Description
The Master’s thesis is done at Konecranes Finland Oy’s Hämeenlinna plant, which includes replacement of case hardening to low-pressure carburizing. The purpose of this thesis is to find out what kind of method is low-pressure carburizing combined with oil/gas quenching and what kind of properties are obtained by the method. The suitability of low-pressure carburizing and oil/gasquenching for Ovako's steel grades 20 CrNiMo2-2 and 18 CrNiMo7-6 is also investigated. In addition, in the investment project, it is important to find out possible equipment suppliers and gas solutions for the heat treatment. The cost savings calculations and preliminary layout plans for the furnace assembly are also discussed at the end.
Factors affecting the durability and properties of carbonized steels include surface and core hardness, carbonized layer thickness, residual stresses, retained austenite and grain size. Low-pressure carburizing provides many advantages over conventional case hardening. The benefits of vacuum carbonization are good mechanical properties in the absence of oxygen from heat treatment, lower dimensional changes, good surface quality, cleaner and brighter surfaces, better work safety, and good energy efficiency and environmental friendliness. In low-pressure carburizing, acetylene is generally used as the carburizing gas because of its efficiency and environmental impact. After carburizing, oil or gas quenching and possibly tempering treatment are performed.
In the acquisition of a large investment, the primary tasks are to map the benefits of the investment and to identify potential equipment suppliers. Based on the cost calculations, low-pressure carburizing achieves significant annual savings compared to case hardening. As the project progressed, ECM Technologies, Ipsen and ALD Vacuum Technologies participated in the cooperation and tender for the vacuum furnace. It is important for the investment project to determine what will be the future quenching method. Initially, nitrogen gas was selected as the quenching medium. Gas quenching would be able to create more uniform deformations and distortions in the components and to obtain slightly cleaner components after treatment. With oil quenching, the quench speed is significantly higher, which greatly influenced the choice of quenching method. Carburizing tests were performed by ECM Technologies, and based on the test results, low-pressure carburizing and nitrogen quenching are not suitable for the treatment of 20 CrNiMo2-2 steel,
at least with the parameters used. The surface hardness and core hardness did not reach the required level for 20 CrNiMo2-2 steel parts. Nitrogen quenching 18 CrNiMo7-6 steel had significantly better results and was therefore well suited for the heat treatment. The surface hardness and core hardness were brought to the required level for 18 CrNiMo7-6 steel parts. In oil quenching tests, the results of both showed that oil is a suitable quenching medium for the used steels grades. The results of those tests proved to be good for 20CrNiMo2-2 -steel.
| Aikajakso | toukok. 2021 |
|---|---|
| Tutkittava | Perttu Kauppi |
| Tunnustuksen arvo | National |