• Journal of Welding and Joining
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• v.13 no.4
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• pp.55-64
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• 1995

A study was made to examine the effects of postweld heat treatment(PWHT) on the toughness and microstructures in the weld heat affected zone(HAZ) of Cu-bearing HSLA-100 steel. The Gleeble thermal/mechanical simulator was used to simulate the weld HAZ. The details between toughness and PWHT of HAZ were studied by impact test, optical microscopy(O.M.), scanning electron microscopy (SEM), transmission electron microscopy(TEM) and differential scanning calorimetry(DSC). The decrease of HAZ toughness in single thermal cycle comparing to base plate is ascribed to the coarsed-grain formed by heating to 1350.deg.C. The increase of HAZ toughness in double thermal cycle comparine to single thermal cycle is due to the fine ferrite(.alpha.) grain transformed from austenite(.gamma.)formed by heating to .alpha./.gamma. two phase region. Cu precipitated during aging for increasing the strength of base metal is dissolved during single thermal cycle to 1350.deg.C and is precipitated little on cooling and heating during subsequent weld thermal cycle. It precipitates by introducing PWHT. Thus, the decrease of toughness in triple thermal cycle of $T_{p1}$ = 1350.deg.C, $T_{p2}$ = 800.deg.C and $T_{p3}$ = 500.deg.C does not occur owing to the precipitation of Cu. The behaviors of Cu=precipitates in HAZ is similar to that in base plate. PWHT at 550.deg.C shows highest hardness and lowest toughness, whereas PWHT at 650.deg.C shows reasonable toughness, which improves the toughness of as-welded state.state.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.89-95
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• 2000

Creep-fatigue crack growth behavior at the heat affected zone of 1Cr-0.5Mo steel weldment has been experimentally studied. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the {TEX}$C_{t}${/TEX} estimated with the equation proposed by the previous finite element analysis work. It was concluded that the {TEX}$C_{t}${/TEX} values calculated from the properties of parent metal were quite comparable to the accurate {TEX}$C_{t}${/TEX} values calculated from both of weld and parent metals. Scatter of data was claimed due to the difference of exact location of the cracks in HAZ. The cracks have a tendency to change their path from the original location eventually to the relatively soft HAZ(ie, near-FGHAZ region, fine grained heat affected zone).

• Corrosion Science and Technology
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• v.7 no.2
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• pp.134-137
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• 2008

Cold arc welding of cast iron has been widely used with repair welding of metal structures. However its welding is often resulted in the galvanic corrosion between weld metal zone and heat affected zone(HAZ) due to increasing of hardness. In this study, corrosion properties such as hardness, corrosion potential, surface microstructures, and variation of corrosion current density of welding zone with parameters of used electrodes for cast iron welding were investigated with an electrochemical evaluation. Hardness of HAZ showed the highest value compared to other welding zone regardless of kinds of used electrodes for cast iron welding. And its corrosion potential was also shifted to more negative direction than other welding zone. In addition, corrosion current density of WM in polarization curves was qualitatively smaller than that of HAZ. Therefore galvanic corrosion may be apparently observed at HAZ. However galvanic corrosion may be somewhat controlled by using an optimum welding electrode.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.73-78
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• 2011

Weldability, especially HAZ cold cracking, weld metal solidification cracking, and HAZ liquation cracking susceptibilities, of ASTM A356 CA6NM martensitic stainless steel casting was investigated and compared with that of 9-12% Cr ferritic steel castings. Irrespective of the Cr and Ni content in the castings, the HAZ maximum hardness increased with an increase of carbon content. CA6NM steel, which has the lowest carbon content, had the lowest HAZ hardness and showed no cold cracking in y-slit cracking tests. CA6NM steel, meanwhile, showed the largest weld metal solidification cracking susceptibility in varestraint tests because of its higher amount of impurity elements, phosphorus, and sulfur. All castings investigated had good high temperature ductility in hot ductility tests and showed little difference in liquation cracking susceptibility.

• Korean Journal of Metals and Materials
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• v.47 no.3
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• pp.139-146
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• 2009

The heat-affected zone (HAZ) of SA508 Gr.4N Ni-Mo-Cr low alloy steel, which has higher Ni and Cr contents than SA508 Gr.3 Mn-Mo-Ni low alloy steel, was investigated on the microstructure and mechanical properties. The HAZ was categorized into seven characteristic zones (CGCG, FGCG, ICCG, SCCG, FGFG, ICIC and SCSC-HAZ) according to the peak temperature from the thermal cycle experienced during multi-pass welding. Post Weld Heat Treatment (PWHT) was conducted in the temperature range of $550{\sim}610^{\circ}C$ for 30 hours to evaluate the effect of PWHT conditions on the microstructure and mechanical properties. Before PWHT, CGHAZ and FGFGHAZ showed high yield strength (YS) ranging from 1000 to 1250 MPa, while YS of SCSCHAZ decreased from 607 MPa (observed for base metal) to 501 MPa. The Charpy impact energies of sub-HAZs fell below 100J at $-29^{\circ}C$, except in the SCSCHAZ. By applying PWHT to sub-HAZ specimens, YS decreased as the PWHT temperature increased. In the case of CGHAZs and FGFGHAZ heat-treated at $610^{\circ}C$, YS dropped drastically to the range of 654~686 MPa. From the Charpy impact test, the upper-shelf energy (USE) increased to approximately 250J and Index temperature ($T_{68J}$) decreased below $-50^{\circ}C$. Specifically, in FGFG, ICIC and SCSC-HAZ, $T_{68J}$ was below -110, which was lower than the case of base metal.

• Journal of Welding and Joining
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• v.28 no.5
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• pp.51-57
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• 2010

Brittle microstructure created in a heat affected zone (HAZ) during the welding of low alloy steel can be eliminated by post-weld heat treatment (PWHT). If the PWHT is not possible during a repair welding, the controlled bead depositions of multi-pass welding should be applied to obtain tempering effect on the HAZ without PWHT. In order to anticipate and control the tempering effect during the temper bead welding, the definition of temperature curve obtained from the analytical solution was suggested in this research. Because the analytical solution for heat flow is expressed as a mathematical equation of weld parameters, it may be effective in anticipating the effect of each weld parameter on the tempering in HAZ during the successive bead depositions. The reheating effect by the successive bead layer on the brittle coarse grained HAZ formed by earlier bead deposition was estimated by comparing the overlapped distance between the temperature curves in the HAZ. Three layered weld specimens of SA508 base metal with A52 filler were prepared by controlling heat input ratio between layers. The tempering effect anticipated by using the overlapped distance between the temperature curves was verified by measuring the micro-hardness distribution in the HAZ of prepared specimens. The temperature curve obtained from analytical solution was expected as a good tool to find optimal temper bead welding conditions.

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.105-110
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• 2009

The objective of this paper is to investigate the statistical properties of Vickers hardness (HV) for friction welded parts in a Ni-based super alloy (Alloy718). In the case of post weld heat treatment (PWHT) parts, hardness tests were repeated for three different applied loads, 100, 200, and 300 g, with a duration time of 10 seconds. The arithmetic means of the Vickers hardness in heat affected zone (HAZ) materials were smaller than those of the base metal (BM) in all of the applied loads. The coefficient of variation (COV) for the BM and HAZ decreased by increasing the applied load. The probability distribution of the Vickers hardness followed the Weibull distribution well. The distribution of the Vickers hardness was not found to be symmetric. The shape parameter and scale parameter increased by increasing the applied load at both the BM and HAZ.

• International Journal of Advanced Culture Technology
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• v.3 no.1
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• pp.61-67
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• 2015

The application of SS400 carbon steel and AISI430 ferritic stainless steel joint has been increased in industries because of the advantage of both metals was able to increase the service lifetime of the important structures. Therefore, a fusion welding process that could produce a sound weld and good joint properties should be optimized. This research is aimed to weld a butt joint of SS400 carbon steel and AISI430 ferritic stainless steel using Gas Metal Arc Welding (GMAW) welding process and to study the effects of welding parameters on joint properties. The experimental results were concluded as follows. The optimized welding parameter that produced the tensile strength of 448 MPa was the welding current of 110A, the welding speed of 400 mm/min and the mixed gas of $80%Ar+20%CO_2$. Increase of the welding current affected to increase and decrease the tensile strength of the joint, respectively. Lower welding current produced the incomplete bonding of the metals and indicated the low tensile strength. Microstructure investigation of the welded joint showed a columnar grain in the weld metal and a coarse grain in the heat affected zone (HAZ). The unknown hard precipitated phases were also found at the grain boundaries of the weld metal and HAZ. The hardness profile did not show the difference of the hardness on the joint that was welded by various welding currents but the hardness of the weld metal was higher than that of the other location.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.16-21
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• 2018

The effect of heat treatment on the fatigue crack growth behavior in welded joints between the heat-affected zone (HAZ) of SA 508 Cl.3 low-alloy steel and HAZ of AISI 316L stainless steel is investigated. When the crack propagates across SA 508 Cl.3 or AISI 316L SS and HAZ into the weldment, the fatigue crack growth rate (FCGR) in the HAZ region does not change or decrease despite the increase in stress intensity factor ${\Delta}K$. The residual stress at the HAZ region is more compressive than that at the base Δ materials and weldment. The effect of the welding residual stress on the crack growth behavior is determined by performing a residual stress relief heat treatment at $650^{\circ}C$ for 1h and subsequent furnace cooling. The FCG behavior in the HAZ region in the as-welded specimen and the residual stress relief heat-treated specimen is discussed in terms of the welding residual stress.

• Journal of Advanced Marine Engineering and Technology
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• v.9 no.2
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• pp.126-142
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• 1985

The plane bending corrosiion fatigue test for the welded metal parats was performed in the air and in the natural sea water with and without applying cathodic protection. The specimens tested were the weld of SM41 steel plates, SM58 steel plates and of SM41 to SM58, which were all prepared by submerged arc welding. The main results obtained from the experiment are summarized as follows: (1) In case with SM41 and SM58 steel plates, lower value of impact strength, higher value of hardness and more noble electrode potential were observed in the welded metal part than in the HAZ and base metal. Also the lowest hardness zone in the HAZ was observed with SM58 which was not found with SM41. In case with weld specimen of SM41 to SM58, the impact strength and the electrode potential of the welded metal part showed again the lowest and most noble value but the hardness value was located between those of SM41 and SM58 base metal. (2) In the fatigue test, the specimens tested in the air and under the cathodic protection were both cracked in a purely mechanical mode, but the specimens tested without cathodic protection were cracked by the combination of mechanical fracture and electro-chemical corrosion. (3) The corrosion fatigue limit of the welded metal parts of the specimen was increased by the cathodic protection. As the protection potential was varied down to -800 mV vs. SCE the fatigue limit was increased to the value tested in the air, and the maximum fatigue limit appeared at the -1, 000 - -1, 200 mV vs. SCE. However, as the protection potential was further decreased below -1, 200 mV vs.SCE, the fatigue limit of weld of SM58 and of SM41-SM58 joining was decreased but the limit was almost constant in the case of weld of SM41. (4) It is suggested that when designing steel ship the corrosion fatigue limit of welded metal parts should be stressed as a designing strength of the structure of steel ship in addition to the conventional basis considering simply tensile strength of steel and safety factor.