The Heat Treatment Process of Steel Pipes

The Heat Treatment Process of Steel Pipes

  1. Why should we have heat treatment on steel pipes
  2. What are the main types of steel pipes’ heat treatment process?

Heat treatment is one of the important processes in the production process of steel pipes. It plays an important role in exploring potential of metal materials, improving the service life of steel pipes and making performance of steel pipes better. The service life as well as performance can be affected by various factors such as the internal micro structure of metal materials including a variety of defects, the size of internal stress, the morphology, size and boundary structure of grains and the form and distribution of the strengthening phase and inclusions. Using different heat treatment processes means that the heating temperature, holding time and cooling rate are different. Through these methods, the steel pipes can have different internal micro structures so as to meet various standards of steel pipes, performance requirements of users and operation requirements of specific conditions.
According to the steel pipes’ standards which have diverse requirements on the micro structure, performance and hardness of steel pipes, the heat treatment process can be summarized into the following five categories.
(1). Heating

The steel material could be heated below the critical point or above critical point. The former heating way can stabilize structure and eliminated the residual stress. The latter way can make material austenitizing.

Austenitizing is to heat steel metal over its critical temperature long time enough, so it could be transformed. If a quenching followed after Austeniting, then the material will be harden. Quenching will take fast enough to transform austenite into martensite. Once reached austenitizing temperature, suitable microstructure and full hardness, the steel pipe material will be attained in further heat treatment processes.

(2). Heat preservation
The purpose of heat preservation is to uniform the heating temperature of steel material, then it will get a reasonable heating organization.

(3). Cooling
The cooling process is the key process in heat treatment, it determines mechanical properties of steel pipe after cooling process.

Four main heat treatment methods in carbon and alloy steel pipe industry

The heat treatment processes for steel pipe includes normalizing, annealing, tempering, quenching and other process.

(4). Normalizing

Heating the steel pipe above the critical temperature, and cooled in the air.

Through normalizing, the steel material stress could be relieved, improves ductility and toughness for the cold working process. Normalizing usually applied for the carbon and low alloy steel pipe material. It will produce different metal structure, pearlite, bainite, some martensite. Which brings harder and stronger steel material, and less ductility than full annealing material.

(5). Annealing

Heating the material to above its critical temperature long enough until microstructure transform to austenite. Then slow cooled in the furnace, get maximum transformation of ferrite and pearlite.

Annealing will eliminate defects, uniform the chemical composition and fine grains. This process usually applied for the high carbon, low alloy and alloy steel pipe need to reduce their hardness and strength, refine the crystal structure, improve the plasticity, ductility, toughness and machinablity.

(6). Quenching

Heating the steel pipe material to critical temperature until microstructure transformation is done, cooling it in a rapid rate.
Quenching purpose is to produce the thermal stress and tissue stress. It can eliminate and improve through the tempering. The combination of quenching and tempering can make the comprehensive performance improved.

(7). Tempering

Heating the steel material to a precise temperature below the critical point, and often done in the air, vacuum or the inert atmospheres. There are low temperature tempering 205 to 595°F (400 to 1105°F), medium temperature and high temperature tempering (to 700℃ 1300℉).

The purpose of tempering is to increase the toughness of steel and alloy steel pipe. Before tempering, these steel is very hard but too brittle for the most application. After process can improve the plasticity and toughness of steel pipe, reduce or eliminate the residual stress and stabilize the steel pipe’s size. Brings good comprehensive mechanical properties, so that it does not change in service.

The tempering treatment of stainless steel pipe

In order to solve the work hardening caused by cold processing of the stainless steel pipe, it is necessary to process the tempering in the subsequent forming process. Therefore, whether the tempering process has a very direct impact on the molding process and costs.
As we all know, when stainless steel is close to or less than room temperature, it will harden and increase the strength and hardness of stainless steel. In essence, not all stainless steel pipes can be expected to be shaped. For example, ferritic 400 stainless steel pipes, when they are cold processing, will only produce a small amount of deformation, or it will produce sudden damage or even cracking. For example, 430 and 446 stainless steel pipes themselves have notch sensitivity, so their supply status needs to be marked as annealed. When it is necessary to shape it, it must be processed by tempering.
The hardened martensitic stainless steel is also supplied by annealing, otherwise the stainless steel is cured by normalizing or by quenching and solidifying. Austenitic stainless steel pipes, however, can be supplied within a wide range of cold working hardness. The mechanical properties of the austenitic 300 series stainless steel pipes under various tempering conditions are listed. Not all austenitic and stainless steel pipes of all sizes and grades can be machined and formed after tempering.
The content of alloy elements is lower 201, 202, 301, 302 and 304 stainless steel are very suitable for cold drawing; alloy element content is high and the cold hardening rate of low stainless steel, tempering products production is greater than 1/2 cold work hardening state is not widely used. 305, 316, 317 and 310 stainless steels belong to the latter category. With the continuous increase of nickel content, the tendency of hardening of stainless steel will be reduced.
It should be noted that some non-standard chromium manganese austenitic stainless steel pipe, but also greatly increased the processing range of cold drawn steel pipe. The tempering dimension relation of the large size stainless steel pipe processed by cold drawing can be seen that the regularity of the small size stainless steel pipe may be changed during processing. When small stainless steel pipes are higher than the hardness of the annealed ones, especially when they are expected to have 1/2 chilling properties, it is necessary to consider the use of specialized equipment for the production of small-size 
stainless steel pipes.

Because of the utilization ratio of raw material, the rate of success is the condition that must be taken into consideration, and the above basic knowledge is beneficial to improve the yield of stainless steel pipe. In the processing of cold drawn stainless steel pipe, the processing dimension must be considered to limit the production of the stainless steel pipe. Because of the price limit, the lubricant performance and the above analysis inherent factors, only certain sizes of stainless steel pipes in a variety of tempering state can be cold drawn processing.

Tempering of Stainless Steel Tube

The purpose of stainless steel tube tempering is to convert quench martensite into tempered martensite, eliminate residual austenite, reduce and eliminate internal stress, get high hardness, wear resistance and red hardness, etc., to stabilize the size and improve mechanics performance, to meet their work needs. The normal tempering temperature of 540 ~ 570 °C, in 100% KNC) 3 salt bath insulation 1 ~ 1.5h, due to high-speed steel tempering martensite precipitation in the dispersion of small W, Mo and V carbide, residual austenite in the III fire process into martensite, so with the “secondary hardening” phenomenon, should be three times the tempering.
In order to ensure the tempering effect of high speed steel, should pay attention to the following questions:
① Stainless steel tube quenching should be immediately after the tempering treatment, otherwise it will stabilize the retained austenite, is not conducive to the elimination of residual austenite.
② Tempering temperature should be uniform, it is recommended that the best in the salt furnace.
③ Stainless steel tube after each tempering must be cooled to room temperature, in order to carry out the next tempering.
④ Stainless steel tube after the end of the tool should be cooled to room temperature to clean, or likely to cause cracking of stainless steel tube.
High temperature stainless steel pipe dry use, do not exceed the limit temperature of high temperature stainless steel pipe, dry use of high temperature stainless steel pipe problem will not be great, but this will greatly shorten the life of high temperature stainless steel pipe, if once The use of high temperature stainless steel tube in the center of the use of cooling liquid, will increase the life of high temperature stainless steel pipe, so you can know in order to ensure high temperature stainless steel pipe life and performance, high temperature stainless steel tube is best not to use dry.

Sizes Tolerance of Stainless Steel Tube

Standard
                 Out Diameter(mm)
       Wall Thickness(%)
Cutting Length(mm)
     Sizes
        Tolerance
Sizes(mm)
          Tolerance
Sizes
Tolerance
GB/T14975-02
10~30
+0.30/-0.30
S≤3
+14/-14
1.0~3.0
+15/0
30~50
+0.40/-0.40
S>3
+12/-10
 
 
D>50
+0.9%/-0.9%
 
 
 
 
GB/T14976-02
6~10
+0.20/-0.20
0.5~1.0
+0.15/-0.15mm
 
+15/0
10~30
+0.30/-0.30
1.0~3.0
+14/-14
30~50
+0.40/-0.40
>3
+12/-10
D>50
+0.9%/-0.9%
 
+12.5/-12.5
GB13296-91
≤140
+1.25%/-1.25%
≤10
+15/-15
 
 
>140
+1%/-1%
>10
 
ASTM213
D<25.4
+0.10/-0.10
D<38.1
+20/0
D<50.8
+3.0/0
25.4~38.1
+0.15/-0.15
38.1~50.8
+0.20/-0.20
50.8~63.5
+0.25/-0.25
D≥38.1
+22/0
D≥50.8
+5.0/0
63.5~76.2
+0.30/-0.30
76.2~101.6
+0.38/-0.38
101.6~190.5
+0.38/-0.64
190.5~228.6
+0.38/-1.14
ASTM A269
D<12.7
+0.13/-0.13
 
+15/-15
 
+3.2/0
12.7~38.1
+10/-10
38.1~88.9
+0.25/-0.25
+4.8/0
88.9~139.7
+0.38/-0.38
139.7~203.2
+0.76/-0.76
ASTM A312
10.29~48.26
+0.40/-0.80
 
+12.5/-12.5
 
+6.0/0
48.26~114.30
+0.80/-0.80
114.30~219.08
+1.60 /-0.80
219.08~457.20
+2.40/-0.80
ASTM A789
D≤12.7
+0.13/-0.13
 
+15/-15
 
+3.0/0
12.7~38.1
+10/-10
38.1~88.9
+0.25/-0.25
+5.0/0
88.9~139.7
+0.38/-0.38
139.7~203.2
+0.76/-0.76
ASTM A790
10.29~48.26
+0.40/-0.80
 
 
 
 
48.26~114.3
+0.80/-0.80
 
 
 
 
114.3~219.08
+1.60/-0.80
 
 
 
 
219.08~457.20
+2.40/-0.80
 
 
 
 
EN17455-02
10~30
+0.30/-0.30
S≤3
+14/-14
1.0~3.0
+15.0/0
30~50
+4.00/-4.00
S>3
+12/-10
D>50
+9%/-9%
 
 
EN17456-02
6~10
+0.20/-0.20
0.5~1.0
+0.15/-0.15
 
+15.0/0
10~30
+0.30/-0.30
1.0~3
+14/-14
 
30~50
+4.00/-4.00
S>3
+12/-10
 
D>50
+0.9%/-0.9%
 
 
 

Source: China Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@metallicsteel.com

Please notice that you might be interested in the other technical articles we’ve published:

  • WHERE TO BUY HIGH QUALITY STEEL PIPES

  • WHERE TO BUY HIGH QUALITY FLANGES

  • WHERE TO BUY HIGH QUALITY PIPE FITTINGS

  • ADVANTAGES OF DUPLEX STAINLESS STEEL PIPE AND SELECTION

  • WHERE TO BUY HIGH QUALITY BELLOW EXPANSION JOINTS

  • Difference Between Pipe Elbow And Pipe Bend

  • Where to get high quality alloy steel pipes

  • Distinguish Inferior Steel Pipes

  • WHERE TO GET HIGH QUALITY HEAT EXCHANGER TUBES

References:

  • http://www.octalsteel.com/faq/heat-treatment-method-for-steel-pipe.html
  • https://www.yaang.com/heat-treatment-process-of-precipitation-hardening-stainless-steel-pipe.html
  • https://www.steeljrv.com

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