Primary Reasons for the Brittleness of Welded Joints in Steel T/P24

The article presents results of tests concerning the susceptibility of welds made of steel T/P24 (7CrMoVTiB10-10) to secondary hardness as well as the structure and the mechanical properties of the welds (KV, Rm, A5, Z and HV1) in the as-made state and after heat treatment performed at temperature restricted within the range of 100°C to 750°C. The tests revealed that the welding process triggered the decomposition of phases hardening steel 7CrMoVTiB10-10 and the transition of alloying components and impurities to the solution of body-centred cubic lattice A2 (bcc). A thesis formulated by the Authors in relation to the test results stated that the primary reason for the deterioration of the plastic properties of the welds was the phenomenon of solid solution hardening. The Authors emphasized the necessity of performing the detailed analysis of interactions of substitution atoms and other defects of the Feα lattice with interstitial atoms. In addition, the Authors indicated the necessity of changing the criteria applied when assessing the weldability of technologically advanced steels as well as pointed mistakes made during the industrial implementation of steel 7CrMoVTiB10-10.

The Effect of Heat Treatment on the Structure and Hardness of Welded Joints in Steel 7CrMoVTiB10-10

The article presents results of tests concerning the effect of heat treatment on the structure and hardness of submerged arc welded joints made in steel 7CrMoVTiB10-10 (T24). The tests revealed that the welds made of steel 7CrMoVTiB10-10 required post-weld heat treatment at a temperature 750°C. The heat treatment was performed in order to protect welded structures from cracking during transport and operation as well as to prevent the development of secondary hardness.

Can Sub-zero Treatment at −75 °C Bring Any Benefits to Tools Manufacturing?

: Vanadis 6 ledeburitic tool steel was subjected to sub-zero treatment at −75 °C for different durations, and for different subsequent tempering regimes. The impact of these treatments on the microstructure, hardness variations, and toughness characteristics of the steel was investigated. The obtained results infer that the retained austenite amount was reduced to one fourth by sub-zero treatment (SZT), and the population density of add-on carbides was increased by factor of three to seven, depending on the duration of SZT. Tempering always reduced the population density of these particles. A hardness increased by 30–60 HV10 was recorded after sub-zero treatment but tempering to the secondary hardness peak induced much more significant hardness decrease than what was established in conventionally quenched steel. The flexural strength was not negatively influenced by sub-zero treatment at −75 °C while the fracture toughness tests gave worse values of this quantity, except the case of steel tempered to the secondary hardness peak.

ПОДВІЙНА ХІМІКО-ТЕРМІЧНА ОБРОБКА ЗУБЧАСТОГО КОЛЕСА ІЗ СТАЛІ ВКС-5

The process of the double chemical-thermal treatment (DCTT) a gear made of heat-resistant steel VKS-5 is quite common and makes it possible to obtain secondary hardness. Double or combined chemical-thermal treatment is designed to increase the contact durability of steels by nitriding final finished parts that these were carburizing, hardened and ground. Comparison of the process of double chemical-thermal treatment with traditional methods of chemical-thermal treatment(CTT) carburizing and nitriding. Object of the study is a gear wheel treated with the DCTO method, after it was compared the hardness of the wheel past the DCTO using gas nitriding and liquid, with other similar CTT processes such as nitriding and carburizing and nitrocarburizing the results were a graph of hardness and the depth of the strengthened layer for each of the processes. Discussion of the developed technology for the preparation of double chemical-thermal treatment and the results of studies on the use of dispensing methods for obtaining DCTO. Efficiency is justified by metallographic studies of the developed technology. Also, metallographic studies have shown the need to control the surface layer the E-phase is formed due to which it is possible to substantially increase the hardness of the surface while preserving the structure of the entire material without cracking thereby providing increased contact durability. We also consider the possibility of using ion-plasma equipment, which allows to significantly increase the speed of the process, control the thickness of the layer of surface phases and also makes it possible to additionally apply the method of surface deformation to create compressive stresses on the surface. This technology allows to obtain a surface combining the advantages of nitriding and carburizing, excluding useing harmful substances affecting a health and ecology, and also economically more beneficial than nitrocarburizing. DCTT can be used to increase the contact endurance of the gear wheels in a large module, and eliminating the need for further machinary treatment of the surface layer after DCTT.

Secondary Hardening of an AISI M3:2 High Speed Steel Sinter 23 Hot Isostatic Pressed

The main aim of this work was to study the behavior of the secondary hardening of AISI M3:2 high speed steel named Sinter 23® produced by powder metallurgy process of hot isostatic pressing (HIP). The M3:2 high speed steel Sinter 23® was submitted to heat treatment of hardening with austenitizing temperatures of 1140 oC, 1160 oC, 1180 oC and 1200 oC and tempering at 540 oC, 560 oC and finally 580 oC. The effectiveness and response of the heat treatment was determined using hardness tests (Vickers and Rockwell C hardness) and had its property of secondary hardness evaluated. The results showed that the secondary hardening peak of Sinter 23® high speed steel (tempering temperature at which maximum hardness is attained) is at 540 °C for the lower austenitization temperatures of 1140 °C and 1160 °C, and it is at 560 °C for the higher austenitizing/quenching temperatures of 1180 °C and 1200°C.

Estimation of the Heat Stability of Hardened Cr-V Cast Irons

The paper describes the structure, properties and heat stability of white cast irons containing 2.5 – 3.0 %C, 14 and 20 %Cr, 3 %V after the secondary hardness treatment (quenching from 1150 °C and double tempering at 560 °C). It is shown that after the secondary hardness treatment M23C6 carbides appear along with the M7C3 phase. Heat stability of the alloys is estimated according to GOST 19265-73 standard. The effect of the temperature and duration of holding at 520–620 °C on structural changes and softening of secondary hardness treated cast irons is considered in comparison with high-speed steel and cast irons of the same composition quenched for the maximum hardness (from 1050 °C). The processes occurring at higher temperatures and long holdings that are responsible for softening of secondary hardness treated cast irons are studied. It is shown that the alloys under consideration after the secondary hardness treatment achieve the hardness of HRC 60 and more, and are able of pertaining it when heated up to 540 °C for 20 hours. This allows using these alloys as wear-resistant materials in the said temperature range.

Characterization of Nanometric-Sized Carbides Formed During Tempering of Carbide-Steel Cermets

The aim of this article of this paper is to present issues related to characterization of nanometric-sized carbides, nitrides and/or carbonitrides formed during tempering of carbide-steel cermets. Closer examination of those materials is important because of hardness growth of carbide-steel cermet after tempering. The results obtained during research show that the upswing of hardness is significantly higher than for high-speed steels. Another interesting fact is the displacement of secondary hardness effect observed for this material to a higher tempering temperature range. Determined influence of the atmosphere in the sintering process on precipitations formed during tempering of carbide-steel cermets. So far examination of carbidesteel cermet produced by powder injection moulding was carried out mainly in the scanning electron microscope. A proper description of nanosized particles is both important and difficult as achievements of nanoscience and nanotechnology confirm the significant influence of nanocrystalline particles on material properties even if its mass fraction is undetectable by standard methods. The following research studies have been carried out using transmission electron microscopy, mainly selected area electron diffraction and energy dispersive spectroscopy. The obtained results and computer simulations comparison were made.

Effect of Chemical Composition on Secondary Hardening of WD1 Steel Used for Warm Work Dies

A new kind of die steel, WD1 used for warm work dies, was developed. The secondary hardening behavior and its affecting factors were studied. The results show that the secondary hardness increases with the content of C, Mo and V elements and Si element can significantly improve the secondary hardening effect though it’s not one of secondary hardening elements. The hardness of WD1 steel tempered at 520°C is more than HRC60, which can meet the requirements of warm work dies.