Talking about the Invalid Situation of Steel for Bolts

Discussion on segregation of carbon elements In terms of chromium and silicon, it is generally believed that segregation of chromium and segregation of carbon are in the same direction, while segregation of silicon and segregation of carbon are reversed, that is, due to the exclusion of silicon. Carbon atoms, so the carbon in the high silicon area tends to be low. However, from the measured results, there is no obvious regularity in the distribution of these two elements, but the Si and Cr contents in the core are slightly lower. It can be considered that the carbon content in the core of the sample does not change significantly. The average carbon content of the layer is 0.387%, and the minimum value of the six data is 0.37%. These six data basically reflect the change of carbon from the edge to the core, so it can be considered that there is no obvious change in carbon. The difference in organization, we believe that it is mainly caused not by the segregation of carbon, but by the difference in the degree of subcooling of the edges and core of the sample during quenching and cooling. The difference in subcooling of small samples is not very large, and the resulting tissue difference is not significant. The difference in hardness is due to tissue differences.

The effect of the box segregation is that there is no comparison sample with a large difference in the same furnace number in all the samples taken, so no positive conclusion can be made. However, it can be seen from the existing samples that although No. 1 and No. 2 have two-stage segregation, the No. 1 sample fails during use, and when the system is changed, there are boxes of about 2 levels. Segregation exists, but it can meet the user's requirements, so box segregation is not the cause of bolt failure. From the average value of each hardness, the hardness of the sample after treatment according to the heat treatment system required by the user (35.5) is higher than that of the failed workpiece (28.5). From this point, the strength of the failed workpiece should be greatly greater than 1200kN/mm. Therefore, the reason for the bolt failure is that the heat treatment process does not meet the requirements of the system and the strength is low. It is generally believed that the existence of box segregation only affects the lateral performance, especially the lateral plasticity and toughness index, and has little effect on the longitudinal performance. The hardness of each point of the bolt section is not much different, which is mainly due to the organization. Caused by the difference.

The effect of the decarburization layer The national standard stipulates that the decarburization layer should be inspected for steels with a carbon content greater than 0.3%. The depth of the total decarburization layer on each side is not greater than 1.5% of the nominal diameter of the steel. This is the maximum value that is allowed to exist in the case where the user has a certain amount of processing, and the heat treatment is the final treatment for the user, and the machining allowance is generally not left before the treatment. The same problem exists for the processing of full-section specimens. The torque of the subject is mainly applied to the outer layer, and the outermost 1mm steel bears 5 times the torque of 1mm at the innermost layer. This means that the presence of the decarburized layer affects the mechanical strength of the material or workpiece. During the inspection process, we also found that there is a decarburization layer of about 0.2 mm on the surface of the failed bolt surface, which also adversely affects the strength of the bolt. The discussion of the heat treatment system puts forward the temperature opinion on the heat treatment system of the sample. Here we discuss the heat treatment system of ML35CrMo. According to the heat treatment system provided by the user, the sample shrinkage is above 60%, and the failure is from the failure. A large necking is also seen on the workpiece. In German DIN1654/4-1989, the material requirement Rb in the quenched and tempered state is from 1250 to 1450, and the material requirement is 7≥400. This shows that according to the user's on-site treatment system, the engineering capacity is too large in terms of surface shrinkage. According to the state of use of bolts, the requirements for plasticity index should be appropriately reduced, and the surface shrinkage rate should be controlled below 50%. According to the inspections stipulated by the national standard, the products are qualified products. However, the requirements for the composition of the national standard range from 0.32% to 0.40%, and the tolerance zone is large. To ensure the stability of the performance of the bolt, on the one hand, the supplier should reduce the tolerance zone to ensure the accuracy of the different steel components. At the same time, the user shall formulate different heat treatment systems according to different ingredients and usage requirements. In addition, the quenching holding time should be shortened appropriately, and the tempering temperature should be lowered to control the delamination, reduce the shrinkage, increase the strength, and fully utilize the characteristics of the steel to better meet the different requirements.

Product introduction
HHCMS-240 type Carbon Molecular Sieve
HHCMS-240 is a new kind of non-polar adsorbent. It is designed to extract nitrogen-rich gas from the air. It is suitable for separating nitrogen from the air.
The most notable features of the carbon molecular sieve are high gas-producing efficiency and low waste, especially nitrogen with a purity higher than 99.9%.

It is widely used in large air separation and sheet making equipment, and the application field covers the high-end aspects such as the storage and transportation of crude oil in yibi ships.

Project parameters

The diameter of:1.0-1.3   1.3-1.5

Packing density:≥680-700kg/m³

The intensity of particle:≥95

Compressive strength abrasion:≤1%

The moisture content:≤0.5%

Standard packing:20Kg/barrel. 40Kg/barrel. 130Kg/barrel

The adsorption time of test condition was 58s with an average pressure of 1-2s

Pay attention to
1. The nitrogen production equipment can reduce the adsorption temperature to better show its excellent nitrogen production performance under conditions;
2. Pay attention to low temperature drying and seal preservation during storage;

Carbon Molecular Sieve HHCMS-240

Carbon Molecular Sieve Nitrogen Generation,Carbon Molecular Sieve Activation,Carbon Molecular Sieves Analysis,Nitrogen Carbon Molecular Sieves

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