Laser Beam Welding of HY80 and HY100 Steels Using Hot Welding Wire Addition

WELDING RESEARCH SUPPLEMENT TO THE WELDING JOURNAL, JUNE 1992 Sponsored by the American Welding Society and the Welding Research Council Laser Beam Welding of HY80 and HY100 Steels Using Hot Welding Wire Addition Good impact properties are attained in high-strength steels welded with the laser beam process using a preheated filler metal BY R. H. PHILLIPS AND E. A. METZBOWER ABSTRACT. Laser beam welds incorpo proved using a fast wire feed compared welding in the heterogeneous mode rating a hot welding wire filler metal ad to a slow wire feed. compared to the autogenous mode can dition technique have been successfully be considered as follows: produced in HY80 and HY100 steels. Introduction 1) Confers the ability to alter the Plate thicknesses of 1 3 and 26 mm were chemical composition and thus the mi welded by this technique in these ex Laser beam welding is a high produc crostructure of the weld metal. This in periments. tivity process that is traditionally used turn can result in improved mechanical This evaluation included radio- in the autogenous mode {i.e., no filler properties of the weld metal, particu graphic and metallographic examina metal is added to the weld pool). How larly notch toughness. It can also result tions, hardness traverses, Charpy V- ever, it can clearly be perceived that on in improved resistance to weld metal so notch tests over the temperature range specific occasions there would be dis lidification cracking. -68° to 20°C and fractographic exami tinct advantages and greater flexibility 2) Results in larger fit-up tolerances. nations. in deploying laser beam welding in the 3) Affords the opportunity for deposit Hardness traverses across the hot wire heterogeneous mode (i.e., by use of filler ing high-quality multipass welds with addition welds showed a significant re metal additions to the weld pool). Sev reduced porosity, compared to autoge duction in weld metal hardness com eral examples of laser beam welding in nous weldments. pared to the autogenous welds. The re corporating cold welding wire feed have In the specific cases of HY80 and duction in hardness was greater for the been reported in the literature in recent HY100 steels, the relatively high carbon "fast" wire addition welds compared to times (Refs. 1-3). (0.1 5-0.1 8 wt-%) and alloy content of the "slow" wire addition welds. The main advantages of laser beam the steels, together with the fast cooling The hot wire feed speed also had a rates associated with autogenous laser concomitant effect on weld metal mi beam welding, ensures the formation of crostructure. The slow wire feed speed untempered martensitic microstructures resulted in a mixed martensite-bainite in the weld metal. This can lead to the microstructure, whereas fast wire feed KEY WORDS formation of weld metal with poor notch speed produced an acicular ferrite mi ductility (Refs. 4, 5). Feed Speed crostructure. By way of comparison, the weld Charpy tests showed that hot wire ad Hardness Testing metal deposited using conventional arc dition significantly improved weldment Hot Welding Wire welding of HY steels characteristically toughness compared to autogenous Hot Wire Additions has a relatively low carbon level rang welds at the plate sulfur level investi HY80 ing from 0.05 to 0.08 wt-%. Under ap gated (0.01 2 wt %) for both HY80 and HY100 propriate welding conditions, this leads HY100 steels. Toughness was further im- Laser Beam Welding to the formation of an acicular ferrite mi Metallography crostructure with a concomitant high Microstructure R. H. PHILLIPS is with the Materials Research toughness profile. Laboratories, Melbourne, Australia, and E. Steel Plate The two methods of filler metal addi A. METZBOWER is with the Naval Research tion that appear to have the best poten Laboratory, Washington, D.C. tials for use with laser beam welding are WELDING RESEARCH SUPPLEMENT I 201-s FOCUSING a plane mirror into a downward-facing concave mirror with a focal length of MIRROR 750 mm (29.5 in.) to provide welding conditions in the flat position. The plates to be welded were 150 X 300 mm (6 X 12 in.) thick, resulting in a 300 X 300- mm (12X12-in.) thick weldment. A schematic diagram of the worksta tion including the hot wire feed unit is shown in Fig. 2A and in greater detail in Fig. 2B. The welds were made by mov ing the workpiece on a traversing table under the stationary laser beam. The REFLECTING angle between the normal to the plate and the laser beam was approximately FLAT MIRROR 3 deg. Helium gas was used for plasma suppression as well as general area shielding of the weld. Plasma suppression was achieved by GAS SHIELD AND directing a jet of helium gas through a W//7rWA PLASMA SUPPRESSION 2-mm (0.08-in.) diameter stainless steel tube (hypo tube) at the point where the WORK focused laser beam would impinge upon the plate surface. The hypo tube was set behind the laser beam at an angle of Fig. 1 — Schematic diagram of beam focusing arrangements and workstation. about 45 deg and was coplaner with the welding direction. The flow rate of the helium gas was approximately 3 L/min welding wire addition or metal powder The paper concentrates on the 3 addition. Charpy V-notch specimens since it has (1.4 ft /h)as determined by a gas flow Of these, welding wire addition ap been demonstrated that the attainment meter calibrated for air. pears to hold the best potential, both of weldments with adequate mechani Precise alignment of the joint to be from the viewpoint of metallurgical cal properties in laser beam welds of welded was made using a helium-neon quality of the weld and also productiv HY80 and 100 is not a problem (Refs. (He-Ne) laser, which was coincident ity. For instance, oxygen and hydrogen 5,6). with the C02 laser beam. Prior to weld pickup in the weld metal would be far ing, tack welds were made at both ends more of a problem for welding with Experimental Procedure of the plate to be welded, which pre metal powders than for welding with and Materials vented relative movement between the wire. two plates due to expansion and con In the experimental work reported, a A 1 5-kW continuous wave, carbon traction of the plates during welding. hot wire addition technique was used dioxide laser in the unstable resonator A longer focal length mirror of 750 so that most of the energy from the laser mode was used for these experiments mm was used for the hot wire addition beam was used to establish and main (Ref. 7). A schematic diagram of the laser experiments compared to a 500-mm tain the keyhole rather than being par beam focusing arrangements is shown (20-in.) focal length mirror for the auto tially dissipated in melting the filler in Fig. 1. The horizontal output beam genous laser beam welding experiments metal. from the laser was reflected upward by (Ref. 4). It was necessary to use the Hot wire designed to skid along base of groove into path of laser beam Laser beam Welding wire Gas lens for He area shield — Solidified weld metal Plasma suppression hypo needle He gas He backing gas Fig. 2 — A — Schematic diagram of experimental setup for laser beam welding with hot welding wire feed; B — detail of hot wire filler metal addition. 202-s I JUNE 1992 Table 1—Composition of Experimental Materials Chemical Composition wt-% C s P Mn Si Ni Cr Mo Cu Al 13-mm-thick HY80 0.16 0.014 0.0007 0.32 0.18 2.32 1.41 0.29 0.13 0.03 Plate 13-mm-thick HY100 0.16 0.016 0.005 0.26 0.21 2.66 1.47 0.41 0.15 0.02 26-mm-thick HY80 0.15 0.002 0.005 0.31 0.31 2.24 1.37 0.28 0.17 0.05 Welding 1.2-mm-diameter 0.065 0.004 0.006 1.50 0.21 2.10 0.10 0.47 0.04 Wire Airco AX90 As- 13-mm HY80 with HWA<a' 0.10 0.009 0.007 0.63 0.29 2.18 0.94 0.36 0.09 0.02 Deposited at 145 mm/s Weld Metal 13-mm HY100 with HWA 0.10 0.009 0.006 0.87 0.28 2.16 0.70 0.47 0.10 0.03 at 145 mm/s 13-mm HY80 with HWA 0.06 0.005 0.008 1.08 0.26 2.28 0.37 0.47 0.08 0.02 at 425 mm/s 26-mm HY80 with HWA 0.07 0.003 0.006 1.16 0.40 2.02 0.35 0.45 0.09 0.03 at 425 mm/s (a) HWA is hot wire addition. longer focal length mirror to enable the marily directed at establishing the most of 1 3 kW; and 2) a travel speed of 8.5 physical location of the hot wire so that appropriate edge preparation and weld mm/s (20 in./min). the incoming laser beam would not im ing conditions for the root pass. pinge upon it. Although the longer focal The compositions of all experimen Results and Discussion length mirror has the advantage of hav tal steels and the welding wire are shown ing a greater depth of field, it has the dis in Table 1. Welding Parameters and Characteristics advantage of having a larger spot diam Two edge profiles were used in the eter at the focal point and hence a some experimental work (stepped and V- Good quality welds with acceptable what reduced power density.

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