Welding cooling rate effects on microstructure of an API 5l x100 steel

The aim of this work was to investigate the influence of five different cooling rates on properties of weld metal (WM) and heat affected zone (HAZ) of an API 5L X100 steel welded by GMAW. Bead on pipe (BOP) welds were made on 100x300 mm sections of a 15.8 mm thickness and 580 mm outside diameter API 5L X100 pipe, through five preheat temperatures (-30, 34, 100, 150 and 200 °C), aiming to obtain different cooling rates. Thermocouples were used to obtain the cooling time from 800 to 500 ºC (Δt8/5) during welding. The microstructures of base metal (BM) and HAZ were analyzed by light microscopy and scanning electron microscopy (SEM). Hardness measurements were made on the BOP welds in order to identify maximum and minimum values. As expected, due to the different cooling rates during welding, the distinct preheat temperatures have influenced the weld properties. Maximum and minimum HAZ microhardness, and weld metal hardness decrease as the preheat temperature increases. HAZ area, grain size of fine grained HAZ and coarse grained HAZ increase with increasing preheat temperature

Effect of autogenous GTAW on the reciprocating sliding wear behavior of a carbon martensitic steel

Martensitic steels have been successfully employed in resource-based industries where components must endure aggressive conditions. In industrial practice, many parts of these components are joined by welding techniques. The aim of this work was to understand the influence of welding on the wear resistance of quenched and tempered carbon martensitic steel subjected to dry linear reciprocating sliding micro-wear tests. Weld-joints were produced using autogenous Gas Tungsten Arc Welding process (GTAW). Micro-wear tests were performed at base metal (BM), weld metal (WM), coarse grained heat affected zone (CG-HAZ) and lowest hardness region of heat affected zone (LHR-HAZ). LHR-HAZ was softened during welding process so plastic deformation was facilitated, and consequently adhesion, material displacement and micro-ploughing. WM and CG-HAZ presented a similar martensitic structure, which explain the similarities found on wear behavior. These regions presented the lowest worn volume average values (w). It was interesting to note that despite its highestmicrohardness value, the highest wwas observed for BM. For some BM samples, debris had a key role promoting material loss by micro-cutting which causes great extent of material removal compared to other micro-wear mechanisms as micro-ploughing and adhesion. Due to debris action BM also presented a great dispersion in wresults. The results suggest that material loss of welded joint and BM was strongly controlled by micro-wear mechanisms

Friction stir spot welding of a TRIP steel : microestructural characterization

Este trabalho tem como objetivo investigar a influência da velocidade de rotação (1.600 RPM e 2.400 RPM) no desenvolvimento microestrutural de um aço TRIP soldado a ponto por fricção e mistura mecânica. Após a execução das soldas, devido aos ciclos térmicos e deformações impostas pelo processo, são observadas três diferentes zonas nas juntas: a zona de mistura (ZM), a zona termomecanicamente afetada (ZTMA), e a zona termicamente afetada (ZTA). O aumento da velocidade de rotação causou um aumento na quantidade de ferrita alotriomorfa formada na ZM, assim como redução na quantidade e tamanho de bainita coalescida e martensita. Na ZTMA a microestrutura é constituída por ferrita, austenita, bainita coalescida e martensita. Enquanto que na ZTA1 a microestrutura é composta por ferrita e austenita retida em todas as velocidades usadas, na ZTA2 há maior transformação da austenita em bainita com o aumento da velocidade de rotação.The aim of this work is to verify the influence of the rotational speed (1600 and 2400 RPM) in the microstructural development of a friction stir spot welded TRIP steel. After the welding, due to the thermal cycles and deformations imposed by the process, three different zones are observed in the joints: the stir zone (SZ), the thermomecanically affected zone (TMAZ), and the heat affected zone (HAZ). The increase in the rotational speed caused an increase in the amount of allotriomorphic ferrite formed in the SZ, and a decrease in the amount and width of the coalesced bainite and martensite. In the TMAZ, the microstructure is composed by ferrite, austenite, coalesced bainite and martensite. While in the HAZ1 the microstructure is constituted by ferrite and retained austenite in all rotational speeds employed, in the HAZ2 there is an increase in the transformation of austenite into bainite by increasing the rotational speed

Boletín oficial de la provincia de Santander: Número 124 - 1887 Noviembre 28

O objetivo do presente trabalho foi verificar o efeito das alterações microestruturais resultantes da soldagem na resistência ao desgaste de uma junta de aço estrutural ASTM A242, comparando com o comportamento do metal base. Utilizou-se o processo de soldagem MAG e arame AWS ER70S-6. A soldagem foi automatizada, na posição plana, utilizando chanfro em V e realizada por uma fonte eletrônica em CC+. A região desgastada e os mecanismos foram caracterizados utilizando microscopia eletrônica de varredura, microscopia ótica e interferometria a laser. A resistência ao desgaste foi analisada por diferentes métodos: ensaio de desgaste Roda de Borracha,definido pela norma ASTM G65-16, e ensaio de microdesgaste por deslizamento linear recíproco, similar ao descrito pela norma ASTM Gl33-16. O ensaio de desgaste roda de borracha representou um comportamento geral da junta soldada,uma vez que a área de abrangência do ensaio é delimitada pela largura da roda de borracha. O resultado do ensaio mostrou que a junta soldada (metal de solda e parte da região da zona afetada pelo calor de grãos grosseiros (ZAC-GG)) apresentou melhor resistência ao desgaste do que o metal base. O ensaio de microdesgaste por deslizamento foi utilizado com o objetivo de analisar cada região da junta soldada, separadamente. Neste sentido, ensaios foram realizados no metal base, no metal de solda e na ZAC-GG, uma vez que esta região foi abrangida pelo ensaio roda de borracha. Neste ensaio,observou-se que a ZAC-GG apresentou maior resistência ao desgaste do que o metal de solda, e o metal base exibiu a menor resistência ao desgaste. Os resultados indicaram que a deformação plástica exibida pela microestrutura do metal base contribuiu para o maior desgaste, em ambos ensaios.Abstract:The aim ofthe present work was to verify the effect of microstructures on the wear resistance of an ASTM A242 structural steel welded joint, comparing it with the behavior of the base metal. The joints were produced using the GMAW process and AWS ER70S-6 wire electrode. The welding was automated, in flat position,using V-groove and with an eletronic power source operating in CC+. Microstructural features of welded joints and worn surfaces as well as wear mechanisms were characterized using scanning electron microscopy, optical microscopy and laser interferometry. The wear resistance was analyzed by different wear tests: Dry Sand/Rubber Wheel Tests, defined by ASTM G65-16 and Linearly Reciprocating Ball-on-Fiat Sliding Microwear,similar to that described by ASTM Gl33-16. The Rubber Wheel wear test indicated a general behavior of the weld joint, since the test rangeis limited by the width of the rubber wheel. In this test weld joint (weld metal and part of the coarse grain heat affected zone (CGHAZ)) showed better wear resistance than the base metal. The sliding microwear was used to analyze weld regions separately. In this sense, tests were performed on the base metal, weld metal and CGHAZ, since this region was covered by the Rubber Wheel wear test. Results showed a higher wear resistance in CGHAZ than in weld metal, and the lower wear resistance was observed in the base metal. This could be attributed to the higher plastic deformation in base metal

Effect of filler material on sliding wear resistance of a structural steel welded by GMAW

O objetivo do presente trabalho foi avaliar o efeito do metal de adição na soldagem, e das microestruturas resultantes, na resistência ao desgaste de juntas soldadas de um aço estrutural ASTM A242, que possui resistência à corrosão atmosférica e é utilizado na fabricação de vagões destinados ao transporte de minério. As amostras foram soldadas através do processo GMAW (Gas Metal Arc Welding), utilizando dois metais de adição que apresentam resistências mecânicas diferentes, AWS ER70S-6 e AWS ER80S-G. A resistência ao desgaste das amostras foi avaliada através de ensaios de microdesgaste por deslizamento linear recíproco, a seco e em uma solução contendo 0,05M NaCl, em três regiões da junta soldada: metal base (MB), metal de solda (MS) e zona afetada pelo calor de grãos grosseiros (ZAC-GG). Após a soldagem, foi observado um aumento nos valores médios de durezas do MS e da ZAC em relação à dureza inicial do metal base. Os resultados dos ensaios de microdesgaste mostraram que o MB apresentou a menor resistência ao desgaste, possivelmente devido à sua microestrutura, que facilitou o desgaste por deformação plástica. A ZAC-GG apresentou a maior resistência ao desgaste entre as três regiões analisadas. Comparando os ensaios realizados nas condições a seco e em solução foi observada uma redução nos valores de coeficiente de atrito quando adicionada uma solução ao sistema, e uma perda de volume das trilhas mais acentuada. Observou-se que a utilização do metal de adição de menor resistência mecânica produziu juntas soldadas com resistência ao desgaste comparável às juntas obtidas com o arame de maior resistência.The aim of the present work was to evaluate the effect of the filler material in the welding and its resulting microstructures on the wear resistance of welded joints of a structural weathering steel ASTM A242 used in wagons for mining. The samples were welded using the GMAW (Gas Metal Arc Welding) process using two filler materials which have different mechanical strength, AWS ER70S-6 and AWS ER80S-G. The wear resistance of the samples was evaluated using a linearly reciprocating sliding microwear test, dry and in a solution containing 0.05M NaCl, in three regions of the welded joint: base metal (BM), weld metal (WM) and coarse grained heat affected zone (CGHAZ).After welding, it was observed an increase in the mean hardness values of the MS and ZAC in comparison to the initial hardness of base metal with the use of both filler metals, and the hardness values in each of these regions were similar. The results of the microwear tests showed that BM presented the lowest wear resistance, possibly due to its microstructure, which facilitated wear by plastic deformation. The CGHAZ showed the highest wear resistance. Comparing the tests carried out under the dry and in solution conditions, a reduction in the coefficient of friction was observed when the solution was added to the system, and the volume loss of the tracks was more pronounced. It was observed that the use of the lower mechanical strength filler material produced welded joints with wear resistance comparable to the joints obtained with the higher strength filler material

Bead geometry prediction in pulsed GMAW welding : a comparative study on the performance of artificial neural network and regression models

Weld bead geometry is a critical factor for determining the quality of welded joints, for this the welding process input parameters play a key role. In this study, the relationships between welding process variables and the size of the weld bead produced by pulsed GMAW process were investigated by a neural network trained with Bayesian-Regulation Back Propagation algorithm and a second degree regression models. A series of experiments were carried out by applying a Box-Behnken design of experiment. The results showed that both models can predict well the bead geometry. However, the neural network model had a slightly better performance than the second-order regression model. Both models can be used for further analyses and using them may surmount or reduce the need of experimental procedures especially in thermal analysis validations of welding finite element modelling

Mechanical and metallurgical properties of DP 1000 steel square butt welded joints with GMAW

In this work, Gas Metal Arc Welding (GMAW) was used to study the influence of heat input (i.e. cooling rate) on mechanical/metallurgical properties of square butt welded joints of DP 1000 sheets. The influence of filler metals of different strengths on the mechanical properties of joints was also tested. A significant decrease in hardness was observed in the Heat Affected Zone (HAZ) due to martensite tempering, in regions where peak temperature was close to isotherm AC1 (calculated in 735 oC for these steel); coincidently, fracture in every tensile test occurred in regions where martensite was tempered, even when a wire of less strength was used. It was noticed that the decrease in ultimate tensile and yield strength of base metal was inherent to welding. When minimum heat input was used, deterioration in mechanical properties was less pronounced, once degree of HAZ softening was smaller. Elongation of joints increased with increasing heat input