The Countermeasures of Low Temperature on Mild Steel Pipe

The Effect of Low Temperature on Mild Steel Pipe

Low temperature can make mild steel tube become more brittle, mainly because steel at low temperature will undergo a phase transition, the strength of the grain boundary increases; crystal twisting deformation and cracking and other mechanisms lead to an increase in brittleness. In addition, low temperatures affect the plasticity and toughness of steel, reducing the fatigue strength and impact toughness of the material.

Cold Embrittlement Test Methods

Commonly used low temperature embrittlement test methods are Charpy impact test and Izod impact test. In both tests, steel samples are impacted at room or low temperatures and the impact work at the time of sample destruction is calculated. Since low-temperature embrittlement is caused by factors such as various microscopic defects and blocking potentials in steel, these defects are significantly enhanced at low temperatures, which leads to an increase in steel embrittlement.

Measures to Prevent Low-temperature Embrittlement

To prevent low temperature embrittlement, specific processing and treatment techniques are required. The following are the main countermeasures:

1. Addition of low-temperature toughness agents: The toughness of steel at low temperatures is increased by the addition of some low-temperature toughness agents such as low-temperature toughness carbides and alloying elements. This method can improve the compressive strength and flexural strength of steel, thus improving the performance of steel in the low temperature environment.

2. Heat treatment: Heat treatment to improve the low-temperature brittleness, so that the grain size tends to be uniform, thereby improving the fatigue strength and toughness of steel. The temperature is controlled so that the grain and organization of the steel becomes more stable. Depending on the mild steel specification, methods such as normalizing, quenching, annealing, quenching and normalizing can be carried out.

3. Quenching: Quenching is a steel machining process in which a cooling medium such as water and oil is poured over the surface of the steel to change the chemical components and physical properties in the steel. In the quenching process, the hardness and toughness of the steel can be substantially increased, and the steel can also maintain its properties at low temperatures.

4. Normalizing treatment: Normalizing treatment is also a steel machining process in which the temperature is controlled so that the steel undergoes a good grain annealing, which results in a uniform grain size. This method improves the toughness and bending strength of the steel, thus improving the performance of the steel at low temperatures.

Summarize

Low temperatures can make mild steel pipe more brittle, and the corresponding countermeasures include the addition of low-temperature toughness agents, heat treatments, quenching, and normalization.