Last time, we looked at the first 25 influences of manganese. Here are the remaining 25.

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 sulfide

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 to iron (Mn = 3.58Å, Fe = 3.44 Å)

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 intermetallic compounds suitable for precipitation-hardened austenitic steels

40. Plays a major role in controlling the precipitation process occurring 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-hardenable 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 (by maraging) 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

Carbon up to 1% does not greatly change the iron-manganese equilibrium (up to about 55% Mn). The main effect at higher manganese contents is to extend the region of austenite stability and to change the morphology of the manganese-rich phases.

The strengthening mechanisms with respect to iron-manganese-carbon alloys are due to:
  • Solid-solution hardening of austenite
  • Deformation hardening together with transformation hardening
  • Carbide precipitation hardening
Finally, hardenability increases dramatically with carbon content due to the increasing retardation of pearlite and pro-eutectoid transformations. This occurs in both hypoeutectoid and hypereutectoid steels. In the case of the latter, austenitizing may be unintentionally carried out in the two-phase (cementite-austenite) region, resulting in undissolved carbides that act as nucleation sites for pearlite formation during quenching. The alloying elements (other than carbon) that have the greatest effect are manganese and molybdenum, the former with high availability and (relatively) low cost compared to the latter.