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Austenitic stainless steels are generally non-magnetic with relative magnetic permeabilities of around 1.0. Permeabilities above 1.0 are associated with the amount of either ferrite or martensite phases present in the ‘austenitic’ steel. Additions of nickel and nitrogen stabilise the austenitic phase, whereas molybdenum, titanium and niobium stabilise ferrite. All elements stabilise austenitic steels to the effect of cold work producing martensite.
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.
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.
Youngs modulus and thermal expansion data is tabulated for a range of commonly used grades shown in BS EN 10088-1. More detailed ‘typical’ data follows for austenitic steel types only from the INCO publication ‘Austenitic chromium-nickel stainless steels-engineering properties at elevated temperatures’, including tensile and shear modulus data, Poisson’s ratio, density, thermal expansion, conductivity, specific heat and electrical resistivity.
Stainless steels can be readily cut using laser methods. The properties of the steel, including magnetic permeability, should not be affected by laser cutting. Any distortion experienced during or after cutting should only be due to the relief of ‘self restraint’ on cutting and not due to any changes in the material from the cutting method.
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.
Ferritic, martensitic and duplex stainless steels are usually classified as magnetic. The effect of different microstructures on magnetic permeability is explained.
The magnetic attraction of ferromagnetic ferritic martensitic and duplex stainless steels is compared to that of the low magnetic permeability austenitic types. Hard and soft ferromagnetic types are compared. The paramagnetic austenitics have relative permeabilities around 1 and can be classed as non-magnetic. The affect of steel composition and degree of cold work on the magnetic permeabilities of austenitic types is discussed, with reference to the nitrogen grades 304LN (1.4311) and 316LN (1.4406) and the high nickel grade 310 (1.4845). Austenitic castings grades and solidified weld metal areas have higher ferrite levels than wrought, parent materials and so have higher magnetic permeability levels.
Guidance on methods for sorting stainless steels from low alloy and carbon steels is shown. These include physical (colour, density, magnetic) and mechanical (hardness) properties and chemical tests (copper sulphate, copper chloride, nitric acid and sulphur tests). A suggested approach to a step-by-step procedure for differentiating stainless steels from carbon steels is tabulated. These methods have not been verified by the BSSA, who take no responsibility for their accuracy of the conclusions reached on steel types.