Quench Cracking Research Articles

Investigating quench crack susceptibility in disc springs: a microstructural analysis of martensitic evolution and its implications

Investigating quench crack susceptibility in disc springs: a microstructural analysis of martensitic evolution and its implications

Mechanism of mitigating quenching cracking for B-containing 9Cr martensitic heat resistant steel by austempering process

B-containing 9Cr martensitic steels are attractive materials for specific industrial applications due to their excellent high-temperature strength and ductility. However, quenching large forgings with water or oil often results in cracking. The correlation between quenching crack and microstructure was established in this work to evaluate the selection of the quench cooling methods, which make it possible to mitigate the quench cracking by tailoring microstructural evolution. Kinetics dynamic analysis, microstructural characterization, and phase-field simulation were used to clarify the mechanism of mitigating quenching cracking. It is demonstrated that austempering produces a mixed microstructure consisting of lathy martensite, ultra-fine martensite, and a small amount of C-riched retained austensite. This mixed microstructure translates into refining the effective grain size and reducing the internal stress, reducing cracking propagation by reducing phase transformation stress and enhancing the coordinated deformation. Thus, the quenching cracking can be inhibition by tailoring the fraction of ultra-fine martensite and retained austensite in B-containing 9Cr steels.

Effect of Steel Inclusion on Heat Treatment Quench Crack - Case Study

Hypoid pinion is a major member in the heavy truck axle as it transmits the power from propeller shaft to hypoid ring gear. This is the first member in axle assembly to receive the power from transmission. Metallurgical quality is inevitable parameter in this part. In this case, a fracture analysis of hypoid pinion carried out, root cause is found & corrections are addressed. The quench crack is generated during the case carburizing treatment. The fractography shows that this crack is initiated from the gross non-metallic inclusion present at the sub surface of the drive pinion. SEM EDS analysis conducted & identified inclusion as Aluminium Oxide predominantly with a dimension 7 mm in length & 1mm in width caused the longitudinal crack on the pinion. The ishikawa diagram plotted for steel mill process to understand the cause. Since the type of inclusion is Al2O3, focused more on ladle refining station, VD process & continuous casting parameters in steel mill process where entrapment could occur. The appropriate corrective action taken in steel mill on VD process, post VD soft rinse, multiple sampling for inclusion from first & last billet, NDT method UT phased array system is introduced by developing the master sample having size same as inclusion. The Inclusion went undetected whole the process starting from steel mill to pinion case carburizing heat treatment & is opened up after quenching due to volumetric difference in crystal, happens during heating & cooling. The mechanism of crack generation is discussed which involves crystallographic changes takes place during carburizing cycles.

Microstructural origins for quench cracking of a boron steel: Boron distribution

Boron is an important trace element and intentionally added for hardenability of low-alloy steels. The forms of B presence in microstructure are believed to be crucial for success or failure of boron steel production. This research addresses atomistic distribution of boron responsible for quench cracking of a boron steel. Boron steel sheets (6 mm thick) with/without quench cracking are carefully characterized with transmission electron microscopy and atom probe tomography to reveal B distribution and to understand quench cracking mechanisms. The quench cracking is brittle intergranular fracture along prior austenite grain boundaries (PAGBs). The PAGBs are decorated with boron-containing Fe3(C, B) precipitates in the cracked steel, but segregated with boron in the uncracked steel. Without the segregation of B at PAGBs, the formation of ferrite and massive acicular-shaped Fe3C during quenching makes cracks easy to initiate and propagate in the steel with deteriorated mechanical properties. Processing parameters important for engineering the distribution of boron are discussed.

Cooling process optimization during hardening steel in water polyalkylene glycol solutions

Objects of investigations are water solutions of polyalkylene glycol (PAG) which are used as the quenchants in the heat-treating industry. They are tested by standard cylindrical probe made of Inconel 600 material. The main and not solved yet is the problem of transition from data achieved for standard probe to data suitable for any form and size of real steel part. It opens possibility to make predictable calculations. Taken this into account, it has been investigated water solutions of PAG of different concentration. It is underlined that cooling intensity of quenchant can be evaluated by Kondratiev number Kn. The mentioned number Kn varies within 0≤Kn≤1 when generalized Biot Biv number varies within 0≤Biv≤∞. As a main achievement of investigation is established correlation between standard Kn number and Kn number of real steel part. In many cases, when film boiling is absent, the established correlation is a linear function. It allows optimizing quenching processes: obtain high surface compressive residual stresses, save alloy elements and improve environment condition. All of this is achieved by tolerating chemical composition of steel with size and form of quenched object as it is proposed by UA Patent No. 114174. Also, the number Kn allows interruption of quench process when surface compressive residual stresses are at their maximum value that essentially improves the quality of steel components. Moreover, interrupted cooling prevents quench crack formation, decreases distortion of quenched steel parts. The results of investigations can be used by engineers in the heat-treating industry and scientists for further research.

Quench Process and Steel Chemistry Optimization to Prevent Quench Cracking during Hardening of Splined Semi – Axles

In the paper the hardening process of splined semi-axles is discussed and physics of preventing the quench crack formation during intensive quenching (IQ) is explained. It is shown that during IQ process at the splined cylindrical surface very high compressive current band residual stresses are formed which prevent the possibility of quench crack formation on splines. It is enough to optimize the stress distribution through the section of semi-axle and perform IQ process in order to prevent quench cracks formation in splines. It is achieved via optimizing depth of surface hardened layer. In this case the depth of surface hardened layer for cylinders and for cylinders with splines are the same. There is no need to create a special thin shell on splines or perform carburization to create such shell. Due to larger martensite specific volume, it results in surface compressive residual stress formation. Absence of martensite phase at the core eliminates core swelling that could be a reason in tensile surface stresses. The idea is supported by FEM calculations and testing of real semi-axles in industrial condition. The new idea simplifies cardinally technological process and makes it less costly.

Failure Analysis of Shipping Container Handler Twistlock Pin

During operation of a shipping container handler, a twistlock pin supporting one side of two stacked shipping containers fractured, causing the shipping containers to fall. An investigation revealed that the alloy steel pin had a ferritic/bainitic microstructure with an average hardness of 29.5 HRC and a typical Charpy V-notch impact energy of 17 J at room temperature. Examination of the fracture surface revealed a cleavage fracture that initiated from a quench crack. It was determined that the primary cause of the failure was improper heat treatment.

Study on the controlling factors for the quenching crack sensitivity of ultra-strong automotive steel

This study examined the controlling factors for the quenching crack sensitivity of ultra-strong martensitic steel with a tensile strength exceeding 1.8 GPa. Two factors, the content of carbon alloyed in the steel and the type of quenchant used in the quenching process, were evaluated in terms of the strain level and diffusible hydrogen concentration, which were measured by electron backscattered diffraction-kernel average misorientation and thermal desorption spectroscopy, respectively. This study demonstrated that specimens with a higher carbon content exhibited larger lattice distortion and a higher dislocation density during the quenching process and may be more susceptible to cracks propagating along the prior-γ grain boundaries. The decrease in quenching rate and diffusible hydrogen concentration can be effective technical strategies for improving the mechanical toughness and mitigating the quench cracking of ultra-strong steels with a tensile strength of 2.0 GPa.

Friction-Induced Hardening Behaviors and Tribological Properties of 60NiTi Alloy Lubricated by Lithium Grease Containing Nano-BN and MoS2

Hardened 60NiTi alloy, which possesses a unique set of desirable properties, has been considered as an attractive candidate for the bearing materials used in space mechanisms. However, the typical hardening process (quenching from high temperatures with a high cooling rate) may result in quench cracking, especially in casting parts. With this in mind, the feasibility of friction-induced surface hardening of 60NiTi under the lubrication of lithium-based greases containing nanoparticles was explored in our research. In addition, the tribological properties of 60NiTi alloy lubricated with lithium-based greases containing different proportions of nanoparticles were investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) were used to characterize the surface of worn 60NiTi. An obvious friction-induced hardening effect on the 60NiTi alloy disc surface was identified, which was due to the formation of a hard metastable Ti3Ni4 phase and B2TiNi phase during the friction process. The lubrication effects of all of the modified grease were superior to those of the base grease, and the antiwear properties were closely related to the types of single nano-additives and the proportion of composite nano-additives.

Rolled Metal Structure Resource Saving Preparation for Long-Length Hardened Bolt Upsetting

Along with design factors, reliability of the work-pieces for machines and mechanisms is a function of the structure and the properties of the implied materials; these properties depend significantly on the kind and the mode of the process treatment. Taking into account hardwares production, along with the increased structural integrity and service reliability, a reduction of costs starts from the rolled metal production to manufacturing of the finished parts of required quality. This is particularly relevant under the conditions of mass-production. The article presents a resource saving process flow for a 40X rolled steel, developed as a result of studying the influence of thermal and plastic treatment modes on its structural and mechanical properties. The purpose of the new process flow is the production of hardened bolts, involving drawing and isothermal treatment, but excluding the volume quenching and tempering. Spheroidizing annealing is substituted with an isothermal operation, patenting, which allows to reduce energy costs and to increase environmental compatibility of production and service reliability of bolted items. This makes it possible to shorten the process chain and to reduce the cost of long-length bolts production. The method prevents any potential quench cracking, eliminates the necessity for work-pieces' straightening, decreases the risk of thread defects.

The occurrence of quenching cracks in high-carbon tool steel depending on the austenitizing temperature

Abstract Heat treatment has the greatest impact on the microstructure and properties, as well as the residual stresses and dimensional control of steel. Most of the problems that occur in heat-treated parts are attributed to improper heat-treatment practices, deficiency in the used grade of steel, poor part design or part defects. Inappropriate heat-treatment practices include overheating, burning, non-uniform heating, incorrectly selected austenitizing temperature and improper quenching. The formation of cracks during and after the quenching of austenitized steels is a major problem. As the carbon content of steel increases, the tendency to crack increases too. The tendency for quench cracking is also increased with higher austenitizing temperatures. The aims of the research were to determine the cause of the cracks in high‑carbon tool steel and to analyze the influence of the austenitizing temperature on the occurrence and propagation of quenching cracks. The results show that the main cause of quenching cracks is a too high austenitizing temperature caused by poor temperature control. A temperature that is too high leads to excessive austenite grain growth, distinctive grain boundaries with coarser martensite and the presence of retained austenite. On the other hand, the best properties and the absence of quenching cracks occur when C85S steel is quenched from a temperature below the Acm temperature.

Evaluation of steam corrosion and water quenching behavior of zirconium-silicide coated LWR fuel claddings

This study investigates steam corrosion of bulk ZrSi2, pure Si, and zirconium-silicide coatings as well as water quenching behavior of ZrSi2 coatings to evaluate its feasibility as a potential accident-tolerant fuel cladding coating material in light water nuclear reactor. The ZrSi2 coating and Zr2Si-ZrSi2 coating were deposited on Zircaloy-4 flats, SiC flats, and cylindrical Zircaloy-4 rodlets using magnetron sputter deposition. Bulk ZrSi2 and pure Si samples showed weight loss after the corrosion test in pure steam at 400 °C and 10.3 MPa for 72 h. Silicon depletion on the ZrSi2 surface during the steam test was related to the surface recession observed in the silicon samples. ZrSi2 coating (∼3.9 μm) pre-oxidized in 700 °C air prevented substrate oxidation but thin porous ZrO2 formed on the coating. The only condition which achieved complete silicon immobilization in the oxide scale in aqueous environments was the formation of ZrSiO4 via ZrSi2 coating oxidation in 1400 °C air. In addition, ZrSi2 coatings were beneficial in enhancing quenching heat transfer - the minimum film boiling temperature increased by 6–8% in the three different environmental conditions tested. During repeated thermal cycles (water quenching from 700 °C to 85 °C for 20 s) performed as a part of quench tests, no spallation and cracking was observed and the coating prevented oxidation of the underlying Zircaloy-4 substrate.

Influences of Cooling Rate After Solution Treatment on Microstructural Evolution and Mechanical Properties of Superalloy Rene 80

Influences of the cooling rate after solution treatment on microstructural evolution and mechanical properties of Rene 80 nickel-based superalloy were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and mechanical test. Results showed that the high cooling rate decreased the size of secondary γ′ particles in the supersaturated matrix, but led to a high coarsening rate of γ′ particles during subsequent aging treatment. Despite various coarsening rates, the size and morphology of γ′ particles in the final microstructures of all samples were close due to the long enough holding time to an equilibrium state. During the aging of 870 °C/2 h, primary MC started to decompose with the carbide reaction: MC + γ → M 6C or M 23C6 + γ′. And a number of observations showed that the coarsening of γ′ particles on grain boundaries resulted in the depletion of γ′ during aging treatment. The test results indicated that high cooling rate resulted in the presence of quench crack, and the air cooling method following solution treatment was an optimum heat treatment method for Rene 80.

Fracture of Hex Bars During Manufacture

A manufacturer of hex bars experienced occasional post heat treatment cracking. Metallography, SEM fractography, and microhardness testing demonstrated that quench cracking was the cause of failure. The manufacturer had the heat treatment modified in order to eliminate the cause of failure.

Analysis of quenching stresses in 35CrMo axle

By using the finite element method (FEM), we comprehensively analyzed the fields of temperature, organization, and stress in 35CrMo train axles during the quenching process is conducted, and experimentally studied the formation and evolution of inner stresses in axles during the quenching process. The results show that in the quenching process, stresses on the axle surface change from tensile to compressive gradually, while stresses in the axle core change from compressive to tensile gradually. Heat stresses and the amount of martensitic transformation are all increased with the increase of cooling rate. As a result, the maximum instantaneous stresses in the axle are increased greatly when the cooling rate is increased with brine quenching. Large instantaneous tensile stress in the axle core with brine quenching is very likely to cause quench cracking and should be avoided.

Influence of Flange Thickness on Quench Crack in Polymer Quenching Process for Large Forged Product

Influence of Flange Thickness on Quench Crack in Polymer Quenching Process for Large Forged Product

Metallurgical Failure Investigation of Quench Cracking in Hexagonal Bolt Head Fasteners

Abstract A particular engine user experienced the repeated fracture of new fixing bolts in combustion chambers upon first tensioning. The heads of the bolts fractured from their shafts upon torque-controlled tensioning. Two affected screws were received from site by the original equipment manufacturer's (OEM) laboratory to perform a metallurgical failure investigation and to determine the metallurgical root cause of failure. From the findings of the failure investigation described in this paper it is concluded that the metallurgical cause of failure in both cases was quench cracking, i. e. the imperfections leading to failure were induced upon manufacture and pre-existed in the bolts, i. e. they did not develop in service. These pre-existing cracks eventually caused failure by torsional overload upon first tensioning in assembly.

Critical conditions for the occurrence of quench cracking in an Al–Zn–Mg–Cu alloy

The occurrence of quench cracking in small cuboidal samples of aluminium alloy AA7150 was determined to be related to the maximum temperature difference (∆T max) between various locations within samples during quenching. When ∆T max between different locations is between 96 and 124 °C, there is some risk of quench cracking under various quenching conditions. When the ∆T max value is higher than 124 °C, quench cracks cannot be avoided. Quench cracks preferentially occur at sample corners and edges and are preferentially propagating in the short transverse direction–long transverse direction plane. Finite element modelling results indirectly indicate that the quench cracking should occur at the very early stages of the quenching process. Microscopy reveals that the quench cracking mode is intergranular, and cracks preferentially occur at high-angle grain boundaries with an average misorientation angle of ~42°. Moreover, quench cracks can penetrate through the whole thickness of a sample quenched from 495 into 20 °C water. Fractography reveals that no constituent particles exist in the quench fracture region, indicating that, unlike impact fracture, the occurrence of quench cracks is not dependent on the presence of coarse particles.

Microstructural and thermo-mechanical analysis of quench cracking during the production of bainitic–martensitic railway wheels

Quench cracking during the production of newly developed low carbon bainitic–martensitic (LCBM) rail wheels was investigated using a microstructural and thermo-mechanical Finite Element (FE) model. The stresses associated with quench cracking during martensite phase transformation were predicted under various quenching conditions for two different grades of LCBM steels with different kinetics of martensite phase transformation. The FE analyses showed that the likelihood of quench cracking can be reduced by using a low coolant spray intensity since the internal stresses generated during the martensitic phase transformation were found to be below the steel’s flow stress. The internal stresses were predicted to be even lower with a low carbon grade LCBM steel. The microstructural and thermo-mechanical model has been used to determine favourable quenching conditions that have the potential to reduce the propensity of quench cracking during the production of LCBM railway wheels.

Application of Numerical Simulation in Quench Cracking Analysis of Vehicle Hub Axles

Abstract. It explained that the quenching crack distribution characteristics and formation mechanism of the vehicle hub axles. Quenching crack of the vehicle hub axles was always the longitudinal crack and distributes in the inner wall .The crack was thin and long with the phenomena of crack cross and associated. The results of finite element simulation show that the internal stress value of the vehicle hub axles is up to 300Kgf / mm2 with the common action of the structure stress and heat stress, it is far more than 40MnBH steel tensile limit. This is the main reason of quenching crack. So for controlling quenching crack, it is need control raw materials, optimization of the quenching process and quenching medium replacement and so on.