Fracture behavior of C-Mn steel and weld metal in notched and precracked specimens: Part I. fracture behavior
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I.
INTRODUCTION
THE correlation
between the Charpy V and the COD test for weld and base metals is different. Some attempts ]1,21 have been made to establish this correlation from a large number of existing results. It has been found that weld metal which presented a lower ductile-to-brittle transition temperature in Charpy V testing had a higher one in COD testing than corresponding values for base metal. For this reason, the COD value of weld metal for offshore structure is specified. This work attempts to lay a physical basis for explaining the different behaviors of weld and base metals in COD and Charpy V tests and to find the prerequisite condition for establishing a correlation between these two tests by measuring the mechanical properties of base and weld metals in notched and precracked specimens at various temperatures and loading rates.
direction was prepared for measuring the work-hardening exponent, n, of the weld metal. The dimensions are shown in Figures 2 and 3 for the toughness and tensile specimens, respectively.
D. Experimental Procedures 1. Tensile testing The tensile tests were carried out by S H I M A D Z U AG-10 TA universal testing machines with crosshead speeds of 5 m m / m i n and 200 m m / m i n over a temperature range of - 110 ~ to 20 ~ The true fracture strain, es, was calculated from Eq. [1].
ef = In 1/(1 - ~b)
Here, ~b is the reduction of area. The true fracture strain, ey, under the plane strain condition was calculated from Kobayashi's relation. [3] e~ = 0.67ey
II.
EXPERIMENTAL
A. Materials The materials used were a C-Mn base steel and C-Mn and Ti-B weld metals, with their compositions shown in Table I.
B. Welding Conditions The welding conditions used are shown in Table II.
C. Specimens The toughness and tensile specimens of weld metals were sampled, as shown schematically in Figure 1 and in TL orientation for base metal. The two types of specimens were sampled at the same part of the metals. The specimen with a square cross section along the welding J.H. CHEN, Professor, H. MA, Lecturer, and G.Z. WANG, Assistant, are with the Welding Department, Gansu University of Technology, Lanzhou, Gansu, People's Republic of China. Manuscript submitted January 4, 1989. METALLURGICAL TRANSACTIONS A
[1]
[2]
The work-hardening exponent, n, was obtained from the slope of log e-log s curve. The symbols e and s represent true strain and stress, respectively.
2. Toughness testing procedures The Charpy V and fatigue-precracked impact (PC) tests were carried out with a CIEM-30CPC instrumented impact testing machine at temperature ranges of - 1 0 0 ~ to 20 ~ and of - 8 0 ~ to 40 ~ respectively. The COD tests were carried out by three-point bending at a crosshead speed of 1 m m / m i n from - 1 1 0 ~ to 20 ~ with the same installation used in the tensile tests. The values of COD and Charpy V of individual specimens were plotted.
3. Determining mechanical properties Typical load-displacement curves obtained in Charpy V, PC, and COD tests at transition temperatures are shown in Figure 4.
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