Published: Jan 1980
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When Type 409 stainless steel (11 percent chromium, balance iron, titanium stabilized) was specified for rectangular mechanical tubing for structural components, brittle fracture concerns were not anticipated because the tube wall thickness was in the plane-stress regime. However, low-temperature impact tests indicated that brittle fractures often occurred in the corner areas of the rectangular tubing, suggesting that residual cold-work influenced impact strength. Laboratory impact tests showed cold-working to strongly affect the ductile-to-brittle transition temperature (DBTT) of 409 stainless. A novel impact specimen allowed direct evaluation of the DBTT of the cold-worked tubing corner, confirming results obtained in conventional Charpy tests. An acceptably low DBTT for heavily cold-worked sections was found for a low-carbon ferritic stainless (11Cr-1Ni-0.03C-Fe) obtained from Crucible Steel Corp. under the trade designation of E-4. The as-welded toughness of E-4 is also improved over 409 due to the formation of low-carbon martensite in weld-heat-affected zones; in this application, however, only the base material properties were of interest.
brittle fracture, 409 stainless, rectangular tubing, low-temperature impact, tubing corners, cold-working, impact transition temperature, E-4 stainless, ferritic stainless steels, fracture toughness
Departmental research engineer, General Motors Research Laboratories, Warren, Mich.