Showing papers on "Tempering published in 1988"

The tempering of iron- carbon martensite; dilatometric and calorimetric analysis

Abstract: The aging behavior of iron-carbon martensite (1.13 wt Pct C) between -190 °C and 450 °C was investigated by quantitative analysis of the corresponding changes in volume and enthalpy. A method to determine activation energies of the occurring solid-state transformations by performing non-isothermal measurements of some physical property of the specimen has been described. Martensitic specimens were prepared by carburizing pure iron and quenching in brine and liquid nitrogen. The dilatometric and calorimetric experiments were supplemented with microhardness measurements. At least five different stages of structural change can be distinguished, which are quantitatively analyzed in terms of their effects on volume and enthalpy: (i) transformation of retained austenite into martensite (between −180 and −100 °C); (ii) redistribution of carbon atoms (below 100 °C); (iii) precipitation of transition carbide (between 80 and 200 °C); (iv) decomposition of retained austenite (between 240 and 320 °C); and (v) conversion of transition carbide into cementite (between 260 and 350 °C).

Analysis of nonisothermal transformation kinetics; tempering of iron-carbon and iron-nitrogen martensites

Abstract: A powerful method for the analysis of solid-state transformation kinetics can be based on non-isothermal analysis where the temperature corresponding to a fixed stage of transformation is measured as a function of heating rate. Adoption of a specific kinetic model is not required for valid application of this method. This removes constraints imposed unnecessarily on so-called Kissinger-like procedures. The method was applied to study and to compare the tempering kinetics of iron-carbon martensite and iron-nitrogen martensite (about 1.1 wt pct interstitials). Dilatometry and differential scanning calorimetry were employed. This combination of experimental techniques allowed distinction between preprecipitation processes as segregation and clustering of interstitials. In contrast with iron-carbon martensite, no indications were obtained for clustering of interstitials in iron-nitrogen martensite. The preprecipitation stages have activation energies of 75 to 85 kJ/mole, which are ascribed to volume diffusion of interstitials. The precipitation of the transition carbide/ nitride (first stage of tempering) occurs with an activation energy of 110 to 125 kJ/mole, which is ascribed to pipe diffusion of iron. The precipitation of the equilibrium carbide/nitride (third stage of tempering) is associated with an activation energy of 195 to 205 kJ/mole which is ascribed to combined pipe and volume diffusion of iron.

Laser transformation hardening of iron-carbon and iron- carbon- chromium steels

Abstract: The laser transformation hardening response of Fe-0.5C-0.8Mn and Fe-0.5C-0.8Mn-0.8Cr steels was examined. A 2 kW CO2 laser was used to scan the steel surfaces at various rates. Complete transformation of pearlite to austenite, and hence to martensite, occurred in the laser heated surface layer of the Fe-C-Mn steel. During equivalent heat treatment of the Fe-C-Mn-Cr steel, incomplete austenitization of the pearlite colonies left the cementite plates largely undissolved. However, the maximum surface hardness was approximately the same for both alloys. Comparison of calculated and measured hardened depths yielded values of the effective coupling coefficient of the laser beam to the steel which varied as a function of beam interaction time. Modeling the process allowed a dis-tinction to be made between the effects of alloying elements and of pearlite spacing upon the depth of complete austenitization. In this case, the effect of the difference in pearlite spacing between the two steels was negligible. In the alloy steel, Cr and Mn were strongly partitioned to the cementite before heat treatment, and remained so after laser processing. Incomplete austenitization of that steel is attributed to partitioning of alloying elements to the cementite and their retarding influence on the diffusion controlled dissolution kinetics of the alloyed carbide.

The effects of tempering and test temperature on the dynamic fracture initiation behavior of an AISI 4340 VAR steel

Abstract: An investigation was conducted into the effect of tempering, test temperature and loading rate on the fracture initiation behavior of an AISI 4340 VAR steel. The fracture initiation tests were conducted by stress wave loading of a prefatigued circumferential crack in a notched round bar. The geometry provides for plane strain conditions at the fracture site, and the instrumentation gives records of average stress at the fracture site and of crack opening displacement, both as functions of time. A stress intensity rate KI of about 2 × 10 6 Mpa m 1 2 s −1 is attained by this technique, and a comparison is presented with results obtained in static loading with the same geometry. Finally, the dynamic and quasi-static stress-strain behavior in shear was determined by loading a thin-walled tubular specimen in a torsional Kolsky bar. The strain rates were γ = 103s−1 and γ = 10−4s−1. In addition, Charpy specimens of the various tempers were tested. These showed a toughness trough indicative of tempered martensite embrittlement in those specimens tempered at 350°C. However, in the fracture initiation tests with the notched round bar the embrittlement trough was observed only in tests conducted below room temperature. Extensive quantitative fractography was performed on the plane strain fracture specimens to identify the dominant mode of fracture initiation for each temper at the different rates and test temperatures.

Covering for the tempering of glass

Abstract: A device for air-tempering, optionally associated with bending of glass plates includes a covering made of a metal fabric and exhibiting a thermal conductivity less than 3 and preferably less than 0.2 W.M -1 .K -1 . It has utility for coverings of frames intended to carry glass plates during their tempering and/or their bending and/or their transport.

Effect of Tempering on the Physical Properties of Shortening

Abstract: A study was conducted to determine physical changes that take place in shortening due to tempering Shortening was tempered at 10°C, 23°C, 265°C, and 30°C for 2 days or 9 days, and then stored at 23°C Solid fat content was measured by pulsed NMR Polarized light-microscopy was used to monitor crystal growth The polymorphic transitions were followed by X ray diffraction and quantified using soft laser scanning densitometry The change in melting behaviour was evaluated by differential scanning calorimetry Results indicate that transitions of beta prime to beta polymorphic forms can be delayed as a result of tempering Firmness and hardness were evaluated using an Instron Universal Testing Machine and a cone penetrometer, respectively Tempering influences the degree to which firmness or hardness increases

Laser melting of T1-high speed tool steel

Abstract: Metallographic (optical, TEM, SEM), spectroscopic, and microhardness investigations of Tl high speed tool steel heated by neodymium-pulsed laser (NPL) are described. Martensite, retained aus-tenite, delta (δ)-ferrite, M6C carbides, and cellular segregations of W, V, and Cr were observed in the laser-melted zone. The high chemical homogeneity and fine structure of the melted zone were attrib-uted to high cooling rates due to the short interaction time with the neodymium-pulsed radiation and relatively small volume of the melted material. Fine precipitates, cellular M6C carbides, and plate-like MC carbides were formed in the melted zone during tempering. An increase in micro-hardness of the laser-melted zone with tempering temperature was observed and attributed to these precipitates and the transformation of the retained austenite.

Low temperature tempering-induced changes in bulk resistivity, temperature coefficient of resistivity and stress in physically vapor-deposited TiN

Abstract: In this work, we explored the annealing behavior of TiN at temperatures compatible with physical vapor deposition processing (300 °C). Bulk resistivity, temperature coefficient of resistivity and macrostress were determined as a function of both air and vacuum tempering. Vacuum or air tempering near the deposition temperature reduces stress levels by 15% – 20%. Resistivity is also reduced by vacuum tempering but remains unstable to air or dry oxygen exposure owing to grain boundary oxidation. Microcracking on secondary f.c.c. slip planes points to the need for better control of as-deposited defect levels in physically vapor-deposited films.

Case-Hardened plate armor and method of making

Abstract: Case-hardened plate armor disclosed includes a steel plate (14,18) that is heat treated to provide carbonitride surfaces and a tough, ductile core, with the carbonitride surfaces having a toughness of at least 66, and preferably at least 67, on the Rockwell C scale to prevent surface penetration, and with the tough, ductile core being softer than the carbonitride surfaces to prevent brittle fracture. The steel plate (14,18) may be made from either rolled homogenous armor which has a final core hardness in the range of 45 to 50 on the Rockwell C scale, or from high-hard armor which has a final core hardness in the range of 52 to 54 on the Rockwell C scale. The steel plate may be made with holes or may be imperforate depending upon weight requirements. The case-hardening of the steel plate is performed by heating in an atmosphere of nitrogen and carbon, quenching of the heated steel plate, thereafter tempering the quenched steel plate, deep freezing of the tempered steel plate, and subsequently again tempering the steel plate after the deep freezing to provide the hard carbonitride surfaces and the softer but tougher and more ductile core.

Production of low alloy high tension seamless steel pipe having fine grained structure

Abstract: PURPOSE: To produce a high tension seamless steel pipe having fine grained structure and excellent sulfide stress cracking resistance and low temp. toughness by controlling the steel components and hot-rolling condition at the time of producing the seamless steel pipe with low alloy steel. CONSTITUTION: The low alloy steel billet containing 0. 05-0. 35wt.% C, 0.01-0.5% Si, 0.15-1.5% Mn, <0.01% S, <0.02% P, 0.05-0.4% Mo and 0.005-0.1% Al or further, one or more kinds of the specific contents among Cr, Ni, V, Ti and B and singly or complexly containing one or more kinds among rare earth element, Ca, Co and Cu in ≥1200°C is rolled at ≥ the recrystallizing temp. of this steel in the last process of the hot piercing continuous rolling and the obtd. hollow raw pipe in the temp. between Ar 3 -Ac 1 points, is heated at 900-1100°C. This is finishing-rolled so that the hot-finishing temp. becomes the temp. of ≥Ar 3 point+50°C and after quenching this finished steel pipe from the temp. of ≤Ar 3 point, 1 the tempering treatment is executed at the temp. of ≤Ac 1 point, to produce the high tension seamless steel pipe. COPYRIGHT: (C)1990,JPO&Japio

Influence of warm working and tempering on fissure formation

Abstract: The influence of warm working and tempering on the formation of fissures on the fractured faces of Charpy V-notch samples has been examined for a variety of ferrite–pearlite steels and iron alloys which had been rolled in the temperature range 600–400°C and tempered in the range 600–725°C. In accordance with fissures being initiated by the ease of intergranular failure along the ferrite grain boundaries, the number of deep fissures produced on warm working increased with the degree of grain boundary alignment in the rolling direction and the grain aspect ratio (maximum grain diameter/minimum grain diameter). Pearlite banding and the presence of grain boundary carbides were found not to influence the number of fissures formed, fissuring behaviour being the same for the Fe–Mn alloys and plain C–Mn steels. The presence of low levels of S and P also did not influence fissure formation. At a given average grain aspect ratio it was found that the introduction of a two phase rolling sequence (760–720°C) ...

Method of producing steel having a low yield ratio

Abstract: A method of producing steel plate having a low yield ratio and high strength and a dual-phase mixed microstructure of ferrite and second-phase carbide comprises heating to at least 950° C. low-carbon slab steel having 0.30% or less carbon, 0.05 to 0.60% silicon, 0.5 to 2.5% manganese, and 0.01 to 0.10% aluminum as the basic components, with the balance being iron and unavoidable impurities, or low-carbon low-alloy slab steel comprising in addition to the above basic components one or more elements selected from copper, nickel, chromium, molybdenum, niobium, vanadium, titanium, boron and calcium, hot rolling it, reheating it and tempering it.

Physical vapor-deposited TiN on cemented carbide: Tempering effects☆

Abstract: The contraction of the expanded crystal lattice, inherent in coatings made by plasma-enhanced vapor deposition, occurs on tempering with an activation energy of about 2.09 eV and is accompanied in the present films by an increase in residual compressive stress and the development of a texture in the plane of the film. The residual compressive stress in the WC phase in the substrate also falls. The scratch test adhesion of the coating increases slightly on tempering.

Tempering Glass with Modulated Cooling Schedules

Abstract: Modulated quenching is a variant of the tempering process that gives one independent control over the strength and fracture characteristics of glass. Thus the strength of nondicing “heat-strengthened” glass can be raised to that of “fully tempered” glass. Conversely, the break pattern of glass having the strength of fully tempered glass can be made to range from nondicing to fine dicing.

Method for producing rolled steel products, particularly threaded steel tension members

Abstract: To produce threaded steel tension members, steel is used with a C-content of 0.50 to 0.80%, preferably 0.75%, a Si-content of 0.20 to 0.50%, preferably 0.25%, and a Mn content of 0.30 to 0.80%, preferably 0.60%. Exiting from the rolling heat at the outlet side of the finishing stand after hot rolling, the tension member or rod is subjected to surface quenching by a cooling medium, preferably water, so that the steel in a rim zone R 1 is transformed immediately and completely into martensite, while the heat content remaining in the core zone K 1 does not effect a tempering of the martensite rim zone during the subsequent cooling beyond the range of the intermediate stage. Steel tension members of this type have a high ductility and toughness at a high yield limit and high strength, they are corrosion-resistant to a great degree and have a wear resistant surface which makes them particularly suitable for threaded tension rods in which the threads are produced either by a cold forming operation or hot rolled ribs.

Method of heat treatment of Al-based alloys containing Li and the product obtained by the method

Abstract: The invention concerns a method for final heat treatment tempering at Al alloys containing Li and at least one other major element selected from the group Cu, Mg and Zn, as well as possible minor elements such as Zr, Mn, Cr, Ni, Hf, Ti and Be, in addition to inevitable impurities such as Fe and Si. The treatment involves a principal tempering operation which takes place at a time and temperature in an area defined by a parallelogram on a temperature log-time diagram, whose corners have the following coordinates: (A) 270° C.--3 min; (B) 270° C.--48 min; (C) 225° C.--9 hrs 30 min; (D) 225° C.--35 min. The heat treatment makes it possible to produce a satisfactory array of mechanical characteristics such as mechanical strength, ductility, or toughness and resistance to corrosion, which are higher than those achieved by means of conventional treatments of type T6 or by under-ageing operations.

Production of steel plate for die having good heat fatigue characteristic

Abstract: PURPOSE:To improve an extremely thick steel plate having excellent heat fatigue characteristic by executing heat-treatment under specific temp. condition after hot-rolling low-medium carbon low alloy steel slab containing the specific quantities of Ni, Cr, Mo, etc., to the thick plate. CONSTITUTION:The steel slab of composition containing 0.15-0. 50 wt.% C, 0.05-0.75% Si, 0.25-2.00% Mn, 0.25-4.00% Ni, 1.00-4.00% Cr, 0.15-3.00% Mo, 0.005-1.50% Sol. Al and 0.0020-0.0500% N or further, one or more kinds among 0.002-0.002%, Ti, 0.0003-0.0100% B, 0.005-0.200% Zr and 0.003-0.50% V, is hot- rolled to the extremely thick plate material having >=250mm thickness. After reheating this to the temp. of Ac3 point+30 deg.-Ac3 point+200 deg.C of this steel by using water soluble quenching liquid near the water or oil, rapidly cooled quenching is executed at <=300 deg.C and successively, tempering is executed at the temp. of <=Ac1 point. The extremely thick steel plate having excellent heat fatigue characteristic for using to hot forging die, plastic die, etc., is produced.

Improvements in or relating to tempering glass

Abstract: The invention relates essentially to tempering in air, optionally in combination with the bending of sheet glass. It proposes a coating comprising a metal cloth exhibiting a thermal conductivity lower than 3 and preferably lower than 0.2 W M K . The invention is applied more particularly to the coating of frames intended to carry sheet glass while it is tempered and/or bent and/or conveyed.

Improvement of AISI D2 steel properties by unconventional vacuum heat treatments

Abstract: The possibility of improving the properties of an AISI D2 steel by an unconventional vacuum heat treatment has been studied. A double quenching, the first quenching from a temperature higher than that for the second quenching, followed by normal tempering enables an excellent combination of toughness and hardness to be obtained as a consequence of (a) the improved microstructural homogeneity due to the dissolution (first quenching) and reprecipitation (second quenching) of carbides, (b) a large amount of fine dispersed carbides in the matrix, (c) a low carbon content of martensite and (d) the possibility of maintaining in the matrix a controlled amount of retained austenite, which plays an important role during the fracture and wear processes. Vacuum furnaces rather than salt bath furnaces are particularly suitable for this double treatment; in addition to the well-known advantages, their flexibility permits several process conditions to be tested in a less expensive way and tools to be produced with properties optimized in relation to the use to which they are subjected.

Steel wire for a spring and method for the production thereof

Abstract: A steel wire, and a method for producing the same, for use in the manufacture of a chassis or suspension automotive spring having a high sag resistance. In accordance with the invention, after a heat treatment is effected, strain is imposed to the steel wire so as to thereby improve the sag resistance. The strain may be imposed either during tempering or at room temperature following tempering.

Hot working tool steel and its manufacture

Abstract: PURPOSE:To manufacture a Cr hot working tool steel enabling an increase in the size of dies by subjecting a steel having a specified compsn. consisting of C, Si, Mn, Ni, Cr, V, Mo, W and Fe to proper heat treatment so as to improve the suitability to bainite hardening. CONSTITUTION:An Ni-contg. Cr hot working tool steel consisting of 0.20-0.35% C, =5.0 during final thermal refining by hardening and tempering. Thus a tool steel having high hardenability is obtd.

Production of extra-thick tempered high tension steel plate having excellent low-temperature toughness

Abstract: PURPOSE:To produce an extra-thick tempered high tension steel plate having excellent low-temp. toughness by subjecting a steel plate of a specific thickness consisting of a specific compsn. successively to heating, air cooling, force cooling, and tempering under specific conditions. CONSTITUTION:The steel plate of 75-200mm thickness which contains, by weight %, 0.03-0.20% C, 0.05-0.50% Si, 3.0% Mn, =2 kinds of 0.01-1.50% Cu, 0.01-1.50% Cr, and 0.01-1.50% Mo, and consists of the balance iron and inevitable impurities and has 26-42 parameter (x) expressed by the formula is prepd. This steel plate is then heated to a 900-1,050 deg.C range and is air-cooled down to 800-850 deg.C, following which the steel plate is forcibly cooled down to =1 deg.C/sec cooling rate and is then tempered at the Ac1 transformation point or below. The extra-thick tempered high tension steel plate having the excellent low-temp. toughness and about >=80kgf/mm tensile strength is obtd.

Fracture mechanisms and mechanics of an 18-4-1 high speed steel

Abstract: Cast, wrought, and directly sintered smooth and precracked beam specimens of BT1 steels were studied in three- and four-point bending at room temperature. Following austenitization at 1250° C and tempering between 500 and 560° C, brittle fracture strengths varied between 1.1 and 2.8 GN m−2 and the fracture toughness of the materials was in the range 18 to 25 MN m−3/2. Combining these data, the critical Griffith-Irwin flaw sizes were calculated to be typically of the order of 100 μm. This is in reasonable agreement with the observed sizes of some failure-initiating sites, particularly pores in sintered material, but generally several times larger than the carbide and grain sizes. In wrought specimens, failure frequently originated from groups of carbides, apparently fracturing on contiguous planes. No evidence of sub-critical cracking of carbides was detected (as in BT42), in contrast to BM2, BT6 and sintered and hot isostatically pressed BT1. Only inter-powder particle parting occurred in this sintered material. Conventional fracture mechanics thus successfully interprets results on sintered specimens, but only on several of the wrought specimens. For the majority of the latter it appears necessary to invoke operation of propagation mechanisms involving “short”, ≈10 μm, cracks under monotonic loading or to associate the brittle fracture stress with that for crack nucleation: e.g. cleavage of a carbide cluster.