The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

Recent advances in friction-stir welding : Process, weldment structure and properties

The metallurgy of zinc-coated steel

Welding Metallurgy of

Wire-feed additive manufacturing (AM) is a promising alternative to traditional subtractive manufacturing for fabricating large expensive metal components with complex geometry. The current research focus on wire-feed AM is trying to produce complex-shaped functional metal components with good geometry accuracy, surface finish and material property to meet the demanding requirements from aerospace, automotive and rapid tooling industry. Wire-feed AM processes generally involve high residual stresses and distortions due to the excessive heat input and high deposition rate. The influences of process conditions, such as energy input, wire-feed rate, welding speed, deposition pattern and deposition sequences, etc., on thermal history and resultant residual stresses of AM-processed components needs to be further understood. In addition, poor accuracy and surface finish of the process limit the applications of wire-feed AM technology. In this paper, after an introduction of various wire-feed AM technologies and its characteristics, an in depth review of various process aspects of wire-feed AM, including quality and accuracy of wire-feed AM processed components, will be presented. The overall objective is to identify the current challenges for wire-feed AM as well as point out the future research direction.

Wire-feed additive manufacturing of metal components: technologies, developments and future interests

Surface characterization of hot-dip Galfan coatings

A process for producing a galvanneal layer on a steel substrate, including forming a Zn-Fe coating having a predetermined Fe content F (wt. %) on the steel substrate; and heat treating the Zn-Fe coating on the substrate from a predetermined starting temperature T 1 (°C.) to a predetermined ending temperature T 2 (°C.) at a predetermined heating rate R (°C./min.), wherein F, T 1 , T 2 , and R are selected so that the following condition is met, a.R.sup.2 +b.T.sup.2 +c.R.F.+d.R.T +e.R+f.T=g where a, b, c, d, e, f and g are predetermined constants, thereby to form a virtually 100% δ 1 phase galvanneal structure. Alternatively, the heat treatment can be preformed until the specimen temperature is just below a minimum temperature of the δ 1 phase stability range at at selected Fe content and heating rate, followed by an isothermal hold for a predetermined time period until transformation to the δ 1 phase occurs.

Method of producing a Zn-Fe galvanneal on a steel substrate

The objective of the present study was to investigate the corrosion behavior of weldable Fe–Al alloys in environments representative of low NOx gas compositions, i.e., high partial pressures of sulfur [p(S2)] and low partial pressures of oxygen [p(O2)]. Using thermogravimetric techniques, binary alloys with 0–12.5 wt% Al were exposed in oxidizing–sulfidizing environments [p(S2) = 10–4 atm and p(O2) = 10–25 atm] at 500–700°C for various times up to 100 h. Post-exposure characterization consisted of surface and cross-sectional microscopy in combination with energy dispersive spectroscopy and/or electron probe microanalysis. It was found that the Fe–Al alloys exhibited three different stages of corrosion behavior: inhibition, breakdown, and steady-state. Observance and/or duration of these stages was directly related to the aluminum content of the alloy. The inhibition stage was characterized by growth of a thin, gamma alumina scale that suppressed rapid degradation of the underlying substrate for al...

Corrosion behavior of weldable Fe–Al alloys in oxidizing–sulfidizing environments

Superaustenitic stainless steel alloys can often pose difficulties dur- ing fusion welding due to the unavoidable microsegregation of Mo and tramp ele- ments, which lead to the loss of corrosion resistance and solidification cracking, re- spectively. A method of producing austenitic welds is proposed that can po- tentially circumvent these issues by de- signing fusion zone compositions that ex- hibit a primary ferrite solidification mode and subsequent solid-state transformation of ferrite to austenite. The ferritic solidifi- cation mode will minimize microsegrega- tion during solidification due to elevated diffusion rates, while a subsequent solid- state transformation of ferrite into austen- ite will create the austenitic matrix that is desired for good toughness. Thermody- namic calculations were used to isolate the range of compositions over which this phase transformation sequence can occur in Fe-Ni-Cr-Mo alloys. Experimental stainless steel alloys with a wide range in Ni, Cr, and Mo concentrations were then prepared with an arc button melting tech- nique to observe the microstructures and validate the thermodynamic diagrams. Four solidification modes (A, AF, FA, F) and three solid-state transformations ( δ→ γ, δ→ (σ+γ), and γ→ martensite) were observed in this alloy system that pro- duced a wide variety of microstructures. Good agreement was shown between ex- periment and thermodynamic calcula- tions in the prediction of solidification mode. The amount of ferrite was also de- termined in each alloy via magnetic mea- surements. Empirical relations were as- sessed that relate the ferrite content to alloy composition, and the data were used for comparison with several weld constitu- tion diagrams. Several alloys were identi- fied that exhibited the desired transfor- mation sequence. Electron probe microanalysis measurements on these al- loys confirmed that Mo was more uni- formly distributed compared to alloys that solidified as austenite. Laser beam welds were also deposited on the surfaces of the button melts in order to observe the influ- ence of higher cooling rates. While no so- lidification mode shifts occurred (with the possible exception of one alloy), the high cooling rate inherent to laser welding caused a δ→γ massive transformation. This massive structure exhibited an en- tirely austenitic microstructure with a uni- form distribution of Mo at the nominal concentration.

The influence of molybdenum on stainless steel weld microstructures : A method of producing austenitic welds is proposed that can potentially circumvent the difficulties normally encountered when fusion welding superaustenitic stainless steels

Single-pass welds and multiple-pass cladding of Fe-Al alloys were deposited on carbon steel substrates using the gas tungsten arc and gas metal arc welding processes. The effect of alloy composition on cold cracking susceptibility was assessed using a dye penetrant technique. The high-temperature (600 C) sulfidation behavior of low-Al alloys (5--10 wt.% Al), which exhibited good weldability, was examined using a thermogravimetric balance in a moderately reducing 0.1% H{sub 2}S--3.0% H{sub 2}-bal. Ar gas. Microstructural characterization was conducted by light optical microscopy, scanning electron microscopy, electron probe microanalysis and Knoop hardness testing. By varying the welding parameters, a range of dilution levels was achieved that resulted in fusion zone compositions with 3--30 wt.% Al. Under these processing conditions, cracking of the Fe-Al cladding is directly related to the aluminum concentration within the deposit. Cracking of the cladding was seen to have occurred by both inter- and transgranular modes for deposits containing greater than 10 wt.% Al. Below this composition limit, cracking did not occur. According to the Fe-Al phase diagram, this composition indicates the microstructural transition from the single-phase region of disordered solid solution ({alpha}) to the two-phase region of {alpha} + ordered Fe{sub 3}Al. The ordered structures of Fe{submore » 3}Al and FeAl have been found to be more susceptible to environmental embrittlement, which has been seen to be the source of the cladding cracking problem, in terms of sulfidation behavior, alloys containing 5--10 wt.% Al exhibited corrosion rates significantly lower than carbon steel and 304 stainless steel. The results of this work indicate that Fe-Al cladding containing 5--10 wt.% Al shows potential promise for applications requiring a combination of weldability and sulfidation resistance in moderately reducing environments.« less

Arnold R. Marder

Papers

Surface characterization of hot-dip Galfan coatings

Method of producing a Zn-Fe galvanneal on a steel substrate

Corrosion behavior of weldable Fe–Al alloys in oxidizing–sulfidizing environments

The influence of molybdenum on stainless steel weld microstructures : A method of producing austenitic welds is proposed that can potentially circumvent the difficulties normally encountered when fusion welding superaustenitic stainless steels

The role of aluminum on the weldability and sulfidation behavior of iron-aluminium cladding