LNG storage tank special cryogenic pressure vessel 45# excellent carbon steel (9 nickel steel)
No. 45 steel is a high-quality carbon structural steel plate, which has high strength and certain deformation resistance. No. 45 steel has good comprehensive mechanical properties after quenching and tempering. There are two categories of quenched and tempered steel: carbon quenched and tempered steel and alloy quenched and tempered steel, whether it is carbon steel or alloy steel, its carbon content is strictly controlled. If the carbon content is too high, the strength of the quenched and tempered workpiece is high, but the toughness is not enough, if the carbon content is too low, the toughness is increased and the strength is insufficient. In order to make the quenched and tempered parts get good comprehensive performance, the carbon content is generally controlled at 0.30~0.50%.
| Chemical composition |
| Tabulation: Depu Steel Date: 2024-01-18 |
| C |
Cr |
Mn |
Ni |
P |
S |
Si |
| ≤ 0.42～0.50 |
≤0.25 |
0.50～0.80 |
≤0.25 |
≤0.035 |
≤0.035 |
0.17～0.37 |
Note:
(1): In order to improve the properties of steel, other trace alloying elements other than the above table can be added, and the data comes from the network and is for reference only.
(2): The allowable deviation of the chemical composition of the finished steel plate should be in line with the provisions of
GB/T222 V. 45# excellent carbon steel mechanical properties: Material: 45# excellent carbon steel Tensile strength: ≥600 Yield strength: ≥355 Elongation %: ≥16 Impact energy %: ≥40 Hardness \ HB: ≤197
Quenching and tempering (heat treatment method)
of No.
45 steel1. No. 45 steel is a medium-carbon structural steel, with good cold and hot processing performance, good mechanical properties, low price and wide sources, so it is widely used. Its biggest weakness is that it has low hardenability, and the workpiece with large cross-sectional size and high requirements is not suitable for use.
2. The quenching temperature of No. 45 steel is A3+(30~50) °C, and in actual operation, the upper limit is generally taken. The high quenching temperature can speed up the heating speed of the workpiece, reduce the surface oxidation, and improve the work efficiency. In order to homogenize the austenite of the workpiece, it is necessary to hold it for a sufficient time. If the actual furnace loading volume is large, it is necessary to extend the holding time appropriately. Otherwise, there may be a lack of hardness due to uneven heating. However, if the holding time is too long, there will also be coarse grains and serious disadvantages of oxidation and decarburization, which will affect the quenching quality. We believe that if the furnace loading volume is greater than the provisions of the process document, the heating and holding time needs to be extended by 1/5.
3. Because the hardenability of No. 45 steel is low, a 10% brine solution with a large cooling rate should be used. If the workpiece is cooled in salt water, it may crack the workpiece, because when the workpiece is cooled to about 180°C, the austenite quickly transforms into martensite and causes excessive microstress caused. Therefore, when the quenched workpiece is quickly cooled to this temperature range, the method of slow cooling should be adopted. Because the temperature of the outlet water is difficult to grasp, it must be operated by experience, and when the workpiece in the water is shaken, the outlet can be air-cooled (if it can be oil-cooled, it is better). In addition, the workpiece should be moved into the water rather than static, and should be moved regularly according to the geometry of the workpiece. The stationary cooling medium combined with the stationary workpiece leads to uneven hardness and uneven stress, which makes the workpiece deformed and even cracked.
4. The hardness of No. 45 steel quenching and tempering parts after quenching should reach HRC56~59, and the possibility of large cross-section is lower, but not lower than HRC48, otherwise, it means that the workpiece has not been completely quenched, and there may be soxenite or even ferrite structure in the structure, which is still retained in the matrix through tempering, and cannot achieve the purpose of quenching and tempering.
5. The heating temperature is usually 560~600 °C after quenching, and the hardness requirement is HRC22~34. Because the purpose of quenching and tempering is to obtain comprehensive mechanical properties, the hardness range is relatively wide. However, if the drawing has hardness requirements, the tempering temperature should be adjusted according to the requirements of the drawings to ensure the hardness. For example, some shafts require high strength, and the hardness requirements are high; However, some gears and shaft parts with keyways have to be milled and inserted after quenching and tempering, and the hardness requirements are lower. Regarding the tempering insulation time, depending on the hardness requirements and the size of the workpiece, we believe that the hardness after tempering depends on the tempering temperature, which has little to do with the tempering time, but it must be reversed, and the general tempering and holding time of the workpiece is always more than one hour.
