Showing papers on "Bainite published in 1986"

Inclusion Phases and the Nucleation of Acicular Ferrite in Submerged Arc Welds in High Strength Low Alloy Steels

Abstract: Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have been examined to study the inclusions and their role in the nucleation of acicular ferrite. Inclusion phases and compositions have been analyzed by electron diffraction and X-ray microanalysis. These analyses have shown that the inclusions contained many different compounds, the proportions of each depending upon both the flux and metallic additions. Six inclusion phases have been identified: galaxite (Al2O3 ⋅ MnO), a titanium-rich compound (probably TiO), a copper sulfide, a manganese sulfide, a silica, and an aluminum-rich phase. No correlation was found between the amount of acicular ferrite in the weld metal and either average inclusion composition or individual inclusion phases. No epitaxial relationships between inclusions and adjacent ferrite grains could be identified. It has been concluded that inclusions nucleate acicular ferrite by acting as inert substrates according to the classical theory of heterogeneous nucleation. Because most inclusions are multi-phase and are touched by several ferrite grains, it has also been concluded that each inclusion can nucleate several ferrite grains, due to local regions of high surface energy on the inclusion.

Microscopic deformation behaviour of martensitic–ferritic dual-phase steels

Abstract: The deformation behaviour of the two phases of three plain carbon dual–phase steels after various treatments has been studied using a scanning electron microscope equipped with a tensile straining stage. The distribution of strains between the ferrite and martensite phases, as well as among the different grains of each phase, was observed to be inhomogeneous. The martensite/ferrite strain ratio, which defines the degree of uniformity of straining between the phases, depends on the microstructural parameters of the steels: it increases with increasing volume fraction of martensite, but decreases as the carbon content of the martensite increases. Tempering at various temperatures causes a decrease in the martensite/ferrite microhardness ratio and hence causes an increase in the strain ratio. The macroscopic strain of the specimen at which the martensite begins to deform was also found to be dependent on the microstructural parameters. Regions of applicability of the existing theories of the strength...

Lower bainite with midrib in hypereutectoid steels

Abstract: The isothermal transformations in five hypereutectoid steels (0.85 to 1.80 wt pct C) have been studied in the temperature range between 623 and 333 K. Two types of lower bainite and a thin plate isothermal martensite were observed. One of the lower bainites was the conventional lower bainite (CLB) formed at the high temperature range of 623 to 473 K, and the other was the newly named “lower bainite with midrib” (LBm) formed at the lower temperature range of 473 to 423 K. The thin plate isothermal martensite (TIM) was also observed below 373 K. This paper brought LBm into focus. Arrhenius plots (transformation ratevs l/T) for each steel revealed an abrupt change in kinetics at the temperature range between 483 and 443 K. This change was considered to correspond to the transition from CLB to LBm. The following two-stage process for the LBm formation is proposed: at the first stage a TIM is formed, which constitutes a midrib of LBm, and secondly the bainitic decomposition of austenite at TIM/austenite interfaces takes place. That is, an LBm is a composite of isothermal martensite and lower bainite.

Austenite formation in manganese-partitioning dual-phase steel

Abstract: Manganese-containing ferritic–pearlitic steels have been studied after intercritical annealing for various times at temperatures of 700 and 725°C, during which austenite formation occurred at ferrite grain boundaries. Light and electron optical microscopy, and scanning transmission electron microanalysis and microdiffraction were employed for the study, in which both microstructural development and manganese redistribution were examined in detail. It was observed that the formation of austenite is associated initially with a migration of ferrite grain boundaries. It is proposed that this boundary migration is induced by manganese diffusion along the boundaries, and that this in turn provides the mechanism for rapidly transporting manganese to the growing austenite. On this basis, we find that austenite formation in these steels is associated with manganese-rich migrated ferrite boundaries, and is not dependent on the presence of cementite particles for nucleation.MST/467

Effect of microstructure on mechanical properties of C-Mn high strength hot rolled sheet steel.

Abstract: Niobium bearing high strength hot rolled sheet steel which had the microstructure consisting of ferrite and 10 to 20% bainite has exhibited good mechanical properties, especially in stretch flangeability. In this study, the effect of the microstructure of C-Mn steels on mechanical properties is discussed comparing them with low C-Nb bearing steel.Though C-Mn steels containing more than 0.1% C showed inferior stretch flangeability compared with low C-Nb bearing steel, it was improved by changing the microstructure to ferrite-bainite. Higher tensile strength could be obtained with ferrite-martensite steel, avoiding the deterioration of tensile strength and elongation combination. However the stretch flangeability of ferrite-martensite steel was quite inferior.C-Mn ferrite-bainite sheet steels of TS grade of 50 and 55kgf/mm2 with good stretch flangeability, elongation, relatively low yield ratio and good surface condition were able to be produced by using a step cooling pattern and a low coiling temperature.

Hydrogen-induced cracking in two linepipe steels

Abstract: Linepipe steels are susceptible to hydrogen-induced cracking (HIC) in wet, sour gas environments. Two commercially produced linepipe steels were investigated with regard to HIC on cathodic charging. Both steels, B and C, showed a high banded microstructure consisting of alternative layers of polygonal ferrite and a mixture of non-ferritic constituents (pearlite, bainite, and martensite-austenite). The degree of banding was higher in Steel B than in Steel C. Also present were elongated inclusions in Steel B, while in Steel C they were more or less equiaxed. On cathodically hydrogen-charging in the absence of external stress, microvoids formed at low current densities at or around inclusions. On prolonged charging, these voids grew and propagated parallel to the bands, running along the interface between ferrite/non-ferrite constituents, along inclusions lodged in the non-ferritic consitituents, and at places through the non-ferritic constituents. Steel B, not unexpectedly, showed more severe permanent microstructural damage than Steel C, leading to the conclusion that a high banded structure and/or the presence of elongated inclusions is deleterious to resistance against HIC.

Wear resistant rails capability of preventing propagation of unstable rupture

Abstract: OF THE DISCLOSURE The wear resistance rail contains 0.50 to 0.85 wt.% of C, 0.10 to 1.0 wt.% of Si, 0.50 to 1.50 wt.% of Ma, less than 0.035 wt.% of P, less than 0.035 wt.% of S, less than 0.050wt.%of Al, and the balance of iron and impurities. The web has a high toughness tempered bainite structure, tempered martensite structure or a tempered mixed structure of bainite and martensite and a head of rail having high wear resistance property preventing unstable destructive crack from propagating. The rail can further contain oneor more of 0.05 to 1.50 wt.%of Cr, 0.05 to 0.20 wt.% of Mo, 0.03 to 0.10 wt.% of V, 0.10 to 1.00 wt.% of Ni, and 0.005 to 0.050 wt.% of Nb.

Manufacture of low yield ratio high tension steel plate superior in cold workability

Abstract: PURPOSE: To obtain the titled steel plate having composite structure of ferritel, bainte and martensite without cooling to normal temp. after end of rolling, by suitably controlling conditions of controlled rolling and accelerated cooling of steel having a prescribed chemical components CONSTITUTION: Steel composed of, by weight % 0.03W0.25 C, 0.01W0.60 Si, 0.30W2.00 Mn, 0.005W0.10 sol Al, if necessary one kind or more among 0.10W0.50 Cu, 0.10W1.00 Ni, 0.05W0.50 Mo, 0.003W0.10 Nb, 0.01W0.10 V, 0.003W0.10 Ti, 0.0003W0.0030 B and 0.05W0.50 Cr and the balance Fe under 0.25W0.45% C equivalent exhibited by a formula is prepd. The steel is heated to 950W1,200°C and rolling is ended at (Ar 3 -40)W(Ar 3 +50)°C in hot rolling, then acceleratedly cooled to ≤350°C at 2W40°/sec rate. Thus, the titled steel plate composed of composite structure of island-shaped martensite of 3W15% vol. ratio, 20W40% bainite and the balance ferrite is obtd. COPYRIGHT: (C)1987,JPO&Japio

High strength low carbon steel wire rods and method of producing them

Abstract: OF THE DISCLOSURE High strength low carbon steel wire rods excellent in the cold drawing property have a composite structure in which an acicular low temperature transformation phase comprising a martensite, bainite and/or the mixed structure thereof that comprises, by weight %, C : 0.02 - 0.30 %, Si : less than 2.5 %, Mn : less than 2.5 % and the balance of iron and inevitable impurities and that may partially contain retained austenite is uniformly dispersed at the volume ratio of from 10 to 70 % in the ferrite phase, and in which the weight of (C+N) in solution in the ferrite phase is less than 40 ppm.

The Effect of Low-Temperature Isothermal Heat Treatments on the Fracture of 4340 Steel

Abstract: Specimens of 4340 steel either quenched and isothermally transformed to martensite or isothermally transformed to lower and upper bainite were subjected to instrumented CVN impact testing. All specimens were tempered at 200‡ C. The tempered martensitic and lower bainitic microstructures absorbed over twice the energy absorbed by the upper bainitic microstructure, 24 versus 11.5 joules. Fracture initiation occured by shear and absorbed the same energy in all microstructures. The low impact toughness of the upper bainite was due to cleavage fracture propagation and the absence of plane-stress-induced shear lip formation which accompanied the unstable fracture propagation in the other microstructures.

A method for manufacturing austempered spheroidal graphite iron.

Abstract: A method for producing austempered spheroidal graphite iron having a microstructure comprising bainite, ferrite and austenite. A nodular-iron casting containing 2-3.5% Si, 0-2% Mn, 0-5% Ni 0-0.3% Sn, 0-03% Cr, 0-3% Mo, 0-1.5% Cu, and 3.3-3.8% C and at most 0.08% P and 0-015% S is partially austenitized by heat treatment at a temperature beneath the temperature at which austenite and graphite or austenite are in equilibrium, but within the temperature range in which ferrite, austenite and graphite are in equilibrium. The temperature of the casting is then rapidly lowered by at least 100 K min , and is held at a constant temperature within a range of 235 and 425 DEG C, wherewith part of the austenite formed is converted to bainite to provide a casting that includes a bainite structure with a residual austenite content of 5-40%, preferably 15-20%, and a ferrite content of 10-15%, preferably 20-40%.

Method of manufacturing dual phase strip steel and steel strip manufactured by the method

Abstract: In a method of manufacturing a dual phase steel a strip of thickness 0.1 to 0.5 mm from an unalloyed low C, low Mn steel composition of 0.02 - 0.15% C and 0.15 - 0.60% Mn, which method includes continuous annealing, a flat product can be obtained without strip fracture if (a) the strip is heated to not above 770°C in the A1-A3 region of the iron-carbon diagram region and thereafter (b) the strip is cooled sufficiently rapidly that austenite is at least partly converted to martensite and/or bainite, the cooling rate is such that the value P = d.V where d is strip thickness in mm and V is average cooling rate in °C/sec from 700°C to 300°C, is in the range 20 to 900 and the time interval between the end of step (a) and the beginning of step (b) is less than 4 seconds.

Pad for disc brake

Abstract: PURPOSE:To prevent noise generation during damping by disc brake, by manufacturing the titled pad with a cast iron having structure of bainite or martensite matrix and graphite flake. CONSTITUTION:A rear metal sheet 1 in the titled pad composed of said sheet 1 and a lining 2 is manufactured by the cast iron contg. by weight 3.7-4.5% C, 1.0-3.0% Si, 0.2-1.5% Mn, <0.1% P, <0.15% S and graphite flakes in bainite or martensite matrix. Vibration generated in damping by the disc brake is absorbed by the rear metal sheet made of cast iron, pad vibration is suppressed, and noise generation is decreased remarkably.

High strength spheroidal graphite cast iron with superior machinability

Abstract: PURPOSE:To obtain high strength spheroidal graphite cast iron with superior machinability by austempering spheroidal graphite cast iron contg prescribed percentages of various elements under prescribed conditions so as to regulte the structure and the Vickers hardness CONSTITUTION:The composition of spheroidal graphite cast iron is composed of, by weight, 3-45% C, 05-3% Si, 02-12% Mn, 002-01% Mg, one or more among <05% Mo, <1% Ni and <15% Cu, and the balance Fe with impurities The cast iron is austempered under conditions during austenitizing by heating at 860-930 degC for 05-1hr and under conditions during isothermal heat treatment by holdin at 370-430 degC for 1-4hr to form a structure consisting of <=70vol% retained austenite, <=3vol% free cementite and the balance bainite The Vickers hardness is regulated to 250-310

Medium carbon air-cooled mn/b bainitic steel

Abstract: It uses Mn, B as essential alloy elements. After heat-manufactured, air-cooled hardness can be over HRC 50. Bainite/martensite duplex structures of high strengt and toughness can be gained after tempering. sigma sub 0.2 kg/sq. mm, sigma sub b is not less than 130 kg/sq. mm. It avoids quenching process saves energy, and decrease cost. The invented steel products can be used for making springs, etc. with properties reaching or exceeding 60 Si2Mn steel.

Relationship between hardness and microstructure of continuously cooled C–Mn–V steels

Abstract: The relationships between hardness and the volume fraction of martensite for continuously cooled steels containing 0·1–0·3%C, 1·6%Mn, 0–0·3% V (all wt-%), which are used to measure the hardenability expressed by the ideal critical diameter, have been established. It has been shown that for steels transformed to a fine mixture of lath martensite and lath bainite it is not possible to measure the volume fraction of martensite by means of quantitative optical metallography and therefore the volume fraction of martensite was determined from dilatometric records of continuously cooled specimens. The continuous cooling transformation diagrams were determined and microstructures of the dilatometric specimens were examined by optical and transmission electron microscopy. The values of the 50% martensite hardness established for the steels containing vanadium were found to be outside the range given by the widely used Hodge and Orehoski relationship. The relevance of the results to the assessment of harde...

Production of tough steel pipe

Abstract: PURPOSE: To produce a tough steel pipe having high strength, excellent corrosion resistance and less anisotropy of toughness, by subjecting a specifically composed ingot successively to heating, hot rolling, quick cooling, reheating, diametral reducing and air cooling under specific conditions. CONSTITUTION: The ingot made of the compsn. contg., by weight %, 0.2W0.55% C, 0.01W0.6% Si, 0.3W1.8% Mn, and 0.005W0.06% Sol Al, and consisting of the balance Fe and unavoidable impurities is heated in a 1,050W1,250°C range. The ingot is then pierced by a piercer and is hot rolled by a mandrel mill. The finishing temp. is set at ≥800°C. The rolled steel is further quickly cooled down to ≤350°C at ≥200°C/min cooling rate in a 800W500°C range to form the structure substantially consisting of ≥50vol% martensite and the balance bainite. The steel is then reheated to the Ac 1 transformation point W (Ac 1 transformation point - 200°C) at which there is substantially no formation of martensite; thereafter, the steel is subjected to the diametral reducing at ≥5% reduction ratio by using a reducer and is air cooled, by which the rolled steel pipe is formed. COPYRIGHT: (C)1988,JPO&Japio

Steel for machine structural use

Abstract: PURPOSE:To obtain the titled steel easy of temp. control at working and hardening operations and having machinability and high toughness by subjecting a steel containing C, Si, Mn, and >=1 element among Pb, S, B, etc., to working at the temp. of austenite zone and then to hardening from the temp. of two phase area of austenite and ferrite. CONSTITUTION:The steel containing 0.1-0.5% C, 0.5-3.0% Si, 0.5-2.0% Mn, and >=1 kind among 0.02-0.3% Pb, 0.02-0.3% S, 0.02-0.3% Bi, 0.001-0.3% Te, 0.01-0.4% Se and 0.0003-0.005% Ca is subjected to working at the temp. of austenite zone and then to hardening from the temp. of two phase area of austenite and ferrite. In this way, a structure in which the area ratio of ferrite is 10-75% and the balance consists of martensite or of martensite and bainite can be formed. The obtained steel can be used for various parts for machine structural use, e.g., automobile connecting rod, crankshaft, steering, etc.

Spheroidal graphite cast iron and its manufacture

Abstract: PURPOSE:To obtain spheroidal graphite cast iron having superior mechanical characteristics and a fine appearance after working by providing a specified composition, forming a bainite structure by slow cooling, and regulating the grain size to a specified value or below. CONSTITUTION:Spheroidal graphite cast iron consisting of, by weight, 2-4% C, 1.5-3% Si, <0.5% Mn, 4-6% Ni, 0.3-2.5% Cu, 0.2-1% Mo, 0.02-0.07% Mg and the balance Fe with inevitable impurities is cast and cooled. In the cooling stage, slow cooling is carried out at 0.1-10 deg.C/min average cooling rate in the temp. range of 700-200 deg.C to regulate the grain size to <=100mum as well as to form a bainite structure as the matrix structure.

Effects of manganese, chromium, and molybdenum on the isothermal transformation of austenite in eutectoid steels

Abstract: Isothermal transformation diagrams of a series of eutectoid steels alloyed with 0.75% C, 0.28% Si, 0.43 to 0.91% Mn, 0 to 0.76% Cr, and 0 to 0.34% Mo were determined using a dilatometer. The effects of manganese, chromium, and molybdenum on the transformation behavior of these eutectoid steels were then evaluated by multiple linear regression analysis of the isothermal transformation diagram data. The regression analysis shows that molybdenum has its greatest effect in delaying the austenite decomposition at high temperatures (650 to 500° C), chromium at intermediate temperatures (550 to 500° C), and manganese at low temperatures (350 to 300° C). The results imply that molybdenum has a much greater effect in suppressing the formation of pearlite than it has in suppressing bainite, while manganese suppresses both the pearlite and the bainite transformation.

A method of making components of steel with high-strength and high toughness

Abstract: A steel with a carbon content of less than 0.3 percent by weight is used for steel-based components which are subjected to hot forming. A predominantly lower bainite structure is achieved by controlled cooling. The advantage is that components, such as truck steering knuckles, which are forged at temperatures of up to about 1300 DEG C., no longer need be subjected to annealing or tempering after cooling in order to possess good ductility in addition to high strength.