Showing papers on "Tempering published in 1974"

Carbide refining heat treatments for 52100 bearing steel

Abstract: The life of through-hardened 52100 anti-friction bearing components is improved if the excess carbides, undissolved during austenitization, are small and uniformly dispersed. One kind of carbide-refining heat treatment consists of 1) dissolving all carbides, 2) isothermally transforming the austenite to pearlite or bainite, and 3) austenitizing, quenching and tempering in the usual manner. Each step in this sequence of treatments was investigated, and the behavior of pearlitic and bainitic microstructures during subsequent austenitization was contrasted with the behavior of ferrite/spheroidized-carbide microstructures. It was shown that: 1) The usual hardening treatments given spheroidize-annealed bearing components result in an inhomogeneous microstructure, possibly due to the faster dissolution of carbides near austenite grain boundaries. 2) Austenitization of pearlite or bainite produces very uniform dispersions of ultra-fine carbides on the order of 0.1 µm diameter or less. 3) Specimens with ultra-fine carbides tend to have more retained austenite. 4) The rate of coarsening of ultra-fine carbides at austenitizing temperatures of 840°C and below, is slow enough so that conventional furnace heat treatments are satisfactory for producing this microstructure.

Tempering of the Bainite and the Bainite/Martensite Duplex Structure in a Low-Carbon Low-Alloy Steel

Abstract: The variation with tempering temperature of the mechanical properties of the bainite and the bainite/martensite duplex structure in a low-carbon highstrength steel has been investigated and compared with that of the martensite. Both the bainite and the duplex structure exhibited much lower impact transition temperatures than the martensite and this can be explained in terms of the unit crack path, which is the mean cleavage crack path.The 350° C embrittlement was more pronounced in the tempered martensite than in the tempered bainitic structures. Tempering at temperatures higher than 600° C greatly improved the toughness of each structure but decreased the strength. It is believed that this improvement in toughness by tempering is attributable to the ferrite matrix properties rather than the effect of the unit crackpath. The optimum combination of toughness and strength can be achieved by producing the tempered bainite/martensite duplex structure at all strength levels.

Electron Microscopy and Diffraction Study of the Carbide Precipitated at the First Stage of Tempering of Martensitic Medium Carbon Steel

Abstract: Crystal structure and precipitation mode of the carbide in a martensitic 0.45 wt%C steel tempered at 120 and 200°C have been studied by means of electron microscopy and selected area diffraction. In both plate-like and lath martensites, the precipitated carbide is η-Fe2C like the previous case of high carbon steel(Acta Met.,20(1972),645). The crystal morphology and the orientation relationships between the carbide and the matrix are also the same. In general, the precipitation occurs along dislocations, but it has been found that grain boundary precipitation also takes place in the non-parallel lath region and that in fine grains in this region the carbide precipitation does not occur. Some discussions are given to the crystal structure and the precipitation mode of the carbide. (Received September 4,1973)

Heat treatment of welds

Abstract: A method is disclosed for heat treating the weld and heat affected zone between a metal pipe and a metal connector. The overall strength of the assembly in the heat affected zone of the weld is brought to a value higher than, or at least matching, that of the strength of the pipe body in a manner to avoid cracking and to insure that the weld or the heat affected zone does not fail. After welding in the conventional manner, the weld is cooled below the transformation temperature, heated above the critical temperature, quenched at a selected rate that avoids cracking and refines the grain structure, followed by tempering, all of which improve the mechanical properties.

Fatigue crack propagation data obtained from parent plate, weld metal and haz in structural steels

Abstract: For low strength materials (unayial yield strength less than approximately 300 N/sq. mm), the slope of the crack propagation curve, representing data obtained from center-notched sheet specimens, may not change at the fracture mode transition. Providing the fracture path is transgranular, the rates of crack propagation in weld metals, HAZs and structural steels in the range of yield strengths 375-636 N/sq. mm are not strongly influenced by the material microstructure. The incidence of intergranular fracture causes the rate of crack propagation to increase. Tempering reduces the incidence of intergranular fracture and consequently improves the fatigue properties of the material.

Method of and apparatus for bending and tempering thin glass sheets

Abstract: A method of and apparatus for bending and tempering a relatively thin glass sheet while supported horizontally and conveyed along a generally horizontal path comprising heating the glass sheet to its softening point, bending the sheet into the desired curvature, reorienting the bent sheet for further processing along said horizontal path, reheating the sheet to the temperature necessary for proper tempering, and finally, chilling the sheets rapidly below the annealing temperature range of the glass.

Effect of prior austenitic grain boundary composition on temper brittleness in a Ni-Cr-Sb steel

Abstract: Grain boundary segregation during temper embrittlement of an Sb-containing, Ni-Cr steel has been examined both by Auger electron analysis and by chemical analysis by neutron activation of residues of surface layers dissolved by etching intercrystalline fracture surfaces. No grain boundary segregation of either alloying additions or impurities was detected during austenitization or tempering. Redistribution of Cr, Ni, and Sb between carbide and ferrite was observed during tempering, but no grain boundary segregation was noted. Both Ni and Sb were observed to segregate to the boundaries during embrittling. The segregated Sb was shown to be uniformly distributed along the prior austenitic grain boundaries and to control the ductile brittle transition temperature of the alloy studied. Ni segregating to the prior austenitic boundaries during embrittling was shown to be localized in a phase other than the ferritic portions of the boundaries. A possible location was shown to be the ferritecarbide interfaces in the grain boundaries. Weakening of these normally tenacious carbide and ferrite interfaces could account for the change in mode of brittle failure from transcrystalline cleavage to intercrystalline along the prior austenitic grain boundaries that is observed in temper brittle steels.

Method for heat treatment of high-toughness weld metals

Abstract: OF THE DISCLOSURE A method for obtaining a weld metal having excellent toughness at low temperatures as below -40°C, which method com-prises heating the weld metal having a specific steel composition to its austenitizing temperature and cooling it or holding it at the temperature not longer than 25 minutes then quenching and tempering it. In order to further improve the low temperature toughness the weld metal is reheated again from the Ac1 to Ac3 range. Excellent low temperature toughness of the weld metal can be obtained without necessity of using any special welding materials.

Electron beam welded joints - between manganese steel and transformation hardenable steel with dual heating of transition hardenable steel

Abstract: Mn steel and components made from transformation hardenable steel the Mn steel being subjected to one single and the other to two heatings in the joint zone when the joint is made. This is pref. done by insertion of an austenitic steel which is first welded to the transformation hardenable steel and then to the manganese steel the heat generated by the second welding operation tempering the first weld seam zone. The methods avoids local excess hardening and consequent cracking.

Stress corrosion cracking of welded joints in high strength steels

Abstract: High strength steels may suffer a form of stress corrosion cracking (SCC) due to hydrogen embritt lement, the hydrogen being liberated by a cathodic corrosion reaction. Most service media w i l l be expected to liberate hydrogen, and the problem affords a considerable drawback to the widespread use of high strength steels. For a number of reasons, fa i l ure may be particularly likely when welding is used for fabrication. Unless the structure is efficiently stress relieved, tensile stresses of yield or proof stress magnitude can remain in the vicinity of the weld, whi le even w i th stress relief, a we ld wi l l constitute a region of stress concentration. During the welding cycle, metallurgical changes may take place causing local microstructures that are particularly sensitive to SCC. The present investigation was initiated to clarify the situation, three particular objectives being identified, namely: 1. To define the relative SCC behavior of a range of high strength steels. 2. To assess the effects of welding and postweld heat treatment on SCC susceptibility. 3. To evaluate the general practical implications of the data obtained. A range ot steels was studied including both conventional medium carbon, low alloy materials and low carbon, p rec ip i ta t ion ha rden ing grades. SCC testing was based on T. G. GOOCH is Group Leader — Austenitic Group, The Welding institute, Abington, Cambridge, Great Britain. Paper was presented at the 55th AWS Annual Meeting held in Houston during May 6-10, 1974. linear elastic fracture mechanics pr inciples using precracked specimens. Testing was carried out in 3% sodium chloride solution as representative of the media causing SCC of high strength steels. Welds were prepared in the experimental alloys and the pre-existing crack located in various regions of the joint, whi le samples were also prepared using The Welding Institute weld thermal simulator to reproduce specific heat-affected zone (HAZ) microstructures. Susceptibil ity was defined in terms of the critical threshold stress intensity to cause cracking, the results obtained being related to material composition and microstructure w i th reference to different heat affected zone and weld metal areas. Fractographic examinat ion was carried out and susceptibility related to failure mechanism. From the results obtained it has been possible to derive a general understanding of the variables affecting weld SCC performance. Susceptibil ity is primarily dependent upon microstructure, and, for a given material, recommendations may be made regarding welding conditions and postweld heat treatment to obtain maximum SCC resistance. The presence of twinned martensite in particular should be avoided, since this ohase has a highly deleterious effect on SCC resistance. Provided postweld heat treatment similar to that specified for base metal is applied, HAZs and matching composit ion weld metals wi l l generally show SCC resistance similar to the base metal; wi thout such heat treatment, increased susceptibility must be anticipated. The presence of segregation and inclusions generally has little detrimental effect on weld metal SCC resistance, although segregation may be particularly significant in precipitat ion hardening systems. SCC failure may take place intergranularly, by cleavage, or by microvoid coalescence, intergranular failure being largely associated w i t h the presence of twinned martensite and high susceptibility. The results suggest that highest SCC resistance wi l l be obtained from low carbon, low alloy systems, since these are unlikely to suffer the development of deep corrosion pits wh ich may act to initiate SCC in service, and wi l l have high resistance to SCC by a cleavage mechanism. Attent ion has been further paid to the practical risk of SCC initiation in service, consideration being given to the effects of environment on SCC initiation and propagation. A preliminary correlation has been obtained between fracture mechanics data and the SCC behavior of uncracked, undressed welds. The information reported thus constitutes a rational basis for understanding the SCC behavior of welded joints. Although direct testing is still necessary to establish the behavior of a given joint in a particular environment, it is possible to maximize SCC resistance in advance by attention to relevant factors.

The effect of an intercritical heat treatment on temper embrittlement of a Ni-Cr-Mo-V rotor steel

Abstract: The effect of an intercritical heat treatment on tempor embrittlement has been investigated for a rotor steel containing 0.25 pct C, 3.5 pct Ni, 1.7 pct Cr, 0.5 pct Mo, 0.1 pct V, and deliberate additions of phosphorus, tin, or antimony. Both martensitic and bainitic steels were held at the intercritical temperature of 1380°F (750°C) for times up to 40 h and were then quenched or cooled to obtain martensitic or bainitic transformation. The steels were then tempered, followed by water quenching or step cooling from the tempering temperature. The residual ferrite maintained a fine plate-like shape even after 40 h at the intercritical temperature. Embrittlement induced by step cooling from the final tempering was mark edly reduced by the intercritical treatment as compared to the embrittlement observed after conventional heat treatment; for example, AFATT, the increase in the Charpy V-notch 50 pct shear fracture transition temperature caused by step cooling, was reduced by at least 80°F (45°C) as a result of the intercritical treatment of steels containing 0.02 pct P. Molybdenum effectively reduced AFATT in intercritlcally heat-treated steels as well as in conventionally treated steels. Possible mechanisms for reducing temper embrittlement with the intercritical treatment are discussed.

Method of making ball studs

Abstract: A method of making a ball stud in which a low carbon steel or a low carbon alloy steel is used as a starting material, the material is coldly formed into the ball stud, a lower carbon content and smaller carburization depth are selected in comparison with an ordinary carburization method and diffusion heat treatment of said material is carried out at substantially the same temperature as the carburization temperature, then said material is subjected to quenching and tempering treatment and finally induction hardening is applied only to the ball portion of said ball stud.

Method for increasing the mechanical features and the resistance against corrosion under tension of heat-treated aluminum alloys

Abstract: The invention relates to a method of heat treatment which is applied to forged aluminum alloys, whereby the mechanical characteristics and resistance against corrosion under tension are increased considerably. This method is characterized by heating prior to tempering, above the temperature of eutectic melting, while remaining below the temperature of the start of the melting at equilibrium. The liquid phase formed temporarily is resorbed progressively, while the formation of pores is avoided by a sufficiently low hydrogen content of the metal. The application of this procedure to several aluminum alloys made it possible to observe increases of the limit of elasticity and of the break load of the order of 7% and a non-rupture stress under tension in 30 days at least equal to 30 hb.

High strength ductile hot rolled nitrogenized steel

Abstract: Aging hot rolled nitrogenized low carbon steel is treated to produce a material having a level of ductility during forming and a yield strength after forming which is comparable to the 80,000 psi yield strength hot rolled low alloy (HSLA) steels. The method includes the steps of (1) rapidly heating the steel within the alpha plus gamma region of the appropriate phase diagram for the steel and quenching; (2) tempering for example at about 400°F. for about 2 minutes and cooling; (3) deforming at least 2 percent, and (4) aging to develop the 80,000 psi yield strength.

Field-ion microscopy of tempered martensite

Abstract: Hydrogen-ion microscopy has been used to study microstructural features of tempered martensite in a commercial FeO8% C-0·4% Mn steel, and a comparison between microstructure and measured microhardness has been made. At peak hardness in the early first stage of tempering, a high density of carbides with {100} habits and primarily in the form of very thin platelets is present. Many of these particles are coherent and some are associated with dislocations. As the hardness decreases, the density of particles decreases and their length and width increase rapidly. Their thickness, however, increases very slowly and coherency is maintained for a large number of particles throughout the first stage of tempering. In the late first stage of tempering large incoherent carbide platelets with {112} and {110} habits begin to form; and in the third stage of tempering where the hardness drops more rapidly, a comparatively low density of these large incoherent carbides is found. These results support the theory t...

Tempering of chocolate or other cocoa butter prods - using viscosity as the control parameter

Abstract: In tempering or annealing of materials containing cocoa butter, particularly chocolate, the material is heated to ensure the melting of all the cocoa butter crystals and the attainment of the unannealed state, and is thereafter tempered by careful cooling and subsequently carefully reheated to its processing temp. e.g. for the prodn. of chocolate bars or coatings. Cooling is carried out to an annealed condition characterised by a considerable rise in the viscosity of the material and the subsequent reheating is initiated by measurement of the viscosity or of a magnitude dependent on the viscosity of the material.

Effects of cooling rates and tempering conditions on the strength and toughness of Mn--Ni--Mo, Cr--Mo steel plates

Abstract: Synopsis : The strength, ductility and notch toughness of Mn-Ni-Mo and Cr-Mo steels for pressure vessel are shown at the different level of cooling rates and tempering conditions. These results are summarized as follows: (1) Along with an increase in the tempering parameter, defined by T(20+log t) where T: temperature and t: holding time, the strength lowered continuously, but the ductility and the toughness gradually improved, passed through a maximum value, and finally lowered. (2) The tempering parameter corresponding to maximum toughness was found to depend on cooling rates for Mn-Ni-Mo steel, but not for Cr-Mo steel. Level of maximum toughness, however, changed with cooling rates for both steels. (3) With respect to ductility, neither tempering parameter corresponding to maximum value nor level of maximum value much depended on cooling rates for both steels.

Thermodynamic analysis of the brittleness of austenitic stainless steels

Abstract: 1. A correlation was found between changes in the thermodynamic characteristics of the formation of chromium carbide Cr23C6 and the susceptibility to embrittlement after tempering of stabilized austenitic steels. Elements raising the solubility of carbide increase the ductility and toughness after tempering. 2. Chromium and manganese have opposite effects on the toughness after tempering, which agrees with their effects on the solubility of chromium carbide. 3. To reduce susceptibility to embrittlement of stabilized austenitic stainless steels after tempering we recommend alloying to change the thermodynamic characteristics of carbide and nitride formation.

Strain aging of martensite and the fatigue strength of structural steel after surface strain hardening

Abstract: 1. Strain aging of martensite in steel 40KhNMA promotes a reduction of the residual compressive stresses resulting from strain hardening of the surface. 2. With strain aging of martensite in the quenched steel (quenching + SPD + tempering) the hardening of the surface layer reduces the decrease of the fatigue limit due to reduction of the residual stresses in the surface layer as the result of tempering. With strain aging of martensite in the tempered steel (quenching + tempering + SPD + aging) the relaxation of compressive stresses is smaller and hardening of the surface layer additionally increases the fatigue limit as compared with that resulting from strain hardening alone. 3. The increase in the fatiguestrength of steel 40KhNMA during strain aging of martensite in the surface layer depends also on the residual compressive stresses — the increase in the fatigue strength is higher for notched samples.

Process of producing a material having good spring properties

Abstract: A process for treating nickel-copper alloys whereby the alloys attain corrosion-resistant and spring-like properties which comprises heat-treating the alloy to a temperature above 900*C; cooling the alloy to room temperature; cold-rolling the alloy; and tempering the alloy at a residence time of at least 1.5 minutes at 350* to 600*C.

Structural characteristics and mechanical properties of carbon steel with niobium and vanadium

Abstract: 1. The addition of 0.6% V and 0.6% Nb to steel with 0.6% C (steel 60BF) resulted, after preliminary normalization at 850°, in an austenite grain size of 2.7 μ (grade 14) that was stable during heating to 850–1050° at rates of 20–60 deg/sec. Isothermal holding for as long as 180 sec at 950° does not lead to grain growth. 2. The austenite grain size of steel 60BF after quenching from 850–1050° is 2.5–2.0 μ. The austenite grain size remains essentially unchanged for the steel subjected to preliminary quenching or normalization. 3. The effect of tempering temperature on the mechanical properties of steel 60BF and 60 in relation to the austenite grain size was investigated. The steels with smaller grains have better properties at all tempering temperatures with the exception of 500–650°. Due to aging processes at these temperatures the ultimate and yield strengths and the modulus of elasticity are higher for steel 60BF with coarse grains than for the steel with fine grains.