This standard specifies the technical requirements, test methods, inspection rules and markings for low temperature steel castings for valves. JB/T 7248-1994 Technical requirements for low temperature steel castings for valves JB/T7248-1994 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
Technical Conditions for Low-Temperature Steel Castings for Valves
Subject Content and Scope of Application
This standard specifies the technical requirements, test methods, inspection rules and markings for low-temperature steel castings for valves. JB/T 7248--- 94
This standard applies to valves, flanges and other pressure-bearing steel castings (hereinafter referred to as castings) used under low temperature conditions of -30 to -101℃. The referenced standards are:
GB 222
GB 2106
GB6397
GB6414
Methods for sampling samples for chemical analysis of steel and allowable deviations of chemical composition of finished products Chemical analysis methods for steel and alloys
Metal tensile test method
Metal Charpy (V-notch) impact test method Metal tensile test specimen
Dimensional tolerance of castings
GB/T 11350
GB/T 11351
GB/T 1J352
GB12231
Machining allowance of castings
Tolerance of casting weight
Carbon steel castings for general engineering
Appearance inspection of steel castings for valves
GB/T 13927
G3/T 6439
G3/T 6440
GB/T 6902
3 Technical requirements
General valve pressure test
Magnetic particle flaw detection of pressure castings of valves
Radiographic inspection of pressure castings of valves
Liquid penetrant inspection method of valve castings
Chemical composition and mechanical properties
The chemical composition of castings shall comply with the provisions of Table 1 Table 1
2.5 Nickel steel
3.5% Nickel steel
Main chemical elements, %
0. 502 0. 202
40. 500. 30
0.040. 045—2. 0~
Note: 1) Within the specified maximum carbon content, for every 0.01% reduction, the maximum allowable manganese content will increase by 0.04% until the maximum manganese value is 1.2 years. 2) The total content of the specified residual elements is 1.00% (maximum value). 3.1.2 The mechanical properties of the castings shall comply with the provisions of Table 2. Approved by the Ministry of Machinery Industry of the People's Republic of China on July 18, 1994, 150
Implementation on July 1, 1995
Types of grades
0.3% aluminum steel
2.5% nickel steel
3.5% nickel steel
3.2 Heat treatment
Tensile strength
150620
485-655
Yield strength
JB/T 7248--94
Elongation
Castings from each smelting furnace should be heat treated, 3.2.1
3.3 Quality requirements
Sectional reduction
! Test temperature
Charles V-notch impact test
One of the samples
The smallest of the three samples
The smallest sample
Castings shall conform to the shape, size and deviation requirements of the approved drawings. If the deviation requirements of the size are not indicated on the drawings, they shall conform to the provisions of 3.3.1
GB6414, GB/T11350 and GB/T11351. 3.3.2 The surface quality of castings shall conform to the provisions of GB12231. 3.3.3 Pressure castings shall be able to withstand shell tests. 3.3.4 Castings shall not be eliminated by hammering, plugging or piercing. 3.3.5 Welding repair
3.3.5.1 The welder who welds the castings shall be qualified according to the regulations of the relevant departments. 3.3.5.2 The welded castings shall comply with the provisions of 3.3.1 and 3.3.2 and be inspected in accordance with the provisions of 4.3. When the order contract requires magnetic particle inspection of the castings, the welded castings shall be inspected in accordance with 1.3.4; when the order contract requires radiographic inspection of the castings, they shall be inspected in accordance with 4.3.5. For castings with shell leakage, castings with welded depression depth exceeding 20% ​​of the wall thickness or 25mm (the smaller value) and castings with welded defect area greater than 65cm, stress relief treatment or heat treatment shall be carried out after welding according to the welding process. 4 Test methods and inspection rules
4.1 Chemical analysis
4.1.1 Melting furnace analysis
The foundry (workshop) shall conduct chemical analysis for each furnace to determine the content of the specified elements. During the analysis, the test blocks fired in the same furnace shall be used. When sampling the cuttings, the samples shall be taken from at least 6.5mm below the surface. The chemical composition shall comply with the provisions of Table 1. 4.7.2 The sampling method for chemical analysis shall comply with the provisions of G13222, and the arbitration analysis of chemical composition shall comply with the provisions of GB223: 4.2 Mechanical properties test
4.2.1 Sampling method
4.2.1.1 The test blocks used to prepare the samples shall be made of molten steel from the same furnace as the castings and cast according to the provisions of GB/T11352. 4.2.1.2 The test blocks shall be heat treated in the same furnace as the castings or in the production furnace according to the same stability process. 4.2.1.3 If necessary, according to the opinions of the foundry (workshop), the samples can be cut from the heat-treated castings. 4.2.1.4 The shape and size of the test samples shall comply with the provisions of GB6397. 4.2.1.5 If machining or casting defects are found in the specimen, a spare specimen shall be taken for retesting. 4.2.2 Tensile test
4.2.2.1 The tensile test method shall comply with the provisions of GI3228. 4.2.2.2 Each melting furnace of steel for castings shall be subjected to a tensile test, and its mechanical properties shall comply with the provisions of Table 2. If not, the casting and the test block may be reheat treated, and the test shall not be repeated more than three times. 4.2.3 Impact test
4.2.3.1 The impact test shall be carried out with three Charpy V-notch impact specimens (10mm×10mm) as a group, and the test shall be carried out according to the overflow specified in Table 2
JB/T 7248--94
4.2.3.2 The average energy value of the three specimens shall not be less than the specified value, and only one value is allowed to be lower than the specified minimum average value, but all values ​​shall not be lower than the specified minimum value of a single specimen. 4.2.4 Shell test
4.2.4.1 Each pressure casting shall be subjected to shell test in accordance with the provisions of GB/T13927. 4.2.4.2 Shell test can be carried out before delivery by the foundry (workshop) or after machining by the purchaser. The foundry (workshop) shall be responsible for the quality problems found in the shell test.
4.3 Nondestructive testing
4.3.1 Sampling method
For the first production of castings, one out of every five castings (including the next five) shall be selected for nondestructive testing. 4.3.2 Inspection method
Radiographic inspection, magnetic particle inspection or liquid penetration inspection shall be carried out. The method adopted can be specified by the user. 4.3.3 Key inspection areas
a. Flange root and welded valve seat area of ​​cast valve body and valve cover: b. Hard alloy sealing surface surfacing area:
c. Repair welding area.
4.3.4 Powder pound inspection of castings
Powder pound inspection shall comply with the provisions of JB/T6439, and the defects of the inspection parts shall not be less than level 2. 4.3.5 Radiographic inspection of castings
Radiographic flaw detection inspection shall comply with the provisions of JB/T6440, and the defects of the inspection parts shall not be less than level 2. 4.3.6 Liquid penetrant inspection of castingsbZxz.net
Liquid penetrant flaw detection inspection shall comply with the provisions of JB/T6902, and the defects of the inspection parts shall not be less than level 2. 4.3.7 If the above inspection fails, the casting shall be inspected in full. 4.4 Inspection by the buyer
4.4.1 The foundry (workshop) shall provide the buyer with the test data of chemical analysis and mechanical properties and the certificate of quality of the casting. 4.4.2 The foundry (workshop) shall provide the necessary convenience for the buyer to ensure that the castings comply with this standard and the provisions contained therein, but the buyer's inspection shall not affect the normal production of the foundry (workshop). 4.4.3 If the buyer finds harmful defects in the casting after acceptance and believes that the casting needs to be returned, the buyer should notify the foundry (workshop) within 30 days of the discovery of the defect and negotiate a solution.
4.4.4 If the buyer objects to the material of the casting, the product shall be kept for 30 days from the date of mailing the test report. The foundry (workshop) may request a re-inspection during this period.
4.4.5 When the purchaser makes a rejection decision based on the test report, the foundry (workshop) should be notified within 30 days of receiving the report. 5 Marking
Pressure castings should be cast with cast steel grade or furnace number markings. When it is difficult to mark the furnace number for pressure castings with a nominal diameter less than 32mm, steel stamping is allowed.
Additional instructions:
This standard is proposed by the National Valve Standardization Technical Committee. This standard is under the jurisdiction of the Hefei General Machinery Research Institute of the Ministry of Machinery Industry. This standard was drafted by the Hefei General Machinery Research Institute of the Ministry of Machinery Industry. The main drafters of this standard are Fang Benxiao, Li Yan, Jiang Jinfang, and Cai Huijun. 152
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