Heat treatment for cold drawing seamless steel pipes

There are seven types of heat treatment,they’re respectively annealing,normalizing,quenching, tempering,quenching and tempering,chemical heat treatment and solution treatment.

Annealing means that heating the metal into suitable temperature,maintaining certain time,then cooling at suitable speed.Common annealing process is re-crystallization annealing,stress relief annealing,spheroidizing annealing,full anneal etc.The purpose of annealing is to reduce hardness,improve machinability,eliminate remaining stress,improve the homogenization of tissues and components,and prepare for the subsequent heat treatment.

Normalizing is a kind of heat treatment of to improve toughness of steel.Heat steel to 30~50℃ more than AC3 or ACM (Upper critical point temperature of steel),keep suitable time,then cool in static air.The purpose of normalizing is increase mechanical properties of carbon steel,improve machinability,eliminate tissue defect,and prepare for next heat treatment.

Quenching is such heat treatment,heat steel to any temperature more than AC3 or ACM (Upper critical point temperature of steel),keep suitable time,then cool at suitable temperature,finally  get Martensite (or bainite) tissue.Common quenching processes include salt bath quenching,martensite quenching,bainite austempering, surface quenching and partial quenching.The purpose of quenching is to get martensite tissue,increase steel hardness,strength and durability,prepare for next heat treatment.

Tempering is such a process,steel after hardening,is heated to any temperature below AC1,keep certain time and cool at room temperature.Common tempering process is low-temperature tempering,medium-temperature tempering,high-temperature tempering and many times tempering.The purpose of tempering is eliminate stress,and make steel have higher hardness and durability,also plasticity and toughness to be needed.

for cold drawing seamless steel pipes

Quenching and tempering is a compound heat treatment to make steel quenched and tempered.The steel is called quenched and tempered steel.It commonly means medium carbon structural steel and medium carbon alloy structural steel,with 0.3-0.6% carbon content.

Chemical heat treatment is a process like this,put steel a kind of active medium with certain temperature and keep warm,make one or some elements infiltrate into its surface layer,in order to change its chemical components,tissue and properties.Common chemical heat treatments include carburizing,nitriding, carbonitriding,aluminizing,boronizing etc.Chemical heat treatment is to increase the hardness of steel surface, durability,anti-corrosion,anti-fatigue strength and oxidation resistance.

Solution treatment is the heating of an alloy to a suitable temperature,holding it at that temperature long enough to cause one or more constituents to enter into a solid solution and then cooling it rapidly enough to hold these constituents in solution.Its main purpose is to improve plasticity and roughness of steel,prepare for precipitation hardening.