How can AISI4145H Drill Collar be prevented from cracking and mechanical properties guaranteed by medium frequency quenching?

In the initial AISI4145H Drill Collar medium frequency quenching process, quenching and cracking scrapping rate of 70%, and mechanical properties unqualified, for this problem, in more than two years of groping and production practice, basically solved the problem, so there are some insights.

Drill collar material for AISI4145H, chemical composition as shown in Table 1. The steel hardenability is good, oil quenching can be quenched Ø80mm, after tempering has high comprehensive mechanical properties, and is a typical oil quenching material.

Table 1 Chemical composition

The mechanical properties of the AISI4145H Drill Collar are specified in SY/T5144-1997, as shown in Table 2, the length of the part is about 10m.

Table 2 Mechanical properties of drill collar SY/T5144-1997 regulations

(3) Medium-frequency induction tempering equipment has been developed in recent years, special equipment for heat treatment of long shaft parts, due to its structural features (specific not in detail), replacing the deep well furnace, and reducing the supporting investment, such as higher traveling crane lifting height of the workshop, large quenching tanks, calibration equipment, etc., has a high degree of substitutability. The only shortcoming is that the quenching coolant can only use water-based coolant.

(4) Process.

The process used is: quenching 840 ~ 860 ℃, with a moving speed of 0.2m/min through the heating inductor, cooling for the tap water three-stage spray, water temperature 10 ~ 40 ℃. After production according to this process, the results obtained are shown in Table 3

Table 3 Mechanical properties

(5) Analysis and measures.

AISI4145H is a typical oil quenching material, the uses of smaller quenching and cooling rate that can meet the quenching requirements, but in the medium-frequency induction quenching equipment currently used in the tap water, which will inevitably increase the quenching tendency. The key to preventing quenching and cracking is to grasp the appropriate amount of water spray to ensure the appropriate quenching and cooling rate.

In addition, to ensure the mechanical properties, the first step is to ensure the quenching quality. If the quenching quality is not high, the M transformation is not enough, the hardness is low, is unable to temper adjustment to get excellent comprehensive performance. Therefore, the quenching should not be done by reducing the cold speed, but by minimizing the cold speed under the premise of guaranteeing the quenching quality, i.e., to find the balance point between the cold speed required to guarantee the quenching quality and prevent cracking. According to this idea, we made a dial to record the amount of water spray, and carried out tests with different amounts of water spray on the basis of the original process, and the results are shown in Table 4.

Table 4 Experimental results at different water spray rates

Note: The scales "4" and "5.5" in the text are dial data and do not represent the exact amount of water sprayed.

As can be seen from Table 4, no more cracks appeared after controlling the amount of water spray, indicating that reducing the quenching cooling rate can solve the crack problem. However, in different water spray volumes, the results have some differences:

The water spray amount of "4", there are strength indicators and toughness indicators are unqualified phenomena, belonging to the quenching organization did not get better, indicating that the cooling rate provided by the small; water spray amount of "5.5", the indicators are qualified, indicating that the provision of cooling Speed basically reached the equilibrium point of the requirements.

In the production and testing process found that the AISI4145H material has a certain tendency to temper brittleness, special attention should be paid to tempering cooling must provide a sufficiently large cooling rate, in order to prevent Akv reduction.

The preceding roughly spoke of the AISI4145H Drill Collar medium frequency induction tempering production process, to prevent quenching cracks and ensure mechanical properties of some ideas and methods, which is also a little bit of our experience in the production test. The implementation of the specific process, also needs to be based on the status of the equipment, power supply stability, water temperature, and other aspects of the comprehensive consideration, including operational details, including the development of detailed process procedures to meet the requirements of the product drawings.

Source: Metalworking (Thermal Processing) Magazine