Seamless Steel Pipe Water Quenching Heat Treatment Process
Date: Jul 8th, 2022
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The established heat treatment process for 42CrMo seamless tubes uses oil or quenching liquids for quenching, but the cost is high and quenching cracks are a serious quality problem that can lead to the scrapping of steel tube parts. ROCHO technical team investigated the use of water as a quenching and cooling medium to develop a heat treatment process for 42CrMo seamless tubes and to provide a continuously operating, highly automated seamless tubes quenching line that would increase throughput and improve process results.
Using water as the quenching and cooling medium, the small batch heat treatment test of 42CrMo seamless steel pipe was first carried out, the size of the pipe was φ98.43mm (outside diameter) * 11.93mm (wall thickness), the material properties required tensile strength > 655MPa, yield strength 552~665MPa, elongation > 20%. Small batch heat treatment quantity is 12pieces, quenching heating temperature is 920 ℃, insulation is 50min, quenching cooling medium is water, quenching to take the immersion of the internal spray method, quenching the tube temperature below 40 ℃, tempering temperature is 735 ℃, insulation is 105min. After the steel pipe was quenched and tempered, the mechanical properties were qualified, but it was found that a large number of cracks appeared on the inner surface of the eight pipes, which led to the scrapping of the steel pipe. In order to analyze the characteristics of cracks, infer the stages and causes of cracks, put forward specific preventive measures, and carry out process improvement and effect verification.
Optimization of the heat treatment process and application effects
According to the analysis of the causes of quenching cracks, the following optimized quenching process measures are proposed.
1, Reduce the quenching heating temperature of the steel pipe to 880°C to reduce the temperature stress.
2, Appropriately reduce the pressure of the internal nozzle pump to reduce the flow rate of water, thus reducing the tissue stress.
3, Reduce the depth of quenching water, so that the circumferential direction of 1/4 of the steel pipe in the water surface, 3/4 of the steel pipe underwater, in order to reduce the tissue stress.
4, Reduce the cooling time of the steel pipe in the water, improve the temperature of the steel pipe out of the water to 120 ~ 160 ℃.
5, The use of residual temperature self-tempering to reduce stress concentration.
6, Tempering process remains at 735°C holding 105min.
Using the optimized heat treatment process for 60 pieces steel pipes heat treatment production, the steel pipe was found to be of good quality with 100% pass rate after ultrasonic testing and surface quality inspection.
The structure and grain size of 42CrMo after the heat treatment process is optimized (500×), the structure of the steel pipe produced by the improved heat treatment process is tempered sorbite, with good hardenability, no strip or block ferrite, carbonization The material is uniformly distributed, the structure is dense, the average grain size is 20 μm, and the average grain size is 8.0, which provides a basis for obtaining good mechanical properties.
The process of using water as the quenching cooling medium reduces the production cost of 42CrMo steel pipe heat treatment. The biggest risk of water quenching is quenching cracks. For quenching cracks, an improved quenching process is proposed, which provides guiding data for the heat treatment of 42CrMo steel pipes with water as a quenching cooling medium.
ROCHO INDUCTION has own induction heat treatment technology department which is constantly developing and improving the process to provide our customers with high quality products. Learn about more information on steel pipe heat treatment process and seamless steel pipe water quenching production line, please contact us today.
