| Summary: | Biodegradable pure iron has gained significant interest as a biomedical material. For biodegradable implant applications, the biodegradation behavior of pure iron is important. In this work, the influence of ferrite grain size on the biodegradation rate for pure iron was studied by means of heat treatment that was annealed below the austenized temperature using as-forged pure iron. Grains were coarsened and a spectrum of ferrite grain sizes was gained by changing the annealed temperature. Biodegradation behavior was studied through weight loss tests, electrochemical measurements and microscopic analyses. Hardness (HV) and biodegradation rate (<i>P<sub>i</sub></i> or <i>P<sub>w</sub></i>) were linearly ferrite grain size-dependent: <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>HV</mi><mo>=</mo><mn>58.9</mn><mo>+</mo><mn>383.2</mn><msup><mi>d</mi><mrow><mo>−</mo><mfrac><mn>1</mn><mn>2</mn></mfrac></mrow></msup></mrow></semantics></math></inline-formula>, and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>P</mi><mi>i</mi></msub><mo>=</mo><mo>−</mo><mn>0.023</mn><mo>+</mo><mn>0.425</mn><msup><mi>d</mi><mo>−</mo></msup><msup><mrow></mrow><mrow><mfrac><mn>1</mn><mn>2</mn></mfrac></mrow></msup></mrow></semantics></math></inline-formula> or <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>P</mi><mi>w</mi></msub><mo>=</mo><mn>0.056</mn><mo>+</mo><mn>0.631</mn><msup><mi>d</mi><mo>−</mo></msup><msup><mrow></mrow><mrow><mfrac><mn>1</mn><mn>2</mn></mfrac></mrow></msup></mrow></semantics></math></inline-formula>. The mechanism by which the role of grain size on biodegradation rate was attributed to the ferrite grain boundary traits.
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