Spheroidizing Heat Treatment Research Articles

Directly spheroidizing during hot deformation in GCr15 steels

The spheroidizing heat treatment is normally required prior to the cold forming in GCr15 steel in order to improve its machinability. In the conventional spheroidizing process, very long annealing time, generally more than 10 h, is needed to assure proper spheroidizing. It results in low productivity, high cost, and especially high energy consumption. Therefore, the possibility of directly spheroidizing during hot deformation in GCr15 steel is preliminarily explored. The effect of hot deformation parameters on the final microstructure and hardness is investigated systematically in order to develop a directly spheroidizing technology. Experimental results illustrate that low deformation temperature and slow cooling rate is the favorite in directly softening and/or spheroidizing during hot deformation, which allows the properties of asrolled GCr15 to be applicable for post-machining without requirement of prior annealing.

耐摩耗鋼板の機械的特性とミクロ組織に及ぼす軟化熱処理の影響

The abrasion-resisting steels are used for structural parts and required for construction machinery parts. Generally, they are so difficult to form the desirable product shape that they must be subjected to a kind of softening heat treatment. In the past, the full annealing treatment with a very extended period of 24 h has been conducted in our production, however, the spheroidizing heat treatment brings about a good machinability with a brief heat treatment time.1) In this study, it is investigated that the effect of the spheroidizing annealing on mechanical properties and microstructure. As a result, we could shorten the heat treatment time and obtain comparable properties to the conventional products by adopting spheroidizing annealing. It was found that, in the proeutectoid ferrite, it is effective to austenitize before spheroidizing period to decrease the yield stress because of coarsening pearlite colony size and spreading the pearlite lamellar spacing.

Evaluation of microstructures of variously heat treated carbon steel by magnetic coercivity measurement

AbstractThe microstructures of variously heat treated 0.85% carbon steel were evaluated by magnetic coercivity measurement. Austenitizing, isothermal transformation, continuous cooling or spheroidization heat treatment was carried out to produce various microstructures. Microstructural parameters such as prior austenite grain size, phase and pearlite interlamellar spacing were measured along with coercivity to investigate the relationships between them. Prior austenite grain size had little effect on the measured coercivity. Coercivity was observed to be high in order of martensite, pearlite and ferrite phase. The linear decrease of coercivity with the increasing pearlite interlamellar spacing was found. Therefore, coercivity was suggested as a potential nondestructive evaluation parameter for assessing the microstructures – pearlite interlamellar spacing and kind of phase – of 0.85% carbon steel. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Heat Treatment on the Microstructure of Spray Formed AISI M2 High-Speed Steel

The effect of heat treatment on the microstructure of spray formed AISI M2 high-speed steel is under evaluation. The objective of this work was to optimise the heat treatments aiming further mechanical working. The M2 steel used in the present work was obtained in a spray forming plant in Brazil, built for processing billets preforms of light alloys and steels. The typical microstructure of spray formed materials, i.e., fine and equiaxial grains, allowed the optimisation of the M2 spheroidization heat treatment. The heat treatment at 1160 ± 10 □C for 12 hours was effective in producing microstructure and hardness suitable for further mechanical working.

Magnetic Evaluation of Microstructures and Strength of Eutectoid Steel

Microstructures and strength of variously heat treated eutectoid steel were evaluated by magnetic property measurements. Isothermal transformation, continuous cooling or spheroidization heat treatment was performed to produce various microstructures. Microstructural parameters (phase, pearlite interlamellar spacing), mechanical properties (fracture strength) and magnetic parameters (coercivity, remanence, hysteresis loss, saturation magnetization) were measured to investigate the relationships among these parameters. Coercivity and remanence were observed to be high in order of martensite, pearlite and ferrite phase. The linear decrease of coercivity and remanence with the interlamellar spacing and the linear increase of those with fracture strength of pearlitic eutectoid steel were found. Coercivity and remanence were suggested as potential magnetic parameters for discriminating phases and quantitatively assessing the pearlite interlamellar spacing as well as strength of eutectoid steel.

구상화 열처리 기술의 발전 동향

구상화 열처리 기술의 발전 동향

Influence of microstructure on machinability of wrought steels

The various ways in which machinability can be evaluated, both in terms of individual or combined machining parameters, or by theoretical energy or force expressions, are reviewed. This background is then used to discuss ways in which the steel microstructure affects the basic requirements of low strength and minimum ductility for good machinability, together with other factors of significance, but excluding the influence of specific additions for free machining. In low-carbon steels, the influence of heat treatment, cold work, and solid-solution strengthening of the ferrite is discussed; spheroidizing heat treatment becomes significant at medium to high carbon levels and may be combined with cold work. In alloy steels, isothermal heat treatment to allow the separation of proeutectoid ferrite during cooling from rolling is a possible alternative to normal annealing. Particular attention is paid to the influence of microstructure on the machinability of highcarbon, chromium bearing steel. The morphology of carbide distribution in both the pearlitic and spheroidized conditions has a marked effect on machinability, as does the introduction of cold work and stress-relief heat treatment.

Experience With Austenitic Steels in High-Temperature Service in Petroleum Industry

Abstract Experience in the petroleum industry shows there are other factors besides tensile, creep, and stress rupture to consider in the use of austenitic steels in high-temperature service. There is no advantage in using stabilized grades in many applications. A spheroidizing heat-treatment is generally effective where stabilized steel is required. The coefficient of expansion and the thermal conductivity have been important factors in thermal-shock and thermal-fatigue failures in austenitic steels.