The effect of multi-step tempering on retained austenite content and mechanical properties of low alloy steel used in the forged cold back-up roll was investigated.Microstructural evolutions were ...characterized by optical microscope,X-ray diffraction,scanning electron microscope and Feritscope,while the mechanical properties were determined by hardness and tensile tests.The results revealed that the content of retained austenite decreased by about 2% after multi-step tempering.However,the content of retained austenite increased from 3.6% to 5.1% by increasing multi-step tempering temperature.The hardness and tensile strength increased as the austenitization temperature changed from 800 to 920 ℃,while above 920 ℃,hardness and tensile strength decreased.In addition,the maximum values of hardness,ultimate and yield strength were obtained via triple tempering at 520 ℃,while beyond 520 ℃,the hardness,ultimate and yield strength decreased sharply.
► The effect of Ca and Zn addition on Mg–Ca and Mg–Ca–Zn were investigated. ► Ca and Zn addition decreased solid fraction at coherency point. ►
T
N–
T
DCP increased by adding Ca and Zn in Mg–Ca and ...Mg–Ca–Zn, respectively. ► Three reactions were detected when Zn/Ca atomic ratio less than 1.25 in Mg–Ca–Zn. ► A new peak Mg
51Zn
20 was identified in Mg–0.5Ca–9Zn in addition of other peaks.
This research described the identification phases by thermal analysis and microscopy inspection of Mg–
xCa and Mg–0.5%Ca–
xZn alloys that were solidified at slow cooling rate. Analysis of cooling curve after Ca addition shows the evolution of the Mg
2Ca intermetallic phase at around 520
°C in addition to α-Mg phase. First derivative curves of alloys after the addition of Zn to Mg–0.5Ca alloy reveals three peaks related to α-Mg, Mg
2Ca and Ca
2Mg
6Zn
3 for alloys that have Zn/Ca atomic ratio less than 1.23. The peak of Mg
2Ca reaction on the first derivative curves disappeared for alloys containing Zn/Ca ratio more than 1.23. A new peak was also observed at 330
°C for Mg–0.5Ca–9Zn which was identified as Mg
51Zn
20. Solid fraction at coherency point decreased with increasing Ca and Zn elements. However, coherency time and difference between the nucleation and coherency temperatures (
T
N–
T
DCP) increased by adding Ca and Zn in Mg–Ca and Mg–Ca–Zn systems.
The influence of hydrofluoric acid (HF) treatment on the corrosion behavior of the Mg-0.5Ca alloys was investigated by immersion specimen in sodium hydroxide and HF solutions with various ...concentrations and durations at room temperature. Microstructural evolutions of the specimens were characterized by atomic force microscopy, X-ray diffraction, field-emission scanning electron microscopy. The corrosion resistance was examined through potentiodynamic polarization and immersion test in Kokubo solution. The results revealed that the fluoride treated Mg-0.5Ca alloys produced by immersion in 40% HF provided more uniform, dense and thicker coating layer (12.6 μm) compared with the 35% HF treated specimen. The electrochemical test showed that the corrosion resistance of fluoride treated specimen was 35 times higher compared with the untreated Mg-0.5Ca alloy specimen in Kokubo solution. In vitro degradation rate of the fluoride treated specimens was much lower than untreated Mg-0.5Ca alloy in Kokubo solution. After immersion test the surface of 40% HF treated sample showed a few corrosion dots, while untreated specimens were fully covered by corrosion products and delamination. Fluoride treated Mg-0.5Ca alloy with 40% HF is a promising candidate as biodegradable implants due to its low degradation kinetics and good biocompatibility.
► Metal wrapping and strip welding in work/back-up rolls contact zone caused spalling. ► MnS inclusion and pore initiated crack which propagated in milling led to spalling. ► Retained austenite ...conversion to α′-martensite accelerated spalling failure. ► Needle shaped carbide (Fe,Mo,Cr)
7C
3, may cause poor service life of back-up roll.
In this paper, premature failure of a forged back-up roll from a continuous tandem mill was investigated. Microstructural evolutions of the spalled specimen and surface of the roll were characterized by optical microscopy, X-ray diffraction, scanning electron microscopy and ferritscopy, while hardness value of the specimen was measured by Vickers hardness testing. The results revealed that the presence of pore and MnS inclusion with spherical and oval morphologies were the main contributing factors responsible for the poor life of the back-up roll. In addition, metal pick up and subsequently strip welding on the surface of the work roll were found as the major causes of failure in work roll which led to spalling occurrence in the back-up roll. Furthermore, relatively high percentage of retained austenite, say 9%, in outer surface of the back-up roll contributed spalling due to conversion of this meta-stable phase to martensite and creation of volume expansion on the outer surface through work hardening during mill campaign.
The thermal parameters of Mg–
x
Zn cast alloys with 0·5–9 wt% Zn were evaluated by using computer aided cooling curve thermal analysis (CA–CCTA), whereas the corrosion behaviour was investigated by ...potentiodynamic polarization and immersion tests. Thermal analysis results revealed that the dendrite coherency temperature (
T
DCP
) decreased from 642·2 to 600 °C with the addition of Zn from 0·5 to 9 wt%. The liquid fraction at coherency point (
) increased by 72% when Zn was increased up to 9 wt%. MgZn intermetallic phase was observed in samples with <3 wt% Zn. At higher percentages of Zn, the Mg
51
Zn
20
intermetallic phase was also detected in addition to
α
-Mg and MgZn by first derivative cooling curves under non-equilibrium solidification. All these phases were observed along the grain boundary when Zn was rejected from the solid/liquid interface and enriched in the triple conjunction of grain boundary. The grain size decreased from 185·2 to 71·5
μ
m when Zn content was increased. The addition of Zn content had a significant effect on the corrosion rate and the corresponding mechanisms. The corrosion rate decreased from 2·1 to 1·81 mmpy as Zn content increased from 0·5 to 3 wt%; afterwards, however, this value increased with further increase of Zn. Mg–3Zn also had the lowest degradation rate and highest corrosion resistance which can be fully utilized for biodegradable orthopedic applications.
Penelitian ini bertujuan untuk mengetahui efek pemberian vitamin D terhadap perubahan kadar kalsiferol serum dan perubahan gejala klinis terhadap penderita rinitis alergi. Penelitian ini menggunakan ...uji klinis (clinical trials) terhadap 40 orang penderita rinitis alergi, dimana 20 pasien menggunakan kortikosteroid intranasal sebagai terapi dengan tambahan vitamin D, dan 20 pasien sebagai kontrol. Pengukuran kadar kalsiferol serum, pengukuran derajat rinitis alergi menurut ARIA, dan pengukuran total nasal symptom score (TNSS) dilakukan sebanyak 2 kali yaitu sebelum perlakuan dan setelah perlakuan. Data kemudian di analisis menggunakan uji-t berpasangan, uji chi-square, dan uji Wilcoxon ranks. Hasil penelitian didapatkan perbedaan bermakna kadar kalsiferol serum antara sebelum perlakuan dan setelah pemberian terapi tambahan vitamin D. Terdapat juga penurunan skor TNSS dan derajat rinitis alergi secara bermakna (p < 0,001) pada kelompok yang diberikan perlakuan berupa terapi tambahan vitamin D. Kemaknaan klinik adalah pemberian terapi tambahan vitamin D akan memperbaiki kadar kalsiferol serum, skor TNSS, dan derajat rinitis alergi jika dibandingkan dengan pemberian terapi standart saja.
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