Local properties of undermatched steel weld metal
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I. INTRODUCTION
UNDERMATCHED welding has become a topic of great interest in joining 690 MPa and stronger steels. Lower strength filler metals are simpler to weld and the weld process envelope can be expanded, offering both cost savings and greater productivity.[1–5] The net strength of the structure is only slightly affected by this reduction in filler metal strength because of triaxial constraint of the joint;[6–9] however, since plastic deformation would be concentrated in the weld metal, the local microstructural and mechanical properties must be understood. The fabrication of the two undermatched welds is described in Section II. The techniques and procedures are presented along with a description of the test system in Section III. Section IV includes chemical and microstructural analyses as well as measurements of inclusion size and distribution. The results of an extensive series of tensile tests are also presented there. Inclusions play an important role in the mechanical properties of these weldments, and those are discussed in Section V. The main points of the work are presented in Section VI. II. WELD DESCRIPTION The double-vee welds were fabricated at the Naval Surface Warfare Center–Carderock Division by the gas metal arc welding process on 50.8-mm-thick HY-100 plate. Figure 1 is an illustration of the nominal and as-deposited geometry.
DAVID A. LaVAN, Research Fellow, is with the Massachusetts Institute of Technology, Cambridge, MA 02139, and Children’s Hospital–Harvard Medical School, Boston, MA 02115. W.N. SHARPE, Jr., Professor, is with The Johns Hopkins University, Baltimore, MD 21218. Manuscript submitted October 22, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
The lower strength weld, “HBA,” was fabricated from MIL70S-6 class filler, ESAB L-TEC Spoolarc 86. The preheat and interpass temperatures were 140 ⬚C, the heat input was 25.5 to 27.5 kJ/cm. The higher strength weld, “HBB,” was fabricated from MIL-100S-1 class filler, Lincoln LA-100, with the same preheat and interpass temperatures and heat input of 31.5 kJ/cm. The nominal yield strength of the filler metal is given by its class designation. The MIL-70S has a nominal yield of 483 MPa, while full-sized, all-weld-metal tensile tests of deposited filler metal report a yield (plus or minus one standard deviation) of 486 ⫾ 12.4 MPa and an ultimate of 607 ⫾ 9.7 MPa.[10] The MIL-100S has a nominal yield of 690 MPa, and the deposited weld metal has a yield of 664 ⫾ 38 MPa and an ultimate of 751 ⫾ 46 MPa.[11] The base plate is HY-100 steel, with a minimum yield of 690 MPa; mill reports for typical heats indicate a yield of 752 ⫾ 30 MPa and an ultimate of 856 ⫾ 34 MPa.[12] III. MICROSAMPLE TESTING TECHNIQUE A novel microsample testing technique was employed to measure the stress-strain behavior of submillimeter regions. The microsample is 3.1-mm long with a gage length of 300 m and nominal gage cross-sectional dimensions of 200 by 200 m, with a bow-tie shape. This shape is self-aligning and requires no clamping or gluing of the sample. The r
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