CN103969284A - Thermal expansion method for measuring temperature enabling carbon in low-carbon steel to be completely dissolved in austenite - Google Patents
Thermal expansion method for measuring temperature enabling carbon in low-carbon steel to be completely dissolved in austenite Download PDFInfo
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Abstract
The invention provides a thermal expansion method for measuring the temperature enabling carbon in low-carbon steel to be completely dissolved in an austenite. The carbon content is lower than or equal to 0.2 wt%. A sample is heated to a preset temperature, the thermal expansion curve in the heating process is measured, and the temperature enabling the carbon to be completely dissolved in the austenite is determined. The thermal expansion method for measuring the temperature enabling carbon in low-carbon steel to be completely dissolved in the austenite, provided by the invention, can provide production reference for the hot rolling manufacturing process of the kind of steel materials in heat treatment technology; the thermal expansion method is sensitive to phase transition process, and the measuring method is stable and reliable, so that the method has strong suitability for low-carbon steel with different composition; compared with the conventional hardness test method and the thermodynamics calculating method, the thermal expansion method is simple, easy to implement, and high in accuracy.
Description
Technical field
The invention belongs to material metallurgical technology field, specifically a kind of dilatometry is measured the method for carbon consoluet temperature in austenite in mild carbon steel.
Background technology
Carbon is one of topmost element in mild carbon steel, and austenitation heat treatment is the topmost heat treatment process of mild carbon steel, its fundamental purpose be the ferrite under normal temperature and cementite are heated to eutectoid temperature more than, make it be transformed into austenite.And carbon is dissolved to temperature in austenite completely often higher than its phase transition temperature.Therefore the selection of austenitation heat treatment temperature, must consider that carbon is dissolved to austenitic temperature completely, provides theoretical foundation for formulating rational Technology for Heating Processing.Ensure to be dissolved in completely in austenite at cooling front carbon.
Before the present invention, carbon determining of complete solution temperature in austenite mainly relies on the method for microstructure observation in conjunction with hardness test, and calculation of thermodynamics, before in these two kinds of methods, a kind of method can only qualitative analysis, then a kind of method is the analysis of the thermodynamic data under a kind of ideal conditions, for actual heat treatment steel part, can there is deviation in theoretical calculating with real data.
Thermal expansion is a kind of physical property of metal material, if metal material undergoes phase transition in heating process, its thermal expansivity can change, and thermal expansion curve will change, the thermal expansion curve of single-phase is straight line, and while undergoing phase transition, thermal expansion curve will bend.The analysis of thermal expansion process can also provide material phase transformation initial temperature and phase transformation final temperature, and phase variable.When carbon incorporates after austenite completely, it is relatively stable that its phase structure has been tending towards, and thermal expansivity also settles out, and is shown as streamlined process on thermal expansion curve, and the starting point of straight-line segment is exactly that carbon is dissolved into austenitic temperature completely.
Summary of the invention
Object of the present invention is just to overcome the deficiencies in the prior art, provide a kind of carbon of measuring in mild carbon steel at the simple effective method of the complete solution temperature of austenite, the method is utilized the thermal expansion character of mild carbon steel, by measuring the thermal expansion amount in mild carbon steel heating process, Accurate Determining carbon is consoluet temperature in austenite.
The object of the invention is to be achieved through the following technical solutions:
In a kind of dilatometry mensuration mild carbon steel, carbon is in the method for the consoluet temperature of austenite, in described mild carbon steel, carbon content is less than or equal to 0.2wt.%, it is characterized in that: utilize sample in heating process because the principle that phase transformation causes swell increment to change, determine carbon consoluet temperature in austenite, concrete steps are as follows:
Step (one)
By sample from room temperature with lower firing rate constant-speed heating to 1000 DEG C, make thermal expansion process fully carry out and phase transition process even; Meanwhile, interval same time is measured the thermal expansion amount of specimen finish direction, and records corresponding temperature;
Step (two)
Do thermal expansion curve according to thermal expansion amount and the corresponding temperature measured, the straight-line segment of close 1000 DEG C of warm areas on heat-obtaining expansion curve, and straight-line segment is done to extended line to low-temperature space, the temperature that the segment of curve on thermal expansion curve is corresponding with the burble point of straight-line segment extended line is carbon consoluet temperature in austenite.
In technical solution of the present invention, because carbon is the larger element of austenitizing phase transition process impact, so be only less than or equal to the mild carbon steel of 0.2wt.% for carbon content.When sample is heated, to ensure that firing rate is within the scope of 0.5 DEG C/S～5 DEG C/S, and homogeneous heating, make expansion process fully carry out and phase transition process even, when measurement, the every rising of temperature once must gather and exceed 1 thermal expansion amount.
In heating process, preferably ensure sample measurement district temperature evenly and sample two ends without External Force Acting, avoid the impact of sample plastic yield on thermal expansion amount precision.
Being heated to the process of high temperature from room temperature, specimen surface is very easily oxidized, and can impact the measuring accuracy of the thermal expansion amount of specimen finish direction, so preferably vacuum state or inert gas shielding state of test environment.
Owing to being heated to behind austenitic area, carbon is still constantly dissolving in austenite, and the consoluet austenitic temperature of carbon district must be the linearly part of section of thermal expansion curve.Therefore, the straight-line segment of close 1000 DEG C of warm areas on heat-obtaining expansion curve, and find the starting point of this straight-line segment on thermal expansion curve can find carbon consoluet temperature in austenite.
The advantage that the present invention has and effect:
Dilatometry of the present invention is measured the method for carbon complete solution temperature in austenite in mild carbon steel, for such steel Technology for Heating Processing in hot rolling production run provides production foundation.Because dilatometry is responsive to phase transition process reaction, and method of testing is reliable and stable, stronger to the mild carbon steel applicability of heterogeneity, compares with calculation of thermodynamics method with hardness test method in the past, and method is simple, easy to implement and precision is higher.
Brief description of the drawings
Fig. 1 is the thermal expansion curve of embodiment 1;
Fig. 2 is the straight-line segment matching schematic diagram near 1000 DEG C of warm areas on the thermal expansion curve of embodiment 1;
Fig. 3 is expansion increment C and temperature relation figure;
Fig. 4 is checking sample structure figure.
Embodiment
For the mild carbon steel that is less than or equal to 0.2wt.% containing carbon content, in thermal expansion testing apparatus, measure sample and be heated to the thermal expansion amount of 1000 DEG C from room temperature, and record temperature and thermal expansion amount, draw the extended line that thermal expansion curve and carbon are dissolved into austenite straight-line segment completely, find the starting point of straight-line segment.
Embodiment 1
1) embodiment composition
Embodiment 1 selects mild carbon steel Q960, and its chemical composition meets standard GB16270-2009 " the modified plate of high-strength structure ", in table 1.
Table 1 embodiment 1 chemical composition (wt.%)
| C | Si | Mn | P | S | Cu | Cr | Ni | Mo |
| ≤0.20 | ≤0.8 | ≤2.0 | ≤0.025 | ≤0.15 | ≤0.50 | ≤1.50 | ≤2.00 | ≤0.70 |
2) the measurement technique of thermal expansion amount
Adopt Gleeble-3500 hot modeling test machine to carry out dilatometric experiment; at the uniform velocity be heated to 1000 DEG C from normal temperature by sample with 50K/min; sample is carried out to vacuum protection simultaneously; the variation that when heating, every rising 0.5 degree is measured sample thermal expansion amount; record temperature and thermal expansion amount data simultaneously, draw thermal expansion curve.
3) when carbon dissolves in austenite completely, temperature determines
Below 1000 DEG C, near the straight-line segment of 1000 DEG C of warm area heat-obtaining expansion curves, as shown in Figure 2, fitting a straight line equation is fitting a straight line:
y＝-0.0678+0.9982*x
Wherein y is thermal expansion amount (mm), x be temperature (DEG C).
Deduct the thermal expansion amount calculated value of fitting a straight line equation corresponding temperature with the thermal expansion amount on original measurement thermal expansion curve, difference, divided by the increment C that obtains expanding of the thermal expansion amount on original measurement thermal expansion curve, is shown below.
Thermal expansion amount on C=(thermal expansion amount-fitting a straight line equation thermal expansion amount calculated value on thermal expansion curve)/thermal expansion curve;
Temperature value in the time that expansion increment C value reaches 0.1% be carbon in the consoluet temperature of austenite, temperature is 899 DEG C, as Fig. 3.In the time that expansion increment is increased to 0.1%, just can think that phase transformation has started to occur, the burble point of the segment of curve on instant heating expansion curve and straight-line segment extended line.
4) checking: measure sample hardness after different temperature retention times under austenite solution temperature
Get 2 as shown in Figure 4 sample test, all samples are heated to carbon complete 899 DEG C of solution temperatures in austenite, and are incubated respectively 3 minutes and 30 minutes, rapid quench is to room temperature (cooling rate of phase change zone is greater than 30 DEG C/S).After thermal treatment, by Japanese Shimadzu HMV-2 microhardness instrument, sample carries out hardness test, and experiment load is 9.807N (HV1), retention time 10s.Survey 10 hardness numbers at specimen surface diverse location, then average.Test result is as shown in table 2.Be incubated 3 minutes consistent with the average microhardness of 30 minutes, illustrate that at 899 DEG C, carbon has been dissolved in austenite completely.
Table 2
Claims (5)
1. a dilatometry is measured in mild carbon steel carbon in the method for the consoluet temperature of austenite, in described mild carbon steel, carbon content is less than or equal to 0.2wt.%, it is characterized in that: utilize sample in heating process because the principle that phase transformation causes swell increment to change, determine carbon consoluet temperature in austenite, concrete steps are as follows:
Step (one)
By sample from room temperature with lower firing rate constant-speed heating to 1000 DEG C, make thermal expansion process fully carry out and phase transition process even; Meanwhile, interval same time is measured the thermal expansion amount of specimen finish direction, and records corresponding temperature;
Step (two)
Do thermal expansion curve according to thermal expansion amount and the corresponding temperature measured, the straight-line segment of close 1000 DEG C of warm areas on heat-obtaining expansion curve, and straight-line segment is done to extended line to low-temperature space, the temperature that the segment of curve on thermal expansion curve is corresponding with the burble point of straight-line segment extended line is carbon consoluet temperature in austenite.
2. in dilatometry mensuration mild carbon steel according to claim 1, carbon, in the method for the consoluet temperature of austenite, is characterized in that: the measuring process of specimen finish direction thermal expansion amount is carried out under vacuum environment or inert gas shielding environment.
3. dilatometry according to claim 1 is measured in mild carbon steel carbon in the method for the consoluet temperature of austenite, it is characterized in that: in heating process, ensure sample measurement district temperature evenly and sample two ends without External Force Acting, avoid the impact of sample plastic yield on thermal expansion amount precision.
4. dilatometry according to claim 1 is measured carbon in mild carbon steel and, in the method for the consoluet temperature of austenite, be it is characterized in that: sample firing rate is 0.5 DEG C/S～5 DEG C/S.
5. dilatometry according to claim 1 is measured in mild carbon steel carbon in the method for the consoluet temperature of austenite, it is characterized in that: the thermal expansion amount calculated value that deducts the fitting a straight line equation corresponding temperature of described straight-line segment with the thermal expansion amount on thermal expansion curve, difference is divided by the increment C that obtains expanding of the thermal expansion amount on thermal expansion curve, do the graph of a relation of expansion increment C and temperature, segment of curve on some instant heating expansion curve in the time that expansion increment C value reaches 0.1% and the burble point of straight-line segment extended line, corresponding temperature is carbon consoluet temperature in austenite.
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| CN105116003A (en) * | 2015-07-28 | 2015-12-02 | 南京钢铁股份有限公司 | Measurement method for calculating two-phase transition ratio by thermal expansion curve |
| CN105136842A (en) * | 2015-07-29 | 2015-12-09 | 南京钢铁股份有限公司 | Expansion curve analysis method for steel critical point test and use thereof |
| CN105181733A (en) * | 2015-08-06 | 2015-12-23 | 江苏安瑞达新材料有限公司 | Method for simulation of polyolefin casting base membrane annealing treatment by DSC |
| CN105271662A (en) * | 2015-10-26 | 2016-01-27 | 成都光明光电股份有限公司 | Acquisition method for precision annealing temperature |
| CN105445309A (en) * | 2014-08-28 | 2016-03-30 | 宝山钢铁股份有限公司 | Method for quantitatively analyzing content of martensite in dual phase steel |
| CN108760797A (en) * | 2018-07-16 | 2018-11-06 | 昆明理工大学 | A kind of processing method of metal material swell increment curve |
| CN110646461A (en) * | 2018-06-27 | 2020-01-03 | 上海梅山钢铁股份有限公司 | Method for measuring continuous cooling phase transition temperature of ultrathin gauge thickness steel plate |
| CN110927201A (en) * | 2019-12-11 | 2020-03-27 | 北京理工大学 | DIC-based thermal expansion phase change measurement method |
| CN111366606A (en) * | 2020-03-27 | 2020-07-03 | 上海交通大学 | Heat treatment deformation prediction method based on expansion curve |
| CN111638238A (en) * | 2020-05-15 | 2020-09-08 | 南京钢铁股份有限公司 | Method for measuring reverse transformation austenite by adopting expansion method |
| CN112305012A (en) * | 2020-06-10 | 2021-02-02 | 上海航空材料结构检测股份有限公司 | Method for measuring titanium/titanium alloy beta phase transition temperature based on dynamic thermal simulator |
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| CN105445309A (en) * | 2014-08-28 | 2016-03-30 | 宝山钢铁股份有限公司 | Method for quantitatively analyzing content of martensite in dual phase steel |
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| CN105116003A (en) * | 2015-07-28 | 2015-12-02 | 南京钢铁股份有限公司 | Measurement method for calculating two-phase transition ratio by thermal expansion curve |
| CN105136842A (en) * | 2015-07-29 | 2015-12-09 | 南京钢铁股份有限公司 | Expansion curve analysis method for steel critical point test and use thereof |
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| CN108760797B (en) * | 2018-07-16 | 2020-12-15 | 昆明理工大学 | Method for processing expansion curve of metal material |
| CN108760797A (en) * | 2018-07-16 | 2018-11-06 | 昆明理工大学 | A kind of processing method of metal material swell increment curve |
| CN110927201A (en) * | 2019-12-11 | 2020-03-27 | 北京理工大学 | DIC-based thermal expansion phase change measurement method |
| CN111366606A (en) * | 2020-03-27 | 2020-07-03 | 上海交通大学 | Heat treatment deformation prediction method based on expansion curve |
| CN111366606B (en) * | 2020-03-27 | 2022-06-24 | 上海交通大学 | Heat treatment deformation prediction method based on expansion curve |
| CN111638238A (en) * | 2020-05-15 | 2020-09-08 | 南京钢铁股份有限公司 | Method for measuring reverse transformation austenite by adopting expansion method |
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