Cr-V Ledeburitic Steel Research Articles

Microstructure and Microhardness of Powder Boronized Vanadis 6 Steel

A Cr-V ledeburitic steel Vanadis 6 was powder boronized for different durations, austenitized, quenched and tempered. All the boronized layers are two-phased, i.e. they are formed by MeB and Me2B compounds. The thickness of boronized compound layers increased moderately with boronizing time. The thickness of MeB individual layer increases more rapidly, and it makes up to 50% of total layer thickness when boronized for 150 min. Boronized layers contain enhanced amount of chromium but they are almost free of other alloying elements. The MeB compound has a microhardness of around 1860 HV 0.1 after short – time boronizing but its microhardness exceeded 2100 HV 0.1 after long – time processing. The microhardness of Me2B was correspondingly lower, its values were around 1760 – 1850 HV 0.1. Transient region manifested enhanced amount of carbides, resulting from carbon transport from growing boronized layers towards the substrate. This phenomenon was reflected in elevated hardness compared to the substrate.

Application of −140 °C Sub-Zero Treatment For Cr-V Ledeburitic Steel Service Performance Improvement

The effect of −140 °C, 17-hour sub-zero treatment and subsequent tempering on the hardness, flexural strength, and fracture toughness of Cr-V ledeburitic steel was investigated. The main purpose was to highlight the role of microstructural alterations, such as a decrease of the retained austenite content, the quantitative parameters of carbide distributions, or others, due to applied treatments. Compared to conventional treatments, the applied sub-zero treatment improves the hardness of the material significantly within the whole range of tempering temperatures used. The hardness enhancement is in the range from 197 to 137 HV10 for tempering at 170 °C to 450 °C. The flexural strength is slightly improved at low tempering conditions up to 170 °C, while there is almost no effect of the sub-zero treatment on flexural strength for higher tempering temperatures. The fracture toughness is substantially improved (by about 3 MPa m1/2) in the untempered state as well as after high-temperature tempering. The fracture toughness is slightly worsened, by about 0.15 to 1 MPa m1/2, within the 170 °C to 450 °C range of tempering temperatures. These changes in fracture toughness are reached with a significant increase of hardness. This steel performance is associated with enhanced fracture surface roughness and an increased ductile microvoid coalescence micromechanism presence in fracture surfaces. The results also show that treatment at −140 °C leads to a greater enhancement of the complex of mechanical properties than can be obtained by soaking the samples in liquid nitrogen.

Investigation of the Microstructural Changes and Hardness Variations of Sub-Zero Treated Cr-V Ledeburitic Tool Steel Due to the Tempering Treatment

The microstructure and tempering response of Cr-V ledeburitic steel Vanadis 6 subjected to sub-zero treatment at − 196 °C for 4 h have been examined with reference to the same steel after conventional heat treatment. The obtained experimental results infer that sub-zero treatment significantly reduces the retained austenite amount, makes an overall refinement of microstructure, and induces a significant increase in the number and population density of small globular carbides with a size 100-500 nm. At low tempering temperatures, the transient M3C-carbides precipitated, whereas their number was enhanced by sub-zero treatment. The presence of chromium-based M7C3 precipitates was evidenced after tempering at the temperature of normal secondary hardening; this phase was detected along with the M3C. Tempering above 470 °C converts almost all the retained austenite in conventionally quenched specimens while the transformation of retained austenite is rather accelerated in sub-zero treated material. As a result of tempering, a decrease in the population density of small globular carbides was recorded; however, the number of these particles retained much higher in sub-zero treated steel. Elevated hardness of sub-zero treated steel can be referred to more completed martensitic transformation and enhanced number of small globular carbides; this state is retained up to a tempering temperature of around 500 °C in certain extent. Correspondingly, lower as-tempered hardness of sub-zero treated steel tempered above 500 °C is referred to much lower contribution of the transformation of retained austenite, and to an expectedly lower amount of precipitated alloy carbides.

Microstructure – Toughness relationships in sub-zero treated and tempered Vanadis 6 steel compared to conventional treatment

The influence of sub-zero treatment and tempering on the microstructure, flexural strength, and fracture toughness of Cr-V ledeburitic steel was examined with reference to the same material processed without the sub-zero period. The experimental results lead to the following findings: (i) Sub-zero treatment induces a considerable reduction of the amount of retained austenite, refinement of newly formed martensite, and increase in population density of small globular carbides. (ii) The hardness is improved by the sub-zero treatment in the prior-to-tempering state as well as in the state after low-temperature tempering; after high-temperature tempering, the situation is changed in favour of conventionally quenched specimens, whereas the secondary hardening peak disappears in sub-zero treated steel. This is due to combined effect of the population density decrease of small globular carbides, accelerated decomposition rate of retained austenite, coarsening of cementitic precipitates, and retardation of precipitation of stable M7C3 carbide. (iii) There is almost no effect of sub-zero treatment on the flexural strength in the low-temperature tempering range but this property is improved after tempering into the secondary hardening range. Sub-zero treatment causes a worsening of fracture toughness after low-temperature tempering but a slight improvement after tempering in the secondary hardening temperature range.

Cr2N - Ag Thin Films - a Short Review

The current paper summarizes briefly the results obtained by comprehensive investigations of magnetron sputtered Cr2N thin films with small additions of silver, whereas the pure Cr2N is used as a reference material. The main aspects reported here are: growth rate of the films, their growth manner, phase constitution, mechanical properties being represented by Young modulus and nanohardness, adhesion on the substrate made from Cr-V ledeburitic steel having a hardness of 60 HRC, tribological performance and effect on the mechanical properties of the substrate.

Evaluation of structural isotropy of Cr-V ledeburitic steel made by powder metallurgy of rapidly solidified particles

Evaluation of structural isotropy of Cr-V ledeburitic steel made by powder metallurgy of rapidly solidified particles

Identification of Carbides in Sub-Zero Treated Vanadis 6 Ledeburitic Steel

Sub-zero processing is an add-on step of heat treatment that includes cooling down, holding at low temperature and re-heating up to room temperature. The aim of this process is to improve some mechanical properties of high-carbon steels. In this research, the Cr-V ledeburitic steel Vanadis 6 produced by powder metallurgy was used. As-received material as well as that after heat treatment contains various types of carbides, which are different in terms of both the nature and the origin. During the austenitizing, a part of the carbides (eutectoid, secondary) undergo dissolution in the austenite while other carbides (eutectic, secondary) remain in the material undissolved. The application of sub-zero treatment leads to increase in the volume fraction of small globular carbides, with a size below 0.3 μm. The volume fraction of secondary carbides was found to be constant, irrespectively to the use of sub-zero processing, but it decreases with increase of the austenitizing temperature. The nature of the carbides was found to be practically unaffected by the sub-zero treatment and it can be described as follows: The eutectic carbides are the vanadium rich MC-phase and the secondary ones are the M7C3. Regarding the nature of small globular particles, their nature is not doubtless because the electron diffraction fixed them as alloyed cementite but the EDX analysis revealed very high chromium content in the particles.

Long-term Sub-zero Treatment of P/M Vanadis 6 Ledeburitic Tool Steel - a Preliminary Study

The microstructure, the phase constitution and the tempering charts of Cr-V ledeburitic steel Vanadis 6 subjected to sub-zero treatment with various soaking times in liquid nitrogen have been investigated. The microstructures have been characterized using the light microscopy, scanning electron microscopy and X-ray diffraction. The hardness has been evaluated by Vickers method. The matrix is martensitic with certain amount of retained austenite, irrespectively to the time of sub-zero treatment. The amount of retained austenite, however, decreases up to the soaking time of 17 h and then remains almost constant. The microstructure of sub-zero treated steel contains enhanced portion of small globular carbides, as compared to conventionally heat treated material. These particles have a size of around 100 nm in most cases. The as-quenched hardness manifests a moderate increase due to the sub-zero treatment. The hardness decreases during subsequent tempering and this decrease is more pronounced in sub-zero treated samples.

Coating of Cr-V Ledeburitic Steel with CrN Containing 7% of Ag

Abstract Samples made from Vanadis 6 PM ledeburitic tool steel were surface machined, ground and mirror polished. Prior the deposition, they were heat treated to a hardness of 60 HRC. CrAg7N-coatings were deposited by magnetron sputtering technique, using pure Cr and Ag targets, in a composite low pressure nitrogen/argon atmosphere and at a temperature of 500 °C. The coatings have an average thickness of 4.3 μm. They grew in a very well visible columnar manner, but, individual silver agglomerates were visible along the columnar crystals, also. The average size of silver agglomerates lies well below 50 nm, e.g. one can suggest that they are capable to be solved and release the Ag atoms to be migrated to the free surface during thermal exposition. The coatings had a good adhesion on the surface - the first critical loads, established by scratch-testing method, ranged between 30 and 39 N.

Metallurgical Aspects of Laser Surface Processing of PM Cr-V Ledeburitic Steel

The Vanadis 6 ledeburitic-type steel was laser surface remelted. Microstructural changes and hardness in laser affected material were investigated using light microscopy, SEM, and EDS-microanalysis. It was found that the laser surface melting and subsequent rapid solidifying led to softening of the material, due to presence of retained austenite. The melting of the material begins with the transformation of M7C3-carbide into a liquid and finishes via the dissolution of primary solid solution grains. The solidification proceeded in a reverse manner while the eutectics became often so-called degenerous form.

Saturation of the Cr-V ledeburitic steel with nitrogen

Saturation of the Cr-V ledeburitic steel with nitrogen