9Cr-1Mo Steel Weld Research Articles

Microstructural zones in the primary solidification structure of weldment of 9Cr-1Mo steel

The present article describes the microstructural heterogeneity in the weldments of 9Cr-1Mo steel, in the as-welded condition. The thermal cycle, which each microscopic region undergoes, depends on its distance from the source of heat. The consequent differences in the type of phase transformations experienced by the various zones are established using detailed analytical transmission electron microscopy studies. Based on these studies, distinct microstructural zones are identified and the temperature profiles of the same are deduced.

Secondary ion mass spectroscopy and surface profilometric characterisation of oxide scales developed over weld metal,heat affected zone, and base metal regions of 9Cr-1 Mo steel weldments

Microstructurally different regions (namely the weld metal, heat affected zone (HAZ), and base metal) were characterised in weldments of 9Cr-1Mo steel, and composite specimens comprising the three regions were oxidised in air at 923 K. As measured by surface profilometry, the weld metal region was found to form a thicker oxide scale than the other regions of the weldment. The difference in thickness between the scales over the weld and adjoining H AZ regions was found to be ∼ 5 μm after 4 h but had increased to ∼ 100, μm in 100 h. Difference in thickness between the scales was also confirmed by a few examinations using scanning electron microscopy (SEM); this method also described the difference in morphology of the scales developed over the three regions. Secondary ion mass spectroscopy (SIMS) depth profiles of iron and chromium in scales developed over the different regions of the weldments have suggested a considerably higher chromium content of the inner scales on the H AZ and base metal than that of the scale over the weld metal; SIMS profiles have also corroborated formation of a thicker scale over the weld metal, as assessed earlier by surface profilometry and SEM

Secondary ion mass spectroscopy and surface profilometric characterisation of oxide scales developed over weld metal,heat affected zone, and base metal regions of 9Cr-1 Mo steel weldments

Secondary ion mass spectroscopy and surface profilometric characterisation of oxide scales developed over weld metal,heat affected zone, and base metal regions of 9Cr-1 Mo steel weldments

Evaluation of microstructures in 2.25Cr-1Mo and 9Cr-1Mo steel weldments using magnetic Barkhausen noise

Magnetic Barkhausen Noise (MBN) measurements have been used to characterise different microstructural regions such as coarse grain region, fine grain region, intercritical structure (composed of retained austenite and tempered ferrite) within the heat affected zone (HAZ) of 2.25Cr-1Mo steel and 9Cr-1Mo steel weldments using simulated HAZ microstructure samples. It is observed that MBN level decreases with increase in hardness corresponding to different microstructures. This behaviour has been confirmed by the measurements on the actual weldments of 2.25Cr-1Mo steel and 9Cr-1Mo steels. It has been observed that the intercritical region and the base metal region can be distinguished from the peak position of MBN which would be useful for measuring the extent of HAZ non-destructively. This study also shows the possibility of measuring the extent of different microstructural regions using miniature MBN probes with prior calibration.

Stress corrosion cracking and hydrogen embrittlement susceptibility studies on modified 9Cr-1Mo steel weldments in acidic and neutral media

Stress corrosion cracking and hydrogen embrittlement susceptibility studies on modified 9Cr-1Mo steel weldments in acidic and neutral media

Stress corrosion cracking and hydrogen embrittlement susceptibility studies on modified 9Cr-1Mo steel weldments in acidic and neutral media

There is much scope for the development of new engineering materials for high temperature applications such as for tubing used in steam generation in fossil fuel and nuclear power plants and in petrochemical cracking units. The materials for such applications are often manufactured from mild steel and low alloy ferritic steels containing up to 9%Cr. Modified 9Cr-1Mo ferritic steel, prepared by incorporating vanadium and niobium, is one of the newer materials extensively used for high temperature applications. A study of weldments of this alloy and its susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement was carried out in acidic and neutral media. The anodic behaviour of modified 9Cr-1Mo under 90% proof stress was also examined. Mechanical properties of the material were assessed before and after SCC and hydrogen embrittlement tests. The SCC tests were made at various anodic potentials in 1M H 2 SO 4 and showed that the welded alloy is not susceptible to SCC in all three critical zones. The alloy was, however, susceptible to SCC in chloride environments, namely a solution containing equal volumes of 1M NaCl and 1M MgCl 2 . Fractographic analysis was carried out to determine the reasons for the failure of this alloy. The hydrogen embrittlement studies in 1M H 2 SO 4 showed that the alloy is prone to delayed hydrogen cracking at more negative potentials. The fractographic examination using scanning electron microscopy revealed the presence of adsorbed hydrogen in microvoids which were responsible for the failure of the alloy. Other possible reasons for the failure of the alloy are also discussed.

Hot tensile properties of simulated heat-affected zone microstructures of 9Cr1Mo weldment

The heat-affected zones (HAZ) of 9Cr1Mo steel weldments consist of coarse-grain martensite with δ-ferrite, coarse-grain martensite, fine-grain martensite and intercritical structure. These HAZ microstructures have been simulated with respect to microstructure, hardness and grain size by isothermal heat treatment cycles in the temperature range 973–1573 K. Tensile tests at a strain rate of 3 × 10 −4s −1 over the range 298–873 K showed that 0·2% YS and UTS values for the various microstructural conditions were in the descending order of coarse-grain martensite, coarse-grain martensite with δ-ferrite, fine-grain martensite, base metal and intercritical structure. The presence of δ-ferrite in the coarse-grain region of HAZ restricted the grain growth, the increase in strength and the decrease in ductility. This minimises the problem of cracking in the coarse-grain region of HAZ in this steel which is often encountered in low-alloy CrMo ferritic steels. The regions with intercritical structure showed the lowest strength and fracture energy. Fine-grain martensite exhibited a good combination of strength and ductility in the HAZ.

The Effect of Operating Temperature Exposure on Non-Post-Weld Heat Treated 2.25Cr–1Mo Steel Weldments

Usually a post-weld heat treatment is performed on weld repairs for heavy section low alloy 2.25Cr–1 Mo steel power plant components. This procedure relieves the stresses in the weldment and results in improvements in both the room and high temperature properties. A significant saving, in both time and cost, could be realized if the post-weld heat treatment could be safely eliminated by an in situ heat treatment or non-post-weld heat treatment.In the present work, two different multi-pass and multi-layer welding procedures were employed and the resulting welds were subjected to a simulated in situ heat treatment of 538°C for up to 4000 h. The first procedure followed the relatively standard weaving method of pressure pipe welding, while the second involved a low heat input ratio temper-bead technique. A refined grain structure, within the HAZ was observed for both welding procedures. After exposure, at the simulated operating temperature of 538°C, there was an initial rapid reduction in hardness and an increase in toughness. Carbide development had a major influence on the mechanical properties. The conventional welding procedure resulted in a higher degree of tempering than the temper-bead weld procedure. Résumé Habituellement, apres une soudure on effectue un traitement thermique sur les soudures de réparation pour les sections lourdes des composants de centrales électriques en acier faiblement allié 2.25Cr–1Mo. Ce procédé soulage les contraintes des soudures et permet d'en améliorer les propriétés aussi bien à haute température qu'a température ambiante. Si on pouvait éliminer, sans risque, le traitement thermique après soudure au profit d'un traitement thermique in-situ ou d'un traitement thermique antérieur à la soudure, on réaliserait d'importantes économies de temps et d'argent.Dans les travaux présentés, on a utilisé deux procédés différents de soudures, un par passages multiples, l'autre par couches multiples. On a soumis les soudures ainsi obtenues à des simulations de traitement thermique in-situ à 538°C pendant 4000 heures. Pour le premier procédé, on a suivi la méthode relativement classique de soudure de tuyaux sous pression au moyen de tissage, alors que pour le second on a utilisé la technique de colliers de recuits à faible taux de chauffage. Les deux procédés de soudure ont permis d'observer une structure de grains affinés au sein du HAZ. Après exposition à la température opérationnelle simulée de 538°C, il y a eu une rapide réduction initiale de la dureté et une augmentation de la ténacité. Le développement de carbures a une influence majeure sur les propriétés meéaniques. Le procédé conventionel de soudure a pour résultat un plus haut degré de revenu que le procédé de soudure par collier de recuit.

The Effect of Operating Temperature Exposure on Non-Post-Weld Heat Treated 2.25Cr–1Mo Steel Weldments

The Effect of Operating Temperature Exposure on Non-Post-Weld Heat Treated 2.25Cr–1Mo Steel Weldments

Oxidation behavior of microstructurally-Different regions in the weldment of 9Cr-1Mo steel

Regions with different microstructures have been identified in the weldments of 9Cr-1 Mo steel. Weldments comprising threthree regions, i.e., weld metal, heat-affected zone (HAZ), and base metal, were oxidized in air at 923 K for different durations up to 500 hr. The crown area of the weld metal was found to form a thicker oxide scale than the other regions of the weldment. When the oxidation kinetics of different regions were compared (by separating out the coupons of the HAZ and the crown and root portions of the weld metal and then oxidizing them), the crown area of the weld was found to oxidize at a much higher rate than the others. Scanning electron microscopy (SEM) was carried out to assess the morphological variations in the different regions of the weldment. The compositional variations in the scales over the different regions have been characterized by the energy-dispersive analyses of X-rays (EDX), and the results thereof have also been corroborated by secondary ion mass spectrometry (SIMS).

The tempering performance of low-alloy steel weldments

High-energy piping systems are frequently fabricated from 1 2 Cr 1 2 Mo 1 4 V steel components joined by multipass 1 4 Cr1 Mo steel weldments. The creep behaviour of these weldments is then related both to the range of microstructures developed during manufacture and the effect of long-term, high-temperature exposure on microstructural changes. In the present work, laboratory aging experiments which simulate in-service tempering have been performed. Results indicate that for conditions equivalent to those encountered up to the nominal weldment design life, tempering effects are consistent with diffusion controlled coarsening of carbides. However, for more extreme situations, coarse grained ferrite of low hardness is developed within the weld heat-affected zone. The implications of these microstructural changes on high-temperature performance are discussed.

General corrosion behaviour of modified 9Cr–1Mo steel weldments in acidic environments

Abstract The general corrosion behaviour of modified 9Cr–1Mo (T91) steel weldments has been studied in acid media (sulphuric and phosphoric acids containing 1% nitric acid).The work has involved weight loss measurements and potentiodynamic polarisation and impedance measurements for different regions of the weldment at different temperatures. The corroded surface and the nature of the corrosion products have been examined and characterised by scanning electron microscopy, electron probe microanalysis (EPMA),and X -ray diffraction. In sulphuric acid the material exhibits more corrosion than in phosphoric acid. The lower rate of corrosion in phosphoric acid is attributed to a possible phosphate film, as confirmed by impedance and other surface examination studies. With an increase in temperature it is found that the overall corrosion rate increases in all zones of the weldment. In general the weld zone and heat affected zone have been found to show greater corrosion than the parent metal. Impedance studies ...

Estimating remaining life of elevated-temperature steam pipes—Part II. Fracture mechanics analyses

Recently developed time-dependent fracture mechanics concepts were employed to establish a remaining life prediction methodology and an inspection criterion for seam-welded steam pipes. The material properties of 2-1 4 Cr-1Mo steel weldments reported in Part I of this paper were utilized to estimate the remaining life of a typical steam pipe. Leak-before-break analysis was performed to determine the flaw inspection criteria. Both continuous loading and interrupted loading conditions were considered in the life prediction analysis. Increasing the frequency of shutdowns was found to reduce the remaining life. The effects of operating pressure and temperature, and material properties on the remaining life of a steam pipe were quantitatively evaluated.

ＦＢＲ用溶接継手の高温低サイクル疲労，クリープ及びクリープ疲労強度評価例

To establish an evaluation method of elevated temperature strength for weldments, a series of investigations1)-5) had been performed on the low-cycle fatigue strength. In this study, the suitable evaluation methods of creep and creep-fatigue strengths for weldments were proposed and were applied to the life prediction of FBR weldments.The following results were obtained.(1) In the evaluation of low-cycle fatigue strength for the weldments, the accuracy of life prediction by the Method (I), Method (II) and FEM was determined mainly by the difference in cyclic deformation resistance between the base metal and the weld metal. The Method (I), Method (II) and FEM were effective for the weldments which have small difference in cyclic deformation resistance such as stainless steel and 21/4 Cr-1 Mo steel with PWHT. But for the weldments which have large difference in cyclic deformation resistance such as the 21/4 Cr-1 Mo steel without PWHT, the Method (I) predicted the life overconservatively and FEM overestimated the life inversely.(2) In the evaluation of creep strength for the weldments, the minimum creep strain rate of the 21/4 Cr-1 Mo steel weldment was predicted by the Independent Method which paid attention to only the weakest part of the weldment and also by the Interaction Method which considered the interaction between the base metal and the weld metal. Both of them were found to be effective for the 21/4 Cr-1 Mo steel weldments.(3) In the evaluation of creep-fatigue strength for the weldments, a new method was proposed which was an extension of the fatigue evaluation method (I) based on the linear damage summation rule. It could predict the life of the 21/4 Cr-1 Mo steel weldments within a factor of two on life.

Hydrogen Attack kinetics of 2.25 Cr-1 Mo steel weld metals

The kinetics of Hydrogen Attack (HA) of the base metals and the weld metals of two Q&T 2.25 Cr-1 Mo steel weldments made by different techniques (SMAW and SAW) were studied in the temperature range 460 to 590°C (860 to 1094 °F) and 10 to 23 MPa of hydrogen. A sensitive dilatometer used to measure the rate of HA showed that the weld metals suffered HA at significantly higher rates than the base metals. The SMAW weld metal was inferior to the SAW weld metal and swelled nearly an order of magnitude faster than the base metal. This behavior is due to a significantly higher bubble density, and a resulting higher contribution of power law creep of the matrix. The SAW behavior was intermediate between those of the base metals and the SMAW. For the same hydrogen pressure the operating limit of the SMAW weld would be roughly 100°C lower than that of the base metals, and that of the SAW roughly 50°C lower.

低温溶接後熱処理時の水素濃度変化と処理条件との関係――低温溶接後処理による２１／４Ｃｒ‐１Ｍｏ鋼厚板突合せ溶接部の横割れ防止について ＩＩＩ

In order to clarify the relationship between the reduction of hydrogen concentration through low temperature postweld heat treatment (LTPWHT) and its treating conditions, the analyses on the diffusion of hydrogen during the treatment were carried out using an analytical computer program in which the influence of the gradient of hydrostatic stress caused by welding residual stress distributions was taken into consideration.As a result, it was found that the ratio of the highest hydrogen concentration at any time during the treatment to the hydrogen concentration at the point right below the final pass of welds just after welding, could be arranged by a parameter (τ+Dptp), where r and Dptp are the parameter of hydrogen diffusion determined from welding conditions and the product obtained by multiplying the diffusion coefficient at a temperature of the postweld heat treatment by its holding time, respectively. The influences of the dimensions of the weld zone, such as plate thickness or groove width, upon its relationship were also clarified.Moreover, the diffusion coefficient of hydrogen for 2 1/4Cr-1Mo steel weldments, which becomes necessary to determine the conditions of the heat treatment for preventing the cracks, was determined in the temperature range of 150°C through 300°C.

２１／４Ｃｒ‐１Ｍｏ鋼厚板溶接部の横割れ防止低温溶接後熱処理条件 低温溶接後熱処理による２１／４Ｃｒ‐１Ｍｏ鋼厚板突合せ溶接部の横割れ防止について ＩＶ

A series of researches has been conducted in order to establish the procedure of the Low Temperature Postweld Heat Treatment (LTPWHT) superseding the conventional intermediate stress relief annealing, by which the prevention of the transverse weld cracks induced in the thick 2-1/4Cr-1Mo steel weldments by submerged arc welding process can be made possible.First we found that this kind of crack could be prevented by only reducing hydrogen concentrations in the weld zone. Then, following this result, the relationship between hydrogen concentrations in the weld zone just after welding and the practical welding conditions was investigated, as was described in Report 2. Next, we proceeded to clarify the relation between the reduction of hydrogen concentrations through LTPWHT and its treating conditions in the previous paper.As the final step of this research, cracking tests were carried out to evaluate the critical hydrogen concentration under which the cracks did not occur at all, by comparing both results of the cracking tests and calculations on the distributions of the hydrogen concentrations obtained in the weld zone under the same conditions as the cracking tests. As a result, it was found that the highest hydrogen concentration had to be reduced to less than 3.3 cc/100 gr after LTPWHT in order to prevent the cracks. Adding this result to the results obtained previously made it possible to determine the appropriate conditions of the LTPWHT for preventing the cracks under a wide variety of the welding conditions, such as plate thickness, groove width, preheat and interpass temperature, and pass interval.An additional investigation clarified that a newly developed material of the low hydrogen flux had a large effect upon the mitigation of the LTPWHT conditions for preventing the cracks.