Manganese is a major alloying element, has complex interactions with carbon and is used to control inclusions. Manganese is beneficial to surface quality in all carbon ranges with the exception of rimmed steels and is particularly beneficial in high-sulfur steels. Manganese provides lesser strength and hardness in comparison to carbon. The increase depends on the carbon content – higher-carbon steels being affected more by manganese. Higher-manganese steels decrease ductility and weldability (but to a lesser extent than carbon). Manganese also increases the rate of carbon penetration during carburizing.
The effects of manganese can be summarized as.1. Lowers the temperature at which austenite begins to decompose 2. Extends the metastable austenitic region and delays the commencement of all the austenite decomposition reactions 3. Favors the formation of lower bainite and suppresses the upper bainite reaction on isothermal transformation 4. Is the most effective alloying addition for lowering the martensite-start (MS) temperature 5.Favors the formation of e-martensite 6.Has little effect on the strength of martensite and on the volume change from austenite to martensite 7. Has little or no solution-hardening effect in austenite and between 30–40 MN/m2 per wt. % in ferrite (by lowering the stacking-fault energy of austenite, manganese increases the work-hardening rate) 8. By lowering the MS temperature, manganese prevents the deleterious effects of auto tempering 9. Lowers the transformation temperature, causing substantial grain refinement 10. In general, lowers the tough-to-brittle impact transition temperature (due to its grain-refinement action) 11. Increases the propensity for weld cracking due to the effect on hardenability. The severity of its influence depends to a great extent on the type of steel and the welding techniques. 12. Does not increase the susceptibility of the steel to delayed fracture due to hydrogen absorption 13. Improves the fatigue limit 14. Reduces the number of cycles to failure under high strain conditions 15. Forms five carbides (Mn23C5, Mn15C4, Mn3C, Mn5C2 and Mn7C3), the dominant one being Mn3C, which forms a continuous range of solid solutions with Fe3C, thus reducing the solubility of carbon in a-iron 16. Prevents the formation of an embrittling grain-boundary cementite. 17. Suppresses the yield extension in deep-drawing steels by virtue of its grain-refinement effect 18. Suppresses strain aging 19. In combination with nitrogen, has a solid-solution hardening effect and improves high-temperature properties 20. Extends the range of use of low-carbon steels 21. Has a strong influence on the pearlite morphology of high-carbon steels 22. Extends the range of use of high-carbon steels through its grain-refining and pearlite-refining actions 23. Raises strength values in bainitic steels by reducing grain size and increasing dispersion hardening 24. Allows bainitic steels to be produced by air hardening 25. Increases hardenability 26. Slows down the temper reactions in martensite 27. Assists interphase precipitation 28. Improves austemper and martemper properties 29. Increases temper embrittlement unless the carbon content is very low and trace element impurities are minimal 30. In spring steels, promotes ductility and fracture toughness without undue loss in tensile strength 31. Removes the risk of hot shortness and hot cracking when the ratio of manganese to sulfur is greater than 20:1 by forming a higher melting-point eutectic with sulfur than iron sulphide 32. Has a major influence on the anisotropy of toughness in wrought steels due to the ability to deform manganese sulfides during hot working 33. Forms three manganese sulfide morphologies (Type I, II and III) dependent upon the state of oxidation of the steel 34. Enhances free-cutting steels 35. Increases the stability of austenite 36. Has similar atomic size as iron 37. Lowers the stacking-fault energy of austenite (in contrast to alloying element additions such as chromium or nickel) 38. Allows lower solution temperatures for precipitation-hardening treatments in highly alloyed austenite due to increased carbon solubility 39. Forms s intermetallic compounds suitable for precipitation-hardened austenitic steel detailing course in kochi 40. Plays a major role in controlling the precipitation process that occurs during isothermal transformation to austenite 41. Increases the rate of carbon penetration during carburizing 42. Contributes, in combination with nitrogen, to the performance of work hard enable austenitic stainless steels 43. Improves hot corrosion resistance in sulfurous atmospheres 44. Enhances wear-resistance in carbon-containing austenitic steels where the manganese content is between 12-14% 45. Improves response of low-alloy steels to thermomechanical treatments 46. Strengthens certain steels by producing an austenitic structure using manganese-containing compounds 47. Enhances the performance of TRIP steels 48. Promotes Ferro-elastic behavior in appropriate steels 49. Less tendency to segregate within the ingot 50. In general, improves surface quality.