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Showing papers on "Bainite published in 1984"


Journal ArticleDOI
TL;DR: In this paper, the authors studied the transformation characteristics of thin plate martensite in Fe-NiC alloys and showed that the interface is essentially mobile and the transformation is somewhat reversible.

102 citations


Journal ArticleDOI
TL;DR: In this paper, the Widmanstatten ferrite series of products, upper bainite, lower binearite, lath martensite, and lath ferrite, is considered as a continuous series and important changes occur in the properties of the α γ interface with decreasing temperature.

63 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that five transformation products are possible in pure iron and dilute substitutional alloys: equiaxed ferrite, massive ferrite and bainitic ferrite.
Abstract: Evidence is presented to show that five transformation products are possible in pure iron and dilute substitutional alloys: equiaxed ferrite, massive ferrite, bainitic ferrite, lath martensite (massive martensite), and twinned martensite. The morphology and transformation temperatures of these products are discussed. In conclusion, the chemical driving force for each of the transformations is calculated as a function of composition.

55 citations


Journal ArticleDOI
TL;DR: The presence of blocky martensite at prior austenite grain boundaries in 300M steel (silicon-modified AISI 4340 steel) subjected to different heat treatments was confirmed in this paper.

36 citations


Journal ArticleDOI
TL;DR: The isothermal formation of martensite in Fe-23Ni-3.9Mn alloy was continuously observed at low temperature, using a cold stage of optical microscope as mentioned in this paper.

29 citations


Journal ArticleDOI
TL;DR: In this article, a systematic investigation has been made (of the mechanical properties and microstructures exhibited by a wide range of controlled-rolled plates of various chemical compositions, produced on a laboratory scale).
Abstract: The future demand for high-grade pipeline materials (API X80 and higher) calls for the development of steels with microstructures showing acicular phases (acicular ferrite, bainite, and martensite-austenite (M A) constituent). A systematic investigation has heen made (of the mechanical properties and microstructures exhibited hy a wide range of controlled-rolled plates (of final thickness 18 mm) of various chemical compositions, produced on a laboratory scale. Low-carhon (∼ 0·06% C) boron-free and boron-containing steels have been examined, as has a boron steel with a Imrer carbon content (0–02% C). The boron-free steels (carbon equivalent ≤0.46%) always exhihited a polygonal ferrite matrix with a dispersed phase consisting mainly of M A constituent, while the horoncontaining steels (carhon equivalent ≤0.40%) invariahly showed an acicular matrix with a lower volume fraction of finely dispersed M A island. Quantitative relationships are ohtained hetween the volume fractions of the microstructural c...

29 citations


Journal ArticleDOI
TL;DR: In this article, a range of heat treatment conditions for SA 508 Class 2 pressure vessel steel has been investigated and the resultant microstructures have been characterized by metallographic and fractographic examination.
Abstract: Tests have been performed to examine the yield stress and the cleavage fracture stress at −196°C of SA 508 Class 2 pressure vessel steel in a range of heat treatment conditions. The heat treatments either varied the austenitization temperature before isothermal transformation at 450°C or varied the tempering treatment after austenitizing at 900°C and transforming at 450°C. The resultant microstructures have been characterized by metallographic and fractographic examination. Austenitization at temperatures below about 1000°C produced a polygonal ferritic structure, whereas an upper bainite was produced following austenitization above this temperature. Increasing the austenitizing temperature caused first the ferrite grain size and then the bainitic packet size to increase. However, the lath width of the bainitic microstructures decreased, which is consistent with an increase in hardenability accompanying the increased prior austenite grain size. Tempering caused the precipitation of rodlike carbide...

27 citations


Journal ArticleDOI
TL;DR: In this article, the influence of the cooling intensity during hardening was investigated and the possibilities and limits of accelerating the cooling rate were studied, and the importance of the transformation heat was discussed.

27 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the plastic flow behavior of a mixture of ferrite + pearlite, cementite + cementite, and austenite+ cementite mixtures in plain carbon steels over the temperature range 500 to 1050 °C, strain rate range 6 x l0−6 to 2 x l 0−2 s−1, and carbon range 0.005C to 1.89C.
Abstract: The plastic-flow behavior of ferrite + pearlite, pearlite + cementite, and austenite + cementite mixtures in plain carbon steels has been examined over the temperature range 500 to 1050 °C, strain-rate range 6 x l0−6 to 2 x l0−2 s−1, and carbon range 0.005C to 1.89C. Up to the eutectoid temperature the strength of the ferrite + pearlite mixture more than doubles as the carbon content increases from 0.005C to 0.7C, so that whereas in low-carbon steels the ferrite is weaker than the higher temperature austenite phase, in eutectoid steels the fully pearlitic structure is stronger than the fully austenitic structure. Manganese and silicon strengthen ferrite more effectively than they do austenite. A 0.17 pct phosphorus addition strengthens the ferrite + pearlite mixture across the range of microstructures from fully ferritic to fully pearlitic. Beyond the eutectoid composition, the amount of proeutectoid cementite does not significantly affect the strength of the pearlite, but above the eutectoid temperature it appreciably strengthens the austenite and cementite mixture at the strain rate of 2 X 10-2 s-1.

22 citations


Patent
Bangaru V. N. Rao1
02 Apr 1984
TL;DR: In this article, a dual phase microstructure consisting of acicular retained austenite particles within a ferrite matrix is produced by a heat treatment comprising heating the steel above the upper critical austenites transformation temperature to produce an austenitic microstructures, quenching to produce a lath martensite microstance, and tempering at a temperature below the lower critical Austenite transformation temperature, to partition carbon and manganese to form cementite particles and to transform the martensites to ferrite.
Abstract: A microalloy-free, high strength, low alloy, low carbon, manganese steel characterized by a dual phase microstructure wherein acicular retained austenite particles are distributed within a ferrite matrix. The ferrite-austenite microstructure is produced by a heat treatment comprising heating the steel above the upper critical austenite transformation temperature to produce an austenite microstructure; quenching to produce a lath martensite microstructure; tempering at a temperature below the lower critical austenite transformation temperature to partition carbon and manganese to form cementite particles and to transform the martensite to ferrite, thereby producing a microstructure comprising cementite particles dispersed within a ferrite matrix; annealing at an intercritical temperature to decompose the cementite and produce austenite particles; and quenching to retain the austenite particles within the ferrite matrix.

20 citations


Journal ArticleDOI
TL;DR: In this article, the isothermal transformation of austenite to bainite has been studied in ductile cast iron with 0.05 % Mn and a silicon content varying from 2.4 to 3.8 %.
Abstract: Using a dilatometer the isothermal transformation of austenite to bainite has been studied in ductile cast iron with 0.05 % Mn and a silicon content varying from 2.4 to 3.8 %. The alloys were austenitized to a carbon content in the matrix of 0.65 %. It appears that silicon retards the formation of carbides in the upper bainite region (400 °C), resulting in an amount of retained austenite up to 40 % present in the final structure at room temperature. Silicon improves the strength; in the lower bainite region the yield strength in particular. An elongation up to 10 % or more is obtained after austempering at 400 °C independent of the silicon content.

Journal ArticleDOI
TL;DR: The formation of austenite from a ferrite-carbide microstructure in an Fe-10Cr-0.2C (wt-%) alloy has been investigated by optical and transmission electron microscopy and microanalysis of partially transformed and quenched samples as discussed by the authors.
Abstract: The formation of austenite from a ferrite–carbide microstructure in an Fe-10Cr-0.2C (wt-%) alloy has been investigated by optical and transmission electron microscopy and microanalysis of partially transformed and quenched samples. Although nucleation of austenite is relatively sluggish (compared to low alloys steels), growth of austenite is rapid and the reaction is complete within 100 s at temperatures above AC 3. The transformation proceeds more rapidly as the temperature increases. Fine undissolved carbides have little effect on the movement of the austenite growth front while closely spaced coarse carbides can pin the interface. Carbides do not dissolve in ferrite or in the ferrite/austenite interface (unless the interface is stationary owing to pinning) but the higher solubility of carbon in austenite allows dissolution of carbides in austenite to occur. The rate of dissolution is controlled by the rate of removal of chromium. Austenite inherits the chromium content of the ferrite and no par...

Journal ArticleDOI
TL;DR: In this paper, a mixed structure of martensite and lower bainite has been used to improve low-temperature mechanical properties of ultra-high strength low alloy steels, such as AISI 4140 and 4340.
Abstract: In many practical applications the use of ultrahigh strength low alloy steels, such as AISI 4140 and 4340, is limited by their poor ductility and notch toughness in low temperature environments. In recent years, considerable effort has been directed toward improving ambient temperature mechanical properties by various heat treating techniques or compositional modification. ~-~2 Unfortunately, these improvements in mechanical properties have not been reflected in the low temperature mechanical properties of the ultrahigh strength low alloy steels. The basic problem is that the martensitic microstructure tempered to retain a high strength level is inherently susceptible to embrittlement which occurs in low temperature environments. We have given one of the potential solutions to this problem by developing 4140 and 4340 type ultrahigh strength steels having a mixed structure of martensite and lower bainite. 13.14,15 The effectiveness of the mixed structure in improving the mechanical properties is attributed to the fact that lower bainite, which appears in acicular form and partitions prior austenite grains, effectively causes a refinement of the martensitic substructure (i .e. , lath width and packet size) which lead to increased strength and that the lower bainite provides a significant increased resistance to brittle fracture at low temperature environments. As noted, the role of the second phase lower bainite in improving the lower temperature mechanical properties has been found to involve a refinement of the martensitic substructure and increasing resistance to low temperature brittle fracture. Thus, it follows that other ductile second phases should have a similar beneficial effect, provided they appear in acicular form and refine the substructure of the parent martensite, resulting in a higher resistance to cracking in low temperature environments. The obvious alternative second phase to consider is highly tempered martensite. This has the great advantage that the required microstructure can be readily achieved by heat treating techniques using interrupted quenching method. 16'17 Also, there is an added advantage that if the resulting microstructure improves the mechanical properties, the heat treating techniques can be applied to larger sections than the new heat treatment reported previously, ~3'Ja''s because the formation of the microstructure predominantly depends upon temperature.

Journal ArticleDOI
TL;DR: In this article, the effects of prior austenite grain size on microstructure and tensile properties of a dual phase (martensite+ferrite) Fe-2.3%Mn 0.05%C-0.03%Nb steel produced by intercritical annealing of specimens with martensite structure have been studied.
Abstract: Microstructure and tensile properties of a dual phase (martensite+ferrite) Fe-2.3%Mn-0.05%C-0.03%Nb steel produced by intercritical annealing of specimens with martensite structure have been studied. In order to assess the effects of prior austenite grain size on microstructure and tensile properties of the dual phase steel, the specimens in a martensitic state with widely different prior austenite grain size were prepared by thermal cycling and thermomechanical processing. Coarse dual phase structure consisting of fibrous martensite and ferrite was obtained by intercritical annealing of the specimens with coarse prior austenite grain size. A characteristic fine dual-phase structure consisting of homogeneously dispersed fine martensite particles and fine ferrite grains was obtained by the intercritical annealing of the specimens with ultra fine prior austenite grain size. The fine dual-phase structure was superior in both strength and ductility to the coarse dual phase structure over a wide range of martensite volume fractions examined. It is concluded that better combination of strength and ductility of the dual-phase steel is achieved by intercritical annealing of the martensitic specimens with ultra-fine prior austenite grain size which is obtained by the thermomechanical processing.

Journal ArticleDOI
TL;DR: In this paper, the influence of tempering on the fracture of a dual phase steel was studied, and the fracture process in the as-quenched dual phase structure began at a much lower strain compared to that in quenched and tempered steels by nucleation of microvoids at ferrite/martensite interfaces.

Journal ArticleDOI
TL;DR: A study has been made of chemical composition, metallurgical structure and mechanical properties of many low-pressure turbine discs that had been retired from service, due to in-service cracking as mentioned in this paper.
Abstract: A study has been made of chemical composition, metallurgical structure and mechanical properties of many low-pressure turbine discs that had been retired from service, due to in-service cracking Determination of the chemical composition involved both bulk chemical analyses and trace element analyses The metallurgical examination involved determination of material microstructure, grain size, and grain boundary composition (Auger analysis) The mechanical properties measured included tensile strength, notch toughness, and fracture toughness It was found that variations in bulk chemical composition do not affect the susceptibility to stress corrosion cracking and no abnormal composition that had contributed to in-service cracking was identified The turbine discs that had cracked in service had widely varying tensile strengths, indicating that stress corrosion susceptibility of these particular discs were independent of their yield strength in the range 734 to 1131 MPa (106 to 164 ksi) The Charpy V-notch impact tests and the fracture toughness tests performed showed that the 35NiCrMoV steels generally had good toughness Temper embrittlement of these steels led to reduced toughness and was related to increased phosphorus segregation to the prior austenite grain boundaries The steels examined had similar tempered bainite microstructures, but varying grain sizes There was no significant microstructural difference among the materials, and there was no evidence of inherent microstructural defects or abnormalities that may have contributed to the in-service cracking

Patent
08 Mar 1984
TL;DR: In this article, the authors proposed to obtain a light wheel for vehicle excellent in strength and formability and suitable for coating by welding a rim made by forming a precipitation hardening type hot roller high tension steel sheet.
Abstract: PURPOSE:To obtain a light wheel for vehicle excellent in strength and formability and suitable for coating, by welding a rim made by forming a precipitation hardening type hot roller high tension steel sheet and a disk made by forming a composite structure type hot rolled high tension steel sheet. CONSTITUTION:For raw sheet of the rim 1 of a wheel for vehicle, a precipitation hardening type hot rolled high tension steel sheet in tensile strength heighten in strength by precipitation hardening and refining the grain size of crystals by hot rolling a steel ingot or continuous casting slab to which a total of 0.01-0.10wt% of niobium, titanium and vanadium are added as reinforcing element to precipitate carbides and nitrides of above-mentioned elements in the matrix of ferrite and finely dispersing these precipitates is used. For raw material of the disk 2, a composite structure type hot rolled high tension steel plate =50kg/mm. in tensile strength in which the second phase of martensite, bainite or residual austenite structure is mixed in ferrite structure of the first phase is used.

Journal ArticleDOI
TL;DR: The formation of austenite during intercritical annealing of ferrite-spheroidized cementite and ferritepearlite microstructures in low carbon steels has been investigated in this paper.
Abstract: The formation of austenite during intercritical annealing of ferrite–spheroidized cementite and ferrite–pearlite microstructures in low carbon steels has been investigated. It has been established that austenite which nucleates at a ferrite grain boundary does so with a Kurdjumov–Sachs crystallographic orientation relationship with one or both ferrite grains. It has been shown also that austenite/ferrite interfaces displaying low energy planar facets need not have a rational crystallographic relationship across them. The size and distribution of cementite particles in the parent material, particularly in relation to ferrite grain boundaries, has a marked effect on the distribution and morphology of austenite; the morphologies are similar to those displayed by proeutectoid ferrite. Austenite growth has been shown to be initially associated with carbon diffusion through austenite and subsequently with carbon diffusion through ferrite. Primary and secondary WidmansHitten sideplates occur only when di...

Patent
10 Aug 1984
TL;DR: In this article, a steel material consisting of 0.10W0.30W 0.050% solAl, and the balance Fe with inevitable impurities is hot rolled so that temp. thereof at exit side of finishing rolling mill becomes Ar 1 WAr 3 range, and to obtain two phase range structure of ferrite and austenite.
Abstract: PURPOSE: To obtain the titled bar steel inexpensively, by hot rolling a low alloy steel material having a specified compsn. at finishing rolling temp. under a limited condition, and cooling said material suddenly and rapidly to recuperate the surface part. CONSTITUTION: A steel material consisting of 0.10W0.50% C, ≤0.50% Si, 0.30W 0.75% Mn, ≤0.030% P, ≤0.030% S, 0.010W0.050% solAl, and the balance Fe with inevitable impurities is hot rolled. Thereat, said material is rolled so that temp. thereof at exit side of finishing rolling mill becomes Ar 1 WAr 3 range, and to obtain two phase range structure of ferrite and austenite. Said material is cooled rapidly and suddenly from the two phases range, thereafter, temp. of the surface is controlled to 200W550°C by recuperation due to sensible heat thereof. By this way, reinforcing bar steel having improved low temp. toughness and ferrite + tempered martensite or ferrite + tempered bainite structure is obtd. COPYRIGHT: (C)1986,JPO&Japio

Patent
20 Jan 1984
TL;DR: In this article, the authors proposed to obtain a high-strength low-carbon steel material having superior heavy workability by preparing a steel material contg. specified percentages of C, Si and Mn in Fe and by providing a metallic structure consisting of specified phases.
Abstract: PURPOSE: To obtain a high-strength low-carbon steel material having superior heavy workability by preparing a steel material contg. specified percentages of C, Si and Mn in Fe and by providing a metallic structure consisting of specified phases. CONSTITUTION: A steel material consisting of, by weight, 0.01W0.30% C, ≤1.5% Si, 0.3W2.5% Mn and the balance Fe with inevitable impurities or further contg. at least one among 0.005W0.20% Nb, 0.005W0.30% V and 0.005W0.30% Ti is prepd. The steel material has a metallic structure contg. acicular martensite, bainite or a mixture of them dispersed uniformly in a ferrite phase by 15W 40vol% basing on the amount of the ferrite phase. The dispersed phase is a phase produced by transformation at a low temp., and it has ≤3μm average grain size. COPYRIGHT: (C)1985,JPO&Japio

Journal ArticleDOI
TL;DR: In this article, the superhardenability effect of high austenitizing temperatures was investigated in a wide range of low-alloy steels and it was shown that the treatment results in large and repeatable hardenability increases due to a strong retardation of the ferrite/pearlite and bainite reactions.
Abstract: The superhardenability treatment, which consists of superheating steel melts to which fairly large aluminum additions have been made, has been studied in a wide range of low-alloy steels. By hardenability testing and dilatometry, it is shown that the treatment results in large and repeat-able hardenability increases due to a strong retardation of the ferrite/pearlite and bainite reactions. Superhardenability multiplying factors and equations which relate the ideal critical diameter of a superhardenable steel to its chemical content have been produced by using a combination of three hardenability tests. A mechanism for the superhardenability effect is proposed on the basis of the experimental finding that high austenitizing temperatures result in a loss of superhardenability.

Journal ArticleDOI
TL;DR: In this article, a TEM characterization of HY-80 steel microstructures resulting from various thermomechanical treatments has been completed, and the microconstituents were typically highly dislocated lath martensite (lath width ⋍ 0.2 μm) with carbide in it, autotempered martensites, typical tempered bainite/martensite duplex structure, and three distinct types of bainites distinguished by the morphology of cementite precipitation within the ferrite laths.

Journal ArticleDOI
TL;DR: In this article, the isothermal decomposition of austenite has been examined in a set of 0.1 C, 1.4 Mn steels containing small amounts of Ti, V, or Nb.
Abstract: The isothermal decomposition of austenite has been examined in a set of 0.1 C, 1.4 Mn steels containing small amounts of Ti, V, or Nb. The volume fraction of ferrite was measured as a function of transformation temperature and holding time, after hot rolling. Precipitation of carbonitrides, in both the austenite and the ferrite, was examined by electron microscopy of extraction replicas. The decomposition is slowest in the Nb-alloyed steel, in which the start of transformation is delayed and ferrite growth rates are much lower than in the other steels. In the V-alloyed steels, ferrite growth rates are lower than in the plain carbon or Ti alloyed steels. These results are discussed in terms of the effects of carbonitride precipitation in the austenite during high temperature deformation and in the ferrite during transformation. The roles of V and Nb in solution are also considered.

Journal ArticleDOI
TL;DR: In this paper, a 0.024 pct C-16 pct Cr-1.5pct Mo-5 pct Ni stainless steel was used to study the phase reactions associated with heat treatments and investigate the strengthening mechanisms of the steel.
Abstract: Metallographic studies have been conducted on a 0.024 pct C-16 pct Cr-1.5 pct Mo-5 pct Ni stainless steel to study the phase reactions associated with heat treatments and investigate the strengthening mechanisms of the steel. In the normalized condition, air cooled from 1010 °C, the microstructure consists of 20 pct ferrite and 80 pct martensite. Tempering in a temperature range between 500 and 600 °C results in a gradual transformation of martensite to a fine mixture of ferrite and austenite. At higher tempering temperatures, between 600 and 800 °C, progressively larger quantities of austenite form and are converted during cooling to proportionally increasing amounts of fresh martensite. The amount of retained austenite in the microstructure is reduced to zero at 800 °C, and the microstructure contains 65 pct re-formed martensite and 35 pct total ferrite. Chromium rich M23C6 carbides precipitate in the single tempered microstructures. The principal strengthening is produced by the presence of martensite in the microstructure. Additional strengthening is provided by a second tempering treatment at 400 °C due to the precipitation of ultrafine (Cr, Mo) (C,N) particles in the ferrite.

Journal ArticleDOI
Fawzy H. Samuel1
TL;DR: In this article, four steels containing 0.1 pct C-1.5 pct Mn-0.003 pct B* in common, with additions of 1 pct Cr, 0.25 pct Mo + 1pct Cr and 0.2 pct Ti + 1 pCT Cr, were designated as Cr, Mo, Mo-Cr, and Cr-Ti steels.
Abstract: The present study was carried out on four steels containing 0.1 pct C-1.5 pct Mn-0.003 pct B* in common, with additions of 1 pct Cr, 0.5 pct Mo, 0.25 pct Mo + 1 pct Cr, 0.2 pct Ti + 1 pct Cr. They were designated, accordingly, as Cr, Mo, Mo-Cr, and Cr-Ti steels. All the steels exhibited a complete lath martensite microstructure with thin interlaths of retained austenite (≈0.05 pct) in the quenched condition. The normalized microstructures, granular bainite, contained massive areas of ferrite and granules of bainite laths. Both microconstituents contained a fine dispersion of cementite particles (size ≈50 A) together with high dislocation densities. A mechanism explaining their for-mation has been given. The Cr steel, due to its low hardenability, showed in addition polygonal ferrite in the neighborhood of the so-called M-A constituent (twinned martensite and/or austenite). The annealed microstructure (using a cooling rate of 0.033 °C s•1) of the Cr steel consisted of coarse ferrite-pearlite. Addition of 0.2 pct Ti to the Cr steel markedly refined the structure, whereas an addition of 0.25 pct Mo altered the microstructure to ferrite-lower bainite. In the 0.5 pct Mo steel, polygonal ferrite was found to be completely missing. The mechanical properties of the four steels after quenching, normalizing, and annealing were investigatedvia hardness and tensile test mea-surements. An empirical equation, relating the ultimate tensile strength to the steel composition, for steels that had granular bainite microstructures in the normalized condition, was proposed. The fracture surfaces exhibited cleavage and variable-size dimples depending on the microstructure and steel composition.

Patent
29 Feb 1984
TL;DR: In this paper, a billet contg. 0.15W 0.80% C, 1.0W 3.0% Si and 0.5W3.5% (Mn+ Cr) is hot-rolled to make a steel sheet and after water cooling, the steel sheet is wound as a hot rolled coil and cooled in air.
Abstract: PURPOSE: To manufacture high tensile steel excellent in strength, workability and ductility by hot-rolling steel contg. Mn or furthermore Cr and making the composition contg. retained austenite of specified quantity. CONSTITUTION: A billet contg. 0.15W0.80% C, 1.0W3.0% Si and 0.5W3.0% (Mn+ Cr) is hot-rolled to make a steel sheet and after water cooling, the steel sheet is wound as a hot rolled coil and cooled in air. By contg. Mn or Cr wherein stable austenite is formed through substituting Cr for Mn, the quantity of retained austenite contained in the system is ≥5% and the balance consists of bainite contg. ≥1.0% fine ferrite of ≤5μ average grain size and high tensile steel sheet excellent in strength, workability and also ductility is obtained. COPYRIGHT: (C)1985,JPO&Japio



Patent
19 Jan 1984
TL;DR: In this article, the magnetic properties of a spheroidal graphite cast iron having a mixed structure of bainite and residual austenite are measured by making use of the appearance of a difference in said curve with the pearlite precipitated on the spherolabeled cast iron.
Abstract: PURPOSE:To permit easy quality control of a spheroidal graphite cast iron having a mixed structure of bainite and residual austenite by measuring the difference in magnetic characteristic of the pearlite precipitated to said cast iron and detecting nondestructively and easily the pearlite with high accuracy. CONSTITUTION:The specific values on a magnetic hysteresis curve, for example, coercive forces 5A, 5B, 5C residual magnetic flux densities 4A, 4B, 4C and satd. magnetic flux densities 3A, 3B, 3C shown in the figure are measured by making use of the appearance of a difference in said curve with the pearlite precipitated on the spheroidal graphite cast iron having a mixed structure of bainite and residual austenite. The hysteresis curve A represents the sample consisting of bainite and austenite, the curve B the sample precipitated with 19% pearlite and the curve C the sample precipitated with 43% pearlite. These magnetic characteristics are respectively in the linear relation with the amt. of the precipitated pearlite as shown in, for example, the figure and therefore the amt. of the pearlite precipitated is made easily discriminatable with high reliability.