Characterization of Cold Forging Properties of Four Ball Bearing Steels and an211 Austenitic Stainless Steel

摘要

A new testing method for characterization of cold-forging properties of steels211u001ehas been developed at the Swedish Institute for Metals Research. This test method 211u001eis able to classify and rank materials in the order of their crack initiation and 211u001epropagation properties. The test method is similar to industrial cold forging 211u001eoperations. In the present investigation, a conical punch with a TiC-coated 211u001esurface has been used to cold-forge cylindrical slugs in order to rank and 211u001einvestigate four ball bearing steels with similar chemical analysis, more exactly 211u001eone steel grade where the chemical composition has been altered under controlled 211u001eforms for some elements, and an austenitic stainless steel with different degrees 211u001eof cold reduction. The investigation shows in the ball bearing case that high 211u001ecopper content significantly affects the crack initiation properties in a 211u001enegative manner and a high silicon content have the same effect on the crack 211u001epropagation rate. For austenitic stainless steel it is shown that high n, strain 211u001ehardening exponent, and K, strength coefficient, values have a significant 211u001enegative influence on the crack propagation rate. However, the mechanical 211u001eproperties does not seem to affect the crack initiation significantly. The test 211u001emethod used in this investigation can, in other words, detect differences in 211u001ecrack initiation and propagation properties of materials caused by differences in 211u001echemical composition and mechanical data. The test method is also able to display 211u001ehow certain alloying elements influence the crack properties.