6669
Retained austenite and transformed martensitic phases exhibited a fine grain structure preferentially along the coarse ferrite grain boundaries .
 material: Retained austenite; concept or principle: grain structure; material: ferrite; engineering feature: boundaries
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
 Entities: Retained austenite, grain structure, ferrite, boundaries 
Answer:
 material: Retained austenite; concept or principle: grain structure; material: ferrite; engineering feature: boundaries