DIRECTIONALITY OF YIELD STRENGTH IN BAKE-HARDENED STEELS

Directionality in the mechanical behaviour of three bake-hardening ste els has been investigated. Tests in uniaxial tension were made after p restrains of 2, 5 and 10 percent and after ageing at 170-degrees, 200- degrees and 230-degrees-C for 20 min. Measurements were made with the direction of extension in the test at 0-degrees and 90-degrees to that in the prestrain. After ageing at 170-degrees-C, 0.2 percent proof st ress values in the 90-degrees tests were 30 to 50 MPa lower than the y ield strengths developed in 0-degrees tests. Ageing in the 200-degrees to 230-degrees-C range was required to give yield strengths in the 90 -degrees tests similar to those attained in 0-degrees tests after agei ng at 170-degrees-C. Detailed consideration is given to the underlying causes of mechanical directionality in strain-aged steels.