Quenched and tempered steels are prone to hydrogen induced cracking in the heat affected zone after welding. The use of austenitic stainless steel consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. In this investigation, an attempt was made to determine a suitable consumable to replace expensive austenitic consumables. Two different consumables, namely, austenitic stainless steel and low hydrogen ferritic steel, were used to fabricate the joints by shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes. The joints fabricated by using low hydrogen ferritic steel consumables showed superior transverse tensile properties, whereas joints fabricated by using austenitic stainless steel consumables exhibited better impact toughness, irrespective of the welding process used. The SMAW joints exhibited superior mechanical and impact properties, irrespective of the consumables used, than their FCAW counterparts.

Effect of Welding Processes and Consumables on Tensile and Impact Properties of High Strength Quenched and Tempered Steel Joints

Microstructures, and hence mechanical properties, of high strength steel weld metals are affected by cooling rate. Weld metal microstructures for a nominal composition of Fe–0·05C–0·3Si–2Mn–3Ni–0·5Cr–0·6Mo (wt-%) were therefore characterised for a range of cooling rates using high resolution scanning electron microscopy, and transformation behaviour, assessed from cooling curves, is presented as a continuous cooling transformation diagram. As deposited last bead microstructure changes gradually from lower bainite and martensite interspersed with coalesced bainite, via a mixture of relatively fine upper and lower bainite, to coarse upper bainite as cooling rate decreases. The microstructure of reheated beads follows the as deposited structure closely and becomes coarse with slower cooling. Mechanical properties correlate with observed microstructure and transformation behaviour. Results suggest high strength and good toughness for cooling rates between 800 and 500°C of about 3–13 s. A fine microstr...

Influence of cooling rate on microstructure and properties of high strength steel weld metal

Prediction of microstructure and mechanical properties of multipass SAW

Influence of welding consumables on tensile and impact properties of multi-pass SMAW Armox 500T steel joints vis-a-vis base metal

The ongoing need to reduce the weight of products while increasing strength has resulted in new generation steel manufacturing using special heat treatments to produce High Strength Steels (HSS) and Ultra High Strength Steels (UHSS) with up to 1700 MPa tensile strength. The high strength level of these steels makes it possible to produce structures with a considerable weight and cost reduction, and such steels have been adopted in the automotive industry and for mobile heavy equipment. Welding of UHSS is, however, not without its complications and welding processes for these steels need careful attention. For instance, their high susceptibility to cracking and Heat Affected Zone (HAZ) softening are risks that need to be borne in mind when choosing welding parameters. This research work discusses the difficulties and challenges of successful welding of UHSS. Common welding methods used in welding of UHSS are briefly reviewed to gain a better understanding of the effects of different welding parameters and methods. The paper finds that UHSS can be satisfactorily welded with laser welding, electron beam welding, resistance welding, and conventional arc welding methods, but the quality of the weld is dependent on appropriate control of several parameters and variables of the welding processes.

Welding of Ultra High Strength Steels

Due to the excellent mechanical properties of high-strength, low-alloy (HSLA) plate steels, fabricators and manufacturers have great interest in the development of high-performance welding electrodes for these steels. Three sets of experimental welding electrodes were designed and manufactured for this research. The first iteration of electrodes was targeted to vary copper from 0.0 to 3.7 wt-%. In the second iteration, chromium was removed and the Ni and Cu contents were adjusted to the ranges of 1.0-3.0 and 1.0-1.5 wt-%, respectively. Niobium was added at 0.03 wt-%. The third iteration lowered the carbon content to 0.03 wt-% and reduced the nitrogen content to 100 ppm maximum. Nickel and copper contents were fine-tuned to 1.0 to 2.3 and 0.8 to 1.0 wt-%, respectively. Standard light and electron metallographic techniques were used to examine the weld metal microstructural evolution. Electron diffraction patterns from the different phases were analyzed. Mechanical testing was performed to characterize the resulting welds. The optimal composition for the HSLA-100 steel weld metals was determined as 0.04 wt-% C, 1.3 wt-% Mn, 2.3 wt-% Ni, 0.55 wt-% Mo, 0.8 wt-% Cu, 90 ppm N, and 270 ppm O. The 0.03 wt-% Nb worked well with Cu to develop synergistic precipitation, which uniformized the hardness fluctuations on weld cross sections. The weld metals that exhibited a predominantly acicular ferrite (AF) structure with some coarse granular bainite presented the best toughness properties. Weld metals with the above composition easily met the U.S. Navy requirement for HSLA-100 steel welds in this work.

Alloying and Microstructural Management in Developing SMAW Electrodes for HSLA-100 Steel To determine the optimal composition of SMA W electrodes for use with HSLA- 100 steel, three sets of experimental welding electrodes were developed

W. Wang

Papers

Alloying and Microstructural Management in Developing SMAW Electrodes for HSLA-100 Steel To determine the optimal composition of SMA W electrodes for use with HSLA- 100 steel, three sets of experimental welding electrodes were developed