The query " improvement " is redirected here, perhaps it should be somewhere to state the more general meaning of the word. See also the word “improvement” in Wiktionary .
Improvement - complex heat treatment of metals , including quenching and subsequent high tempering .
Description
As a result of steel hardening, the structure of martensite with some residual austenite is most often obtained, sometimes the structure of sorbitol , troostite or bainite . Martensite has high strength , hardness , low ductility , and is destroyed during processing due to its brittleness . The structure of martensite is non-equilibrium, there are residual stresses . High tempering (heating to a temperature of 20–40 ° below the Ac1 point of the “Iron-Cementite” diagram) and exposure at 450..700 [1] ° C leads to a decrease in internal stresses due to the decomposition of quenching martensite and the formation of sorbitol tempering. As a result, tempering decreases the hardness of 270 ... 320 HB [1] and strength; ductility and toughness increase. In the absence of requirements for toughness and ductility, a more economical method of heat treatment is used - normalization .
Examples of steels being improved
- Constructional steels : 30, 35, 40, 45, 50
- Alloyed steels : 40Х, 45Х, 40ХР, 40ХН, 40ХНА, 40ХНМА, 30Х2Н4МА, 38ХН3МА, 38Х2НМА, 30ХГСА , 30ХГС-Ш
Literature
- Filinov S. A., Figer I. V. - Thermist Handbook. ed. "Engineering". Leningrad 1969.