On March 10, 2005, about 1943 eastern standard time, a Cirrus Design Corporation SR20, N8160C, suffered separation of the nose landing gear during landing at Craig Municipal Airport, Jacksonville, Florida, while on a 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and an instrument flight rules flight plan was filed. The airplane received minor damage and the private-rated pilot and one passenger were not injured. The flight last departed Fort Pierce, Florida, the same day, about 1845. The pilot stated that while approaching to land on runway 5 at Craig Municipal Airport, he approached at a faster than normal airspeed. During the landing flare, the airplane porpoised a couple of times. On the second porpoise, the airplane touched down on the nose and the nose landing gear collapsed. The propeller struck the runway and the airplane skidded to a stop about 10 feet past sand bags, which marked the beginning of a construction zone on the runway. He stated the touch down was not any harder than the occasional hard landings made during flight training. Postincident examination of the nose landing gear showed it had separated at the point the gear is welded to the strut. The airplane's nose landing gear was sent to the NTSB Materials Laboratory in Washington DC for further inspection. The inspection reveled that the strut assembly was fractured through the weld between the strut tube and the spindle assembly. Severe and course abrasive grinding was evident on the lower edge of the nose wheel fork. The weld is a fish mouth notch cut that travels the periphery diameter of the nose gear strut. Magnified examination found that the fracture was almost entirely contained within the fusion zone of the weld. The fracture was consistent with a rearward bending overstress, and no indications of preexisting cracking such as fatigue or significant corrosion were uncovered. Several large and many small pores were exposed in the fusion zone by the fracture. The large pores were consistent with gas voids measuring up to 0.078 inch in diameter, while the small pores were typical of shrinkage porosity and measured between 0.005 and 0.013 inch in diameter. "Discontinuity Acceptance Criteria" of the Cirrus "Ferrous Alloys Welding Process Specification" specifies the maximum acceptable size and the minimum acceptable spacing of subsurface porosity. The size and spacing of the existing porosity was not acceptable for class A welds using these criteria. Examinations of the fracture surfaces also showed areas of incomplete penetration of the weld to the root of the joint. Approximately 1/3 of the total weld length did not display penetration to the inner diameter of the tube section of the weld joint. The weld bead penetrated as little as an estimated 33% of the joint.