The Effect of High Boron Additions on the Microstructure of Cast Steel

Abstract

This study summarizes research into the effect of high boron additions on the microstructure of cast steel under the certain carbon (0.42 C wt.%) and chromium (11.65 Cr wt.%) content. Varying amounts of boron between 0.48 -4.75 wt.% was added into steel melt. The boron analysis of the alloys was conducted by wet chemical analysis. The microstructure of the specimens was characterized with optical microscope, Scanning Electron Microscope with Energy Dispersive X-Ray Analysis (SEM/EDX) and X-Ray Diffraction (X-RD). The experimental results showed that high boron steel was successfully produced by sand casting with high casting yield. The microstructure of boron alloyed high chromium cast steel consists of three dimensional networks of M 2 B borides surrounding the martensitic matrix in as cast condition. Under the certain carbon and chromium content, boron carbide volume fraction is directly depended on the boron additions. Due to the high amount of chromium and boron, carbides and borides were embedded in each other in all additions. In the specimens having less than 2.44 B wt.%, carbide/boride structure was fishbone type with dendritic distribution over the matrix whereas rod/needle like structure with randomly distribute was observed in specimens having 2.44 -4.75 B wt.%. In all specimens containing boron, M 2 B and M 7 (C, B) 5 type carbides/boride peaks were detected by X-RD analysis.

1040 Kalite Çeliğin Korozif Aşınma Davranışına Farklı Oranlarda İlave Edilen Borun Etkisi

“…Bilindiği üzere, dünya bor rezervinin %73'lük kısmı ülkemiz topraklarında bulunmaktadır. Bunun yanında bor, çeliklere ilave edildiğinde daha üstün aşınma, korozyon ve mukavemet özellikleri kazandırmaktadır [1][2][3][4][5][6][7][8][9].…”

“…Çünkü bu oranın üzerinde ilave edilen bor miktarları çeliklerde yüksek sıcaklıkta kırılganlıklara, dökme demirde ise çatlamalara neden olur [1]. Bor çeliklerde % 0,007 oranına kadar sertleştirme derinliğini artırır, dökme demirlerde ise % 0,005'e kadar grafitin çekirdekleşmesine ve yapının düzgün bir şekilde dağılmasına sebep olur [1,3]. Takım çeliklerine bor ilâvesi sertleşme kabiliyetini arttırmaktadır [1,4].…”