![](https://cos-cdn.shuashuati.com/pipixue-web/2020-1231-2005-12/ti_inject-812ce.png)
Chapter 9, Problem 57 What types of microstructures are produced by tempering a plain-carbon steel with more than 0.2 percent carbon in the temperature ranges (i) 20–250C, (ii) 250–350°C, and (iii) 400–600°C? (b) What causes the decrease in hardness during the tempering of a plain-carbon steel?