Toughness Of Welded Joints Research Articles

Influence of Inclusions on Strength and Toughness of X70 Pipeline Steel Girth Weld

In this paper, SEM, EPMA, and micro shear experimental method were applied to analyse the structure, inclusion morphology and composition, micro-area strength and toughness of the X70 pipeline steel girth weld joint. The results show that inclusions are mainly nonmetallic oxides, sulfides and calcium compounds. The length of inclusions can be up to 1mm, which have substantially reduced the strength and toughness of weld joint. By the combining effect of internal and external force, cracks tend to initiate around inclusions and propagate along the direction of inclusions, and finally reduce the impact toughness of girth weld.

Effect of Microstructure on CTOD of Welded Joints for Offshore High-Strength Steel

Based on the CTOD test, metallographic test is done. The effect of microstructure on CTOD of welded joints for offshore high-strength steel has been analyzed by SEM. The microstructure of different samples in a welding procedure and two different welding procedures are compared. From the microscopic point of view, the reasons why the toughness of the second group welded joints is better than the first group’s and why the toughness of the same group welded joints is different have been determined. And the main microstructure found in EQ70 steel welded joints is the ferrite, tempered sorbite and a small amount of pearlite. Besides some carbide particles are on the matrix of tempered sorbite. The material toughness with a small amount of acicular ferrite is better. Inclusions and pores also seriously affect the toughness of welded joints. Reducing the welding heat input appropriately can refine the grain of CGHAZ and improve toughness. But hardened microstructure may occur owing to too low welding heat input.

Effect of welding conditions on the impact toughness of welded joints in titanium alloys

Effect of the welding conditions and annealing on the impact strength of different heat-affected areas of the titanium welded joints is studied. Maximum impact strength is established in the range of 350–550°C, in practice this coincides with the temperature peaks for short-time strength and fatigue life.

Pulse Discharge Strengthening of 16Mn Welded Joint and Mechanical Performance

The way of pulse discharge strengthening is introduced, and the electromagnetic heat pulse discharge method can increase the strength and toughness of welded joints. 16Mn low alloy steel welded joints are used in the ZL-2 super pulse current generator, and the test of pulse discharge strengthening is carried out. And the mechanical performance comparison test of welded joint is finished. On the universal tensile machine, tensile strength test before and after strengthening has been done. On the S-4800 scanning electron microscope, micro-fracture morphology is analyzed. The results show that electromagnetic heat strengthening test is carried out based on the appropriate discharge parameters. In the junction of weld and base metal near the heat affected zone of the fracture, there is a white layer organization. It appears to improve the mechanical performance of welded joint, and enhance strength and toughness of welded joints.

Influencia de la cantidad de O2 adicionado al CO2 en el gas de protección sobre la microestructura del metal depositado en uniones soldadas de bordes rectos en aceros de bajo contenido de carbono con el proceso GMAW

La presencia de ferrita acicular (FA) en la microestructura del cordón de soldadura, dentro de determinado rango de valores, eleva considerablemente la tenacidad de las uniones soldadas. Es por ello, que el presente trabajo trata sobre un estudio que relaciona la cantidad de ferrita acicular en el cordón en función del contenido de oxígeno presente en la mezcla activa CO2+O2, durante la realización de uniones soldadas de bordes rectos en aceros de bajo carbono con el proceso con electrodo fusible y protección gaseosa (GMAW) en condiciones invariables de parámetros de proceso (corriente de soldadura, voltaje de arco, velocidad de soldadura, longitud libre y flujo de gas protector). Como resultado del trabajo se estableció la relación gráfica existente entre la ferrita acicular y el contenido de oxígeno en la mezcla.

Effect of mechanical mismatching on the ductile-to-brittle transition curve of welded joints

The effect of mechanical mismatching (ratio between the yield strength of base and weld metal) on the toughness of welded joints at different temperatures was analysed and the ductile-to-brittle transition curves of these welded joints were experimentally obtained. The filler metal of the joints was always the same, varying the base metal and the width of the welded zone. Two base metals were selected, one with a higher strength than the filler metal (undermatched joint) and the other with a lower strength than the filler metal (overmatched joint). In addition, the joints were made using two different weld widths, 20 and 10 mm. The fracture behaviour of the joints were determined at different temperatures using SE(B) specimens provided with short cracks ( a/ W = 0.22). Besides, long crack specimens ( a/ W = 0.5) were also used for comparison. In the case of overmatched joints, the J-values for ductile crack growth are larger than for the undermatched joints. In addition, the ductile-to-brittle transition curve is displaced towards lower-temperatures and higher-toughness values and the toughness for cleavage fracture is also larger for overmatching than for undermatching. All these effects are more significant as the weld width decreases and have been explained in terms of constraint modifications.

The application of crack tip opening displacement test in the fabrication of offshore jacket structures

According to the British Standard BS7448, the article presents a method to determine crack tip opening displacement (CTOD) and has evaluated the toughness of welded joints in offshore jacket structures (wall thickness is 90 mm) by this method. The results show that (1) it is excellent to evaluate the toughness of welded joint with the CTOD test, (2) the CTOD test can be taken as the acceptable test of welding craft, and (3) the particular offshore jacket structures tested no longer need heat treatment.

Improving the toughness of welded joints by post‐weld heat treatment: HAZ toughness in 780 and 980 MPa class HSLA steels welded with high heat inputs (4th report)

Summary To determine optimum PWHT (post‐weld heat treatment) parameters for improvement of the HAZ toughness of 780 and 980 MPa class high‐strength steels welded with high heat inputs, this paper describes a systematic investigation of the effect of PWHT on the toughness of the simulated weld HAZ of the steels in relation to decomposition of the M‐A (martensite‐austenite) constituent. The optimum PWHT time and temperature proposed with regard to practical workability are 623 K × 8 hr for the weld CGHAZ (coarse‐grained HAZ for high heat input welding) and ICCGHAZ (intercritically reheated CGHAZ for multipass welding) of these steels. The optimum PWHT parameters are tested on specimens actually welded with a heat input twice as high as that conventionally applied. The toughness of the welds specimens as estimated from the CTOD value is significantly improved by the proposed PWHT conditions and meets practical workability requirements. The tensile strength of the specimens welded with a heat input twice as h...

Effect of preliminary heat treatment on the impact toughness of welded joints in a high-strength steel

Investigations were carried out into structural changes in preliminary heat treatment which affect the increase of impact toughness of welded joints in the conditions after strengthening by heat treatment. These investigations were made on electron beam welded joints produced in 35KhS2N3M1F steel 15 mm thick

Structural and mechanical heterogeneity of heat affected zone and impact toughness of welded joints in structural steels

Structural and mechanical heterogeneity of heat affected zone and impact toughness of welded joints in structural steels

High-strain fatigue characteristics and fracture toughness of welded joints in components of water turbines

High-strain fatigue characteristics and fracture toughness of welded joints in components of water turbines

Local uniform heat treatment and its effects on the toughness of welded C-Mn pressure vessel steel

The present paper gives the results of a research programme on the influence of a local postweld heat treatment on the toughness of welded joints in a C-Mn pressure vessel steel. The welded test plates, 50 mm thick, were locally heat treated using electrical resistance heating over a width of about 200 mm. The influence of the local heat treatment on the toughness of the welded joints was evaluated using wide plate test specimens. The results indicate that an important improvement in toughness is obtained by the local heat treatment, resulting in toughness levels which are comparable to those obtained by a furnace stress relief heat treatment.

Effects of a stress relief heat treatment on the toughness of pressure vessel quality steels—Influence of the plate thickness

This paper gives the results of the third phase of a research programme on the influence of post weld heat treatments on the toughness of welded joints in pressure vessel quality steels. Special attention is paid to the minimum plate thickness for which a post weld heat treatment should be recommended. In addition to the qualification tests, several large-scale tests were carried out on test plates of various thicknesses. The results indicate that, although the present code requirements are satisfactory for a C-Mn steel, they should be completely altered for an Nb-microalloyed steel, welded with a high heat input.

Effects of a stress relief heat treatment on the toughness of pressure vessel quality steels welded with high heat input processes

The research described in this paper is an extension of an earlier research programme on the influence of a post weld heat treatment on the toughness of welded joints in pressure vessel quality steels. 1 In this part of the work special attention was paid to the heat input of the welding process involved and the influence of the subsequent heat treatment. In addition to the qualification tests, several wide plate tests were carried out. The results indicate that, while for some steels the influence of a stress relief heat treatment on the toughness of the joint depends considerably on the heat input of the welding process, it is independent of the heat input of the welding process for other types of steel.

Impact toughness of welded joints of niobium alloys

1. It was found that the impact toughness of welded joints of niobium alloys varies with the welding speed. 2. The impact toughness reaches the highest values at welding speeds of 40–60 m/h and then remains constant. The impact toughness changes least for niobium alloys with solid solution hardening. 3. Separation of the impact toughness into its component parts showed that higher welding speeds are preferable. 4. The optimum conditions for heat treating weld seams in alloys 2 and 4 are 1200 and 1200–1300°C respectively with holding for 1h.