Introduction of terms commonly used in stainless steel square tube standards

(1) General Terms

1 delivery status

It refers to the state of final plastic deformation or final heat treatment of the delivered product. The hot-rolled or cold-drawn (rolled) state or manufacturing state generally delivered without heat treatment; the heat treatment state after heat treatment delivery, or the normalizing, tempering, solid solution, annealing according to the type of heat treatment status. When ordering, the delivery status must be stated in the contract.

2 Delivery according to actual weight or delivery according to theoretical weight

Actual weight - at the time of delivery, the weight of its product is delivered according to the weighing (weighing) weight;

Theoretical Weight - The weight of the product at the time of delivery is calculated from the nominal size of the steel. The calculation formula is as follows (If delivery is required by theoretical weight, it must be specified in the contract):

The theoretical weight per square meter of stainless steel square tube (steel density is 7.85kg/dm3) is calculated as:


Where: W-- theoretical weight per meter of steel pipe, kg/m;

D--the nominal diameter of steel pipe, mm;

S--Nominal wall thickness of steel pipe, mm.

3 Guarantee conditions

According to the provisions of the current standards of the project to carry out inspections and ensure compliance with the provisions of the standard, known as the guarantee conditions. Guarantee conditions are divided into:

A, basic guarantee conditions (also known as guaranteed conditions). Whether or not the customer stated in the contract. All of these tests must be carried out in accordance with the standards and ensure that the test results meet the standards.

Such as chemical composition, mechanical properties, dimensional deviations, surface quality, and flaw detection, water pressure testing, or flattening or flaring process performance tests, are guaranteed conditions.

B. Agreement guarantee conditions: In addition to the basic guarantee conditions in the standard, there are still "according to the requirements of the buyer, negotiated by the supply and demand sides, and note in the contract?" or "When the demander requests ..., they should note in the contract. "Ming "; and other customers, put forward stringent requirements (such as composition, mechanical properties, size deviations, etc.) or increase inspection items (such as the ellipticity of the steel pipe, uneven wall thickness, etc.) of the basic guarantee conditions in the standard. The above terms and requirements, At the time of ordering, the supply and demand parties negotiate and sign the supply technical agreement and specify it in the contract.Thus, these conditions are also referred to as agreement guarantee conditions.Products with agreed terms and conditions are generally subject to price increase.

Batch 4

The "batch" in the standard refers to a test unit, that is, an inspection lot. If batches are delivered in delivery units, they are called delivery batches. When the delivery lot is large, one delivery lot can include several inspection lots; when the delivery lot size is small, one inspection lot can be divided into several delivery lots.

The composition of a "batch" usually has the following provisions (see relevant standards for details):

A. Each batch shall consist of steel pipes of the same grade (steel grade), the same furnace (tank) number or the same parent furnace number, the same specification and the same heat treatment system (heating times).

B. For high-quality carbon steel structural pipes and fluid pipes, they can be composed of steel pipes of the same grade, the same specification, and the same heat treatment system (heating times) of different furnaces (cans).

C. Each batch of welded steel pipe shall consist of the same grade (steel grade) and steel pipe of the same specification.

5 high-quality steel and high-grade steel

In GB/T699-1999 and GB/T3077-1999 standards, those with the "A" character behind the brand name are high quality steels, and vice versa.

High-quality steel is superior to high-quality steel in some or all of the following:

A, reduce the content range of ingredients;

B, reduce the harmful elements (such as *, phosphorus, copper) content;

C, to ensure a higher degree of purity (requires less content of non-metallic inclusions);

D, to ensure higher mechanical properties and process performance.

6 portrait and landscape

In the standard, the longitudinal direction refers to the direction parallel to the machining direction (that is, the direction of the machining process); the lateral direction refers to the direction perpendicular to the machining direction (the machining direction is the axial direction of the steel pipe).

When the impact work was done, the fracture of the longitudinal specimen was perpendicular to the machining direction. Therefore, it is called transverse fracture; the fracture of transverse specimen is parallel to the processing direction, so it is called longitudinal fracture.

(2) Steel pipe shape, size terms

1 nominal size and actual size

A. Nominal size: It is the nominal size specified in the standard. It is the ideal size that users and production companies hope to obtain. It is also the order size specified in the contract.

B. Actual size: It is the actual size obtained in the production process, and this size is often larger or smaller than the nominal size. This phenomenon that is larger or smaller than the nominal size is called deviation.

2 Deviation and Tolerance

A, deviation: In the production process, because the actual size is difficult to achieve the nominal size requirements, that is often more or less than the nominal size, so the standard allows a difference between the actual size and the nominal size. Positive values ​​are called positive deviations, and negative values ​​are called negative deviations.

B. Tolerances: The sum of the absolute values ​​of positive and negative deviations specified in the standard is called tolerances, also called "tolerance zone."

The deviation is directional, that is, expressed as "positive" or "negative"; the tolerance is not directional, therefore, it is wrong to call the deviation value "positive tolerance" or "negative tolerance".

3 delivery length

The length of delivery is also called the length of the user's requirement or the length of the contract. The standard provides the following specifications for the length of delivery:

A, usually length (also known as non-fixed length): Where the length is within the standard length range and no fixed length requirements, are called the normal length. For example, structural pipe standards stipulate that: hot-rolled (extruded, expanded) steel pipes are 3000mm to 12000mm, and cold drawn (rolled) steel pipes are 2000m to 10500mm.

B. Length of fixed length: The length of the fixed length shall be within the normal length range, which is a fixed length dimension required in the contract. However, it is not possible to cut out the absolute length in actual operation. Therefore, the standard defines the allowable positive deviation value for the length of the cut length.

The structural standards are:

The cut length of the production length-length pipe is larger than that of the normal length pipe, and the production company's request for fare increase is reasonable. The rate of increase in price varies from company to company, and generally increases about 10% on the basis of the base price.

C. Length of doubler: The length of the doubler should be within the normal length range. The length of the doubler and the multiple of the total length should be specified in the contract (for example, 3000mm×3, ie, 3 times of 3000mm, total length is 9000mm). In actual operation, the allowable positive deviation of 20mm shall be added on the basis of the total length, plus the allowance for each single-fold length. Taking the structural pipe as an example, it is specified that the remaining allowance for the cut is: outer diameter ≤ 159mm is 5 to 10mm; outer diameter is 159mm is 10 to 15mm.

If there is no double-length deviation and cutting allowance specified in the standard, it shall be negotiated between the supplier and the buyer and specified in the contract. The length scale is the same as the length of the fixed length, which will greatly reduce the finished product rate. Therefore, the production company proposes a reasonable price increase, and its price increase range is basically the same as the fixed length length.

D. Range length: The length of the range is within the normal length range. When the user requests one of the fixed lengths, it must be specified in the contract.

For example, the length is usually 3000 to 12000 mm, and the length of the range is 6000 to 8000 mm or 8000 to 10000 mm.

Obviously, the length of the range is looser than that of the length scale and the length of the doubler, but it is more severe than the usual length, and it also brings about a reduction in the finished product rate for the production enterprises. Therefore, it is reasonable for production companies to raise their prices, and the rate of price increase is generally about 4% above the base price.

4 uneven wall thickness

The wall thickness of the steel pipe cannot be the same everywhere. There is an unequal wall thickness in the cross-section and the longitudinal pipe body, ie, the wall thickness is uneven. In order to control this non-uniformity, the allowable index of uneven wall thickness is stipulated in some steel pipe standards. The general rule does not exceed 80% of the wall thickness tolerance (executed after consultation between supply and demand sides).

5 Ovality

In the cross-section of a circular steel pipe, there is a phenomenon that the outer diameter is not equal, that is, there is a maximum outer diameter and a minimum outer diameter that are not necessarily mutually perpendicular, and the difference between the maximum outer diameter and the minimum outer diameter is ellipticity (or not Roundness). In order to control the degree of ellipticity, some steel pipe standards specify the allowable index of ellipticity, which is generally specified as not to exceed 80% of the outer diameter tolerance (performed after consultation by the supply and demand sides).

6 curvature

The steel pipe is curved in the length direction, and its degree of curvature, which is called curvature, is represented by numbers. The bending degree specified in the standard is generally divided into the following two types:

A, local curvature: using a one-meter long ruler on the maximum bending of the steel pipe, measure the chord height (mm), which is the local bending value, the unit is mm/m, said the method such as 2.5mm/m . This method also applies to tube end curvature.

B. Full-length total bending: Using a string, pull from both ends of the tube, measure the maximum chord height (mm) at the bend of the steel tube, and convert it into the percentage of the length (in meters), which is the length of the steel tube. The full length of the bend.

For example, if the length of steel pipe is 8m and the maximum measured string height is 30mm, the full-length bending of the pipe should be:


7 size difference

The size is too bad or the size exceeds the allowable deviation of the standard. The "size" here mainly refers to the outer diameter and wall thickness of the steel pipe. Some people usually use the "extraordinary tolerance" as the over-dimension of the dimension. This method of equating deviation and tolerance is not strict, and should be called "deviation". The deviation here may be "positive" or "negative", and the phenomenon that the "positive and negative" deviations are rarely observed in the same batch of steel pipes is rarely observed.

(3) Chemical Analysis Terms

The chemical composition of steel is one of the important factors that affect the quality and end-use performance of steel products. It is also the main basis for the preparation of heat treatment systems for steel products and even final products. Therefore, in the technical requirements section of the steel standards, the first item often stipulates the grades (steel grades) and their chemical components that are applicable to steel products, and is included in the standard in the form of a table. It is the chemical composition of steel and steel for acceptance by production companies and customers. The important basis. 1 steel melting components

The chemical components specified in the general standard refer to smelting components. It refers to the chemical composition of the finished steel smelting and mid-pouring. In order to make it representative, that means the average composition of the furnace or tank, in the standard sampling method, the molten steel is cast into small ingots in the sample, and the sampling chips are taken or drilled on it to meet the specified standards. The method (GB/T223) is analyzed, and the result must meet the scope of the standard chemical composition, and it is also the basis for customer acceptance.

2 finished ingredients

The finished product component is also called the verification analysis component. It is a chemical component derived from the finished steel product that has been drilled or shaved by the prescribed method (GB/T222) and analyzed according to the specified standard method (GB/T223). In the crystallization and subsequent plastic deformation, due to the uneven distribution of the alloying elements in the steel (segregation), there is a deviation between the finished product component and the standard component range (smelting component), and the deviation value shall comply with the requirements of GB/T222 .

The final composition of steel products is mainly used by the use department or quality inspection department to inspect the quality of steel products. Production companies generally do not perform finished product analysis (except for user requirements), but they should ensure that the finished product analysis meets the standards.

3 Arbitration analysis

When there are significant differences between the two laboratories in analyzing the same sample and exceed the allowable analysis error of the two laboratories, or when the production company and the use department, the demander and the supplier have different opinions on the same sample or the finished product analysis of the same batch of steel products. , may be re-analyzed by an authoritative entity (such as the China Iron and Steel Research Institute or an inspection department with qualifications for commodity inspection) with rich analytical experience from a third party, which is called arbitration analysis. The results of the arbitration analysis are the basis for the final decision.

(4) Mechanical properties

The mechanical properties of steel are an important indicator to ensure the end-use performance (mechanical properties) of the steel. It depends on the chemical composition of the steel and the heat treatment system. In the steel pipe standard, tensile properties (tensile strength, yield strength or yield point, elongation), and hardness and toughness indexes, as well as high and low temperature performance required by users, are stipulated in accordance with different application requirements.

1 Tensile strength (σb)

The maximum force (Fb) at which the specimen is subjected to tensile breaking during the drawing process is the tensile stress (σ) obtained by taking the original cross-sectional area (So) of the specimen, which is called the tensile strength (σb). N/mm2 (MPa). It represents the maximum ability of a metal material to resist damage under the action of a tensile force. The formula is:

In the formula: Fb - the maximum force when the specimen pulls off, N (Newton);

So - the original cross-sectional area of ​​the sample, mm2.

2 Yield point (σs)

Metal material with a yield phenomenon, the specimen does not increase (hold constant) in the tensile process can still continue to stretch the stress, known as the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).

The upper yield point (σsu): the maximum stress before the force drops for the first time when the sample yields;

Lower yield point (σsl): The minimum stress in the yield phase when the initial transient effect is not taken into account.

The formula for yield point is:

Where: Fs - specimen yield force (constant), N (Newtons);

So - the original cross-sectional area of ​​the sample, mm2.

3 elongation after breaking (σ)

In the tensile test, the percentage of the gauge length and the original gauge length after the specimen is broken is called elongation. Expressed in σ, the unit is %. The formula is:

Where: L1-- specimen gauge length after breaking, mm;

L0 - original gauge length, mm.

4 Section shrinkage (ψ)

In a tensile test, the percentage of the reduction in the cross-sectional area at the reduced diameter of the specimen after it is broken and the percentage of the original cross-sectional area is called the reduction of area. Expressed in ψ, the unit is %. Calculated as follows:

Where: S0 - the original sample cross-sectional area, mm2;

S1--The minimum cross-sectional area at the reduced diameter after the specimen is broken, mm2.

5 hardness index

The ability of a metal material to resist the collapse of a hard object is called hardness. According to the test method and application range, the hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. For the pipe commonly used are Brinell, Rockwell, Vickers hardness three.

A, Brinell hardness (HB)

With a certain diameter of steel ball or cemented carbide ball, with the specified test force (F) pressed into the surface of the model, after the specified retention time to remove the test force, measure the indentation diameter (L) of the sample surface. The Brinell hardness value is the quotient obtained by dividing the test force by the ball surface area of ​​the indentation. Expressed in HBS (steel ball), the unit is N/mm2 (MPa).

Its calculation formula is:

In the formula: F - the test force pressed into the surface of the metal sample, N;

D--Test ball diameter, mm;

D--average diameter of indentation, mm.

The determination of Brinell hardness is more accurate and reliable, but generally HBS is only suitable for metal materials below 450N/mm2 (MPa), not for harder steel or thinner sheet. In the steel pipe standard, Brinell hardness is the most widely used, and the hardness of the material is often represented by the indentation diameter d, which is intuitive and convenient.

Example: 120HBS10/1000130: It means that the Brinell hardness value measured with a 10mm steel ball under a test force of 1000Kgf (9.807KN) for 30 seconds (seconds) is 120N/mm2 (MPa).

B. Rockwell hardness (HK)

The Rockwell hardness test, like the Brinell hardness test, is an indentation test method. The difference is that it measures the depth of the indentation. That is, under the sequential effect of the initial test force (Fo) and the total test force (F), the indenter (Gold Steel Factory cone or steel ball) is pressed into the surface of the sample, and after the prescribed holding time, the main is removed. Test force, hardness value is calculated using the measured residual indentation depth increment (e). The value is an unnamed number, represented by the symbol HR. The scales used are 9 rulers A, B, C, D, E, F, G, H, and K. Among them, the scales commonly used in the steel hardness test are generally A, B, C, namely HRA, HRB, HRC.

The hardness value is calculated by the following formula:

When tested with A and C scales, HR=100-e

When tested with the B scale, HR=130-e

In the formula, the residual depth of indentation is expressed in terms of the specified unit of 0.002mm. That is, when the indenter is displaced axially by one unit (0.002mm), it is equivalent to a change in Rockwell hardness. The greater the value of e, the lower the hardness of the metal, and the higher the hardness.

The scope of application of the above three scales is as follows:

HRA (Diamond Cone Indenter) 20-88

HRC (Diamond Cone Indenter) 20-70

HRB (ball diameter 1.588mm head) 20-100

The Rockwell hardness test is a widely used method at present, and HRC is used in the steel pipe standard only after the Brinell hardness HB. Rockwell hardness can be applied to the determination of very soft to extremely hard metal materials, it makes up for the Brookfield method is not, simpler than the Brookfield method, can read the hardness value directly from the dial of the hardness machine. However, because of its small indentation, the hardness value is not as accurate as the Brookfield method.

C, Vickers hardness (HV)

The Vickers hardness test is also an indentation test method in which a positive quadrangular pyramid diamond indenter with a relative plane angle of 1360 is pressed into the test surface with a selected test force (F), and the test is performed after a prescribed holding time. Force, measure the length of two diagonals of the indentation.

The Vickers hardness value is the quotient of the test force divided by the indentation surface area, and its calculation formula is:

In the formula: HV - Vickers hardness symbol, N/mm2 (MPa);

F--test force, N;

d - The arithmetic average of the two diagonals of the indentation, mm.

The Vickers hardness test force F is 5 (49.03), 10 (98.07), 20 (196.1), 30 (294.2), 50 (490.3), 100 (980.7) Kgf (N), etc. The range is 5 to 1000 HV.

An example of the expression method: 640 HV 30/20 indicates that the Vickers hardness value measured with a test force of 30 Hgf (294.2 N) for 20 seconds (seconds) is 640 N/mm 2 (MPa).

The Vickers hardness method can be used to determine very thin metallic materials and surface layer hardness. It has the main advantages of Brinell and Rockwell, and overcomes their basic shortcomings, but it is not as easy as Rockwell's method. Vickers is rarely used in steel pipe standards.

6 Impact toughness index

Impact toughness is the ability to reflect the resistance of metal to external impact load, generally expressed by the impact toughness value (ak) and impact energy (Ak). Its unit is J/cm2 and J (joule) respectively.

Impact toughness or impact energy test (referred to as "impact test"), due to the different test temperature is divided into three kinds of room temperature, low temperature and high temperature impact test; according to the sample notch shape can be divided into "V"-shaped gap and "U" Notch impact test two kinds.

Impact test: Use a sample of a certain size and shape (10×10×55mm) (“U” type or “V” type notch in the middle of the length direction, notch depth 2mm) under the impact load from the prescribed testing machine. The fracture was broken at the test.

A. Shock absorption work Akv(u)--A metal pattern with a certain size and shape, the work absorbed when breaking under impact load. The unit is Joule (J) or Kgf. m.

B. Impact toughness value akv(u)—The quotient of the impact absorption work divided by the cross-sectional area at the bottom of the specimen notch. The unit is Joules/cm 2 (J/cm 2 ) or Kg. m/cm2 (Kgf.m/cm2). The formula is:

In the formula: Akv (u) - The work absorbed when the sample breaks, Kgf. m(J);

S - The cross-sectional area at the bottom of the specimen notch, cm2.

The normal temperature impact test temperature is 20±50C; the low temperature impact test temperature range is <15~-1920C; the high temperature impact test temperature range is 35~10000C. The cooling medium used in the low temperature impact test is generally a non-toxic, safe, non-corrosive metal and liquid or gas that does not freeze at the test temperature. Such as anhydrous ethanol (alcohol), solid carbon dioxide (dry ice) or liquid nitrogen atomization gas (liquid nitrogen) and so on.


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