Tempering

Abstract: Iron and its interstitial solid solutions * The strengthening of iron and its alloys * The iron-carbon equilibrium diagram and plain carbon steels * The effects of alloying elements in iron-carbon alloys * Formation of martensite * The bainite reaction * Acicular ferrite * The heat treatment of steels - hardenability * The tempering of martensite * Commercial Steels: New material to include Nanostructured Steels, Steels for the Energy and Automobile Industries * The embrittlement and fracture of steels * Stainless steel * Weld microstructures * Modelling of microstructure and properties *

Abstract: In this Second Edition, new information and references are integrated into chapters. Emphasis is still on processing, alloying, microstructure, deformation, fracture and properties of major steel types ranging from low-carbon sheet steels, pearlitic rail and wire steels, to quench and tempered medium- and high-carbon martensitic steels. Microstructural aspects of steelmaking, hardenability, tempering, surface hardening, and embrittlement phenomena are updated, and chapters on stainless and tool steels remain in the Second edition. The work is intended to be tutorial and is an essential state-of-the-art reference for anyone that makes, uses, studies and designs with steel.

Abstract: Hardness values as well as yield and tensile strength values were compiled for over 150 nonaustenitic, hypoeutectoid steels having a wide range of compositions and a variety of microstructures. The microstructures include ferrite, pearlite, martensite, bainite, and complex multiphase structures. The yield strength of the steels ranged from approximately 300 MPa to over 1700 MPa. Tensile strength varied over the range of 450-2350 MPa. Regression analysis was used to determine the correlation of the yield strength and the tensile strength to the diamond pyramid hardness values for these steels. Both the yield strength and tensile strength of the steels exhibited a linear correlation with the hardness over the entire range of strength values. Empirical relationships are provided that enable the estimation of strength from a bulk hardness measurement. A weak effect of strain-hardening potential on the hardness-yield strength relationship was also observed.

Abstract: A novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described. This involves quenching to below the martensite-start temperature and directly ageing, either at, or above, the initial quench temperature. If competing reactions, principally carbide precipitation, are suppressed by appropriate alloying, the carbon partitions from the supersaturated martensite phase to the untransformed austenite phase, thereby increasing the stability of the residual austenite upon subsequent cooling to room temperature. This novel treatment has been termed ‘quenching and partitioning’ (Q&P), to distinguish it from quenching and tempering, and can be used to generate microstructures with martensite/austenite combinations giving attractive properties. Another approach that has been used to produce austenite-containing microstructures is by alloying to suppress carbide precipitation during the formation of bainitic structures, and interesting comparisons can be made between the two approaches. Moreover, formation of carbide-free bainite during the Q&P partitioning treatment may be a reaction competing for carbon, although this could also be used constructively as an additional stage of Q&P partitioning to form part of the final microstructure. Amongst the ferrous alloys examined so far are medium carbon bar steels and low carbon formable TRIP-assisted sheet steels.

Abstract: Tempering of martensitic steels involves the segregation of carbon, the precipitation of carbides, the decomposition of retained austenite, and the recovery and recrystallization of the martensitic structure Because these several reactions overlap and occur on such a fine scale, it is only recently that our knowledge of the resulting structures has become reasonably complete Our present understanding of the processes involved in the tempering of iron-carbon martensites and how they are affected by alloying elements is reviewed