Retained Austenite Content Research Articles

Minimizing Deformations in High-Temperature Vacuum Carburizing.

This article presents the results of a study on reducing deformations resulting from high-temperature vacuum carburizing and post-carburizing heat treatment. The idea was to increase the strength of steel at elevated temperatures by pre-carburizing at heat-up to the process temperature (SC-stage carburizing). It has been shown that the use of carburizing in stages from a lower temperature to the target temperature, compared to traditional vacuum carburizing at a constant temperature (Constant-Temperature Carburizing-CTC), has a significant impact on the chemical and phase composition of the technological layer, surface after the process and, consequently, on its mechanical properties. It was shown that the retained austenite content after stage carburizing was reduced by approximately 45%, as was the thickness of the gear teeth measured at the pitch diameter. Additionally, uniform stress distribution was demonstrated for the SC process. Carbon saturation of austenite increases the yield strength, and therefore the dimensional stability of steel heat-treated at elevated temperatures also improves, which effectively permits high-temperature treatment of critical steel parts such as, for example, gear wheels, for which high dimensional accuracy is required.

Optimization of Aging Temperature and Heat-Treatment Pathways in Additively Manufactured 17-4PH Stainless Steel.

This study investigates the tensile behaviors of additively manufactured (AM) 17-4PH stainless steels heat-treated within various temperature ranges from 400 °C to 700 °C in order to identify the effective aging temperature. Despite an aging treatment of 400-460 °C increasing the retained austenite content, an enhancement of the tensile properties was achieved without a strength-ductility trade-off owing to precipitation hardening by the Cu particles. Due to the intricate evolution of the microstructure, aging treatments above 490 °C led to a loss in yield strength and ductility. A considerable rise in strength and a decrease in ductility were brought about by the increase in the fraction of precipitation-hardened martensitic matrix in aging treatments over 640 °C. The impact of heat-treatment pathways on aging effectiveness and tensile anisotropy was then examined. Direct aging at 482 °C for an hour had hardly any effect on wrought 17-4PH, but it increased the yield strength of AM counterparts from 436-457 to 588-604 MPa. A solid-solution treatment at 1038 °C for one hour resulted in a significant drop in the austenite fraction, which led to an increase in the yield (from 436-457 to 841-919 MPa) and tensile strengths (from 1106-1127 to 1254-1256 MPa) with a sacrifice in ductility. Improved strength and ductility were realized by a solid-solution followed by an aging treatment, achieving 1371-1399 MPa. The tensile behaviors of AM 17-4PH were isotropic both parallel and perpendicular to the building direction.

Processing of Carbon Nanoparticle-Enriched AISI H11 Tool Steel Powder Mixtures in DED-LB/M for the AM of Forging Tools with Tailored Properties (Part II): Influence of Nanoscale Carbon Additives on Microstructure and Mechanical Properties

A promising approach for producing parts with outstanding properties in directed energy deposition (DED-LB/M) provides the application of tailored powder mixtures processed by applying in situ alloying strategies. In this work, DED-LB/M was used to manufacture multilayer specimens from AISI H11 steel powders enriched with carbon nanoparticles (C-np) in concentrations of 0.1 wt.-% and 0.2 wt.-%. The scientific aim was to investigate the impact of C-np on the microstructural (particularly retained austenite content (RA-c) and grain size) and mechanical properties (specifically hardness and compression yield strength) of the manufactured specimens. It was shown that the addition of C-np to the H11 powder leads to a stronger distortion of martensite as well as significantly enhancing the RA-c. Furthermore, the C-np seem to favor the formation of finer martensite, as can be verified with XRD and EBSD. Under as-built conditions, the mean hardness increases from 653 ± 10 HV1 for the H11 sample to 770 ± 14 HV1 for the sample reinforced with 0.2 wt.-% C-np. At the same time, Y0.2% rises up from 1839 ± 61 MPa to 2134 ± 68 MPa. The hardness- and strength-increasing effect of the added C-np is retained even after heat treatment, similarly to the industrial standard.

Effect of second-step austempering temperature on mechanical damping of austempered ductile iron

Austempered ductile iron(ADI) has good strength and toughness, which is widely used in aerospace, engineering machinery and automobile manufacturing. In the above application fields, the requirements of safety and comfort are gradually increasing, so ADI is required not only to have excellent mechanical properties, but also to have high damping properties. The performance of ADI is closely related to its heat treatment method. Therefore, it provides a theoretical basis for the application of ADI, and reveals its mechanism to some extent. The influence of two-step ADI’s mechanical properties and damping properties due to two-step austempering quenching temperature is the main content of this paper. The retained austenite with obvious coarsening of bundle ferrite and increased size is the experimental result obtained after the increase of austempering temperature in the second step. After that, when the austempering temperature in the second step increases, the retained austenite content will directly decrease. The tensile strength of ADI will increase first and then decrease with the increase of austempering temperature in the second step. And the value reaches the maximum of 1350MPa at 360°C. The yield strength of ADI, which reaches the maximum value (1252MPa) at 400 °C, will follow the increase of austempering temperature in the second step, and the elongation and impact energy of ADI will gradually decrease. The elongation and impact energy of ADI will gradually decrease with the increase of austempering temperature in the second step. The minimum values of 4.8% and 42J are obtained when the austempering temperature in the second step reaches 400 °C. The impact fracture morphology shows that the fracture mechanism will change from ductile fracture to brittle fracture with the increase of austempering temperature in the second step. The reason why the internal friction value (Q−1) of ADI with different austempering temperatures in the second step increases gradually is the increase of strain amplitude. There are obvious S-K peaks and Ge peaks, that is, the damping characteristics change with frequency.

Effect of Volumetric Energy Density and Part Height on the Material Properties of Low‐Alloyed Steels Manufactured by Laser‐Based Powder Bed Fusion of Metals

The layer‐by‐layer manufacturing approach in laser powder bed fusion of metals (PBF‐LB/M) leads to heat accumulation in the workpiece with increasing part heights. The effect of this heat accumulation on the resulting material properties has, however, only barely been studied for low‐alloyed steels. The goal of this work is to analyze the influence of different PBF‐LB/M‐specific boundary conditions like varying part heights and volumetric energy densities (VED) on the resulting material properties. It isfound that lower part regions possess similar hardness (380–410 HV1) and retained austenite values (7%–8%), independent of the applied VED. Higher energy inputs lead to higher retained austenite contents of up to 20% due to an incomplete transformation upon cooling. This rise in retained austenite content is also linked to a decreased material hardness down to 320 HV1. In higher part regions, this effect is reversed as the retained austenite content starts to decrease for the highest investigated VED. This is caused by the in situ preheating temperatures caused by heat accumulation, which favor a bainitic transformation. The part height‐specific properties indicate that the microstructure formation forms through a continuous transformation in lower part regions and through an isothermal transformation in higher regions.

Superior mechanical properties of M35 high-speed steel obtained by controlling carbide precipitation and distribution via electropulsing treatment

Carbide precipitation and distribution always significantly affect the mechanical properties of High-speed Steel (HSS). Thus, the effect of electropulsing treatment (EPT) on the microstructure and mechanical properties of M35 HSS was investigated in this paper. The results show that the electropulsing austenitising then quenched, followed by electropulsing tempered (EQ + ET) samples, showed a 2.3% increase in Rockwell hardness, a 9.7% increase in the bending strength, and the impact toughness increased by 10.3% compared with the conventional heat treatment (CQ + CT) samples. The superior mechanical properties were attributed to the reduction of retained austenite (RA), the uniform distribution of the carbide, and the refinement of the prior austenite grains. Under the action of the current, Ms increased in response to various combinations of alloying elements, thereby reducing the content of RA. Compared to conventional heat treatments, the electropulsing treatment provides additional Gibbs free energy, as well as a large number of dislocations generated by the thermo-compressive stresses, which increase the carbide nucleation sites, resulting in a large number of small-sized carbides precipitating and uniformly distributed in the matrix. The fracture morphology indicates that micro-cracks arise between the carbide and martensite, and the larger carbide provides a preferential path for crack initiation.

Effect of Cold Rolling Reduction Rate on the Microstructure and Properties of Q&P Steel with a Ferrite-Pearlite Initial Structure.

Quenching and partitioning (Q&P) steel has garnered attention as a promising third-generation automotive steel. While the conventional production (CP) method for Q&P steel involves a significant cumulative cold rolling reduction rate (CRRR) of 60-70%, the thin slab casting and rolling (TSCR) process has emerged as a potential alternative to reduce or eliminate the need for cold rolling, characterized with a streamline production chain, high-energy efficiency, mitigated CO2 emission and economical cost. However, the effect of the CRRR on the microstructure and properties of Q&P steel with an initial ferrite-pearlite microstructure has been overlooked, preventing the extensive application of TSCR in producing Q&P steel. In this work, investigations involving different degrees of CRRRs reveal a direct relationship between increased reduction and decreased yield strength and plasticity. Notably, changes in the microstructure were observed, including reduced size and proportion of martensite blocks, increased ferrite proportion and decreased retained austenite content. The decrease in yield strength was primarily attributed to the increased proportion of the softer ferrite phase, while the reduction in plasticity was primarily linked to the decrease in retained austenite content. This study provides valuable insights for optimizing the TSCR process of Q&P steel, facilitating its wider adoption in the automotive sector.

Effect of austempering temperature on microstructure evolution, mechanical properties and wear resistance of carbon-free nano-bainite steel

Carbide-free nano-bainite steel holds significant potential for applications in mining as an ultra-high strength wear-resistant steel, but the wear mechanisms are not yet fully understood. This study aims to explore the effect of austempering temperature on microstructure, mechanical properties and wear resistance of carbide-free nano-bainitic steel. The relationship between the content and mechanical stability of retained austenite (RA) and mechanical properties was investigated to elucidate the mechanisms of pin-on-disc wear and impact wear. The results show that in the range of Ms∼300 °C, the phase transformation incubation period and completion time significantly increase with decreasing austempering temperature, which is mainly related to higher phase transformation driving force resulting from a larger subcooling degree and slow growth of carbon content in RA. Optimal strength and hardness of 2099 MPa and 615 HBW, respectively, are achieved after austempering at 210 °C for 83 h. Austempering at 270 °C for 11 h yields the best balance of strength and plasticity, with a strength-plasticity product of 28.8 GPa%. The micro-cutting mechanism of pin-on-disc wear leads to serious weight loss. The RA with poor mechanical stability accelerates the stress-induced martensite transformation, while internal stress support due to volume expansion reduces the penetration depth of abrasive particles. The weight loss in impact wear is primarily caused by shedding due to fatigue failure. With the increase of RA content and mechanical stability, the persistent stress-induced martensite transformation effectively hinders micro-crack propagation, thereby enhancing impact wear resistance.

Investigations on the Effect of Cooling Rate on Quenching & Partitioning (Q&P) in Martensitic Stainless Steels

Abstract Quenching and partitioning (Q&P) is a heat treatment used to adjust the retained austenite content in the microstructure. Such heat treatment is used mainly for low-alloyed steels. However, the partitioning effect has an influence on higher alloyed steels also, such as martensitic stainless steels. The typical heat treatment for these steels is quenching and tempering (Q&T). In large-scale tools the cooling rate in the inner area is lower than in the peripheral area, and the central region of the tool might not be cooled down completely to room temperature before the tempering step takes place, resulting in a Q&P instead of a Q&T treatment. This article deals with these effects through dilatometric investigation of steels X40Cr14, “X25CrN13” and “X50CrMoN17-1” at two different austenitizing temperatures and two cooling rates, with a variation of the quenching temperature. It was found that partitioning takes place even at slow cooling rates. However, due to partial pearlite formation and pre-carbide precipitation/coarsening, the retained austenite content may be lower than with rapid cooling. Further, autopartitioning was also detected at slow cooling rates.

Evaluation of Retained Austenite in Carburized Bearing Steel Using Magneto-Inductive Method

The present work explores the magneto-inductive method to evaluate different levels of retained austenite content in carburized 20NiCrMo7 bearing steel while comparing the corresponding measurements by X-ray diffractometry and image analysis by optical microscope. The content of retained austenite in carburized 20NiCrMo7 steel was modified with additional tempering to yield three samples with distinct ranges of retained austenite profiles in the carburized region of the steel. The retained austenite measured at different depths in these samples using the magneto-inductive method had an outcome comparable to other methods. Further discussion based on data suggests that the magneto–induction method yields precise (with an average deviation of 0.5%) results with sufficient sensitivity at different levels (including below 5 vol. %.) of retained austenite.

Resistance spot welding behaviour of novel medium manganese (M-Mn) steels - Role of welding parameters on weld microstructure and mechanical properties

Medium Mn (M-Mn) steels are classified as third-generation advanced high-strength steels (3G-AHSS) and have demonstrated outstanding mechanical properties. As a result, they are being considered as potential materials for use in the automotive industry. Spot weldability of materials is an essential requirement for the body in white (BIW) structures in automotive vehicles. Resistance spot welding (RSW) M-Mn steel can be challenging because it can lead to the formation of a fully martensitic microstructure. This work established the weld growth curve on M-Mn steel in the 4 to 8 kA current range. Based on this, single pulse (6 kA) and double pulse current (first pulse of 6 kA followed by the second pulse of 4 to 7 kA) were employed to investigate the microstructure, elemental segregation, cross-tensile strength (CTS), and fracture behaviour of the M-Mn steel welds. These welds, in all conditions, exhibited a martensitic microstructure with retained austenite content of <10 %. In all welding conditions, martensite softens along the heat-affected zone (HAZ) boundary, yielding tempered martensite and carbides. A study of chemical homogeneity using electron probe microanalysis (EPMA) demonstrated that Mn and Si segregate along the weld nugget (WN) edge during single (6 kA) and double (6–6 kA and 6–7 kA) pulsing. Mn and Si segregation is less prominent in double pulse welds at lower pulse currents (<6–6 kA). The elemental segregation at higher pulse currents is higher due to the more pronounced thermal gradient within the weld nugget, which promotes elemental segregation at the interface. Based on the cross-tension test results, the double pulse welds (6–7 kA) had the maximum CTS (1.26 kN) and energy absorption (2 J). The failure mode in this condition is a predominantly partial interfacial failure (PIF) with a plug ratio of about 50 %. This is attributed to the larger nugget diameter and refined martensitic structure. Complete interfacial failure (IF) leading to interdendritic fracture and a plug ratio of 0 % was observed when two equal pulse currents (6–6 kA) were applied. This can be attributed to remelting of WN and a high degree of Mn and Si segregation. From the above studies, we can conclude that M-Mn steel is weldable; however, further strategies are necessary to enhance the CTS of M-Mn steel welds.

Experimental Analysis of the Stability of Retained Austenite in a Low‐Alloy 42CrSi Steel after Different Quenching and Partitioning Heat Treatments

Quenching and partitioning (Q&amp;P) steels are characterized by an excellent combination of strength and ductility, opening up great potentials for advanced lightweight components. The Q&amp;P treatment results in microstructures with a martensitic matrix being responsible for increased strength whereas interstitially enriched metastable retained austenite (RA) contributes to excellent ductility. Herein, a comprehensive experimental characterization of microstructure evolution and austenite stability is carried out on a 42CrSi steel being subjected to different Q&amp;P treatments. The microstructure of both conditions is characterized by scanning electron microscopy as well as X‐ray diffraction (XRD) phase analysis. Besides macroscopic standard tensile tests, RA evolution under tensile loading is investigated by in situ XRD using synchrotron and laboratory methods. As a result of different quenching temperatures, the two conditions considered are characterized by different RA contents and morphologies, resulting in different strain hardening behaviors as well as strength and ductility values under tensile loading. In situ synchrotron measurements show differences in the transformation kinetics being rationalized by the different morphologies of the RA. Eventually, the evolution of the phase specific stresses can be explained by the well‐known Masing model.

Effect of tempering temperature and subzero treatment on microstructures, retained austenite, and hardness of AISI D2 tool steel

The presence of retained austenite in the hardening process of tool steel often causes the lower hardness compared to the hardness requirements and poor dimensional stability in the tool steel. The purpose of the present research is to determine the relationships between the tempering process with and without cryogenic treatment to the hardness and retained austenite amount of as-hardened D2 tool steel. The austenitizing temperature was 1020 °C, the tempering temperatures have variations of 180 °C, 280 °C, 380 °C, 480 °C, and 580 °C, and the subzero treatment has a temperature of −172 °C, followed by tempering at 180 °C, 380 °C, and 580 °C. This study aims to determine the appropriate treatment to obtain a minimum retained austenite percentage to prevent and mitigate the failure of AISI D2 tool steel in the industrial application process. An optical microscope with image processing software (Image-J analysis), as well as Brinell and Vickers hardness testing, is the characterization method used in this work. In general, plate martensite, bainite, retained austenite, and primary and secondary carbides are the phases contained in the microstructure. Tempering temperatures have the effect of increasing the secondary carbide precipitation and decreasing the retained austenite content (γr 3,671%–2,769%). However, the cryogenic treatment can provide a more efficient martensitic phase transformation process and minimal retained austenite content (γr 2,257%–1,199%). The increase in tempering temperature causes a decrease in hardness at a temperature of 180 °C–380 °C. On the other hand, the secondary hardening and phase transformation phenomena cause an increase in the hardness of the as-tempered sample at a temperature of 480 °C, before the sample reexperiences a significant decrease in hardness at a temperature of 580 °C due to diffusion that decreases the carbon content.

Effect of torsional deformation on crystallographic evolution of carbide-free nano-bainitic steels prepared at two different austempering temperatures

The current study investigates the nature and extent of crystallographic change after torsional deformation in nano-structured bainite. This is extremely useful as nano-structured bainite is not stable under mechanical deformation and the evolved structure under torsion is finally going to determine other mechanical responses like fracture and fatigue. Two blocks of nano-bainitic steels were prepared after austenitization at 950°C and austempering at 250°C (NB250) and 350°C (NB350) respectively. It was found that there was a decrease in the bainitic ferrite (BF) and retained austenite (RA) length scale with a reduction in austempering temperature along with reduction in the RA content. Specimens from the undeformed two blocks (NB250-UD and NB350-UD) were subjected to torsional deformation till failure (NB250-T and NB350-T) and the crystallographic characteristics of the torsion-tested and undeformed specimens were obtained using electron back-scattered diffraction (EBSD). The orientation relationship (OR) between BF and RA for NB250-UD and NB350-UD was close to Kurdjumov-Sachs (K-S) which changed to predominantly Nishiyama Wassermann (NW) after torsion deformation (NB250-T and NB350-T). Significant refinement in packet and block was observed as a result of torsional deformation. Variant selection was stricter for NB350-UD than NB250-UD but torsional deformation led to weakening of variant selection. The extent of lowest misorientation V1-V4 variant pairing was higher for NB350-UD but it did not change much with torsion in case of NB250-T whereas NB350-T displayed a reduction. Fractography revealed that the dimple size corresponded to block size range between the undeformed and torsion-tested sample for the respective austempering condition.

Effectively improving the hardness-strength-toughness of carburized bearing steel via nanoprecipitates and fine grain structure

Cryogenic treatments are fast and efficient methods used to improve the mechanical properties of metal components by promoting retained austenite (RA) transformation. However, the relationship between the evolution of RA with the gradient changes in content and hardness-strength-toughness improvements during this period are unclear. The present study investigated the beneficial effects of a cryogenic treatment on the microstructural evolution and mechanical properties of a gradient-structured carburized M50NiL bearing steel. The results revealed that the RA average sizes, the densities of the high-angle grain boundaries (DHAGBs) and low-angle grain boundaries (DLAGBs), and the hardness of the carburized layer changed with increasing distance from the surface. Compared with the untreated samples, the cryogenically treated samples demonstrated a 30% greater effective hardened layer thickness as well as 15.6% and 22.9% higher strength and toughness, respectively. The synergistic enhancements of the hardness, strength, and toughness provided by the cryogenic treatment were attributed to the increased nanoprecipitate content and finer grain structure generated in situ during transformation and further decomposition of the RA, which resulted in reductions of up to 83.6% in the RA content. This work provided new ideas for innovative enhancements of gradient-structured materials with superior mechanical properties.

Microstructure and mechanical properties of medium manganese steel in intercritical annealing

A new type of cold-rolled medium manganese steel was investigated. The test steel was treated by Q&P process. With the increase in annealing temperature, the grain size gradually increases, the carbides dissolve progressively and the fine lath grains transform into massive or equiaxed grains. Both the volume fraction and the stability of the retained austenite are continuously decreasing, which together affect the change of mechanical properties. At the intercritical annealing temperature of 680°C, the specimens have higher retained austenite content and transformation rate. At the same time, due to the discontinuous TRIP effect caused by the retained austenite stability gradient inside the specimen, it exhibits excellent comprehensive mechanical properties, and the product of strength and elongation is 43.5GPa·%.

Microstructure and Dry/Wet Tribological Behaviors of 1% Cu-Alloyed Austempered Ductile Iron

In this study, different austempering conditions were applied to 1 wt.% Cu-alloyed ductile iron to produce various austempered ductile irons (ADIs). The study aimed to explore the variations in microstructure, hardness, and dry/wet wear behaviors of the ADIs. The experimental results indicated that the microstructure of the 300 °C-ADI has denser needle-like ausferrite, lower retained austenite content, and higher carbon content in austenite compared with the 360 °C-ADI. As the austempering time increased, the retained austenite content decreased, while the carbon content of austenite increased. Regardless of dry or wet abrasive behavior, the wear resistance of the ADIs was significantly superior to that of the as-cast material. The ADI obtained at 300 °C for 10 h demonstrated the best wear resistance performance.

Exploring the Influence Mechanisms of Tempering Temperature and N‐alloying on Mechanical Properties of AISI M42 High‐Speed Steel

The variations in microstructure and mechanical properties of N‐free and high‐nitrogen (0.18 wt%) M42 HSS with tempering temperatures are investigated. The microstructure of steels after austenitizing primarily consists of martensite, retained austenite (RA), undissolved M2C, and M6C carbides. With increasing tempering temperature (450–600 °C), the RA content and martensite lattice strain of steels gradually decrease. At 540 and 600 °C, RA is almost or fully transformed into martensite, and massive nanosized M2C secondary carbides are precipitated. The M2C secondary carbides at 600 °C obviously coarse compared to those at 540 °C. Further, the addition of N increases RA content and martensite lattice strain. With increasing tempering temperature, the bulk hardness and compressive strength of steels first increase and then decrease, whereas their impact toughness shows an opposite trend. This is ascribed to the combined effect of RA decomposition, precipitation and coarsening of secondary precipitates, and decrease in dislocation density and martensite lattice strain. Compared to N‐free steel, 0.18N steel tempered at peak‐hardening temperature (540 °C) and above has higher bulk hardness and compressive strength because of the increased solid solution, dislocation, and precipitation strengthening, but lower impact toughness owing to higher matrix hardness and martensite lattice strain.

Evaluation of the Impact and Fracture Toughness of a Nanostructured Bainitic Steel with Low Retained Austenite Content

The impact and fracture toughness of a nanostructured, kinetically activated bainitic steel was determined using Standard methods. Prior to testing, the steel was quenched in oil and aged naturally for a period of 10 days in order to obtain a fully bainitic microstructure with a retained austenite content below 1%, resulting in a high hardness of 62HRC. The high hardness originated from the very fine microstructure of bainitic ferrite plates formed at low temperatures. It was determined that the impact toughness of the steel in the fully aged condition improved remarkably, whereas the fracture toughness was in line with expectations based on the extrapolated data available in the literature. This suggests that a very fine microstructure is most beneficial to rapid loading conditions, whereas material flaws such as coarse nitrides and non-metallic inclusions are the major limitation for obtaining a high fracture toughness.

Effect of pulsed magnetic field on retained austenite of quenched 8Cr4Mo4V steel under cryogenic condition

High-intensity pulsed magnetic field was applied to modify the microstructure and mechanical propertis of quenched 8Cr4Mo4V bearing steel under the cryogenic environment. The microstructual transformation in 8Cr4Mo4V bearing steel was investigated by X-ray diffraction (XRD), Vibrating sample magnetometer (VSM) and Electron Backscatter Diffraction (EBSD) and so on. The results revealed that individual deep cryogenic treatment (DCT) promote the transformation from retained austenite (RA) in quenched steel to martensite. However, this phase transformation will be inhibited by coupling high-intensity magnetic field with deep cryogenic treatment (MDCT). For instance, the relative reduction of RA content in DCT samples was 10 ± 2%, while that in MDCT samples was 3 ± 3%. Furthermore, the modified Williamson-Hall method was utilized to estimate the dislocation characteristics based on XRD profile analysis. It exhibited that the proportion of edge dislocation significantly decrease from 61.8% to 43.7% by DCT, while this type of dislocation remains almost unchanged after MDCT. Moreover, the microhardness of quenched 8Cr4Mo4V steel became more uniform after MDCT than that of DCT. It can be indicated that the martensite transformation is blocked and carbon cluster is dissolved under the condition of coupling pulsed magnetic field treatment.