• 한국표면공학회지
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• 제8권3호
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• pp.5-11
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• 1975

The boronizing method using ferroborn and NaBF4 powder mixture was studied for surface hardening of medium carbon steel. This boride layer was compared with a boride layer that was formed in ferroboron and KBF4 powder mixture. The frequency factor and activation energy were discussed in this paper. The main results obtained can be summerized as follow. 1) The optimum range of NaBF4 content is 10 to 15% of weight to obtain a thick and dense boride layer. 2) The depth of the boride layer was approximately expressed by the following equation : {{{{d=100 exp (-18,000/RT) SQRT { t} }} 3) The oxidating resistance of boronized steel proved to be good at 800$^{\circ}C$ but almost unacceptable near at 900 $^{\circ}C$. 4) The NaBF4 effect was the same as that reported for KBF4.

• The Korean Journal of Ceramics
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• 제6권1호
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• pp.27-31
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• 2000

A series experiments were performed to evaluate mechanical behavior of non-oxide boride type ceramics formed on the AISI 1040 plain carbon steel. Boronizing was performed in a slurry salt bath consisting of borax, boric acid, and ferro-silicon at $950^{\circ}C$ for 2-6h. The AISI 1040 steel used as substrate material was containing 0.4%C, 0.13%Si, 0.65%Mn, 0.02%P, 0.014%S. The presence of non-oxide boride type ceramics $Fe_2B $ and FeB formed on the surface of steel was confirmed by metallographic technique and X-ray diffraction (XRD) analysis. The hardness of borides measured via Vickers indenter with a load of 2N reached a microhardness of up to 1800 DPN. The hardness of unborided steel was 185 DPN. The fracture toughness of borides measured by means of Vickers indenter with a load of 10N was about 2.30 MPa.$m^{1/2}$. The thickness of boride layers ranged from 72$\mu\textrm{m}$ to 145$\mu\textrm{m}$. Boride layers have a columnar morphology.

• 한국표면공학회지
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• 제32권1호
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• pp.67-77
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• 1999

The Ni base superalloy Mar-M247 substrate was aluminized or aluminized after boronizing by the pack cementation under Ar atmosphere. The hot corrosion resistance and after-heat-treatment effect of aluminized specimens were studied by the cyclic hot corrosion test in $Na_2SO_4$-NaCl molten salt. XRD analysis showed that the $Ni_2Al_3$ phase was formed between the coated layer and substrate below 1273K but the NiAl phase above 1273K. The peak of the NiAl phase was developed after heat treatment. Corrosion test showed that corrosion resistance of the specimen with the NiAl phase was better than that with the $Ni_2Al_3$ phase. Corrosion resistance could be improved by heat treatment to form ductile NiAl phase, where cracks were not formed by thermal shock on coating layer. Moreover, it appeared that heat treatment played a role to improve corrosion resistance of Al diffusion coating above 1273K. The existence of boron in the Al diffusion coating layer obstructed outwared diffusion of Cr from the substrate, and it influenced on corrosion resistance of the coating layer by weakening adherence of the oxide scale.