• Korean Journal of Materials Research
• /
• v.30 no.6
• /
• pp.315-320
• /
• 2020

This study deals with the yielding behavior and strain aging properties of three bake hardening steels with dual-phase microstructure, fabricated by varying the annealing temperature. Bake hardening and aging tests are performed to examine the correlation of martensite volume fraction with yielding behavior and strain aging properties of the bake hardening steels with dual-phase microstructure. The volume fraction of martensite increases with increasing annealing temperature. Room-temperature tensile test results show that the yielding behavior changes from discontinuous-type to continuous-type with increasing volume fraction of martensite due to higher mobile dislocation density. According to the bake hardening and aging tests, the specimen with the highest fraction of martensite exhibited high bake hardening with low aging index because solute carbon atoms in ferrite and martensite effectively diffuse to dislocations during the bake hardening test, while in the aging test they diffuse at only ferrite due to lower aging temperature.

• Korean Journal of Metals and Materials
• /
• v.48 no.7
• /
• pp.605-614
• /
• 2010

Conventional rolling (symmetric) and differential speed rolling (DSR) were both applied to AA1050 sheets at various velocity ratios, from 1 to 2 between the top and bottom rolls. An electron backscatter diffraction (EBSD) technique was used to measure texture inhomogeneity through the thickness direction. After the annealing process, the annealing texture of the DSR processed sheets was different from that of conventionally rolled sheets. The velocity ratio between the top and bottom rolls affected the texture inhomogeneity and macroscopic plastic strain ratio of the AA1050 sheets. A prediction for the macroscopic plastic strain ratio of AA1050 sheets was carried out using a visco-plastic self-consistent (VPSC) polycrystal model. The strain ratio directionality that was predicted using the VPSC polycrystal model was in good agreement with experimental results.

• Korean Journal of Materials Research
• /
• v.30 no.1
• /
• pp.44-49
• /
• 2020

The effect of intercritical annealing temperature on the microstructure and mechanical properties of Fe-9Mn-0.2C-3Al-0.5Si medium manganese steels containing Cu and Ni is investigated in this study. Six kinds of medium manganese steels are fabricated by varying the chemical composition and intercritical annealing temperature. Hardness and tensile tests are performed to examine the correlation of microstructure and mechanical properties for the intercritical annealed medium manganese steels containing Cu and Ni. The microstructures of all the steels are composed mostly of lath ferrite, reverted austenite and cementite, regardless of annealing temperature. The room-temperature tensile test results show that the yield and tensile strengths decrease with increasing intercritical annealing temperature due to higher volume fraction and larger thickness of reverted austenite. On the other hand, total and uniform elongations, and strain hardening exponent increase due to higher dislocation density because transformation-induced plasticity is promoted with increasing annealing temperature by reduction in reverted austenite stability.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.05a
• /
• pp.159-163
• /
• 2006

The effects of annealing temperature and time on mechanical properties and microstructures were studied in cold drawn pearlitic steel wires containing 0.84wt% Si. Annealing was performed from $200^{\circ}C$ to $450^{\circ}C$ with different time of 30sec, 1min, 15min and 1hr. The increase of tensile strength at low temperature was related with strain ageing. The decrease of tensile strength at high annealing temperature was related with spherodization of cementite and the occurrence of recovery of the lamellar ferrite in the pearlite. The improvement of ductility was connected with spherodization of cementite plate in pearlite and recovery process by reduction of high dislocation density at short time annealing temperature of $400^{\circ}C$.

• Journal of Korea Foundry Society
• /
• v.40 no.5
• /
• pp.129-133
• /
• 2020

The outcomes of solution annealing and stress corrosion cracking in cold-worked 316L austenitic stainless steel have been studied using x-ray diffraction (XRD) and the slow strain rate test (SSRT) technique. The good compatibility with a high-temperature water environment allows 316L austenitic stainless steel to be widely adopted as an internal structural material in light water reactors. However, stress corrosion cracking (SCC) has recently been highlighted in the stainless steels used in commercial pressurized water reactor (PWR) plants. In this paper, SCC and inter granular cracking (IGC) are discussed on the basis of solution annealing in a chloride environment. It was found that the martensitic contents of cold-worked 316L stainless steel decreased as the solution annealing time was increased at a high temperature. Moreover, mode of SCC was closely related to use of a chloride environment. The results here provide evidence of the vital role of a chloride environment during the SCC of cold-worked 316L.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.127-132
• /
• 2003

In a today industry, the welding is doing a many portion in structure manufacture. This study is simulated heat of heat-effected zone and researched a mechanical properties and ultrasonic characteristic in used the SS400 and the STS304. As the result mechanical properties of steel that become drawing decreased because of remaining stress by strain gardening according as simulated heat temperature rises, but according as temperature rises in material that do simulated heat after have done annealing, mechanical propensity was improved. The velocity and attenuation become different by effect of remaining stress than effect of material internal microstructure in ultrasonic wave test. In the case of STS304, there was change in mechanical properties by effect that is by strain hardening, but there was no change in material that simulated heat after annealing. When become drawing in ultrasonic waves test, according as simulated heat temperatures rise, change of attenuation coefficient is looked, but material that simulated heat after annealing was no change almost both the volocity and attenuation.

• Journal of IKEEE
• /
• v.14 no.3
• /
• pp.219-223
• /
• 2010

In this study, we fabricated the HgSe nanoparticle-based thin film transistors (TFTs) of back gate structure with PVA gate dielectric. The fabricated TFTs show the improved electrical characteristics in the mobility of $16\;cm^2$/Vs and the on/off ratio of $10^4$ after annealing process at $100^{\circ}C$ for 5 min. AFM images demonstrate that the decrease in surface roughness according to annealing process leads to the improvement of electrical characteristics. The change in drain current caused from the conditions of flexible substrate is investigated under 0.6% strain.

• Journal of the Korean Society for Heat Treatment
• /
• v.28 no.4
• /
• pp.171-180
• /
• 2015

The variation in microstructure and texture during continuous annealing was examined in a series of 1.6% Mn-0.1% Cr-0.3% Mo-0.005% B steels with carbon contents in the range of 0.010 to 0.030%. It was found that microstructure of hot band consisted of ferrite and pearlite as a consequence of high coiling temperature, and eutectoid carbon content was between 0.011% and 0.016%. Martensite ranged in volume fraction from 1.5% to 4.0% when annealed at $820{\circ}C$ according to the typical continuous annealing cycle. The critical martensite content for the continuous yielding was about 4% from stress-strain curves. The continuous yielding was obtained in the 0.030% carbon steel and 0.010% to 0.020% carbon steels revealed some yield point elongation ranging from 0.8% to 2.2% in as-annealed conditions. Higher tensile strength in the higher carbon steel is due to both increase in the martensite volume fraction and ferrite grain refinement. Decreasing the carbon content to 0.01% strengthened the intensities of ${\gamma}$-fiber textures, resulting in the increase in the $r_m$ value, which was caused by the lower volume fraction of martensite. The higher carbon steels showed the lower $r_m$ value of about 1.0.

• Journal of the Korean Society for Heat Treatment
• /
• v.31 no.1
• /
• pp.12-17
• /
• 2018

We investigated the corrosion behavior of commercially pure cold working processed (CP)-Ti with coarse-grained (CG) microstructure heat-treated at $400^{\circ}C$ and $600^{\circ}C$, respectively. It is observed that corrosion resistance of as-received CP-Ti heat-treated at $400^{\circ}C$, at which recrystallization proceeds, is largely improved. Interestingly, the mechanical property of CP-Ti sample at $400^{\circ}C$ was scarcely deteriorated. It is attributed to the decrease of the defects such as strain variance and dislocation density. On the other hand, the annealing treatment at $600^{\circ}C$ of CP-Ti plate causes to grain growth with the noticeable reduction of mechanical property. Hence, it is considered that defect density such as strain and dislocation density is important microstructural parameter for the improvement of corrosion resistance. The introduction of proper annealing treatment can help to improve corrosion resistance without scarifying mechanical property of CP-Ti.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.231-234
• /
• 2009

The effects of annealing temperature and time on mechanical properties and microstructures were already investigated in cold drawn pearlitic steel wires. During annealing, the increment of the tensile strength at low temperatures found to be due to age hardening, while the decrease in the tensile strength at high temperatures was attributed to age softening, involving the spheroidization of lamellar cementite and recovery of lamellar ferrite. Since Between increase of tensile strength and the occurrence of the delamination would be closely related to the dissolution of cementite, the increase of drawing strain by lower annealing temperature caused the between higher tensile strength and the easier occurrence of the delamination in cold drawn pearlitic steel wires.