灰口铸铁的等温淬火和渗硼等温淬火

Austempering and Boroaustempering Treatments for Gray Cast Iron

等温淬火能显著改善灰口铸铁的力学性能,而通过渗硼等化学热处理提高其表面硬度能进一步扩展它的应用范围。本文研究用灰口铸铁试样的成分为3.6%C-2.1%Si-0.43%Mn-0.26%Cr-bal Fe。等温淬火工艺采用900℃奥氏体化,随后在240℃、300℃和360℃的盐浴中分别保持1 h、2 h、3 h和4 h后空冷。对另一组试样进行渗硼等温淬火处理,其工艺为在950℃熔融硼砂中渗硼2-4 h,随后在240℃、300℃和360℃盐浴中分别保持1 h、2h、3 h和4 h后空冷。这种工艺不需为了等温淬火而另外加热。通过试样显微硬度的测定和黏着磨损性能试验发现,等温淬火显著提高了灰口铸铁的性能,而渗硼等温淬火则更进一步改善了灰口铸铁的性能。

Austempering heat treatment of gray cast iron can significantly improve its mechanical properties. In addition,increasing its surface hardness by means of thermochemical treatments such as boronizing can further extend its range of use. In this work,gray cast iron samples with the composition 3. 6% C-2. 1% Si-0. 43% Mn-0. 26% Cr-bal Fe were subjected to austempering treatment using austenitizing at 900 ℃,with subsequent cooling using austempering salt baths at temperatures of 240 ℃,300 ℃ and 360 ℃ for 1,2,3 and 4 hours with subsequent cooling in air. Another set of samples was subjected to boroaustempering treatments,which consisted of boriding at 950 ℃ for 2 to 4 hours in molten borax and followed by cooling in salt baths at temperatures of 240,300 and 360 ℃ for 1,2,3 and 4 hours,with subsequent air cooling. This approach avoids the need for further heating the work piece to perform the austempering treatment. Subsequently,the samples were characterized for microhardness and adhesive wear behavior. The austempering treatment significantly increased material performance and the boroaustempering treatment further improved its properties.