Category: Cold Forming-Drawing & Pressing
Forming, Machining & Heat Treatment
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The influence of nickel content on deep drawing and stretch forming capability in austenitic grades 304, 305 and 316 are discussed. The affects on magnetic permeability and ‘orange peel’ after forming are mentioned.
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Austenitic stainless steels are generally non-magnetic with relative magnetic permeabilities of around 1.0. Cold working can partially transform the austenitic phase to martensite, leading to higher magnetic permeabilities, for example at sharp corners, sheared edges or machined surfaces. The increase in permeability can be reversed by full solution annealing.
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Forming methods are discussed and include cutting, sawing, shearing, plasma cutting, blanking, punching, piercing, bending, drawing, spinning and tube bending. A minimum bend radius of 2 times tube diameter is quoted as a guide. Extra force is required for these operations when working with austenitic stainless steels due to their tendency to work harden.
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Stainless steel can be formed in the same way and using the same type of equipment as for most types of steel. The high work hardening rates of austenitic stainless steels means that tool/machinery capability and rigidity requirements are higher than for carbon steels. The techniques for drawing and spinning are discussed.
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Austenitic stainless steels are usually described as non-magnetic, with a relative magnetic permeability of around 1.0. Permeabilities above 1.0 are associated with the amount of ferrite or martensite phases present in the austenitic steel. These depend on the precise chemical composition and the effects of cold working and heat treatment.
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Paper originally delivered at the BSSA Conference ‘Stainless Solutions for a Sustainable Future’ held in Rotherham on 3rd April 2003. This paper describes a study where 2 high strength austenitic stainless steels and 3 carbon steels used at Volvo Cars Body Components, were compared. The differences in formability and crash absorbing capability of specific components made from these steels, during plastic deformation, are shown. Tensile, (stress-strain curves), and forming limit curves are compared. Forming limit dome tests are better for assessing steels subject to microstructural changes during deformation. Component stamping trials are described and analysed.
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