Production and processing temperature characteristics of seamless pipes

Seamless pipes are made from medium carbon alloy tool steel, offering excellent mechanical properties for hot and cold drawing machinery and equipment. They are widely used due to their good performance, affordability, and availability. However, they have low workability, making them unsuitable for products requiring high precision and complex cross-section specifications.

Heat Treatment Process

Temperature Range: 

The heat treatment process for seamless pipes typically operates at A3+(30~50)℃. This temperature range is generally maintained to ensure optimal results. Higher temperatures can speed up the heating rate, reduce surface oxidation, and promote uniform austenite formation in the workpiece.

Thermal Insulation: 

Adequate thermal insulation time is crucial for uniform temperature distribution and sufficient compressive strength. If the furnace is heavily loaded, increasing the insulation time is necessary to prevent uneven heating. However, excessive insulation can lead to coarse grain formation and issues like oxidation and nitriding, which can degrade the heat treatment quality. As a rule of thumb, if the furnace load exceeds the specified process capacity, both heating and insulation times should be increased by 20%.

Cooling Process: 

Due to the low workability of seamless pipes, a cooling solution with a high cooling rate (e.g., 10% saltwater solution) is recommended. The workpiece should be quenched in the solution without cooling completely through to avoid cracking. When the temperature of the workpiece reaches approximately 180℃, austenite transforms rapidly into martensite, causing significant structural stress. To mitigate this, a slower cooling method should be used when the workpiece is in this temperature range.

Controlled Cooling: 

The cooling process must be carefully managed based on experience, as precise control over effluent temperatures is challenging. Shaking the workpiece in water during cooling helps ensure even cooling and prevents deformation or cracking. The water should be drained once the workpiece stops moving and air cooling should follow. Oil cooling can be a stronger alternative if needed. It's essential to avoid static cooling solutions and workpieces to prevent uneven compressive strength and stress distribution, which can cause deformation or cracking.

By adhering to these guidelines for heat treatment and cooling, the production and processing of seamless pipes can achieve optimal quality and performance.