のじん性分布

多層盛溶接熱影響部の組織分布とじん性に関する研究 ＩＩ 高張力鋼多層盛溶接熱影響部のじん性分布

Tensile Strength of Welded Joints for TMCP Type 50kgf/mm2-Class High Tensile Steel Plates

50 kgf/mm2-class high-tensile steel plate produced by newly developed TMCP (thermo-mechanical control process) is superior to conventional rolled steel plate in weldability (resistance to low-temperature cracking) as well as in toughness of HAZ of the high heat-input welded joint.However, HAZ of high heat-input welded joint softens because of the low carbon equivalent.The authors investigated the tensile strength of the welded joint with soft HAZ in ship hull and other heavy steel structures.As a result, it was found that even with the maximum heat-input welding process prevalently in use in most of the domestic ship-yards, the tensile strength of the welded joint thereby produced in wide plate would be 50 kgf/mm2 or more and approximate that of the base metal when Ceq. _≥0.23%.

低窒素鋼の再現熱影響部のじん性とＴｉ及びＡｌの影響

Effects of Ti and Al in steels on the notch toughness of the synthetic weld heat affected zone have been investigated using 41 kgf/mm2 grade steels containing various quantities of N. The results obtained are as follows: (1) Synthetic HAZ toughness of the steel containing 13 ppm of N is the most superior to the other all steels. Charpy transition temperature (vTrs) is droped about 15°C per the decreasing of 10 ppm of N. When N in steels is less than 20 ppm, additions of Ti and/or Al deteriorate the notch toughness. (2) Notch toughness is improved by Ti addition, especially, when Ti is added about 3.4 times of N content, the notch toughness becomes the best, because of the decreasing of free N content and the refining of microstructures on each N content of 20 to 60 ppm. (3) Even if the ratio of Ti and N contents, Ti/N, is 3.4, the notch toughness is improved with the decrease in N content of steels. However, when 0.06 wt% of Al is added in steels containing more than 0.015 wt% Ti and more than 50 ppm N the notch toughness is further improved. (4) Optimum Ti content neccesary to improve the notch toughness is 0 wt% in steels containing 10 ppm N, and about 3.4 times of N content in more than 20 ppm N. (5) vTrs of synthetic HAZ of steels containing optimum content of Ti is very low comparing to steel without Ti and this tendency becomes remarkably as N content increases. While the additions of Al are effective in steels with nitrogen above 35 ppm.

Development of NK-HIWEL steels suitable for high-heat-input welding

This paper deals with the notch toughness of weld HAZs made by high-heat-input welding. New ideas to improve the HAZ toughness with a radical reduction of free-N in HAZ were applied to the C-Mn steel for LPG, the EH36 grade steel for large-scale arctic offshore structures, and the high-tensile-strength C-Mn steel used in low-temperature regions. The HAZ toughness of these steels was investigated. As a result, it was demonstrated that these NK-HIWEL series steels of the high-Al, low-N, micro-Ti type produce welds of excellent toughness, even under high-heat-input welding conditions.

Ｎｂ‐Ｖ系高張力鋼再現溶接熱影響部の応力除去焼なましぜい化におよぼす溶接入熱の影響

Studies are made on stress relief embrittlement of duplicated weld HAZ for 50 kgf/mm2 HTS. Degree of stress relief embrittlement expressed by Δ∇Ts is a function of weld thermal cycle cooling rate, and results showed that the highest notch toughness of stress-relieved weld HAZ was achieved in microstructure containing slight polygonal ferrite. That sort of microstructure can be obtained with thermal cycles cooling time of around 30 seconds from 800°C to 500°C for steels investigated, which shows the effectiveness for obtaining the safety of welded joints and the efficiency of welding fabrication by using comparatively high heat input of around Cf cooling time in SH-CCT diagram.Furthermore, grain boundary fracture was little found for both as duplicated and duplicated and stress-relieved HAZ, showing the significance of niobium and vanadium nitride and carbide coherent precipitation for stress relief embrittlement in weld HAZ, as it occurs transgranular cleavage fracture easily.

６０ｋｇ／ｍｍ｀２´級高張力鋼の大入熱溶接

The notch toughness of weld-HAZs deteriorates with the increase in welding heat input. The degradation of notch toughness is caused by the austenite grain growth and heterogeneous transformation products. 60 kg/mm2 grade high tensile strength steel's weld-HAZ has a stronger tendency to increase the unfabourable transformation products, for example M-A constituent, than 50 kg/mm2 grade steel's weld-HAZ, because of its higher hardnability. So it was concluded that 60 kg/mm2 grade steel's weld-HAZ showed lower notch toughness than 50 kg/mm2 grade steel's weld-HAZ, when the high heat input welding processes were used.This investigation was carried out to clarify the factors which govern the HAZ toughness and to develop the 60 kg/mm2 grade steel suitable for high heat input welding. The results were summalized as follows.(1) 60 kg/mm2 grade steel's weldment made by the electrogas are welding technique showed low notch toughness at the weld-HAZ. These deterioration could be recognized not only at the coarse grained region but also at the fine grained region in HAZ.(2) When the welding heat input was higher than 60 kJ/cm, HAZ toughness was improved with decreasing the heat input. On the other hand, HAZ toughness became to deteriorate with decreasing the heat input, when the welding heat input was lower than 60 kJ/cm.(3) Welding heat input dependency on HAZ toughness mentioned above could not be explained by metallurgical point of view. But it could be interpreted by correlation between notch position and hardness distribution. That is, when the discontinuity of strength existed near the notch, the brittle crack initiated at the notch root deviated and propagated towards weaker region. And obtained values were govrened by the characteristics of weaker region.(4) The experiment was conducted to improve the HAZ toughness. As a result, HAZ toughness of 60 kg/mm2 grade steel's weld-HAZ toughness was improved by reduction of carbonequivalent. This improvement was resulted from reduction of M-A constituent and formation of pearlite.(5) The tensile strength of low carbon equivalent type 60 kg/mm2 grade steel's weld-HAZ had a tendency to decrease at the inverse of heat input. In practice, however it was concluded that lowering the carbon equivalent in a range investigated in this study got no trouble.

Effect of heat input on HAZ toughness in HSLA steels

Commercial HSLA steel plates having different process routes, compositions, and microstructures have been welded at heat inputs from 1·5 to 9 kJ mm−1. Charpy V-notch tests were used to characterize the toughness of the resulting HAZ in the as-welded and post-weld heat-treated conditions. In general, increasing the heat input lowered the low-temperature impact toughness through the formation of high-temperature transformation products such as proeutectoid ferrite, Widmanstätten ferrite, and upper bainite. However, a controlled-rolled low-carbon HSLA steel containing nickel and molybdenum exhibited good impact toughness in all welding conditions, this being attributable to a HAZ consisting mostly of acicular ferrite. Low-carbon controlled-rolled steels had better impact characteristics than quenched-and-tempered steels. Stress relief after welding generally had no significant effect on the low-temperature toughness. Hardness values in the HAZ indicated that the steels were unlikely to be susceptible to hydrogen-induced cold cracking.

The Assessment of HAZ Toughness of Line Pipe Steels

The methodology for assessing notch toughness of the HAZ of line pipe welds was examined by studying the effect of factors such as loading rate, the significance of Gleeble simulation, and notch orientation. Increasing the loading rate from slow bend to impact testing resulted in an increase in fracture transition temperature in the CGHAZ of approximately 70° C. The notch toughness of a Gleeble simulated CGHAZ structure was comparable to that of the CGHAZ of a high heat input SAW weld for a direct quenched experimental steel. The notch toughness of the CGHAZ depended on the orientation of the notch. For surface notched specimens, one line-pipe steel had a higher toughness than another; whereas for a through-thickness notch an opposite rating was observed for the same steels. Résumé La méthodologie nécessaire pour évaluer la ténacité à l'entaille des zones influencées par la chaleur (HAZ) des soudures de pipelines a étté éxaminée en étudiant l'effet de certains facteurs tels que la vitesse de mise en charge, la signification de la simulation à l'aide de la machine Gleeble et l'orientation de l'entaille. L'accroissement de la vitesse de mise en charge à partir d'une flexion lente jusqu' à un essai d'impact a provoqué une augmentation de la température de transition de la zone à gros grains (CGHAZ) d'environ 70 %. La ténacité à l'entaille d'une structure CGHAZ obtenue à l'aide d'une machine Gleeble était comparable à celle de la CGHAZ d'une soudure SAW à grande chaleur absorbée pour un acier expérimental trempé directement. La ténacité à l'entaille de la CGHAZ dépendait de l'orientation de l'entaille. Pour des échantillons entailles à la surface, un acier avait une plus grande ténacité qu'un autre alors que pour une entaille dans le sens de l' épaisseur le classement était inversé.

The Assessment of HAZ Toughness of Line Pipe Steels

The methodology for assessing notch toughness of the HAZ of line pipe welds was examined by studying the effect of factors such as loading rate, the significance of Gleeble simulation, and notch orientation. Increasing the loading rate from slow bend to impact testing resulted in an increase in fracture transition temperature in the CGHAZ of approximately 70° C. The notch toughness of a Gleeble simulated CGHAZ structure was comparable to that of the CGHAZ of a high heat input SAW weld for a direct quenched experimental steel. The notch toughness of the CGHAZ depended on the orientation of the notch. For surface notched specimens, one line-pipe steel had a higher toughness than another; whereas for a through-thickness notch an opposite rating was observed for the same steels. Résumé La méthodologie nécessaire pour évaluer la ténacité à l'entaille des zones influencées par la chaleur (HAZ) des soudures de pipelines a étté éxaminée en étudiant l'effet de certains facteurs tels que la vitesse de mise en charge, la signification de la simulation à l'aide de la machine Gleeble et l'orientation de l'entaille. L'accroissement de la vitesse de mise en charge à partir d'une flexion lente jusqu' à un essai d'impact a provoqué une augmentation de la température de transition de la zone à gros grains (CGHAZ) d'environ 70 %. La ténacité à l'entaille d'une structure CGHAZ obtenue à l'aide d'une machine Gleeble était comparable à celle de la CGHAZ d'une soudure SAW à grande chaleur absorbée pour un acier expérimental trempé directement. La ténacité à l'entaille de la CGHAZ dépendait de l'orientation de l'entaille. Pour des échantillons entailles à la surface, un acier avait une plus grande ténacité qu'un autre alors que pour une entaille dans le sens de l' épaisseur le classement était inversé.

5.5% Ni鋼再現溶接熱影響部のじん性に及ぼす残留オーステナイトの効果

This investigation has been made of the influence of precipitated and retained austenite on impact toughness in the synthetic HAZ of 5.5% Ni cryogenic steels. Specimens were heated and cooled through the selected thermal cycles by induction heating and then the instrumental Charpy test was employed for the determination of crack-initiation and crack-propagation energy.From the result, the sufficient requirment is that the ductile fracture with plastic deformation occurs, that is, the temperature of impact test should be above the ductile-to-brittle transition temperature (DB-TT) in order to present a beneficial effect of retained austenite in HAZ on impact toughness. So the beneficial effect range of retained austenite on toughness in synthetic HAZ of 5.5% Ni steel represents the schematical diagram, lst cycle peak temperature vs. DBTT. The instrumented Charpy test reveals that the austenite phase produced by wled thermal cycles takes part in the energy of crack-propagation rather than crack-initiation.

高張力鋼の再現熱影響部の切欠靭性

Following the previous paper, the notch toughness of the weld HAZ microstructures of high strength steels was evaluated by means of the synthetic apparatus. Summalizing the whole results, including previous tests, the effects of steel composition, microstructure and other factors on the notch toughness of weld HAZ specimens have been clarified. From these discussions, the following conclusions were summalized ;(1) The notch toughness of coarsened HAZ microstructures in high strength steels was generally decreased compared that of their unaffected base metals, especially in quenched and tempered steels.(2) The toughness of HAZ microstructures was decreased in accordance with the order of decreasing hardness, namely, martensite, mixed structure (martensite and bainite), coarse bainite and pearlite or ferrite.(3) The critical carbon content at which the martensite toughness in weld HAZ was markedly declined, may be about 0.18%.(4) The superiority of the test steels, when compared to the toughness of reproduced HAZ microstructures, was convinced by the test to agree with that of the tensile ductility which obtained by synthetic HAZ ductility tests in previous studies.