Low Alloy Steel Weld Research Articles

Influence of oxygen-rich inclusions on the ??? phase transformation in high-strength low-alloy (HSLA) steel weld metals

Reducing the oxygen content of two submerged-arc, high-strength, low-alloy (HSLA) steel weld metals has been shown to depress γ→α transformation temperatures and produce a marked change in the resultant microstructures. In weld metal of composition 0.12wt% C, 1.35wt% Mn, 0.29 wt% Si, 0.03 wt% Nb reducing the oxygen content from about 300 ppm to about 60 ppm decreased the transformation initiation temperature by about 30° C and changed the microstructure from acicular ferrite to parallel lath ferrite. In weld metal of composition 0.1 wt% C, 0.8 wt% Mn, 0.1 wt% Si, 0.01 wt% Nb reducing the oxygen content from about 600 ppm to about 300 ppm decreased the transformation initiation temperature by approximately 20° C and favoured the development of ferrite side-plates and acicular ferrite at the expense of the polygonal ferrite microstructure. In both weld metals the depressed transformation temperature is thought to be due to the larger γ-phase grain size developed when the volume fraction of small de-oxidation products is reduced. The marked microstructural change from fine-grained acicular ferrite to parallel lath ferrite which occurred when virtually all the de-oxidation products were removed suggests that these small de-oxidation products may also be of fundamental importance to the nucleation of acicular ferrite.

X-Ray microanalysis of grain boundary segregations in steels using the scanning transmission electron microscope

This paper describes an analysis which allows real composition segregation profiles to planar grain boundaries to be determined quantitatively from STEM X-ray microanalysis on thin foils. This analysis is applied to the measurement of such segregations in ironbased alloys. The influence of electron beam spreading within the foil is evaluated and an analysis is developed which allows solute composition profiles to be obtained from measured X-ray intensity profiles. The influence of various experimental parameters on the measured X-ray intensity profile are examined and discussed. The analysis procedure is applied to experimental measurements of tin segregated to prior austenite grain boundaries within the heat affected zone of a ’/2 PGt CrMoV low alloy steel weldment taken from a boiler steam chest.

Acoustic Emission Monitoring of Weldments

Abstract Weld tests were performed on low-carbon and high-strength, low-alloy steel weldments. The weldments were monitored with an acoustic emission detector during both the “in-process” and the “in-cooling” phases of the welding operation. Artificial defects were induced in several of the welds to promote cracking. Some high-strength weldments were designed to produce welds subject to high restraint. Nondestructive and destructive evaluation of the completed weldments revealed that high acoustic emission activity during in-cooling could be correlated with embedded defects and cold-cracking. Copious emission activity was also detected from unflawed weldments. Acoustic emissions were detected in high-strength steel weldments for periods up to 265 h. However, there was no clear relation between the duration of acoustic emission activity and cracking. On a per-electrode-deposited basis, high-stressed welds produced more emissions than low-stressed welds.

Effect of hot rolling on the structure and properties of low-alloy steel welds

Despite the versatility and popularity of welding for fabrication, the weld seam usually has detrimental effects, owing to inferior properties of fatique strength and corrosion resistance. It would be advantageous if, by some economical post-weld treatment, the properties of the weld seam and those of the base metal could be equalised. In this paper the authors discuss the effect of hot rolling on the structure and properties of low-alloy steel (13 Cr Mo 44) welds. Butt-welded metal sheets were rolled in a 2-high mill, with reductions ranging from 10% to 40%, and at temperatures ranging from 800°C to 1100°C. After rolling, the mechanical properties of the weld (tensile strength, yield strength, fracture elongation, percentage reduction in area of cross-section, true fracture strength, impact strength and hardness) were determined. The macro- and microstructures of the weld were examined, whilst the fractured surfaces of the tensile specimens were studied using a scanning electron microscope. The results of the experiments show that at a rolling temperature of 1000°C, a reduction of 30% results in the securing of very nearly equal mechanical properties of the base metal and the weld seam.

The influence of thickness in fatigue crack propagation rates in a low alloy steel weld metal above and below general yield

Fatigue crack propagation rates have been measured in a low alloy steel weld metal for various thicknesses and at stresses above and below general yield. There is no effect of thickness for tests made below general yield but at higher stress levels the thinner specimens show higher crack propagation rates. These observations are discussed with reference to the operative fracture mechanism and available models of crack-tip plasticity; shortcomings in the models are pointed out. Previous conclusions that the effect of plane stress is to accelerate crack growth rates may have neglected the contribution of general yielding.

低温用鋼材のCO<SUB>2</SUB>-O<SUB>2</SUB>アーク溶接について(第3報)

As it was difficult to improve the impact value of weld metal to as high value as that of low nickel alloy steel base metal by addition of various elements, other improvements of the notch toughness of weld metal were experimentally examined by some heat treatments and by welding of low nickel alloy steel with austenitic electrode wires.(1) The more the fine grained structure increased in a low nickel alloy steel weld metal by multipass welding, the higher its impact value became.(2) The impact value of an as-welded metal of low nickel alloy steel was considerably improved by a heat treatment of normalizing from 900°C.(3) A post-weld low temperature annealing below A1 point lowered the impact value of 2 1/2% nickel steel weld metal. This is attributed to granularization of boundary cementite.(4) If low nickel alloy steel is to be welded by austenitic electrode wire to secure notch toughness of weld metal comparable to that of the base metal, the composition of the electrode wire must be so selected as to give a completely austenitic structure in weld metal, considering the dilution of base metal.

低温用鋼材のCO<SUB>2</SUB>-O<SUB>2</SUB>アーク溶接について(第2報)

The effect of several elements on impact value of low nickel alloy steel weld metals was investigated by a bead-on-plate experiment, with deposit by the CO2-O2 arc welding using several electrode wires of various compositions. The following results were obtained:(1) If a low nickel alloy steel is welded by high current automatic welding with an electrode wire of which composition is the same as base metal, it is difficult to get an as-welded metal, of which the impact value is equal to that of base metal.(2) Though it is generally said that nickel has a highly beneficial effect on the low temperature notch toughness of steel, nickel of as-welded metals of low nickel alloy steels did not improve its impact value so effectively as that of heat-treated base metal.(3) In as-welded metal molybdenum was more effective than nickel to improve the impact value.

International association for testing materials

The new low-chromium steel grades T/P23 and T/P24 are candidate materials for components of ultra-supercritical power plants, and as potential replacement materials of conventional low alloy ferritic steels such as T/P22 in older plants. Higher creep strengths relative to that of T22 were obtained by additions of tungsten, vanadium and niobium in steel T23, and titanium and vanadium in steel T24. In addition, the new grades have the advantage that they do not require PWHT due to the lower carbon content of these steels. Long-term creep performance, microstructural evolution, welding characteristics and other properties are however not fully understood. For example, recent experience on the use of T23/T24 materials showed that stress corrosion cracking (SCC) and stress relief cracking can be major service concerns for such steels. In this chapter, welding and weldability data, including weld repairs, and the types of cracking that can occur in low alloy steel weldments, have been examined in some detail.