Fundamental Research Of Free-cutting Stainless Steel With Tin-calcium Combined Treatment

Stainless steels are widely used as its excellent corrosion resistance, high temperatureresistant, antimagnetic features. However, because of high toughness, high hot strength, andlow conductivity factor, stainless steels are difficult to machine. Problems such as poor surfacefinish, high tool wear, low production efficiency and high processing costs, which lead to theapplication of stainless steel has been limited. Many attempts have been made to improve themachinability of these steels by adding free-machining elements, such as sulfur, lead,selenium and tellurium. However, there are some problems and shortcomings with theseelements in the stainless steels, such as, sulfide inclusions deteriorate corrosion resistance andhave an adverse effect of thermal processing and mechanical properties of stainless steels.Lead in steels is difficult to uniformly distribute and lead is toxic. There are the sameproblems about thermal processing and corrosion resistance of Selenium, and Selenium areexpensive.In view of this situation, a new type of non-leaded free-cutting steel by adding tin andcalcium was researched and developed, which will avoid toxic elements such as lead,Selenium impact on human health and reduce the adverse effects of sulfur on the performanceof stainless steels because of lower sulfur content.This paper describes the preparation of the new environmentally and friendly free-cuttingstainless steel. Through theoretical analysis, observation of the inclusions and the tests ofmachinability, mechanical properties, corrosion resistance of the new steel, we get thefollowing conclusions:(1) The addition of tin in the430stainless steel will improve the life of carbide cuttingtools within a certain range and the tool life is increased with increasing tin content in the steel.Tin slightly increases the steel’s tensile strength, yield strength and section shrinkage andexhibited a better surface finish. Tin addition resulted in improving corrosion resistance of thesteel, and with the increase of tin content in the steel, the corrosion resistance of steel thebetter.(2) The inclusions with single components of MnS were going to turn into slight andspheroid composite inclusions (Ca, Mn) S with the shell of CaS by calcium treatment in430Stainless Steel. In addition, part of calcium in molten steel would combine with hard phaselike Al2O3, SiO2to form CaO-Al2O3-SiO2composite inclusions. Calcium treatment can reducethe surface roughness of the workpiece, improve the life of carbide cutting tools and the toollife in accordance with calcium content in the steel within a certain range, at the same time,calcium treatment has little effect on the mechanical properties and corrosion resistance of thestainless steel.(3) Compared with tin addition in the430stainless steel, the program of Sn-Ca combinedtreatment is better in terms of machinability, corrosion resistance and mechanical properties.