Temper Brittleness of Seamless Steel Tubes

The seamless pipe has a hollow cross-section and is widely used as a pipeline for conveying fluids, such as octg pipes for conveying oil, natural gas, gas, water, and pipes for certain solid materials. Compared with solid steel such as round steel, the steel pipe is lighter in weight when the bending and torsional strength is the same, and it is an economical section steel.

Seamless steel pipe has the characteristics of high strength, good cutting performance, good ductility, small heat treatment deformation, high temperature stress relaxation strength and high long-term strength. It is used to produce steel castings with higher strength and higher heat treatment section than 35CrMo seamless steel pipes, such as driving wheels for traction belts of electric locomotives, transmission gears of turbocharger transmission systems, transmission gears of high-pressure containers, rear axles of automobiles , crankshaft connecting rod, spring hoop, etc. The load is large, and it can be used for drilling tool joints, fishing tools and bending dies for deep-water wells below 2,000 meters.

Temper brittleness of seamless steel pipe refers to quenching in the temperature range of 450-600°C after heat treatment of seamless steel pipe to obtain austenite structure. Or after quenching at 650°C, go through 350-600°C at a slow cooling rate; or after quenching at 650°C, the steel pipe will be heated at a temperature range of 350-650°C for a long time, which will cause the steel pipe to age. If the aged seamless steel pipe continues to be heated to 650°C and then rapidly cooled, the elasticity can be restored, so it is also called reversible temper brittleness. The high temperature temper brittleness is mainly manifested in the increase of the ductility-ductility transition temperature of the seamless pipe. High-temperature tempering brittleness and sensitivity are generally indicated by the difference between the ductility-ductility transition temperature of the toughened condition and the aged condition.

The effects of elements in seamless steel pipes on high temperature temper brittleness are divided into:

1) Residual elements such as phosphorus, tin, antimony, etc. that cause high-temperature tempering brittleness of precision bright tubes.

2) Promote or alleviate high temperature temper brittle aluminum alloy elements in different ways and degrees. Chromium, manganese, nickel, silicon, etc. play a driving role, while molybdenum, tungsten, titanium, etc. play a slowing role; carbon also plays a driving role. Generally, carbon seamless pipes are sensitive to high temperature tempering brittleness, and are usually binary or multiple aluminum alloys containing chromium, manganese, nickel, and silicon.

Seamless steel pipe is a nickel-iron-chromium heat-resistant alloy, which has good high-temperature strength by adding a certain amount of silicon. Because seamless steel pipes have high high-temperature strength, excellent high-temperature oxidation resistance and material corrosion resistance, they are more and more widely used in aerospace + petrochemical equipment and chemical steel industries. Because the coal dry distillation process uses high-temperature liquefied gas to pyrolyze low-grade coal at low temperature, the liquefied gas is heated in a liquefied gas heat treatment furnace and then enters the furnace wall pyrolysis section to pyrolyze coal. The liquefied gas contains water vapor, a small amount of H2S and other corrosive gases, so it is required that the raw materials for making heat treatment furnaces must have good heat and corrosion resistance.

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