• Journal of the Korean Society for Heat Treatment
• /
• v.12 no.1
• /
• pp.9-20
• /
• 1999

The effect of post oxidation, water-quenched after holding in air for 5~420 seconds or cooling or furnace cooling, on corrosion resistance and phase formation characteristics of the surface layer of SM20C and SM45C carbon steels after gas nirtrocarbursing in the $NH_3-5%CO_2-N_2$ gas atmosphere at $580^{\circ}C$ for 3hours is studied. The compound layers of two steels consist of ${\varepsilon}-Fe_{2-3}N$, ${\gamma}^{\prime}-Fe_4N$ and $Fe_3O_4$, phases, however, the quantity of ${\gamma}^{\prime}-Fe_4N$ phase increases for the furnace cooled specimen compared to that of air cooling specimen. With increasing $NH_3$ content in the gas mixture and also increasing the keeping time in the air after gas nitrocarburising, the ${\varepsilon}-Fe_{2-3}N$ phase of compound layer increases, while the decreased current density recognizing the improvement of corrosion resistance are shown. the passive current density of SM45C steel is lower than that of SM20C steel at the same nitrocarburising conditions.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.28 no.1
• /
• pp.129-141
• /
• 2001

When oral microorganisms were sampled from occlusal surfaces of caries and non-caries teeth, $3.43\times10^5$ CFU and $3.47\times10^3$ CFU of bacteria were counted on MSB agar plates, respectively. All the 20 colonies isolated from a caries surface were Streptococcus mutans but, only two of 20 colonies were identified as Streptococcus mutans by API test. S. mutans SM1 from caries tooth and S. mutans SM2 from non-caries tooth showed the same results except for $\alpha-galactosidase$ activity on sugar fermentation tests and biochemical tests. For the bacterial replication, both SM1 and SM2 were actively multiplicated at pH 5.5. And the viability of SM1 was high at 20% of sucrose, while that of SM2 was high at 5% of sucrose in the media. SM1 actively replicated at 16mM of $CaCl_2$, 160mM of KCl, and 6.4mM of $MgCl_2$, and the replication of SM2 was increased at 16mM of $CaCl_2$, 40mM of KCl, 6.4mM of $MgCl_2$. At 1mM of sodium bicarbonate and sodium phosphate, both bacteria were actively multiplicated. SM1 and SM2 were actively replicated at 1mM and 10mM of Tris, respectively. For potassium phosphate buffer, SM1 grew well proportionally to the concentration up to 100mM, while the growth of SM2 were inhibited by the increase of concentration. The 4.6 kb of gtf gene was amplified with a pair of primer, gtfB-F961 and gtfC-R5574 by polymerase chain reaction from the chromosomal DNA of SM1 and SM2. When 4.6kb bands were eluted from gel and were treated with restriction enzyme, EcoR I produced the same RFLP like 0.8kb and 3.8kb of DNA fragments for S. mutans GS-5, SM1 and SM2. By Hind III, the PCR products weren't digested for S. mutans GS-5 and SM1, but 3 fragments such as 2.4kb, 1.8kb and 400bp were examined for SM2. These results indicated the difference between gtf genes of SM1 and SM2. BamH I treatment showed 4 fragments for SM1 and SM2, while the 3 fragments for S. mutans GS-5. The PCR products were not digested by Kpn I, Sma I, Xho I and Pst I.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.05a
• /
• pp.856-860
• /
• 2002

The main objective of this study is to consider the effect of fatigue crack behavior on the variable depth of micro hole defects in SM20C at the symmetric position. The fatigue crack propagation test is performed by rotary bending fatigue test machine. The relationship between crack length(2a), cycles(N) and crack growth rate(da/dN) are investigated in this study. The result from the rotary bending fatigue test under the applied stress at 250MPa turned out that the fatigue life illustrated almost constant when the depth of symmetric micro hole deflects is both part A and B at the hope depth(h) = 0.5mm.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.15 no.4
• /
• pp.49-55
• /
• 2006

This study deals with the friction welding of SM25C and SCNCrM-2B; The friction time was variable conditions under the conditions of spindle revolution 2,000rpm, friction pressure of 100MPa, upset pressure of l50MPa, and upset time of 4.0 seconds. Under these conditions, the microstructure of weld interface, tensile fracture surface and mechanical tests were studied, and so the results were as follows. 1. When the friction time is 2.0 seconds, the tensile strength of friction welds was 874MPa, which is around as much as 117% of the tensile strength of base metal(SM25C), the bending strength of friction welds was 1,354MPa, which is around as much as 108.9% of the bending strength of base metal(SM25C). 2. At the same condition, the maximum vickers hardness was Hv443 at SCNCrM-2B nearby weld interface, which is higher Hv20 than condition of the friction time 0.5 seconds. 3. The results of microstructure analysis show that the structures of two base materials have fractionated and rearranged along a column due to heating and axial force during friction, which has affected in raising hardness and tensile strength.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.21 no.6
• /
• pp.932-937
• /
• 2012

In the presented study, SM45C carbon steel parts were joined by friction welding. The welding process was carried out under optimized conditions using statistical approach. The study of SM45C is conducted with various combinations of process parameters. Parameter optimization, microstructure and mechanical property correlation are the major contribution of the study. The welded joints were produced by varying spindle revolution speed, friction pressure, upset pressure and burn-off length. Tension tests were applied to welded parts to obtain the strength of the joints. Fracturs properties were additionally obtained experimentally under fluctuated tensile loads. Microstructures using microphotographs were examined in the weld interface and weld region and heat affected zone and base metal and flash zone of welded parts. Finally, Hardness variations in welding zone and base metal were also obtained. Through these tests, the optimum conditions of parameters for ${\phi}20$ SM45C in friction welding were obtained when the friction spindle revolution was 1,950 rpm, the friction pressures was 30 MPs, upset pressures was 50 MPs.

• Journal of the Korean Institute of Gas
• /
• v.3 no.3 s.8
• /
• pp.39-44
• /
• 1999

In the study, corrosion characteristics under various corrosion environments(neutral solution, acid solution), for various hinge materials(SM20C, BsC3 and STC4H), were investigated by immersion test, and the behaviour of fretting wear under atmosphere was studied. In immersion test, corrosion potential of those materials showed to be noble in the sequence of $0.5\%HNO_3$> underground water> $0.5\%\;H_2SO_4$ solution, and potential of a sole material, except BsC3, was more noble than these of mixed materials. In same material SM20C, the fretting wear loss of rotary materials increased about 1.9 times to that of moving materials, because of surface hardening by frictional force.

• Applied Chemistry for Engineering
• /
• v.28 no.1
• /
• pp.73-79
• /
• 2017

Maleic anhydride (MAH) grafted polypropylene (PP-g-MAH) copolymers were prepared by changing MAH and styrene monomer (SM) content, using a twin screw extruder at $190^{\circ}C$. The grafting degree was measured by non-aqueous back titration method. The grafting degree of PP-g-MAH-SM copolymer was higher than that of PP-g-MAH at the same MAH content. PP-g-MAH-SM/kenaf fiber (KF) composites were also prepared by using a PP-g-MAH as a matrix at $200^{\circ}C$ and the KF content was fixed at 20 wt%. Based on the degradation temperature investigated by TGA, the thermal stability of PP-g-MAH-SM/KF composites was more enhanced than that of PP-g-MAH only. Mechanical properties of the composites were also improved when MAH and SM applied together. The adhesion degree between the copolymer and KF was confirmed by both SEM pictures of the fractured surface and contact angles.

• Journal of the Korean Magnetics Society
• /
• v.12 no.5
• /
• pp.189-194
• /
• 2002

Microstructure and magnetic properties of Sm-Co sintered magnet were investigated with the variation of Zr content and their solution treatment and aging temperatures. The fraction of eutectic structure and the size of eutectic area decreased with increasing x value of cast Sm(C $O_{.688-x}$F $e_{.242}$C $u_{.07}$Z $r_{x}$)$_{7.404}$ alloys. On the other hand, x=0.022 ingot had finer dendritic structure compared to the other alloys. The sintered magnet of Sm(C $O_{.688-x}$F $e_{.242}$C $u_{.07}$Z $r_{x}$)$_{7.404}$ had well defined cell structure which is composed of cell boundary Sm $Co_{5}$ and cell interior S $m_2$Co/ssub 17/ phase. Cell boundary Sm $Co_{5}$ phase has 20nm thickness and its relative angle was 120$^{\circ}$ in x=0.018 and 0.022 alloys. Cell size was decreased with increasing Zr contents. But, x=0.026 alloy has diffuse cell boundary and irregular shape compared to x=0.022 and 0.018 alloys. Maximum value of coercive force and maximum energy Product were obtained from x=0.022 alloys. Optimum solution treatment temperature of Sm(C $O_{.688-x}$F $e_{.242}$C $u_{.07}$Z $r_{x}$)$_{7.404}$ alloy was 1170 $^{\circ}C$ and 1st aging temperature of two step aging process for higher coercivity was 850 $^{\circ}C$.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.23 no.6
• /
• pp.618-623
• /
• 2014

This study, analyzed the waveform and mechanical properties of flux cored arc Welding on SM45C. $CO_2$ 10% + Ar 90% shows the lowest standard deviation and shunt ratio at which the arc was most stable. $CO_2$ 10% + Ar 90% is equal to $CO_2$ 20% + Ar 80%. therefore, $CO_2$ 20% + Ar 80% is the best of mixture gases. The hardness test result for the gas mixture ratio of $CO_2$ 10% + Ar 90% was HV 249.7 which is the highest measured value. According to tensile test results, the tensile strength increased with increasing Ar in the mixture gas. This was because of the inertness of the argon, which does not combine with other elements, causing $CO_2$ to combine with pearlite and ferrite and decreasing the maximum tensile strength. Microstructural examination results show that with increasing Ar, ferrite generation decreases while the mild microstructure increases which influences the hardness.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.12
• /
• pp.3899-3908
• /
• 1996

In order to clarify the effects of nonmetallic inclusion contents insteels (SM45C & SCM440) on the tool life, cutting experiment was performed under various cutting conditions. Tool life, cutting force, roughness of machined surface and cutting mechanism are examined on these two kinds of steel. The following conclusions were obtained from the analysis (1) Cutting force of the steels was not affected by chemical component and nonmetallic inclusion. (2) If the rate of amount, Ca/S has a value grater than about 0.2 and addition of less amount of Al, Mn, tool wear of tips decreasesinturning. (3) It is also proved that higher contents of nonmetallic inclusion improve roughness of the surface. (4) Less amount of Ca, higher amount of S, Mn and Al improve the chip breakability.