Annealing, Normalizing, Quenching and Tempering Process of Seamless Steel Pipe

Posted On Thu, April 22, 2021, 3:26 PM
Annealing, normalizing, quenching and tempering process of seamless steel pipe

1) Annealing process of seamless steel pipe:
The seamless steel pipe is heated to a certain temperature, kept for a certain period of time, and then slowly cooled to room temperature.

Purpose of annealing:
a. Reduce hardness and improve plasticity to facilitate cutting and cold deformation processing;
b. Refine the grain, uniform the structure of the steel, improve the performance of the steel and prepare for the subsequent heat treatment;

c. Eliminate internal stress of steel and prevent deformation and cracking of parts after processing.

Annealing category of seamless steel pipe:
1. Fully annealed

Process: Heat the steel parts to the critical temperature (the critical temperature of different steels is different, generally 710~750°C, and the critical temperature of individual alloy steels can reach 800~900°C) 30~50°C, keep it for a certain period of time, and then slowly cool down with the furnace (Or bury it in sand to cool down).

Purpose: Refine grain, uniform structure, reduce hardness, and fully eliminate internal stress. Complete annealing is suitable for forgings or steel castings with carbon content (mass fraction) below 0.8%.

2. Spheroidizing annealing

Process: The steel parts are heated to 20-30°C above the critical temperature, and after heat preservation, they are slowly cooled to below 500°C and then air-cooled out of the furnace.

Purpose: Reduce hardness, improve cutting performance, and prepare for subsequent quenching to reduce deformation and cracking after quenching. Spheroidizing annealing is suitable for carbon steel and alloy tool steel with carbon content (mass fraction) greater than 0.8%.

3. Stress relief annealing
Process: Heat the steel to 500~650°C, keep it warm for a certain period of time, and then slowly cool down (usually cooling with the furnace)

Purpose: Eliminate internal stress generated during welding and cold straightening of steel parts, eliminate internal stress generated during cutting of precision parts, to prevent deformation during subsequent processing and use. Stress relief annealing is suitable for all kinds of castings, forgings, welded parts and cold extruded parts.

2) Normalizing of seamless steel pipe

Process: The steel parts are heated to 40~60°C above the critical temperature, kept for a certain period of time, and then cooled and heat treated in the air.

Purpose: 
①Improve the organization structure and cutting performance;
②For parts with low requirements for mechanical properties, normalizing is often used as the final heat treatment;
③ Eliminate internal stress.

3) Seamless steel pipe quenching treatment
Process: The steel parts are heated to the quenching temperature, kept for a period of time, and then rapidly cooled in water, salt water or oil (individual materials are in the air).

Purpose: 
①To obtain higher hardness and wear resistance of steel parts;

②Make the steel parts get some special properties after tempering, such as higher strength, elasticity and toughness, etc.

Seamless steel pipe quenching category:
a. Single liquid quenching
Process: The steel parts are heated to the quenching temperature, and after heat preservation, they are cooled in a quenching agent. Single-liquid quenching is only suitable for carbon steel and alloy steel parts with simple shapes and low technical requirements. When quenching, for carbon steel parts with a diameter or thickness greater than 5-8mm, use salt water or water cooling: alloy steel parts use oil cooling.

Purpose:
① Make steel parts obtain higher hardness and wear resistance;
② Make the steel parts get some special properties after tempering, such as higher strength, elasticity and toughness.

b. Double liquid quenching of seamless steel pipe
Process: The steel parts are heated to the quenching temperature. After heat preservation, they are quickly cooled to 300~400C in water, and then moved into oil for cooling.

Purpose:
① Make steel parts obtain higher hardness and wear resistance;
② Make the steel parts get some special properties after tempering, such as higher strength, elasticity and toughness.

c. Flame surface quenching of seamless steel pipe
Process: Spray a flame of mixed combustion of acetylene and oxygen on the surface of the part to quickly heat the part to the quenching temperature, and then immediately spray water on the surface of the part. Flame surface hardening is suitable for single-piece or small batch production. The surface requires hard and wear-resistant large-scale medium-carbon steel and medium-carbon alloy steel parts, such as crankshafts, gears and guide rails, which can withstand impact loads.

Purpose:
① Make steel parts obtain higher hardness and wear resistance;
② Make the steel parts get some special properties after tempering, such as higher strength, elasticity and toughness.

d. Surface induction heating quenching
Process: Put the steel part in the inductor, the inductor generates a magnetic field under the action of a certain frequency of alternating current, and the steel part generates an induced current under the action of the magnetic field, so that the surface of the steel part is rapidly heated (2~10min) to the melting temperature. At this time, water is immediately sprayed onto the surface of the seamless steel pipe. The seamless steel pipe quenched by surface induction heating has a hard and wear-resistant surface, while the core maintains good strength and toughness. Surface induction heating quenching is suitable for medium carbon steel and alloy steel pipes with medium carbon content.

Purpose:
① Make steel parts obtain higher hardness and wear resistance;
②Make the steel parts get some special properties after tempering, such as higher strength, elasticity and toughness.

4) Tempering treatment of seamless steel pipe
Process: The quenched steel parts are heated to below the critical temperature, kept for a period of time, and then cooled in air or oil. Tempering is carried out immediately after quenching and is also the last process of heat treatment.

Purpose:
① Obtain the required mechanical properties. Under normal circumstances, the strength and hardness of parts after quenching are greatly improved, but the plasticity and toughness are significantly reduced, and the actual workpiece conditions of the parts require good strength and initial properties. After selecting an appropriate tempering temperature for tempering, the required mechanical properties can be obtained.
② Stable organization and stable size.
③ Eliminate internal stress.

Tips: ASTM A53 (https://www.permanentsteel.com/newsshow/astm-a53-steel-pipe-specifications.html) covers seamless and welded steel pipe with nominal wall thickness. The surface condition is usually black and hot-dipped galvanized. ASTM A53 is produced mainly for pressure and mechanical applications, and is also used for transport of steam, water, gas line pipes.

Know more about seamless steel pipe, pls visit: https://www.permanentsteel.com/product/carbon-steel-pipe.html

 


Contact Information:
lvy lee
lvy@permanentsteel.com

This press release is posted under categories Business, Automobile

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