CN115655938A - Conversion method of hardness in Rich and Brinell of P91 steel - Google Patents

Abstract

The invention discloses a conversion method of hardness in Rich and Brinell of P91 steel, belonging to the field of on-site hardness test of P91 steel commonly used in the power industry.

Description

Conversion method of hardness in Rich and Brinell of P91 steel

Technical Field

The invention relates to the field of field hardness-in-place test of P91 steel commonly used in the power industry, in particular to a conversion method of hardness-in-place and Brinell hardness of P91 steel.

Background

With the rapid development of the power industry, the high-capacity and high-parameter unit is put into use, the grade of metal materials is continuously improved, and the 91 steel is widely applied to important metal parts of a main steam pipeline, a reheating steam pipeline, a high-temperature header and the like of the unit. However, in recent years, the problem of abnormal hardness of 91 steel is more and more common in the metal detection process, and certain risks are brought to the safe operation of a unit.

The hardness of the metal material is tested by using the portable Richter scale hardness tester, so that the hardness value of the material can be rapidly measured, and meanwhile, the material cannot be damaged, and the portable Richter scale hardness tester is widely applied to the fields of the power industry and other engineering. However, years of practice and research show that the richter hardness tester and the brinell hardness tester have certain deviation in detection results, and the phenomenon is more obvious particularly for 91 steel with abnormal hardness. On the one hand, this is due to the different working principles of the richter and the brinell hardness testers; on the other hand, the scope of the internal test material of the Leeb hardness tester covers carbon steel, alloy tool steel, stainless steel, bearing steel, aluminum, brass, bronze, pure copper and other materials, and does not include martensite stainless steel materials such as P91 steel, P92 steel and the like; strictly speaking, the hardness of the P91 steel is not measured by the richter scale.

The deviation caused by the instrument causes that the material cannot be accurately and effectively evaluated and judged, even an error conclusion can be obtained, and great troubles and misleading are brought to detection personnel. For this purpose, the electric power row standard DL/T438-2016 metal technology supervision of thermal power plants was subject to a targeted revision compared to 2009 edition, item 7.1.5 of which states: when the hardness deviates from the specified value of the standard, a portable Brinell hardness tester is preferably used for measurement and check.

The portable brinell hardness tester that uses commonly at present mainly has magnetic-type brinell hardness tester, hammer impact formula brinell hardness tester and fluid pressure type brinell hardness tester, but these above-mentioned three kinds of brinell hardness testers all have certain shortcoming and limitation. The magnetic force type Brinell hardness tester requires that a magnetic force loading surface is symmetrical, flat and suitable for loading, and cannot be applied to different parts such as elbows, tees, large heads and small heads; hammer brinell hardnesses require the necessary hammer space and direction, limited space and bottom area are not available; the hydraulic Brinell hardness tester is large and heavy, and is not suitable for complex working condition scenes on site. Limited by the factors, when the actual detection working condition on site cannot meet the working requirement of the equipment, the hardness test or check of the P91 steel is overwhelmed, and the damage sampling is just the final choice.

Disclosure of Invention

The invention aims to provide a convenient and accurate hardness testing method for P91 steel, overcomes the defects in the prior art and equipment by a conversion method between the Richter hardness and the Brinell hardness, and can accurately obtain the Brinell hardness value of the P91 steel by using a portable Richter hardness tester on site.

The technical scheme adopted by the invention for solving the problems is as follows: a conversion method of the Brinell hardness and the Brinell hardness of P91 steel is characterized by comprising the following steps:

step 1: preparing hardness testing equipment; preparing a table Brinell hardness tester and a portable Leeb hardness tester respectively, wherein the two devices are qualified by measurement of a measurement unit and are both standard grade or above;

step 2: preparing a comparative sample; selecting 5 comparative samples which are made of P91 steel, wherein the diameter D =90mm, the height h =50mm and the length error of the comparative samples are +/-1 mm, obtaining hardness values from low to high through different heat treatment processes, and covering the range of the standard hardness values of the P91 steel (180-250 HBW);

and 3, step 3: performing a hardness comparison test; 5 groups of comparative hardness tests are carried out on each comparative sample, and each comparative group is surrounded by 5 Brinell hardness impact marks; and (3) removing 1 highest value and 1 lowest value from the 5 Leeb hardness values, and taking the average value of the rest 3 Leeb hardness values to obtain a pair of comparison values with the Brinell hardness values. Therefore, each comparison sample can obtain 5 comparison values, the Leeb hardness value and the Brinell hardness value in the 5 comparison values are respectively averaged, and each comparison sample can obtain a pair of conversion calculation values;

and 4, step 4: drawing a coordinate system; an X axis represents a Leeb hardness value (HLD), a Y axis represents a Brinell hardness value (HBW), a rectangular coordinate system is established, and 5 pairs of conversion calculation values are marked in the coordinate system to obtain 5 coordinate points;

and 5: fitting a curve function; fitting the 5 coordinate points by using curve fitting software to obtain a curve function formula;

step 6: the use of a curve function; the hardness value of P91 steel was obtained by directly performing the hardness test on P91 steel and converting the hardness value by substituting the hardness value into the curve function expression.

Furthermore, in the hardness comparison test, the distance between the impact marks and the indentations of the comparison hardness is enough to avoid the influence of stress, and the impact marks and the indentations are close to each other as much as possible to ensure the uniformity of local hardness.

Further, the hardness conversion method is also suitable for conversion of the hardness of T91, T/P92 and other grades of metal materials in the hardness of Rockwell hardness and Brinell hardness.

Compared with the prior art, the invention has the following advantages and effects: according to the invention, the Brinell hardness test of the P91 steel can be rapidly and accurately finished by using the portable Brinell hardness tester without using a portable Brinell hardness tester or even a means of destroying sampling, and the method can adapt to various complicated and limited working conditions on site.

Drawings

FIG. 1 is a graph of the distribution of the impact marks and Brinell hardness marks for the hardness comparison tests in the examples of the present invention.

FIG. 2 is a graph fitted with comparative scaled calculations for an embodiment of the invention.

In the figure: the impact mark 1 of the hardness of the Reishi, the indentation mark 2 of the Brinell hardness and the comparative sample 3.

Detailed Description

The present invention will be described in further detail below by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting the present invention.

Examples are given.

The invention provides a conversion method of the Rich hardness and the Brinell hardness of P91 steel, which comprises the following specific implementation steps of:

step 1: preparing hardness testing equipment; preparing a bench Brinell hardness tester and a portable Leeb hardness tester respectively, wherein the model of the bench Brinell hardness tester is Huayin 400HBS-3000A, the model of the portable Leeb hardness tester is American Jie Rui HT-2000A, and the two devices are qualified by measurement of a measurement unit and are calibrated by a standard hardness test block;

and 2, step: preparing a comparative sample; preparing 5 pieces of comparison sample 3, wherein the materials are all P91 steel, the diameter D =90mm, the height h =50mm and the length error is allowed to be +/-1mm, and the hardness value from low to high is obtained by the 5 pieces of comparison sample 3 through different heat treatment processes in a laboratory;

and step 3: a hardness comparison test; as shown in fig. 1, 5 sets of comparative hardness tests were performed on each of the comparative samples 3, each of which was surrounded by 5 vickers hardness impact marks 1 by one brinell hardness indentation 2; and (3) removing 1 highest value and 1 lowest value from the 5 Leeb hardness values, and taking the average value of the remaining 3 Leeb hardness values to form a pair of comparison values with the Brinell hardness value. Therefore, 5 set of comparison values can be obtained on each sample, the Leeb hardness value and the Brinell hardness value in the 5 set of comparison values are respectively averaged, a pair of conversion calculation values can be obtained on each sample, 5 pairs of conversion calculation values are obtained after the comparison test is finished, and the results of the hardness comparison test are shown in tables 1 to 5;

table 1 hardness comparative test results of comparative sample one

TABLE 2 hardness comparative test results for comparative sample two

TABLE 3 hardness comparison test results for comparative sample III

TABLE 4 hardness comparative test results for comparative sample four

TABLE 5 hardness comparative test results for comparative sample V

And 4, step 4: drawing a coordinate system; an x axis represents a Leeb hardness value (HLD), a y axis represents a Brinell hardness value (HBW), a rectangular coordinate system is established, and 5 pairs of conversion calculation values are marked in the coordinate system to obtain 5 coordinate points, as shown in FIG. 2;

and 5: fitting a curve function; fitting the 5 coordinate points by using curve fitting software, as shown in fig. 2, it can be seen that a linear relationship exists between the richter hardness value and the brinell hardness value, the coefficient (R-square) is determined to be 0.99777, and the linear function formula of the curve obtained by fitting is as follows: y =0.77646x-168.880;

step 6: the application of a curve function formula; directly carrying out a Richter hardness test on a P91 steel blind sample, wherein the average Richter hardness value of the 5-point test is 475HLD, and carrying out conversion between the Richter hardness value and the Brinell hardness value by using the curve function formula to obtain a converted Brinell hardness value of the P91 steel, namely 199.9385HBW, and taking an integer value of 200HBW;

in order to verify the accuracy of the conversion method, a desktop Brinell hardness tester is adopted to carry out hardness test on the blind sample, the average Brinell hardness value is 200.1HBW after 5 times of tests, the hardness is highly consistent with the conversion value, other blind samples are taken to repeat the steps, the test result is consistent, and the accuracy of the method can completely meet the requirements of field work.

Those not described in detail in this specification are well within the skill of the art.

Although the present invention has been described with reference to the above embodiments, it should be understood that the scope of the present invention is not limited thereto, and that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims (2)

1. A method for converting the Rich hardness and the Brinell hardness of P91 steel is characterized by comprising the following steps of:

step 1: preparing hardness testing equipment; preparing a table Brinell hardness tester and a portable Leeb hardness tester, wherein the two devices are qualified by measurement of a measurement unit and are both standard grade or above;

step 2: preparing a comparative sample; 5 pieces of the comparison sample (3) are selected, the material of the comparison sample is P91 steel, the diameter D =90mm, the height h =50mm and the length error is allowed to be +/-1 mm, the hardness value from low to high is obtained through different heat treatment processes, and the standard hardness value range of the P91 steel is covered;

and step 3: carrying out a hardness comparison test; 5 groups of comparative hardness tests are carried out on each comparative sample (3), and each comparative group consists of 5 Brinell hardness impact marks (1) surrounding one Brinell hardness indentation (2); removing 1 highest value and 1 lowest value from the 5 Leeb hardness values, taking the average value of the remaining 3 Leeb hardness values, and obtaining a group of comparison values with the Brinell hardness values; 5 pairing specific values can be obtained on each comparison sample (3), the Leeb hardness value and the Brinell hardness value in the 5 pairing specific values are respectively averaged, and each comparison sample (3) can obtain a pair of conversion calculation values;

and 4, step 4: drawing a coordinate system; expressing the hardness value of the Leeb by an X axis, expressing the hardness value of the Brinell by a Y axis, establishing a rectangular coordinate system, and marking 5 pairs of conversion calculation values in a coordinate system to obtain 5 coordinate points;

and 5: fitting a curve function; fitting the 5 coordinate points to obtain a curve function formula;

step 6: carrying out hardness conversion by using a curve function formula; the hardness value of P91 steel was obtained by directly performing the hardness test on P91 steel and converting the hardness value by substituting the hardness value into the curve function expression.

2. The method for converting the hardness of P91 steel in the form of richter to the brinell hardness as claimed in claim 1, wherein the conversion method is also applicable to the conversion of the hardness of other grades of metal materials in the hardness comparison test.

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