Effect of heat treatment on the fracture toughness of hot-rolled corrosion-resistant austenitic high-nitrogen 0.4Cr20Ni6Mn11Mo2N0.5 steel

The effect of water quenching from rolling heating at 1100°C on the structure, the mechanical properties, and the static fracture toughness of corrosion-resistant austenitic high-nitrogen 0.4Cr20Ni6Mn11Mo2N0.5 steel shot-rolled at 1100–900°C is studied. It is found that, after quenching, the initially hot-deformed steel possesses a quite high fracture toughness, although quenching from 1100°C decreases its fracture toughness by 11.4%. An analysis of fracture surfaces indicates a ductile character of failed quenched steel specimens. The specimens have fracture regions close to a quasi-cleavage at the stage of stable crack growth.     

Martensitic steel with 13% Cr for corrosion-resistant oil pipe

The temperature ranges corresponding to phase transitions in the heating and cooling of L80 steel of 13Cr type according to the API 5CT/ISO 11961 standard are determined (the Russian analog is 20X13 steel). The influence of the heat treatment on the structure and mechanical properties of the steel is investigated. It proves expedient to reduce the initial temperature in quenching from 1030–1040°C to 930–960°C, so as to improve the impact strength of the steel at negative temperatures. The influence of additional alloying of L80-13Cr steel with manganese and molybdenum on its strength and plasticity is studied. The use of steel with 13% Cr and with 1–2% nickel and manganese is promising for low-temperature pipe resistant to carbondioxide corrosion.     

Effect of cooling rate on the as-quenched microstructure and mechanical properties of HSLA-100 steel plates

The effect of cooling rate on the as-quenched microstructure and mechanical properties of a 14-mm-thick HSLA-100 steel using various cooling media such as brine, water, oil, air, and furnace has been studied. While quenching in brine, water, and oil resulted in lath martensite structures, the granular bainite and martensite-austenite (M-A) constituents were found in air- or furnace-cooled specimens. The average lath spacing increased slightly on decreasing the cooling rate (300 nm in brine-quenched specimen to 400 nm in oil-quenched specimen). The precipitates of Cu and Nb(C, N) were observed in all the quenching conditions except in the brine-quenched specimen. The as-quenched strength and toughness of the brine-, water-, and oil-quenched specimens were higher (yield strength: 894 to 997 MPa, ultimate tensile strength: 1119 to 1153 MPa, and Charpy V-notch energies: 65 to 70 J at −85 °C) than those of air- and furnace-cooled specimens (yield strength: 640 to 670 MPa, ultimate tensile strength: 944 to 1001 MPa, and Charpy V-notch energies: 10 to 20 J at −85 °C). For industrial production of HSLA-100 steel plates, oil or water quenching is recommended in lower thickness plates (<25 mm). For production of thicker plates, however, water quenching is more suitable.     

Influence of thermomechanical treatments on the microstructure and mechanical properties of HSLA-100 steel plates

The influence of thermomechanical treatment (TMT), i.e., controlled rolling and direct quenching, as a function of rolling temperature and deformation on the microstructure and mechanical properties of HSLA-100 steel have been studied. The optical microstructure of the direct quenched (DQ) and tempered steel rooled at lower temperatures (800 °C and 900 °C) showed elongated and deformed grains, whereas complete equiaxed grains were visible after rolling at 1000 °C. The transmission electron microscope (TEM) microstructure of the 800 °C rooled DQ steel showed shorter, irregular, and closer martensite laths with extremely fine Cu and Nb(C,N) precipitates after tempering at 450 °C. The precipitates coarsened somewhat after tempering at 650 °C; the degree of coarsening was, however, less compared to that of the reheat-quenched (RQ) and tempered steel, indicating that the DQ steel was slightly more resistant to tempering. Similar to the RQ steel, at a 450 °C tempering condition, the DQ steel exhibited peak strength with extremely poor impact toughness. After tempering at 650 °C, the toughness of the DQ steel improved significantly, but at the expense of its strength. In general, the strength of the DQ and tempered steel was good and comparable to that of the RQ and tempered steel, although, its impact toughness was marginally less than the latter. The optimum combination of strength and toughness in the DQ steels was achieved after 900 °C rolling with 50 pct deformation, followed by direct quenching and tempering at 650 °C (yield strength (YS)=903 MPa, ultimate tensile strength (UTS)=928 MPa, and Charpy V-notch (CVN) strength=143 J at −85 °C).     

A comparison of fracture behavior of low alloy steel with different sizes of carbide particles

The fracture behaviors of low alloy steels with similar grain sizes but different sizes of carbide particles were investigated using precracked and notched specimens. The results indicate that in precracked specimens (COD), steel with coarser carbide particles has a lower toughness than steel with finer carbide particles over a temperature range from –196 °C to – 90 °C. However, in notched specimens (four-point bending (4PB) and Charpy V), these two steels shows similar toughness at low temperature where specimens are fractured by cleavage without fibrous cracking. In the transition temperature range, the steel with coarser carbide particles conversely shows a little higher toughness due to the longer extension length of the fibrous crack. This phenomenon indicates that in precracked specimens, the second-phase particles play a leading role in cleavage fracture, while in notched specimens, the grain size dominates the fracture behavior.     

Fatigue and fracture of porous steels and Cu-infiltrated porous steels

The effects of Cu infiltration on the monotonic fracture resistance and fatigue crack growth behavior of a powder metallurgy (P/M) processed, porous plain carbon steel were examined after systematically changing the matrix strength via heat treatment. After austenitization and quenching, three tempering temperatures were chosen (177 °C, 428 °C, and 704 °C) to vary the strength level and steel microstructure. The reductions in strength which occurred after tempering at the highest temperature were accompanied by the coarsening of carbides in the tempered martensitic steel matrix, as confirmed by optical microscopy and by microhardness measurements of the steel. Each steel-Cu composite, containing approximately 10 vol pct infiltrated Cu, had superior fracture toughness and fatigue properties compared to the porous matrix material given the same heat treatment. Although the heat treatments given did not significantly change the fatigue behavior of the porous steel specimens, the fatigue curves (da/dN vs ΔK) and fracture properties were distinctly different for the steel-Cu composites given the same three heat treatments. The fracture toughness (K _IC and J _IC ), tearing modulus, and ΔK _TH values for the composites were highest after tempering at 704 °C and lowest after tempering at 177 °C. In addition, the fracture morphology of both the fracture and fatigue specimens was affected by changes in strength level, toughness, and ΔK. These fractographic features in fatigue and overload are rationalized by comparing the size of the plastic zone to the microstructural scale in the composite. This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee.     

Mechanical Properties and Corrosion–Abrasion Wear Behavior of Low-Alloy MnSiCrB Cast Steels Containing Cu

Two medium carbon low-alloy MnSiCrB cast steels containing different Cu contents (0.01 wt pct and 0.62 wt pct) were designed, and the effect of Cu on the mechanical properties and corrosion–abrasion wear behavior of the cast steels was studied. The results showed that the low-alloy MnSiCrB cast steels obtained excellent hardenability by a cheap alloying scheme. The microstructure of the MnSiCrB cast steels after water quenching from 1123 K (850 °C) consists of lath martensite and retained austenite. After tempering at 503 K (230 °C), carbides precipitated, and the hardness of the cast steels reached 51 to 52 HRC. The addition of Cu was detrimental to the ductility and impact toughness but was beneficial to the wear resistance in a corrosion–abrasion wear test. The MnSiCrB cast steel with Cu by the simple alloying scheme and heat treatment has the advantages of being high performance, low cost, and environmentally friendly. It is a potential, advanced wear-resistant cast steel for corrosion–abrasion wear conditions.     

Influence of tempering on the microstructure and mechanical properties of HSLA-100 steel plates

The influence of tempering on the microstructure and mechanical properties of HSLA-100 steel (with C-0.04, Mn-0.87, Cu-1.77, Cr-0.58, Mo-0.57, Ni-3.54, and Nb-.038 pct) has been studied. The plate samples were tempered from 300 °C to 700 °C for 1 hour after austenitizing and water quenching. The transmission electron microscopy (TEM) studies of the as-quenched steel revealed a predominantly lath martensite structure along with fine precipitates of Cu and Nb(C, N). A very small amount of retained austenite could be seen in the lath boundaries in the quenched condition. Profuse precipitation of Cu could be noticed on tempering at 450 °C, which enhanced the strength of the steel significantly (yield strength (YS)—1168 MPa, and ultimate tensile strength (UTS)—1219 MPa), though at the cost of its notch toughness, which dropped to 37 and 14 J at 25 °C and −85 °C, respectively. The precipitates became considerably coarsened and elongated on tempering at 650 °C, resulting in a phenomenal rise in impact toughness (Charpy V-notch (CVN) of 196 and 149 J, respectively, at 25 °C and −85 °C) at the expense of YS and UTS. The best combination of strength and toughness has been obtained on tempering at 600 °C for 1 hour (YS-1015 MPa and UTS-1068 MPa, with 88 J at −85 °C).     

Microstructure and Mechanical Properties in Hot-Rolled Extra High-Yield-Strength Steel Plates for Offshore Structure and Shipbuilding

Key parameters for a thermomechanically controlled processing and accelerated cooling process (TMCP-AcC) were determined for integrated mass production to produce extra high-yield-strength microalloyed low carbon SiMnCrNiCu steel plates for offshore structure and bulk shipbuilding. Confocal scanning microscopy was used to make in-situ observations on the austenite grain growth during reheating. A Gleeble 3800 thermomechanical simulator was employed to investigate the flow stress behavior, static recrystallization (SRX) of austenite, and decomposition behavior of the TMCP conditioned austenite during continuous cooling. The Kocks–Mecking model was employed to describe the constitutive behavior, while the Johnson–Mehl–Avrami–Kolmogorov (JMAK) approach was used to predict the SRX kinetics. The effects of hot rolling schedule and AcC on microstructure and properties were investigated by test-scale rolling trials. The bridging between the laboratory observations and the process parameter determination to optimize the mass production was made by integrated industrial production trials on a set of a 5-m heavy plate mill equipped with an accelerated cooling system. Successful production of 60- and 50-mm-thick plates with yield strength in excess of 460 MPa and excellent toughness at low temperature (213 K (–60 °C)) in the parent metal and the simulated coarse-grained heat affected zone (CGHAZ) provides a useful integrated database for developing advanced high-strength steel plates via TMCP-AcC.     

The effect of testing temperature on fracture toughness of austempered ductile iron

The effect of testing temperature (− 150 °C, 25 °C, and + 150 °C) on the fracture toughness of austempered ductile iron (ADI) was studied. Specimens were first austenitized at 900 °C for 1.5 hours and then salt-bath quenched to 360 °C or 300 °C, for 1, 2, or 3 hours of isothermal holding before cooling to room temperature. The resulting matrices of the iron were of upper-ausferrite and lower-ausferrite. It was found that raising the testing temperature to 150 °C from ambient improved the fracture toughness by 18, 30, and 7 pct for the as-cast/lower-ausferrite ADI/upper-ausferrite ADI, respectively. Lowering the testing temperature to −150 °C produced a decrease of −15, −35, and −48 pct. Optical microscopy, X-ray diffraction analysis, and scanning electron microscopy (SEM) fractography were applied to correlate the toughness variation with testing temperatures.     

Development and Commercial Use of Weldable High-Strength Cold-Resistant Steel for Load-Bearing Structures in Transportation Engineering

Ural'skaya Stal' has developed and introduced new grade of steel 12KhGN2MA. The steel is designed for use on the frames of quarry trucks, mining machinery, and other metal structures used at low temperatures. The steel is distinguished by its excellent cold resistance (KCV⁻⁷⁰ ≥ 50 J/cm²) and good weldability, and it has satisfactorily high strength and ductility (σ_0.2 ≥ 690 N/mm², δ_u ≥ 790 N/mm², and δ₅ ≥ 16%) after quenching and tempering. The cold-shortness threshold — corresponding to 50% ductile component in the fracture — is below −40°C for steel 12KhGN2MA (25-mm thick plate). Alloying the steel with elements that help stabilize austenite (chromium, nickel, molybdenum, and magnesium) ensures the formation of a martensite-bainite structure. The technology used to make the steel provides for its refining in electric-arc furnaces, rolling of the steel on a 2800 mill, and subsequent heat treatment of the plates in high-productivity regimes. The weldability of the steel was studied by simulating the effects of the thermal welding cycle on the structure and properties of the metal in the near-weld zone. This metal is given good cold resistance down to −70°C by using cooling rates corresponding to the types and regimes of welding actually used. Ural'skaya Stal' has successfully begun production of plates of the new steel in the 10–45-mm thickness range. __________ Translated from Metallurg, No. 5, pp. 55–58, May, 2005.     

Quality of Ст3сп steel reinforcement (class A500S) thermally hardened in a 280 mill

Thermal hardening of Ст3сп steel rolled in the 280 mill at the LPZ casting and rolling plant is developed, so as to produce reinforcement (diameter 14–18 mm) of strength class A500S according to the STO ASChM 7–93 standard. The strength of the metal, whether supplied to the mill in the hot or cold state, is the result of discontinuous quenching with variation in mean-mass self-tempering temperature within the range 565–575°C. The macrostructure, microstructure, and fine structure of the thermally hardened bar is investigated. The properties of the bar are ensured by the structure formed as a result of hardening and subsequent cooling on the roller conveyer and in the cooling unit: mainly tempered martensite in the surface layer; ferrite and cementite in the core of the bar.     

Melting and Thermomechanical Processing of High Strength 0.3%C–CrMoV (ESR) Steel

0.3%C–CrMoV steel were processed through electric arc furnace melting followed by electro slag refining. 2800 mm diameter class of rolled rings and 8 mm thick plates required for fabrication of solid rocket booster motorcase were realized. Tensile and fracture toughness properties were evaluated as a part of characterization of the steel. Low fracture toughness in initial melts was investigated using optical and scanning electron microscopy. Modifications in methods of alloying additions/processing were suggested and incorporated to achieve the desired mechanical properties in industrial scale melts. Process was also fine-tuned by incorporating additional thermomechanical working and heat treatment cycles to achieve the required mechanical properties. Hardening cycle of 925 °C for 1 h followed by oil quenching and tempering cycle of 505 °C for 2 h followed by oil quenching was found to result in optimum combination of mechanical properties. Repeatability in processing and consistency in achieving the mechanical properties of the steel at industrial scale was demonstrated by processing 24 melts of 6 tons each into large size rings and plates.     

Microstructure and Properties of Hot Working Die Steel H13MOD

Compared with H13 steel, the influences of different heat treatment process on the microstructure and properties of the new type of hot working die steel H13MOD were studied. The results show that the complete austenitizing temperature of H13MOD is around 1030 °C and the quenching hardness achieves the maximum value at this temperature. While for H13, the complete austenitizing temperature is above 1100 °C and the quenching hardness rise constantly with the quenching temperature increasing. In quenching process, the undissolved MC carbides can prevent the coarsening of grain in both steels. With the rise of quenching temperature, when MC carbides dissolve completely, the grain grows quickly. The hardness and strength of H13MOD at higher tempering temperature (above 570 °C) are nearly the same as those of H13, but its toughness is higher than that of H13. Mo₂ C carbide is the main strengthening phase in H13MOD, which is attributed to the higher content of Mo. The quantity of VC eutectic carbides is reduced because of lower content of V in H13MOD, which plays an important role in enhancing the impact toughness of H13MOD. Under a certain strength condition, H13MOD steel can be used in the environment that higher toughness is required and the service life of die casting mold can be improved.     

Fracture toughness of the lean duplex stainless steel LDX 2101

Fracture toughness testing was performed on the recently developed lean duplex stainless steel LDX 2101 (EN 1.4162, UNS S32101). The results were evaluated by master curve analysis, including deriving a reference temperature. The master curve approach, originally developed for ferritic steels, has been used successfully. The reference temperature corresponds to a fracture toughness of 100 MPa√m, which characterizes the onset of cleavage cracking at elastic or elastic-plastic instabilities. The reference temperature, T ₀, was −112 °C and −92 °C for the base and weld materials, respectively. In addition, the fracture toughness is compared with impact toughness results. Complementary crack tip opening displacements (CTODs) have also been calculated. The toughness properties found in traditional duplex stainless steels (DSS) are generally good. The current study verifies a high fracture toughness for both base and weld materials and for the low alloyed grade LDX 2101. Even though the fracture toughness was somewhat lower than for duplex stainless steel 2205, it is still sufficiently high for most low-temperature applications.     

Kinetics of the σ-phase formation in Fe-Cr-Co hard magnetic alloys

Three magnetic hard alloys 22Kh15K, 25Kh15KYuBF and 30Kh5K of the Fe-Cr-Co system are used to study the kinetics of σ phase formation after quenching from 1300–1100°C and tempering in the temperature range 700–800°C by measuring HV ₃₀₀ hardness, X-ray diffraction, and metallographic analysis. The main σ-forming element in these alloys is shown to be cobalt. The rate of formation of σ-phase during tempering is maximal at 750°C.     

Hardenability in high carbon steels

Multiplying factors (MF) for the hardenability effects of Mn, Si, Cr, Ni, Mo, Al, and B at high carbon levels were successfully derived to a pure iron or alloy free base for austenitizing conditions ranging from 1475°F (800°C) to 1700°F (927°C). Base factors were also determined for carbon in the range of 0.60 to 1.10 pct. These data supersede a similar set of MF’s determined previously by the author to a reference or base composition of 1.0 pct C and 0.25 pct of each of Mn, Si, Cr, and Ni. The new MF’s are presented in both tabular and graphical form and can be used to predict hardenability from composition for homogeneous high carbon steels as well as the so-called “case” hardenability of high carbon regions in carburizing grades. Case hardenability can be calculated for both the single quench practice wherein the steel is hardened by direct or delay quenching from carburizing, and for the double quench practice wherein the steel is reheated for hardening to some lower temperature after a prior air cooling (normalizing) or quenching from the carburizing treatment. The accuracy of hardenability prediction using these new factors has been found to be within ±10 pct of the measured hardenability atD _I’s as high as 26 in. (660 mm). This paper is based on a presentation made at a symposium on “Hardenability” held at the Cleveland Meeting of The Metallurgical Society of AIME, October 17, 1972, under the sponsorship of the IMD Heat Treatment Committee.     

Ferritic Fine Structure Characteristics in Hot Die Forged Powder Steels. I. Effect of Heating Temperature during Die Forging on Ferritic Fine Structure in Specimens of Powder Technical Grade Iron and Carbon Steels

We have studied the effect of the composition and heating temperature during die forging on the microstructure and fine structure of ferrite in powder iron and powder carbon steels. From the structural characteristics obtained for different planes of the blank, we used harmonic analysis of the x-ray line shape to establish the nonuniformity of deformation over the volume. We have established the heating temperature during die forging of powder technical grade iron and carbon steels, for which the deformation is close to uniform over the die forging volume: 1050 °C for technical grade iron and low-carbon steel, 1100 °C for carbon steel. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 108–119, May–June, 2005.     

Effect of silicon on the wear resistance of high-carbon steels with the structures of isothermal decomposition of austenite during friction and abrasive action

The hardness and wear resistance during sliding and abrasive friction of 80S2 (0.83% C, 1.66% Si) and U8 (0.83% C) steels subjected to the isothermal γ → α decomposition in the temperature range 330–650°C and additional 5-min annealing at 650°C are compared. The optimum decomposition temperature is found to be 550°C. At this temperature, fine lamellar pearlite with the maximum hardness and wear resistance as compared to other pearlitic and bainitic structures forms in the silicon steel. The silicon-alloyed fine lamellar pearlite of 80S2 steel is found to have high hardness and abrasive wear resistance as compared to the similar structure in plain U8 steel; however, this pearlite has no advantages in the wear resistance under conditions of sliding friction on a steel plate. Silicon alloying of the bainitic structures in the eutectoid steel leads to a noticeable decrease in the wear resistance during sliding friction and abrasive action. Friction oxidation is shown to negatively affect the abrasive wear resistance of the silicon steel.     

Efficiently alloyed ultra-cold-resistant steel for containers used to store and transport liquified natural gas

The storage and transport of natural gas in the liquified state (LNG) has become an important issue in connection with the development of new natural-gas fields on the shores of the Barentz Sea in the Artic region. Ferritic nickel-bearing steels 0N6 and 0N9 — which are more efficiently alloyed than austenitic stainless steel 10Kh18N10T — are well-suited for the thick-walled shells of isothermal containers used for LNG storage and transport. These steels have excellent resistance to cold — down to −164°C. The technology developed to make them allows the production of rolled plates that have a thickness of up to 40 mm and meet the requisite standards on mechanical properties and cold resistance. The article examines features of the microstructure of the steels that allow them to resist temperatures down to −164°C. __________ Translated from Metallurg, No. 4, pp. 63–65, April, 2006.