Immersion Boronizing of Steels by Boric Acid and Potassium Borate

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  • ホウ酸，ホウ酸カリウムによる鋼の浸せきホウ化処理
  • ホウサン ホウサン カリウム ニヨル コウ ノ シンセキ ホウカ ショリ

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Abstract

Boronizing of steels has an advantage over carburizing or nitriding in being able to get harder surface of steels. Besides, boronizing is easier in treatments and does not require special equipments. Usually, as a main salt composition for immersion boronizing of steels, B4C, Na2B4O7·10H2O, Fe-B, KBF4, CaB6 or BN among others has been used.<br>This paper describes the immersion boronizing which utilizes relatively inexpensive boric acid and potassium borate as major salt compositions and magnesium powder as a reducing agent. The results obtained were as follows:<br>(1) A favorable boride layer was obtained by using magnesium powder as a reducing agent and boric acid and potassium borate as sources of boron supply. From the view point of economical efficiency in boronizing of steels, the best condition for boronizing was composed with H3BO3: 40 wt%, K2B4O7·5H2O: 20wt%, NaF: 15wt%, K2CO3: 15wt% and Mg powder: 10wt%.<br>(2) In these experiments, the treatment for boronizing at 700°C did not yield any boride layer on steel, but the treatment above 750°C could yield boride layer. The satisfactory temperature for boronizing of steels was 900°C.<br>(3) The composition of the boride layer was only Fe2B.<br>(4) The microhardness of boride layer was from 1200 to 1800 for HV (0.1kg).<br>(5) With increasing viscosity of salt, the thickness of boride layer tended to become more uneven.<br>(6) The effect of the material of crucibles on the thickness of boride layer was not so noticeable for corundom and stainless steel crucibles.<br>(7) In the case of carbon steels, the thickness of boride layer decreased slightly with increasing carbon content in steels.

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