Heat Affected Zone Of Base Metal Research Articles

Study of Tensile Deformation and Damage Law in Undermatching X80 Pipeline Steel Welded Joints

This study used a digital imaging technique (DIC) to obtain the strain distribution at various locations in undermatching X80 pipe girth-weld joints under uniaxial tensile loading. In addition, the microstructure characteristics and deformation patterns in different regions were analyzed by scanning electron microscopy (SEM). The results showed that there was strain heterogeneity between the various regions of the welded joint. Strain concentration existed only in the 12.8 mm base metal heat-affected zone (HAZ) and only in the elastic deformation stage. There was strain concentration in the weld metal (WM) and both sides of the HAZ close to the near-fracture stage, and the maximum deformation was in the WM. When εM = 12.2%, the KC was 6.27 and the KF was 1.73, and the KF was 113% and 152% of the KC and the KG, respectively. The large number of slip strips generated indicated serious damage in the WM near the fracture stage. In the elastic deformation stage, the strain concentration of the N1 HAZ was caused by the softened ferrite. The maximum deformation of the WM near the fracture stage was caused by the large grain size and the non-uniform martensite–austenite (M–A) islands, which may also lead to better local toughness of the cover weld and further affect the fracture mechanism of the welded joint.

Qualification of Electroslag Welds made from HPS 485W (70W) and 345W (50W) Steels

Electroslag welding (ESW) is a highly efficient welding process for completing single-pass complete joint penetration welds that offers production gains over conventional welding processes. This gain in productivity requires very high heat inputs, often to the detriment of the base metal's heat-affected zone (HAZ) impact energy. U.S. bridge-welding codes recognize the ESW Narrow Gap (termed ESW-NG) process developed in the early 1980s to remedy the substandard weld and HAZ impact energies found in bridges across the United States fabricated with the original ESW process used roughly from 1967 to 1977. ESW-NG process is limited to certain base metals; particularly, ESW-NG with quenched and tempered (Q&T), and thermo-mechanically controlled processed steels are prohibited because they are not part of the ESW-NG process development. This study was specifically performed to evaluate whether the existing ESW-NG process could be qualified for use with grade HPS 485W (70W) Q&T bridge steel and hybrid weldments between grade HPS 485W (70W) Q&T and conventionally processed grade 345W (50W) bridge steels. None of the weldments met fracture critical impact requirements. The weldment of just Q&T steel and the hybrid weldment met nonfracture critical requirements. However, the weldment of just Q&T had tension and impact resistance results right on the margin, leaving little room for error.

Mechanical resistance of stepped lamination defects in a welded section of oil and gas pipeline: a finite element analysis

The mechanical resistance of API 5L X52 steel with stepping lamination in the base metal (BM), heat affected zone (HAZ) and welding bead (WB) was studied by using the finite element method (FEM) in the present work. Both internal working pressure in the pipelines and internal pressure in the stepping laminations were studied to analyze the mechanical behavior of the pipelines. 3D FEM models and kinematic hardening were activated in the software used, while tests for the mechanical properties (true stress–strain curve) of BM, HAZ and WB were also conducted. The results demonstrated that stepping laminations in the BM–HAZ–WB zone reduced the ability to support internal pressure; therefore, the failure pressure (Pf) is also reduced. Pipeline failures occurred when the Von Mises stresses reached or exceeded the ultimate tensile stress (σUTS) of the material in the outer and inner wall and the stepping lamination sizes were too large. Failure in pipelines with stepping laminations occurred on the left side of the crack on the outer wall of the BM–HAZ zone; on the inner right side of the stepping laminations, the failure takes place on the inner wall in the WB.

Weldability of wrought Haynes\xae 282\xae repair welded using manual gas tungsten arc welding

The ability of the precipitation hardening superalloy Haynes® 282® to be repaired by multi-pass gas tungsten arc welding is investigated in this study. The repair welding has been carried out on forged discs having four pre weld heat treatments, resulting in different grain sizes and precipitate structures of the base material. Another set of discs has additionally been put through a post weld heat treatment. The tendency to form cracks in the heat-affected zone and the fusion zone has been investigated metallographically. No cracks in the base metal heat-affected zone were found, whereas solidification cracks were present in the weld fusion zone of all tested conditions. While high heat input during welding increased cracking by a factor of 1.5, none of the heat treatments had a measurable influence on the cracking behaviour. Voids with solid state crack-like appearance turned out to be aluminium-rich oxides being present from the deposition of previous weld deposit layers.

An investigation on ductility-dip cracking in the base metal heat-affected zone of wrought nickel base alloys—part I: metallurgical effects and cracking mechanism

Ductility-dip cracking (DDC) in the heat-affected zone (HAZ) of NiCr15Fe-type alloys was studied using the programmable-deformation-crack (PVR) and the strain-to-fracture (STF) test. This paper concentrates on the cracking morphology and the effect of metallurgical factors for DDC susceptibility. The obtained results are discussed in the context of the underlying cracking mechanism. Evidence was found that DDC in the heat-affected base metal occurs due to a relative grain boundary movement, which induces high strain buildup at grain boundary triple points, subsequent cavity formation, and intergranular crack propagation. Base metal grain size and intergranular carbide precipitation are shown to have a significant effect on DDC susceptibility and are discussed in the context of the observed grain boundary sliding mechanism.

An investigation of ductility-dip cracking in the base metal heat-affected zone of wrought nickel base alloys—part II: correlation of PVR and STF results

Ductility-dip cracking (DDC) in the base metal heat-affected zone (HAZ) of NiCr15Fe-type alloys was studied using the programmable-deformation-crack (PVR) and the strain-to-fracture (STF) test. This paper concentrates on the correlation of the different cracking criteria used in both tests for DDC susceptibility assessment. Full temperature-strain curves were developed for three base metal NiCr15Fe-alloy variants using the STF test. The results were compared to a previous material ranking obtained by PVR testing. To determine a local cracking criterion for base metal DDC in the PVR test, a finite element analysis (FEM) was conducted on the thermomechanical aspects of crack initiation during PVR testing. The local temperature and strain conditions associated with DDC in the PVR base metal HAZ were observed and discussed with regard to the comparability and transferability of the cracking criteria used in the PVR and STF test.

Welding of nickel-based alloy 617 using modified dip arc processes

The widespread application of nickel-based alloys as structural materials in chemical, nuclear and power generation industries is often limited due to weldability issues. Technological and metallurgical problems such as lack of fusion or hot cracking require specific welding guidelines as well as knowledge of the welding metallurgy to produce welds that fulfill high quality requirements. Due to the lower heat input modified dip arc welding is a potential alternative joining technique for hot crack sensitive nickel-based alloys. This paper contributes to the application of modified dip arc processes for butt welding of alloy 617 (2.4663). The influence of reduced heat input on microstructural and mechanical properties were investigated. Particular attention was given to the occurrence of hot cracking in the weld metal and base metal HAZ (heat-affected zone) using light optical microscopy, EDS analysis and electron probe microanalysis. The results indicate that the modified dip arc processes provide excellent weld quality and economic efficiency. However, microstructural observations showed that hot cracking in the form of microcracks could not be completely avoided. The modified dip arc welded joints exhibited good tensile strength and impact toughness. The mechanical properties are comparable to commonly GMA (gas metal arc) pulsed arc welding and are not influenced by the microcracks.

Fusion zone and heat affected zone cracking susceptibility of stabilised austenitic stainless steels

Fusion zone (FZ) and heat affected zone (HAZ) cracking behaviour of three stabilised stainless steels were studied using the Varestraint hot cracking test. Materials ranged in solidification mode from fully austenitic D9 to primary austenitic 347 and primary ferritic 321. The materials exhibited high cracking susceptibility in the FZ and base metal HAZ. In the weld metal HAZ, type 347 was highly susceptible, while alloy D9 and type 321 were resistant to cracking. The FZ cracking behaviour could be related to the stabilisation ratio (Nb, Ti)/C rather than the P + S content and Creq/Nieq ratio, as in unstabilised stainless steels. In fact, analysis of cracking data using the Creq/Nieq ν. P + S content diagram did not reveal any systematic trend in cracking susceptibility. In the base metal HAZ, the high cracking in type 347 as well as in type 321 was found to be caused by the high impurity levels in conjunction with the presence of niobium and titanium. Cracking occurred much less in alloy D9.

Fusion zone and heat affected zone cracking susceptibility of stabilised austenitic stainless steels

Fusion zone (FZ) and heat affected zone (HAZ) cracking behaviour of three stabilised stainless steels were studied using the Varestraint hot cracking test. Materials ranged in solidification mode from fully austenitic D9 to primary austenitic 347 and primary ferritic 321. The materials exhibited high cracking susceptibility in the FZ and base metal HAZ. In the weld metal HAZ, type 347 was highly susceptible, while alloy D9 and type 321 were resistant to cracking. The FZ cracking behaviour could be related to the stabilisation ratio (Nb, Ti)/C rather than the P + S content and Creq/Nieq ratio, as in unstabilised stainless steels. In fact, analysis of cracking data using the Creq/Nieq ν. P + S content diagram did not reveal any systematic trend in cracking susceptibility. In the base metal HAZ, the high cracking in type 347 as well as in type 321 was found to be caused by the high impurity levels in conjunction with the presence of niobium and titanium. Cracking occurred much less in alloy D9.

Thermal history of ht-9 weldment heat-affected zones during welding

The microstructure in weldments of HT-9, a commercial 12Cr-1Mo ferritic steel, has been observed to vary over short distances as a function of the varying thermal history during welding. The mechanical behavior response of “local” weldment microstructures can be characterized by simulation of the structure in larger usable volumes of material, if the “local” thermal history during welding is known. An empirical equation for describing the thermal history of HT-9 weldment heat-affected zones during gas tungsten-arc welding is presented in this paper. Peak temperatures and cool-down cycles are both predictable at any location in the base metal heat-affected zone for welding of plate under conditions of two-dimensional heat flow anticipated for first wall component fabrication. Power input and preheat effects are included in the equation. The equation is expected to apply to materials having a chemistry and thermal properties similar to HT-9. This includes low activation alloys based on the composition of HT-9.

原子炉用HT70鋼大型溶接継手のクリープラプチャに関する研究(第2報)

The creep rupture configuration of large welded specimens, having the shape as welded, was very different from that of conventional small welded specimens, cut off from the weld joint. The initiation of crack in rupture occurred at the toe of weld metal and the intersection of the bonds of both side weld metal. The crack propergated along the grain boundary of austenite of bond in the heat-affected zone of base metal.The mechanism of creep rupture for large welded specimens was investigated with results of high temperature tensile test and creep rupture test at 500°C for synthetic HAZ specimens. The specimens were synthesized the coarse grain part near bond (max. heating temperature 1, 350°C), the fine grain part (max. heating temperature 900°C) and the intermediate part (max. heating temperature 1, 100°C) in the heat-affected zone of base metal.By results of tests, high temperature tensile and creep rupture properties of the coarse grain part near bond were inferior to the other parts and the rupture occurred in austenite boundary. Especially, the absorbed energy to rupture of the coarse grain part near bond was smaller than that of the other parts above 400°C. Consequently, the creep rupture of large welded specimens may be occurred along the grain boundary of austenite of bond in the heat-affected zone of base metal.

原子炉用HT70鋼大型溶接継手のクリープラプチャに関する研究(第1報)

In the foregoing reports, comparison in creep rupture strength between large and small size welded specimens, discussion on the mechanism of creep rupture and the influence of heat treatment after welding were made. In this report, the difference in rupture configuration between large and small size welded specimens, and welding methods viewed from creep rupture configuration are discussed.The large size welded specimens are ruptured at the heataffected zone of base metal (HAZ) near the bond, while the small size welded specimens are ruptured at HAZ near the base metal. The plate thickness of the steel used is 30 mm, and the welded joints are made by multi-layer welding. Therefore, it may be considered that the properties at welded joint of specimens of both sizes are different. It is clear from the foregoing report that creep strength may be proportionate to the absorbed energy to rupture in a high temperature tensile test. Therefore, tensile tests at 450°C on synthetic HAZ specimens, with respect to the coarse grain part near bond and the fine grain part near base metal in HAZ of small size welded specimens, are carried out to measure the absorbed energy. The value of absorbed energy in fine grain part is less than that in coarse grain part. Consequently, it may be considered that small size welded specimens are ruptured at fine grain part of HAZ near base metal, while large size welded specimens are ruptured at coarse grain part of HAZ near bond.The creep rupture configurations of large size specimens are discussed in various ways. As a result, it is believed to be desirable for improving the creep rupture strength of welded joint to make the pentration of the final bead as shallow as possible.

321型および347型ステンレス鋼溶接部の高温強度

The present study was carried out to clarify the high temperature properties of stainless steel welded joints of AISI types 347 and 321 in as-welded condition, and the effect of post-heating on the creep rupture properties of these joints.To prepare test pieces, stainless steel plates of types 347 and 321 with 25mm thick were welded using 16 Cr-8Ni-2Mo and 19 Cr-8Ni-1Mo electrode, Some of these welded joints were given post-heating at 1050°C for 1hr and at 900°C for 2hrs.In the tension test, specimens as-welded fractured at base metal, and their tensile strength was equal to that of base metal. Tensile strength of specimen post-heated was slightly lower than when it was left as-weld. (Fig. 4, 5)Type 321 stainless steel welded joint using 16-8-2 electrode had the best fatigue properties among the joints in as-welded condition. (Table 2)In creep rupture test, type 347 stainless steel welded joint as-welded fractured at the heat-affected zone of base metal and its rupture strength was very poor. However type 347 stainless steel welded, joint recovered considerable rupture strength by post-heating at 900°C and 1050°C. (Table 4) It seems that this decay of the heat-affected zone is caused by the strain, near the weld groove. By post-heating at 1050°C, coarsening of grain and softening occurred at the heat-affected zone. (Fig. 3, Photo. 1, 2) It seems that this zone has been slightly hot-cold worked during weld by thermal stress caused from temperature gradient and contraction of weld metal. On the other hand, type 321 stainless steel welded joint as-welded fractured at base metal and showed no decay such as shown by type 347 stainless steel welded joint in the rupture test. 1050°C post-heating make its weld boundary so weak, that the creep specimen ruptured at the boundary along the bond. But, 900°C post-heating didn't produce such a decay. (Table 4, Photo. 4, 5) It is not clear why such a decay occur in type 321 stainless steel welded joint.

原子炉用ステンレスクラッド鋼溶接継手の高温における応力破断に関する研究

Stress rupture tests with 40 ton tester were conducted at 500 and 600°C for large welded specimens of stainless clad steel, Mn-Mo-Ni steel ASTM A 302 B claded with AISI 304 L, which is essential to nuclear applications. The large specimen, 38 mm thick and 40 mm wide, showed much inferior property to usual small welded specimen.The results of test at 600°C under a stress of 12 kg/mm2 are : (1) The rupture time of transverse as-welded specimen was 55 % of base metal. (2) The rupture times of transverse welded specimens decreased through heat treatment after welding at 550, 650 and 870°C × 1.5 hr as low as to 40, 60 and 90 %, respectively, of as welded specimen. (3) Machining the reinforcement flush with the surface of base metal increased the rupture time of 550°C × 1.5 hr heat treated specimen by 1.5 times. (4) Longitudinal welded specimen was approximately equivalent to base metal in rupture time. (5) Transverse specimen manually welded showed about 50% longer rupture time than submerged-arc welded specimen.Macroscopic and microscopic examinations showed that cracking in rupture occurred along bond in the graphitized heat-affected zone of base metal. The initiation of cracking occurred mostly at the intersection between the surface of bond of stainless weld metal and the cladding surface, viz., the line along which concentration of strees and local strain were most extreme. Crack initiation in backing steel ocurred frequently at the toe of carbon steel weld metal. If the bottom of stainless weld metal were made smooth with cladding surface, the rupture time of transverse welded specimen would become identical to base metal.The test results at 500°C, however, showed 45 degrees shear type fracture which is different from that at 600°C in which fracture occurred along bond.

原子炉用ステンレス・クラッド鋼溶接継手の高温における応力破断に関する研究

Stress rupture tests with 40ton tester were conducted at 500 and 600°C for large welded specimens of stainless clad steel, Mn-Mo-Ni steel ASTM A 302 B clad with AISI 304L, which is essential to nuclear applications. The large specimen, 38mm thick and 40mm wide, showed much inferior property to usual small welded specimen.The results of test at 600°C under a stress of 12kg/mm2 are:(1) The rupture time of transverse as-welded specimen was 55% of base metal.(2) The rupture times of transverse welded specimens decreased through heat treatment after welding at 550, 650 and 870°C×1.5hr as low as to 40, 60 and 90%, respectively, of as-welded specimen.(3) Machining the reinforcement flush with the surface of bese metal increased the rupture time of 550°C×1.5hr heat treated specimen by 1.5 times.(4) Longitudinal welded specimen was approximately equivalent to base metal in rupture time.(5) Transverse specimen manually welded showed about 50% longer rupture time than submerged-arc welded specimen.Macroscopic and microscopic examinations showed that cracking in rupture occurred along bond in the graphitized heat-affected zone of base metal. The initiation of cracking occurred mostly at the intersection between the surface of bond of stainless weld metal and the cladding surface, viz., the line along which concentration of stress and local strain were most extreme. Crack initiation in backing steel occurred frequently at the toe of carbon steel weld metal. If the bottom of stainless weld metal were made smooth with cladding surface, the rupture time of transverse welded specimen would become identical to base metal.The test results at 500°C, however, showed 45 degrees shear type fracture which is different from that at 600°C in which fracture occurred along bond.

Cr系不銹鋼板の熔接性(第1報)

Weldability tests have been made of 7 different kinds of stainles steel electrodes (mostly, 3.2mm dia.) on 5 kinds of 13-Cr steel plates (mostly, 2.3mm thick) having C content ranging 0.07-0.23.The following results were obtained :1) In longitudinal bead bending test there occurred no case of 180° bending angle without crack development in the heat-affected zone, independently of C content of steel plate and electrode type. The bending angles for ones of 0.07%C content are relatively high and stable.2) As to the hardness of weld metal zone, a wide variance is observed, depending on electrode types. In austenite types which produced excellent elongation values of all deposit metals, conside-rable martensite transformation was seen in weld meta zone, making it unadvisable to use such electrodes as appreciably increase hardness.3) In the case of 0.23%C content, cracks appeared in the heat-affected zone even under non-con-straint conditions. With 0.16%C content some developed longitudinal cracks in the heat-affected zone under constraint test, while below 0.11%C content no cracks occurred.Exceptions are fusion zone cracks being observed sometimes when steel plates with 0.09% C content are welded with Mn-Cr electrode.4) These facts can be roughly explained by the relations between C content of steel plates and martensite transformation in the heat-affected zone of base metal and by dilution of weld metal with steel plate.